Evidence of a Donor–Acceptor (Ir–H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate

The ionic iridacycle [(2-phenylenepyridine-κN,κC)IrCp*(NCMe)][BArF24] ([2][BArF24]) displays a remarkable capability to catalyze the O-dehydrosilylation of alcohols at room temperature (0.4 × 103 < TON < 103, 8 × 103 < TOFi < 1.9 × 105 h–1 for primary alcohols) that is explained by its exothermic reaction with Et3SiH, which affords the new cationic hydrido-Ir(III)-silylium species [3][BArF24]. Isothermal calorimetric titration (ITC) indicates that the reaction of [2][BArF24] with Et3SiH requires 3 equiv of the latter and releases an enthalpy of −46 kcal/mol in chlorobenzene. Density functional theory (DFT) calculations indicate that the thermochemistry of this reaction is largely dominated by the concomitant bis-hydrosilylation of the released MeCN ligand. Attempts to produce [3][BF4] and [3][OTf] salts resulted in the formation of a known neutral hydrido-iridium(III) complex, i.e. 4, and the release of Et3SiF and Et3SiOTf, respectively. In both cases formation of the cationic μ-hydrido-bridged bis-iridac...