Chemistry Research Laboratories , Mansfield Road, Oxford OX1 3TA, United Kingdom.
School of Chemistry, University of Edinburgh , Edinburgh EH9 3FJ, United Kingdom.
J Am Chem Soc. 2018 Jan 31;140(4):1481-1495. doi: 10.1021/jacs.7b11975. Epub 2018 Jan 22.
A systematic study of the catalyst structure and overall charge for the dehydropolymerization of HB·NMeH to form N-methyl polyaminoborane is reported using catalysts based upon neutral and cationic {Rh(Xantphos-R)} fragments in which PR groups are selected from Et, Pr, and Bu. The most efficient systems are based upon {Rh(Xantphos-Pr)}, i.e., [Rh(κ-P,O,P-Xantphos-Pr)(H)(η-HB·NMe)][BAr], 6, and Rh(κ-P,O,P-Xantphos-Pr)H, 11. While H evolution kinetics show both are fast catalysts (ToF ≈ 1500 h) and polymer growth kinetics for dehydropolymerization suggest a classical chain growth process for both, neutral 11 (M = 28 000 g mol, Đ = 1.9) promotes significantly higher degrees of polymerization than cationic 6 (M = 9000 g mol, Đ = 2.9). For 6 isotopic labeling studies suggest a rate-determining NH activation, while speciation studies, coupled with DFT calculations, show the formation of a dimetalloborylene [{Rh(κ-P,O,P-Xantphos-Pr)}B] as the, likely dormant, end product of catalysis. A dual mechanism is proposed for dehydropolymerization in which neutral hydrides (formed by hydride transfer in cationic 6 to form a boronium coproduct) are the active catalysts for dehydrogenation to form aminoborane. Contemporaneous chain-growth polymer propagation is suggested to occur on a separate metal center via head-to-tail end chain B-N bond formation of the aminoborane monomer, templated by an aminoborohydride motif on the metal.
报道了一种系统的研究，即研究 HB·NMeH 脱水聚合形成 N-甲基聚氨基硼烷的催化剂结构和整体电荷，所使用的催化剂基于中性和阳离子 {Rh(Xantphos-R)} 片段，其中 PR 基团选自 Et、Pr 和 Bu。最有效的体系基于 {Rh(Xantphos-Pr)}，即 [Rh(κ-P,O,P-Xantphos-Pr)(H)(η-HB·NMe)][BAr]，6 和 Rh(κ-P,O,P-Xantphos-Pr)H，11。虽然 H 演化动力学表明这两种都是快速催化剂（ToF ≈ 1500 h），而且脱水聚合的聚合物生长动力学表明这两种都是经典的链增长过程，但中性 11（M = 28 000 g mol，Đ = 1.9）促进的聚合度明显高于阳离子 6（M = 9000 g mol，Đ = 2.9）。对于 6，同位素标记研究表明 NH 活化是速率决定步骤，而形态研究结合 DFT 计算表明形成了二亚硼烯 [{Rh(κ-P,O,P-Xantphos-Pr)}B]，这是催化的可能休眠终产物。提出了一种双机制用于脱水聚合，其中中性氢化物（通过阳离子 6 中的氢化物转移形成硼翁副产物形成）是脱氢形成氨基硼烷的活性催化剂。同时建议通过氨基硼烷单体的头到尾端链 B-N 键形成，在金属上的氨基硼氢化物基序模板作用下，在单独的金属中心上同时发生链增长聚合物的聚合。
