Source: Dissertation Abstracts International, Volume: 57-02, Section: B, page: 1096.

Director: Robert Howard Crabtree.

It has been shown that hydrogen bonding with transition metal hydrides can be extended to intermolecular cases using suitable hydrogen bond donors. The crystal structure of (ReH$\sb5$(PPh$\sb3)\sb3\rbrack\cdot\rm C\sb8H\sb6NH\cdot C\sb6H\sb6$ shows this clearly. The side-on bonding seen in the crystal structure is consistent with the model of a sigma-bond complex. Calculations on ReH$\sb5\rm (PH\sb3)\sb3\cdot NH\sb3$ confirm the asymmetric 3-centered hydrogen bonding interaction. Infrared data using various complexes and hydrogen bond donors show that intermolecular H-bonding is not limited to complex 1 and that the major interaction is that between the M-H bond and the H-bond donor, with the metal lone pair playing, at most, a minor role, at least in the cases studied here.

Further investigation of oxidation by t-butyl hydroperoxide (TBHP) with (Mn$\rm \sb3O\sb4bipy\sb4(H\sb2O)\sb2\rbrack(ClO\sb4)\sb4$ (1) as catalyst indicates that the mechanism probably involves a radical chain autoxidation with a dimeric species as the active catalyst, not the nonradical mechanism catalyzed by the trimeric species originally suggested. Electron paramagnetic resonance (EPR) studies show that an organic radical, presumably the t-butylperoxy species, is formed on reaction of the catalyst with TBHP, with concomitant formation of a $\mu$-oxo dimer. The observation of trans- 9-decalol as a major product in oxidation of cis- decalin confirms the radical nature of the mechanism. The involvement of oxygen is shown by the observation that a nitrogen atmosphere reduces the amount of alcohol and ketone products formed, while increasing the amount of mixed peroxide product and is also suggested by the observation of typical autoxidation products in oxidations of alkenes.

Use of TBAO as primary oxidant with (Mn$\rm \sb3O\sb4bipy\sb4(H\sb2O)\sb2\rbrack(ClO\sb4)\sb4$ as catalyst shows markedly different reactivity to the TBHP system. In the oxidation of alkanes, a much higher selectivity for ketone is seen, as well as higher 3$\sp\circ$/2$\sp\circ$ selectivity. Additionally, whereas the TBHP system gives allylic oxidation or cleavage products with alkenes, tetrabutylammonium oxone (TBAO) gives mostly epoxides. The mechanism probably involves formation of a metal-oxo species. Epoxidation of cis- stilbene gives some trans- epoxide as well as benzophenone and trans- stilbene. This is most consistent with an epoxidation mechanism involving first a one-electron transfer possibly followed by collapse to a cationic species which then leads to the oxidation products.