Interaction of tetracyanoethylene with some organo-tin and -mercury compounds

Abstract

The reactions of tetracyanoethylene (TCNE) with organo-tin and -mercury compounds containing carbonmetal, metalsulphur and metalmetal bonds have been studied. With completely substituted benzyl organometallics in CH 2Cl 2 the reaction proceeds via quantitative insertion of TCNE into the metalbenzyl bond to yield metallated derivatives of 1,1,2,2-tetracyanopropyl-benzene PhCH 2C(CN) 2C(CN) 2M (M  SnMe 3, HgCH 2Ph), whose structure was established by elemental analysis, IR and PMR spectra, and by a study of their chemical properties. The rate of the insertion reactions was found to depend both on the nature of the metal atom (Sn Hg) and on the type of the substituent in the benzene ring of dibenzylmercury ( p-CF 3<< H < p-CH 3). The data obtained are discussed in terms of the general problem of a dual (σ- or π-) regioselectivity of the reactions of π-acids with ambiofunctional organometallic donors. The reactions of TNCE with tin mercaptides either yield stable complexes, (PhS) 4Sn, or (as is the case with PhSSnMe 3) proceed via quantitative insertion into the SSn bond to give PhSC(CN) 2C(CN) 2SnMe 3 whose structure was established by elemental analysis, IR and PMR spectra, and by examination of its chemical properties. The products of TCNE insertion into the carbonmetal bond exhibit a dual reactivity in acid and thermal cleavage reactions, which can be attributed to the presence in their structure of two competing σ,π- and σ,σ-conjugated chains of the Cmetal bonds with neighbouring α- and β-nitrile groups. The reaction of TCNE with hexamethyldistannane in CH 2Cl 2 produces a colourless 1/2 adduct identified by elemental analysis, IR and PMR spectroscopy, and the results of acid cleavage, as dimetallated tetracyanoethane complexes with a second TCNE molecule (Me 3SnC(CN) 2C-(CN) 2SnMe 3 - TCNE). This latter compound exhibits extremely high susceptibility to homolysis resulting in the formation of the iminotricyanoallyl radical Me 3SnNCC(CN)C(CN) 2. This suggests a new two-stage mechanism for the formation of a radical species in the reaction of Me 6Sn 2 with TCNE. The mechanism involves the insertion of a π-acid into the tintin bond as the first stage with the subsequent homolysis or atmospheric oxidation of the unstable adduct.