Ru-Catalyzed Cross Dehydrogenative Coupling Leading to Si−O and Si−S Bond Formations and Also Stimulating an Alternative Scope for Hydrogenation of C=O, C=N and N=N Bonds

Graphical Abstract

The advantage of the weak Si−H bond in hydrosilane, Me₃SiH has been exploited to carry out Cross Dehydrogenative Coupling (CDC) reactions with water, alcohol and thiol, resulting in Si−O and Si−S bond formations. Density functional calculations have been carried out to predict the pathways involved in H₂-release by a neutral Ru-complex, [Ru(H₂)(trop₂dad)]. Turnover frequency and catalytic efficiency of the catalyst has been investigated theoretically. An alternative pathway leading to hydrogenation of C=O, C=N and N=N bonds has also been predicted.

Abstract

Reaction pathways involved in catalytic Cross Dehydrogenative Coupling (CDC) reactions leading to formation of Si−O and Si−S bonds have been formulated and explored theoretically using Density Functional Theory (DFT). The advantage of the weak Si−H bond has been exploited to carry out coupling with water, alcohol and thiol, along with H₂ release. Ru complex, [K(dme)₂][Ru(H)(trop₂dad)] when reacts with water generates a neutral complex, [Ru(trop₂dad)]. This neutral complex has been employed to act as a catalyst in CDC reactions. It has also been found that the complex, [Ru(H₂)(trop₂dad)] formed within the catalytic cycle may also be used for hydrogenation of C=O, C=N and N=N bonds. The optimized geometries of all the complexes and transition states have been obtained using wB97xd functional in conjunction with 6-31++G(d,p) basis set. The whole assisting phenomena in solvent medium has been investigated through the implementation of conductor-like screening solvation model (COSMO) considering tetrahydrofuran as the bulk solvent medium. The Turnover frequency (TOF) has been calculated by Energetic Span Model. The theoretical investigation extends the role of the ruthenium catalyst to the regime of ‘element to element’ bond formation, along with H₂ release, which may be significant in the field of energy storage, and also triggers an alternative possibility of hydrogenation of carbonyls, imines and diazo compounds.