Scope and Mechanism of Nickel-Isocyanide-Catalyzed Imine Hydrosilylation for ALD-Relevant Aminosilanes

Aminosilanes are an important class of compounds for the precision growth of silicon oxide and nitride films in microelectronics manufacturing. The traditional industrial methods by which aminosilanes are synthesized are inherently atom-inefficient and wasteful, often producing ammonium salts as byproducts that require removal and disposal. While catalytic methods for the production of aminosilanes have been reported, most require forcing conditions, additives, high-catalyst loadings, significant excesses of silane reagent, or produce byproducts such as H₂. Here, we report a well-defined organometallic nickel precatalyst (Ni(COD)(CNAr^Mes2)₂ (1); COD = 1,5-cyclooctadiene; (Ar^Mes2 = 2,6-(2,4,6-(CH₃)₃C₆H₂)₂C₆H₃)) that efficiently produces aminosilanes via catalytic imine hydrosilylation with n-hexylsilane (H₃SiⁿHex; ⁿHex = n-C₆H₁₃). Near quantitative conversion (>99%) of imine substrate can be achieved at room temperature using only a slight excess of H₃SiⁿHex (1.1 equiv) and catalyst loadings as low as 0.5 mol %, with good selectivity for imine hydrosilylation over silane dehydrocoupling. This imine hydrosilylation system is compatible with a range of low molecular weight imines to form analogues of industrially relevant aminosilanes (e.g., N,N-diisopropylaminosilane). Additionally, the system shows excellent scalability for performance on gram scale reactions. Test reactions on both small scale (∼0.04 mmol) and large scale (∼0.23 mol) show that 1 is capable of mediating imine hydrosilylation with SiH₄ gas. Activation studies on precatalyst 1 indicate the olefinic moieties of the COD ligand are hydrosilylated, thereby implicating the two-coordinate, zerovalent nickel complex, Ni(CNAr^Mes2)₂, as the active species. Mechanistic investigations in the form of initial rate kinetics under pseudo-first-order conditions indicated that the reaction rate depends on both the concentration of H₃SiⁿHex and of the imine. Kinetic isotope effect studies using H₃SiⁿHex/D₃SiⁿHex (KIE = k_H/k_D = 1.6(1)) and density functional theory (DFT) calculations suggest that full oxidative addition of the Si-H bond to the nickel center is not mechanistically operative. Rather, the Ni(CNAr^Mes2)₂ fragment facilitates ligand-to-ligand hydride transfer between silane and imine as the key mechanistic step for imine hydrosilylation.