Synthesis and Applications of RuCl₂(CHR‘)(PR₃)₂: The Influence of the Alkylidene Moiety on Metathesis Activity

The reactions of RuCl2(PPh3)3 with a number of diazoalkanes were surveyed, and alkylidene transfer to give RuCl2(CHR)(PPh3)2 (R = Me (1), Et (2)) and RuCl2(CH-p-C6H4X)(PPh3)2 (X = H (3), NMe2 (4), OMe (5), Me (6), F (7), Cl (8), NO2 (9)) was observed for alkyl diazoalkanes RCHN2 and various para-substituted aryl diazoalkanes p-C6H4XCHN2. Kinetic studies on the living ring-opening metathesis polymerization (ROMP) of norbornene using complexes 3−9 as catalysts have shown that initiation is in all cases faster than propagation (ki/kp = 9 for 3) and that the electronic effect of X on the metathesis activity of 3−9 is relatively small. Phosphine exchange in 3−9 with tricyclohexylphosphine leads to RuCl2(CH-p-C6H4X)(PCy3)2 10−16, which are efficient catalysts for ROMP of cyclooctene (PDI = 1.51−1.63) and 1,5-cyclooctadiene (PDI = 1.56−1.67). The crystal structure of RuCl2(CH-p-C6H4Cl)(PCy3)2 (15) indicated a distorted square-pyramidal geometry, in which the two phosphines are trans to each other, and the alkylidene unit lies in the Cl−Ru−Cl plane. The benzylidenes RuCl2(CHPh)(PR3)2 (R = Cy (cyclohexyl) (10), Cp (cyclopentyl) (17), i-Pr (18)) are quantitatively available via one-pot synthesis with RuCl2(PPh3)3, PhCHN2, and PR3 as reaction components. 10 is an efficient catalyst for metathesis of acyclic olefins: On reaction with excess ethylene, the methylidene complex RuCl2(CH2)(PCy3)2 (19) is formed quantitatively, and various alkylidene compounds RuCl2(CHR)(PCy3)3 (R = Me (20), Et (21), n-Bu (22)) are isolated as the kinetic products from the reaction of 10 with an excess of the corresponding terminal or disubstituted olefins. Metathesis of conjugated and cumulated olefins with 10 results in the formation of vinylalkylidene and vinylidene complexes, as shown by the synthesis of RuCl2(CHCHCH2)(PCy3)2 (23) and RuCl2(CCH2)(PCy3)2 (24) from 1,3-butadiene or 1,2-propadiene, respectively. Also, functional groups such as −OAc, −Cl, and −OH can be introduced into the alkylidene moiety via cross metathesis with the appropriate alkene.本研究考察了三(三苯基膦)二氯化钌(RuCl₂(PPh₃)₃)与多种重氮烷烃的反应，观察到发生亚烷基转移反应，生成RuCl₂(=CHR)(PPh₃)₂（R=Me（1）、Et（2））以及RuCl₂(=CH-p-C₆H₄X)(PPh₃)₂（X=H（3）、NMe₂（4）、OMe（5）、Me（6）、F（7）、Cl（8）、NO₂（9）），其中烷基重氮烷烃RCHN₂和各类对位取代芳基重氮烷烃p-C₆H₄XCHN₂均可参与该反应。以配合物3~9为催化剂，对降冰片烯的活性开环易位聚合（ring-opening metathesis polymerization, ROMP）开展动力学研究，结果表明所有体系的引发速率均快于增长速率（配合物3的k_i/k_p=9），且取代基X的电子效应对3~9的易位催化活性影响相对较小。将配合物3~9与三环己基膦进行膦配体交换反应，可得到RuCl₂(=CH-p-C₆H₄X)(PCy₃)₂（10~16），该类配合物是环辛烯（多分散性指数PDI=1.51~1.63）与1,5-环辛二烯（PDI=1.56~1.67）开环易位聚合的高效催化剂。对配合物RuCl₂(=CH-p-C₆H₄Cl)(PCy₃)₂（15）的晶体结构解析结果显示，其具有扭曲的四方锥几何构型：两个膦配体相互处于反位，亚烷基单元位于Cl-Ru-Cl平面内。亚苄基配合物RuCl₂(=CHPh)(PR₃)₂（R=Cy（环己基，10）、Cp（环戊基，17）、i-Pr（异丙基，18））可通过以RuCl₂(PPh₃)₃、PhCHN₂与PR₃为原料的一锅法反应定量制备。配合物10是无环烯烃易位反应的高效催化剂：当与过量乙烯反应时，可定量生成亚甲基配合物RuCl₂(=CH₂)(PCy₃)₂（19）；将10与过量对应末端或双取代烯烃反应时，可分离得到各类动力学产物亚烷基化合物RuCl₂(=CHR)(PCy₃)₃（R=Me（20）、Et（21）、n-Bu（22））。利用配合物10与共轭及累积烯烃发生易位反应，可生成乙烯基亚烷基与亚乙烯基配合物：例如分别以1,3-丁二烯与1,2-丙二烯为原料，可合成RuCl₂(=CHCH=CH₂)(PCy₃)₂（23）与RuCl₂(=C=CH₂)(PCy₃)₂（24）。此外，通过与对应烯烃的交叉易位反应，可将-OAc（乙酰氧基）、-Cl与-OH等官能团引入亚烷基配体骨架中。