A novel mechanism for the fluxional behaviour of [Pd(η2-tetramethylethylenetetracarboxylate)(2-methylthiomethylpyridine)]

The fluxional behaviour of [Pd(η2-tmetc)(NSMe)] (tmetc=tetramethylethylenetetracarboxylate, NSMe=2-methylthiomethylpyridine) in CD2Cl2 is governed by two mechanisms: (i) the concentration independent inversion at sulfur which averages the methylenic signals and collapses the four methyl signals of tmetc to two; (ii) the concentration dependent mechanism occurring via a dimeric intermediate with CS symmetry which collapses the two residual tmetc signals into a singlet.