Selective reduction and homologation of carbon monoxide by organometallic iron complexes.

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.

Ligand influences on homoleptic Group 12 m-terphenyl complexes.

Three m-terphenyl ligands 2,6-Ar2C6H3(-) [Ar = 2,6-Me2C6H3 (2,6-Xyl); 3,5-Me2C6H3 (3,5-Xyl); 2,3,4,5,6-Me5C6 (Pmp)] have been used to stabilise three series of two-coordinate Group 12 diaryl complexes; (2,6-Ar2C6H3)2M [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.

Cubane and dicubane complexes stabilised by sterically demanding m-terphenyl ligands.

The reaction between sterically demanding m-terphenyl lithiate complexes and cadmium dihalides yields unusual cubanes where changes in ligand bulk afford different formulations, in particular a rare heterodicubane structure.

Conformational isomerism in monomeric, low-coordinate group†12 complexes stabilized by a naphthyl-substituted m-terphenyl ligand.

The synthesis and characterization of the first series of low-coordinate bis(terphenyl) complexes of the Group 12 metals, [Zn(2,6-Naph2 C6 H3 )2 ] (1), [Cd(OEt2 )(2,6-Naph2 C6 H3 )2 ] (2) and [Hg(OEt2 )(2,6-Naph2 C6 H3 )2 ] (3) (Naph=1-C10 H7 ) are described. The naphthyl substituents of the terphenyl ligands confer considerable steric bulk, and as a result of limited flexibility introduce multiple conformations to these unusual systems. In the solid state, complex 1 features a two-coordinate Zn centre with the ligands oriented in a syn/anti conformation, whereas the three-coordinate distorted T-shaped complexes 2 and 3 feature the ligands in the syn/syn configurations. The results of DFT calculations are in good agreement with the solid-state configurations for these complexes and support the spectroscopic measurements, which indicate several conformers in solution.

Low-coordinate cobalt(II) terphenyl complexes: precursors to sterically encumbered ketones.

Cobalt(II) diaryl complexes react with CO to afford Co(2)(CO)(8) and sterically encumbered ketones whose structure varies depending on the nature of the aryl ligands.