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)] (<b>1</b>), [(η⁵-C₅Me₅)RhCl(L¹)] (<b>2</b>), [(η⁶-<i>p</i>-Pr<i>i</i>C₆H₄Me)RuCl(L¹)] (<b>3</b>) and [(η⁶-C₆Me₆)RuCl(L¹)] (<b>4</b>) have been synthesised from pyrazine-2-carboxylic acid (HL¹) and the corresponding complexes [{(η⁵-C₅Me₅)IrCl₂}₂], [{(η⁵-C₅Me₅)RhCl₂}₂], [{(η⁶-<i>p</i>-Pr<i>ⁱ</i>C₆H₄Me)RuCl₂}₂], and [{(η⁶-C₆Me₆)RuCl₂}₂], respectively. The related dinuclear complexes [{(η⁵-C₅Me₅)IrCl}₂ (μ-L²)] (<b>5</b>), [{(η⁵-C₅Me₅)RhCl}₂ (μ-L²)] (<b>6</b>), [{(η⁶-<i>p</i>-Pr<i>ⁱ</i>C₆H₄Me)RuCl}₂ (μ-L²)] (<b>7</b>) and [{(η⁶-C₆Me₆)RuCl}₂ (μ-L²)] (<b>8</b>) 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)] (<b>9</b>), [{(η⁵-C₅Me₅)RhCl}₂ (μ-L³)] (<b>10</b>), [{(<i>p</i>-Pr<i>ⁱ</i>C₆H₄Me)RuCl}₂ (μ-L³)] (<b>11</b>) and [{(η⁶-C₆Me₆)RuCl}₂ (μ-L³)] (<b>12</b>), have been prepared by using pyrazine-2,3-dicarboxylic acid (H₂L₃) instead of H₂L₂. The molecular structures of <b>2</b> and <b>3</b>, determined by X-ray diffraction analysis, show the pyrazine-2-carboxylato moiety to act as an <i>N,O</i>-chelating ligand, while the structure analyses of <b>5–7</b>, confirm that the pyrazine-2,5-dicarboxylato unit bridges two metal centres. The electrochemical behaviour of selected representatives has been studied by voltammetric techniques.