Subvalent Group 4B metal alkyls and amides. Part 6. Oxidative addition of an alkyl or aryl halide to bis[bis(trimethylsilyl)methyl]tin(II); hydrogen-1 nuclear magnetic resonance data on the tin(IV) adducts and a single-crystal X-ray study of tris[bis(trimethylsilyl)methyl]chlorotin(IV)

Abstract

Addition of an alkyl or aryl halide RX to Sn[CH(SiMe₃)₂]₂, (1), occurs readily at 20 °C in C₆H₆ or n-C₆H₁₄ to give SnX[CH(SiMe₃)₂]₂R, (2). Similarly CH₂X′₂(X′= Br or I) and (1) give CH₂{SnX′[CH(SiMe₃)₂]₂}₂, (3). A side-product of some of the former reactions is SnX₂[CH(SiMe₃)₂]₂; a radical mechanism is proposed with SnX[CH(SiMe₃)₂]₂˙ as the intermediate, for which R· and RX are in competition. Infrared spectra support a covalent monomeric tin(IV) structure for the chlorides (2). Hydrogen-1, and in some cases ¹³C, n.m.r. spectra for (2) or (3) in benzene or methylene chloride solutions are consistent with a monomeric C_s molecular structure, showing diastereotopically distinct SiMe₃ groups. Addition of (CD₃)₂SO or C₅D₅N leads to collapse of these doublets or, for R = Bu^t, a decrease in their separation, suggestive (with i.r. data) of a stereochemically non-rigid, five-co-ordinate, tin compound. A single-crystal X-ray analysis of SnCl[CH(SiMe₃)₂]₃ shows a covalent monomeric structure with the three alkyl groups slightly flattened from the tetrahedral : Sn–Cl 2.380(3), Sn–C (av.)ca. 2.18 Å; C–Sn–Cl (av.)ca. 103.9, C–Sn–C (av.)ca. 114.4°.