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

Iridium(III) bis(thiophosphinite) complexes of the type [( R PSCSP R )Ir(H)(Cl)(py)] ( R PSCSP R = κ 3 -(2,6-SPR 2 )C 6 H 3 ) (R = t Bu, iPr, Ph) can be prepared from the ligand precursors 1,3-(SPR 2 )C 6 H 4 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 Ph PSCSP Ph ligand, P-S activation results in the formation of a thiophosphine stabilised Ir(III) hydride complex [( Ph PSCSP Ph )Ir(H)(Cl)(PPh 2 SH)] (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 NaO t Bu and tert -butylethylene, likely due to decomposition of the Ir complex in the presence of base at higher temperature.