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(SiMe(3))(2)}(2) (M = Ge, Sn, or Pb) with the sterically encumbered primary phosphine Ar'PH(2) (2), Ar' = C(6)H(3)-2,6-(C(6)H(3)-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 M(2)P(2) ring cores, of which 4 and 5 have 50/50 P atom disorder, consistent with either a planar four-membered M(2)P(2) arrangement with anti aryl groups or with an M(2)P(2) ring folded along the M-M axis with syn aryl groups. A syn-folded structure was resolved for the Ge(2)P(2) 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'PH(2) 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.