A computational study on high-valent mono-oxo-rhenium(V) complex-catalyzed hydrosilylation of carbonyls: What a difference an oxo ligand makes

Activation of Si-H and B-H bonds by Lewis acidic transition metals and p-block elements: same, but different

In this Perspective we discuss the ability of transition metal complexes to activate and cleave the Si-H and B-H bonds of hydrosilanes and hydroboranes (tri- and tetra-coordinated) in an electrophilic manner, avoiding the need for the metal centre to undergo two-electron processes (oxidative addition/reductive elimination). A formal polarization of E-H bonds (E = Si, B) upon their coordination to the metal centre to form σ-EH complexes (with coordination modes η1 or η2) favors this type of bond activation that can lead to reactivities involving the formation of transient silylium and borenium/boronium cations similar to those proposed in silylation and borylation processes catalysed by boron and aluminium Lewis acids. We compare the reactivity of transition metal complexes and boron/aluminium Lewis acids through a series of catalytic reactions in which pieces of evidence suggest mechanisms involving electrophilic reaction pathways.

Hydrosilylation Reactions Catalyzed by Rhenium

Hydrosilylation is an important process, not only in the silicon industry to produce silicon polymers, but also in fine chemistry. In this review, the development of rhenium-based catalysts for the hydrosilylation of unsaturated bonds in carbonyl-, cyano-, nitro-, carboxylic acid derivatives and alkenes is summarized. Mechanisms of rhenium-catalyzed hydrosilylation are discussed.

Cationic rhenium(iii) complexes: synthesis, characterization, and reactivity for hydrosilylation of aldehydes

A series of novel cationic Re(iii) complexes [(DAAm)Re(CO)(NCCH₃)₂][X] [DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C₆F₅ (a), Mes (b)] [X = OTf (2), BAr^F₄ [BAr^F₄ = tetrakis[3,5-(trifluoromethyl)phenyl]borate] (3), BF₄ (4), PF₆ (5)], and their analogue [(DAmA)Re(CO)(Cl)₂] [DAmA = N,N-bis(2-arylamineethyl)methylamino; aryl = C₆F₅] (6) were synthesized. The catalytic efficiency for the hydrosilylation reaction of aldehydes using 4a (0.03 mol%) has been demonstrated to be significantly more active than rhenium catalysts previously reported in the literature. The data suggest that electron-withdrawing substituents at the diamido amine ligand increase the catalytic efficiency of the complexes. Excellent yields were achieved at ambient temperature under neat conditions using dimethylphenylsilane. The reaction affords TONs of up to 9200 and a TOF of up to 126 h^-1. Kinetic and mechanistic studies were performed, and the data suggest that the reaction is via a non-hydride ionic hydrosilylation mechanism.

Reduction of carbon dioxide and organic carbonyls by hydrosilanes catalysed by the perrhenate anion

A simple quaternary ammonium perrhenate salt catalyses the hydrosilylation of aldehydes, ketones, and carbon dioxide, and the methylation of amines using carbon dioxide. DFT calculations show that a perrhenate hypervalent silicate interacts directly with CO₂.