Combined x-ray crystallographic, single-crystal EPR, and theoretical study of metal-centered radicals of the type [.eta.5C5R5Cr(CO)2L] (R = H, Me; L = CO, tertiary phosphine)

EPR Spectra of [Cr(CO)2L(η-C6Me6)]+ (L = PEt3, PPh3, P(OEt)3, P(OPh)3): Analysis of Line Widths and Determination of Ground State Configuration from Interpretation of 31P Couplings

“…An EPR study of [Cr(CO) 3 (η-C 5 Ph 5 )] in frozen toluene suggested the possibility of two conformations in temperature-dependent equilibrium . The single-crystal X-ray structure of this complex showed two somewhat differently distorted molecules per unit cell; the OC−Cr−CO bond angles of the two molecules match approximately the predictions of Fortier et al for the ground state conformations corresponding to 2 A‘ and 2 A‘‘ . Thus, small environmental effects can lead to either ground state for the tricarbonyl complexes.…”

“…The ground state electronic configuration of Cr(I) “piano-stool” complexes such as [Cr(CO) 2 L(η-C 5 R 5 )], L = CO, phosphine, or phosphite, has been the subject of considerable experimental and theoretical interest. The parent tricarbonyl complexes are orbitally degenerate in idealized C 3 v geometry and thus undergo a Jahn−Teller distortion to C s symmetry and either a 2 A‘ or 2 A‘‘ ground state . EPR spectroscopic studies of [Cr(CO) 3 (η-C 5 H 5 )] and [Cr(CO) 3 (η-C 5 Me 5 )], doped into single crystals of the Mn(I) analogs, indicated 2 A‘ and 2 A‘‘ ground states, respectively.…”

“…The parent tricarbonyl complexes are orbitally degenerate in idealized C 3 v geometry and thus undergo a Jahn−Teller distortion to C s symmetry and either a 2 A‘ or 2 A‘‘ ground state . EPR spectroscopic studies of [Cr(CO) 3 (η-C 5 H 5 )] and [Cr(CO) 3 (η-C 5 Me 5 )], doped into single crystals of the Mn(I) analogs, indicated 2 A‘ and 2 A‘‘ ground states, respectively. An LCAO-HFS-MO study 1 of [Cr(CO) 3 (η-C 5 H 5 )] showed that the two ground states differ primarily in the OC−Cr−CO bond angles: the optimum conformation for 2 A‘ has angles of 85, 100, and 100° whereas 2 A‘‘ has angles of 92, 84, and 84°.…”

Synthesis of Fulvalene-Bridged Bimetallic Compounds Containing a Substituted Cyclopentadienyl Group Based on Pauson−Khand Chemistry

“…For 17 , there are two molecules in the asymmetric unit, with the dihedral angles between the two Cp rings being 28.1(1)° and 31.4(2)°. The Mn atom in 13 and 17 has the usual piano-stool coordination characteristic of the cyclopentadienyl complexes . The Mn atom in 13 is located 1.776(2) Å below the plane of the cyclopentadienyl ring; in 17 the distances are 1.777(1) and 1.772(1) Å.…”

Organometallic Radicals: Thermodynamics, Kinetics, and Reaction Mechanisms

“…Some introduction to the literature is provided here for the interested reader who wishes to look up the data on representative structures. The structures of Cr(CO) 2 (PPh 3 )(Cp) 24 and (h 5 -C 5 Ph 5 )Cr(CO) 3 25 have been determined. The structures of the 18 e À complex Mn(CO)(dppe)(h 5 -C 6 H 6 Ph) and the 17 e À cation radical Mn(CO) (dppe)(h 5 -C 6 H 6 Ph) þ were determined and found to be quite similar.…”