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Dalton Trans. 2017 Mar 27;46(13):4373-4381. doi: 10.1039/c7dt00312a.

Base assisted C-C coupling between carbonyl and polypyridyl ligands in a Ru-NADH-type carbonyl complex.

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Institute for Cell-Material Sciences, Kyoto University, ACT-Kyoto #507, Jibucho 105, Fushimi-ku, Kyoto 612-8374, Japan.
Institute for Cell-Material Sciences, Kyoto University, Int'tech Center #016, Katsura, Nishikyo-ku, Kyoto 615-8530, Japan.
Institute for Cell-Material Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan.
Institute for Liberal Arts and Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan.


A reaction of a ruthenium(ii) NAD-type complex, [Ru(tpy)(pbn)(Cl)]+ (tpy = 2,2':6',2''-terpyridine; pbn = 2-(pyridin-2-yl)benzo[b][1,5]naphthyridine), with pressurized CO (2 MPa) at 150 °C in H2O selectively produced a two-electron reduced ruthenium(ii)-NADH-type carbonyl complex, [Ru(tpy)(pbnHH)(CO)]2+ (pbnHH = 2-(pyridin-2-yl)-5,10-dihydrobenzo[b][1,5]naphthyridine), rather than the oxidized [Ru(tpy)(pbn)(CO)]2+ complex. Indeed, [Ru(tpy)(pbnHH)(CO)]2+ was quantitatively oxidized to [Ru(tpy)(pbn)(CO)]2+ upon treatment with one equiv. of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). The reactivity of [Ru(tpy)(pbnHH)(CO)]2+ with various bases was studied herein. Treatment of [Ru(tpy)(pbnHH)(CO)]2+ with a suitable organic base, 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), resulted in the formation of a new five-membered Ru-CO-bridge metallacycle quantitatively in acetonitrile under air at room temperature. A probable mechanism was proposed for this reaction based on UV-vis, NMR, and EPR spectral studies and other experimental data. Furthermore, a reaction of the five membered Ru-CO-bridge metallacycle with NH4PF6 in CH3CN : H2O (1 : 1) under air smoothly produced another new six-membered Ru-OCO-bridge complex. A mechanism for the formation of a Ru-OCO-bridge complex was also proposed here on the basis of H2O18 experiments, DDQ treatment and other experimental data. These newly synthesized complexes appended with NAD-type ligands may have potential use as renewable hydride sources for organic reductions.


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