Methylene-bridged tri- and tetratin compounds as Lewis acids

Syntheses of a series of trinuclear tin compounds, (Ph2XSnCH2)(2)SnXPh (2, X = Ph; 6, X = F; 8, X = Cl) and (PhCl2SnCH2)(2)SnCl2 (10) and tetranuclear tin compounds (Ph2XSnCH2SnXPh)(2)CH2 (3, X = Ph; 7, X = F; 9, X = Cl) are reported, and the crystal structure of [(Ph2FSnCH2)(2)SnFPh . F](-)[C12H24O6 . K](+) (6b) is described. Variable temperature Sn-119 and F-19 NMR studies indicate that the structure observed for the anion in 6b in the solid state is retained in solution. There is no NMR evidence for the formation of 1:2 adducts with fluoride ion, although such species are identified in acetonitrile solutions from electrospray mass spectrometry (ESMS). Sn-119 NMR spectral data indicate that reaction of trinuclear tin compound 8 with [(Ph3P)(2)N]Cl-+(-) and HMPA results in formation of the 1:1 complexes [(Ph2ClSnCH2)(2)SnClPh . Cl](-)[(Ph3P)(2)N](+) (8a) and (Ph2ClSnCH2)(2)SnClPh .[(CH3)(2)N](3)PO (8b), respectively. In contrast, F-19 and Sn-119 NMR data show that the tetranuclear tin compound 7 reacts with fluoride ion to give a stable 1:2 adduct [(Ph2FSnCH2SnFPh)(2)CH2 . 2F](2-)2[Bu4N](+) (7b) in solution, being no NMR evidence for formation of a 1:1 adduct. However, ESMS indicates the presence of both 1:1 and 1:2 adducts in acetonitrile solution.