Mapping the Transformation [{Ru^II(CO)₃Cl₂}₂]→[Ru^I₂(CO)₄]²⁺: Implications in Binuclear Water–Gas Shift Chemistry

Abstract

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.

Bimetallic Catalysis Involving Dipalladium(I) and Diruthenium(I) Complexes

“…Room temperature activation of the CH bond,4 and formation of the CC bond5 have been performed at the axial site of the metal–metal singly bonded ‘Ru 2 (CO) 4 ’ core. In a recent report, we have described bimetallic water–gas shift (WGS) chemistry executed on a diruthenium platform 6. These stoichiometric reactions have provided valuable insight on fundamental organometallic processes on a dimetal unit.…”

“…In a recent report, we have described bimetallic water-gas shift (WGS) chemistry executed on a diruthenium platform. [6] These stoichiometric reactions have provided valuable insight on fundamental organometallic processes on a dimetal unit. The present work seeks to evaluate the catalytic activity of metal-metal bonded dimetal compounds in organic transformations.…”

Contrasting Reactivity of 2-Mesityl-1,8-Naphthyridine (Mes-NP) with Singly-Bonded [RhII–RhII] and [RuI–RuI] Compounds

“…[17][18][19][20][21][22][23][24][25][26][27][28][29][30] It is our assertion that weak axial interactions lead to shorter metalmetal distance in compound 1. [8,9] The reaction of cis-[Ru 2 (CO) 4 (2) in high yield. The four carbonyls do not allow cis to trans isomerization, and as a result the Ru-Ru bond is cleaved.…”

“…[1] The flexibility and adaptability are the key attributes of NP ligands which make them suitable for use in bimetallic catalysis. [2][3][4] We explored NP-R (2-(2-R)-1,8-naphthyridine) ligands in our pursuit of dimetallic chemistry. [5][6][7] Covalent attachment of a donor group, for example, the thiazolyl at 2-position of the NP (tz-NP), provides a tridentate ligand that bridges the dimetal unit and simultaneously binds one axial site, as illustrated in Fig.…”

Chain Reaction for Isomerization from trans(Cl) to cis(Cl)‐Ru(bpy)(CO)2Cl2 (bpy = 2,2′‐Bipyridine) Induced by NaBH4

“…It showed an absorption at 1561 cm -1 , which suggests that crude trans(Cl)-1 contains the formate or hydroxy carbonyl derivative as an impurity. [20] We suppose that the formate or hydroxy carbonyl species give hydride complexes, which induce the trans-cis isomerization.…”