The performance of six newly synthesized benzo[h]quinoline-derived acetonitrilo pentamethylcyclopentadienyl iridium(III) tetrakis(3,5-bis-trifluoromethylphenyl)borate salts bearing different substituents À X (À OMe, À H, À Cl, À Br, À NO 2 and À (NO 2 ) 2 ) on the heterochelating ligand were evaluated in the dehydro-O-silylation of benzyl alcohol and the monohydrosilylation of 4-methoxybenzonitrile by Et 3 SiH, two reactions involving the electrophilic activation of the SiÀ H bond. The benchmark shows a direct dependence of the catalytic efficiency with the electronic effect of À X, which is confirmed by theoretical assessment of the intrinsic silylicities Π of hydridoiridium(III)-silylium adducts and by the theoretical evaluation of the propensity of hydridospecies to transfer the hydrido ligand to the activated substrate. The revisited analysis of the IrÀ SiÀ H interactions shows that the most cohesive bond in hydridoiridium(III)-silylium adducts is the IrÀ H one, while the IrÀ Si is a weak donor-acceptor dative bond. The Si…H interaction in all the cases is noncovalent in nature and dominated by electrostatics confirming the heterolytic cleavage of the hydrosilane's SiÀ H bond in this key catalytically relevant species.
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