STERICALLY HINDERED ORGANOTIN COMPOUNDS .2. SYNTHESIS OF THE ORGANOTIN HALIDES (MESITYL)2SNXNY2-N, (MESITYL)SNXNY3-N AND R4SN2X2 (R = 2,4,6-IPR3C6H2, X = CL, Y = BR) - CRYSTAL-STRUCTURE OF THE DITIN SPECIES (R2BRSN)2

Reaction of mesityllithium with SnCl4 (2:1) gives (mesityl)2SnCl2, While the corresponding reaction using mesitylmagnesium bromide gives a mixture of halogenato-products (MeSityl)2SnCl2, (mesityl)2SnBr2 and (mesityl)2SnClBr. Reaction of this latter mixture with SnCl4 (1:1) gives the full range of (mesityl)SnXnY3-n (X = Cl, Y = Br). In contrast, the more sterically demanding carbanion source 2,4,6-iPr3C6H2Li reacts with SnCl4 or SnBr4 (1:1) to give the coupled ditin product (2,4,6-iPr3C6H2)4Sn2(hal)2. The structure of the bromide, [(2,4,6-iPr3C6H2)4Sn2Br2] (Sn-Sn) has been determined and shown to consist of molecular units in an approximately staggered conformation, with an Sn-Sn distance of 2.841(1) angstrom. The molecule is highly sterically congested, leading to non-equivalence of methyl groups in some isopropyl units owing to hindered rotation about C-C and C-Sn bonds.