THE SYNTHESIS AND NMR SPECTROSCOPIC EXAMINATION OF COORDINATION-COMPLEXES OF 2-TELLURAINDANE WITH RHODIUM

Rhodium complexes of 2-telluraindane were synthesised and the nature o f metal-ligand interactions in solution were studied using NMR spectro scopy. Two complexes were prepared; [(CpRh)(C8H8Te)][O3SCF3](2) (1) w as prepared by the reaction of [CpRhCl2](2) with 2-telluraindane in t he presence of silver triflate while [(CpRhCl2)(C8H8Te)] (2) was synt hesised 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 direct ly 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 A B quartet for the methylene protons (J(AB) = 16 Hz) is as expected for 2-telluraindane coordinated in this manner. In contrast, complex 2 sh ows 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 reconci lable in terms of a dissociative mechanism in which the equilibrium po pulations 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 shi fts and that required to effectively decouple the Te-125-Rh-103 intera ction. (C) 1998 Elsevier Science S.A. All rights reserved.