Intramolecular H...H interactions between hydrogen-bond proton donors and transition metal hydrides can be extended to intermolecular cases by cocrystallization of ReH5(PPh3)(2)L and suitable hydrogen-bond donors, as is shown in the neutron and X-ray crystal structures of 6 (L = PPh3; donor = indole) and 7 (L = imidazole; donor = lattice imidazole of solvation), respectively. Short N-H...H-Re distances are found for these unconventional hydrogen bonds in both cases: 6, 1.734(8) Angstrom; 7, 1.68(3) Angstrom (sum of van der Waals radii for H...H = 2.4 Angstrom). IR data indicate a correlation between the pK(a) of the hydrogen-bond donor and the strengths of the H...H interactions. DFT calculations on ReH5(PH3)(3) . NH3 show the presence of a significant attractive interaction between the rhenium fragment and the proton donor, independent of the Re-H bonds chosen. Experimentally, the least hindered Re hydride is involved in the interaction in each case. The influence of the occupied metal d orbital (Re(V), d(2)) is minimal. Molecules like OPPh3 that can act as a hydrogen-bond acceptor do not show an attractive interaction with the Re complex, as confirmed by the absence of an attractive potential between ReH5(PH3)(3) and OPH3.

Tetrabutylammonium monopersulfate (2NBu4HSO5·NBu4HSO4·(NBu4)2SO4) is an effective primary oxidant with a high tendency to promote oxo transfer rather than radical pathways in catalysis. Nonradical hydrocarbon oxidation is seen with the complex [Mn3O4bipy4(H2O)2](ClO4)4 as catalyst as indicated by mechanistic studies; this contrasts with the radical pathways found for the same catalyst with t-BuOOH as the primary oxidant. The catalyst is robust, giving up to 15000 catalytic turnovers, and very efficient, the rate of 1-alkene epoxidation being 4000 turnovers/h.

Drei Wasserstoffatome sind an der ungewöhnlichen Wasserstoffbrückenbindung im Komplex 1 beteiligt, den man erhält, wenn die Rheniumverbindung und Indol gemeinsam aus Benzol kristallisieren. Die Struktur von 1 konnte mit Neutronenbeugungsmethoden aufgeklärt werden (H‐H‐Abstände 1.75 und 2.25 Å). Die H‐Brücke hat nach IR‐spektroskopischen Untersuchungen einen Energieinhalt von 4.3 ± 0.5 kcal mol1. Dieser Wert wird ebenso wie die Struktur von 1 durch Rechnungen mit Dichtefunktionalmethoden gut reproduziert. Indol könnte vielleicht allgemeiner als Kristallisationshilfsmittel für schwer kristallisierbare Verbindungen mit H‐Brückenacceptor‐Einheiten verwendet werden. magnified image

Three hydrogen atoms participate in the unusual hydrogen bond in complex 1, which is obtained when the rhenium compound is cocrystallized with indole from benzene. The structure of 1 was elucidated by means of neutron diffraction (HN …︁ HM distances of 1.75 and 2.25 Å). The energy of the hydrogen bond was determined by IR spectroscopy (ΔH° = 4.3 ± 0.5 kcal mol−1). All these values were also reproduced by theoretical calculations. Indole may be a useful additive for crystal growing in general.

Intermolecular hydrogen bonds form between a variety of weak proton acids such as indole and 2,4,6-Me3C6H2OH and the transition-metal hydrides [ReH5(PPh3)3], [ReH7(Ph2PCH2CH2PPh2)] and [WH4(PMePh2)4]; the strengths of the hydrogen-bond interactions are compared by IR data.