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Title: Crowded complexes of diphenylcarborane
Author: Cowie, Jill
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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This work concerns the synthesis of a number of new metal derivatives of diphenylcarborane 1,2-Ph2-1,2-closo-C2B10H10, in which intramolecular crowding was expected to produce either unusual cage geometry or unexpected metal co-ordination. The (η5-C5Me5)Ir and several (η6-arene)Ru complexes of diphenylcarborane, and a less congested methylphenylcarborane derivative, were prepared and structurally characterised. These compounds are found to exhibit deviations from the usual closo geometry and in the former cases have been termed pseudocloso. Detailed analysis suggests that this distortion is accompanied by a significant loss of electron density at the boron cluster vertices. The relevance of these compounds to the 'isocloso/hypercloso' debate is considered. During attempts to synthesise a truly hypercloso carbaruthenacarborane two new compounds were prepared. In one of these the carborane dianion was found to have undergone protonation, with the metal fragment, {(PPh3)2RuCl}, attached in an exo-nido fashion via three Ru-H-B bridges. This complex apparently exists as two species in solution and attempts are made to rationalise this behaviour in the light of detailed n.m.r. studies. The identical reaction in a non-protonic solvent gave a dicationic Ru dimer with two nido-carborane cages acting only as counterions. The failure to synthesise the intended hypercloso species is discussed. Three (η6-arene)Ru-carborane complexes of increasing steric congestion were exposed to elevated temperatures. All were unchanged at 65oC with the most crowded (pseudocloso) cluster rearranging [3,1,2-RuC2B9 → 3,1,11-RuC2B9] at 110oC. This isomerisation is examined with respect to the metal fragment geometry. Attempts were made to incorporate a single {CuPR3} fragment into the Ph2C2B9 polyhedron. Although this was unsuccessful, products containing two {CuPR3} units are achieved in high yield. In these complexes one metal atom is found to be bonded in an exo-nido fashion, while the other ligates the open five-membered face. In contrast with analogous complexes of less sterically demanding cages the metals are non-bonding and are found to be dramatically slipped from their preferred positions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available