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Mapping the transformation [{RuII (CO)3Cl 2}2]→[RuI 2 (CO) 4]2+: Implications in binuclear water-gas shift chemistry
M. Majumdar, , , S.K. Patra, N. Sadhukhan, S.M.W. Rahaman, J.K. Bera
Published in
Volume: 16
Issue: 8
Pages: 2574 - 2585
The complete sequence of reactions in the base-promoted reduction of [{RuII(CO)3Cl2}2] to [RuI 2 (CO)4]2+ has been unraveled. Several μ-OH, μ:k2-CO2H-bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal-coordinated carbonyls by hydroxides. The isolated compounds are [Ru2(CO) 4(μ:k2-C,O-CO2H) 2(μ-OH)(NPF-Am) 2][PF6] (1; NPF-Am=2-amino-5,7-trifluoromethyl- 1,8-naphthyridine) and [Ru 2 (CO) 4(μ:k2- C,O-CO2H)(μ-OH) (NP-Me2)2][BF4]2 (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru4(CO) 8(H2O) 2(μ3- OH)2(μ:k2-C,O-CO2H) 4][CF3SO3]2 (3) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a pdonor chlorido ligand, which results in [Ru2(CO)4(μ:k2-C,O-CO 2H) 2(μ-Cl)- (NP-PhOMe)2][BF4] (4). The production of [Ru2(CO)4]2+ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl)- diruthenium( II) complex to a dihydrido- diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the RuI-RuI single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru 2(CO)4(CH3CN)6]2+ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by TlI salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear RuI2RuII complex [{Ru(NP-Am) 2(CO)}{Ru2(NP-Am)2(CO) 2(μ-CO) 2}(μ3:k3-C,O,O'- CO 2)][BF4]2 (6). These unprecedented diruthenium compounds are the dinuclear congeners of the water-gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry. © 2010 Wiley-VCH Verlag 2574 GmbH&Co. KGaA, Weinheim.
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JournalChemistry - A European Journal