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Title: Guanidines and their anions : versatile ligands for metallo-organic chemistry
Author: Pace, Stuart
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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There are a large number of highly stable systems which are isostructural and isoelectronic to carboxylates. One of these, amidinates, the 1,3-nitrogen analogues of carboxylates, show a rich and varied coordination to both main group and transition metals. However, the triaza analogues, substituted guanidinates, had received little or no attention as ligands prior to this work, in which the ligand chemistry of neutral, mono- and dianionic guanidines has been explored. The synthesis and characterisation of tri-substituted guanidines containing a variety of alkyl (iPr, lBu, Cyx) and aryl (Ph, p-tol) substituents is described herein. Preparation of the homochiral substituted N,N',N"-tris((s)-(-)-amethylbenzyl)guanidine and the X-ray crystal structure of its HPF6 salt are also presented. In the solid state the central CN3 unit exhibits local C3 symmetry and has steric elements on one of the plane resulting in two stereochemically different faces. The formation of tetra-substituted N,N-diethyl-N',N"-diphenylguanidine is also detailed. Formation of complexes containing neutral guanidine ligands was achieved in the reactions of N,N',N"-triphenylguanidine with CoCl2 and Ag(SO3CF3). The complexes formed, [Co{PhN=C(NHPh)2]2Cl2] and [Ag{PhN=C(NHPh)2}2][SO3CF3] respectively, were characterised by X-ray crystallography and found to contain monodentate guanidine ligands bound through their imine nitrogen alone. The cobalt complex adopts pseudo-tetrahedral geometry while [Ag{PhN=C(NHPh)2}2] is perfectly linear at silver with the triflate acting only as a counterion. Cleavage reactions of the ruthenium chloro-bridged dimers [(p-cymene)RuCl2]2 and [Cp*RuCl2]2 with various tri-substituted guanidines were undertaken. Two product obtained from these reactions, namely [(p-cymene)Ru{h2-(iPrN)2CNHiPr}Cl] and [Cp*Ru{(h6-p-tol)N=C(NHp-tol)2}]+, were characterised by X-ray crystallography. The first of these contains a ruthenium centre with a h6-arene, terminal chloride and monodeprotonated chelating guanidinate ligand. Meanwhile the second is a sandwich compound in which the guanidine is bound through an arene substituent and not one of its nitrogens.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available