A Highly Effective Ruthenium System for the Catalyzed Dehydrogenative Cyclization of Amine-Boranes to Cyclic Boranes under Mild Conditions.

We recently disclosed a new ruthenium-catalyzed dehydrogenative cyclization process (CDC) of diamine-monoboranes leading to cyclic diaminoboranes. In the present study, the CDC reaction has been successfully extended to a larger number of diamine-monoboranes (4-7) and to one amine-borane alcohol precursor (8). The corresponding NB(H)N- and NB(H)O-containing cyclic diaminoboranes (12-15) and oxazaborolidine (16) were obtained in good to high yields. Multiple substitution patterns on the starting amine-borane substrates were evaluated and the reaction was also performed with chiral substrates. Efforts have been spent to understand the mechanism of the ruthenium CDC process. In addition to a computational approach, a strategy enabling the kinetic discrimination on successive events of the catalytic process leading to the formation of the NB(H)N linkage was performed on the six-carbon chain diamine-monoborane 21 and completed with a (15) N NMR study. The long-life bis-σ-borane ruthenium intermediate 23 possessing a reactive NHMe ending was characterized in situ and proved to catalyze the dehydrogenative cyclization of 1, ascertaining that bis σ-borane ruthenium complexes are key intermediates in the CDC process.

Electronic structure and formation of simple ferryloxo complexes: mechanism of the Fenton reaction.

The Fenton reaction is a famous reaction in inorganic chemistry, with relevance to topics such as bioinorganic oxidation and fundamental redox chemistry of water and oxygen. It is also a reaction concerning which there has been very extensive mechanistic debate, with experimental and computational work leading to extensive evidence concerning its mechanism-not all of which is consistent. Here, we use this reaction as a challenge to modern electronic structure theory methods and show that density functional theory, when validated by accurate ab initio methods, can yield a picture of this reaction that is consistent with experiment. The article also highlights some of the challenges in accurate studies of reaction mechanisms of ionic species in water solution.

Atmospheric hydrocarbon activation by the hydroxyl radical: a simple yet accurate computational protocol for calculating rate coefficients.

The overall rate coefficient at standard temperature and pressure for the hydrogen abstraction reaction by the hydroxyl radical (HO˙) from common saturated volatile organic compounds (VOCs) is derived theoretically using electronic structure calculations and transition state theory (TST). The computational approach used is based on relatively efficient methods, and hence is applicable to a large number of compounds with only a modest use of computer resources. The key methods used are density functional theory (for the calculation of barrier heights) and simple transition state theory (TST), including a simple correction for tunnelling. All thermally relevant conformers of the reactant and the abstraction TS are included in the study. For all compounds in a test set of thirty-four, the calculated rate coefficient agrees with the experimental value to within better than an order of magnitude, and to within better than a factor of three for all but six cases, so that the accuracy is of predictive utility.

Ruthenium agostic (phosphinoaryl)borane complexes: multinuclear solid-state and solution NMR, X-ray, and DFT studies.

The reactivity of the (o-phosphinophenyl)(amino)borane compound HB(N(i)Pr(2))C(6)H(4)(o-PPh(2)) prepared from Li(C(6)H(4))PPh(2) and HBCl(N(i)Pr(2)) toward the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1) was studied by a combination of DFT, X-ray, and multinuclear NMR techniques including solid-state NMR, a technique rarely employed in organometallic chemistry. The study showed that the complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3))(2) (3), isolated in excellent yield as yellow crystals and characterized by X-ray diffraction, led in solution to PCy(3) dissociation and formation of an unsaturated 16-electron complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3)) (4), with a hydride trans to a vacant site. In both cases, the (phosphinoaryl)(amino)borane acts as a bifunctional ligand through the phosphine moiety and a Ru-H-B interaction, thus featuring an agostic interaction.