SYNTHESIS, CHARACTERIZATION, AND CRYSTAL-STRUCTURE OF THE (ETA-5-C5PH5)CR(CO)3 RADICAL

The reaction between Cr(CO)6 and Na(C5Ph5) in refluxing diglyme yields [Na(diglyme)3/2][(C5Ph5)Cr(CO)3], 1. Metathesis Of 1 With [Ph3P=N=PPh3]Cl in CH2Cl2 yields [Ph3P=N=PPh3] [(C5Ph5)Cr(CO)3], 2. Oxidation of 1 by AgBF4 in cold THF under an argon atmosphere produces (C5Ph5)Cr(CO)3,3. Complexes 2 and 3 form a redox pair connected by a quasireversible one-electron process, E-degrees = -0.69 V vs ferrocene in CH2Cl2, E-degrees = -0.50 V in CH3CN, k(s) = 0.12 cm/s. ESR spectra of 3 in toluene at 90 K gave a rhombic g-tensor with components 2.1366, 2.0224, and 1.9953, consistent with the expected low-spin d5 electronic configuration. The largest g-tensor component was significantly temperature dependent, suggesting an equilibrium between conformations with A-2' and A-2'' ground states. Crystals of 2 belong to the space group P1BAR with Z = 2. The unit-cell parameters are a - 12.190 (3) angstrom, b = 13.019 (3) angstrom, c = 19.842 (4) angstrom, alpha = 96.598 (17)-degrees, beta = 103.719 (17)-degrees, gamma = 94.322 (18)-degrees, and V = 3021.5 (11) angstrom3 with final values of R(F) = 6.72% and R(wF) = 7.57 %. Crystals of 3.C6H6 belong to the space group P2(1)/c with Z = 8. The unit-cell parameters are a = 33.307 (9) angstrom, b = 8.978 (3) angstrom, c = 22.702 (6) angstrom, beta = 91.73 (2)-degrees, and V = 6798 (3) angstroms with final values of R(F) = 7.69% and R(wF) = 7.68%.