Molybdenum alkylidene complexes with linked cycloheptatrienyl–phosphane ligands for potential use in olefin metathesis

Abstract

The synthesis of cycloheptatrienyl molybdenum complexes incorporating the linked cycloheptatrienyl–phosphane ligand [2-(diisopropylphosphanyl)phenyl]cycloheptatrienyl, o- iPr 2P-C 6H 4-C 7H 6, is described. Reaction of the 17-electron dibromide [( o- iPr 2PC 6H 4-η 7-C 7H 6)MoBr 2( P-Mo)] ( 1) with NaBH 4 furnishes a tetrahydroborate complex, which can be directly converted into the acetate complex [( o- iPr 2PC 6H 4-η 7-C 7H 6)Mo(η 2-O 2CCH 3)( P-Mo)] ( 2). The acetate ligand can be cleaved upon treatment with diazoalkanes, N 2CHR, in the presence of Me 3SiCl affording the molybdenum alkylidenes [( o- iPr 2PC 6H 4-η 7-C 7H 6)MoCl(CHR)( P-Mo)] ( 4a, R=Ph; 4b, R=SiMe 3). Complexes 4 might serve as a source for the preparation of potential olefin metathesis catalysts of the type [( o- iPr 2PC 6H 4-η 7-C 7H 6)Mo(CHR)( P-Mo)] + by halide abstraction. CH 2 insertion into the metal–carbon bond of the diphenylacetylene complex 5 resulted in the formation of the cationic η 3-vinylcarbene complex 6, which can be regarded as an alkene adduct of a 16-electron complex of just that kind. In addition, the X-ray crystal structures of 2 and 6 are reported.