Vasanthakumar Aathith, Price Jeffrey S, Emslie David J H
Department of Chemistry, McMaster University 1280 Main Street West Hamilton Ontario L8S 4M1 Canada
Chem Sci. 2023 Jul 24;14(32):8514-8523. doi: 10.1039/d3sc01830j. eCollection 2023 Aug 16.
A palladium-catalyzed coupling reaction between 4,5-dibromo-2,7-di--butyl-9,9-dimethylxanthene and 2 equiv. of 1,3-diisopropylimidazolin-2-imine afforded the rigid neutral 2,7-di--butyl-4,5-bis(1,3-diisopropylimidazolin-2-imino)-9,9-dimethylxanthene (XII) pincer ligand. Reaction of XII with YCl(THF) provided [(XII)YCl] (1). However, compound 1 failed to react cleanly with 3 equiv. of LiCHSiMe, and the reaction of XII with [Y(CHSiMe)(THF)] afforded a complex mixture of products. To access group 3 alkyl complexes without the intermediacy of [(XII)M(CHSiMe)], the XII ligand was protonated using [H(OEt)][B(CF)] to form [H(XII)][B(CF)], and subsequent reaction with [M(CHSiMe)(THF)] (M = Y, Sc) directly afforded the cationic scandium and yttrium dialkyl complexes [(XII)M(CHSiMe)][B(CF)] {M = Y (2) and Sc (3)}. Reaction of 3 with B(CF) in CDBr afforded dicationic [(XII)Sc(CHSiMeCHSiMe)][MeB(CF)][B(CF)] (4) featuring a CHSiMeCHSiMe ligand, formed as a result of methyl anion abstraction from silicon, with concomitant migration of the neighbouring CHSiMe group from scandium to silicon. The MeB(CF) anion in 4 forms a contact ion pair. By contrast, reaction of 1 with [CPh][B(CF)] in CDBr/toluene or -CHF/toluene afforded dicationic [(XII)Sc(CHSiMe)(η-toluene)][B(CF)] (5). Compounds 2-4 showed negligible ethylene polymerization activity, whereas 5 is highly active (up to 870 kg mol h atm in -CHF/toluene under 1 atm of ethylene at room temperature).
4,5 - 二溴 - 2,7 - 二 - 丁基 - 9,9 - 二甲基呫吨与2当量的1,3 - 二异丙基咪唑啉 - 2 - 亚胺之间的钯催化偶联反应得到了刚性中性的2,7 - 二 - 丁基 - 4,5 - 双（1,3 - 二异丙基咪唑啉 - 2 - 亚氨基） - 9,9 - 二甲基呫吨（XII）钳形配体。XII与YCl（THF）反应得到[(XII)YCl]（1）。然而，化合物1与3当量的LiCHSiMe反应不彻底，且XII与[Y(CHSiMe)(THF)]反应得到的是复杂的产物混合物。为了在不经过[(XII)M(CHSiMe)]中间体的情况下得到第3族烷基配合物，使用[H(OEt)][B(CF)]将XII配体质子化形成[H(XII)][B(CF)]，随后与[M(CHSiMe)(THF)]（M = Y，Sc）反应直接得到阳离子钪和钇二烷基配合物[(XII)M(CHSiMe)][B(CF)] {M = Y (2)和Sc (3)}。3与B(CF)在CDBr中反应得到二价阳离子[(XII)Sc(CHSiMeCHSiMe)][MeB(CF)][B(CF)]（4），其具有一个CHSiMeCHSiMe配体，这是由于甲基阴离子从硅上夺取而形成的，同时相邻的CHSiMe基团从钪迁移到了硅上。4中的MeB(CF)阴离子形成了一个接触离子对。相比之下，1与[CPh][B(CF)]在CDBr/甲苯或 - CHF/甲苯中反应得到二价阳离子[(XII)Sc(CHSiMe)(η - 甲苯)][B(CF)]（5）。化合物2 - 4显示出可忽略不计的乙烯聚合活性，而5具有高活性（在室温下1个大气压的乙烯存在下，在 - CHF/甲苯中高达870 kg mol h atm）。
