Iron and Cobalt Diazoalkane Complexes Supported by β-Diketiminate Ligands: A Synthetic, Spectroscopic, and Computational Investigation

Diazoalkanes are interesting redox-active ligands and also precursors to carbene fragments. We describe a systematic study of the binding and electronic structure of diphenyldiazomethane complexes of beta-diketiminate supported iron and cobalt, which span a range of formal d-electron counts of 7-9. In end-on diazoalkane complexes of formally monovalent three-coordinate transition metals, the electronic structures are best described as having the metal in the +2 oxidation state with an antiferromagnetically coupled radical anion diazoalkane as shown by crystallography, spectroscopy, and computations. A formally zerovalent cobalt complex has different structures depending on whether potassium binds; potassium binding gives transfer of two electrons into the eta(2)-diazoalkane, but the removal of the potassium with crown ether leads to a form with only one electron transferred into an eta(1)-diazoalkane. These results demonstrate the influence of potassium binding and metal oxidation state on the charge localization in the diazoalkane complexes. Interestingly, none of these reduced complexes yield carbene fragments, but the new cobalt(II) complex (LCoPF6)-Co-tBu(L-tBu = bulky beta-diketiminate) does catalyze the formation of an azine from its cognate diazoalkane, suggesting N-2 loss and transient carbene formation.