WEBVTT 00:02.467 --> 00:04.427 J. MICHAEL MCBRIDE: OK, we're still talking about 00:04.433 --> 00:07.633 addition to alkenes. 00:07.633 --> 00:11.733 And we've looked at these various electrophile cum 00:11.733 --> 00:14.673 nucleophiles adding to alkenes. 00:14.667 --> 00:18.227 And now, at the beginning last time, we introduced the idea 00:18.233 --> 00:21.733 of osmium tetroxide and we'll go on to permanganate as 00:21.733 --> 00:25.473 reagents for dihydroxylation of alkenes. 00:25.467 --> 00:28.827 Then we'll go onto things involving transition metals, 00:28.833 --> 00:34.233 catalytic hydrogenation, and also metathesis and catalyzed 00:34.233 --> 00:36.873 polymerization. 00:36.867 --> 00:39.967 So last time, we looked at the end at OsO4, which looked a 00:39.967 --> 00:44.667 little bit like O3 and could do the same trick O3 could do, 00:44.667 --> 00:49.067 to give this osmate ester, which is like an acetal. 00:49.067 --> 00:54.497 So it's possible to add water and get the osmium equivalent 00:54.500 --> 00:58.370 of a carbonyl group, and the two hydroxyl groups added to 00:58.367 --> 01:00.827 the termini of the alkene. 01:00.833 --> 01:07.003 So the problem with this is OsO4 is a very efficient 01:07.000 --> 01:09.730 reagent for that, but it's poisonous, and 01:09.733 --> 01:11.703 it's also very expensive. 01:11.700 --> 01:15.530 So you have to figure out some way not to use so much of it. 01:15.533 --> 01:18.703 And the way you could do it is to use just a little bit of it 01:18.700 --> 01:23.630 as a catalyst, and put hydrogen peroxide in there, in 01:23.633 --> 01:27.403 order to convert the osmium equivalent of trioxide back to 01:27.400 --> 01:31.570 the tetroxide again, so it can cycle around and keep doing 01:31.567 --> 01:33.067 the reaction. 01:33.067 --> 01:38.267 In fact, it was improved in 1976, by using a different 01:38.267 --> 01:46.397 oxidizing agent, this N-oxide, the morpholine oxide. 01:46.400 --> 01:49.070 And in fact, this is called the Upjohn process, which is 01:49.067 --> 01:51.867 relevant because the guy whose picture is over here, whose 01:51.867 --> 01:55.027 estate gave the money for redoing this room awhile back, 01:55.033 --> 01:59.833 was the research director at Upjohn Laboratories. 01:59.833 --> 02:01.403 So anyhow, that was a good way to do it. 02:01.400 --> 02:04.000 But then, we should notice something about the 02:04.000 --> 02:06.400 stereochemistry of this. 02:06.400 --> 02:09.100 We showed here a trans-2-butene. 02:09.100 --> 02:12.000 And of course, if it's like ozone, the two oxygens will 02:12.000 --> 02:15.500 add at the same time, therefore to the same face. 02:15.500 --> 02:20.000 So the configuration you get at the two carbons, where the 02:20.000 --> 02:23.100 OH's add, are related to one another. 02:23.100 --> 02:25.770 They could be S, S, as shown here. 02:25.767 --> 02:28.327 Of course, the osmium tetroxide could equally well 02:28.333 --> 02:32.973 have come in from the bottom, or the 2-butene could have 02:32.967 --> 02:36.497 been turned over, and then you would have gotten R, R. So of 02:36.500 --> 02:38.530 course you don't get chirality without 02:38.533 --> 02:40.333 starting with chirality. 02:40.333 --> 02:42.903 That is, a single chirality. 02:42.900 --> 02:47.000 However, you can start with it in a ligand that attaches to 02:47.000 --> 02:49.000 the to the osmium. 02:49.000 --> 02:53.530 So if you use a chiral amine ligand, then, you only get one 02:53.533 --> 03:01.533 of the two enantiomers of the dihydroxylated alkene. 03:01.533 --> 03:03.673 And this, you won't be surprised to hear, was also 03:03.667 --> 03:06.597 invented by Professor Sharpless, whom we talked about 03:06.600 --> 03:10.930 last semester with respect to adding oxygen. 03:10.933 --> 03:13.303 And so this is called the Sharpless asymmetric 03:13.300 --> 03:14.500 dihydroxylation. 03:14.500 --> 03:18.300 He invented it in 1988, and I think this room was the first 03:18.300 --> 03:20.300 place he talked about it in public. 03:20.300 --> 03:23.300 He was standing right there, and in fact, he did a 03:23.300 --> 03:27.430 demonstration on this table, as I'm going to do in the end. 03:27.433 --> 03:31.473 But I'm going to do a different demonstration. 03:31.467 --> 03:33.897 Because osmium tetroxide which he used, is very 03:33.900 --> 03:35.400 dangerous and poisonous. 03:35.400 --> 03:38.230 And he actually spilled it on this table. 03:38.233 --> 03:41.573 I think it's now long gone, since that was 1988. 03:41.567 --> 03:44.327 But at least what I'm going to do just uses vinegar, so you 03:44.333 --> 03:46.903 don't have to worry about that. 03:46.900 --> 03:50.430 OK, so anyhow, here's a specific example of using 03:50.433 --> 03:52.973 Sharpless asymmetric dihydroxylation with that 03:52.967 --> 03:57.927 diene. It gives a 97% enantiomer excess of the 03:57.933 --> 04:01.903 indicated configuration here. 04:01.900 --> 04:06.800 Now, the permanganate is much cheaper, and looks very much 04:06.800 --> 04:10.070 like osmium tetroxide, so it won't surprise you that it 04:10.067 --> 04:12.427 also can do this trick. 04:12.433 --> 04:17.103 And here, you get 85% yield with cyclohexene. 04:17.100 --> 04:20.570 And again, it's a syn addition, the two OH's come in 04:20.567 --> 04:22.097 on the same face. 04:22.100 --> 04:24.730 But that's not one where there's a catalyst that'll 04:24.733 --> 04:25.973 make it give only one enantiomer. 04:28.700 --> 04:31.700 Now on to catalytic hydrogenation. 04:31.700 --> 04:35.830 So we looked before at the idea of drawing two curved 04:35.833 --> 04:38.733 arrows and making H2 add to an alkene. 04:38.733 --> 04:41.203 And saw that the orbitals weren't set up for that. 04:41.200 --> 04:44.700 HOMO wouldn't match HOMO, LUMO with LUMO, so there's no 04:44.700 --> 04:46.170 profit in that. 04:46.167 --> 04:50.427 However, we said, even though that doesn't work, that it 04:50.433 --> 04:53.803 does work if you have a metal catalyst, like palladium or 04:53.800 --> 04:57.230 platinum, or many other transition metals. 04:57.233 --> 05:00.173 So let's look a little bit at how it is that palladium does 05:00.167 --> 05:01.467 this trick. 05:01.467 --> 05:04.797 It does it by providing orbital variety. 05:04.800 --> 05:07.130 Rather than just having the orbitals that we showed 05:07.133 --> 05:11.403 before, the sigma and sigma-star of the H-H bond, 05:11.400 --> 05:14.570 and the pi and pi-star of the alkene, you have lots of 05:14.567 --> 05:16.827 different shapes of orbitals on the metal. 05:16.833 --> 05:22.873 For example, in ethylene, we have the pi, and the pi-star, 05:22.867 --> 05:29.427 but in the metal, palladium has 4d10, 5s0, and 5p0. 05:29.433 --> 05:33.073 So the occupied orbitals of palladium, 05:33.067 --> 05:35.597 then, are this dz squared. 05:35.600 --> 05:38.970 Now, is that set up to overlap well with pi-star? 05:38.967 --> 05:42.867 The HOMO below and the LUMO above? 05:42.867 --> 05:46.727 What do you think, is that going to be a good reaction? 05:46.733 --> 05:49.433 Who's got an opinion, Karl? 05:49.433 --> 05:53.433 STUDENT: I don't think so because how you have the red 05:53.433 --> 05:56.833 on one side of the blue and on the other side of the blue you 05:56.833 --> 06:00.703 might be able to get one side of the red to overlap? 06:00.700 --> 06:03.670 PROFESSOR: Maybe on one side, but not as shown there. 06:03.667 --> 06:03.997 Right? 06:04.000 --> 06:05.030 That's what you're saying there? 06:05.033 --> 06:08.003 And you're right, they're orthogonal as drawn. 06:08.000 --> 06:09.730 But there are other d orbitals. 06:09.733 --> 06:12.103 There are five of these d orbitals, so we could check 06:12.100 --> 06:13.100 out others. 06:13.100 --> 06:15.730 How about the dyz, is that going to do the trick? 06:15.733 --> 06:19.603 Are you going to get overlap if you bring that up? 06:19.600 --> 06:20.900 Kate, what do you say? 06:24.167 --> 06:25.927 If you turned it, you could... 06:25.933 --> 06:26.003 STUDENT: Yes. 06:26.000 --> 06:28.330 PROFESSOR: but as shown, it's orthogonal. 06:28.333 --> 06:29.603 Right? 06:29.600 --> 06:32.430 OK, how about that one? 06:32.433 --> 06:34.403 Is that going to do the trick? 06:34.400 --> 06:34.700 No? 06:34.700 --> 06:35.900 Chris is shaking his head. 06:35.900 --> 06:36.500 That won't do it. 06:36.500 --> 06:39.230 How about that one? 06:39.233 --> 06:39.573 No? 06:39.567 --> 06:42.167 It's still that one of them is symmetrical right to left, the 06:42.167 --> 06:44.327 other is antisymmetric right to left, so 06:44.333 --> 06:45.803 they'd have no overlap. 06:45.800 --> 06:47.570 How about that one? 06:47.567 --> 06:49.727 Ah, just right. 06:49.733 --> 06:53.333 OK, so that one can come up and overlap, and stabilize the 06:53.333 --> 06:55.333 electrons that were on the metal. 06:55.333 --> 06:57.673 And that new orbital shown there is, in 06:57.667 --> 06:59.197 fact, the HOMO-4. 06:59.200 --> 07:01.700 It's gotten quite stable, right? 07:01.700 --> 07:04.270 In fact, part of the reason it got stable is the nature of 07:04.267 --> 07:06.967 the orbitals changes as atoms come up, and 07:06.967 --> 07:08.767 the geometry changes. 07:08.767 --> 07:12.527 So although it looks very much like those two original 07:12.533 --> 07:16.103 orbitals, and in a sense, came from them, by the time it gets 07:16.100 --> 07:21.400 to this point at the complex, it's 40% of that dxy orbital 07:21.400 --> 07:22.570 on the bottom. 07:22.567 --> 07:27.867 47%, actually, on the top is sigma C-H's, but 13% is still 07:27.867 --> 07:28.667 the pi-star. 07:28.667 --> 07:32.197 So that's just to tell you the ugly truth. 07:32.200 --> 07:35.130 But the fact is that the reaction began, and went 07:35.133 --> 07:36.703 through a transition state because of the 07:36.700 --> 07:38.100 mixing of those orbitals. 07:38.100 --> 07:39.870 So that's two electrons. 07:39.867 --> 07:41.597 But how about the other way around? 07:41.600 --> 07:43.900 How about if we use the HOMO on the top? 07:43.900 --> 07:46.270 Now, of course, we have all these d orbitals on the 07:46.267 --> 07:50.697 bottom, and few of them would overlap, and even that one 07:50.700 --> 07:53.530 which does overlap you don't care about, because 07:53.533 --> 07:56.373 it's HOMO with HOMO. 07:56.367 --> 07:59.367 We want unoccupied orbitals on the bottom, which 07:59.367 --> 08:02.067 means that 5s and 5p. 08:02.067 --> 08:03.867 So there's the 5p. 08:03.867 --> 08:06.967 That's an unoccupied orbital, that's going to overlap well, 08:06.967 --> 08:08.267 and there's the 5s. 08:08.267 --> 08:09.567 It'll overlap. 08:09.567 --> 08:11.497 So you use some mixture of those two. 08:11.500 --> 08:12.830 You'll use a hybrid orbital. 08:12.833 --> 08:15.503 An sp hybrid of some sort on the palladium, which will 08:15.500 --> 08:18.770 overlap with that HOMO and stabilize another pair of 08:18.767 --> 08:19.467 electrons. 08:19.467 --> 08:21.067 And there it is in the complex. 08:21.067 --> 08:24.127 You see, it's a hybrid orbital below, and the pi orbital 08:24.133 --> 08:28.573 above, forming that new bond, stabilizing those electrons. 08:28.567 --> 08:31.867 In fact, if you look at the ugly truth on this one, by the 08:31.867 --> 08:33.767 time you get to the complex, it's changed. 08:33.767 --> 08:40.927 It's 67% of pi, and it's 11% of an sp hybrid. 08:40.933 --> 08:44.603 But it's also 15% of that d orbital that we showed at the 08:44.600 --> 08:46.670 beginning, so things have gotten mixed up. 08:46.667 --> 08:48.497 But that's the way it happened, because you had 08:48.500 --> 08:51.470 these vacant orbitals that could overlap from below on 08:51.467 --> 08:54.967 the metal, overlap with pi, you had the filled orbital, 08:54.967 --> 08:57.727 the particular one, the orbital that could overlap 08:57.733 --> 08:58.733 with pi-star. 08:58.733 --> 09:01.733 So you stabilize two pairs of electrons. 09:01.733 --> 09:05.233 That means you make two new bonds to the alkene. 09:07.733 --> 09:11.373 So the palladium, or platinum, or many of these transition 09:11.367 --> 09:15.627 metals can do this trick of adding two at the same time to 09:15.633 --> 09:17.903 the alkene. 09:17.900 --> 09:21.200 Now you can also do it to sigma bonds. 09:21.200 --> 09:23.930 So here's palladium reacting with H2. 09:23.933 --> 09:27.133 It's just sigma and sigma-star now. 09:27.133 --> 09:29.403 But if that's the energy of the starting material in a 09:29.400 --> 09:33.870 pretty crummy calculation, so don't hang your hat on this, 09:33.867 --> 09:37.227 these are successive stages as you go left to right. 09:37.233 --> 09:41.433 First, you begin to associate the H2 with the palladium, and 09:41.433 --> 09:42.503 bond to it. 09:42.500 --> 09:45.700 Then the H2 gets even closer, and as it gets closer and 09:45.700 --> 09:48.400 closer, the hydrogens spread apart. 09:48.400 --> 09:51.000 And the reason I've drawn them up and down a little bit is to 09:51.000 --> 09:55.800 show energy minima and transition states. 09:55.800 --> 09:59.700 So first, you get the H2 associated with palladium, 09:59.700 --> 10:02.070 without very close contact. 10:02.067 --> 10:05.467 Then it gets closer, and goes over a transition state, and 10:05.467 --> 10:08.127 becomes this one, which is closer bonded. 10:08.133 --> 10:12.033 And then, the two hydrogens come apart, and 10:12.033 --> 10:13.903 get quite far apart. 10:13.900 --> 10:16.500 But notice, at least in this calculation, and in some 10:16.500 --> 10:19.470 others, as you'll see, it goes up hill a little bit. 10:19.467 --> 10:21.127 So that would seem to be unfavorable. 10:21.133 --> 10:23.433 You could do it, you could split the hydrogen apart on 10:23.433 --> 10:27.533 the metal, but in terms of enthalpy, kilocalories per 10:27.533 --> 10:29.003 mole, it's uphill. 10:29.000 --> 10:32.170 However, once it gets up there, these hydrogens can 10:32.167 --> 10:34.997 move from one metal to the next, because we're talking a 10:35.000 --> 10:37.900 solid metal, in this case. 10:37.900 --> 10:42.270 So in fact, it dissociates on the palladium surface, and 10:42.267 --> 10:43.827 then the hydrides move. 10:43.833 --> 10:46.933 So you get an advantage from entropy, from the hydrogens 10:46.933 --> 10:48.603 getting apart, even though it's uphill a 10:48.600 --> 10:50.200 little bit in energy. 10:50.200 --> 10:53.530 It's very favorable to move them apart in entropy, rather 10:53.533 --> 10:55.773 than having to have them right next to one another. 10:55.767 --> 11:00.327 So it's possible to dissociate hydrogen on palladium. 11:00.333 --> 11:04.673 Now here's a calculation certainly better than the 11:04.667 --> 11:05.567 previous one. 11:05.567 --> 11:07.097 It was published in the Journal of Physical 11:07.100 --> 11:08.970 Chemistry in 2004. 11:08.967 --> 11:11.827 And it shows the same thing, palladium approaching hydrogen 11:11.833 --> 11:15.033 above, palladium approaching methane below. 11:15.033 --> 11:17.773 And again, I don't think that these are great numbers, 11:17.767 --> 11:20.497 probably, but it gives you the idea of what I showed on the 11:20.500 --> 11:24.270 previous slide, and some specific geometries. 11:24.267 --> 11:27.427 OK, now, catalytic hydrogenation puts these two 11:27.433 --> 11:30.103 reactions together that we just looked at. 11:30.100 --> 11:34.000 You have what inorganic chemists 11:34.000 --> 11:36.470 call "oxidative addition." 11:36.467 --> 11:40.497 That's where we do this, which we just saw is possible, two 11:40.500 --> 11:43.030 electrons can get stabilized because of the orbitals that 11:43.033 --> 11:45.173 are available, to form something like a 11:45.167 --> 11:47.467 three-member ring here. 11:47.467 --> 11:49.467 And that's called oxidative addition. 11:49.467 --> 11:52.497 The reason it's called oxidative is the way inorganic 11:52.500 --> 11:54.030 chemists count electrons. 11:54.033 --> 11:58.003 They say that if you have a bond to metal, those electrons 11:58.000 --> 12:01.430 belong to the ligand, not to the metal. 12:01.433 --> 12:04.133 So electrons, formally, have been taken 12:04.133 --> 12:05.403 away from the metal. 12:05.400 --> 12:07.070 We'll talk more about oxidation and 12:07.067 --> 12:08.797 reduction before too long. 12:08.800 --> 12:11.230 But anyhow, that's called oxidative addition. 12:11.233 --> 12:13.633 But of course, you could do the reverse, as well. 12:13.633 --> 12:16.503 You could do reductive elimination, and pull the 12:16.500 --> 12:19.100 alkene back off again. 12:19.100 --> 12:22.930 OK, now you do the same thing with hydrogen, as we just saw. 12:22.933 --> 12:25.803 So you could have oxidative addition, those two arrows 12:25.800 --> 12:30.400 move like that, to give that, and then the blue reverse, the 12:30.400 --> 12:34.170 reductive elimination, and you're back where you started. 12:34.167 --> 12:37.827 But now, suppose you do both of these things. 12:37.833 --> 12:41.373 Let's suppose that we first do the oxidative addition, the 12:41.367 --> 12:44.997 insertion of palladium into the H-H bond, and one of the 12:45.000 --> 12:47.370 H's, let's say, moves away. 12:47.367 --> 12:49.897 And now we have room on the surface of the palladium, 12:49.900 --> 12:52.270 there, to bring in the alkene and do its trick. 12:56.433 --> 12:59.533 So now, we have this form. 12:59.533 --> 13:02.703 Now of course, you could do reductive elimination again. 13:02.700 --> 13:06.300 Now incidentally, in that form, the experts discuss just 13:06.300 --> 13:08.200 how much the different bonds are formed. 13:08.200 --> 13:10.900 Sometimes they draw it this way, and just say the alkene 13:10.900 --> 13:12.370 is complexed. 13:12.367 --> 13:16.197 But that begs the question of what is it that's holding the 13:16.200 --> 13:18.370 alkene there, and it's those orbital interactions 13:18.367 --> 13:19.167 that we looked at. 13:19.167 --> 13:20.967 The electrons going one way, the 13:20.967 --> 13:22.527 electrons going the other. 13:22.533 --> 13:27.833 So we'll for our purposes of our lecture today, we'll say 13:27.833 --> 13:29.933 that the bonds are completely formed, even though 13:29.933 --> 13:32.233 they may not be. 13:32.233 --> 13:34.333 OK, so you can do reductive elimination, it 13:34.333 --> 13:35.773 could come off again. 13:35.767 --> 13:39.927 But suppose you did the other reductive elimination? 13:39.933 --> 13:41.303 Suppose you did that one? 13:44.833 --> 13:45.873 Now you're over here. 13:45.867 --> 13:48.667 And you've put hydrogen on one carbon, and 13:48.667 --> 13:51.497 palladium on the other. 13:51.500 --> 13:53.800 Now suppose we have that hydrogen that's wandering 13:53.800 --> 13:57.300 around the surface, suppose we bring it back? 13:57.300 --> 13:58.830 Can you see what I'm going to do now? 14:07.267 --> 14:11.267 Chris, do you have an idea of what step is next? 14:11.267 --> 14:12.727 Look at the title of the slide. 14:12.733 --> 14:16.473 STUDENT: We might hydrogenate? 14:16.467 --> 14:18.697 PROFESSOR: Yeah, we want to put a hydrogen on each of the 14:18.700 --> 14:21.100 carbons, how are we going to do that? 14:21.100 --> 14:25.470 We've got a hydrogen on the right carbon already, how do 14:25.467 --> 14:27.967 we get a hydrogen on the left carbon? 14:27.967 --> 14:29.397 STUDENT: We have a hydrogen nearby, that's 14:29.400 --> 14:30.830 bonded to the palladium. 14:30.833 --> 14:33.033 PROFESSOR: Yeah, and the carbon is bonded to palladium. 14:33.033 --> 14:37.933 And what will we call the process that gets the hydrogen 14:37.933 --> 14:41.403 bonded to carbon, instead of the carbon and the hydrogen 14:41.400 --> 14:42.400 bonded to palladium? 14:42.400 --> 14:43.900 STUDENT: Substitution? 14:43.900 --> 14:45.130 PROFESSOR: Nope. 14:49.867 --> 14:50.767 It's that. 14:50.767 --> 14:53.727 Anybody got a name for that? 14:53.733 --> 14:55.833 That's the reductive elimination, the blue thing 14:55.833 --> 14:57.473 we've been talking about, all these, right? 14:57.467 --> 15:00.227 They come on, they come off, they come on, they come off. 15:00.233 --> 15:02.733 But if you put them on one way, and take them off a 15:02.733 --> 15:05.433 different way, you've done the trick. 15:05.433 --> 15:07.003 Got it? 15:07.000 --> 15:08.670 OK. 15:08.667 --> 15:12.667 Now, notice, that that addition of the palladium, the 15:12.667 --> 15:16.497 oxidative addition of alkene to palladium, happened two at 15:16.500 --> 15:19.000 the same time, so they come in on the same face. 15:19.000 --> 15:20.930 It's a syn addition. 15:20.933 --> 15:26.603 And then, when the hydrogens replace palladium, they come 15:26.600 --> 15:27.770 in on the front side. 15:27.767 --> 15:30.967 It's not a backside attack. 15:30.967 --> 15:32.827 When we curve those two arrows, it's 15:32.833 --> 15:34.673 not attacking backside. 15:34.667 --> 15:38.127 So, they come in from the same side as well, so the overall 15:38.133 --> 15:40.173 product is syn addition. 15:40.167 --> 15:42.027 The H's came in on the same-- 15:42.033 --> 15:44.473 here, the bottom face of the double bond. 15:44.467 --> 15:46.867 And of course, if you put methyl groups on there, and it 15:46.867 --> 15:50.397 were 2-butene, then you'd expect to get that particular 15:50.400 --> 15:54.470 isomer of the 2-butene, where the two hydrogens operated, 15:54.467 --> 15:55.997 added on same side. 15:56.000 --> 15:58.770 Of course, you couldn't tell it, because the other two 15:58.767 --> 16:00.767 things would be hydrogens as well. 16:00.767 --> 16:03.667 How could you tell? 16:03.667 --> 16:06.527 How could you tell that the two came in on the same side? 16:09.700 --> 16:11.270 PROFESSOR: You wouldn't you use hydrogen, 16:11.267 --> 16:11.667 what would you use? 16:11.667 --> 16:13.027 STUDENT: Deuterium. 16:13.033 --> 16:14.173 PROFESSOR: You'd use deuterium, as you say. 16:14.167 --> 16:16.367 Yeah, so then you could tell. 16:16.367 --> 16:19.127 And here's an example, from the book, where they use 16:19.133 --> 16:23.433 deuterium and platinum oxide, in this case, and the two D's 16:23.433 --> 16:26.603 came in on the same side. 16:26.600 --> 16:30.200 That was not necessary, in this case, to tell, because 16:30.200 --> 16:32.730 you also have the cyclohexane ring there. 16:32.733 --> 16:35.173 So, it says here that deuterium is 16:35.167 --> 16:36.697 added in a syn fashion. 16:36.700 --> 16:38.130 It's a syn addition. 16:38.133 --> 16:41.833 And here's a typical passage from another textbook, the 16:41.833 --> 16:44.033 Loudon textbook that we used several years ago, about 16:44.033 --> 16:47.433 stereochemistry of this addition reaction, catalytic 16:47.433 --> 16:48.773 hydrogenation. 16:48.767 --> 16:52.027 And it says, "stereospecific syn-addition" happens, it 16:52.033 --> 16:56.373 says, for "most alkenes." And it gives this example. 16:56.367 --> 16:59.867 But I'm actually doing this little bit to show you how to 16:59.867 --> 17:02.997 read text books. 17:03.000 --> 17:06.500 So it says, most alkenes do this, and give stereospecific 17:06.500 --> 17:08.100 syn-addition, and it gives an example. 17:08.100 --> 17:12.100 But notice, it doesn't say what the yield is. 17:12.100 --> 17:14.300 It could be one of these things-- remember last time, 17:14.300 --> 17:19.400 we said there was a 55:45, that was said to be specific, 17:19.400 --> 17:21.800 or to favor one over the other. 17:21.800 --> 17:24.130 So it doesn't say what the yield is. 17:24.133 --> 17:26.633 And it doesn't give any reference to the literature 17:26.633 --> 17:28.903 where you could look up and see what they yield was, or 17:28.900 --> 17:32.330 how they did it, or how much of the other isomer there 17:32.333 --> 17:33.703 might have been there. 17:33.700 --> 17:36.070 Now this is very typical for textbooks, and I have no doubt 17:36.067 --> 17:40.027 that this happens with high specificity, in this case. 17:40.033 --> 17:42.033 But on the other hand, you shouldn't be 17:42.033 --> 17:43.673 satisfied with that. 17:43.667 --> 17:47.527 So you would look in another book, like this book from 1972 17:47.533 --> 17:49.703 by House, Modern Synthetic Chemistry. 17:49.700 --> 17:51.870 Now this is a graduate-level text. 17:51.867 --> 17:55.327 So it shows an example, here, using palladium on carbon as 17:55.333 --> 17:57.933 the catalyst. Palladium on carbon means you have 17:57.933 --> 18:00.733 palladium metal, but you don't want to have a big chunk of 18:00.733 --> 18:02.303 metal, because there's not much surface. 18:02.300 --> 18:04.570 So you want it to be very finely divided, but you want 18:04.567 --> 18:05.597 to be able to handle it. 18:05.600 --> 18:08.470 You don't have very much, so you put it on charcoal. 18:08.467 --> 18:10.467 It's absorbed on the surface of the charcoal. 18:10.467 --> 18:12.767 So that's what palladium on carbon is. 18:12.767 --> 18:16.067 So it's done in acetic acid, with hydrogen gas at one 18:16.067 --> 18:18.927 atmosphere, and you have that double bond. 18:18.933 --> 18:21.273 And what do you would notice about the stereochemistry of 18:21.267 --> 18:22.227 the product? 18:22.233 --> 18:25.003 Is it a syn addition? 18:25.000 --> 18:28.230 Which is the product of syn addition? 18:28.233 --> 18:28.703 Sebastian? 18:28.700 --> 18:30.400 The one on the left or the right? 18:30.400 --> 18:31.200 STUDENT: The one on the left. 18:31.200 --> 18:31.930 PROFESSOR: The one on the left. 18:31.933 --> 18:33.433 The two came in on the same side. 18:33.433 --> 18:35.973 On the right, one came in on the top, one on the bottom. 18:35.967 --> 18:41.027 And 90% of the product is the wrong one, the one the book 18:41.033 --> 18:43.303 tells you, or almost any book will tell 18:43.300 --> 18:44.330 you, is a syn addition. 18:44.333 --> 18:47.233 And it often is. 18:47.233 --> 18:51.503 Now, look at this example from 1948. 18:51.500 --> 18:52.400 What's going on here? 18:52.400 --> 18:55.500 This is Barton in 1948. 18:55.500 --> 18:58.400 Anybody else remember what Barton was talking about in 18:58.400 --> 19:01.330 1948 or '49, from last semester? 19:06.633 --> 19:09.003 That was the first conformational analysis. 19:09.000 --> 19:11.530 And it was molecules very like this. 19:11.533 --> 19:14.833 So this is what he was working on, these steroids. 19:14.833 --> 19:18.703 But notice these two compounds are allylic isomers. 19:18.700 --> 19:21.530 They only differ in the position of that double bond. 19:21.533 --> 19:24.473 There are three carbons in a row, and a double bond between 19:24.467 --> 19:25.997 two of them. 19:26.000 --> 19:27.870 That's an allylic system. 19:27.867 --> 19:31.767 So these are isomers where you move a hydrogen from the top 19:31.767 --> 19:34.427 to the bottom, and now you have a double bond here and a 19:34.433 --> 19:35.403 single bond here. 19:35.400 --> 19:38.470 So those are allylic isomers. 19:38.467 --> 19:41.497 And now if you look at the details of this primary 19:41.500 --> 19:44.530 literature, it says that there's a rearrangement of one 19:44.533 --> 19:47.573 of these compounds to the other, right? 19:47.567 --> 19:50.697 And it says that it happens in 80% yield. 19:50.700 --> 19:54.430 80% of the product has gone from here to here. 19:54.433 --> 19:56.803 Now, this is what you would use for catalytic 19:56.800 --> 19:58.200 hydrogenation. 19:58.200 --> 20:01.830 But instead of hydrogenating, it first went by allylic 20:01.833 --> 20:03.433 rearrangement. 20:03.433 --> 20:05.073 Now, how did that happen? 20:05.067 --> 20:07.727 So let's look back again at the mechanism of the catalytic 20:07.733 --> 20:08.603 hydrogenation. 20:08.600 --> 20:12.230 First, you have the oxidative addition of the double bond, 20:12.233 --> 20:14.403 and then you have the reductive elimination, on the 20:14.400 --> 20:17.200 right, to put the first hydrogen on. 20:17.200 --> 20:19.200 And then you put the other hydrogen on 20:19.200 --> 20:21.500 the left, and continue. 20:21.500 --> 20:23.970 Of course that reaction would be reversible. 20:23.967 --> 20:31.697 You could have taken this back off again, in the wrong way, 20:31.700 --> 20:37.500 and instead of going there, pardon me, you could go there. 20:37.500 --> 20:42.530 But the other thing you could have done is, if there's an 20:42.533 --> 20:45.803 allylic hydrogen in the compound you're talking about, 20:45.800 --> 20:48.470 so not only the alkene, but the next door carbon has a 20:48.467 --> 20:50.367 hydrogen on it, you're here, you're here, you're here, 20:50.367 --> 20:54.297 you're here, you get to there. 20:54.300 --> 20:55.070 OK? 20:55.067 --> 20:58.927 And now, one possibility is to reverse that way. 20:58.933 --> 21:02.673 That's the reductive elimination, or pardon me, 21:02.667 --> 21:05.367 oxidative addition that takes you back here, that undoes 21:05.367 --> 21:08.467 those blue arrows, and would take you back. 21:08.467 --> 21:09.927 But what other option is there? 21:09.933 --> 21:11.473 Can anybody see another option? 21:17.600 --> 21:18.070 Liang? 21:18.067 --> 21:19.427 STUDENT: The other side. 21:19.433 --> 21:23.233 PROFESSOR: Aha, that compound is symmetric, if you have an 21:23.233 --> 21:25.673 allylic hydrogen. 21:25.667 --> 21:27.727 So it could unzip that way, too. 21:31.000 --> 21:37.630 And now, instead of going back to this, you go back to this. 21:37.633 --> 21:42.533 And if that does the reductive elimination, 21:42.533 --> 21:44.503 you come back here. 21:44.500 --> 21:49.230 And now, you'll notice that has isomerized the alkene. 21:49.233 --> 21:50.903 The double bond moved next door. 21:53.733 --> 21:56.273 So it's all these oxidative addition reductive 21:56.267 --> 21:59.097 eliminations, but if you go through that symmetric 21:59.100 --> 22:01.700 intermediate, then you can take the wrong one off as you 22:01.700 --> 22:04.600 go back toward starting material. 22:04.600 --> 22:07.330 So the starting material is actually isomerized product. 22:07.333 --> 22:09.803 So that's presumably how it happens. 22:09.800 --> 22:13.830 So catalytic hydrogenation can lead to allylic rearrangement. 22:13.833 --> 22:17.833 And now let's go back and look at that paper. 22:17.833 --> 22:22.933 And we see that if we had that rearrangement, this could go 22:22.933 --> 22:25.303 to this, in fact, it could go to four different isomers. 22:25.300 --> 22:26.730 It could be the double bond here, or 22:26.733 --> 22:29.333 here, or here, or here. 22:29.333 --> 22:30.773 So we could come back to this. 22:30.767 --> 22:34.327 And now, once you're here, if you add hydrogen, even if you 22:34.333 --> 22:37.633 add them from the same side, those two hydrogens, they 22:37.633 --> 22:39.403 could be the opposite side from where the 22:39.400 --> 22:42.070 first hydrogen was. 22:42.067 --> 22:45.127 So now you could expect to get this, and you'd expect more of 22:45.133 --> 22:48.803 this than this, because that form is more stable. 22:48.800 --> 22:54.000 It's conformationally a better structure. 22:54.000 --> 22:55.500 OK, so 90% there. 22:55.500 --> 22:58.370 Now, the nice thing is you don't have to even look at the 22:58.367 --> 23:01.067 secondary literature, you go back to the primary 23:01.067 --> 23:03.427 literature, because it gives a reference here. 23:03.433 --> 23:06.403 So we can look at that reference, and see here where 23:06.400 --> 23:09.630 they give the table about studying these things. 23:09.633 --> 23:12.803 And down here, in row 7, you see they're talking about 23:12.800 --> 23:16.900 compound VII, delta-9,10-octalin So the ring 23:16.900 --> 23:19.400 is numbered in a certain way, and that double bond is 23:19.400 --> 23:22.670 between nine and ten. 23:22.667 --> 23:27.167 Now, if they started with that material, you see they got 90% 23:27.167 --> 23:28.667 of the trans product. 23:28.667 --> 23:33.897 That's this one, that's what shown here: 90%, 10%. 23:33.900 --> 23:37.430 But if they did only partial hydrogenation, they still got 23:37.433 --> 23:41.673 90% of this, but they had 100%-- 23:41.667 --> 23:44.467 after doing 80% of the hydrogenation. 23:44.467 --> 23:46.897 It says down here they did it 80%. 23:46.900 --> 23:49.970 After doing that, they don't have any of this stuff. 23:49.967 --> 23:52.697 It's all this stuff. 23:52.700 --> 23:57.630 So if these things can go back and forth, it must be that the 23:57.633 --> 24:00.403 equilibrium lies in this direction. 24:00.400 --> 24:02.430 And occasionally, when you get over here, you 24:02.433 --> 24:05.473 go on to the product. 24:05.467 --> 24:08.127 And that's the explanation of it. 24:08.133 --> 24:10.973 But it's interesting to look even a little closer, to look 24:10.967 --> 24:13.927 at what happened if they started with VIII. 24:13.933 --> 24:17.533 So suppose they start with VIII. 24:17.533 --> 24:21.403 If you start at VII, and you can go through VIII to get 24:21.400 --> 24:24.030 down here, you get 90% of the product. 24:24.033 --> 24:25.933 That's their explanation. 24:25.933 --> 24:27.903 Suppose you start with pure VIII. 24:27.900 --> 24:29.170 What should you get? 24:32.300 --> 24:33.270 In terms of the product. 24:33.267 --> 24:37.227 If you didn't have VII, if you start with VIII. 24:37.233 --> 24:38.733 Debby, you got an idea? 24:38.733 --> 24:41.573 STUDENT: Wouldn't you get the one below? 24:41.567 --> 24:45.567 PROFESSOR: You should get at least this much, maybe more. 24:45.567 --> 24:46.227 Right? 24:46.233 --> 24:49.633 If the way you get here-- if some of it goes this way, and 24:49.633 --> 24:53.333 some of it goes this way, and you start here and get 10 to 24:53.333 --> 24:56.373 90, if you start here, you should get even 24:56.367 --> 24:59.027 more than 90 to 10. 24:59.033 --> 25:00.403 Because you don't have the chance 25:00.400 --> 25:02.400 of going here initially. 25:02.400 --> 25:03.700 Got it? 25:03.700 --> 25:07.130 OK, what does it say? 25:07.133 --> 25:10.633 You get 80%. 25:10.633 --> 25:13.003 So there's something rotten here, but no one's ever 25:13.000 --> 25:14.130 talked about it. 25:14.133 --> 25:16.333 It could be just that the experiments weren't done 25:16.333 --> 25:19.733 really carefully, or maybe the catalyst was a little bit 25:19.733 --> 25:21.273 different in one case than the other. 25:21.267 --> 25:22.997 I don't know what the answer is. 25:23.000 --> 25:26.870 But it's when you go back to dig in to where the real 25:26.867 --> 25:30.197 results are that you find things that are interesting. 25:30.200 --> 25:33.970 So evidently, this isn't 100% understood. 25:33.967 --> 25:38.367 But I have no doubt that this allylic rearrangement is a big 25:38.367 --> 25:41.497 source of getting what appears to be the wrong addition. 25:41.500 --> 25:44.930 that it really is syn addition, but it happens after 25:44.933 --> 25:46.103 you've rearranged things. 25:46.100 --> 25:50.400 So the product isn't what you would have expected, naively. 25:50.400 --> 25:56.130 OK, now, a process called metathesis of an alkene. 25:56.133 --> 26:01.703 This was reported when I first came here to Yale, the first 26:01.700 --> 26:04.000 year I was here, and it was amazing. 26:04.000 --> 26:06.500 People were amazed by this reaction. 26:06.500 --> 26:11.400 And the mechanism was quite speculative. 26:11.400 --> 26:13.970 Nobody had any idea what happened at the beginning. 26:13.967 --> 26:17.567 But in the subsequent whatever number of years, 45 years, 26:17.567 --> 26:19.067 it's been figured out. 26:19.067 --> 26:22.367 And what is involved is a double bond from 26:22.367 --> 26:24.427 the metal to carbon. 26:24.433 --> 26:26.773 Of course, there are there two other things on the carbon. 26:26.767 --> 26:29.527 But this is called an alkylidene complex. 26:29.533 --> 26:34.473 And in fact, this process was the basis for the Nobel Prize 26:34.467 --> 26:39.127 in 2005, which went to Grubbs. 26:39.133 --> 26:42.733 So this is a metal alkylidene complex. 26:42.733 --> 26:48.373 We can come in with an alkene, and do the oxidative addition, 26:48.367 --> 26:51.097 to form that, and a reductive elimination. 26:51.100 --> 26:54.300 So it gives a metalla- cyclobutane 26:54.300 --> 26:57.030 a cyclobutane that has a metal in it. 26:57.033 --> 26:59.133 Just by the same processes we talked about on 26:59.133 --> 27:01.973 the previous slide. 27:01.967 --> 27:05.267 Now, those processes are reversible. 27:05.267 --> 27:07.227 And what do you notice about reversing it? 27:07.233 --> 27:08.773 Liang? 27:08.767 --> 27:10.767 What about the intermediate here? 27:10.767 --> 27:11.767 STUDENT: It's symmetrical. 27:11.767 --> 27:13.397 PROFESSOR: It's symmetrical. 27:13.400 --> 27:18.770 So you can reverse the other direction, to go to there, and 27:18.767 --> 27:21.427 then that can come apart. 27:21.433 --> 27:25.473 And you've put the central carbon, the one that's here, 27:25.467 --> 27:27.797 changed it from being attached to this carbon to being 27:27.800 --> 27:29.330 attached to this carbon. 27:29.333 --> 27:33.233 So you can take, effectively, two alkenes, and mix up their 27:33.233 --> 27:37.773 carbons, which is double- bonded to which. 27:37.767 --> 27:44.427 Now, you've heard of Professor Ziegler, who last semester 27:44.433 --> 27:48.103 taught the other organic course. 27:48.100 --> 27:50.130 I don't know if you've seen him around in the lab, maybe. 27:50.133 --> 27:53.773 He's unusually tall, he's 6' 6", or something like that. 27:53.767 --> 27:55.727 And I point out, here, that he's not 27:55.733 --> 27:57.133 Professor Karl Ziegler. 27:57.133 --> 27:58.633 We'll talk about Professor Karl Ziegler 27:58.633 --> 28:00.633 a few slides later. 28:00.633 --> 28:04.803 But he was visiting Japan, in 1986, and this delegation of 28:04.800 --> 28:08.370 junior high girls thought he was so tall, they should get 28:08.367 --> 28:10.797 their picture taken with him, which is here. 28:10.800 --> 28:12.900 But he wasn't the only tall guy visiting 28:12.900 --> 28:14.100 Japan at that time. 28:14.100 --> 28:17.470 Here he is, touring together with Professor Grubbs, the guy 28:17.467 --> 28:21.227 that got the Nobel Prize in 2005, who's equally tall. 28:21.233 --> 28:24.503 In fact, Professor Grubbs's daughter played 28:24.500 --> 28:25.730 basketball at Yale. 28:25.733 --> 28:26.403 She's quite tall. 28:26.400 --> 28:28.700 I think she holds the rebounding record for women's 28:28.700 --> 28:30.100 basketball at Yale. 28:30.100 --> 28:34.170 So this'll help you remember Professor Grubbs, I hope. 28:34.167 --> 28:36.427 In fact, they took another picture together with their 28:36.433 --> 28:39.873 host, Professor Murahashi. 28:39.867 --> 28:44.097 So again, I underline that they're unusually tall people. 28:44.100 --> 28:48.470 OK, but Grubbs invented a process called ROMP: 28:48.467 --> 28:52.997 ring-opening metathesis polymerization. 28:53.000 --> 28:56.900 Now here's a double bond where both of the carbons in the 28:56.900 --> 29:00.800 double bond are part of the same molecule, I mean, the 29:00.800 --> 29:02.530 same framework. 29:02.533 --> 29:06.103 So if you cleave that double bond, and exchange partners 29:06.100 --> 29:10.570 with something else, you still have the two linked together 29:10.567 --> 29:13.097 through this other ring. 29:13.100 --> 29:16.130 So if you bring in this alkylidene compound, and do 29:16.133 --> 29:20.533 the trick of metathesis, you get that. 29:20.533 --> 29:26.203 And now the product is still an alkylidene ruthenium here, 29:26.200 --> 29:27.330 so you can do that with another 29:27.333 --> 29:29.033 one of these molecules. 29:29.033 --> 29:32.433 In fact, you can do with the n of the molecules, and they'll 29:32.433 --> 29:36.673 all link together in a chain like this, to give a polymer. 29:36.667 --> 29:40.667 So this ring opening metathesis was a very 29:40.667 --> 29:44.767 important part of this Nobel Prize work 29:44.767 --> 29:47.397 to generate a polymer. 29:47.400 --> 29:50.270 OK, now catalytic hydrogenation, we 29:50.267 --> 29:52.327 saw, looked like this. 29:52.333 --> 29:55.903 But Ziegler-Natta polymerization, this is the 29:55.900 --> 30:01.400 other Ziegler, Karl Ziegler, a German, looks very similar. 30:01.400 --> 30:06.800 So it has titanium, with an R group on it. 30:06.800 --> 30:13.700 An alkene comes in, oxidative addition, to give this. 30:13.700 --> 30:18.630 Reductive elimination, on the other side gives that. 30:18.633 --> 30:23.573 But now, that we could just call a different R group. 30:23.567 --> 30:25.927 It's not the original R group, it's the R group with two 30:25.933 --> 30:29.433 carbons in between, that we just brought in. 30:29.433 --> 30:30.673 Now what can you do? 30:34.167 --> 30:37.467 You can bring it back to start over again, right? 30:37.467 --> 30:40.097 And that'll be the R, and then you bring it in, and that's 30:40.100 --> 30:42.700 the R. And then you do it again, and again, and again, 30:42.700 --> 30:46.430 and you can make a very long chain of ethylene molecules, 30:46.433 --> 30:47.773 for example. 30:47.767 --> 30:49.267 Now, Ziegler found this-- 30:49.267 --> 30:53.627 I contacted Grubbs, yesterday, in order to get permission to 30:53.633 --> 30:57.633 show his picture to you, and Murahashi as well, and 30:57.633 --> 30:58.933 Ziegler, incidentally. 30:58.933 --> 31:02.933 But he told me an interesting story of how Ziegler 31:02.933 --> 31:04.833 discovered this. 31:04.833 --> 31:08.003 It was during the second World War, and in Germany they were 31:08.000 --> 31:10.030 short of lubricating oil. 31:10.033 --> 31:13.173 So he was trying to figure out how to use triethyl aluminum 31:13.167 --> 31:17.827 to add to alkenes, and then polymerize on the basis of 31:17.833 --> 31:20.833 that to get things that could be lubricating oils. 31:20.833 --> 31:23.733 And after the war, he continued that work, but 31:23.733 --> 31:27.373 sometimes they found different products, rather than these 31:27.367 --> 31:28.697 oils they were trying to make. 31:28.700 --> 31:31.300 And they traced it to the presence of 31:31.300 --> 31:33.870 metals in the reactor. 31:33.867 --> 31:36.327 So then they tried all different salts, and when they 31:36.333 --> 31:40.673 used titanium tetrachloride, they found that they had made 31:40.667 --> 31:45.527 a heterogeneous catalyst for polymerization, the thing that 31:45.533 --> 31:46.533 I've shown here. 31:46.533 --> 31:49.103 Now I underline that this is heterogeneous. 31:49.100 --> 31:51.800 You mix these things together, it's a witch's brew, and 31:51.800 --> 31:54.630 nobody knows, really, exactly what's in there. 31:54.633 --> 31:58.773 And the reason you don't know is because it's a solid. 31:58.767 --> 32:01.627 It's not a pure crystalline compound, it's not something 32:01.633 --> 32:04.273 in solution that you could do spectroscopy on to figure out 32:04.267 --> 32:05.697 exactly what it is. 32:05.700 --> 32:08.130 So it's very hard to study mechanism with these 32:08.133 --> 32:09.803 heterogeneous catalysts. 32:09.800 --> 32:12.000 But that doesn't mean they're not useful. 32:12.000 --> 32:15.600 For example, high density polyethylene, the number two 32:15.600 --> 32:20.430 of your recycling thing, with ns of from 800 to a quarter 32:20.433 --> 32:25.833 million chain lengths, was made in 2004 to the tune of 25 32:25.833 --> 32:29.933 times 10 to the sixth tons, 25 million tons. 32:29.933 --> 32:36.003 Or polypropylene, with up to 10 to the 5 units in a chain, 32:36.000 --> 32:39.970 again, 45 million tons in 2007. 32:39.967 --> 32:43.997 So this Ziegler-Natta catalyst was a really revolutionary 32:44.000 --> 32:46.400 thing for making polymers. 32:46.400 --> 32:50.330 But it was hard to do the mechanisms. 32:50.333 --> 32:54.603 Now, one thing that we'll see later, that free radicals also 32:54.600 --> 33:00.570 can polymerize things, can polymerize alkenes. 33:00.567 --> 33:04.427 But a difference here is that these are isotactic, that you 33:04.433 --> 33:08.573 get from Ziegler-Natta polymerization. 33:08.567 --> 33:12.567 So I should tell you what tacticity is. 33:12.567 --> 33:16.667 So if you have a polymer chain, and the alkenes had, 33:16.667 --> 33:20.227 say, methyl groups on them, propylene instead of ethylene, 33:20.233 --> 33:21.573 then you have a bunch of stereocenters. 33:24.233 --> 33:28.233 Now, notice that every alkene went in head to tail, that is, 33:28.233 --> 33:34.103 CH2 then CH, CH2, CHCH3, CH2, CHCH3. 33:34.100 --> 33:36.300 CH2, CH, CH3. 33:36.300 --> 33:40.070 So it's head to tail, but it's stereoregular. 33:40.067 --> 33:42.497 All the methyls are coming out that you. 33:42.500 --> 33:45.730 And that's called isotactic. 33:45.733 --> 33:49.533 An alternative would be all head to tail 33:49.533 --> 33:54.003 but syndiotactic: out, back, out, back, out, 33:54.000 --> 33:55.270 back, every other one. 33:58.033 --> 34:00.773 And of course it could be random. 34:00.767 --> 34:02.227 Out and back. 34:02.233 --> 34:05.603 So there are these three different fundamental types of 34:05.600 --> 34:10.130 polymers: isotactic, syndiotactic, and atactic. 34:10.133 --> 34:12.203 And they have different properties, and we'll talk 34:12.200 --> 34:15.070 about polymer properties in the next lecture, and why they 34:15.067 --> 34:16.397 should be different. 34:16.400 --> 34:20.770 So for some purposes you'd want one, for some another. 34:20.767 --> 34:23.167 Now there are two questions that we'll address here. 34:23.167 --> 34:25.227 One is, how do you know which is which? 34:25.233 --> 34:27.703 How do you know whether you have an isotactic or a 34:27.700 --> 34:29.230 syndiotactic or atactic. 34:29.233 --> 34:32.033 And for that, you've got to wait until we get to NMR, it's 34:32.033 --> 34:33.003 coming very soon. 34:33.000 --> 34:36.100 It's a really neat way to figure out which is which. 34:36.100 --> 34:38.870 But a more fundamental question is, how do you 34:38.867 --> 34:42.327 control what you make? 34:42.333 --> 34:46.573 So there are these catalysts, instead of using titanium, use 34:46.567 --> 34:50.327 these zirconium catalysts, which are homogeneous. 34:50.333 --> 34:53.903 That means they're dissolved they're not some solid that's 34:53.900 --> 34:55.400 in there. So it's possible to do 34:55.400 --> 34:57.230 spectroscopy on these things. 34:57.233 --> 35:00.103 And Kaminsky, the name associated with this 35:00.100 --> 35:04.530 catalysis, has to do with his accidental discovery that 35:04.533 --> 35:08.633 adding MAO makes these very reactive. 35:08.633 --> 35:13.403 MAO is methylaluminoxane, which is a sophisticated name 35:13.400 --> 35:16.630 for something that nobody knows what it is. 35:16.633 --> 35:19.273 You mix stuff together and you get that, and it's 35:19.267 --> 35:20.697 not always the same. 35:20.700 --> 35:25.400 But if you add it to the zirconium dichloride 35:25.400 --> 35:29.530 complexes, you get a very active catalyst. So there have 35:29.533 --> 35:33.633 been, I think, since this was discovered in 1980, there have 35:33.633 --> 35:37.033 been something like 7,000 papers written on it, or 35:37.033 --> 35:41.273 something like that, and 2,000 patents. 35:41.267 --> 35:44.727 Now one thing that's pretty much agreed on is that what 35:44.733 --> 35:49.233 this methylaluminoxane takes the chlorides off, puts an R 35:49.233 --> 35:51.903 group like methyl on the zirconium, and 35:51.900 --> 35:53.170 leaves it as a cation. 35:55.467 --> 35:57.927 Now, what happens next? 35:57.933 --> 36:03.503 The alkenes approach, but they approach from alternate faces. 36:03.500 --> 36:05.100 Let's see what that means. 36:05.100 --> 36:08.400 So here we take propylene, and bring it into the front to 36:08.400 --> 36:10.930 make one of these complexes. 36:10.933 --> 36:16.233 And then the R group shifts across, and you make a bond. 36:16.233 --> 36:20.033 Have you ever seen a reaction like that, where you have a 36:20.033 --> 36:23.103 metal with a group attached to it, alkene comes up, and you 36:23.100 --> 36:25.200 form a bond here and this thing comes over? 36:30.633 --> 36:33.573 The BH, hydroboration, is exactly that 36:33.567 --> 36:34.797 same kind of thing. 36:37.000 --> 36:40.130 So we'll call that new group R prime. 36:40.133 --> 36:41.933 The original one was R . 36:41.933 --> 36:45.033 But now the next alkene comes in and associates with the 36:45.033 --> 36:48.133 zirconium, but what's different from 36:48.133 --> 36:50.673 the first one I drew? 36:50.667 --> 36:53.227 It's now in the back. 36:53.233 --> 36:55.433 The first alkene came in in the front. 36:55.433 --> 36:58.903 So it goes in the back, now the R prime moves back there, 36:58.900 --> 37:02.430 and then the next alkene comes in in front. 37:02.433 --> 37:03.903 And it comes over there. 37:03.900 --> 37:05.000 And so on, and so on. 37:05.000 --> 37:07.070 And you build a long chain. 37:07.067 --> 37:10.797 But notice, every other one is reacting in front, in back, in 37:10.800 --> 37:12.270 front, in back. 37:12.267 --> 37:15.027 Now let's compare the front and back of 37:15.033 --> 37:17.903 this zirconium complex. 37:17.900 --> 37:21.530 Notice it has an axis of symmetry there. 37:21.533 --> 37:24.703 If you rotate 180 degrees about that axis of symmetry, 37:24.700 --> 37:26.600 you get the same thing again. 37:26.600 --> 37:28.830 So the front and the back are superimposable. 37:28.833 --> 37:30.733 They look just the same. 37:30.733 --> 37:33.033 So whatever happens in front with respect to 37:33.033 --> 37:37.203 stereochemistry will happen the same way in back. 37:37.200 --> 37:41.870 So the two faces, front and back, are homotopic, they're 37:41.867 --> 37:45.767 the same, so you'll get the same chemistry, the same 37:45.767 --> 37:48.067 stereochemistry, at either one. 37:48.067 --> 37:51.267 Now how is it different in this case? That instead of 37:51.267 --> 37:54.567 having an axis of symmetry has a mirror plane of symmetry. 37:54.567 --> 37:57.727 What does that mean about the front and the back? 37:57.733 --> 37:58.033 Sebastian? 37:58.033 --> 38:00.273 What do you say? 38:00.267 --> 38:01.667 What's the relationship between the 38:01.667 --> 38:03.467 front and the back? 38:03.467 --> 38:05.467 Are they superimposable? 38:05.467 --> 38:06.827 STUDENT: No. 38:06.833 --> 38:08.433 PROFESSOR: So what would you call them? 38:08.433 --> 38:09.303 STUDENT: Enantiotopic 38:09.300 --> 38:11.270 PROFESSOR: Right, so those are enantiotopic. 38:11.267 --> 38:13.797 So whatever the one's face does, the other one will do 38:13.800 --> 38:15.800 the opposite. 38:15.800 --> 38:18.100 And as you bounce back and forth, what product are you 38:18.100 --> 38:19.270 going to get now? 38:19.267 --> 38:20.667 STUDENT: Syndiotactic 38:20.667 --> 38:21.927 PROFESSOR: It'll be syndiotactic. 38:24.667 --> 38:27.867 And now suppose you take this one, which has a horizontal 38:27.867 --> 38:31.627 plane, which means the top and the bottom are both 38:31.633 --> 38:32.203 accessible. 38:32.200 --> 38:35.770 On the front, you can go either to the top or to the 38:35.767 --> 38:37.527 bottom, equally. 38:37.533 --> 38:38.873 So there's no selection. 38:38.867 --> 38:42.027 So what do you think you're going to get now? 38:42.033 --> 38:44.033 If it doesn't make any difference which way you go. 38:47.133 --> 38:50.233 Now the faces are achiral, and you get an atactic product. 38:50.233 --> 38:53.173 So you can control which one you get by choosing the 38:53.167 --> 38:57.427 symmetry of the ligand that's attached to the zirconium. 39:00.233 --> 39:03.373 Now as I said, as I promised, you can also do free-radical 39:03.367 --> 39:04.167 polymerization. 39:04.167 --> 39:06.867 I said we'd discuss that. 39:06.867 --> 39:10.297 This was the earliest kind of polymerization studied in 39:10.300 --> 39:11.800 laboratories. 39:11.800 --> 39:15.470 So alkene comes in, bingo. 39:15.467 --> 39:16.667 Another one, bingo. 39:16.667 --> 39:17.127 Bingo. 39:17.133 --> 39:17.503 Bingo. 39:17.500 --> 39:17.800 Bingo. 39:17.800 --> 39:19.730 So we're growing a long chain. 39:19.733 --> 39:23.333 But the difference is that in this case, you can get 39:23.333 --> 39:28.903 rotation around this bond to get that form. 39:28.900 --> 39:33.300 And when you do, that radical is close to this hydrogen. 39:33.300 --> 39:36.170 And you can go from a primary radical 39:36.167 --> 39:39.867 to a secondary radical. 39:39.867 --> 39:42.367 That's downhill. 39:42.367 --> 39:44.797 And now you can add an alkene to that. 39:47.533 --> 39:51.273 So if you do radical polymerization, as opposed to 39:51.267 --> 39:55.227 doing these metal-catalyzed polymerizations, you can get 39:55.233 --> 40:00.003 branches, you get occasional butyl chains, C4 chains, stuck 40:00.000 --> 40:01.500 on your long chain. 40:01.500 --> 40:04.830 And that means that they don't pack together as efficiently, 40:04.833 --> 40:07.733 so it's not as crystalline. 40:07.733 --> 40:11.733 So since it doesn't pack as well, it's not as dense. 40:11.733 --> 40:15.133 So that gives low density polyethylene, the kind of 40:15.133 --> 40:18.933 stuff that you get in dry cleaner bags, the flimsy 40:18.933 --> 40:22.173 stuff, as opposed to what you would get in a supermarket 40:22.167 --> 40:26.267 to carry groceries in, which is tougher, and opaque. 40:28.733 --> 40:29.933 Now let's look at it again. 40:29.933 --> 40:32.733 We start polymerization going, fine, free-radical 40:32.733 --> 40:33.973 polymerization. 40:33.967 --> 40:38.197 But, we may not want it to keep going, because properties 40:38.200 --> 40:41.470 of the polymer, like its viscosity, its melting point, 40:41.467 --> 40:43.267 depend on how long the chain is. 40:43.267 --> 40:45.667 We may want to control how long the chain is. 40:45.667 --> 40:49.727 How could we control the length of the chain? 40:49.733 --> 40:53.233 One way to control the polymer chain length is to add a 40:53.233 --> 40:55.933 molecule, like carbon tetrachloride. 40:55.933 --> 40:58.033 There are many such reagents, not just carbon 40:58.033 --> 40:59.473 tetrachloride. 40:59.467 --> 41:01.697 OK, now, the radical can attack the 41:01.700 --> 41:03.400 chlorine, like this. 41:06.433 --> 41:08.573 And now you have a trichloromethyl radical, and 41:08.567 --> 41:10.997 your chain is done. 41:11.000 --> 41:14.370 But, you have the trichloromethyl radical. So it 41:14.367 --> 41:15.797 can add to another alkene. 41:19.267 --> 41:22.227 And then that one can grow a new chain. 41:22.233 --> 41:26.833 So you see, what you've done by this is used what's called 41:26.833 --> 41:29.133 a chain-transfer agent. 41:29.133 --> 41:34.273 It doesn't destroy the kinetic chain. The radical still keeps 41:34.267 --> 41:36.827 working, but on a new molecule. 41:36.833 --> 41:40.073 So you shorten the polymer molecules without terminating 41:40.067 --> 41:41.427 the chain reaction. 41:41.433 --> 41:44.303 So if you add more of the chain- transfer agent, you get 41:44.300 --> 41:46.230 shorter chains. 41:46.233 --> 41:49.373 So if you measure the rate of the transfer, the reaction 41:49.367 --> 41:52.367 with the carbon tetrachloride, versus the rate constant for 41:52.367 --> 41:55.997 polymerization, in the particular case of styrene and 41:56.000 --> 42:00.670 carbon tetrachloride, that ratio was 0.01. 42:00.667 --> 42:04.767 So, if you don't have to worry about radicals finding 42:04.767 --> 42:08.167 radicals, they're rather dilute, then the molecular 42:08.167 --> 42:13.227 length will be how likely it is to react with styrene 42:13.233 --> 42:15.733 compared to how likely it is to react with carbon 42:15.733 --> 42:18.203 tetrachloride and terminate the chain. 42:18.200 --> 42:20.730 But that depends on the concentration of styrene, and 42:20.733 --> 42:21.333 the concentration. 42:21.333 --> 42:27.503 So if you know these two, you can then work out-- 42:27.500 --> 42:35.370 since the transfer reaction with this process here is only 42:35.367 --> 42:36.727 1% as fast. 42:36.733 --> 42:39.333 So if you had equal amounts of styrene and carbon 42:39.333 --> 42:43.603 tetrachloride, you'd tend to go about 100 molecules before 42:43.600 --> 42:44.930 you got a chain transfer. 42:44.933 --> 42:48.703 So you get, on average, about 100 molecular-- 42:48.700 --> 42:50.630 100 units in a chain. 42:50.633 --> 42:52.933 If you had more carbon tetrachloride, you'd get 42:52.933 --> 42:53.703 shorter chains. 42:53.700 --> 42:55.270 If you had less, you'd get longer chains. 42:55.267 --> 42:57.767 So you can control it, but not precisely. 42:57.767 --> 43:01.897 There's a property called dispersity, which is they're 43:01.900 --> 43:04.300 not all exactly the same length, they're average that, 43:04.300 --> 43:05.770 but some are longer, some are shorter. 43:05.767 --> 43:10.027 And how wide is this determines something about, 43:10.033 --> 43:14.073 obviously, the properties of the material you get. 43:14.067 --> 43:16.397 Ok, we won't go into that any further. 43:16.400 --> 43:19.330 Now alkene and diene oligomerization and 43:19.333 --> 43:22.833 polymerization, using carbon electrophiles 43:22.833 --> 43:24.673 as the active reagents. 43:24.667 --> 43:28.567 Now oligo- means a few, so oligomerization is putting 43:28.567 --> 43:31.197 just a few such units together. 43:31.200 --> 43:35.570 And so we're going to use either sigma-star of R with a 43:35.567 --> 43:41.727 leaving group, or R cations as the reagent to do the 43:41.733 --> 43:44.033 polymerization. 43:44.033 --> 43:49.233 So if you have R+ as an electrophile, you do a really 43:49.233 --> 43:51.173 interesting reaction. 43:51.167 --> 43:55.227 Notice you can take isobutane and isobutylene, react them 43:55.233 --> 44:01.073 with H2SO4, and add the elements of the isobutane, and 44:01.067 --> 44:04.327 I've colored them because you can do isotopic labeling to 44:04.333 --> 44:05.603 see what's what. 44:05.600 --> 44:08.400 Notice that what added to the alkene was 44:08.400 --> 44:11.970 this C-H sigma bond. 44:11.967 --> 44:14.097 How do you like that, Noelle? 44:14.100 --> 44:16.830 Can you see any problem with doing a reaction like that? 44:19.733 --> 44:25.503 What's the HOMO and LUMO of the purple molecule here? 44:25.500 --> 44:26.470 STUDENT: There doesn't seem to be any. 44:26.467 --> 44:28.667 PROFESSOR: There's no functional group there. 44:28.667 --> 44:30.367 How can you do it? 44:30.367 --> 44:33.367 Well, tell me what would happen first, if you have a 44:33.367 --> 44:36.667 sulfuric acid and react with this mixture. 44:36.667 --> 44:39.927 What you think would happen first? 44:42.833 --> 44:45.733 Where is there a functional group? 44:45.733 --> 44:47.073 STUDENT: The pi. 44:47.067 --> 44:48.027 PROFESSOR: The pi bond. 44:48.033 --> 44:51.703 So proton would attack the pi electrons. 44:51.700 --> 44:53.430 And which end would it attack? 44:53.433 --> 44:56.233 Would you put the proton here, or would you put the proton on 44:56.233 --> 44:58.103 the more substituted carbon? 44:58.100 --> 44:59.530 STUDENT: It would be Markovnikov. 44:59.533 --> 45:01.103 PROFESSOR: It would be Markovnikov. You'd want to get 45:01.100 --> 45:02.900 a t-butyl cation. 45:02.900 --> 45:04.570 OK, so we'll do that. 45:04.567 --> 45:07.467 And incidentally, this product was not irrelevant, 45:07.467 --> 45:11.227 because that's what they mean when they say octane. 45:11.233 --> 45:15.073 That compound is defined as 100 octane, for the engine 45:15.067 --> 45:16.097 performance. 45:16.100 --> 45:19.600 So this was being worked on, during the Second World War, 45:19.600 --> 45:24.000 to try to make high-quality fuel for airplanes. 45:24.000 --> 45:27.430 OK, so we'll follow what Noelle says, and 45:27.433 --> 45:29.333 make the t-butyl cation. 45:29.333 --> 45:31.973 And now the t-butyl cation can react with the 45:31.967 --> 45:34.597 alkene, to give this. 45:34.600 --> 45:37.930 And now you'd say, why don't we just keep going? 45:37.933 --> 45:41.703 Well, it depends on what the situation is, and you'll see 45:41.700 --> 45:43.070 it can do that. 45:43.067 --> 45:46.227 But another thing it could do is react with this. 45:46.233 --> 45:48.403 Watch this. 45:48.400 --> 45:51.130 This is a tertiary cation. 45:51.133 --> 45:54.573 But it's rather hindered. 45:54.567 --> 45:58.227 This one, if you transfer this with its electrons, curved 45:58.233 --> 46:03.003 arrow there, that's a hydride shift. 46:03.000 --> 46:05.530 We've seen hydride shifts before. 46:05.533 --> 46:07.973 The difference is this is happening between two 46:07.967 --> 46:10.727 molecules, rather than for one carbon to the next in the 46:10.733 --> 46:12.233 same molecule. 46:12.233 --> 46:15.903 But it was shown by Bartlett in 1944 that this process 46:15.900 --> 46:18.700 happens, using isotopic labels. 46:18.700 --> 46:21.730 So it gives isooctane, and what's the other product? 46:21.733 --> 46:24.273 What's the purple product? 46:24.267 --> 46:25.227 The H went-- 46:25.233 --> 46:28.533 the hydride, not proton, hydride, the H with its 46:28.533 --> 46:29.903 electrons went up here. 46:29.900 --> 46:32.570 What was left behind? 46:32.567 --> 46:34.827 The t-butyl cation. 46:34.833 --> 46:36.003 But that's what you need here. 46:36.000 --> 46:38.530 So this is a chain, it can go round and round. 46:38.533 --> 46:40.873 So you add isobutane to isobutylene. 46:43.433 --> 46:50.533 Now, if you don't have the isobutane there, then it turns 46:50.533 --> 46:54.703 out that it could do this polymerization, add another 46:54.700 --> 46:57.370 one and another one, et cetera, et cetera. 46:57.367 --> 46:59.927 And that gives polyisobutylene, which is 46:59.933 --> 47:01.673 called butyl rubber. 47:01.667 --> 47:05.097 And it's not a very strong material, but it has the 47:05.100 --> 47:07.630 virtue of being airtight. 47:07.633 --> 47:10.573 So that's what's made to seal tires. 47:10.567 --> 47:12.897 When they made inner tubes in those days, they were made out 47:12.900 --> 47:17.730 of butyl rubber, to hold the air in. 47:17.733 --> 47:21.633 OK, so now these electrophiles in terpene and steroid 47:21.633 --> 47:22.873 biogenesis. 47:25.067 --> 47:29.427 Now I'm going to get on to this next time, but since I 47:29.433 --> 47:31.773 brought stuff here, I'm going to entertain you 47:31.767 --> 47:33.397 with show-and-tell. 47:33.400 --> 47:35.930 It comes after this set of slides. 47:35.933 --> 47:39.603 But since I've got it here, I'm going to do it. 47:44.567 --> 47:46.297 So we'll turn on the light here. 47:46.300 --> 47:53.700 And what I have here, is water and vinegar, dilute acetic 47:53.700 --> 47:57.470 acid, and this stuff that I bought down at the art supply 47:57.467 --> 47:59.667 store called mold builder. 47:59.667 --> 48:05.027 But if I read here, it says, it's ammonia, 100% natural 48:05.033 --> 48:07.233 latex, that means it came right out of 48:07.233 --> 48:08.973 the tree, and water. 48:08.967 --> 48:15.167 So all that's in there is tree sap, and water, and ammonia. 48:15.167 --> 48:17.327 So I'm going to pour some into the water here. 48:23.200 --> 48:24.370 I'm going to take my jacket off and 48:24.367 --> 48:27.527 tuck my tie in actually. 48:27.533 --> 48:29.373 I think that might be prudent. 48:33.900 --> 48:35.330 OK. 48:35.333 --> 48:38.633 So we're going to open it up here, and we'll 48:38.633 --> 48:39.873 pour some in there. 48:48.267 --> 48:51.627 OK, now the ammonia keeps the molecules-- 48:51.633 --> 48:53.373 we'll talk about this next time -- 48:53.367 --> 48:55.697 apart from one another of this latex. 49:04.533 --> 49:06.973 But if we add some vinegar, it'll get rid of the ammonia. 49:18.867 --> 49:22.027 Obviously I didn't measure it very carefully. 49:22.033 --> 49:25.473 Oh, there, we're doing it. 49:25.467 --> 49:27.167 So now the molecules are coming together. 49:30.800 --> 50:01.300 So if I reach in here and grab it, get rid of that water, dry 50:01.300 --> 50:02.530 it a few times here. 50:22.067 --> 50:23.397 So we've made a rubber ball. 50:30.200 --> 50:30.600 Good. 50:30.600 --> 50:32.470 OK, if anybody wants to make a rubber ball, you 50:32.467 --> 50:33.427 can come and do it. 50:33.433 --> 50:36.433 Thank you.