- Rapid synthesis of Group VI carbonyl complexes by coupling borohydride catalysis and microwave heating
-
Several Group VI tetracarbonyl phosphine and tertiary amine complexes [M(CO)4 L2, M = Cr, Mo, W, L2 = 2PPh 3, dppm, dppe, dppp, dppb, bpy, phen, dppf] were synthesized in minutes in the microwave at moderate temperature, atmospheric pressure, and utilizing NaBH4 as a catalyst. The reactions were optimized by careful solvent selection. The octahedral complexes were isolated in percent yields ranging from 17 to 95. The lower temperatures, shorter reaction times, benign solvents, and lower pressures as compared to the traditional thermal syntheses provide a rapid, eco-friendly synthetic route to these common Group VI complexes.
- Birdwhistell, Kurt R.,Schulz, Brian E.,Dizon, Paula M.
-
-
- A cw EPR and ENDOR investigation on a series of Cr(i) carbonyl complexes with relevance to alkene oligomerization catalysis: [Cr(CO)4L] + (L = Ph2PN(R)PPh2, Ph2P(R)PPh 2)
-
The preparation and characterisation of the Cr(i) complexes [Cr(CO) 4L]+ (L = Ph2PN(R)PPh2, Ph 2P(R)PPh2), which are used as pre-catalysts for the selective oligomerization of ethylene, are reported. The electronic properties and structural features of these complexes in frozen solution have been established via continuous wave X-band Electron Paramagnetic Resonance (cw-EPR) and continuous wave 1H, 14N and 31P Electron Nuclear Double Resonance (cw-ENDOR) spectroscopy. The EPR spectra are dominated by the g anisotropy, with notably large PA couplings from the two equivalent 31P nuclei. The spin Hamiltonian parameters (g (g xx = gyy) > ge > g∥ (gzz)) are consistent with a low-spin d5 system possessing C2v symmetry, with a SOMO where the metal contribution is primarily dxy for all complexes. The isotropic Fermi contact term ( Paiso, determined by EPR and ENDOR) was found to be largest for complexes containing ligands e, d, f and g, indicating that the 31P 3 s character in the SOMO is higher for the PNP type ligands than the PCP type. Subtle structural differences in the complexes were also identified through variations in the Δg shifts (identified by EPR), and through differences in the phenyl ring conformations (identified by 1H ENDOR). Attempts to correlate trends in EPR-derived parameters with data measured for catalysis using these pre-catalysts are also made, but no clear connections were found. The Royal Society of Chemistry 2010.
- McDyre, Lucia E.,Hamilton, Tracy,Murphy, Damien M.,Cavell, Kingsley J.,Gabrielli, William F.,Hanton, Martin J.,Smith, David M.
-
p. 7792 - 7799
(2010/10/04)
-
- Ligand substitution kinetics in M(CO)4(η2:2-norbornadiene) complexes (M=Cr, Mo, W): Displacement of norbornadiene by bis(diphenylphosphino)alkanes
-
The thermal substitution kinetics of norbornadiene (NBD) by bis(diphenylphosphino)alkanes (PP), (C6H5)2P(CH2)nP(C 6H5)2 (n=1, 2, 3) in M(CO)4(η2:2-NBD) complexes (M=Cr, Mo, W), were studied by quantitative FT-IR spectroscopy. The reaction rate exhibits first-order dependence on the concentration of the starting complex, and the observed rate constant depends on the concentration of the leaving NBD ligand and on the concentration and the nature of the entering PP ligand. In the proposed mechanism there are two competing initial steps: an associative reaction involving the attachment of the entering PP ligand to the transition metal center and a dissociative reaction involving the stepwise detachment of the diolefin ligand from the transition metal center. A rate law is derived from the proposed mechanism. The activation parameters are obtained from the evaluation of the kinetic data. It is found that at higher concentrations of the entering ligand, the associative path is dominant, while at lower concentrations the contribution of the dissociative path becomes significant. Both the observed rate constant and the activation parameters show noticeable variation with the chain length of the diphosphine ligand.
- Tekkaya, Aysin,Oezkar, Saim
-
p. 208 - 216
(2007/10/03)
-
- Substitution and addition reactions of the (CO)3(η7-tropylium)M cations (M = Cr, Mo, W) with tertiary diphosphines
-
The reactions of the title compounds I-III, [(η7-C7H7)M(CO)3]BF4 (M = Cr, Mo, and W, respectively), with the diphosphines PPh2(CH2)nPPh2 (n = 1-4) at low temperatures (-40 to -60°C) form two new series of complexes which are quite different from previous carbonyl substitution products. The first series (IV-VI) formed by the diphosphines (n = 1-3) comprise 7-exo ring adducts involving the bonding of only one phosphorus atom of the diphosphine to ring carbon atom 7 of I. The second series (VII and VIII) are diphosphine ring linked dimers, e.g. [(7,7′-exo-dppb){η6-C7H7)Cr(CO) 3}2] [BF4]2, for which X-ray crystallography confirms a diphosphine linked ring-ring structure with the Cr(CO)3 moieties situated on opposite sides of the ring systems. The ring C-phosphorus bond length of 1.852 A? indicates a relatively weak bond, consistent with facile cleavage of these adducts on reaction with nucleophiles such as hydride.
- Brown, David A.,Burns, John,Glass, William K.,Cunningham, Desmond,Higgins, Tim,McArdle, Patrick,Salama, Mabrouk M.
-
p. 2662 - 2667
(2008/10/08)
-
- Substituted metal carbonyls IV. Studies of the synthesis and decomposition of singly-bridging 1,3-bis(diphenylphosphino)propanedimetal decacarbonyls of chromium, molybdenum and tungsten
-
Singly-bridging diphosphine complexes M2(CO)10(μ-dppp) (M=Cr, W; dppp=Ph2P(CH2)3PPh2 have been isolated in a facile synthesis via an oxidative decarbonylation of M(CO)6 using trimethylamine-N-oxide as the initiator.The thermal decomposition of these complexes, together with the molybdenum analogue, have been studied in refluxing acetonitrile, benzene or toluene under N2 or CO.The characterisations and thermal stabilities of these species are described and discussed.Conversion of the 1,3-bis(diphenylphosphino)propanedimetal decacarbonyl complexes of chromium, molybdenum and tungsten into the chelate M(CO)4(η2-dppp) is promoted by free dppp but inhibited by CO gas.
- Hor, Andy T. S.
-
-