Stabilisation of nucleophilic carbenes co-ordinated to transition metals

Abstract

Transition-metal compounds of the type (CO)₅CrC(Y)X have been investigated in cases where there is a possibility of stabilising the empty carbene carbon p_z orbital from both X and Y. The systems in which Y is either vinyl or a 2-substituted five-membered heterocyclic ring and X is O^–, NH₂ or OEt have been prepared and it is found, largely on the basis of spectroscopic evidence, that extensive stabilisation occurs when Y is C₄Y₃Z (Z = O, S, NMe) while no such definite evidence has been obtained in the case where Y is vinyl. Conjugative release is more important than π→p interaction from Y.