Ruthenium-catalyzed carbonylations proposed mechanism

Allyl methylcarbonate reacts with norbornene following a ruthenium-catalyzed carbonylative cyclization under carbon monoxide pressure to give cyclopentenone derivatives 12 (Scheme 4).32 Catalyst loading, amine and CO pressure have been optimized to give the cyclopentenone compound in 80% yield and a total control of the stereoselectivity (exo 100%). Aromatic or bidentate amines inhibit the reaction certainly by a too strong interaction with ruthenium. A plausible mechanism is proposed. Stereoselective CM-carboruthenation of norbornene with allyl-ruthenium complex 13 followed by carbon monoxide insertion generates an acylruthenium intermediate 15. Intramolecular carboruthenation and /3-hydride elimination of 16 afford the -olefin 17. Isomerization of the double bond under experimental conditions allows formation of the cyclopentenone derivative 12. 

Scheme 7.14 Proposed mechanism for ruthenium-catalyzed carbonylation and cyclization of aliphatic amides.

I/Ru ratio critical, 34 112 proposed mechanism, 34 112 ruthenium-carbonyl complexes, 34 113 species involved, 34 110-113 -catalyzed homologation, 34 115 proposed mechanism, 34 115 compensation behavior of, 26 285, 286 complex catalyst... 

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]). 

Unlike previous alkyne-aldehyde additions [23], the generation of an alkynyl carbanion is unlikely owing to the large pK, difference between the terminal acetylene and the solvent water [24]. A mechanism was proposed involving the simultaneous activation of the C-H bond of alkyne by the ruthenium catalyst and the aldehyde carbonyl by the indium ion. The ruthenium intermediate then underwent Grignard-type addition followed by an in situ hydrolysis in water to give the desired carbonyl addition product and regenerated the ruthenium and indium catalysts to catalyze further reactions (Fig. 3). 

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