SYNTHESIS, CHARACTERIZATION, AND MOLECULAR-STRUCTURE OF BIS(TETRAPHENYLCYCLOPENTADIENYL)RHODIUM(II)

A 5 day diglyme reflux of Rh(acac)(3) and K(C(5)HPh(4)), followed by treatment with aqueous HPF6, produces orange-yellow [(C(5)HPh(4))(2)Rh]PF6 in 40-50% yield. Reduction of[(C(5)HPh(4))(2)- Rh]PF6 with sodium amalgam in THF yields olive green (C(5)HPh(4))(2)Rh in 70% yield. (C(5-)HPh(4))(2)Rh crystallizes in the triclinic space group P ($) over bar 1 with unit-cell parameters of a = 8.622(3) Angstrom, b = 10.778(4) Angstrom, c = 12.894(5) Angstrom, alpha = 65.58(3)degrees, beta = 72.66(3)degrees, gamma = 83.52(3)degrees, and Z = 1. The least-squares data refined to R(F) = 7.63% and R(wF) = 10.12% for the 2479 independent observed reflections with F-0 > 5 sigma(F-0). The metal-centroid distance is 1.904 Angstrom and all other bond lengths and angles are similar to known octaphenylmetallocenes. ESR spectra of(C-5- HPh(4))(2)Rh in low-temperature glasses display a rhombic g tenser with resolution of Rh hyperfine splitting on one g component. Analysis of the spectral parameters is consistent with a d(7) configuration derived from a nearly degenerate d(x2), d(y2) ground state. Voltammetry and coulometry establish the electron-transfer series (C(5)HPh(4))(2)Rh-1+/0/1- with E(0) values of -1.44 V and -2.13 V vs ferrocene. The heterogeneous charge transfer rate of the second reduction is about 3 orders of magnitude lower than that of the first.