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Title: The reduction and isomerization of carboranes and metallacarboranes
Author: Zlatogorsky, Sergey
ISNI:       0000 0001 3578 0180
Awarding Body: Heriot-Watt University
Current Institution: Heriot-Watt University
Date of Award: 2007
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Abstract:
Chapter 1 gives a brief introduction into carborane and metallacarborane chemistry and provides a short review ofliterature relevant to the topic ofthe thesis. Chapter 2 describes the syntheses of metallacarboranes starting from 1,12-diphenyl1,12- carborane. This includes reduction and metallation at both room temperature and low temperature (_42°C and -78°C). As a result of these reactions 4,1,6, 4,1,8, 4,1,10, 4,1,11 and 4,1,12 isomers of l,x-Ph2-4-(p-cymene)-4,I,x-c!oso-RuC2BlOHlO were obtained, the 4,1,11 isomer being the first example of 13-vertex 4,1,11-MC2BlO and 4,1,8 being the first example of 4,1,8-RuC2BlO. This synthetic work together with some related computational studies reveals the mechanism of reduction of 1,12-carborane (involving the initial formation of 1,7 and 4,7 isomers of [x,y-Ph2-x,y-nido-C2BlOHlOt and 3,7, 7,9 and 7,10 isomers by the subsequent rearrangement of 1,7 and 4,7) and defines the role of phenyl substituents on the carborane cage (lowering the temperature of isomerisation of reduced species). Experimental facts were in accord with the calculated energies of the five nido dianionic isomers which increase in the order 7,9<7,10<4,7<3,7<1,7. Chapter 3 describes similar work (reduction and metallation at room temperature and at -78°C) starting from 1,2-diphenyl-l,2-carborane and 1,7-diphenyl-l,7-carborane. In the former case experimental and computational results mainly coincide, although some more work is required to explain the results of the room temperature reaction. The interpretation of results obtained experimentally and those from computational studies for 1,7-carborane is not so straightforward and more work is required in this area. Chapter 4 focusses on the properties of the 13-vertex monometallacarboranes synthesized. Study ofthe rearrangements of 13-vertex ruthenacarboraries 4,I,x-RuC2BlO establish the 4,1,6 ~ 4,1,8 ~ 4,1,12 isomerization, previously reported for cobaltacarboranes only. The 4,1,1O~4,1,12 pathway, known from literature for nonphenylated compounds, was also established, as well as the 4,1, 11 ~ 4,1,8 isomerization. Putting together these experimental results and the calculated stabilities of 4,I,x-RuC2BlO isomers allowed a mapping of these isomerisation pathways. Under this scheme each individual isomerization step is explained as a move to the next lower energy isomer accessible by a single TFR. Reduction-metallation and reduction-oxidation reactions of diphenylated 4,1,8- and 4,1,12-RuC1BlO are also described. Comparison of these reactions with those starting from non-phenylated analogues allowed the proposition that the presence of phenyl groups leads to the rearrangement (at or below room temperature) of the reduced form of 4,1,8 to species analogous to those formed at the reduction of 4,1,12 isomer. Thus it was shown that the reduction and metallation of both phenylated 4,1,8 and 4,1,12 isomers led to the same 14-vertex species (1,14,2,10 isomer). In the case of the 4,1,8 compound partial cage degradation (removal of B5) occurred leading to the rare 12-vertex 8,1,2-RuC1B9 isomer on oxidation and 13-vertex 4,5,1,6-RulC1B9 on metallation. Chapter 5 (the synthetic work for this Chapter was carried out by MChem student Ross McLellan under the supervision of the author) attempts to quantify the effect of Ph group addition by the reduction and metallation of 1-phenyl-l, 12-carborane. It is shown that in these reactions one Ph group has the same net effect as two Ph groups since the reduction and metallation of I-Ph-1,12-closo-C2BlOHll at room temperature produces the 4,1,6 isomer of the metallacarborane. It is also shown that reactions starting either from 1-phenyl-I,12-carborane or 1-phenyl-1,2-carborane lead to the 4,1,6 isomer having the Ph substituent located exclusively on the four-connected C1 rather than fiveconnected C6. Chapter 6 gives experimental details of all the reactions performed and also provides spectroscopic and analytical data for all compounds synthesized. In the 'Suggestions for Future Work' section the possible reactions which elaborate or develop the ideas ofthis thesis are summarized. Appendix 1 provides some details of the crystal structure determination of compounds synthesized. Appendix 2 (provided on compact disk) gives the appropriate files in RTF and CIF (or MOL2) format.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.490955  DOI: Not available
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