Electrophilic Si−H Activation by Acetonitrilo Benzo[h]quinoline Iridacycles: Influence of Electronic Effects in Catalysis

Abstract

AbstractThe performance of six newly synthesized benzo[h]quinoline‐derived acetonitrilo pentamethylcyclopentadienyl iridium(III) tetrakis(3,5‐bis‐trifluoromethylphenyl)borate salts bearing different substituents −X (−OMe, −H, −Cl, −Br, −NO2and −(NO2)2) on the heterochelating ligand were evaluated in the dehydro‐O‐silylation of benzyl alcohol and the monohydrosilylation of 4‐methoxybenzonitrile by Et3SiH, two reactions involving the electrophilic activation of the Si−H bond. The benchmark shows a direct dependence of the catalytic efficiency with the electronic effect of −X, which is confirmed by theoretical assessment of the intrinsic silylicitiesΠof 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 Ir−Si−H interactions shows that the most cohesive bond in hydridoiridium(III)‐silylium adducts is the Ir−H one, while the Ir−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 Si−H bond in this key catalytically relevant species.