Rhodium(I) complexes of new ferrocenyl benzimidazol-2-ylidene ligands:The importance of the chelating effect for ketone hydrosilylation catalysis

N-[(1-Phosphanylferrocen-1-yl)methyl] -N-[(2,4,6-trimethyl-phenyl)methyl] -5,6-di-X-benzimidazolium tetrafluoroboratesalts (X = H, 5a and Me, 5b), precursors of new phosphane-benzimidazol-2-ylidene bifunctional ligands, and relatedferrocenyl 5,6-di-X-benzimidazol-2-ylidene iodide salts (X =H, 6a and Me, 6b), precursors of monodentate benzimidazol-2-ylidene ligands, have been prepared for the first time. Cat-ionic rhodium(I) complexes 7a and 7b and neutral rhodium(I)complexes 8a and 8b have been obtained in good yields andhave been fully characterised. Cationic rhodium(I) com-plexes 10a and 10b were prepared from 8a and 8b, for comparison with complexes 7, but not isolated. All complexesshowed good activities for the catalytic hydrosilylation ofacetophenone derivatives. The activities are much greaterthan for related imidazol-2-ylidene systems, and the cationiccomplexes are more active than the neutral complexes; thehighest activity is observed for the more soluble complex 7b. The use of bidentate ligands proved to be essential for ob-taining good selectivities of the desired alcohol. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009