Mono and dinuclear iridium, rhodium and ruthenium complexes containing chelating carboxylato pyrazine ligands: Synthesis, molecular structure and electrochemistry

The mononuclear complexes [(η5-C5Me5)IrCl(L1)] (1), [(η5-C5Me5)RhCl(L1)] (2), [(η6-p-PriC6H4Me)RuCl(L1)] (3) and [(η6-C6Me6)RuCl(L1)] (4) have been synthesised from pyrazine-2-carboxylic acid (HL1) and the corresponding complexes [{(η5-C5Me5)IrCl2}2], [{(η5-C5Me5)RhCl2}2], [{(η6-p-PriC6H4Me)RuCl2}2], and [{(η6-C6Me6)RuCl2}2], respectively. The related dinuclear complexes [{(η5-C5Me5)IrCl}2(μ-L2)] (5), [{(η5-C5Me5)RhCl}2(μ-L2)] (6), [{(η6-p-PriC6H4Me)RuCl}2(μ-L2)] (7) and [{(η6-C6Me6)RuCl}2(μ-L2)] (8) have been obtained in a similar manner from pyrazine-2,5-dicarboxylic acid (H2L2). Compounds isomeric to the latter series, [{(η5-C5Me5)IrCl}2(μ-L3)] (9), [{(η5-C5Me5)RhCl}2(μ-L3)] (10), [{(p-PriC6H4Me)RuCl}2(μ-L3)] (11) and [{(η6-C6Me6)RuCl}2(μ-L3)] (12), have been prepared by using pyrazine-2,3-dicarboxylic acid (H2L3) instead of H2L2. The molecular structures of 2 and 3, determined by X-ray diffraction analysis, show the pyrazine-2-carboxylato moiety to act as an N,O-chelating ligand, while the structure analyses of 5–7, confirm that the pyrazine-2,5-dicarboxylato unit bridges two metal centres. The electrochemical behaviour of selected representatives has been studied by voltammetric techniques.