Journal of Molecular Catalysis A-Chemical, Vol.254, No.1-2, 165-173, 2006
In situ NMR investigations into the ADMET-reaction of 1,4-diheptyloxy-2,5-divinylbenzene via a Schrock-type molybdenum alkylidene complex
The acyclic diene metathesis (ADMET) polycondensation of 1,4-diheptyloxy-2,5-divinylbenzene (DHepODVB) with the Schrock-type alkylidene complex Mo(NArMe2)(CHCMe2Ph)[OCMe(CF3)(2)](2) was investigated by means of in situ H-1/C-13 NMR spectroscopy. Efforts were made to a gain insight into the reaction mechanism and explain the relatively high reaction temperatures (> 60 degrees C instead of room temperature in the case of the diheptylsubstituted analog) necessary to achieve useful reaction rates. Different reaction charges were investigated in dependence on reaction time and ratio catalyst/monomer. At least four novel alkylidene species were detected of which three species could be assigned to structures (two of which are binuclear, presumably due to the nearly stoichiometric ratios catalyst/monomer). These three structures show a Mo-coordination from the oxygen of a heptyloxy side chain from the substrate resulting in stabilized intermediates. These intermediates act as low energy "traps" that make the higher reaction temperatures necessary. The stabilization also seems to effect decomposition of active species, substantially slowing it down. Even after 24 days, alkylidene signals could be detected without noticeable reduction in relative amount. (c) 2006 Elsevier B.V. All rights reserved.