Sterically hindered organotin compounds II. 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

Article abstract of DOI:10.1016/0022-328X(92)83397-Z

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) Angstroem.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.