The synthesis and NMR spectroscopic examination of coordination complexes of 2-telluraindane with rhodium
作者:Karanbir Badyal、William R McWhinnie、John Homer、Michael C Perry
DOI:10.1016/s0022-328x(98)00380-5
日期:1998.3
Rhodium complexes of 2-telluraindane were synthesised and the nature of metal-ligand interactions in solution were studied using NMR spectroscopy. Two complexes were prepared; [(Cp*Rh)(C8H8Te)][O3SCF3](2) (1) was prepared by the reaction of [Cp*RhCl2](2) with 2-telluraindane in the presence of silver triflate while [(Cp*RhCl2)(C8H8Te)] (2) was synthesised by a direct reaction between the rhodium dimer and the ligand. Complex 1 gives a Te-125 coordination shift of + 260 ppm and a Te-125-Rh-103 coupling constant of 65.9 Hz implying that the metal is directly bonded to the tellurium in the ligand and not to the aryl ring (i.e eta(1) not eta(6) coordination is envisaged). The observation of an AB quartet for the methylene protons (J(AB) = 16 Hz) is as expected for 2-telluraindane coordinated in this manner. In contrast, complex 2 shows a broad singlet for these methylene protons at room temperature (r.t.) which sharpens on heating to 323 K and resolves into the expected AB quartet (J(AB) = 13.5 Hz) on cooling to 223 K, however the Te-125 spectrum is a singlet at r.t. but resolves into a doublet at 238 K (J(103)Rh-Te-125 = 108 Hz). It is argued that these data are only reconcilable in terms of a dissociative mechanism in which the equilibrium populations of the free species are small and where the rate of exchange at r.t. lies between that required to average the Te-125 chemical shifts and that required to effectively decouple the Te-125-Rh-103 interaction. (C) 1998 Elsevier Science S.A. All rights reserved.