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A series of new tetradentate, nitrogen–sulfur donor proligands with amido or amino donor groups have been synthesized and their rhenium and technetium oxo-complexes prepared. The substitution pattern and length of the ligand backbone can be varied without affecting the co-ordination chemistry. The NS 3 H 3 amido-proligands reacted rapidly with the technetium(V) precursor [TcOCl 4 ] - at reflux in methanol to give the technetium(IV) species [TcO(NS 3 )] - in very high radiochemical purity (ca. 100%), but these complexes decompose over a period of hours or days. They also reacted with the rhenium(V) precursors [ReO 2 (py) 4 ]Cl (py = pyridine) or [ReOCl 3 (PPh 3 ) 2 ] at reflux in methanol, but only in the presence of a base. Stable neutral rhenium(V) complexes of the type [ReO(NS 3 )] were formed, and the crystal structures of two determined. A reduced amino version of the NS 3 H 3 proligand gave an analogous [ReO(NS 3 )] complex, and its crystal structure was determined.

Complexes of YIII, LaIII, GdIII and DyIII with an 18-membered hexaaza tetraimine macrocyclic ligand (L1) containing backbone cyclohexyl units have been prepared and characterized. The crystal structure of [GdL1(H2O)3]Cl3·3H2O shows a nine-co-ordinate gadolinium ion bound to three water oxygens and six nitrogen donors from the macrocyclic ligand. Solution studies with radiolabelled 90Y indicated that, in competition with the very strong chelator diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (H5dtpa), a 90YIIIL1 macrocyclic unit is maintained for 1 h. The relaxivity of the gadolinium(III) complex, [GdL1(H2O)3]3+, is higher than those of [Gd(dtpa)(H2O)]2– and [GdL(H2O)]–(H4L = 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid), both of which are currently used as contrast agents in magnetic resonance imaging. A tetramethyl analogue of L1, i.e. L2, has been synthesized for the first time and a crystal structure determination showed that it adopts a stepped conformation, the direction of folding being dictated by the racemic conformation of the cyclohexane.

The bis(diazenido)technetium(III) complex [TcCl(NNR)2(PPh3)2](R = C6H4Cl-4) reacted with bidentate ligands L with loss of one diazenide ligand to give [Tc(NNR)L2(PPh3)](L = S2CNR2) and [TcCl(NNR)L(PPh3)2](HL = maltol) in high yield. With dianionic tetradentate ligands L′ complexes of the type cis-[Tc(NNR)L′(PPh3)][L′= dianion of N,N′-bis(salicylidene)ethane-1,2-diamine (salen), S(CH2)2NMe(CH2)2NMe(CH2)2S or O2S(CH2)2NMe(CH2)2NMe(CH2)2SO2] were obtained. The crystal structure of the complex with L′= salen has been determined. It shows pseudo-octahedral co-ordination about the Tc with the NNR and PPh3 ligands cis. Direct reaction of [TcO4]– with arylhydrazine hydrochlorides generated a diazenide species in situ which reacts with S2CNR2 to give [TcCl(NNR)2(S2CNR2)2] and 2,2′-bipyridine (bipy) to give [TcCl(NNR)(bipy)2]+ isolated as a BPh4– salt.

Two new hexaaza macrocycles H4L1 and H4L2 substituted with 2-hydroxy-3,5-dimethylbenzyl groups on the secondary amine nitrogens have been synthesized; the crystal structure of H4L2 shows that the six nitrogen donor atoms adopt a chair conformation in the solid state, and the gadolinium(III) complex of monodeprotonated H4L1, [Gd(H3L1)(NO3)]NO3.3H2O, has a nine-co-ordinate gadolinium bound to one phenolic oxygen atom, two oxygen atoms from one nitrate and six nitrogen donors from the macrocyclic ligand.

The reaction of [TcNCl4]– with bidentate diphosphines P–P gives the cationic complexes [TcNCl(P–P)2]+[A]–[P–P = Ph2PCH2CH2PPh2 or Me2PCH2CH2PMe2(dmpe), A = BPh4 or PF6] in good yield. An analogous complex was prepared with Me2PCH2CH2NMe(CH2)3NMeCH2CH2PMe2 whereas the bulky Pri2PCH2CH2PPRi2(dippe) gave a binuclear complex [Tc2N2Cl4(dippe)2] which on the basis of 31P NMR spectroscopy has bridging chloride groups. An X-ray crystal structure of [TcNCl(dmpe)2][BPh4] revealed a distorted trans-octahedral geometry about technetium with an exceptionally long TcN bond distance of 1.853(6)A. Reaction of [TcNBr4]– with 2,2′-bipyridyl (bipy) in ethanol gives [TcNBr(bipy)2]2[TcBr4]. An X-ray crystal structure revealed a cis-octahedral structure for the nitrido-cation [TcN 1.621(20)A] with the novel tetrahedral tetrabromotechnetate(II) dianion.

Relative energies of platinum olefin and acetylene complexes, obtained from non-iterative semi-empirical one-electron molecular-orbital (NISEMO) calculations, are in qualitative agreement with available experimental results. Based on a synthesis of these calculations and the experimental results, mechanisms are proposed for (a) olefin–vinyl rearrangement, (b) HCl addition to π-bonded acetylene, and (c)π-bonded acetylene–acetylide-hydride rearrangement. This method provides a reasonable and economical approach to predicting the mechanisms and courses of reaction of fairly large molecules.