Synthesis and Structural Characterization of a Series of Dimeric Metal(II) Imido Complexes {M(μ-NAr#)}2 = [M = Ge, Sn, Pb; Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2] and the Related Monomeric Primary Amido Derivatives M{N(H)Ar#}2 (M = Ge, Sn, Pb): Spectroscopic Manifestations of Secondary Metal Ligand Interactions

The solvent-free reaction of M{N(SiMe3)(2)}(2) (M = Ge, Sn, or Pb) with the sterically encumbered primary amine 2,6-dimesitylaniline (ArNH2)-N-# [Ar-#=C6H3-2,6(C6H2-2,4,6-Me-3)(2)] at ca. 165-175 degrees C afforded the highly colored imido dimers {M(mu-NAr#)}(2), where M = Ge (1), Sn (2), or Pb (3), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 1-3 were very similar and had nonplanar four-membered M2N2 ring cores that are folded along the M M axis. The nitrogen atoms are planar-coordinated, and the M N distances are consistent with single bonding. The reaction of M{N(SiMe3)(2)}(2) with (ArNH2)-N-# in a 2:1 ratio in solution at lower temperature afforded the relatively stable monomeric primary amido species M{N(H)Ar-#}(2), where M = Ge (4), Sn (5), or Pb (6). Complexes 4-6 displayed V-shaped MN2 structures, and 5 and 6 revealed close approaches between the metal atom and ipso-carbon atoms of two flanking Mes groups of the terphenyl substituents [Sn-II-C (2.957 angstrom) and Pb-II-C (2.965 angstrom)]. The secondary metal ligand interactions exerted large effects on their electronic and NMR spectra.