Search for: All records

We report a family of cobalt complexes based on bidentate phosphine ligands with two, one, or zero pendent amine groups in the ligand backbone. The pendent amine complexes are active electrocatalysts for the formate oxidation reaction, generating CO2 with near-quantitative faradaic efficiency at moderate overpotentials (0.45−0.57 V in acetonitrile). Thermodynamic measurements reveal that these complexes are energetically primed for formate oxidation via hydride transfer to the cobalt center, followed by deprotonation of the resulting cobalt-hydride by formate acting as a base. The complex featuring a single pendent amine arm is the fastest electrocatalyst in this series, with an observed rate constant for formate oxidation of 135 ± 8 h−1 at 25 °C, surpassing the activity of the bis-pendent amine analogue. Electrocatalytic turnover is not observed for the complex with no pendent amine groups: decomposition of the complex is evident in the presence of high formate concentrations. Thus, the application of thermodynamic considerations to electrocatalyst design is demonstrated as a successful strategy, while also highlighting the delicate balance of ligand properties necessary for achieving productive turnover. 

We report a family of cobalt complexes based on bidentate phosphine ligands with two, one, or zero pendent amine groups in the ligand backbone. The pendent amine complexes are active electrocatalysts for the formate oxidation reaction, generating CO2 with near-quantitative faradaic efficiency at moderate overpotentials (0.45 – 0.57 V in acetonitrile). These homogeneous electrocatalysts are the first cobalt example and second first-row transition metal example for formate oxidation. Thermodynamic measurements reveal these complexes are energetically primed for formate oxidation via hydride transfer to the cobalt center, followed by deprotonation of the resulting cobalt-hydride by formate acting as a base. The complex with the strongest cobalt- hydride bond, given by its thermodynamic hydricity, is the fastest electrocatalyst in this series, with an observed rate constant for formate oxidation of 135 ± 8 h−1 at 25 °C. Electrocatalytic turnover is not observed for the complex with no pendent amine groups: decomposition of the complex structure is evident in the presence of high formate concentrations. 

Reaction of FeBr 2 with 1.5 equiv. of LiNCPh 2 and 2 equiv. of Zn, in THF, results in the formation of the tetrametallic iron ketimide cluster [Fe 4 (NCPh 2 ) 6 ] ( 1 ) in moderate yield. Formally, two Fe centers in 1 are Fe( i ) and two are Fe( ii ); however, Mössbauer spectroscopy and SQUID magnetometry suggests that the [Fe 4 ] 6+ core of 1 exhibits complete valence electron delocalization, with a thermally-persistent spin ground state of S = 7. AC and DC SQUID magnetometry reveals the presence of slow magnetic relaxation in 1 , indicative of single-molecule magnetic (SMM) behaviour with a relaxation barrier of U eff = 29 cm −1 . Remarkably, very little quantum tunnelling or Raman relaxation is observed down to 1.8 K, which leads to an open hysteresis loop and long relaxation times (up to 34 s at 1.8 K and zero field and 440 s at 1.67 kOe). These results suggest that transition metal ketimide clusters represent a promising avenue to create long-lifetime single molecule magnets.