Laboratory of Organometallic Chemistry and Homogeneous Catalysis, Institut de Chimie (B6a), Université de Liège, Sart-Tilman par 4000 Liège, Belgium.
Dalton Trans. 2013 May 28;42(20):7287-96. doi: 10.1039/c2dt31520c.
The deprotonation of 1,3-dimesitylbenzimidazolium tetrafluoroborate with a strong base afforded 1,3-dimesitylbenzimidazol-2-ylidene (BMes), which was further reacted in situ with rhodium or ruthenium complexes to afford three new organometallic products. The compounds [RhCl(COD)(BMes)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BMes)] were used to probe the steric and electronic parameters of BMes. Comparison of the percentage of buried volume (%V(Bur)) and of the Tolman electronic parameter (TEP) of BMes with those determined previously for 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-dimesitylimidazolin-2-ylidene (SIMes) revealed that the three N-heterocyclic carbenes (NHCs) had very similar profiles. Nonetheless, changes in the hydrocarbon backbone subtly affected the stereoelectronic properties of these ligands. Accordingly, the corresponding [RuCl2(PCy3)(NHC)(=CHPh)] complexes displayed different catalytic behaviors in the ring-closing metathesis (RCM) of α,ω-dienes. In the benchmark cyclization of diethyl 2,2-diallylmalonate, the new [RuCl2(PCy3)(BMes)(=CHPh)] compound (1d) performed slightly better than the Grubbs second-generation catalyst (1a), which was in turn significantly more active than the related [RuCl2(PCy3)(IMes)(=CHPh)] initiator (1b). For the formation of a model trisubstituted cycloolefin, complex 1d ranked in-between catalyst precursors 1a and 1b, whereas in the RCM of tetrasubstituted cycloalkenes it lost its catalytic efficiency much more rapidly.
用强碱将 1,3-二甲基苯并咪唑𬭩四氟硼酸盐去质子化得到 1,3-二甲基苯并咪唑-2-亚基（BMes），然后将其与铑或钌配合物就地反应，得到三种新的有机金属产物。化合物 [RhCl(COD)(BMes)]（COD 是 1,5-环辛二烯）和 cis-[RhCl(CO)2(BMes)] 用于探究 BMes 的空间和电子参数。将 BMes 的埋藏体积百分比（%V(Bur)）和 Tolman 电子参数（TEP）与之前确定的 1,3-二甲基咪唑-2-亚基（IMes）和 1,3-二甲基咪唑啉-2-亚基（SIMes）进行比较，结果表明三种 N-杂环卡宾（NHC）具有非常相似的特性。尽管如此，烃基骨架的变化还是会微妙地影响这些配体的立体电子性质。因此，相应的 [RuCl2(PCy3)(NHC)(=CHPh)] 配合物在 α,ω-二烯的闭环复分解（RCM）中表现出不同的催化行为。在二乙基 2,2-二烯丙基丙二酸酯的基准环化反应中，新的 [RuCl2(PCy3)(BMes)(=CHPh)] 化合物（1d）的性能略优于第二代 Grubbs 催化剂（1a），而 1a 又明显比相关的 [RuCl2(PCy3)(IMes)(=CHPh)] 引发剂（1b）更具活性。对于模型三取代环烯烃的形成，1d 排名在催化剂前体 1a 和 1b 之间，而在四取代环烯烃的 RCM 中，其催化效率迅速下降。
