In situ studies on homogeneous nickel alkene oligomerisation catalysts
In situ studies on homogeneous nickel alkene oligomerisation catalysts
In situ studies have been performed on a series of homogeneous nickel alkene oligomerisation catalysts using the techniques of Extended X-ray Fine Structure (EXAFS) and NMR, with the characterisation of catalytic species being supported by the study of standard compounds.
For the ethene oligomerisation catalyst formed by addition of Ph2PCH2C(CF3)2OH to Ni(cod)2 in toluene, both 1H and 31P NMR show the nickel hydride observed before the addition of alkene to be [(Ph2PCH2C(CF3)2O)NiH(Ph2PCH2C(CF3)2OH)]. On addition of ethene similar phosophorus coordination is seen by 31P NMR, but the hydride is lost, indicating formation of [(Ph2PCH2C(CF3)2)O)NiR(Ph2PCH2C(CF3)2OH)] (R= alkyl). The presence of such alkyl species was confirmed by Ni K-edge EXAFS, with an observed increase in the coordination number of light backscatterers (carbon/oxygen) at ca. 2.0AA, on addition of alkene to the catalyst solution.
The in situ 31P NMR of the propene dimerisation catalyst formed when (allyl)NiBrPPh3 is activated by AlEt3, in toluene, shows the phosphine remains coordinated to the nickel centre but in the form of at least five different nickel species. For the EXAFS of this system during catalysis, with a 1:5 excess of AlEt3 and propene present, the Ni and Br K-edge results both show loss of bromine from the nickel coordination sphere, with the Br K-edge indicating the halide has transferred to the aluminium centre. The number of carbon backscatterers observed by the Ni K-edge EXAFS increases on activation, inferring that alkylation of the metal centre has occurred. Furthermore the formation of bridged Ni-C-Al species is suggested by a Ni-Al distance of ca. 3.2AA. The Ni and Br K-edge EXAFS of the (allyl)NiBrPPh3/AlEt3 catalyst in the absence of propene gave conflicting results, indicating the activation process is a finely balanced equilibrium.
University of Southampton
1993
Andrews, Paul
(1993)
In situ studies on homogeneous nickel alkene oligomerisation catalysts.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
In situ studies have been performed on a series of homogeneous nickel alkene oligomerisation catalysts using the techniques of Extended X-ray Fine Structure (EXAFS) and NMR, with the characterisation of catalytic species being supported by the study of standard compounds.
For the ethene oligomerisation catalyst formed by addition of Ph2PCH2C(CF3)2OH to Ni(cod)2 in toluene, both 1H and 31P NMR show the nickel hydride observed before the addition of alkene to be [(Ph2PCH2C(CF3)2O)NiH(Ph2PCH2C(CF3)2OH)]. On addition of ethene similar phosophorus coordination is seen by 31P NMR, but the hydride is lost, indicating formation of [(Ph2PCH2C(CF3)2)O)NiR(Ph2PCH2C(CF3)2OH)] (R= alkyl). The presence of such alkyl species was confirmed by Ni K-edge EXAFS, with an observed increase in the coordination number of light backscatterers (carbon/oxygen) at ca. 2.0AA, on addition of alkene to the catalyst solution.
The in situ 31P NMR of the propene dimerisation catalyst formed when (allyl)NiBrPPh3 is activated by AlEt3, in toluene, shows the phosphine remains coordinated to the nickel centre but in the form of at least five different nickel species. For the EXAFS of this system during catalysis, with a 1:5 excess of AlEt3 and propene present, the Ni and Br K-edge results both show loss of bromine from the nickel coordination sphere, with the Br K-edge indicating the halide has transferred to the aluminium centre. The number of carbon backscatterers observed by the Ni K-edge EXAFS increases on activation, inferring that alkylation of the metal centre has occurred. Furthermore the formation of bridged Ni-C-Al species is suggested by a Ni-Al distance of ca. 3.2AA. The Ni and Br K-edge EXAFS of the (allyl)NiBrPPh3/AlEt3 catalyst in the absence of propene gave conflicting results, indicating the activation process is a finely balanced equilibrium.
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Published date: 1993
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Local EPrints ID: 462494
URI: http://eprints.soton.ac.uk/id/eprint/462494
PURE UUID: d1231677-90ae-46c4-87a4-891985c45816
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Date deposited: 04 Jul 2022 19:09
Last modified: 04 Jul 2022 19:09
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Author:
Paul Andrews
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