Boosting homogeneous chemoselective hydrogenation of olefins mediated by a bis(silylenyl)terphenyl-nickel(0) pre-catalyst.

Marcel-Philip Lücke,Shenglai Yao,Matthias Driess

doi:10.1039/d0sc06471h

Abstract

The isolable chelating bis(N-heterocyclic silylenyl)-substituted terphenyl ligand [SiII(Terp)SiII] as well as its bis(phosphine) analogue [PIII(Terp)PIII] have been synthesised and fully characterised. Their reaction with Ni(cod)2 (cod = cycloocta-1,5-diene) affords the corresponding 16 VE nickel(0) complexes with an intramolecular η2-arene coordination of Ni, [E(Terp)E]Ni(η2-arene) (E = PIII, SiII; arene = phenylene spacer). Due to a strong cooperativity of the Si and Ni sites in H2 activation and H atom transfer, [SiII(Terp)SiII]Ni(η2-arene) mediates very effectively and chemoselectively the homogeneously catalysed hydrogenation of olefins bearing functional groups at 1 bar H2 pressure and room temperature; in contrast, the bis(phosphine) analogous complex shows only poor activity. Catalytic and stoichiometric experiments revealed the important role of the η2-coordination of the Ni(0) site by the intramolecular phenylene with respect to the hydrogenation activity of [SiII(Terp)SiII]Ni(η2-arene). The mechanism has been established by kinetic measurements, including kinetic isotope effect (KIE) and Hammet-plot correlation. With this system, the currently highest performance of a homogeneous nickel-based hydrogenation catalyst of olefins (TON = 9800, TOF = 6800 h−1) could be realised.

Highlights

The transition-metal (TM) catalysed hydrogenation of unsaturated organic compounds is one of the most important reactions, where precious metals (Rh, Ir, Ru, Pd) proved to be suitable.[1]
Since 2001, isolable silylenes in particular N-heterocyclic silylenes (NHSis)4a have been demonstrated to act as effective steering ligands in various TM-mediated catalytic transformations.4b NHSis, the heavier analogues of N-heterocyclic carbenes (NHCs), exhibit a singlet electronic ground state with a strong s-donor and p-acceptor character of the Si(II) center towards TM sites
In order to determine the catalytic activity of 5 with respect to turnover number (TON) and turnover frequency (TOF, hÀ1), hydrogenation reactions were performed in a Schlenk-tube containing a metal-free te on-coated stir bar (1400 minÀ1)

Summary

Introduction

The transition-metal (TM) catalysed hydrogenation of unsaturated organic compounds is one of the most important reactions, where precious metals (Rh, Ir, Ru, Pd) proved to be suitable.[1]. Inspired by the work of Agapie and coworkers, a para-terphenyl-based bis(NHSi) ligand scaffold was targeted containing an intramolecular phenylene as an additional donor (Fig. 1, bottom).[14] we report the synthesis of the new terphenyl-based chelating bis(NHSi) ligand [SiII(Terp)SiII] (3) and its 16 VE Ni(0)-complex [Si(Terp)Si]Ni(h2-arene) 5 which acts as an efficient and chemoselective catalyst for the hydrogenation of even functionalised ole ns under ambient reaction conditions (1 bar, rt).

Results

Conclusion