Amino-, amido- and oxy-bipyridyl complexes of copper, ruthenium, molybdenum and rhodium.

Abstract

The work described in this thesis concerns the synthesis and study of the coordination behaviour of the 6-anilino-2,2'-bipyridyl (Habipy), 6-N-methylanilino-2,2'-bipyridyl (mabipy), 6-piperidyl2,2'.- bipyridyl (pipbipy) and 2,2'-bipyridin-6-one (Hobipy) ligands. Chapter one reviews the coordination chemistry of the 2-aminopyridyl (Rap), 2-hydroxypyridyl (Hhp) and the 2-(2-pyridyl)-I,8-naphthyridine (pynp) ligands. These ligands are closely related to Habipy, mabipy, pipbipy and Hobipy in that they share a common NCN or NCO fragment. Thus the review of their coordination behaviour provides insight into the expected coordination of the Habipy, mabipy, pipbipy and Hobipy ligands. The synthesis and characteristaion of the novel Habipy, mabipy and pipbipy ligands are reported in Chapter two. X-ray crystal structure determinations of mabipy and pipbipy reveal that the geometry about the exocyclic nitrogen atom in both ligands is nearly planer, suggesting substantial overlap of the nitrogen lone pair orbital with the 1t electron system of the bipyridyl rings. In both mabipy and pipbipy the N3-C 10 bond lengths are shorter then normal N-C single bonds. In Chapter three -the synthesis and characterisation of copper(I) complexes containing mabipy, pipbipy and Habipy, and a copper(II) complex containing mabipy are reported. The copper(I) complexes have the general formula [Cu(l12-L)2r, where L= mabipy 1, pipbipy 2 or Habipy 3. The structures of complexes 1 and 2 are determined by X-ray crystallography. In complexes 1- 3 the bipyridyl fragments of mabipy, pipbipy and Habipy chelate while the exocyclic nitrogen atoms remain free. The crystal structures of 1 and 2 reveal that the exocyclic nitrogens have a planar geometry as was the case in the uncoordinated ligand. The crystal structure of [Cu(1l2-mabipY)2f+ (4) is determined by X-ray crystallography and is very similar to that of the copper(I) species. Coordination of the mabipy ligand in 4 is the same as that in 1 and the exocyclic nitrogen in 4 is also planar. The redox couple 4/1 is shown to be electrochemically reversible with EV2= 0.45 V. In Chapter four the synthesis and chararcterisation of dinuclear complexes containing the Ru2 2+, Ru/+, Mo24+and ~4+ cores are reported in which the abipy ligand bridges two metal centres.

The complexes [Rulll-L)lCO)4], where L= abipy 5 or obipy 6, were synthesised by the r~action of the free ligands with [{RuiCO)102CCH3)2}n] in toluene. The structures of5 and 6 are determined by X-ray crystallography and show the ligands bridging the Ru(I) atoms in a head to tail fashion and occupy mutually cis positions about the octahedral Ru(I) atoms. The Ru-Ru separations in 5 and 6 are 2.668(1) and 2.671(1) A respectively. The reaction of Habipy with [Rui02CCH3)4CI]n was found to afford the mixed valence species [Ruill-abipy)(02CCH3)3CI] (7), the structure of which is determined by X-ray diffraction methods. The structure of7 reveals one abipy ligand bridging the two ruthenium atoms as in 5. The Ru-Ru separation in 7 is 2.294(2) A. The reaction of [Moi02CCH3)4] with habipy in methanol affords (Moill-abipy)(02CCH3)3] (8). The structure of 8 is determined by X-ray diffraction methods and reveals one abipy ligand bridging two quadruply bonded molybdenum atoms which have a Mo-Mo separation of 2.094(2) A. The [Rhlll~abipy)(02CCH3)iH20)] (9) is formed from the reaction of [Rh i02CCH3)4] with Habipy in methanol. The structure of [Rh2(Il-abipy)(02CCH3)iNCPh)] is determined by X-ray diffraction methods and shows the abipy ligand bridging two Rh(II) atoms which are separated by 2.399(1) A. This chapter is concluded with a discussion of the possiblity of substitution of more than one acetate ligand by the abipy ligand in terms of 'hard' and' soft' acid-base theory and synthetic methods.