钴催化的氨硼烷脱氢：氢化钴-氨基硼烷配合物的机理分析与分离,Organometallics

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钴催化的氨硼烷脱氢：氢化钴-氨基硼烷配合物的机理分析与分离
Organometallics ( IF 2.5 ) Pub Date : 2020-07-28 , DOI: 10.1021/acs.organomet.0c00459
Joseph W. Nugent ₁ , Max García-Melchor ₂ , Alison R. Fout ₁

Affiliation

Co（I）络合物，具有富电子的单阴离子双（卡宾）芳基钳夹配体（^Mes CCC）（^Mes CCC =双（2,4,6-三甲基苯基-苯并咪唑-2-亚基）苯基），（^Mes CCC）发现Co-py（1）在60°C下将四氢呋喃中的氨硼烷（NH ₃ BH ₃，AB）催化脱氢。该过程每个AB释放1.7±0.1当量的H ₂，同时形成可溶性（硼嗪和聚硼氮烯）和不溶性（聚（氨基硼烷））含BN的物质。为帮助阐明在催化条件下存在的Co物种，在室温下将1与化学计量的AB在THF中反应，生成（^MesCCC）CoH（NH ₂ BH ₃）（2），是第一种表征的后期过渡金属氢化物-氨基硼烷络合物。该络合物的特征在于多核（¹ H，¹¹ B和¹³ C）NMR和IR光谱学以及X射线晶体学。的形成2经由跨越的钴（I）中心AB的N-H活化1通过的反应确认1与AB的氘化同位素异数，并通过密度泛函理论（DFT）计算的方法计算支持。分离物2被证明可催化AB脱氢，形成类似于1的含BN产物，尽管速度较慢。在两个以1或2作为催化剂的反应中，在AB的整个催化脱氢过程中均观察到2。DFT计算揭示了从2形成氨基硼烷（NH ₂ BH ₂）的可行途径，可溶性含BN产物的产生以及AB的金属上低聚以产生不溶性聚合物。本文报道的络合物代表AB脱氢的均相钴催化剂的稀有实例。

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Cobalt-Catalyzed Ammonia Borane Dehydrogenation: Mechanistic Insight and Isolation of a Cobalt Hydride-Amidoborane Complex

A Co(I) complex featuring the electron-rich monoanionic bis(carbene) aryl pincer ligand (^MesCCC) (^MesCCC = bis(2,4,6-trimethylphenyl-benzimidazol-2-ylidene)phenyl), (^MesCCC)Co-py (1), was found to catalytically dehydrogenate ammonia borane (NH₃BH₃, AB) in THF at 60 °C. This process releases 1.7 ± 0.1 equiv of H₂ per AB with simultaneous formation of both soluble (borazine and polyborazylene) and insoluble (poly(aminoborane)) BN-containing species. To help elucidate the Co species present under the catalytic conditions, 1 was reacted with a stoichiometric amount of AB in THF at room temperature, yielding (^MesCCC)CoH(NH₂BH₃) (2), the first characterized hydride-amidoborane complex of a late transition metal. This complex was characterized by multinuclear (¹H, ¹¹B, and ¹³C) NMR and IR spectroscopies as well as X-ray crystallography. Formation of 2 via N–H activation of AB across the Co(I) center of 1 was confirmed by the reaction of 1 with the deuterated isotopologues of AB and was supported computationally by means of density functional theory (DFT) calculations. Isolated 2 was shown to catalyze AB dehydrogenation, forming BN-containing products similar to 1, albeit at a slower rate. In both reactions starting with 1 or 2 as the catalyst, 2 is observed throughout the catalytic dehydrogenation of AB. DFT calculations revealed plausible pathways for the formation of aminoborane (NH₂BH₂) from 2, the generation of soluble BN-containing products, as well as the on-metal oligomerization of AB to produce the insoluble polymeric species. The complexes reported herein represent rare examples of homogeneous cobalt catalysts for the dehydrogenation of AB.

更新日期：2020-08-10

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