Ni(I)-Alkyl Complexes Bearing Phenanthroline Ligands: Experimental Evidence for CO2 Insertion at Ni(I) Centers.

Marc F Obst,Carlota Odena,Kathrin H Hopmann,Ruben Martin,Nilay Hazari,Rosie J Somerville

doi:10.1021/jacs.0c04695

Abstract

Although the catalytic carboxylation of unactivated alkyl electrophiles has reached remarkable levels of sophistication, the intermediacy of (phenanthroline)Ni(I)–alkyl species—complexes proposed in numerous Ni-catalyzed reductive cross-coupling reactions—has been subject to speculation. Herein we report the synthesis of such elusive (phenanthroline)Ni(I) species and their reactivity with CO2, allowing us to address a long-standing question related to Ni-catalyzed carboxylation reactions.

Highlights

O ver the past decade, Ni-catalyzed reductive carboxylation reactions involving organichalides and carbon dioxide have received considerable attention as methodologies for the preparation of many synthetically useful carboxylic acids.[1]
Proposed Reductive Carboxylation Mechanism via CO2 Insertion at Phen-Ligated Ni(I)−Alkyl SpeciesNi(I)−alkyl complexes have been structurally characterized or even observed spectroscopically, probably because of the fleeting nature and high reactivity of these paramagnetic species.[9]. Elegant efforts toward this goal were recently described by Diao, and cultimated in the synthesis ofNi(I)−alkyl complexes and investigations into their reactivity with CO2.10,11 diphosphine ligands have not been shown to facilitate the Ni-catalyzed carboxylation of unactivated alkylhalides (Scheme 1).[2,12]
114.25(13). Calculated spin-density plot of 3 with a spin population of 0.94 on Ni (PBE-D3BJ/def2-TZVP, isovalue = 0.01; Figure at preparing well-defined Ni(I)−alkyl complexes bearing catalytically relevant phen ligands would represent (a) an opportunity to study the reactivity of elusive Ni(I)−alkyl complexes supported by nitrogen-donor ligands, (b) a foundation for investigating the mechanistic intricacies of catalytic reductive carboxylation reactions, and (c) a starting point for understanding the speciation of Ni catalysts supported by phen ligands in related cross-coupling and chain-walking reactions.[4]

Summary

Introduction

O ver the past decade, Ni-catalyzed reductive carboxylation reactions involving organic (pseudo)halides and carbon dioxide have received considerable attention as methodologies for the preparation of many synthetically useful carboxylic acids.[1]. Proposed Reductive Carboxylation Mechanism via CO2 Insertion at Phen-Ligated Ni(I)−Alkyl Species (phen)Ni(I)−alkyl complexes have been structurally characterized or even observed spectroscopically, probably because of the fleeting nature and high reactivity of these paramagnetic species.[9] Elegant efforts toward this goal were recently described by Diao, and cultimated in the synthesis of (diphosphine)Ni(I)−alkyl complexes and investigations into their reactivity with CO2.10,11 diphosphine ligands have not been shown to facilitate the Ni-catalyzed carboxylation of unactivated alkyl (pseudo)halides (Scheme 1).[2,12] a study aimed

Results

Conclusion