The synthesis, spectroscopic and structural characterization of the monomeric, four-membered group 13 metal(I) heterocycles ([:M{eta2-N,N'-(Ar)NC(NCy2)N(Ar)}], M = Ga or In, Ar = C6H3Pri2-2,6) and an isomeric thallium complex are reported. Theoretical studies on these complexes, which are analogues of four-membered N-heterocyclic carbenes, suggest they should act as good sigma-donor ligands.

Reaction of lanthanum with Hg(C6F5)2 and bulky N,N'-bis(2,6-diisopropylphenyl)formamidine (HDippForm) in tetrahydrofuran gives [LaF{DippForm}2(THF)] with a rare terminal Ln-F bond, and a high yield of a novel functionalized formamidine, DippForm((CH2)4OC6F4H-o).

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Cation-exchange chromatographic techniques have been developed to separate stereoisomers of polymetallic complexes, using SP Sephadex C-25 as support. Through the example of the ligand-bridged dinuclear cation [{Ru(dmbpy) 2 } 2 (µ-bipym)] 4ϩ (dmbpy = 4,4Ј-dimethyl-2,2Ј-bipyridine, bipym = 2,2Ј-bipyrimidine), the isolation and characterisation of the meso and rac diastereoisomers by elution with aqueous sodium toluene-4-sulfonate solution are demonstrated. The effects of variation in salt concentration and temperature on the efficacy of the separation are discussed. The enantiomeric pair of the rac diastereoisomer (∆∆ and ΛΛ) was subsequently chromatographically resolved on SP Sephadex C-25, relying upon the inherent chirality of the support. Optical resolutions using eluents with chiral anions [aqueous sodium (ϩ)-O,OЈ-dibenzoyl--tartrate and sodium (Ϫ)-O,OЈ-dibenzoyl--tartrate] were investigated, with the (Ϫ)-enantiomer demonstrating a positive [the (ϩ)-enantiomer a negative] synergistic effect in combination with the Sephadex support. Crystals of the meso form were isolated, allowing an X-ray structural determination.The study of polymetallic 'supramolecular' assemblies is a rapidly expanding field of chemistry, largely because of their potential application in materials for such diverse purposes as photochemical molecular devices, 1-4 and as photoprobes of structure and function of polynucleotides such as DNA. 5-9 In particular, much attention has been focused upon the polypyridyl complexes of ruthenium and osmium as the basis for such assemblies as a result of their favourable photochemical and redox characteristics. 1 When bidentate ligands are involved in such centres, stereoisomerism is inherent in the resultant assemblies, but surprisingly this problem has until recently received only tacit attention.In general, studies of chirality in octahedral tris(bidentate ligand)ruthenium() centres have been limited to mononuclear species, and isolation of enantiomers has relied on the sometimes inefficient technique of diastereoisomer formation using chiral auxiliary anions. 10-13 Such complexes can then be used as chiral building blocks for larger assemblies, 12 but this approach requires tedious synthetic procedures where care must be taken to preserve the chiral integrity at each metal centre during every reaction step. Additionally, in the vast majority of the targets studied, crystallisation has proved the most favourable method of diastereoisomeric discrimination. Our aim was to develop general chromatographic techniques for the separation of stereoisomers not only of mononuclear complexes, but also of oligomeric transition-metal assemblies containing polypyridyl ligands. In the latter case the simplest example is that of a dinuclear complex of the type [{Ru(pp) 2 } 2 (µ-L b )] nϩ [pp is a symmetrical bidentate ligand, L b is a bis(bidentate) bridging ligand]. There are the possibilities of the meso (Λ∆) and the rac diastereoisomers, the rac form consisting of an enantiomeric pair (ΛΛ and ∆∆), as illustrat...