posted on 2021-04-26, 14:34authored byDae Ho Hong, Ricardo B. Ferreira, Vincent J. Catalano, Ricardo García-Serres, Jason Shearer, Leslie J. Murray
CO2 insertion into tri(μ-hydrido)triiron(II)
clusters
ligated by a tris(β-diketiminate) cyclophane is demonstrated
to be balanced by sterics for CO2 approach and hydride
accessibility. Time-resolved NMR and UV–vis spectra for this
reaction for a complex in which methoxy groups border the pocket of
the hydride donor (Fe3H3L2, 4) result in a decreased activation
barrier and increased kinetic isotope effect consistent with the reduced
sterics. For the ethyl congener Fe3H3L1 (2), no correlation is found
between rate and reaction solvent or added Lewis acids, implying CO2 coordination to an Fe center in the mechanism. The estimated
hydricity (50 kcal/mol) based on observed H/D exchange with BD3 requires Fe–O bond formation in the product to offset
an endergonic CO2 insertion. μ3-hydride
coordination is noted to lower the activation barrier for the first
CO2 insertion event in DFT calculations.