Pentabenzylcyclopentadienyl molybdenum and tungsten hydrides: Syntheses, structures and electrochemistry of [MHCpBz(CO)2(L)] (L = CO, PMe3, PPh3)

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 2 Ph) 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 3 CN)]BF 4 ( 8 ), is described. The cleavage of M–H bonds takes place upon oxidation or reduction. Cations [MCp Bz (CO) 2 L(CH 3 CN)] + form in solvent-assisted M–H bond breaking upon oxidation of [MHCp Bz (CO) 2 L] (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.