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 Cs molecular structure, showing diastereotopically distinct SiMe3 groups. Addition of (CD3)2SO or C5D5N leads to collapse of these doublets or, for R = But, 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°.