Mapping the Transformation [{Ru-II(CO)(3)Cl-2}(2)]->[Ru-2(I)(CO)(4)](2+): Implications in Binuclear Water Gas Shift Chemistry

作者：Majumdar Moumita; Sinha Arup; Ghatak Tapas; Patra Sanjib K; Sadhukhan Nabanita; Rahaman S M Wahidur; Bera Jitendra K^*

来源：Chemistry - A European Journal, 2010, 16(8): 2574-2585.

DOI：10.1002/chem.200902797

• carbonyl ligands
• hydroxides
• organometallics
• reaction mechanisms
• ruthenium

The complete sequence of reactions in the base-promoted reduction of [{Ru-II(CO)(3)Cl-2}(2)] to [Ru-2(I)(CO)(4)](2+) has been unraveled. Several mu-OH, mu:kappa(2)-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 [Ru-2(CO)(4)(mu:kappa(2)-C,O-CO2H)(2)(mu-OH)(NPF-Am)(2)][PF6] (1; NPF-Am=-2-amino-5,7-trifluoromethyl-1,8-naphthyridine) and [Ru-2(CO)(4)(mu:kappa C-2,O-CO2H)(mu-OH)(NP-Me-2)(2)][BF4](2) (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru-4(CO)(8)(H2O)(2)(mu(3)-OH)(2)(mu:kappa(2)-C,O-CO2H)(4)][CF3SO3](2) (3) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a pi-donor chlorido ligand, which results in [Ru-2(CO)(4)(mu:kappa C-2,O-CO2H)(mu-Cl)-(NP-PHoMe2)(2)][BF4] (4). The production of [Ru-2(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 Rut Rut 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 Tl-I 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 (Ru2RuII)-Ru-I complex [{Ru(NP-Am)(2)(CO)}{Ru-2(NP-Am)(2)(CO)(2)(mu-CO)(2)}(mu(3):kappa(3)-C,O,O'-CO2)][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.

• 出版日期2010