EPR-SPECTRA OF [CR(CO)(2)L(ETA-C6ME6)](- ANALYSIS OF LINE WIDTHS AND DETERMINATION OF GROUND-STATE CONFIGURATION FROM INTERPRETATION OF P-31 COUPLINGS() (L = PET3, PPH3, P(OET)(3), P(OPH)(3)) )

The preparation and characterization of [Cr(CO)(2)L(eta-C6Me6)] (L = P Et3, PPh3, P(OEt)(3) and P(OPh)(3), are reported. One-electron oxidati on affords unstable Cr(I) cations, [Cr(CO)(2)L(eta-C6Me6)](+), EPR spe ctra of which are reported. Detailed analysis of the anisotropic P-31 hyperfine interaction indicates that, in frozen CH2Cl2/THF, the phosph ine and phosphite complexes have (2)A' and (2)A '' ground states, resp ectively. The hyperfine anisotropy can be accounted for by dipolar int eraction of the P-31 nucleus with spin density on Cr and, in the case of the phosphite complexes, with similar to 0.01 P 3p(y) spin density resulting from pi-backbonding. Line width anomalies observed in EPR sp ectra of these and other Cr(I) and Mn(II) ''piano stool'' complexes ca n be understood in terms of molecular distortions resulting from solva tion in frozen solutions.