Selective reduction and homologation of carbon monoxide by organometallic iron complexes

Helen R Sharpe,Laurence J Taylor,Jonathan Mcmaster,Deborah L Kays,E Stephen Davies,Benjamin M Gridley,Alexander J Blake,William Lewis,Toby J Blundell,David Robinson,Ana M Geer

doi:10.1038/s41467-018-06242-w

Abstract

Carbon monoxide is a key C1 feedstock for the industrial production of hydrocarbons, where it is used to make millions of tonnes of chemicals, fuels, and solvents per annum. Many transition metal complexes can coordinate CO, but the formation of new C−C bonds in well-defined compounds from the scission and subsequent coupling of two or more CO moieties at a transition metal centre remains a challenge. Herein, we report the use of low-coordinate iron(II) complexes for the selective scission and homologation of CO affording unusual squaraines and iron carboxylates at ambient temperature and pressure. A modification of the ligand framework allows for the isolation and structural characterisation of a proposed metallacyclic Fe(II) carbene intermediate. These results indicate that, with the appropriate choice of supporting ligands, it is possible to cleave and homologate carbon monoxide under mild conditions using an abundant and environmentally benign low-coordinate, first row transition metal.

Highlights

Carbon monoxide is a key C1 feedstock for the industrial production of hydrocarbons, where it is used to make millions of tonnes of chemicals, fuels, and solvents per annum
More interesting still is the chemistry reported for several zirconium complexes, where CO is inserted into the M−H bond, but the reductive coupling of two or more CO molecules has been reported[11,12,13,14]
Previous work on C4 ring formation via CO activation has yielded squarates (C4O42‒) from uranium complexes, which does not require the scission of C≡O bonds[27]

Summary

Introduction

Carbon monoxide is a key C1 feedstock for the industrial production of hydrocarbons, where it is used to make millions of tonnes of chemicals, fuels, and solvents per annum. A modification of the ligand framework allows for the isolation and structural characterisation of a proposed metallacyclic Fe(II) carbene intermediate These results indicate that, with the appropriate choice of supporting ligands, it is possible to cleave and homologate carbon monoxide under mild conditions using an abundant and environmentally benign low-coordinate, first row transition metal. The study of model systems such as [(η5-C5H5)Fe (CO)3]+, aided by the addition of reducing agents and Lewis base, allowed the fundamental steps in these processes to be elucidated[4,5,6,7] Such electron-rich systems, are unable to undergo facile carbonylation; requiring borohydrides for carbonyl reduction and the use of relatively strong electrophiles to release homologated products[3]. Previously reported reactions between transition metal m-terphenyl complexes and CO afforded only insertion products such as acyl complexes[48,49] and sterically encumbered ketones[50]

Methods

Results

Conclusion