Synthesis and Characterization of the M(II) (M = Ge, Sn, or Pb) Phosphinidene Dimers {M(μ-PAr′)}2 (Ar′ = C6H3-2,6-(C6H3-2,6-Pr i 2)2)

Reaction of M{N(SiMe3)2}2 (M = Ge, Sn, or Pb) with the sterically encumbered primary phosphine Ar′PH2 (2), Ar′ = C6H3-2,6-(C6H3-2,6-Pr i 2), at ca. 200 °C afforded the highly colored phosphinidene dimers {M(μ-PAr′)}2, M = Ge(3), Sn(4), or Pb(5), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 3, 4, and 5 featured similar M2P2 ring cores, of which 4 and 5 have 50/50 P atom disorder, consistent with either a planar four-membered M2P2 arrangement with anti aryl groups or with an M2P2 ring folded along the M−M axis with syn aryl groups. A syn-folded structure was resolved for the Ge2P2 ring in compound 3. The M−P distances resembled those in M(II) phosphido complexes and are consistent with single bonding. The coordination geometries at the phosphorus atoms are pyramidal. DFT calculations on the gas phase models {M(μ-PMe)}2 (M = Ge, Sn, Pb) agreed with the syn (M−M folded) structural interpretation of the X-ray data. The synthesis of the bulky phosphine Ar′PH2 2 with the use of the aryl transfer agent Ar′MgBr(THF)2 is also reported. This route afforded a significantly higher yield of product than that which was obtained using LiAr′, which tends to result in aryl halide elimination and the observation of insoluble red phosphorus.