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.

Abstract:Three m-terphenyl ligands 2,6-Ar 2 C 6 H 3 -[Ar = 2,6-Me 2 C 6 H 3 (2,6-Xyl); 3,5-Me 2 C 6 H 3 (3,5-Xyl); 2,3,4,5,6-Me 5 C 6 (Pmp)] have been used to stabilise three series of two-coordinate Group 12 diaryl complexes; (2,6-Ar 2 C 6 H 3 ) 2 M [M = Zn, Cd, Hg; Ar = 2,6-Xyl 1-3; 3,5-Xyl 4-6; Pmp 7-9], where differing steric demands on the metal centres are imparted. These are the first homoleptic d-block complexes featuring any of these ligands. Complexes 1-9 have been characterised in solution and the solid state; the analysis of structural changes produced by differences in ligand properties is reported. In particular, complexes 4-6 show smaller C-M-C bond angles and contain secondary ligand interactions that are not seen in the analogous complexes 1-3 and 7-9. † Electronic supplementary information (ESI) available: Crystallographic data for complexes 1-9, molecular structures and crystallographic data for iodides 2,6-Ar 2 C 6 H 3 I (Ar = 2,6-Xyl, 3,5-Xyl, Pmp) and [2,

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Low-coordinate m-terphenyl complexes are precatalysts for dehydrocoupling of dimethylamine–borane, where small changes in coordination environment effect significant mechanistic differences.