Ruthenium complexes with vinyl, styryl, and vinylpyrenyl ligands: A case of non-innocence in organometallic chemistry

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Journal of the American Chemical Society, 130 (1): 259--268 (2008)
DOI: 10.1021/ja075547t


A series of vinylruthenium bis-phosphine five- and six-coordinated complexes with non-conjugated 1-hexenyl, conjugated styryl and pyrenylethenyl ligands were prepd.; the effects of conjugation of the arom. system with vinyl p-bond on oxidn. potential, stability of the oxidated species, ESR spectra and IR CO-stretching bands were systematically explored by IR-spectroelectrochem. and DFT calcns. Hydrometalation of 1-hexyne, phenylacetylene and 1-ethynylpyrene affords the corresponding five-coordinated ruthenium complexes (PR3)2Cl(CO)RuCH:CHR1 (1a-3a; R = Ph, R1 = Bu, Ph, 1-pyrenyl; 1c-3c; R = iPr, same R1) and their octahedral pyridine adducts (PPh3)2Cl(CO)(4-EtO2CC5H4N-kN)RuCH:CHR1 (1b-3b; same R1). Crystal structures of 1b, 1c, 3c and 3a·PPh3 and enynyl complex Ru(CO)Cl(PPh3)2(h1:h2-nBuHC:CHC$\equiv$CnBu), the result of coupling of the hexenyl ligand of complex 1a with another mol. of 1-hexyne, are reported. All vinyl complexes undergo a one-electron oxidn. at fairly low potentials and a second oxidn. at more pos. potentials. Anodic half-wave or peak potentials show a progressive shift to lower values as p-conjugation within the vinyl ligand increases. Carbonyl band shifts of the metal-bonded CO ligand upon monooxidn. are significantly smaller than is expected of a metal-centered oxidn. process and are further diminished as the vinyl CH:CH entity is incorporated into a more extended p-system. ESR spectra of the electrogenerated radical cations display negligible g-value anisotropies and small deviations of the av. g-value from that of the free electron. The vinyl ligands thus strongly contribute to or even dominate the anodic oxidn. processes. This renders them a class of truly \dqnon-innocent\dq ligands in organometallic ruthenium chem. Exptl. findings are fully supported by quantum chem. calcns. The contribution of the vinyl ligand to the HOMO increases from 46\% (Ru-vinyl delocalized) to 84\% (vinyl dominated) as R changes from Bu to 1-pyrenyl. on SciFinder(R)



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