STABILIZATION OF 16-ELECTRON PARAMAGNETIC ORGANOIRON SPECIES VERSUS COORDINATION OF DINITROGEN - X-RAY CRYSTAL-STRUCTURES OF [FE(ETA(5)-C5H5)(N-2)(DIPPE)][BPH(4)], [FE(ETA(5)-C(5)ME(5))(DIPPE)][BPH(4)], AND [FE(ETA(5)-C5H5)CL(DIPPE)][BPH(4)] (DIPPE=1,2-BIS(DIISOPROPYLPHOSPHINO)ETHANE)

The purple compound [CpFeCl(dippe)] (Cp = C5H5; dippe = 1,2-bis(diisDpropylphosphino)ethane) reacts with dinitrogen and Na[BPh(4)] in EtOH or MeOH, to furnish the novel half-sandwich end-on dinitrogen complex [CpFe(N-2)(dippe)][BPh(4)] (1). This compound is diamagnetic and dissociates dinitrogen reversibly in thf or acetone solution, to yield the paramagnetic complex [CpFe(dippe)][BPh(4)] (2). 1 and 2 are in equilibrium in acetone solution under dinitrogen. Thermodynamic parameters for such equilibrium have been estimated. The related complex [Cp*FeCl(dippe)] (Cp* = C(5)Me(5)) dissolves in MeOH or EtOH to yield only [Cp*Fe(dippe)](+), and no dinitrogen uptake is observed. The X-ray crystal structure of [Cp*Fe(dippe)][BPh(4)] (3) has been determined. The complexes 1-3 react with a variety of neutral donors L (L = CNBu(t), CO, MeCN) furnishing the corresponding adducts [CpFe(L)(dippe)][BPh(4)] or [Cp*Fe(L)(dippe)][BPh(4)], as expected. The insertion of SnCl2 into the FeCl bond only occurs in [FeCpCl(dippe)], yielding [CpFe(SnCl3)(dippe)]. Both [CpFeCl(dippe)] and [Cp*FeCl(dippe)] are readily oxidized by atmospheric oxygen in alcoholic solution to the corresponding Fe-III derivatives, [CpFeCl(dippe)](+) and [Cp*FeCl(dippe)](+), respectively The X-ray crystal structure has been determined for [CpFeCl(dippe)][BPh(4)].