Redmond, Simon Paul; (1998) Linking metal centres with π-conjugated diimido bridges. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes the preparation and study of metal systems, bound by imido ligands, with extended π-conjugated substituents. The preparation, characterisation and study of a series of ditungsten complexes of the type [{WCl2(CO)(PMePh2)2}2(NXN)] linked by a variety of diimido organic bridges, (NXN), is discussed with particular reference to the degree of communication indicated between the metal centres. These complexes were prepared by oxidative-addition of diisocyanates to [WCl2(PMePh2)4] and three such compounds were characterised crystallographically (X: 2-methylphenylene, 2,2'-dimethoxybiphenylene and 1,5-naphthalene). Electrochemical studies and molecular orbital calculations were performed with a view to clarifying the extent of the communication. A series of molybdenum monoimido complexes, viz. [Mo(NXNH2)Cl2(S2CNEt2)2], is presented and our failure to prepare diimido complexes from diamines discussed. In the course of this work a number of acetylenic amines and isocyanates were prepared, via metal-catalysed coupling reactions, as precursors to π-conjugated diimido organic bridges. Attempts to prepare bis(diimido) molybdenum complexes by two methods, from sodium molybdate and by imido substitution reactions, gave rise to insoluble materials. The compounds [Mo(S2PPh2)2(NtBu)2] and [Mo(S2PPh2)2(2,6- NiPr2C6H3)2] where the bis(imido) metal centre is chelated by dithiophosphinate ligands were successfully synthesised. Three rhenium diimido complexes [{ReCl3(PPh3)2}2(NXN)] (X: phenylene, 2,3-dimethylphenylene and 2,3,5,6-tetramethylphenylene) were synthesised but their poor solubility hampered characterisation. The preparation of tungsten, molybdenum and rhenium iodophenylimido compounds and the molecular structure of the tungsten complex are reported. Experiments aimed at achieving coupling of these iodo-complexes are described.

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