On the Electronic Nature of Open-Shell Germylene Complexes of M^I Cations (M = Fe, Co, Ni)

While the coordination chemistry of heavier tetrylene ligands is generally well established, their effect on the electronic nature of open-shell metal centers is underexplored. This work takes steps to define these effects in an analogous series of cationic germylene-M^I complexes (M═Fe, Co, Ni). First, the electronic ground-states of toluene-coordinated M^I synthons, [IPr·M(η⁶-tol)]⁺ (IPr = [{(H)CN(Dip)}₂C:]; Dip = 2,6-C₆H₃) are elucidated using CAS-SCF calculations, defining a rare non-Aufbau for the Fe(I) derivative. Following this, a combination of experimental and computational investigations on novel paramagnetic germylene complexes 2 (Fe), 3 (Co), and 4 (Ni) uncover a doubly quasi-degenerate iron(I) complex, with additional low-energy excited states for Fe (∼0.1 eV) and Co (∼0.2 eV), despite the highly unsymmetrical ligand sphere. In all cases significant spin-polarization on the ligand's Ge center is found, which lends these systems higher than expected magnetic moments, correlating with known spin-orbit effects for the heavier p-block elements. This study thus gives new insights into the nature of electronic communication between heavier tetrylenes and open-shell 3d-metal centers.