Abstract
Reactions of diaryl complexes [Ru(CO)2RR′(PMe2Ph)2] with Me3CNC yield the acyl complexes [Ru(CO)(CNCMe3)(COR)R′(PMe2Ph)2]. Rate-determining combination of aryl and carbonyl ligands is followed by rapid attack by isonitrile trans to the acyl ligand. In symmetrical diaryl complexes, rates are increased by electron-releasing substituents in the para position of the aryl ring. A methyl substituent in the meta position has a rather large accelerating effect, presumably for steric reasons. In unsymmetrical diaryl complexes, the aryl ligand bearing the more electron-releasing substituent becomes incorporated in the acyl ligand. Variations in the aryl ligand not directly involved in the reaction have little effect on rate, and solvent effects are relatively small. The fairly large negative entropies of activation are attributed to the formation in the transition state of a three-membered metal–carbonyl–aryl ring, in which the aryl ring has presumably lost its freedom of rotation.
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