Kinetic Analysis and Sequencing of Si–H and C–H Bond Activation Reactions: Direct Silylation of Arenes Catalyzed by an Iridium-Polyhydride

Abstract

The saturated trihydride IrH 3 {κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (1; xant(P i Pr 2 ) 2 = 9,9-dimethyl-4,5bis(diisopropylphosphino)xanthene) coordinates the Si-H bond of triethylsilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, and triphenylsilane to give the σ-complexes IrH 3 (η 2 -H-SiR 3 ){κ 2 -cis-P,P-[xant(P i Pr 2 ) 2 ]}, which evolve to the dihydride-silyl derivatives IrH 2 (SiR 3 ){κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (SiR 3 = SiEt 3 (2), SiMe(OSiMe 3 ) 2 (3), SiPh 3 (4)) by means of the oxidative addition of the coordinated bond and the subsequent reductive elimination of H 2 . Complexes 2-4 activate a C-H bond of symmetrically and asymmetrically substituted arenes to form silylated arenes and to regenerate 1. This sequence of reactions defines a cycle for the catalytic direct C-H silylation of arenes. Stoichiometric isotopic experiments and the kinetic analysis of the transformations demonstrate that the C-H bond rupture is the rate determining step of the catalysis. As consequence, the selectivity of the silylation of substituted arenes is generally governed by ligand-substrate steric interactions.

A Combined Computational and Experimental Study of Rh-Catalyzed C–H Silylation with Silacyclobutanes: Insights Leading to a More Efficient Catalyst System

“…Why do aryl C–H bonds react faster than benzylic C–H bonds? To the best of our knowledge, mechanistic studies on C–H silylations mainly focused on hydrosilanes − and theoretical studies on SCBs focused on cycloadditions. − While the collective body of knowledge about C–H silylations is undoubtedly inspirational, the answers to the above questions are not readily clear. We thus strived to decode the puzzle to further capitalize the potential of SCBs and the Rh/diphosphine catalyst system in C–H silylations.…”

C–Cl Oxidative Addition and C–C Reductive Elimination Reactions in the Context of the Rhodium-Promoted Direct Arylation

“…20e , 22 Accordingly, diphosphine xant(P i Pr 2 ) 2 allows structural changes in its complexes, to adapt the metal coordination sphere to the needs of the reactions. As a result, a number of metal derivatives stabilized by this ligand have proven to be active catalysts for a range of interesting organic transformations, 10h , 20a , 20d , 21b , 21f − 21h , 23 including cross-coupling reactions that involve elemental steps of σ-bond activation in both substrates such as the borylation 10g , 24 and silylation 25 of arenes. As a part of the chemistry of the Rh-xant(P i Pr 2 ) 2 moiety, we have previously reported that the square-planar rhodium(I)-hydride complex RhH{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} activates C–H and C–Cl bonds of arenes to afford the corresponding rhodium(III) species RhH 2 (aryl){κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} and RhH(aryl)Cl{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]}, which eliminate H 2 and HCl, respectively, to form a wide variety of square-planar derivatives Rh(aryl){κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]}.…”

Repercussion of a 1,3-Hydrogen Shift in a Hydride-Osmium-Allenylidene Complex

“… 3 The reason for this fact is because they are ideal for setting unsaturated organic molecules at metal fragments, 4 can generate radicals with Markovnikov selectivity by H· transfer, 5 and have demonstrated a marked ability to functionalize C–H bonds as consequence of their capacity to activate σ-bonds. 6 Thus, complexes bearing both classes of ligands have an enormous potentiality, being the stabilization and control over their chemical properties a challenge of first magnitude.…”