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Title: Synthesis and study of carbametallaboranes which exhibit facile polytopal rearrangements
Author: Kyd, Gwenda O.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1993
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Chapter 1 begins with a brief description of the terminology commonly associated with polyboron chemistry and some relevant synthetic routes. This is followed by a discussion of observed structural distortions in carbaborane and carbametallaborane complexes. To illustrate this the structures of mono- and diphenyl-substituted closo- carbaborane are described. This is followed by a survey of a selection of the known metalla-complexes containing phenyl-substituted carbaborane ligands. The chapter ends with a brief description of a few {ML2}-carbametallaboranes. Chapter 2 describes the synthesis and structural characterisation of the complex, 1-Ph-3,3-(PMe2Ph)2-3,1,2-PtC2B9H10, 1. Crucially, the plane through the metal fragment is rotated away from its predicted (on the basis of an E.H.M.O. calculation) orientation with respect to the ligated carbaborane ligand. 1 is thus considered to be ground-state destabilised, by virtue of phenyl substitution, and this may influence the observed facile isomerisation. At +55°C (328K) 1 undergoes a polytopal rearrangement to yield two 3,1,11-isomers 2 and 3. In the former the (C-Ph) unit occupies position 11 while in 3 the (C-H) is situated at this location. The structures of these complexes have been determined by another group. This type of isomerisation is well known and several reported examples are discussed as well as the principal suggested mechanisms. The diphenyl substituted carbaborane complex, 4, is then described. A crystal structure determination reveals this to be the 3,1,11-isomer 1,11-Ph2-3,3-(PMe2Ph)2-3,1,11-PtC2B9H9. In this case the 3,1,2-isomer is not isolated, and isomerisation occurs at, or below room temperature. Increased steric demands of the carbaborane ligand are thought to facilitate this process. In Chapter 3 the spectroscopic characterisation of the two series of complexes, analogous to 1 and 4, containing other phosphine/phosphite ligands, is described. This shows that the behaviour of these species is largely independent of the electronic and steric properties of the phosphorus ligands. All the analogues of 1 undergo polytopal isomerisation at elevated temperature. Complexes with smaller phosphine ligands tend to form two 3,1,11-isomers, whereas complexes with larger phosphorus ligands tend to form a single isomer. Each analogue of 4 forms with a 3,1,11-framework, and even for the complexes with the smallest metal fragment no 3,1,2-species is isolated. Finally, a preliminary study of the electrochemistry of each series of complexes is described.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available