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Issue 13, 2017
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Base assisted C–C coupling between carbonyl and polypyridyl ligands in a Ru-NADH-type carbonyl complex

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Abstract

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.

Graphical abstract: Base assisted C–C coupling between carbonyl and polypyridyl ligands in a Ru-NADH-type carbonyl complex

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Publication details

The article was received on 26 Jan 2017, accepted on 24 Feb 2017 and first published on 28 Feb 2017


Article type: Paper
DOI: 10.1039/C7DT00312A
Citation: Dalton Trans., 2017,46, 4373-4381
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    Base assisted C–C coupling between carbonyl and polypyridyl ligands in a Ru-NADH-type carbonyl complex

    D. Ghosh, T. Fukushima, K. Kobayashi, S. Sen, S. Kitagawa, T. kato and K. Tanaka, Dalton Trans., 2017, 46, 4373
    DOI: 10.1039/C7DT00312A

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