Platinum-catalyzed carbonylations

The binuclear palladium complex [(tBu2PH)PdPtBu2]2 with oxygen gave a very efficient catalyst for the hydrogenation of a,/3-unsaturated carbonyls. 0 Glueck and co-workers have undertaken studies on aspects of platinum-catalyzed hydrophosphinations of activated olefins.71,72... 

The addition of platinum group metals to the Co-catalyzed carbonylation significantly lowers reaction requirements. A catalyst mixture of 2.7 parts cobalt acetate, 3 parts iodine, 1.2 parts bis(triphenylphosphine)-palladium(II) chloride and 2.4 parts adi-ponitrile converts methanol to acetic acid at 120 C and 25 MPa. 

Platinum catalyzed reactions of nitriles with o-bis(dimethylsilyl)benzene give 2,1,4-benz-azadisilines in high yields <92CL45>. Also, platinum catalyzed dehydrogenative double silylation of several carbonyl compounds (aldehydes and ketenes) with o-bis(dimethylsilyl)benzene results in H-... 

The individual steps in the mechanism proposed for the ruthenium catalyzed oxidation of triphenylphosphine are similar to those of the platinum catalyzed reaction. However, the stoichiometry of one step and the relative rates of several other steps appear to be somewhat different. The observed rate laws are quite different from those of the platimun complex. The rate equations for the proposed mechanism are shovm in equation (71) for the dioxygen complex and equation (72) for the carbonyl complex (RuOj = [Ru(NCSXN0XPPh3)j(02)] RuCO = [Ru(NCSXCOXNOXPPh3)2]). 

Platinum complexes also exhibit catalytic activity toward the carbonylation of allene with CO and aliphatic thiol can react with allene regioselectively [12]. The PtCl2(PPh3)2-catalyzed carbonylative thiolation of cyclohexylallene with I " Hex-SH) as an aliphatic thiol carbon monoxide by the use of aliphatic thiol ( Hex-CH) proceeds regioselectively at the terminal double bond of the allene. In the case of Pt(PPh3)4-catalyzed reaction, the thiolative carbonylation takes place at both terminal and central double bonds (Scheme 11.9). 

Kusama et al. also developed the PtCl2-catalyzed benzannulation using o-alkynylbenzoates 41 or benzothioates with vinyl ethers 8. The reaction proceeded at room temperature and naphthyl ketones 42 were obtained [28]. They proposed that the reaction proceeded through [3 -I- 2]-cycloaddition of the platinum-containing carbonyl ylides 43 with 8, followed by 1,2-alkyl migration, as shown in Scheme 15.16. 

Platinum(O) complexes such as Pt(PPh3)4 also catalyze carbonylative thiolation of allenes, affording a,p- and p,y-unsaturated thioesters in good yields [116]. When 2-iodobenzenethiols are employed for the palladium-catalyzed carbonylation with... 

Ogawa A, Kawahe K, Kawakami J, Mihara M, Hirao T, Sonoda N (1998) Platinum(O)-catalyzed carbonylative lactonization of 5-hydroxy-l-pentyne with carbon monoxide in the presence of thiols. Organometallics 17 3111-3114... 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

Platinum complexes with chiral phosphorus ligands have been extensively used in asymmetric hydroformylation. In most cases, styrene has been used as the substrate to evaluate the efficiency of the catalyst systems. In addition, styrere was of interest as a model intermediate in the synthesis of arylpropionic acids, a family of anti-inflammatory drugs.308,309 Until 1993 the best enantio-selectivities in asymmetric hydroformylation were provided by platinum complexes, although the activities and regioselectivities were, in many cases, far from the obtained for rhodium catalysts. A report on asymmetric carbonylation was published in 1993.310 Two reviews dedicated to asymmetric hydroformylation, which appeared in 1995, include the most important studies and results on platinum-catalogued asymmetric hydroformylation.80,81 A report appeared in 1999 about hydrocarbonylation of carbon-carbon double bonds catalyzed by Ptn complexes, including a proposal for a mechanism for this process.311... 

Most of the reports on Rh-catalyzed asymmetric hydroformylation are concerned with asymmetric hydroformylation of vinyl aromatics, which are model substrates of interest to the pharmaceutical industry. In 1993 and 1995, reports were published describing the state of the art in hydroformylation with both rhodium and platinum systems.80,81 310 Two reports appeared in 1999 and 2000 on carbonylation and rhodium asymmetric hydroformylation respectively.311,345... 

My last comment concerns the reaction of palladium olefin complexes with carbon monoxide discovered by Tsuji. I agree that this is most likely to proceed by an insertion rather than an ionic mechanism. Chloride attack on coordinated olefin is rare however. Chloride ion is an inhibitor, for example in the palladous chloride catalyzed hydration of ethylene (0). I, therefore, wondered whether carbon monoxide was affecting the ease with which chloride attacks olefin. One can postulate that carbon monoxide participates in this insertion either as a gas phase reactant or by first forming a carbonyl olefin complex. Such complexes of the noble metals were unknown, but examining the reaction between carbon monoxide and the halogen bridged olefin complexes of platinum revealed that they are formed very readily... 

An attempt was also made to produce 0-iodo acyl iodides by the reaction of iodine, carbon monoxide and olefins in the presence of palladium or platinum chloride. This is, in effect, an attempt to make Dr. Tsuji s reaction catalytic rather than stoichiometric. No carbonyl insertion occurred at 1 atm. of carbon monoxide. However, it was found that iodination of the olefin was catalyzed by platinum olefin complexes and that an additional increase in catalytic activity accompanied the presence of carbon monoxide. There has been much speculation at this conference concerning the possibility of affecting catalytic activity by changing the ligands in the coordination sphere of the catalyst. This would appear to be such a case. 

The metal hydride mechanism was first described for the cobalt-carbonyl-catalyzed ester formation by analogy with hydroformylation.152 It was later adapted to carboxylation processes catalyzed by palladium136 153 154 and platinum complexes.137 As in the hydroformylation mechanism, the olefin inserts itself into the... 

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