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A cw EPR and ENDOR investigation on a series of Cr(I) carbonyl complexes with relevance to alkene oligomerization catalysis: [Cr(CO)(4)L](+) (L = Ph2PN(R)PPh2, Ph2P(R)PPh2)

McDyre, Lucia, Hamilton, Tracy, Murphy, Damien Martin, Cavell, Kingsley John, Gabrielli, William F., Hanton, Martin J. and Smith, David M. 2010. A cw EPR and ENDOR investigation on a series of Cr(I) carbonyl complexes with relevance to alkene oligomerization catalysis: [Cr(CO)(4)L](+) (L = Ph2PN(R)PPh2, Ph2P(R)PPh2). Dalton Transactions 39 (33) , pp. 7792-7799. 10.1039/C0DT00127A

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Abstract

The preparation and characterisation of the Cr(I) complexes [Cr(CO)4L]+ (L = Ph2PN(R)PPh2, Ph2P(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⊥ (gxx = 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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Subjects: Q Science > QD Chemistry
Publisher: RSC
ISSN: 1477-9226
Funders: EPSRC
Last Modified: 04 Feb 2018 01:19
URI: http://orca.cf.ac.uk/id/eprint/12852

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