Mapping the transformation [{Ru(II)(CO)(3)Cl(2)}(2)]-->[Ru(I) (2)(CO)(4)](2+): implications in binuclear water-gas shift chemistry.
The complete sequence of reactions in the base-promoted reduction of [{Ru(II)(CO)(3)Cl(2)}(2)] to [Ru(I) (2)(CO)(4)](2+) has been unraveled. Several mu-OH, mu:kappa(2)-CO(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(2)(CO)(4)(mu:kappa(2)-C,O-CO(2)H)(2)(mu-OH)(NP(F)-Am)(2)][PF(6)] (1; NP(F)-Am=2-amino-5,7-trifluoromethyl-1,8-naphthyridine) and [Ru(2)(CO)(4)(mu:kappa(2)-C,O-CO(2)H)(mu-OH)(NP-Me(2))(2)][BF(4)](2) (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru(4)(CO)(8)(H(2)O)(2)(mu(3)-OH)(2)(mu:kappa(2)-C,O-CO(2)H)(4)][CF(3)SO(3)](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(2)-C,O-CO(2)H)(2)(mu-Cl)(NP-PhOMe)(2)][BF(4)] (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 Ru(I)--Ru(I) single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru(2)(CO)(4)(CH(3)CN)(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 Ru(I) (2)Ru(II) complex [{Ru(NP-Am)(2)(CO)}{Ru(2)(NP-Am)(2)(CO)(2)(mu-CO)(2)}(mu(3):kappa(3)-C,O,O'-CO(2))][BF(4)](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.
Majumdar
Moumita
M
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.
Sinha
Arup
A
Ghatak
Tapas
T
Patra
Sanjib K
SK
Sadhukhan
Nabanita
N
Rahaman
S M Wahidur
SM
Bera
Jitendra K
JK