Studies on copper complexes containing ambidentate ligands : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University

Abstract

Coordination compounds resulting from the interaction of sulphur­ and nitrogen-containing ligands with copper salts have been synthesised and characterised by spectroscopic, magnetic, and crystallographic techniques. These ligand systems are shown to undergo novel copper-promoted reactions in which new ligands are formed. The reaction products of a series of aliphatic thiol-containing carboxylic acids with copper(II) have been characterised. With mercaptoacetate, ligand desulphurisation occurs resulting in the formation of oxalate ions. In contrast, 2- and 3-mercaptopropionic acids are oxidised to their respective disulphides (DTDIP and DTDP) which coordinate to the copper. The resulting copper(II)-disulphide complexes, [Cu 1 1( bipy)( DTDIP)]·3H20 and [Cu 1 1( bipy)(DTDP)]·22H0, have been characterised by X-ray crystallography (bipy = 2,2'-bipyridyl). The latter complex contains no Cu-S bonding interaction. The former, in contrast to previously reported copper(II)-disulphide structures (which possess weak Cu-S coordination or none at all), displays moderately strong axial Cu-S bonding (Cu-S = 2.678(2) A).

Methimazole has been shown to undergo a copper-promoted reaction resulting in the new ligand 1,1'-dimethyl-2,2'-diimidazolylsulphide (dmimS) which coordinates to the copper(II) ion forming the complex [Cu 1 1(dmimS)2 (H2 0)2 ](Cl04)2·2H20. This complex has been characterised by X-ray crystallography.

Phenylthiourea has been shown to undergo a copper-promoted desulphurisation reaction resulting in the formation of phenylcyanamide anipns which coordinate to the copper(II) ion. The copper coordination chemistry of the phenylcyanamide ligand has been examined, complexes with empirical formulations of [Cu( bipy)( L)2 ] , [Cu(phen)(L)2 ] , [Cu(pip) 2(L)2 ] , and [Cu( py)2(L)2 ] having been

prepared and characterised piperidine, py = pyridine).

(phen 1,10-phenanthroline, pip = The crystal structure determinations of

the complexes [{Cu 1 1( phen)( m-Cl-PC)A(c)}2]·2H20, [{ Cu1(dp pe)1 _ 5 ( p-Cl-PC)2}]·2(CH3 ) 2CO, and are reported (where PC (Ph-N-C=N)-, PPh3 = triphenylphosphine, dppe = 1,2-bis(diphenylphosphino)ethane, and Ac= acetate). These complexes represent the first examples of copper complexes incorporating phenylcyanamido ligands that have been characterised using X-ray crystallography. These structures show that the phenylcyanamide moiety may coordinate to a metal in a number of different ways. In the 2,2'-bipyridyl complex, the phenylcyanamide anions exhibit two coordination modes: a monodentate ligand which coordinates to the copper through the cyano nitrogen, and a bridging ligand which coordinates to the copper atoms of the dimer via the cyano and amido nitrogens. The 1,10-phenanthroline complex is also dimeric and contains m-Cl-phenylcyanamide anions which bridge the two copper atoms of the dimer via the cyano nitrogen. The copper(I)-phosphine complexes are also dimeric. In the dppe complex, the p-Cl-PC ligand is monodentate to the copper and coordinates through the cyano nitrogen, whereas in the PPh3 complex, the p-Me-PC ligand bridges the two copper atoms of the dimer via the cyano and amido nitrogen atoms.