[(η5-C5Me5)Fe(Ph2PCH2CH2CH2PPh2)][SO3CF3], a Stable 16-Electron Complex with a Coordinating Counteranion and without Agostic Interaction: The Dramatic Role of a Trivial Methylene Group

The iron chloro complex Cp*(dppp)FeCl (Cp* = pentamethylcyclopentadienyl, dppp = 1,3-bis(diphenylphosphino)propane; 2) was prepared from FeCl2(dppp) and Cp*Li in 85% yield. The air-stable compound 2 was characterized by IR-FT, 1H, 31P, and 13C NMR, cyclic voltammetry (CV), and X-ray crystal analysis. The experimental data indicate that this complex possesses the same electronic properties as its homologue Cp*(dppe)FeCl (dppe = 1,2-bis(diphenylphosphino)ethane; 2‘), but shorter distances between the chlorine atom and the hydrogen atoms of the dppp ligand give rise to through-space interactions. The hydride 3 was obtained by treatment of the chloro derivative 2 with LiAlH4 (95%). The changes in the Fe−H bond stretching and redox potential induced by replacement of dppe by dppp is in agreement with the existence of two conformers for the iron hydrides 3 and 3‘. The 16-electron species [Cp*(dppp)Fe][OSO2CF3] (4[OTf]) is obtained by treatment of 3 with methyl triflate in diethyl ether (82%). The pseudo-C2v con...