Restoration of catalytic activity by the preservation of ligand structure: Cu-catalysed asymmetric conjugate addition with 1,1-diborylmethane.

Hong Geun Lee,Byeongdo Roh,Changhee Kim

doi:10.1039/d0sc06543a

Hong Geun Lee, Byeongdo Roh + Show 1 more

Open Access

https://doi.org/10.1039/d0sc06543a

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Abstract

Reported herein is a novel reaction engineering protocol to enhance the efficiency of a transition metal-catalysed process by strategically preventing ligand degradation. Based on spectroscopic investigations, a decomposition pathway of a chiral phosphoramidite ligand during a Cu-catalysed reaction was identified. The involvement of the destructive process could be minimized under the modified reaction conditions that control the amount of nucleophilic alkoxide base, which is the origin of ligand decomposition. Overall, the strategy has been successfully applied to a new class of asymmetric conjugate addition reactions with bis[(pinacolato)boryl]methane, in which α,β-unsaturated enones are utilised as substrates.

Highlights

The introduction of novel supporting ligands for transition metals has contributed signi cantly to the development of homogeneous catalysis based on transition metals
On the other hand, the ligand originally administered had been converted into an inactive state by structural modi cations (L to L00), the catalytic system would lose its ability to mediate the targeted reaction (Scheme 1a, path c)
It can be difficult to assess the catalyst performance accurately, as either the inherent incompetence of the system or the destruction of the given ligand structure can be the cause of the substandard reactivity

Summary

Introduction

The introduction of novel supporting ligands for transition metals has contributed signi cantly to the development of homogeneous catalysis based on transition metals. Constructive in situ ligand modi cations have been reported in the context of cross-coupling[2] or addition reactions of organometallic species (Scheme 1a, path b).[3] In such cases, the spontaneous conversion of the ligand (L to L0) eventually facilitated the desired reactivity of the catalytic system.

Results

Conclusion