U385587.pdf (112.89 MB)
Crystal structures relating to the interactions of small molecules with transition metals.
thesisposted on 2015-11-19, 08:44 authored by John Allan. Evans
The results of crystal structure investigations on several rhodium and platinum organometallic complexes are given. Some amplification of the X-ray methods used, and of some general features of the complexes studied, is initially made. A review of previous structural data on olefin complexes is included. The structures illustrate either the co-ordination of some small unsaturated molecule in the complex, or the reaction of such a molecule at a transition metal. The former complexes generally involve co-ordinated tetrafluoro-ethylene and the results are discussed in terms of the Chatt-Dewar bonding scheme. The latter group are examples of the use of X-ray methods to determine the nature of a reaction product. Comparison of the molecular geometries (in particular the Rh-C distances) of the complexes Rh(acac)(C2F4)(C2H4) and Rh(acac)(C2H4)2 indicates that C2F4 is more closely bound to rhodium than ethylene, a consequence of increased ?-bonding. The complexes Pt(bipy)(C2F4) and Pt(PMe2Ph)2(C2F4) have greatly different J(Pt-F). A difference in the structures is also apparent, the degree of bending of the four fluorine atoms away from the C=C bond is greater in the bipy complex. This is understood to indicate greater ?-bonding and sp3 character of the olefin carbon atoms in the bipy complex. The structure determination of [Rh(MeCN) (C2F4)(acac)]2 serves to confirm the formulation given this compound in the literature and also to provide additional data on the non-planarity of co-ordinated tetrafluoroethylene. Rh(C9H7F6O2)(C6(CF3)6) is formed by the reaction of four moles of C4F6 with one of Rh(cod)(acac). The structure shows that while 3 molecules of C4F6 per rhodium cyclize to a C6(CF3)6 ring, the remaining molecule adds 1-4 to the rhodium-acac ring. A study of the product [RhC12(C8H15O2)(4-Mepy)2] shows that RhCl3.3H2O reacts with 2-methyl allyl alcohol to form a Rh-saturated furan ring system. The geometry clearly indicates the trans effect of a o-carbon atom. The structure of [Pt(S2CF)(PPh3)2][HF2] shows that carbon disulphide inserts into a Pt-F bond on reaction with [PtF(PPh3)3][HF2]. The molecular geometry shows some asymmetry which is discussed.
Date of award1972-01-01
Awarding institutionUniversity of Leicester