Iridium(III) bis(thiophosphinite) pincer complexes: synthesis, ligand activation and applications in catalysis

Iridium(III) bis(thiophosphinite) complexes of the type [((PSCSPR)-P-R)Ir(H)(Cl)(py)] ((PSCSPR)-P-R = kappa(3)-(2,6-SPR2)C6H3) (R = tBu, iPr, Ph) can be prepared from the ligand precursors 1,3-(SPR2)C6H4 by C-H activation at Ir using [Ir(COE)(2)Cl](2) or [Ir(COD)Cl](2). Optimisation of the protocol for complexation showed that direct cyclometallation in the absence or presence of pyridine, as well as C-H activation in the presence of H-2 are viable options that, depending on the phosphine substituent furnish the five-coordinate Ir(III) hydride chloride complexes 2-R or the base stabilised species 3-R in good yields. In case of the (PSCSPPh)-P-Ph ligand, P-S activation results in the formation of a thiophosphine stabilised Ir(III) hydride complex [((PSCSPPh)-P-Ph)Ir(H)(Cl)(PPh2SH)] (4). Reaction of 2-tBu with H-2 in the presence of base furnishes an Ir(III) dihydride complex (5) via a labile Ir(III) dihydride-dihydrogen complex (6). All complexes are inactive for transfer dehydrogenation of cyclooctane in the presence of NaOtBu and tert-butylethylene, likely due to decomposition of the Ir complex in the presence of base at higher temperature.