A Pyrrole-Based Pincer Ligand Permits Access to Three Oxidation States of Iron in Organometallic Complexes

Treatment of FeCl2(thf)1.5 with the sodium salt of bis(dicyclohexylphosphinomethyl)pyrrole (NaCyPNP) in the presence of pyridine (py) affords the high-spin, five-coordinate iron(II) complex [FeCl(py)(CyPNP)]. The chloride complex serves as a starting point for a variety of organometallic iron(II) compounds including S = 1 square planar alkyls, [FeR(CyPNP)] (R = Me, Et, Bn, Ph). Treatment of [FeCl(py)(CyPNP)] with NaBEt3H does not generate an analogous square-planar hydride complex, but rather a bimetallic high-spin iron(II) species containing bridging hydride ligands. Analogous transmetalation reactions in the presence of carbon monoxide produced six-coordinate low-spin species [FeR(CO)2(CyPNP)] (R = Et, Ph, and H). Reduction of [FeCl(py)(CyPNP)] under CO afforded the low-spin iron(I) carbonyl complex [Fe(CO)2(CyPNP)]. This species could be further reduced with KC8 to afford the anionic iron(0) complex K[Fe(CO)2(CyPNP)]·thf. The breadth of coordination numbers, spin states, and valencies supported by this...