S = 3/2 Iron(I)-Bisphosphine-Ate Complexes: Synthesis, Characterization, and Reactivity for Electrophile Activation.

Iron bisphosphine complexes represent an important class of sustainable catalysts for a variety of important chemical transformations due to the high abundance, low toxicity, and redox-rich chemistry inherent to iron-based systems. In particular, transient, low-coordinate Fe(I) species are postulated to play a pivotal role in multiple catalytic transformations as the principal species for C─X bond activation (X = Cl, Br, I). However, insight into the electronic structure, bonding, and reactivity of Fe(I)-bisphosphine complexes remains poorly developed. In the present study, we report the development of four-coordinate (4C), high-spin (S = 3/2) Fe(I)-bisphosphine-ates. Several novel Fe(I) complexes were structurally characterized, and their electronic structure and bonding were evaluated using a combined spectroscopic, synthetic, and computational approach. Additionally, this study highlights the potential role of charged species in synthetically relevant contexts via in situ formation of (4C) Fe(I)-bisphosphine-ates in the presence of ubiquitous additives (e.g. MgBr2). Lastly, we demonstrate the utility of these Fe(I)-bisphosphine-ates toward rapid C─X homolytic cleavage of common alkyl- and aryl-halide electrophiles, as well as the ability to serve as synthons for further development of new high-spin Fe(I)-bisphosphine-ate complexes through transmetalation.