Syntheses and structures of mononuclear {Re(CO)3Cl(NN)} ‘complex ligands’ with a pendant imino–pyridine binding site, and preparation of some heterodinuclear Re(I)–lanthanide(III) complexes

A series of potentially dinucleating ligands, each with two bidentate imino–pyridine compartments, has been used to prepare the mononuclear complexes [Re(CO)3Cl(Ln)] (n=1–4) which each have a vacant binding site and so constitute ‘complex ligands’ for the stepwise synthesis of heterodinuclear complexes. Three of the complexes (with L1, L2 and L4) have been structurally characterised. The mononuclear complex [Re(CO)3Cl(L5)], arising from decomposition of [Re(CO)3Cl(L3)] by hydrolysis of the non-coordinated imine unit, was also isolated and structurally characterised. Luminescence studies show that these compounds are only very weak emitters. The ‘complex ligand’ [Re(CO)3Cl(L1)] has been reacted with [Ln(hfac)3]·2H2O (Ln=Yb, Er) to prepare the heterodinuclear complexes [Re(CO)3Cl(μ-L1)Ln(hfac)3] in which the {Ln(hfac)}3 unit is attached to the second bidentate imino–pyridine site of [Re(CO)3Cl(L1)]. The crystal structures of these show that the bridging ligand has to twist to accommodate the two bulky metal fragments, and that the lanthanide units have an 8-coordinate square-antiprismatic geometry.