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Structural transformation and catalytic hydrogenation activity of amidinate-protected copper hydride clusters.

ABSTRACT: Copper hydrides are important hydrogenation catalysts, but their poor stability hinders the practical applications. Ligand engineering is an effective strategy to tackle this issue. An amidinate ligand, N,N'-Di(5-trifluoromethyl-2-pyridyl)formamidinate (Tf-dpf) with four N-donors has been applied as a protecting agent in the synthesis of stable copper hydride clusters: Cu₁₁H₃(Tf-dpf)₆(OAc)₂ (Cu₁₁) with three interfacial μ₅-H and [Cu₁₂H₃(Tf-dpf)₆(OAc)₂]·OAc (Cu₁₂) with three interstitial μ₆-H. A solvent-triggered reversible interconversion between Cu₁₁ and Cu₁₂ has been observed thanks to the flexibility of Tf-dpf. Cu₁₁ shows high activity in the reduction of 4-nitrophenol to 4-aminophenol, while Cu₁₂ displays very low activity. Deuteration experiments prove that the type of hydride is the key in dictating the catalytic activity, for the interfacial μ₅-H species in Cu₁₁ are involved in the catalytic cycle whereas the interstitial μ₆-H species in Cu₁₂ are not. This work highlights the role of hydrides with regard to catalytic hydrogenation activity.

SUBMITTER: Liu CY

PROVIDER: S-EPMC9018778 | biostudies-literature | 2022 Apr

REPOSITORIES: biostudies-literature

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Structural transformation and catalytic hydrogenation activity of amidinate-protected copper hydride clusters.

Liu Chun-Yu CY Yuan Shang-Fu SF Wang Song S Guan Zong-Jie ZJ Jiang De-En DE Wang Quan-Ming QM

Nature communications 20220419 1

Copper hydrides are important hydrogenation catalysts, but their poor stability hinders the practical applications. Ligand engineering is an effective strategy to tackle this issue. An amidinate ligand, N,N'-Di(5-trifluoromethyl-2-pyridyl)formamidinate (Tf-dpf) with four N-donors has been applied as a protecting agent in the synthesis of stable copper hydride clusters: Cu11H3(Tf-dpf)6(OAc)2 (Cu11) with three interfacial μ5-H and [ ...[more]

PMID: 35440582

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Project description:Abstract Recently, it was shown that the double Ca−H−Ca‐bridged calcium hydride cation dimer [LCaH2CaL]2+ when stabilized by a larger macrocyclic N,N’,N’’,N’’’,N’’’’‐pentadentate ligand showed evidently higher activity than when stabilized by a smaller N,N’,N’’,N’’’‐tetradentate ligand in the catalytic hydrogenation of unactivated 1‐alkenes. In this DFT‐mechanistic work, the origin of the observed ring‐size effect is examined in detail using 1‐hexene, CH2=CH2 and H2 as substrates. It is shown that, at room temperature, both the N,N’,N’’,N’’’,N’’’’‐stabilized dimer and the monomer are not coordinated by THF in solution, while the corresponding N,N’,N’’,N’’’‐stabilized structures are coordinated by one THF molecule mimicking the fifth N‐coordination. Catalytic 1‐alkene hydrogenation may occur via anti‐Markovnikov addition over the terminal Ca−H bonds of transient monomers, followed by faster Ca−C bond hydrogenolysis. The higher catalytic activity of the larger N,N’,N’’,N’’’,N’’’’‐stabilized dimer is due to not only easier formation of but also due to the higher reactivity of the catalytic monomeric species. In contrast, despite unfavorable THF‐coordination in solution, the smaller N,N’,N’’,N’’’‐stabilized dimer shows a 3.2 kcal mol−1 lower barrier via a dinuclear cooperative Ca−H−Ca bridge for H2 isotope exchange than the large N,N’,N’’,N’’’,N’’’’‐stabilized dimer, mainly due to less steric hindrance. The observed ring‐size effect can be understood mainly by a subtle interplay of solvent, steric and cooperative effects that can be resolved in detail by state‐of‐the‐art quantum chemistry calculations. The catalytic activity of double Ca−H−Ca‐bridged calcium hydride cation dimer complexes is influenced by using macrocyclic tetra‐ or pentadentate ligands. Extensive dispersion‐corrected DFT calculations disclose that this influence is due to a subtle balance of solvent, steric and dinuclear cooperative effects that also depend on the substrate.

Dataset Information

Structural transformation and catalytic hydrogenation activity of amidinate-protected copper hydride clusters.

Publications

Structural transformation and catalytic hydrogenation activity of amidinate-protected copper hydride clusters.

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