This work describes synthetic routes from the known precursor [IrClH{κP,P,Si-Si(Me)(CH-2-PiPr)}] (1) to new hydride and polyhydride derivatives. Substituting the chloride ligand with triflate leads to the five-coordinate complex [IrH{κO-OS(CF)}{κP,P,Si-Si(Me)(CH-2-PiPr)}] (2), which can undergo reversible coordination of water (HO) or dihydrogen (H) to generate respectively the cationic derivative [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}(OH)](CFSO) (3) or the neutral trans-hydride-dihydrogen [IrH{κO-OS(CF)}{κP,P,Si-Si(Me)(CH-2-PiPr)}(η-H)] (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 NaBH affords the tetrahydroborate derivative [IrH{κH-HBH}{κP,P,Si-Si(Me)(CH-2-PiPr)}] (7), which can be protonated with triflic acid to form 2 or with HBF to give the dinuclear cationic derivative [(μ:κH,κH-BH)[IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}]](BF) (8). The reactions of 7 with alcohols afford either the dihydride-carbonyl [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}(CO)] (9) or the known tetrahydride [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}] (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 [IrH{κP,P,Si-Si(Me)(CH-2-PiPr)}]Na (11), which exists as a mixture of fac and mer isomers in equilibrium.

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The five-coordinate hydrido complex [IrH(OTf)(PSiP)] ( 1 ) catalytically transforms 2-butyne into a mixture of its isomer 1,3-butadiene, and [3]dendralene and linear hexatriene dimerization products: ( E )-4-methyl-3-methylene-1,4-hexadiene and (3 Z )-3,4-dimethyl-1,3,5-hexatriene, respectively. Under the conditions of the catalytic reaction, benzene, and 363 K, the hexatriene further undergoes thermal electrocyclization into 2,3-dimethyl-1,3-cyclohexadiene. The reactions between 1 and the alkyne substrate allow isolation or nuclear magnetic resonance (NMR) observation of catalyst resting states and possible reaction intermediates, including complexes with the former PSiP pincer ligands disassembled into PSi and PC chelates, and species coordinating allyl or carbene fragments en route to products. The density functional theory (DFT) calculations guided by these experimental observations disclose competing mechanisms for C–H bond elaboration that move H atoms either classically, as hydrides, or as protons transported by the triflate. This latter role of triflate, previously recognized only for more basic anions such as carboxylates, is discussed to result from combining the unfavorable charge separation in the nonpolar solvent and the low electronic demand from the metal to the anion at coordination positions trans to silicon. Triflate deprotonation of methyl groups is key to release highly coordinating diene products from stable allyl intermediates, thus enabling catalytic cycling.