Heterogeneous Olefin Hydrogenation Enabled by a Highly-Reduced Nickel(-II) Catalyst Precursor.
Thomas M Maier1, Sebastian Sandl2, Peter Melzl3
1University of Regensburg, Institute of Inorganic Chemistry, 93040, Regensburg, Germany.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|February 9, 2020
Summary
A novel nickel catalyst enables efficient hydrogenation of diverse unsaturated compounds, including challenging sterically hindered olefins. Mild reaction conditions are compatible with various functional groups, suggesting broad applicability in organic synthesis.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Organic Synthesis
Background:
- Hydrogenation is a fundamental transformation in organic chemistry, crucial for synthesizing various valuable compounds.
- Developing efficient and selective catalysts for hydrogenation, especially for challenging substrates like sterically hindered olefins, remains an active area of research.
- Nickel-based catalysts offer a cost-effective alternative to precious metal catalysts, but their application in broad hydrogenation reactions requires careful catalyst design.
Purpose of the Study:
- To develop a novel pre-catalyst for efficient hydrogenation of a wide range of unsaturated substrates.
- To investigate the compatibility of the catalytic system with diverse functional groups under mild conditions.
- To elucidate the catalytic mechanism, particularly the role of nickel nanoparticles.
Main Methods:
- Synthesis and characterization of the dilithiumbis(cycloocta-1,5-diene)nickelate(-II) pre-catalyst.
- Hydrogenation reactions of various olefins, styrenes, enoates, imines, and sterically hindered tri-substituted olefins.
- Mechanistic investigations including reaction progress analysis, poisoning experiments, and multinuclear NMR spectroscopy.
Main Results:
- The pre-catalyst successfully facilitated the hydrogenation of a broad spectrum of unsaturated compounds, including sterically demanding substrates.
- The catalytic system demonstrated tolerance towards hydroxyl, halide, ester, and lactone functionalities, highlighting its functional group compatibility.
- Mechanistic studies provided evidence for a heterotopic catalytic system involving nickel nanoparticles.
Conclusions:
- Dilithiumbis(cycloocta-1,5-diene)nickelate(-II) serves as an effective pre-catalyst for mild and functional-group-tolerant hydrogenation.
- The catalytic process operates via a heterotopic nickel nanoparticle mechanism.
- This methodology offers a valuable new tool for organic synthesis, particularly for the reduction of challenging olefins.
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