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-iPr2)2) with LiCCR (R = SiMe3 or tBu) afforded the orange-red, alkynyl-substituted, symmetric distannene Ar′(Me3SiCC)SnSn(CCSiMe3)Ar′ (1) or the blue unsymmetric stannylstannylene Ar′SnSn(CCtBu)2Ar′ (2), respectively, whose structures were determined by X-ray crystallography. In solution at room temperature, however, both compounds have very similar UV−vis and 1H 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 tBu) resulted in the exclusive formation of digermene derivatives Ar′(RCC)GeGe(CCR)Ar′ (R = SiMe3 (3), tBu (4)), which maintain their dimeric structures in solution.