An nmr study of the interaction of α-diimines (rnchchnr) with cyclometallated palladium(ii) compounds [{2-me2nch(z)c6h4pdx}2] (z  h or (s)-me; x  cl, br)

Abstract

When [{2.Me2NCH(Z)C6H4PdX}2] is treated with an α-diimine (RNCHCHNR; R-dim) an equilibrium mixture of starting material and [{2-Me2NCH(Z)C6H4PdX}n(R-dim)] (n  1 or 2) is obtained, the composition depending on the metal complex/ligand ratio. Intermolecular exchange in these mixtures is slow on the NMR time scale.The mononuclear complexes [2-Me2NCH(Z)C6H4PdX(R-dim)] show an intramolecular dynamic behaviour which is slow on the NMR time scale at -50°C (13C NMR) and -80° C (1H NMR). In the slow exchange limit the complex is a four-coordinate PdII complex having the halogen atom trans to the C atom and cis to a monodentate (σ-N)-bonded R-dim ligand. In the fast exchange a rapid head-to-tail rearrangement occurs in which the R-dim ligand changes its point of attachment to the PdII centre (σ-N ⇄ σ N′ rearrangement).In solution the dinuclear complex has a structure consisting of two 2-Me2-NCH(Z)C6H4PdX units containing trans-positioned C and X ligands; these units are bridged by a R-dim ligand in the s-trans conformation. The NMR data for these complexes are compared with those of stable palladium and platinum analogues [{MCl2(ER′3)}n(R-dim)] (n  1 or 2; R  t-Bu, EtMe2C-; E  As, P; R′  n-Bu, Ph).