Phosphabicyclononane-containing ru complexes: efficient pre-catalysts for olefin metathesis reactions.

The catalytic performances of three Phosphabicyclononane (Phoban)-containing ruthenium-based pre-catalysts have been evaluated for metathesis transformations. A wide screening of substrates in ring-closing metathesis reactions reveals the greater efficiency of pre-catalyst 4. Comparison of the catalytic activities of 4 with Grubbs' first-generation pre-catalyst illustrates the key role of the Phoban ligand. Additionally, a comparative study of three Phoban-containing pre-catalysts has been conducted for the self-metathesis of 1-octene at low catalyst loading (25-100 ppm).

High-resolution solid-state NMR studies of poly(vinyl phosphonic acid) proton-conducting polymer: molecular structure and proton dynamics.

The structure and the local proton mobility of poly(vinyl phosphonic acid) were studied by solid-state NMR under fast magic-angle spinning. At elevated temperatures, the signature of the hydrogen-bonded P-OH protons is observed in 1H magic-angle spinning (MAS) NMR as a single resonance at 10.5 ppm. Both 1H double-quantum NMR and variable-temperature experiments demonstrate that P-OH protons are mobile and thus able to contribute to proton conductivity. Below room temperature, two different types of hydrogen-bonded P-OH resonances are observed at 10.5 and 15 ppm, and 1H double-quantum NMR demonstrates that these protons are immobile on the NMR time scale. By means of first-principles calculations of a model polymer, we have assigned the additional hydrogen-bonded species at lower temperatures to phosphonic acid anhydride and charged anhydride. Also, in the 31P MAS NMR spectrum, two distinct resonances appear, arising from "normal" phosphonic acid and phosphonic acid anhydride. 31P double-quantum NMR experiments reveal that there is no phase segregation between normal and phosphonic acid anhydride and the condensation reaction occurs randomly throughout the system. The formation of acid anhydride leads to a decrease in proton conductivity through two mechanisms, (1) decrease in the number of charge carriers and (2) blockage of charge transport pathways through immobilization of charge carriers together with a hindered reorientation of the anhydride group. Our results provide strong evidence for these mechanisms by demonstrating that the conductivity is greatly influenced by the presence of phosphonic acid anhydride.

DFT prediction and experimental observation of substrate-induced catalyst decomposition in ruthenium-catalyzed olefin metathesis.

Ruthenacyclobutane decomposition, involving competitive beta-hydride transfer to Ru and reductive olefin elimination during ruthenium-catalyzed olefin metathesis, is predicted by density functional theory calculations and experimentally confirmed by propene and butene formation during degenerate Ru-methylidene-catalyzed metathesis of ethylene. The results provide new focus on the nature of ruthenium metathesis catalyst decomposition under catalytic conditions.

Preparation and characterisation of palladium, platinum and manganese di(organo)carbene complexes from quinolinone and quinolinium precursors.

A series of palladium, platinum and manganese di(organo)carbene complexes have been prepared from 4-chloro-N-methylquinolinone by processes that involve alkylation before or after attachment to the metal unit; the nucleophilic heteroatoms are separated from the C-donor atom by three bonds.