Thallium tris dimerization

Thallium(I) cyanide was introduced by Taylor and McKillop as a reagent. Aromatic and heteroaromatic acyl cyanides are produced in go yield, whereas aliphatic acid halides lead under these conditions mainly to dimerization products. 18-Crown-6 is a good catalyst for the preparation of cyanoformate in methylene chloride with potassium cyanide and chloroformates. Similarly, tetraethylammonium cyanide gives cyanoformates in high yield under very mild conditions. Aroyl cyanides are generated easily by phase transfer catalysis with tetra-n-butylammonium bromide. Tri- -butyltin cyanide proved successful only with aromatic acid halides, leading to dimerization products with aliphatic compounds. ... 

The structures of four tri-t-butoxysilanthiolates 210-213 have been reported. Whereas 210 is tetrameric with a nearly planar eight-membered ring, 211 and 212 are dimeric. In addition to the two thiolate S atoms the thallium atoms in 211 are also coordinated, albeit more weakly, by one butoxy O atom at a distance of 2.799(4) A. A similar (2+1) coordination is found for the mercury atoms in the monomeric species 212 [d(Hg-O) = 2.878(4) A]. Remarkably short Si-S distances are found in 213 and, in particular, 211 [2.078(2) A], suggesting that the M-S bonds (M = Pb, Tl) may exhibit a marked degree of ionicity in these compounds. 

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