Bis(acetylacetonato)ruthenium(II) complexes containing bulky tertiary phosphines. Formation and redox behaviour of Ru(acac)2 (PR 3) (R = iPr, Cy) complexes with ethene, carbon monoxide, and bridging dinitrogen

Martin A. Bennett*, Matthew J. Byrnes, Guandolina Chung, Alison J. Edwards, Anthony C. Willis

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    25 Citations (Scopus)

    Abstract

    Reaction of cis-[Ru(acac)22-C8H 14)2] (1) (acac = acetylacetonato) with two equivalents of PiPr3 in THF at -25°C gives trans-[Ru(acac) 2(PiPr3)2], trans-3, which rapidly isomerizes to cis-3 at room temperature. The poorly soluble complex [Ru(acac)2(PCy3)2] (4), which is isolated similarly from cis-[Ru(acac)22-C2H 4)2] (2) and PCy3, appears to exist in the cis-configuration in solution according to NMR data, although an X-ray diffraction study of a single crystal shows the presence of trans-4. In benzene or toluene 2 reacts with PiPr3 or PCy3 to give exclusively cis-[Ru(acac)22-C2H 4)(L)] [L = PiPr3 (5), PCy3 (6)], whereas in THF species believed to be either square pyramidal [Ru(acac) 2L], with apical L, or the corresponding THF adducts, can be detected by 31P NMR spectroscopy. Complexes 3-6 react with CO (1 bar) giving trans-[Ru(acac)2(CO)(L)] [L = PiPr3 (trans-8), PCy3 (trans-9)], which are converted irreversibly into the cis-isomers in refluxing benzene. Complex 5 scavenges traces of dinitrogen from industrial grade dihydrogen giving a bridging dinitrogen complex, cis-[{Ru(acac)2(PiPr3)} 2(μ- N2)] (10). The structures of cis-3, trans-4, 5, 6 and 10 • C6H14 have been determined by single-crystal X-ray diffraction. Complexes trans- and cis-3, 5, 6, cis-8, and trans- and cis-9 each show fully reversible one-electron oxidation by cyclic voltammetry in CH 2Cl2 at -50°C with E1/2(Ru3+/2+) values spanning -0.14 to +0.92 V (versus Ag/AgCl), whereas for the vinylidene complexes [Ru(acac)2 (CCHR)(PiPr3)] [R = SiMe3 (11), Ph (12)] the process is irreversible at potentials of +0.75 and +0.62 V, respectively. The trend in potentials reflects the order of expected π-acceptor ability of the ligands: PiPr3, PCy3 <C 2H4 < CCHR < CO. The UV-Vis spectrum of the thermally unstable, electrogenerated RuIII-ethene cation 6+ has been observed at -50°C. Cyclic voltammetry of the μ-dinitrogen complex 10 shows two, fully reversible processes in CH 2Cl2 at -50°C at +0.30 and +0.90 V (versus Ag/AgCl) corresponding to the formation of 10+ (RuII,III) and 102+ (RuIII,III). The former, generated electrochemically at -50°C, shows a band in the near IR at ca. 8900 cm-1 (w 1/2 ca. 3700 cm-1) consistent with the presence of a valence delocalized system. The comproportionation constant for the equilibrium 10 + 102+ ⇌ 2 10+ at 223 K is estimated as 10 13.6.

    Original languageEnglish
    Pages (from-to)1692-1708
    Number of pages17
    JournalInorganica Chimica Acta
    Volume358
    Issue number5 SPEC. ISS.
    DOIs
    Publication statusPublished - 15 Mar 2005

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