Heterolytic Si-H Bond Cleavage at a Molybdenum-Oxido-Based Lewis Pair.

ABSTRACT: The reaction of a molybdenum(VI) oxido imido complex with the strong Lewis acid B(C6 F5 )3 gave access to the Lewis adduct [Mo{OB(C6 F5 )3 }(NtBu)L2 ] featuring reversible B-O bonding in solution. The resulting frustrated Lewis pair (FLP)-like reactivity is reflected by the compound's ability to heterolytically cleave Si-H bonds, leading to a clean formation of the novel cationic MoVI species 3?a (R=Et) and 3?b (R=Ph) of the general formula [Mo(OSiR3 )(NtBu)L2 ][HB(C6 F5 )3 ]. These compounds possess properties highly unusual for molybdenum d0 species such as an intensive, charge-transfer-based color as well as a reversible redox couple at very low potentials, both dependent on the silane used. Single-crystal X-ray diffraction analyses of 2 and 4?b, a derivative of 3?b featuring the [FB(C6 F5 )3 ]- anion, picture the stepwise elongation of the Mo=O bond, leading to a large increase in the electrophilicity of the metal center. The reaction of 3?a and 3?b with benzaldehyde allowed for the regeneration of compound?2 by hydrosilylation of the benzaldehyde. NMR spectroscopy suggested an unusual mechanism for the transformation, involving a substrate insertion in the B-H bond of the borohydride anion.

SUBMITTER: Zwettler N 

PROVIDER: S-EPMC6001527 | biostudies-other | 2018 May

REPOSITORIES: biostudies-other