Imidazole Based Ruthenium(IV) Complexes as Highly Efficient Bifunctional Catalysts for the Redox Isomerization of Allylic Alcohols in Aqueous Medium: Water as Cooperating Ligand

Abstract

Bis-allyl ruthenium(IV) complexes containing 1,3 azole β-N-H protic ligands [Ru(η 3 :η 3 -C 10 H 16 )Cl 2 L] (C 10 H 16 = 2,7-dimethylocta-2,6-diene-1,8-diyl) (L = imidazole (1a), benzimidazole (1b)), and N-methylimidazole (1c) are highly active precatalysts in the redox isomerization of allylic alcohols into carbonyl compounds in aqueous medium and in the absence of base. A wide series of primary and secondary allylic alcohols can be isomerized into the corresponding carbonyl compounds. Remarkably, complex 1b has been found to be the most efficient catalyst reported to date for the isomerization of 1-octen-3-ol in water leading to a turnover frequency (TOF) value of 60 000 h −1 . Moreover, catalyst 1b can be recycled remaining active up to seven cycles. Density functional theory (DFT) calculations give evidence that the hydroxo complexes derived from 1a−c species can be formed in aqueous solution and that they can act as the catalytic active species in a bifunctional catalyzed process. This study demonstrate that in water the participation of the β-N-H protic group of the 1,3-azole ligands in the bifunctional catalysis is not required, provided that a water molecule can act as cooperating ligand.

Beyond Continuum Solvent Models in Computational Homogeneous Catalysis

“…A combined experimental and computational study of the ruthenium-catalyzed isomerization of allylic alcohols in aqueous medium (Fig. 11) disclosed another possible role that water solvent molecules can play: they not only can coordinate but can act as cooperating ligand in metal-ligand bifunctional mechanisms [74].…”

Water Participation in Catalysis: An Atomistic Approach to Solvent Effects in the Catalytic Isomerization of Allylic Alcohols

“…14 Theoretical studies 2 have been used to substantiate the involvement of water in catalytic processes akin to the allylic alcohol isomerisation. [15][16][17] Only a very small number of water molecules were however explicitly taken into account in these studies. The processes through which water molecules assist the catalytic reaction, particularly by stabilising specific reactive conformers in solution, remain largely obscure.…”

Steps Ahead in Understanding the Catalytic Isomerization Mechanism of Linear Allylic Alcohols in Water: Dynamics, Bonding Analysis, and Crystal Structure of an η2-Allyl-Intermediate

“…Despite it has been shown that some catalysts require the presence of a base, including water, to stabilize specific intermediates during the catalytic cycle, [13][14][15] we have develop metal complexes that catalyzes this reaction just in water. Scheme 1.…”