Chemistry of low-valent molybdenum phosphite complexes: Models of seven-coordinate reaction intermediates

摘要

A simple synthesis of the zerovalent complex Mo[P(OCH3)3]6 has been devised from a potassium reduction of MoCl4(tetrahydrofuran)2 followed by reaction with trimethyl phosphite at 70°. Protonation of this octahedral complex gave only low yields of the expected seven-coordinate hydride, HMo[P(OCH3)3]6⁺. The major product was an octahedral nonhydridic cation, Mo[P(OCH3)3]5P(OCH3)2⁺, derived from proton cleavage of the P—O phosphite ester bond. This octahedral cation was stereochemically nonrigid, apparently through facile methoxy group migration. Close packing by methoxy groups in this fluxional cation was established through an x-ray crystallographic study of Mo[P(OCH3)3]5P(OCH₃)₂⁺-PF₆^-. Extended reaction of trifluoroactic acid with Mo[P(OCH₃)₃]₆ yielded the seven-coordinate hydride, HMo[P(OCH₃)₃]₄(O₂CCF₃), which was near pentagonal bipyramidal and was stereochemically nonrigid.