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

Eric Keske, Thomas West, Guy C. Lloyd-jones

Research output: Contribution to journalArticlepeer-review

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 (13C/15N) 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 (13C/15N); 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.
Original languageEnglish
Pages (from-to)8932-8940
Number of pages17
JournalACS Catalysis
Volume8
Issue number9
Early online date14 Aug 2018
DOIs
Publication statusPublished - Sep 2018

Keywords

  • rhodium
  • C-C bond activation
  • disilanes
  • induction
  • isotopic labeling
  • autoinduction
  • kinetics
  • isonitriles
  • CARBON-CYANO BONDS
  • CROSS-COUPLING REACTIONS
  • SI-SI
  • IODINE(III) OXIDANT
  • DIRECT ARYLATION
  • TRIPLE BONDS
  • FLUORIDE-ION
  • COMPLEXES
  • NITRILES
  • BORYLATION

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