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 μ‐OH, μ:κ 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 (μ:κ 2 ‐ C , O ‐CO 2 H) 2 (μ‐OH)(NP F ‐Am) 2 ][PF 6 ] ( 1 ; NP F ‐Am=2‐amino‐5,7‐trifluoromethyl‐1,8‐naphthyridine) and [Ru 2 (CO) 4 (μ:κ 2 ‐ C , O ‐CO 2 H)(μ‐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 (μ 3 ‐OH) 2 (μ:κ 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 π‐donor chlorido ligand, which results in [Ru 2 (CO) 4 (μ:κ 2 ‐ C , O ‐CO 2 H) 2 (μ‐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 (μ‐CO) 2 }(μ 3 :κ 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.