A Caged Neutral 17-Valence-Electron Iron(I) Radical [Fe(CO)(Cl)(P((CH))P)]: Synthetic, Structural, Spectroscopic, Redox, and Computational Studies.

UV irradiation of yellow CHCl solutions of -Fe(CO)(P((CH))P) () and PMe (10 equiv) gives, in addition to the previously reported dibridgehead diphosphine P((CH))P (46%), a green paramagnetic complex that crystallography shows to be the trigonal-bipyramidal iron(I) radical -[Fe(CO)(Cl)(P((CH))P)] (; 31% after workup). This is a rare example of an isolable species of the formula [Fe(CO)(L)(X)] ( = 0-3, L = two-electron-donor ligand; X = one-electron-donor ligand). Analogous precursors with longer P(CH)P segments ( = 12, 14, 16, 18) give only the demetalated diphosphines, and a rationale is proposed. The magnetic susceptibility of , assayed by Evans' method and SQUID measurements, indicates a spin () of /. Cyclic voltammetry shows that undergoes a partially reversible one-electron oxidation, but no facile reduction. The UV-visible, EPR, and Fe Mössbauer spectra are analyzed in detail. Complex is similarly studied, and, despite the extra valence electron, exhibits a comparable oxidation potential (Δ ≤ 0.04 V). The crystal structure shows a cage conformation, solvation level, disorder motif, and unit cell parameters essentially identical to those of . DFT calculations provide much insight regarding the structural, redox, and spectroscopic properties.