Synthesis and Structures of Low-Valent Alkynyl Tin and Germanium Complexes Supported by Terphenyl Ligands: Heavier Group 14 Element Enediyne Analogues

The reaction of (Ar'SnCl)(2) (Ar' = -C6H3-2,6-(C6H3-2,6-Pr-i(2))(2)) with LiC CR (R = SiMe3 or Bu-t) afforded the orange-red, alkynyl-substituted, symmetric distannene Ar'(Me3SiC C)SnSn-(C CSiMe3)Ar' (1) or the blue unsymmetric stannylstannylene Ar'SnSn(C C'Bu)(2)Ar' (2), respectively, whose structures were determined by X-ray crystallography. In solution at room temperature, however, both compounds have very similar UV-vis and H-1 NMR spectra, consistent with the formation of monomeric stannylene units. Cooling a solution of 1 resulted in a color change to pink and the appearance of a new UV-vis absorption at 506 nm, consistent with the formation of a symmetric dimeric structure at low temperature. The different structures of 1 and 2 in the solid state are probably a result of packing effects. In contrast, the analogous reactions of (Ar'GeCl)(2) with LiC CR (R = SiMe3 or Bu-t) resulted in the exclusive formation of digermene derivatives Ar'(RC C)GeGe-(C CR)Ar' (R = SiMe3 (3), Bu-t (4)), which maintain their dimeric structures in solution.