The free energy for hydride transfer reactions of transition metal hydrides is known to be influenced by solvent effects. The first-row transition metal hydride [HNi­(dmpe)2]­[BF4] (dmpe = 1,2-bis­(dimethylphosphino)­ethane) has starkly different hydride transfer reactivities with CO2 in different solvents. A binary mixture of water and acetonitrile was used to tune the hydride transfer reactivity of HNi­(dmpe)2 + with CO2 so that the free energy for this reaction approached zero. Various mole fractions of water were tested and a linear relationship between the hydride transfer free energy and solvent composition was established for 0–0.24 mole fraction of water. A deviation from linearity was found upon moving toward higher mole fractions of water. The tuning of the free energy for hydride transfer allowed HNi­(dmpe)2 + to be used as a catalyst for the hydrogenation of CO2. The optimized catalyst conditions produced 58 turnovers at room temperature in 0.082 mole fraction of water using 60 atm of a 1:1 mixture of H2 to CO2 gas.

trans-Resveratrol (resveratrol) has been shown to have various health benefits. As a consequence, there is an effort to determine plentiful sources of this molecule. Certain plants, such as grapes, synthesize resveratrol and therefore appear to be an excellent source of this chemical. Annual pruning of grapevine yields significant amounts of cane material that is normally mulched or simply burned. Previous studies have shown this grape cane to contain economically useful resveratrol. Texas is the seventh largest producer of grapes in the USA with over 162 ha currently under cultivation. As a result it is estimated that more than $3.2 million of resveratrol could be extracted from grape canes in Texas each year. In this study resveratrol was isolated by a non-optimized protocol from ten varieties of grape cane grown in central Texas, USA. HPLC analysis showed the cultivars Lenoir and Cabernet Sauvignon yielded the greatest relative amounts of resveratrol (52.3 and 49.6 mg/kgDW). A statistical grouping of the ten varieties suggests that Norton, Blanca du bois, Cabernet Sauvignon, and Lenoir are the best candidates to use for further resveratrol isolation.

Treatment of the tetrahedral cluster H2Ru3(CO)9(μ3-S) (1) with 2-(diphenylphosphino)­thioanisole (PS) furnishes the cluster H2Ru3(CO)7(κ2-PS)­(μ3-S) (2). Cluster 2, which exhibits a chelated thiophosphine ligand (κ2-PS), exists as a pair of diastereomers with K eq = 1.55 at 298 K that differ in their disposition of ligands at the Ru­(CO)­(κ2-PS) center. The PS ligand occupies the equatorial sites (Peq,Seq) in the kinetic isomer and axial and equatorial sites (Pax,Seq) in the thermodynamically favored species. The solid-state structure of the kinetic isomer of 2 has been established by X-ray diffraction analysis, and the reversible first-order kinetics to equilibrium have been measured experimentally by NMR spectroscopy and HPLC over the temperature range 293–323 K. The substitution reaction involving 1 and the isomerization of the PS ligand in 2 were investigated by DFT calculations. The computational results support a phosphine-induced expansion of the cluster polyhedron that is triggered by the associative addition of the PS donor to 1. The vertex opening in 1 is selective and leads to the cleavage of a hydride-bridged Ru–Ru bond to give the phosphine-substituted cluster H2Ru3(CO)9(κ1-PS)­(μ3-S) as the initial adduct. Chelation of the pendant MeS moiety follows with a loss of CO to give the kinetic substitution product H2Ru3(CO)7(κ2-Peq,Seq)­(μ3-S) (2). The observed isomerization of the PS ligand in 2 is best explained by a tripodal rotation of the CO and PS groups at the Ru­(CO)­(κ2-PS) center that is preceded by a regiospecific migration of one of the edge-bridging hydrides to the nonhydride-bridged Ru–Ru bond in 2.

The reaction of the halo‐bridged dimer [BrRe(CO)4]2 with the ambidentate donor 2‐(diphenylphosphanyl)pyridine (PN) has been investigated. The substitution reaction is rapid at room temperature and regioselective for phosphorus coordination to yield exclusively cis‐BrRe(CO)4(κP‐PN) (1). Thermolysis of 1 furnishes the PN‐chelated product fac‐BrRe(CO)3(κP,N‐PN) (2) and CO. The kinetics for the conversion of 1 → 2 + CO have been measured by UV/Vis spectroscopy in toluene over the temperature range of 323–343 K. On the basis of the activation parameters [ΔH‡ = 28.0(0.9) kcal/mol and ΔS‡ = 31(3) eu], a dissociative process is supported, and this was corroborated by electronic structure calculations. The regioselectivity in the ligand‐substitution reaction involving [BrRe(CO)4]2 and the tridentate donor 6‐(diphenylphosphanyl)‐2‐formylpyridine (PON) was also studied, and consistent with the PN donor, only the κP‐product, cis‐BrRe(CO)4(κP‐PON) (3) is formed. The reaction of the dimer [BrRe(CO)4]2 with 2‐(diphenylphosphanyl)pyridine (PN) has been computationally modeled by DFT calculations. The energetics for the creation of an unsaturated intermediate through the cleavage of one of the bridging bromide ligands, followed by the addition of the donor to the unsaturated rhenium center versus the direct attack of the pnictogen donor on the dimer have been evaluated. The latter process is computed as the preferred route for dimer activation, with an attack of the pyridyl moiety slightly favored compared to the phosphine moiety. The computed pnictogen preference agrees with the kinetic data published by Zingales and coworkers. Concerning the reaction of the PN ligand with [BrRe(CO)4]2, we predict the initial formation of the κN‐isomer of 1 as the kinetic product of substitution, which in turn undergoes a rapid isomerization to furnish the thermodynamically more stable κP‐isomer through a reversible ligand dissociation process. The intramolecular linkage isomerization of κN‐1 to κP‐1 in 1 was also investigated by DFT, and the concerted process was found to lie 6.5 kcal/mol above the two‐step process involving ligand dissociation.