Max Planck Research Group - Synergistic Organometallic Catalysis

In nature, chemical bonds are constructed and ruptured with exceptional levels of precision. Synergies and cooperation within the constituent parts are crucial to these systems. As a catalyst works synchronously with its surroundings, it creates favorable kinetic and thermodynamic conditions for activating, breaking, and transforming chemical bonds. By imitating this approach, researchers have been able to activate and convert a variety of small inert molecules with significant biological and industrial implications. Traditional catalytic protocols convert substrates into a single product, preferably or even exclusively. In contrast, catalysts can also be viewed as systems whose activity can be adjusted by fine-tuning reaction conditions to convey distinct product platforms.

Developing dynamic and adaptive molecular systems capable of controlling challenging bond activation processes is essential to our research program.^[1]

One of our projects aimed to investigate whether a catalyst could, based on the reaction conditions, open divergent reaction pathways by engaging the intrinsic chemical bonds of a primary functional group (e.g., aldehyde, Figure 1).^[2] Using aldehyde as an example, such a system might be able to address C=O (Figure 1, blue) and C-H (Figure 1, red) bonds separately in order to generate different products. As a result, nitriles and amides could be generated in highly selective manners under mild reaction conditions.

In a complementary approach, we hypothesized that implementing a polarized cooperative domain within a catalytic system might develop an adaptive platform.^[3] Specifically, our approach involved using a ligand environment presenting an attached borane arm to challenge and tame the reactivity of the metal center (Figure 2). Because both partners have unique electronic properties, a polarized environment is created, which can capture, lock, activate, and convert substrates. The developed system was tested for the hydrogenation of nitroarenes to evaluate the reactivity of the catalyst and its propensity to adapt its reactivity. As a result, our system has been found to provide anilines (complete hydrogenation) and hydroxylamines (controlled hydrogenation) in excellent yields under mild conditions while preserving the integrity of other potentially vulnerable functional groups.

The selective activation of C-F bonds remains challenging, particularly for electron-rich substrates. To tackle this challenge of bond activation, we took advantage of a delicate interaction between Rh(DMPE)₂H fragments and secondary phosphine oxides (HP(O)nBu₂) to catalyze the hydrodefluorination of perfluoroarenes (Figure 3).^[4] Aside from substrates with electron-withdrawing functional groups, this system was highly tolerant of extremely rare electron-donating functionalities.

In a recent initiative, our research concentrated on the formation of carbon-carbon bonds, with a particular focus on integrating a single carbon atom into aldehydes to synthesize silyl enol ethers.^[5] Our approach was to devise a strategy that would meet the specific requirements of the substrate. Central to our methodology is a novel catalytic system that merges a cobalt catalyst with a boron site, working in tandem to optimize substrate activation. Specifically, the boron site is directed towards the carbonyl group, whereas the cobalt site engages with (trimethylsilyl)diazomethane. This dual activation strategy is pivotal for the efficient carbon atom transfer that is fundamental to the carbon-carbon bond formation. This process not only successfully attaches the -SiMe₃ group to the resulting alcohol functionality but also ensures that nitrogen is the sole byproduct (Figure 4).