Tertiary phosphine adducts of manganese(II) dialkyls. Part 1. Synthesis, properties and structures of alkyl-bridged dimers

Abstract

The reactions of manganese(II) dialkyls with tertiary phosphines or of MnCl₂ with magnesium dialkyls in the presence of phosphines leads to dimeric complexes of stoicheiometry Mn₂R₄(PMe₃)₂(R = CH₂SiMe₃, CH₂CMe₃, and CH₂Ph) and Mn₂(CH₂SiMe₃)₄(PR₃)₂[R₃= Et₃, Me₂Ph, McPh₂, and (cyclo-C₆H₁₁)₃]. The X-ray crystal structures of Mn₂(CH₂CMe₃)₄(PMe₃)₂, Mn₂(CH₂Ph)₄(PMe₃)₂, and Mn₂(CH₂SiMe₃)₄(PMePh₂)₂ have been determined. In the dimers there are two asymmetrically bridging alkyl groups with one additional terminal alkyl and one phosphine per manganese. The structures show a variation in bond lengths probably due to steric effects, with Mn–Mn distances of 2.667(1)–2.828(1)Å, and long Mn–P distances [2.562(1)–2.684(1)Å]. There is a close contact between one hydrogen atom on each of the bridging methylene groups and the manganese atom (Mn ⋯ H–C 2.15–2.29 Å). Infrared and e.s.r. spectra of the compounds are discussed.