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

• Published in: Chemistry : a European journal 2010-02, Vol.16 (8), p.2574-2585
• Main Authors: Majumdar, Moumita, Sinha, Arup, Ghatak, Tapas, Patra, SanjibK, Sadhukhan, Nabanita, Rahaman, SMWahidur, Bera, JitendraK
• Format: Article
• Language: English
• Subjects: Activation; Coordination compounds; Decarboxylation; Derivatives; Formations; Heating; Hydrogen; Ligands
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200902797

The complete sequence of reactions in the base-promoted reduction of [{Ru super(II)(CO) sub(3)Cl sub(2)} sub(2)] to [Ru super(I) sub(2)(CO) sub(4)] super(2+) has been unraveled. Several mu -OH, mu : Kappa super(2)-CO sub(2)H-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 sub(2)(CO) sub(4)( mu : Kappa super(2)-C,O-CO sub(2)H) sub(2)( mu -OH )(NP super(F)-Am) sub(2)][PF sub(6)] (1; NP super(F)-Am=2-amino-5,7-trifluoromethyl-1,8-n aphthyridine) and [Ru sub(2)(CO) sub(4)( mu : Kappa super(2)-C,O-CO sub(2)H)( mu -OH)(NP-M e sub(2)) sub(2)][BF sub(4)] sub(2) (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru sub(4)(CO) sub(8)(H sub(2)O) sub(2)( mu super(3)-OH) sub(2)( mu : Kappa super(2 )-C,O-CO sub(2)H) sub(4)][CF sub(3)SO sub(3)] sub(2) (3) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a pi -donor chlorido ligand, which results in [Ru sub(2)(CO) sub(4)( mu : Kappa super(2)-C,O-CO sub(2)H) sub(2)( mu -Cl )(NP-PhOMe) sub(2)][BF sub(4)] (4). The production of [Ru sub(2)(CO) sub(4)] super(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 Ru super(I)--Ru super(I) single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru sub(2)(CO) sub(4)(CH sub(3)CN) sub(6)] super(2+) precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by Tl super(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 Ru super(I) sub(2)Ru super(II) complex [{Ru(NP-Am) sub(2)(CO)}{Ru sub(2) (NP-Am) sub(2)(CO) sub(2)( mu -CO) sub(2)}( mu sub(3): Kappa super(3)-C,O ,O'-CO sub(2))][BF sub(4)] sub(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