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Title: An investigation into the reactivity and electrochemical properties of "higher" nuclearity clusters with nitrogen heterocyclic ligands : a chemical, electrochemical, and spectroscopic study
Author: Freeman, Gideon
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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In Chapter One the concept of the surface cluster analogy is discussed and examples are given of its application in resolving the nature of chemisorbed molecules and molecular fragments on metal surfaces. This is then followed by a review of previous studies into the reactivity of metal carbonyl clusters with nitrogen heterocyclic ligands. This highlights the substitution of carbonyl ligands for nitrogen heterocycles and the process of orthometallation, and emphasises how earlier work has typically concentrated on the trinuclear clusters, with examples involving higher nuclearities being rare. Consequently the need to study such cluster's reactivity further is made apparent. The second chapter details the synthesis of a series of disubstituted tetranuclear clusters of the general formula M4(μ-H)4(CO)10(L-L) {M= Ru, Os; L-L= bidentate heterocyclic ligand or (pyridine)2} which have been prepared from the reaction between the parent cluster M4(μ-H)4(CO)12 and principally 2.2 equivalents of the decarbonylating reagent Me3NO. Our studies have shown that disubstitution of the cluster is favoured whether 1.1, 2.2, or 4.2 equivalents of Me3NO are used, and thus implies the inherent stability of the M4(μ-H)4(CO)10(L-L) species. In particular, it is found that in its reaction with pyridine and 1.1 equivalents of Me3NO the M4(μ-H)4(CO)10(py)2 cluster is formed as the major product, being present in a significantly higher yield than the expected monosubstituted derivative. This reactivity is accounted for mechanistically by comparison with similarly observed substitution patterns for the Ir4(CO)12 cluster. Full X-ray and spectroscopic analyses are discussed in detail. In Chapter Three the previous work of Dutton 1 into thermal activation of the Ru5 cluster, primarily with pyridine, is discussed and contrasted to the chemical activation process using Me3NO utilised in this study. The Ru5C(CO)15 cluster has been found to react in the presence of 2.2 equivalents of Me3NO with both 2,2'-bipyridyl and 1,10-phenanthroline to yield the Ru5C(CO)14(L-L) cluster as the major product. Hence loss of only a single carbonyl ligand occurs to yield a 76 electron bridged butterfly cluster which has been characterised both spectroscopically and by single crystal X-ray diffraction. When a second carbonyl ligand is removed from the cluster the orthometallated species Ru5(μ-H)C(CO)13(L-L) is produced, but in relatively lower yield. Again this species has been characterised by spectroscopy, and in addition for the 2,2'-bipyridyl derivative, by X-ray crystallography. In addition, it has been discovered that the Ru6C(CO)17 cluster undergoes cluster degradation in the presence of 2,2'-bipyridyl or 1,10-phenathroline and 2.2 equivalents of Me3NO with the loss of an Ru(CO)3 fragment in the formation of the Ru5(C(CO)14(L-L) cluster, which had been previously prepared directly from the Ru5C(CO)15 cluster. Also produced in comparable yield was the expected Ru6 species Ru6C(CO)15(L-L) which is relatively unstable and decomposes over time.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available