The ionic iridacycle [(2-phenylenepyridine-κN,κC)-IrCp*(NCMe)][BArF 24 ] ([2][BArF 24 ]) displays a remarkable capability to catalyze the O-dehydrosilylation of alcohols at room temperature (0.4 × 10 3 < TON < 10 3 , 8 × 10 3 < TOF i < 1.9 × 10 5 h −1 for primary alcohols) that is explained by its exothermic reaction with Et 3 SiH, which affords the new cationic hydrido-Ir(III)-silylium species [3][BArF 24 ]. Isothermal calorimetric titration (ITC) indicates that the reaction of [2][BArF 24 ] with Et 3 SiH 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][BF 4 ] and [3][OTf] salts resulted in the formation of a known neutral hydrido-iridium(III) complex, i.e. 4, and the release of Et 3 SiF and Et 3 SiOTf, respectively. In both cases formation of the cationic μ-hydrido-bridged bis-iridacyclic complexes [5][BF 4 ] and [5][OTf], respectively, was observed. The structure of [5][OTf] was established by X-ray diffraction analysis. Conversion of [3][BArF 24 ] into 4 upon reaction with either 4-N,N-dimethylaminopyridine or [nBu 4 ] [OTf] indicates that the Ir center holds a +III formal oxidation state and that the Et 3 Si + moiety behaves as a Z-type ligand according to Green's formalism.[3][BArF 24 ], which was trapped and structurally characterized and its electronic structure investigated by state-of-the-art DFT methods (DFT-D, EDA, ETS-NOCV, QTAIM, ELF, NCI plots and NBO), displays the features of a cohesive hydridoiridium(III)→silylium donor−acceptor complex. This study suggests that the fate of [3] + in the O-dehydrosilylation of alcohols is conditioned by the nature of the associated counteranion and by the absence of Lewis base in the medium capable of irreversibly capturing the silylium species. ■ INTRODUCTIONMetal−silane complexes are central to many chemical transformations that aim for the synthesis of high-value organic molecules and materials. 1 The most documented 1,2 types of metal−silane adducts are the σ-complexes (η 1,2 -R 3 Si-H)M n (n = formal oxidation state) arising from the isohypsic 3 (i.e., n = constant; by definition the isohypsic term refers to reactions occurring at a given reactive center with no change in its formal oxidation state) metal coordination of silane 4 and R 3 Si-M n+2 -H complexes arising from oxidative addition of the Si−H bond at M n . 5 However, intermediary situations considered as so-called "arrested states" toward the Si−H bond cleavage by oxidative addition were also pointed out and raised sustained attention. 6 M−silane adducts are commonly categorized according to the bonding relationships existing within the M−Si−H motif, i.e. two-center−two-electron and three-center−two-electron interactions. 7 Subcategories of stabilizing interactions referred to as IHI (interligand hypervalent interactions) and SISHA 8 (secondary interac...

The set of iridacycles [{C,N}­Cp*IrIII-Cl] ({C,N} = benzo­[h]­quinoline, dibenzo­[f,h]­quinoline) containing the (pentamethylcyclopentadienyl)­iridium­(III) unit were synthesized and derivatized into cations [{C,N}­Cp*Ir-NCMe]+ associated with BArF-type anions. The latter salts were benchmarked for their potential catalytic properties toward HSiEt3 in a H2-releasing test reaction. The best-performing BArF-type salts demonstrated the capability to promote with a low catalytic load of ca. 0.5–1 mol % the autotandem hydrosilylation of acetonitrile, propionitrile, and a series of arylnitrile substrates. Mechanistic investigations confirmed the preliminary formation of a silane–iridacycle adduct by electrophilic and heterolytic activation of the Si–H bond. The molecular structure of a new example of such an adduct was resolved by X-ray diffraction analysis. Theoretical considerations support a donor–acceptor [{C,N}­Cp*IrIII-H]→[SiEt3]+ ({C,N} = benzo­[h]­quinolinyl) formulation where the cationic silyl moiety acting as a Z ligand binds both Ir and H centers. Under the conditions of the catalysis, the latter adduct is assumed to transfer readily the electrophilic [SiEt3]+ moiety to the nucleophilic nitrile substrate to form a N-silylnitrilium cation and the neutral [{C,N}­Cp*Ir-H]. The latter reduces the N-silylnitrilium into the corresponding N-silylimine, which undergoes further N-silylation and reduction to yield the final N,N-disilylamine. Under optimal conditions of low catalyst load (70 °C, 0.5 mol %) the autotandem hydrosilylation of arylnitriles produces the silylated amines in yields >80% in 24 h.