Pentabenzylcyclopentadienyl molybdenum and tungsten hydrides: Syntheses, structures and electrochemistry of [MHCp Bz(CO) 2(L)] (L = CO, PMe 3, PPh 3)

Abstract

Complexes [MHCp Bz(CO) 2(PR 3)] (R = CH 3, M = Mo ( 1); M = W ( 2); R = Ph, M = Mo ( 3); Cp Bz = C 5(CH 2Ph) 5) were prepared by thermal decarbonylation of the corresponding [MHCp Bz(CO) 3] in the presence of trimethyl- or triphenyl-phosphine. In solution the NMR spectra of all compounds show the presence of cis and trans isomers that interconvert at room temperature. In the solid state the molecular structures obtained for compounds 1 and 2 correspond to the trans isomers, while for 3 the cis isomer is present. The electrochemistry of [MoHCp Bz(CO) 2(PMe 3)] ( 1), [MoHCp Bz(CO) 3] ( 5), [WHCp Bz(CO) 3] ( 6), [WCp Bz(CO) 3] 2 ( 7), and [MCp Bz(CO) 3(CH 3CN)]BF 4 ( 8), is described. The cleavage of M–H bonds takes place upon oxidation or reduction. Cations [MCp Bz(CO) 2L(CH 3CN)] + form in solvent-assisted M–H bond breaking upon oxidation of [MHCp Bz(CO) 2L] (L = PMe 3, CO). Reduction of [MHCp Bz(CO) 3] gives [MCp Bz(CO) 3] − and H 2. The presence of one PMe 3 ligand lowers the reduction potential and precludes the observation of reduction waves.