Reactions of aluminium(i) with transition metal carbonyls: scope, mechanism and selectivity of CO homologation.

Richard Y Kong,Mark R Crimmin,Maria Batuecas

doi:10.1039/d1sc04940b

Abstract

Over the past few decades, numerous model systems have been discovered that create carbon–carbon bonds from CO. These reactions are of potential relevance to the Fischer–Tropsch process, a technology that converts syngas (H2/CO) into mixtures of hydrocarbons. In this paper, a homogeneous model system that constructs carbon chains from CO is reported. The system exploits the cooperative effect of a transition metal complex and main group reductant. An entire reaction sequence from C1 → C2 → C3 → C4 has been synthetically verified. The scope of reactivity is broad and includes a variety of transition metals (M = Cr, Mo, W, Mn, Re, Co), including those found in industrial heterogeneous Fischer–Tropsch catalysts. Variation of the transition metal fragment impacts the relative rate of the steps of chain growth, allowing isolation and structural characterisation of a rare C2 intermediate. The selectivity of carbon chain growth is also impacted by this variable; two distinct isomers of the C3 carbon chain were observed to form in different ratios with different transition metal reagents. Based on a combination of experiments (isotope labelling studies, study of intermediates) and calculations (DFT, NBO, ETS-NOCV) we propose a complete mechanism for chain growth that involves defined reactivity at both transition metal and main group centres.

Highlights

Chemical reactions that allow the formation of useful ne chemicals from C1 building blocks such as CO or CO2 are of contemporary interest.[1]
E-mail: m.crimmin@imperial. ac.uk † Electronic supplementary information (ESI) available: X-ray crystallographic data for 2–4 are available from the Cambridge Crystallographic Data Centre (CCDC 2095244–2095254) as a .cif le, full details of the experiments and calculations are available as a .pdf
We have previously reported the reaction of [Al] with [W(CO)6] and the isolation of the C3 homologation product and its chain growth to a C4 analogue

Summary

Introduction

Chemical reactions that allow the formation of useful ne chemicals from C1 building blocks such as CO or CO2 are of contemporary interest.[1]. These reactions proceeded from a de ned transition metal carbonyl starting material, but they led to the isolation of intermediates and products bearing reactive Al– C bonds allowing us, for the rst time, to elucidate the mechanism of chain growth from C1 / C3 / C4 species.

Results

Conclusion