Ferrocenyl carbene complexes of chromium, tungsten, and manganese. Models of the α-ferrocenyl carbonium ion

Abstract

The preparation of a series of complexes, [(CO)₅MC(Fc)X](M = Cr, W; X = O^–NMe₄⁺, OMe, OEt, NH₂, NMe₂, NC₄H₈) and [(π-C₅H₄Me)(CO)₂MnC(Fc)OMe](Fc = ferroconyl) is reported. The results of spectroscopic (i.r., u.v.-visible, n.m.r., and mass) measurements are used to demonstrate the profound consequences of the introduction of a ferrocenyl substituent into the carbene ligand in the complexes. The ferrocenyl group acts as a potent electron donor by means of a resonance interaction with the carbene carbon atom. The nature of the stabilisation provided by the α-ferrocenyl group is discussed. Some of these new compounds function as specific hydrogenation catalysts. Attempts to prepare β-ferrocenyl carbene complexes are described. Ferrocenyl-lithium does not react with (π-C₅H₅)Co(CO)₂ or with (π-C₅H₅)V(CO)₄.