Straightforward Access to High-Performance Organometallic Catalysts by Fluoride Activation: Proof of Principle on Asymmetric Cyanation, Asymmetric Michael Addition, CO₂ Addition to Epoxide, and Reductive Alkylation of Amines by Tetrahydrofuran

Abstract

We demonstrate that well-known transition metal catalysts can be transformed into high-performance versions by the simple use of a fluoride anion source. In situ fluoride-activated catalysts are highly active catalytic species. The isolation may lead to degradation of the species or a decrease in catalytic activity. Fluoride activation of known, relatively simple catalysts resulted in the development of one of the most efficient catalytic systems for the asymmetric cyanation of aldehydes, asymmetric Michael addition, and synthesis of cyclic carbonates. Furthermore, the fluoride-assisted reductive opening of tetrahydrofuran (THF) with amines was developed. We believe that the proposed approach can find broad applications in the enhancement of known catalytic processes and in the design of new ones.

Fluoride Additive as a Simple Tool to Qualitatively Improve Performance of Nickel-Catalyzed Asymmetric Michael Addition of Malonates to Nitroolefins

“…13 C {1H} NMR (101 MHz, CDCl 3 ): δ 167.9, 167.4, 160.0, 137.9, 130.2, 119.9, 114.0, 113.8, 77.4, 55.4, 54.8, 53.2, 53.0, 43.0. NMR spectra are in agreement with the literature data …”

“…Moreover, complex F is stabilized by the hydrogen bond interaction and thus thermodynamically is much more favorable than complex F2 . It is noteworthy that, in our previous report, we noted the activation of the Ni-diamine Evans complex with fluoride, and only activity of that catalyst increased, while the selectivity was the same as without fluoride. Therefore, in that case, the mechanism of that Michael addition should be the same as described by Evans’ group in their first reports , and later studied by Klimochkin’s group .…”

“…Development of highly efficient and available catalytic systems is a great challenge to overcome by the catalytic community, and research in this field is on the cutting edge of the modern chemistry. − Currently, the main trend to obtain a high-performance chemical transformation is preparation of new and progressively more complicated catalysts aiming at increasing their selectivity and activity. However, this results in the low availability of these catalysts to the synthetic community. , Hence, novel approaches toward simple catalysts with high activity and selectivity are highly desirable.…”

“…In a previous work, we developed an efficient way to improve the activity of the organometallic catalysts using in situ activation by the fluoride source (Scheme , a) . This in situ approach can be effective due to the following reasons.…”

“…The role of asymmetric Michael addition is hard to overestimate. − Evans and Seidel developed a highly popular nickel-salan catalyst, allowing us to achieve high yield and enantioselectivity using 2 mol % of the catalyst in general (they discussed that the lowest amount of such a catalyst would be 0.1 mol %). , In our previous work, we showed that the in situ catalyst activation by the fluoride additive allowed us to achieve the same result using as low as 250 ppm of the nickel catalyst (Scheme , b) …”