Iron PCP Pincer Complexes in Three Oxidation States: Reversible Ligand Protonation To Afford an Fe(0) Complex with an Agostic C-H Arene Bond.

In the current investigation, the reaction of Fe(CO) with the ligand precursor 2-chloro-N,N-bis(diisopropylphosphanyl)-N,N-diethylbenzene-1,3-diamine (P(C-Cl)P- iPr) (1) was investigated. When a suspension of Fe(CO) and 1 in CHCN was transferred in a sealed microwave glass vial and stirred for 18 h at 110 °C the complex [Fe(PCP- iPr)(CO)Cl] (2) was obtained. In an attempt to prepare the hydride Fe(II) complex [Fe(PCP- iPr)(CO)H] (3), 2 was reacted with 1 equiv of Li[HBEt] in THF. Instead of ligand substitution, this complex underwent a one electron reduction which led to the formation of the low-spin d Fe(I) complex [Fe(PCP- iPr)(CO)] (4). Exposure of a benzene solution of 4 to NO gas (1 bar) at room temperature affords the diamagnetic complex [Fe(PCP- iPr)(CO)(NO)] (5). This is the first iron PCP nitrosyl complex. Protonation of 5 with HBF·EtO affords the cationic Fe(0) complex [Fe(κ P,CH,P-P(CH)P- iPr)(CO)(NO)]BF (6) which features an η-C-H agostic bond. Even with relatively weak bases such as NEt the agostic C-H bond can be deprotonated with reformation of the starting material 5. Therefore, protonation of 5 is completely reversible.