Rethinking the Claisen-Tishchenko Reaction.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Aldehyde disproportionation is a crucial organic transformation.
• Developing efficient and selective catalysts for this reaction remains an active area of research.
• Outer-sphere catalysis offers a distinct mechanistic pathway for chemical transformations.

Purpose of the Study:

• To investigate the catalytic activity of novel pincer-type osmium complexes in aldehyde disproportionation.
• To elucidate the reaction mechanism, focusing on the role of the N-H group.
• To achieve high catalytic efficiency in terms of turnover frequencies.

Main Methods:

• Synthesis and characterization of pincer-type osmium complexes.
• Catalytic testing of the complexes in aldehyde disproportionation reactions.
• Density Functional Theory (DFT) calculations to probe the reaction mechanism.

Main Results:

• The synthesized osmium complexes, [OsH2(CO){PyCH2NHCH2CH2NHPtBu2}] and [OsH2(CO){HN(CH2CH2PiPr2)2}], effectively catalyze aldehyde disproportionation.
• The reaction proceeds via an outer-sphere bifunctional mechanism.
• Turnover frequencies reached up to 14,000 h⁻¹.
• DFT calculations confirmed the crucial role of the N-H group in the catalytic cycle.

Conclusions:

• Pincer-type osmium complexes with an N-H group are highly active catalysts for aldehyde disproportionation.
• The outer-sphere bifunctional mechanism, facilitated by the N-H group, enables high catalytic efficiency.
• These findings contribute to the development of advanced catalytic systems for organic synthesis.