Synthesis, characterization, and crystal structure of the chromium complex (.eta.5-C5Ph5)Cr(CO)3 radical

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 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°. 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‘‘ .…”

“…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.…”

TEMPO-Mediated Catalysis of the Sterically Hindered Hydrogen Atom Transfer Reaction between (C5Ph5)Cr(CO)3H and a Trityl Radical

“…Both the metalloradical (C 5 Ph 5 )Cr(CO) 3 • and Ar 3 C• are monomeric in solution, 5,6 and we do not observe any coupling between them. Ingold and co-workers have reported that there is no measurable trapping of trityl radical by TEMPO, consistent with earlier reports, 7 any coupling of these radicals.…”

Cyclopentadienyl Complexes of Chromium, Molybdenum and Tungsten

“…148 ' 149 The radical species can be stabilized by employing bulky Cp ligands or by phosphine substitution (which occurs by an associative mechanism); thus [Cr 2 (CO) 6 Cp* 2 ], which in the solid state has a Cr-Cr bond even longer than its Cp analogue, is approximately 90% dissociated in solution, 6 * 2 9 ' 1 5 0 and {Cr(CO) 3 (r|-C 5 Ph 5 )} exists solely as the monomer even in the solid state. 151 Similarly {Cr(CO) 2 (PPh 3 )Cp}, which was previously assumed to be dimeric, has been shown to be a stable radical; the crystal structures o f this compound and of {Cr(CO) 2 (PMe 3 )Cp*} consist of three-legged piano stools with closed-in OC-Cr-CO angles of 80.9°a nd 79.9° respectively, showing that the singly occupied orbital lies in this region, consistent with theoretical predictions. 144 ' 152 The single crystal ESR spectra of {Cr(CO) 2 LCp} (L = CO, PPh 3 ) and {Cr(CO) 3 Cp*} doped into their isostructural diamagnetic manganese analogues also show 2 A" ground states consistent with the unpaired electron residing in an orbital of largely d xy character.…”