Latent and Air-Stable Pre-Catalysts for the Polymerization of Dicyclopentadiene: From Penta- to Hexacoordination in Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes.

The pentacoordinated, 16-valence electron (VE) Mo imido alkylidene N-heterocyclic carbene (NHC) complexes I1-I5 and the hexacoordinated 18-VE Mo imido alkylidene NHC complexes 1-4, 8, 10 and 12 containing a chelating ligand have been prepared and used as thermally latent catalysts in the ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD). Both 10 and 12 are the first Mo imido alkylidene complexes with a chelating alkylidene featuring a carboxylate group. Complexes I1-I3 and I5 as well as 1-4 proved to be fully thermally latent in the presence of DCPD. With the changes in both the electronic and steric situation at the imido ligand provided by these pre-catalysts, different temperatures of the onset of polymerization (Tonset =65-140 °C) and for the exothermic maximum of the curing curve (Texo,max =98-183 °C) of DCPD were achieved. Also, the degree of crosslinking was successfully varied as indicated by swelling experiments in toluene, which revealed degrees of swelling between 0 and 50 %. While the introduction of a chelating alkylidene increases Tonset , the introduction of more electron-donating anionic ligands (tert-butoxide, phenoxide) resulted in a drastic reduction in Tonset , underlining the high flexibility of these systems. The hexacoordinated high-oxidation state molybdenum imido alkylidene NHC complexes 2, 3 and 4 were stable under air for at least twelve hours in the solid state.

制备了五配位、16价电子（VE）的钼亚氨基卡宾（NHC）配合物I1 - I5以及含有螯合配体的六配位、18价电子的钼亚氨基卡宾NHC配合物1 - 4、8、10和12，并将它们用作双环戊二烯（DCPD）开环易位聚合（ROMP）的热潜伏性催化剂。10和12是首批具有含羧酸盐基团的螯合亚烷基的钼亚氨基卡宾配合物。配合物I1 - I3、I5以及1 - 4在DCPD存在下被证明是完全热潜伏的。通过这些预催化剂在亚氨基配体上的电子和空间情况的改变，实现了DCPD不同的聚合起始温度（起始温度\(T_{onset}=65 - 140^{\circ}C\)）以及固化曲线的放热最大值温度（\(T_{exo,max}=98 - 183^{\circ}C\)）。此外，如甲苯中的溶胀实验所示，交联程度也成功地发生了变化，溶胀度在0到50%之间。虽然螯合亚烷基的引入提高了起始温度，但更多供电子的阴离子配体（叔丁氧基、苯氧基）的引入导致起始温度大幅降低，这突出了这些体系的高度灵活性。六配位的高氧化态钼亚氨基卡宾NHC配合物2、3和4在固态下在空气中至少稳定12小时。