Cationic, Neutral, and Anionic Hydrides of Iridium with PSiP Pincers

Abstract

This work describes synthetic routes from the known precursor [IrClH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (1) to new hydride and polyhydride derivatives. Substituting the chloride ligand with triflate leads to the five-coordinate complex [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (2), which can undergo reversible coordination of water (H2O) or dihydrogen (H2) to generate respectively the cationic derivative [IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(OH2)2](CF3SO3) (3) or the neutral trans-hydride-dihydrogen [IrH{κO-O3S(CF3)}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(η2-H2)] (6) in equilibrium. The use of acetonitrile or carbon monoxide (CO) excess instead of water produces stable analogues of 3 (complexes 4 or 5, respectively). The reaction between 1 and NaBH4 affords the tetrahydroborate derivative [IrH{κ2H-H2BH2}{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (7), which can be protonated with triflic acid to form 2 or with HBF4 to give the dinuclear cationic derivative [(μ:κ2H,κ2H-BH4)[IrH{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]2](BF4) (8). The reactions of 7 with alcohols afford either the dihydride-carbonyl [IrH2{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}(CO)] (9) or the known tetrahydride [IrH4{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}] (10), depending on the ease of alcohol decarbonylation. NMR observations and density functional theory calculations on the fluxional behavior of 10 indicate that the spatial contour of the mer PSiP framework conditions hydride-ligand exchanges. Complex 10 reacts with NaH in tetrahydrofuran to form the anionic trihydride [IrH3{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]Na (11), which exists as a mixture of fac and mer isomers in equilibrium.