Lecture Catalytic Organometallics 22 - 18.06.14
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GastrinPlatinPalladiumProcess (computing)GoldConnective tissueChemical reactionChemistrySystemic therapyAcetateWursthülleNickelMetallbindungMetalFunctional groupMetallorganische ChemieCarbon (fiber)IonenbindungLecture/Conference
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PolymerNitrileNickelChemical reactionLactitolLigandAcetatePhosphineChiralität <Chemie>PalladiumFunctional groupHydrocyanierungBiosynthesisCyanidionLigandMultiprotein complexAbbruchreaktionPhosphideZincAcidAddition reactionLecture/Conference
08:24
NickelFunctional groupEnantiomereLecture/Conference
09:19
PhosphideLecture/Conference
10:15
Chemical reactionNaproxenAnti-inflammatoryProcess (computing)BASF-AktiengesellschaftChemistryGene expressionPharmacyHalideCell cycleCopperBromideReppe, WalterWaterAcrylic acidCarbon (fiber)NickeltetracarbonylNickelMaterials scienceLecture/Conference
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KaliumhydroxidTetrahydrofuranTetrahydropyranFunctional groupCyclooctatetraenChemical reactionSetzen <Verfahrenstechnik>Process (computing)Materials scienceBiosynthesisPolymerLactoneNickelSystemic therapyEsterOxideChemistryCombine harvesterIsotopenmarkierungIsomerLigandHeterodimereWursthülleCycloadditionBy-productOmega-6-FettsäurenAcetyleneBenzeneCyclododecanPressureHydrogenLecture/Conference
21:23
Cyclische VerbindungenTriphenylphosphinLigandBiosynthesisHuman body temperaturePressurePropeneEthyleneChemical reactionSystemic therapyAcetyleneHydrogenDieneNickelElectronAutoclavePhosphideCycloadditionStyrolNaturstoffSetzen <Verfahrenstechnik>Functional groupHeterodimereSteelPolyethyleneLecture/Conference
29:11
Chiralität <Chemie>Grignard-ReaktionAzo couplingEnantiomereYield (engineering)Chemical reactionNickelLecture/Conference
30:57
ButyllithiumPalladiumKohlenstoff-14HalideAryl halideChlorideNickelVinylverbindungenCombine harvesterAzo couplingLecture/Conference
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Yield (engineering)NickelButadienLecture/Conference
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Chiralität <Chemie>ButadienIonenbindungNickelChemical structureEnantiomereSetzen <Verfahrenstechnik>Chemical reactionWursthülleYield (engineering)MixtureBiosynthesisRacemizationLigandAlpha particleAusgangsgesteinZincChlorideLecture/Conference
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CigaretteNickelPalladiumYield (engineering)EsterFunctional groupPotassiumProcess (computing)Pivalic acidAzo couplingChemical reactionTriphenylphosphinBoronsäurenButylWaterWalkingBromidePhosphateLecture/Conference
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Azo couplingBenzeneLecture/Conference
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CigaretteNickelHuman body temperatureGesundheitsstörungPhenyl groupFunctional groupChemical reactionPhosphineCyclohexanPivalic acidTolueneBoronAzo couplingChlorideIonenbindungLecture/Conference
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Alpha particleAddition reactionAlkyneProcess (computing)StereoselectivityNaturstoffFunctional groupKohlenstoffgruppeWursthülleComplication (medicine)SpeciesBiosynthesisYield (engineering)Grignard-ReaktionChromiumNitrileNickelChemical reactionAllylVinylverbindungenTachyphylaxieOxygenierungLecture/Conference
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Allyl alcoholNickelIonenbindungAzo couplingCombine harvesterReaction mechanismBoraneReducing agentAlkyneProcess (computing)Setzen <Verfahrenstechnik>Lecture/Conference
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Chemical reactionElimination reactionEthyleneActivity (UML)HydrogenIonenbindungLecture/Conference
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AlcoholAlkeneAllyl alcoholAbbruchreaktionGesundheitsstörungChemical reactionBenzaldehydeLecture/Conference
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Computer animation
Transcript: English(auto-generated)
00:05
Welcome to part 22 of lecture on catalytic organometallics. Well, let's have a look at the group 10 metals. That's nickel, palladium, and platinum.
00:27
And as you certainly remember, we talk about palladium catalyzed reactions. Certainly, palladium catalysis offers the richest
00:42
and most versatile catalytic systems. So most versatile, a rich catalytic chemistry.
01:00
What about platinum? Well, we discussed some platinum catalyzed reaction in connection or in comparison with gold catalyzed processes. However, platinum carbon bonds are known to be significantly more stable than palladium
01:26
carbon bonds. And more stable carbon metal bonds means slower in catalytic processes. So it is useful in special cases,
01:41
but compared to palladium chemistry, it does not really compete. Well, what about nickel? Well, so nickel was known to be less active generally.
02:07
You need a higher catalyst loading, well, in the range of 3% to 20% catalyst loading.
02:24
As you know, with palladium chemistry, we normally start our test reactions with 5% to 10% palladium. On the other hand, later on, one tries to optimize until maybe 0.001% palladium.
02:44
However, as we'll see later on, nickel can be far more active in certain cases than palladium. And of course, nickel has a very simple advantage. It is much cheaper.
03:03
So palladium acetate is 300 times more expensive than nickel acetate. And this is certainly an important argument for applications in industry.
03:23
Well, therefore, let's start with nickel catalyzed reactions in industry. First of all, the well-known Dupont adiponitrile process.
03:53
It's about the synthesis of adiponitrile. And you start with butadiene, with adding
04:22
HCN to the butadiene, catalytically with a nickel catalyst. So HCN, butadiene, and the nickel catalyst
04:43
will give a nickel alu, pi alu complex to ligands at nickel cyano group here.
05:04
And in an equilibrium process, either this branched nitrile
05:30
is formed, or the linear one, usually in range one to two.
05:47
Since these are reversible processes, you can, I summarize this one to that one.
06:02
In addition, it is possible to, I summarize that one in the presence of an additional Lewis acid. So again, HCN, zinc chloride, and a nickel catalyst,
06:25
usually a nickel phosphine or a nickel phosphide catalyst to a product with a terminal olefin, which then can
06:46
undergo a hydrocyanation reaction again, a second hydrocyanation, forming the final product,
07:07
the adipo nitrile. So this is an important starting material
07:20
for polymer synthesis. For instance, reducing that hydrogenating for the, to get to the this amino compound, and so on. Well, the hydrocyanation has also
07:45
been tried in the last 20 years to perform that enantioselectively. The first example, already from 1979, the group of elms.
08:11
Well, used in that case, palladium diop complex.
08:21
Diop is a chiral bidentate phosphine ligand we already discussed, but low enantioselectivity.
08:43
However, to my knowledge, best example from 1995, a group of Rajan Babu. And he applied nickel catalysis,
09:12
nickel COD, cyclooctadiene ligand, HCN, hexane,
09:30
room temperature, a chiral phosphide ligand.
09:48
And well, the best result for better 90%
10:09
EE was, yeah, well, he achieved better than 90% EE. And you might imagine in which context
10:24
this reaction was done. Well, we already discussed some examples of that anti-inflammatory drug, naproxene was the name.
10:46
Well, problem is the low turnover number, or relatively low for an industrial process. Turnover number is less than 750.
11:09
Well, now to some nickel-catalyzed processes which are indeed relevant for industrial application
11:21
with high turnovers. One of the first was developed by Walter Reppe. He was chemist at the BASF. And well, the expression Reppe chemistry
11:46
is well known in industry also today, nowadays. So important industrial processes like
12:01
to start from cheap starting materials are ethylene, carbon monoxide, and water. So a nickel carbonyl catalyst, about 200 bar pressure,
12:31
300 degrees as temperature, will lead to propionic acid.
12:43
Still one of the important processes for the synthesis of that. And here you can see how versatile also nickel chemistry can be.
13:01
Essentially, the same process, but starting from acetylene. Well, nickel bromide and copper halide as the co-catalyst, 50 bar, lower temperature, 200 degrees.
13:29
And this is a nice process for the production of acrylic acid.
13:41
Also under the label of Reppe chemistry is this process, acetylene, nickel, cyanide, calcium,
14:12
carbide, THF, 60 degrees, 15 bars, pressure.
14:25
On first glimpse, one could guess that benzene is formed. Well, benzene, the cyclotrimerization
14:41
of acetylene we discussed yesterday is a byproduct of that type of reaction. But you can trigger that process that indeed the cyclooctatetraene
15:05
is formed in up to 90% yield. Not for industrial purposes, but for lab science,
15:26
scientific purposes. This reaction has been modified.
15:44
Also with this starting material, two equivalents, two units of that, are cyclized with a nickel catalyst to the cyclooctatetraene moiety.
16:18
E is the abbreviation for ester here.
16:22
And of course, all of you should know that the cyclooctatetraene is not an anti-aromatic system. Because for being anti-aromatic, it should be planar. But it is not.
16:41
Some kind of boat-like confouleur is formed.
17:09
So this was 90%. 89%, I report, in that case. If they would optimize it, they would also get 90%, I would guess.
17:21
Well, OK. Rather similar, since also an eight-membered ring is formed, is the dimerization of butadiene,
17:55
forming this 1,5-cyclooctadiene, which is,
18:03
yeah, this is this COD ligand we already talked about. And depending on the reaction conditions, also a cyclotrimerization can be achieved, mainly
18:37
to that trans-trans-cis isomer.
18:43
So these reactions have been developed also by a repel, to my knowledge, originally with nickel catalyst. Nowadays, the industrial process
19:01
is frequently based on the titanium-aluminum combination with regard to the Ziegler-Natta catalysts.
19:25
However, a nickel catalyst is normally applied for the hydrogenation reaction, the last step,
19:43
forming, finally forming this cyclododecane. So what are these good for? Well, you can selectively monooxygenate that, forming the cyclododecanone.
20:04
Well, this might be interesting for perfumery. On the other hand, biovuliger oxidation will form a macrocyclic lactone. You can open that up for polymer synthesis
20:23
or for some special kind of fatty acids. Well, interesting materials for industrial purposes. For this type of cyclization, 4 plus 4 cyclization,
20:48
there are also interesting examples from academics. Paul Wender in 1988, at that time already at Stanford
21:12
University, performed that 4 plus 4 cycloaddition reaction
21:26
intramolecularly in the context of a natural product
21:45
synthesis with nickel COD, triphenylphosphine. Oh, well, OK.
22:01
You can try to figure out what will be that cyclization product. It's not that difficult. This one
22:24
with a 67% yield, while all those hydrogens at the stereogenic centers are on the same side of that ring
22:42
system. And also from Paul Wender's group is a 2 plus 4 cycloaddition reaction, again,
23:08
intramolecularly. Again, nickel COD.
23:24
Well, the ligand then had to be optimized. The phosphide reaction conditions, toluene, just at room temperatures, 25 degrees.
23:52
So as I said, it's just a 2 plus 4 cycloaddition reaction.
24:12
Which one, of course, can call a Diels-Alder reaction
24:21
Excellent yield, 98%. But it is not a normal Diels-Alder reaction. In a normal Diels-Alder reaction, you have an electron-rich diene and an electron-poor
24:45
dienophile. If you have a Diels-Alder reaction with inverse electron demand, then it's the opposite. But here, in this case, electron-rich diene and an especially electron-rich TMS acetylene.
25:05
This does not react at room temperature at all, although it's an intramolecular setup. You need that catalytic system for the reaction to proceed.
25:25
I already mentioned the Ziegler-Natta catalysts.
25:42
Well, Ziegler-Natta catalysts are known for the polymerization of olefins,
26:04
mainly ethylene and propylene at lower pressure and lower temperature. So polyethylene is produced.
26:24
So and already Ziegler at the Max Planck Institute for Kohl-Forschung in Mülheim found that nickel impurities,
26:47
the presence of nickel impurities, which just came from the autoclave, the steel of the autoclave.
27:03
And there is some nickel in there, of course. In the presence of nickel impurities, that reaction of ethylene with itself stops already at the stage of a dimer.
27:23
This means only two units of that react when it stops at the stage of 1.15.
27:41
Well, this might be also useful. And most interestingly, in recent years, some industrially-oriented research groups tested it, this type of process, for an unselective catalysis,
28:10
combining styrene plus ethylene, 0.01%
28:24
of the chiral nickel catalyst, a mido-phosphite as ligand. I think we have seen that one as ligand before
28:44
in the course of this lecture.
29:09
So what a huge setup for synthesizing such a small chiral molecule.
29:26
Well, about 89% yield, 91% EE. There are some examples with a higher yield
29:44
and somewhat higher enantioselectivity. However, with a higher catalyst loading, this reaction was found by Walter Leitner, who also
30:03
was, a couple of years at the Max Planck Institute for Cold Fortune, is now a professor at Aachen University.
30:22
So what else is on the list of nickel catalysis? We have mentioned nickel catalysis before in the context of the kumada coupling process.
30:49
What was the kumada coupling? Well, essentially, you have the Grignard.
31:04
So and R might be alkyl, aryl, or vinyl. Then you have a vinyl or aryl halide.
31:36
So R prime, generally vinyl or aryl, the leaving group,
31:49
chloride, bromide, iodide, triflate, and in some examples, even fluoride.
32:04
And with palladium catalyst or nickel catalyst, you get a C-C coupling, some extension of kumada coupling
32:33
where you can combine SP3-centred carbon atoms with each other have been
32:43
invented in recent years, but then based on nickel catalysis. For instance, an octyl chloride
33:03
combined with an butyl lithium halide gives, well, this is dodecane.
33:21
Consequently, I write it that way. An octyl combined with an butyl, 96% yield. This is achieved with 3% nickel chloride, THF, 25 degrees.
33:51
And what is essential, you need the presence of a butadiene that
34:05
might be the parent butadiene, but it can also be isoprene. It is essential. And those nickel butadiene complexes,
34:23
it is rather complicated, rather complicated structure. There's already a C-C bond formed between two of those butadiene units. While there's lots of details we don't need to discuss.
34:42
What is more interesting for us is that this type of process, or similar process, has also been applied for enantioselective C-C bond formation.
35:02
Here we have a very nice example, an alpha bromoamide,
35:23
which is a chiral compound that was applied in this reaction as racemic mixture. The organometallic reagent, in this case not Grignier,
35:45
but an n-hexyl zinc bromide, nickel chloride as the catalyst, and the pie box ligand
36:12
delivered the chiral information.
36:35
So you achieve the synthesis of the enantioselectively
36:47
enriched product, 90% yield and 96% EE.
37:14
That means that chiral center is epimerized
37:23
during that reaction. During the reaction there is than. At some stage, no chiral center. And all the chiral information than comes from the pie box nickel complex. 90% yield, 96% EE means that even
37:47
the wrong enantiomer here gives the right one there. So further interesting reactions based on nickel catalysis.
38:19
Well, let's have a look at the nickel-catalyzed Suzuki
38:24
coupling reaction, which becomes more and more important in recent years. So examples, well, the nickel-catalyzed Suzuki coupling is especially successful with chloroarenes,
38:50
which tend to be less active in palladium-catalyzed processes.
39:02
So with 10% of nickel chloride, with a DPPF ligand,
39:28
the BiAru product is obtained with 94% yield. Whereas the corresponding palladium complex,
39:44
you get less than 1% yield. And a very nice example of a stepwise Suzuki coupling
40:01
was published in 2008 in the Journal of the American Chemical Society on page 14,422.
40:24
Neil Gark's group at the UCLA. So it's worth having a look into that publication.
40:46
A pivaloyl group here. So what is pivaloyl? That is this tertiary butyl substituted ester there.
41:03
Bromide on this side, pivaloyl here. First step with this indole-substituted boronic acid
41:29
ester, and the triphenylphosphine as the catalyst, potassium phosphate as base, toluene,
41:53
bit of water in there, 90 degrees. And the normal Suzuki coupling product was obtained.
42:34
Ah, I forgot there is an alated benzene ring.
42:50
So this is the normal coupling product as anticipated. Yield, 90%.
43:02
Now to the fascinating, interesting, very valuable part. Well, this is also valuable. Suzuki coupling is clear. Next step, a nickel catalyst based
43:20
on a nickel chloride phosphine, tris cyclohexyl phosphine complex, 5% of that. All the other reaction conditions the same,
43:44
except temperature was a toluene solvent, temperature was 110 degrees. And that simple boronic acid, phenyl boronic acid,
44:01
as the coupling component. Then, indeed, this pivaloyl group is the one who reacts. Within that nickel catalyzed Suzuki coupling, the CO bond is broken.
44:22
And I think this is remarkable. You can start from a phenyl making the pivaloyl acid, ester, and then performing that nickel catalyzed Suzuki coupling. So this is the result.
44:56
And for the last step, 88% yield.
45:04
As I said, quite remarkable. So two more nickel catalyzed processes. One is already a name reaction, Nozaki-Hiyama-Kishi reaction, sometimes abbreviated
45:40
as NHK reaction.
45:45
So what is that? Essentially, you have a vinyl or an allyl halide,
46:04
then an aldehyde.
46:21
You need for the Nozaki-Hiyama-Kishi reaction chromium chloride, unfortunately in excess.
46:41
The nickel catalyst then sometimes rather complicate ligands, which can be chiral. You need a strong base, a proton-spung solvent.
47:14
And what you get then is that alcohol,
47:33
what reminds us of simple Grignard process. One, two addition of an organometallic species
47:48
to an aldehyde. So when are you using the NHK, special NHK process?
48:02
Well, in cases where you need an especially high selectivity for the one, two process, which also works for alpha better unsaturated carbon groups.
48:21
And you need a functional group tolerance. For instance, ketones, esters, amides, and nitriles are tolerated, even a solvent. You can't do that with Grignard, for instance.
48:41
Can achieve high selectivity for the process. Well, here's one example for real complicated set up of R prime and R. And you achieve 100% yield
49:01
that was developed in the context of Kishi's polytoxin synthesis that complicate natural product with 64 stereogenic centers, as you might remember. And then you can also achieve that with an extremely
49:23
high diastereoselectivity. So if you have worked maybe one year synthesizing this one with a complicated set up and another year
49:41
for another guy, another year with that and a complicated R prime there, and you want to go sure that you get a good yield out of the process. Well, OK, the Nutsaki-Hiyama-Kishi process might be the process of choice.
50:03
So another interesting process, well, recently invented. It's a nickel-catalyzed reductive coupling of alkynes.
50:22
So R and R prime can be aryl, alkyl, and it can even be just hydrogen, also terminal
50:44
alkynes, then an aldehyde, nickel COD, additional ligand,
51:16
some reducing agent.
51:22
So the ligand, for instance, butyphosphine, and a reducing agent often applied is this borane.
51:42
Then the coupling process finally leads to this result, an allylic alcohol.
52:04
So a reductive combination with CC bond formation of an alkyne and an aldehyde. So for the mechanism of the process,
52:26
the nickel complex coordinates both the alkyne and the aldehyde, forming a metallocycle
53:36
like this.
53:49
The reaction then with the triethylborane will lead to this intermediate.
54:28
So and now a better hydrogen elimination can take place.
55:10
Ethylene is set free.
55:22
Well, and now no problem. Reductive elimination forming the carbon-hydrogen bond.
55:45
Again, the active catalyst, and I'm now not quite sure is this one hydrolyzed later on, or maybe it doesn't survive the reaction conditions.
56:01
Later on, you have the alcohol here. Well, one example, benzaldehyde and the terminal octene gave this allylic alcohol
56:45
with a yield of better, 75%, and 96% of the E olefin.
57:07
As I said, a rather new development if you want to look that up in literature. Again, in the Journal of the American Chemical Society,
57:21
2011, page 5728. I think that's enough for today. Thank you for listening. Have a nice holiday tomorrow, and see you next week.
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