Ruthenium(IV)‐Catalyzed Isomerization of the CC Bond of O‐Allylic Substrates: A Theoretical and Experimental Study

Abstract

A general mechanism to rationalize Ru(IV) -catalyzed isomerization of the C=C bond in O-allylic substrates is proposed. Calculations supporting the proposed mechanism were performed at the MPWB1K/6-311+G(d,p)+SDD level of theory. All experimental observations in different solvents (water and THF) and under different pH conditions (neutral and basic) can be interpreted in terms of the new mechanism. Theoretical analysis of the transformation from precatalyst to catalyst led to structural identification of the active species in different media. The experimentally observed induction period is related to the magnitudes of the energy barriers computed for that process. The theoretical energy profile for the catalytic cycle requires application of relatively high temperatures, as is experimentally observed. Participation of a water molecule in the reaction coordinate is mechanistically essential when the reaction is carried out in aqueous medium. The new mechanistic proposal helped to develop a new experimental procedure for isomerization of allyl ethers to 1-propenyl ethers under neutral aqueous conditions. This process is an unique example of efficient and selective catalytic isomerization of allyl ethers in aqueous medium.

Highly Efficient Redox Isomerisation of Allylic Alcohols Catalysed by Pyrazole‐Based Ruthenium(IV) Complexes in Water: Mechanisms of Bifunctional Catalysis in Water

“…Under neutral conditions, water exchange processes and coordination of the allylic alcohol G (Figure 2) can be considered. Recently, DFT calculations on the mechanism, inclusive of the coordination of water molecules in the intermediate active species, have been performed 9. The theoretical energy profile for the catalytic cycle and overall energy barrier is in accordance with the relatively high temperature required for the reaction to occur (75 °C).…”

Ruthenium(II) Complexes with η6-Coordinated 3-Phenylpropanol and 2-Phenylethanol as Catalysts for the Tandem Isomerization/Claisen Rearrangement of Diallyl Ethers in Water

“…Our group has been for long time interested in aqueous catalysis, describing different ruthenium(II) and ruthenium(IV) complexes able to promote the migration of allylic C=C bonds in aqueous environments. Substrates covered in our previous works include allyl-alcohols, 15 -ethers, 16 -amines 17 and -benzenes. 18 As a continuation, we report herein the successful application of a series of hydrophilic half-sandwich ruthenium(II) complexes, containing  6 -coordinated 2-phenylethanol and 3phenylpropanol ligands (compounds 1-2a-f in Figure 1), in the tandem isomerization/Claisen rearrangement of diallyl ethers in water.…”

Unraveling the Mechanism of the IrIII‐Catalyzed Regiospecific Synthesis of α‐Chlorocarbonyl Compounds from Allylic Alcohols

“…The first step is the coordination of substrate 1 e to the Ir III complex Int0 . This can take place either through the C=C double bond to give η 2 ‐olefin complex Int1 , or through the hydroxy group to give Int1 a [11] . The two complexes are calculated to be higher in energy than Int0 by 3.8 and 5.3 kcal mol −1 , respectively.…”

“…The first step is the coordination of substrate 1e to the Ir III complex Int0.T his can take place either throught he C=C double bond to give h 2 -olefin complex Int1,orthrough the hydroxy group to give Int1 a. [11] The two complexesa re calculated to be higher in energy than Int0 by 3.8 and 5.3 kcal mol À1 , respectively.A lthough Int1 is the lower in energy of these two, the next step, the dissociation of chloride via TS1,t akes place preferentially from Int1 a.T he calculated barrier is 10.0 kcal mol À1 relative to Int0,c ompared to ab arriero f1 5.5 kcal mol À1 for the pathway via Int1.…”