Use this URL to cite or link to this record in EThOS:
Title: In situ studies on homogeneous nickel alkene oligomerisation catalysts
Author: Andrews, Paul
ISNI:       0000 0001 3424 2655
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1993
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: X-ray fine structure