Timofei Privalov

A molecular ruthenium catalyst with water-oxidation activity comparable to that of photosystem II

Across chemical disciplines, an interest in developing artificial water splitting to O(2) and H(2), driven by sunlight, has been motivated by the need for practical and environmentally friendly power generation without the consumption of fossil fuels. The central issue in light-driven water splitting is the efficiency of the water oxidation, which in the best-known catalysts falls short of the desired level by approximately two orders of magnitude. Here, we show that it is possible to close that two orders of magnitude gap with a rationally designed molecular catalyst [Ru(bda)(isoq)(2)] (H(2)bdaxa0=xa02,2-bipyridine-6,6-dicarboxylic acid; isoqxa0=xa0isoquinoline). This speeds up the water oxidation to an unprecedentedly high reaction rate with a turnover frequency of >300xa0s(-1). This value is, for the first time, moderately comparable with the reaction rate of 100-400xa0s(-1) of the oxygen-evolving complex of photosystem II in vivo.

Structural Modifications of Mononuclear Ruthenium Complexes: A Combined Experimental and Theoretical Study on the Kinetics of Ruthenium‐Catalyzed Water Oxidation

Structural Modifications of Mononuclear Ruthenium Complexes : A Combined Experimental and Theoretical Study on the Kinetics of Ruthenium-Catalyzed Water Oxidation

Evolution of O2 in a Seven-Coordinate RuIV Dimer Complex with a [HOHOH]- Bridge: A Computational Study

Evolution of O-2 in a Seven-Coordinate Ru-IV Dimer Complex with a [HOHOH] (-) Bridge : A Computational Study

Water Oxidation by Single-Site Ruthenium Complexes : Using Ligands as Redox and Proton Transfer Mediators

Water Oxidation by Single-Site Ruthenium Complexes : Using Ligands as Redox and Proton Transfer Mediators

Regeneration of Oxidized Organic Photo‐Sensitizers in Grätzel Solar Cells: Quantum‐Chemical Portrait of a General Mechanism

Regeneration of Oxidized Organic Photo-Sensitizers in Gratzel Solar Cells : Quantum-Chemical Portrait of a General Mechanism

On the Possibility of Conversion of Alcohols to Ketones and Aldehydes by Phosphinoboranes R2PBR′R′′: A Computational Study

Can phosphinoboranes promote hydrogenation of carbonyl moieties? By means of B3LYP and MPW1K density functional calculations the likelihood of the oxidation of alcohols by phosphinoboranes R(2)PBR(2) (1) was explored. As a proof-of-principle, a theoretical study that tests the reversibility of the alcohol oxidation is reported. The potential of 1 as a metal-free hydrogenation mediator is discussed for a series of hydrogen sources such as primary and secondary alcohols.

On the possibility of catalytic reduction of carbonyl moieties with tris(pentafluorophenyl)borane and H2: a computational study

The study thoroughly examines the Gibbs free energy surfaces of a new mechanism for reduction of ketones/aldehydes by tris(pentafluorophenyl)borane (1) and H(2). Key elements of the proposed mechanism are the proton and the hydride transfer steps similar to Stephans catalytic reduction of imines by 1. The proton is transferred to the ketone/aldehyde in the process of H(2) cleavage by the carbonyl-borane couple and the hydride is transferred in a nucleophilic attack on the carbonyl carbon by the hydridoborate in the ionic pair, [HOCRR](+)[HB(C(6)F(5))(3)](-). The in solvent Gibbs free energy barriers of H(2) splitting by adducts of B(C(6)F(5))(3) with acetone, acetophenone and benzaldehyde are predicted to be in the range of 24.5 +/- 2.5 kcal mol(-1), which corresponds to potential energy barriers in the range of 17.0 +/- 2.0 kcal mol(-1). Significantly lower barrier of H(2) activation is predicted in cases of bulky ketones such as 2,2,4,4-tetramethylpentan-3-one. With respect to the hydridoborate intermediate, the nucleophilic attack on the activated carbon is predicted to have a relatively low barrier for the sterically unhindered substrates, while this barrier is considerably higher for the sterically encumbered substrates. Since the formation of the hydridoborate intermediates is found to be endothermic, the transition state of the nucleophilic attack is the highest point of the computed energy profile for all tested substrates. Overall, according to in solvent density function calculations the proposed reduction of compact ketones/aldehydes by 1 and H(2) is allowed both thermodynamically and kinetically at elevated temperature, but it is expected to be slower and more substrate specific than the corresponding reduction of imines.

The O-O bonding in water oxidation: the electronic structure portrayal of a concerted oxygen atom-proton transfer pathway.

The two-phased reaction: Calculations on the monomeric ruthenium catalyst with 1,10-phenanthroline-2,9-dicarboxylic acid reveals an interaction of the RuV=O complex with water that proceeds through ...

Racemization of Alcohols Catalyzed by [RuCl(CO)2(η5-pentaphenylcyclopentadienyl)]-Mechanistic Insights from Theoretical Modeling

Two possible pathways of inner-sphere racemization of sec-alcohols by using the [RuCl(CO)(2)(eta(5)-pentaphenylcyclopentadienyl)] catalyst (1) have been thoroughly investigated by means of density function calculations. To be able to racemize alcohols, catalyst 1 needs to have a free coordination site on the metal. This can be achieved either by a eta(5)-->eta(3) ring slippage or by dissociation of a carbon monoxide (CO) ligand. The eta(5)-->eta(3) ring-slip pathway was found to have a high potential energy barrier, 42 kcal mol(-1), which can be explained by steric congestion in the transition state. On the other hand, CO dissociation to give a 16-electron complex has a barrier of only 22.6 kcal mol(-1). We have computationally discovered a mechanism involving CO participation that does not require eta(5)-->eta(3) ring slippage. The key features of this mechanism are 1) CO-assisted exchange of chloride for alkoxide, 2) alcohol-alkoxide exchange, and 3) generation of an active 16-electron complex through CO dissociation with subsequent beta-hydride elimination as the racemization step. We have found a low-energy pathway for reaction of 1 with potassium tert-butoxide and a pathway for fast alkoxide exchange with interaction between the incoming/leaving alcohol and one of the two CO ligands. We predict that dissociation of a Ru-bound CO ligand does not occur in these exchange reactions. Dissociation of one of the two Ru-bound CO ligands has been found necessary only at a later stage of the reaction. Though this barrier is still quite high, our results indicate that it is not necessary to cross the CO dissociation barrier for the racemization of each new alcohol. Thus, the dissociation of a CO ligand is interpreted as a rate-limiting reaction step in order to create a catalytically active 16-electron complex.

Uncovering the role of intra- and intermolecular motion in frustrated Lewis acid/base chemistry: ab initio molecular dynamics study of CO2 binding by phosphorus/boron frustrated Lewis pair [tBu3P/B(C6F5)3].

The role of the intra- and intermolecular motion, i.e., molecular vibrations and the relative motion of reactants, remains largely unexplored in the frustrated Lewis acid/base chemistry. Here, we address the issue with the ab initio molecular dynamics (AIMD) study of CO2 binding by a Lewis acid (LA) and a Lewis base (LB), i.e., tBu3P + CO2 + B(C6F5)3 → tBu3P-C(O)O-B(C6F5)3 ([1]). Reasonably large ensemble of AIMD trajectories propagated at 300 K from structures in the saddle region as well as trajectories propagated directly from the reactants region revealed an effect arising from significant recrossing of the saddle area. The effect is that transient complexes composed of weakly interacting reactants nearly cease to progress along the segment of the minimum energy pathway (MEP) at the saddle region for a (subpicosecond) period of time during which the dominant factor is the light-to-heavy type of relative motion of the vibrating reactants, i.e., the bouncing-like movement of CO2 with respect to much heavier phosphine and borane as main contributor to the mode that is perpendicular to the MEP-direction. In terms of how P···C and B···O distances change with time, the roaming-like patterns of typical AIMD trajectories, reactive and nonreactive alike, extend far beyond the saddle region. In addition to the dynamical portrayal of [1], we provide the energy-landscape perspective that takes into account the hierarchy of time scales. The verifiable implication of the effect found here is that the isotopically substituted (heavier) LB/LA pair should be less reactive that the normal and thus lighter counterpart.