Chemical and electrochemical oxidation of mer/fac-Cr(CO)3(.eta.1-L-L)(.eta.2-L-L) containing a pendant donor atom: ESR studies of the cations mer-[Cr(CO)3(.eta.1-L-L)(.eta.2-L-L)]+ and trans-[Cr(CO)2(.eta.2-L-L)2]+ (L-L = bidentate group 15 ligand

Unravelling the Photochemical Transformations of Chromium(I) 1,3 Bis(diphenylphosphino), [Cr(CO)4(dppp)]+, by EPR Spectroscopy

“…The spin Hamiltonian parameters for this trans -[Cr­(CO) 2 (dppp) 2 ] + complex, obtained by simulation of the spectra, are in good agreement with the DFT derived values (Table ). The observed parameters are also analogous to those previously reported in the literature for structurally similar complexes, − but in those cases, the complexes were typically formed via chemical or electrochemical oxidation of the Cr(0) mer -[Cr­(CO) 3 (κ 1 -L 2 ) (κ 2 -L 2 )] 0 (L 2 = bidentate phosphine) structures yielding the paramagnetic Cr­(I) system which then slowly decays to the trans -[Cr­(CO) 2 (L 2 ) 2 ] + complex (Table ). In the current work, the EPR spectrum of trans -[Cr­(CO) 2 (dppp) 2 ] + (Figure b,c) remained unchanged following storage in the dark at 298 K for 48 h, indicating that this complex is kinetically inert.…”

“…This is the first observation of a photochemically formed mer -[Cr­(CO) 3 (κ 1 -dppp)­(κ 2 -dppp)] + complex, although previous work demonstrated that the 17-electron mer -[Cr­(CO) 3 (κ 1 -L 2 )­(κ 2 -L 2 )] + is the only carbonyl-containing species observed on the electrochemical time scale following electrochemical oxidation of mer -[Cr­(CO) 3 (κ 1 -L 2 )­(κ 2 -L 2 )]. − The monodentate (κ 1 -dppp) ligand may alter its coordination role more readily than the bidentate analogues, and therefore, the choice of backbone linker chain length is expected to be extremely important in determining the thermodynamic and kinetic stability of the 17-electron complexes. It is also known that the facial ( fac- ) complexes rapidly isomerize to meridional ( mer -) ones by a thermally activated process, so one would not expect to see the fac - complex by EPR.…”

On the Failure To Observe Isotropic Electron Paramagnetic Resonance Spectra for Certain Chromium(I) Carbonyl Complexes

“…Despite extensive efforts using in situ electron paramagnetic resonance (EPR) and voltammetric techniques or chemical oxidation at temperatures down to 200 K, isotropic EPR spectra are not observed for fac -[Cr(CO) 3 L 3 ] + 2,3 (L is a phosphine, phosphite, or phosphonite ligand), fac -[Cr(CO) 3 (η 2 -LL)(η 1 -LL)] + (LL = Ph 2 P(CH 2 ) n PPh 2 , n = 1, 2, or pompom = (MeO) 2 PCH 2 CH 2 P(OMe) 2 , , [Cr(CO) 3 (η 6 -arene)] + , cis -[Cr(CO) 2 L 4 ] + , cis- [Cr(CO) 2 (η 2 LL) 2 ] + , or Cr(CO) 3 (η 5 -C 5 Ph 5 )) mer -[Cr(CO) 3 L 3 ] + , , mer- [Cr(CO) 3 (η 2 -LL)(η 1 -LL), , trans -[Cr(CO) 2 L 4 ] + , , and trans -[Cr(CO) 2 (η 2 -LL) 2 ] + 4,5 and the reasonably well-resolved frozen solution spectra of fac -[Cr(CO) 3 (triphos)] + (triphos = (Ph 2 P) 3 CH, fac -[Cr(CO) 3 (η 2 -pompom)(η 1 -pompom)] + , and Cr(CO) 3 (η 5 -C 5 Ph 5 )) . We have sought an explanation for these apparent discrepancies for some years.…”

Elucidation of the Wide Range of Reaction Pathways That Accompany the Electrochemical Oxidation ofcis,mer-[Mn(CO)2(η1-dpm)(η2-dpm)X] (dpm = Ph2PCH2PPh2; X = Cl, Br)

“…(a) The resulting cation is highly stable. In this case a chemically reversible one-electron process is observed. − …”

“…Electrochemical oxidation of neutral 18-electron transition metal organometallic complexes containing combinations of carbon monoxide and phosphine ligands has received much attention. − Upon one-electron oxidation, a number of reaction routes for the initially formed isostructural 17-electron cation are possible on either the voltammetric (short) or bulk electrolysis (long) time scales:…”