Carbon-13 and proton NMR parameters of mono- and di-organothallium(III) derivatives

Abstract

Carbon-13 and proton coupling constants and chemical shifts are reported for di- and mono-organothallium(III) compounds of the types TlR 2 X and TlRX 2 respectively (X = anionic species). The nature of R was varied over thirty acyclic alkyl, alicyclic alkyl and alkenyl groups. Series of related derivatives were studied to identify the major factors upon which the NMR parameters depend. Several new organothallium(III) derivatives have been synthesised. The effects of solvent and anion (X) changes on the NMR parameters are generally minor. The major factor influencing J (Tl-C) and J (Tl-H) is the number of R groups attached to thallium and the ratios of analogous couplings in TlR 2 X and TlRX 2 are generally close to the value of 1 2.2 predicted on the assumption that the Fermi contact contribution dominates these coupling constants. Couplings to thallium for acyclic alkyl R groups depend on the degree of substitution in R and follow the patterns | 1 J | > | 3 J | > | 2 J | > | 4 J |, ± 1 J , ∓ 2 J , ± 3 J for J (Tl-C) and, with few exceptions, | 3 J | > | 2 J | > | 4 J |, ∓ 2 J , ± 3 J , ± 4 J for J (Tl-H). Values of 3 J (Tl-H) for cyclopropyl derivatives are included with existing data to quantify Karplus-type stereochemical dependence. The values of 3 J (Tl-C) and 3 J (Tl-H) for TlR 2 X (R = cyclohexyl) suggest a preference for equatorial substitution by thallium, and a similar conclusion seems reasonable for R = cyclopentyl. | n J (Tl-C)| in alkenyl derivatives follows the same pattern as for R = acyclic alkyl, but in contrast to alkyl derivatives, 1 J and 2 J have the same sign. Thallium-proton couplings 2 J and 3 J also have the same sign for R = alkenyl. Compounds with α,β-unsaturated R groups have very large values of 1 J (Tl-C) compared to those with saturated R groups. These increases can be partly attributed to changes in hybridization at the α-carbon atom. The effects of the Cl substituent on 1 J (Tl-C), 2 J (Tl-H) and 1 J (C-H) for Tl(ClCH 2 )X 2 are discussed in terms of the Fermi contact contribution to these coupling constants. Substituent effects on carbon-13 chemical shifts are reported.