H/D EXCHANGE-REACTIONS OF AN IRIDIUM DITHIOL COMPLEX

The complex [Ir(H)2(HS(CH2)3SH)(PCy3)2]BF4 (1) which contains an unprecedented chelating dithiol ligand was prepared by the action of 1,3-propanedithiol and HBF4.Et2O on IrH5(PCy3)2. The acidic thiol protons of 1(pK(alpha) almost-equal-to 9) exchange much more rapidly than the hydride ligands with deuterium from MeOD. This allows a unique opportunity to measure by H-1 NMR the rate constant for intramolecular H/D transfer, [Ir(H)(DSR)]+ reversible [Ir(D)(HSR)]+, a process which likely proceeds via an unobserved [Ir(eta2-HD)(SR)]+ complex. The reaction of 1 with D2 deuterates both the thiol and hydride hydrogens; this and the observation of similar stable dihydrogen complexes support the proposal of an eta2-HD intermediate.