Synthesis of 2-picolyl functionalized η5-cyclopentadienyl derivatives of rhodium(I) and iridium(I) and preliminary study of their reaction with ruthenium(II) for assembling hetero-bimetallic complexes

The 2-picolylcyclopentadienyl derivatives of rhodium(I) and iridium(I) of formula [M{η5-C5H4(2-CH2C5H4N)}(η4-C8H12)] (3) (M = Rh) and (4) (M = Ir) are obtained in good yields by reacting 2-picolylcyclopentadienyllithium (7) with [RhCl(η4-C8H12)]2 and [IrCl(η4-C8H12)]2, respectively. The corresponding dicarbonyl derivatives, [M{η5-C5H4(2-CH2C5H4N)}(CO)2] (5) (M = Rh) and 6 (M = Ir), are obtained in good yields by reacting 2-picolylcyclopentadienylthallium(I) (8) with [RhCl(CO)2]2 and [IrCl(C5H5N)(CO)2], respectively. 5 has already been reported in the literature. The new complexes were characterized by elemental analysis, mass spectrometry, 1H NMR, FT-IR, and UV–Vis (210–330 nm) spectroscopy. The UV–Vis spectra indicate the existence of some electronic interaction between the 2-picolinic chromophore and the cyclopentadienyl-metal moiety. The study of the electrochemical behaviour of 3–6 by cyclic voltammetry (CV) allows the interpretation of the electrode processes and gives information about the location of the redox sites. Moreover, various synthetic strategies were tested in order to try to coordinate the complexes 3–6 to a ruthenium(II) centre, but most of them failed. Instead, the hetero-bimetallic complex bis(2,2′-bipyridine)[(η5-2-picolylcyclopentadienyl)(η4-cycloocta-1,5-diene)rhodium(I)]chlororuthenium(II)-(hexafluorophosphate) (13), was obtained, although in poor yields (10%), by reacting the nitrosyl complex [RuCl(bipy)2(NO)][PF6]214 (bipy = 2,2′-bipyridine) first with potassium azide and then with the rhodium(I) complex 3. The analogous complex bis(2,2′-bipyridine)(2-picoline)chlororuthenium(II)-(hexafluorophosphate) (15), that carries a ruthenium-bonded 2-picoline molecule instead of 3, has prepared in the same way. 13 and 15 were characterized by elemental analysis, mass spectrometry, and 1H NMR.