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.