Mechanistic investigations of the Fe(II) mediated synthesis of squaraines

Yu Liu; Nathan T. Coles; Nathalia Cajiao; Laurence J. Taylor; E. Stephen Davies; Alistair Barbour; Patrick J. Morgan; Kevin Butler; Ben Pointer-Gleadhill; Stephen P. Argent; Jonathan McMaster; Michael L. Neidig; David Robinson; Deborah L. Kays

doi:10.1039/D4SC01286K

Mechanistic investigations of the Fe(ii) mediated synthesis of squaraines†

Yu Liu,

‡^a Nathan T. Coles,

‡*^a Nathalia Cajiao,

^bc Laurence J. Taylor,

^a E. Stephen Davies,^a Alistair Barbour,^a Patrick J. Morgan,^a Kevin Butler,

^a Ben Pointer-Gleadhill,^a Stephen P. Argent,

^a Jonathan McMaster,^a Michael L. Neidig,

^b David Robinson

^d and Deborah L. Kays

*^a

Author affiliations

* Corresponding authors

^a School of Chemistry, University of Nottingham, University Park, Nottingham, UK
E-mail: Deborah.Kays@nottingham.ac.uk, Nathan.Coles@nottingham.ac.uk

^b Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford, UK

^c Department of Chemistry, University of Rochester, Rochester, New York 14627, USA

^d Department of Chemistry and Forensics, School of Science and Technology, Nottingham Trent University, Nottingham, UK

Abstract

The scission and homologation of CO is a fundamental process in the Fischer–Tropsch reaction. However, given the heterogeneous nature of the catalyst and forcing reaction conditions, it is difficult to determine the intermediates of this reaction. Here we report detailed mechanistic insight into the scission/homologation of CO by two-coordinate iron terphenyl complexes. Mechanistic investigations, conducted using in situ monitoring and reaction sampling techniques (IR, NMR, EPR and Mössbauer spectroscopy) and structural characterisation of isolable species, identify a number of proposed intermediates. Crystallographic and IR spectroscopic data reveal a series of migratory insertion reactions from 1^Mes to 4^Mes. Further studies past the formation of 4^Mes suggest that ketene complexes are formed en route to squaraine 2^Mes and iron carboxylate 3^Mes, with a number of ketene containing structures being isolated, in addition to the formation of unbound, protonated ketene (8). The synthetic and mechanistic studies are supported by DFT calculations.

This article is part of the themed collection: 2024 Chemical Science HOT Article Collection

Chemical Science

Mechanistic investigations of the Fe(ii) mediated synthesis of squaraines†

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