Analysis of Autoinduction, Inhibition, and Autoinhibition in a Rh-Catalyzed C–C Cleavage: Mechanism of Decyanative Aryl Silylation

Abstract

The mechanism the Chatani-Tobisu rhodium-catalyzed decyanative silylation of aryl nitriles by hexamethyldisilane (Me3Si-SiMe3) has been investigated by in-situ NMR spectroscopy. The production of Ar-SiMe3 evolves in three distinct phases: slow catalyst induction is followed by a period of rapidly-accelerating turnover, and then, after approximately three catalyst turnovers, the onset of progressive inhibition. The processes giving rise to these phenomena have been elucidated by isotopic labelling (13 C/ 15 N) and kinetic analysis, and it is shown that, in addition to facilitating catalyst turnover to generate Ar-SiMe3, the reactants serve other roles. Me3Si-SiMe3 functions as a slow exogenous precatalyst activator, and as a moderately powerful catalyst inhibitor. In contrast ArCN acts as a precatalyst inhibitor. Moreover, the co-product from the reaction (trimethylsilyl cyanide, Me3SiCN), acts as a powerful endogenous precatalyst activator and catalyst inhibitor, together giving rise to sigmoidal temporal concentration profiles for [Ar-SiMe3]. Kinetic studies of the reaction during the phase of progressive inhibition suggest that, for a given initial catalyst concentration, the maximum rate of turnover is achieved when the concentration of [Me3Si-SiMe3] and [ArCN] partition the Rh equally between two major resting states, one on-cycle, the other off-cycle. The off-cycle resting-state was identified as a Rh(III) complex: (Me3Si)3Rh(CN-SiMe3)3, as confirmed by independent synthesis and isotopic labelling (13 C/ 15 N); the on-cycle resting state has been tentatively assigned as (Me3Si-NC)3RhAr. Overall the results indicate that the catalytic process can in principle be made much more efficient by engendering a pathway or process for Me3SiCN sequestration.

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

“…6 ) under standard conditions. Surprisingly, the experiment displayed a counter-intuitive sigmoidal kinetic profile 83 – 85 , differing from saturation kinetics observed our previously reported XB-catalyzed strain-release glycosylation 44 . Superimposition of the product formation profile of 3al with the depletion profiles of both reactants (Fig.…”

Recent Developments in Hydrodecyanation and Decyanative Functionalization Reactions

“…In this silylation reaction, first a SiÀ Si bond and then the CÀ CN bonds were cleaved by a Rh-catalyst (Scheme 16). [32] A wide range of aryl nitriles participated in this reaction conditions to form the corresponding organosilanes. Functional groups including esters, ethers and tertiary amines were well tolerated in this catalytic process.…”

Cyano-borrowing reaction: nickel-catalyzed direct conversion of cyanohydrins and aldehydes/ketones to β-cyano ketone

“…Nitriles are important synthesis intermediates in transformation1 and are key components in various natural products, medicinal pharmacophores and drugs,2 and in organic synthesis, the cyano group is equivalent to an amine or carbonyl group. The catalytic addition of the cyano group to the CC bond has been established as one of the most direct pathways for the synthesis of nitriles 3,4.…”