Beyond the triple bond: unlocking dinitrogen activation with tailored superbase phosphines†

IF 3.5 3区 化学 Q2 CHEMISTRY, INORGANIC & NUCLEAR
Vilakkathala U. Krishnapriya and Cherumuttathu H. Suresh
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Abstract

Activating atmospheric dinitrogen (N2), a molecule with a remarkably strong triple bond, remains a major challenge in chemistry. This theoretical study explores the potential of superbase phosphines, specifically those decorated with imidazolin-2-imine ((ImN)3P) and imidazolin-2-methylidene ((ImCH)3P) to facilitate N2 activation and subsequent hydrazine (H2NNH2) formation. Using density functional theory (DFT) at the M06L/6-311++G(d,p) level, we investigated the interactions between these phosphines and N2. Mono-phosphine–N2 complexes exhibit weak, noncovalent interactions (−0.6 to −7.1 kcal mol−1). Notably, two superbasic phosphines also form high-energy hypervalent complexes with N2, albeit at significantly higher energies. The superbasic nature and potential for the hypervalency of these phosphines lead to substantial N2 activation in bis-phosphine–N2 complexes, where N2 is “sandwiched” between two phosphine moieties through hypervalent P–N bonds. Among the phosphines studied, only (ImN)3P forms an exothermic sandwich complex with N2, stabilized by hydrogen bonding between the ImN substituents and the central N2 molecule. A two-step, exothermic hydrogen transfer pathway from (ImN)3P to N2 results in the formation of a bis-phosphine–diimine (HNNH) sandwich complex. Subsequent hydrogen transfer leads to the formation of a bis-phosphine–hydrazine (H2NNH2) complex, a process that, although endothermic, exhibits surmountable activation barriers. The relatively low energy requirements for this overall transformation suggest its potential feasibility under the optimized conditions. This theoretical exploration highlights the promise of superbase phosphines as a strategy for metal-free N2 activation, opening doors for the development of more efficient and sustainable nitrogen fixation and utilization methods.

Abstract Image

超越三键:利用太湖超碱基膦实现二氮活化
大气中的二氮(N2)是一种具有极强三键的分子,激活这种分子仍然是化学领域的一大挑战。本理论研究探讨了超碱基膦的潜力,特别是那些用咪唑啉-2-亚胺((ImN)3P)和咪唑啉-2-亚甲基((ImCH)3P)装饰的膦,以促进 N2 的活化和随后肼(H2NNH2)的形成。我们在 M06L/6-311++G(d,p) 水平上利用密度泛函理论(DFT)研究了这些膦与 N2 之间的相互作用。单膦-N2 复合物表现出弱的非共价相互作用(-0.6 至 -7.1 kcal/mol)。值得注意的是,两种超碱基膦也能与 N2 形成高能超价络合物,尽管能量要高得多。这些膦的超基性和潜在的高价性导致 N2 在双膦-N2 复合物中被大量活化,在这种复合物中,N2 通过高价 P-N 键被 "沙织 "在两个膦分子之间。在所研究的膦中,只有 (ImN)3P 与 N2 形成了放热的夹心复合物,并通过 ImN- 取代基与中心 N2 分子之间的氢键而稳定下来。从 (ImN)3P 到 N2 的两步放热氢转移途径导致形成双膦二胺(HNNH)夹心复合物。随后的氢转移导致形成双膦-肼(H2NNH2)复合物,这一过程虽然是内热的,但却表现出可以克服的活化障碍。这种整体转化所需的能量相对较低,这表明它在优化条件下具有潜在的可行性。这一理论探索凸显了超级碱基膦作为一种无金属氮活化策略的前景,为开发更高效、更可持续的氮固定和利用方法打开了大门。
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来源期刊
Dalton Transactions
Dalton Transactions 化学-无机化学与核化学
CiteScore
6.60
自引率
7.50%
发文量
1832
审稿时长
1.5 months
期刊介绍: Dalton Transactions is a journal for all areas of inorganic chemistry, which encompasses the organometallic, bioinorganic and materials chemistry of the elements, with applications including synthesis, catalysis, energy conversion/storage, electrical devices and medicine. Dalton Transactions welcomes high-quality, original submissions in all of these areas and more, where the advancement of knowledge in inorganic chemistry is significant.
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