Nozaki K, Komaki H, Kawashima Y, Hiyama T, Matsubara T
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501 Japan.
J Am Chem Soc. 2001 Jan 31;123(4):534-44. doi: 10.1021/ja001395p.
The regioselectivity of styrene insertion to an acyl-Pd bond was studied by NMR in (i) a stoichiomeric reaction and (ii) a copolymerization with CO. In the stoichiometric reaction of styrene with [(CH(3)CO)Pd(CH(3)CN)[(R,S)-BINAPHOS]].[B3,5-(CF(3))(2)C(6)H(3)], both 1,2- and 2,1-products were given. To mimic the real polymerization conditions, a polyketone-substituted complex [[CH(3)(CH(2)CHCH(3)CO)(n)]Pd[(R,S)-BINAPHOS]].[B(3,5-(CF(3))(2)C(6)H(3))(4)] (n approximately 14) was prepared. When this polymer-attached Pd species was treated with styrene, the 1,2-insertion product was the only detectable species. Thus, exclusive 1,2-insertion is demonstrated to be responsible for the styrene-CO copolymerization, in sharp contrast to the predominant 2,1-insertion with conventional nitrogen ligands. Chain-end analysis revealed that beta-hydride elimination took place from the 2,1-complex but not from the 1,2-complex. Thus, once 2,1-insertion occurs, rapid beta-hydride elimination proceeds to terminate the polymerization, as is common to the other phosphorus-ligand systems. The resulting Pd-H species re-initiates the copolymerization, as was proven by MALDI-TOF mass analysis of the product copolymers.
通过核磁共振研究了苯乙烯插入酰基钯键的区域选择性，具体包括：（i）化学计量反应，以及（ii）与一氧化碳的共聚反应。在苯乙烯与[(CH(3)CO)Pd(CH(3)CN)[(R,S)-BINAPHOS]].[B3,5-(CF(3))(2)C(6)H(3)]的化学计量反应中，同时生成了1,2-和2,1-产物。为模拟实际聚合条件，制备了一种聚酮取代的配合物[[CH(3)(CH(2)CHCH(3)CO)(n)]Pd[(R,S)-BINAPHOS]].[B(3,5-(CF(3))(2)C(6)H(3))(4)]（n约为14）。当用苯乙烯处理这种聚合物连接的钯物种时，唯一可检测到的物种是1,2-插入产物。因此，已证明专一的1,2-插入是苯乙烯-一氧化碳共聚反应的原因，这与使用传统氮配体时主要的2,1-插入形成鲜明对比。链端分析表明，β-氢消除发生在2,1-配合物上，而不是1,2-配合物上。因此，一旦发生2,1-插入，快速的β-氢消除就会使聚合反应终止，这在其他磷配体体系中很常见。产物共聚物的基质辅助激光解吸电离飞行时间质谱分析证明，生成的钯-氢物种会重新引发共聚反应。
