Revealing the machinery of homogeneous catalysis by Ni^I cyclam: characterization of ligand-dependent activation of N₂ and CO₂ with variable temperature ion chemistry and vibrational spectroscopy

We exploit advances in cryogenic, gas-phase ion methods to capture and characterize the complexes formed by CO₂ and N₂ with Ni^I cyclam and Ni^I L-N₄Me₂. The measurements furnish key information about the mechanism of small molecule activation and provide a crucial test of electronic structure methods used to rationalize catalytic activity and guide catalyst development.

One of the most important challenges in catalysis is the transformation of N₂ and CO₂ to high value chemicals (e.g. ammonia and ethanol). In principle, the methods of organometallic chemistry can tailor transition metal complex electronic structure to drive desired product formation. However, studying the activity of reactive transition metal centers is challenging because they are inherently unstable and thus difficult to capture and characterize. We harness cryogenic gas-phase ion methods to overcome these difficulties and collect infrared spectra and small-molecule thermal binding curves. Electronic structure calculations constrained by infrared spectra offer insight into complex structure and mechanism of activation.