Step-growth titanium-catalysed dehydropolymerisation of amine-boranes.
Step-growth titanium-catalysed dehydropolymerisation of amine-boranes.
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DOI：
10.1039/c7sc05395a
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发表时间：
2018-04-07
期刊：
影响因子：
8.4
通讯作者：
Manners I
中科院分区：
文献类型：
--
作者：
Jurca T;Dellermann T;Stubbs NE;Resendiz-Lara DA;Whittell GR;Manners I
伯胺硼烷的钛催化脱氢聚合被发现是通过逐步增长而不是链增长机制进行的。对伯胺-硼烷的脱氢聚合有活性的预催化剂通常基于中或后过渡金属。发现由CpR_2 TiCl_2和2nBuLi组成的预催化体系对仲胺硼烷Me_2NH·BH_3脱氢生成环状二硼氮烷[Me_2N-BH_2]_2的催化活性随CpR的供电子性增加而显著增加。将活性最高的预催化体系（CpR = η-C5 Me 5）应用于伯胺-硼烷MeNH 2·BH 3，首次实现了用前过渡金属催化剂合成高摩尔质量聚N-甲基氨基硼烷[MeNH-BH 2]n（聚丙烯的BN类似物）。值得注意的是，与其他用于MeNH 2·BH 3的脱氢聚合预催化剂如[Ir（POCOP）H2]、骨架镍和[Rh（COD）Cl]2不同，Ti预催化剂体系对包括BzNH 2·BH 3（Bz =苄基）在内的一系列底物也具有活性，从而产生高摩尔质量聚合物。此外，与后过渡金属催化的MeNH 2·BH 3的脱氢聚合以及烯烃的齐格勒-纳塔聚合相反，研究表明Ti催化的脱氢聚合反应通过逐步增长而不是链增长机制进行。
Titanium-catalysed dehydropolymerisation of primary amine–boranes was found to proceed via a step-growth rather than a chain-growth mechanism. Precatalysts active for the dehydropolymerisation of primary amine–boranes are generally based on mid or late transition metal. We have found that the activity of the precatalyst system formed from CpR2TiCl2 and 2nBuLi towards the dehydrogenation of the secondary amine–borane Me2NH·BH3, to yield the cyclic diborazane [Me2N–BH2]2, increases dramatically with increasing electron-donating character of the cyclopentadienyl rings (CpR). Application of the most active precatalyst system (CpR = η-C5Me5) to the primary amine–borane MeNH2·BH3 enabled the first synthesis of high molar mass poly(N-methylaminoborane), [MeNH–BH2]n, the BN analogue of polypropylene, by an early transition metal such as catalyst. Significantly, unlike other dehydropolymerization precatalysts for MeNH2·BH3 such as [Ir(POCOP)H2], skeletal nickel, and [Rh(COD)Cl]2, the Ti precatalyst system was also active towards a range of substrates including BzNH2·BH3 (Bz = benzyl) yielding high molar mass polymer. Moreover, in contrast to the late transition metal catalysed dehydropolymerisation of MeNH2·BH3 and also the Ziegler–Natta polymerisation of olefins, studies indicate that the Ti-catalyzed dehydropolymerization reactions proceed by a step-growth rather than a chain-growth mechanism.
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