Trimethylplatinum(IV) complexes of dithiocarbamato ligands: an experimental NMR study on the barrier to C-N bond rotation

摘要

The trimethylplatinum(IV) complexes of a number of dithiocarbamato ligands have been prepared. The complexes are dimeric in the solid state and in solution, with the ligands acting in both a bridging and chelating fashion. Restricted rotation about the ligand C-N bonds in solution leads to the formation of four rotomers. The kinetics of the restricted rotation was measured by a variety of dynamic NMR techniques in the slow and intermediate exchange regimes. Two distinct processes are observed, namely the independent rotation about each C-N bond and correlated rotation about both C-N bonds. The free energies of activation, which are strongly dependent on the nature of the ligand substituents, are in the range 65-88 kJ mol(-1) at 298 K. The origins of the barrier to rotation and the effects of the nitrogen substituents are discussed. The crystal structures of fac-[PtMe3(Me2NCS2)](2) and fac-[PtMe3(Ph(H)NCS2)](2) are reported. [References: 48]