102132-80-9Relevant academic research and scientific papers
EPR study of photochemical reactions of fac- and mer-[Cr(CO)3(η1-L2)(η2-L 2)]+ (L2 = bidentate phosphine, arsine, or phosphonite ligand)
Rieger, Anne L.,Rieger, Philip H.
, p. 5868 - 5873 (2008/10/08)
Rearrangement of fac-[Cr(CO)3(η2-L2)(η1-L 2)]+ to mer-(CO)3(η2-L2)(η1-L2 )]+ (L2 is a bidentate phosphine or arsine ligand) is a rapid thermally activated process. Loss of CO from mer-[Cr(CO)3(η2-L2)(η1-L 2)]- to form trans-[Cr(CO)2(η2-L2)2]- is shown to be a clean photochemical process, perhaps the first example of a quantitative photochemical transformation for a Cr(I) complex. The bidentate phosphonite ligand, L2 = (MeO)2PCH2CH2P(OMe)2, behaves quite differently: fac-[Cr(CO)3(η2-L2)(η1-L 2)]- undergoes photochemical loss of CO to form a five-coordinate complex which converts slowly via thermal activation to trans[Cr(CO)2(η2-L2)2]+ .
Chemical and electrochemical oxidation of mer/fac-Cr(CO)3(η1-L-L)(η2-L-L) containing a pendant donor atom: ESR studies of the cations mer-[Cr(CO)3(η1-L-L)(η2-L-L)] + and trans-[Cr(CO)2(η2-L-L)2]+ (L-L = bidentate group 15 ligand)
Bagchi, Ramen N.,Bond, Alan M.,Colton, Ray,Creece, Ian,McGregor, Katherine,Whyte, Tania
, p. 2611 - 2615 (2008/10/08)
Reactions between Cr(CO)3(C7H8) and Ph2PCH2CH2AsPh2 (ape) and Ph2AsCH2CH2AsPh2 (dae) give mer-Cr(CO)3(η1-ape)(η2-ape) and fac-Cr(CO)3(η1-dae)(η2-dae), respectively. Phosphorus-31 NMR studies show that the monodentate ape ligand is coordinated through phosphorus. Upon electrochemical oxidation in dichloromethane (0.1 M Bu4NClO4) at platinum electrodes, mer-Cr(CO)3(η1-ape)(η2-ape) is reversibly oxidized to mer-[Cr(CO)3(η1-ape)(η2-ape)] + whilst fac-Cr(CO)3(η1-dae)(η2-dae) gives fac-[Cr(CO)3(η1-dae)(η2-dae)] +, which rapidly isomerizes to mer-[Cr(CO)3(η1-dae)(η2-dae)] +. In addition, for each complex a further irreversible 1-electron process is observed at very positive potentials. ESR studies on several mer-[Cr(CO)3(η1-L-L)(η2-L-L)] + cations (L-L = bidentate group 15 ligand), electrochemically generated in a sealed tube within the ESR microwave cavity, show that they decompose very slowly to trans-[Cr-(CO)2(η2-L-L)2]+. The rate of decomposition to trans-[Cr(CO)2(η2-L-L)2]+ is faster in a nonsealed tube with nitrogen purging. The ESR spectra of the tricarbonyl and dicarbonyl 17-electron cations show both phosphorus and arsenic hyperfine structure with very similar values for the coupling constants. Chemical oxidation of mer/fac-Cr(CO)3(η1-L-L)(η2-L-L) with an equimolar (or greater) quantity of AgClO4 also gives mer-[Cr(CO)3(η1-L-L)(η2-L-L)] +. In one case, (L-L = Ph2PCH2PPh2(dpm)), when 0.5 molar equiv of AgClO4 is used, a diamagnetic intermediate silver complex is identified by phosphorus-31 NMR spectroscopy. In the presence of excess of AgClO4, the rate of decomposition of mer-[Cr(CO)3(η1-L-L)(η2-L-L)] + to trans-[Cr(CO)2(η2-L-L)2]+ is greatly enhanced, further confirming that the silver ion is a noninnocent oxidant when a pendant donor atom is present.
Influence of isomeric form, chelated ring size, and the metal on the oxidation of facial and meridional chromium, molybdenum, and tungsten tricarbonyl bis(bis(diphenylphosphino)methane) and bis(1,2-bis(diphenylphosphino)ethane) complexes
Bond, Alan M.,Colton, Ray,McGregor, Katherine
, p. 2378 - 2384 (2008/10/08)
A series of complexes of the kind M(CO)3(η1-P-P)(η2-P-P) (M = Cr, Mo, W; P-P = Ph2PCH2PPh2 (dpm), Ph2PCH2CH2PPh2 (dpe)) have been synthesized and characterized by electrochemical, infrared, and 31P NMR studies. The electrochemical oxidation of fac- and mer-M(CO)3(η1-P-P)(η2-P-P) and the subsequent reduction of the oxidized products at platinum electrodes in acetone and dichloromethane provide substantial thermodyriamic, kinetic, and synthetic information on the influence of isomeric form, chelate ring size, and the metal in the formal oxidation states M(0), M(I), and M(II). One-electron oxidation of mer-Cr(CO)3(η1-dpm)(η2-dpm) produces the stable mer-[Cr(CO)3(η1-dpm)(η2-dpm)] + cation, which on further oxidation produces a highly reactive chromium(II) complex, which is believed to be [Cr(CO)3(η2-dpm)2]2+. One-electron oxidation of fac-Cr(CO)3(η1-dpe)(η2-dpe) produces the species fac-[Cr(CO)3(η1-dpe)(η2-dpe)] +, which rapidly isomerizes to mer-[Cr(CO)3(η1-dpe)(η2-dpe)] +. Further oxidation of the mer+ compound leads to complete decomposition. A catalytic process involving a redcx cross-reaction or direct electrochemical reduction of mer-[Cr(CO)3(η1-dpe)(η2-dpe)] + enables the previously unknown mer-Cr(CO)3(η1-dpe)(η2-dpe) to be isolated. Oxidation of fac- and mer-M(CO)3(η1-P-P)(η2-P-P) (M = Mo, W) occurs via either wo one-electron steps or via a single two-electron step to produce the seven-coordinate [M(CO)3(η2-P-P)2]2+ cation. The isomeric form of the starting material is important in both thermodynamic and kinetic aspects of the oxidation processes. The stability of the seven-coordinate, 18-electron M(II) complex is far greater than of the chromium analogues. For the dpe complexes the intermediates mer-[M(CO)3(η1-dpe)(η2-dpe)] + are relatively stable, unlike the case with dpm where rapid disproportionation of the M(I) complex occurs, thus demonstrating the importance of the chelate ring size. Reduction of both the M(I) and M(II) complexes leads exclusively to mer-M(CO)3(η1-P-P)(η2-P-P).
