(NHC)Ni(0)-Catalyzed Branched-Selective Alkene Hydrosilylation with Secondary and Tertiary Silanes

Nickel-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination

The fluoroalkyl-containing organic molecules are widely used in drug discovery and material science. Herein, we report ligand regulated nickel(0)-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination, providing an atom- and step-economical synthesis route of two types of fluoroalkyl substituted silanes with exclusive regioselectivity. The anti-Markovnikov addition products (β-fluoroalkyl substituted silanes) are formed with monodentate phosphine ligand. Noteworthy, the bidentate phosphine ligand promote the generation of the more challenging Markovnikov products (α-fluoroalkyl substituted silanes) with tetrasubstituted saturated carbon centers. This protocol features with easy available starting materials and commercially available nickel catalysis, a wide range of substrates and excellent regioselectivity. The structure divergent products undergo a variety of transformations. Comprehensive mechanistic studies including the inverse kinetic isotope effects demonstrate the regioselectivity controlled by ligand structure through α-CF3 nickel intermediate. DFT calculations reveal a distinctive mechanism involving an open-shell singlet state, which is crucial for generating intricate tetra-substituted Markovnikov products.

Alkene Isomerization Using a Heterogeneous Nickel-Hydride Catalyst

Transition metal-catalyzed alkene isomerization is an enabling technology used to install an alkene distal to its original site. Due to their well-defined structure, homogeneous catalysts can be fine-tuned to optimize reactivity, stereoselectivity, and positional selectivity, but they often suffer from instability and nonrecyclability. Heterogeneous catalysts are generally highly robust but continue to lack active-site specificity and are challenging to rationally improve through structural modification. Known single-site heterogeneous catalysts for alkene isomerization utilize precious metals and bespoke, expensive, and synthetically intense supports. Additionally, they generally have mediocre reactivity, inspiring us to develop a heterogeneous catalyst with an active site made from readily available compounds made of Earth-abundant elements. Previous work demonstrated that a very active homogeneous catalyst is formed upon protonation of Ni[P(OEt)3]4 by H2SO4, generating a [Ni-H]+ active site. This catalyst is incredibly active, but also decomposes readily, which severely limits its utility. Herein we show that by using a solid acid (sulfated zirconia, SZO300), not only is this decomposition prevented, but high activity is maintained, improved selectivity is achieved, and a broader scope of functional groups is tolerated. Preliminary mechanistic experiments suggest that the catalytic reaction likely goes through an intermolecular, two-electron pathway. A detailed kinetic study comparing the state-of-the-art Ni and Pd isomerization catalysts reveals that the highest activity and selectivity is seen with the Ni/SZO300 system. The reactivity of Ni/SZO300, is not limited to alkene isomerization; it is also a competent catalyst for hydroalkenylation, hydroboration, and hydrosilylation, demonstrating the broad application of this heterogeneous catalyst.

Simply accessible platinum(II) complexes enabling alkene hydrosilylation at ppm catalyst loadings

An efficient olefin hydrosilylation protocol utilising Pt(II)-thioether-based pre-catalysts is reported. These simple and readily available complexes exhibit excellent catalytic performance and offer significant advantages over existing alternatives, enabling rapid and high conversions at ppm-level catalyst loadings.

Nickel-Catalyzed Exhaustive Hydrodefluorination of Perfluoroalkyl Arenes

Perfluoroalkyl compounds are persistent environmental pollutants due to their strong C(sp³)-F bonds. Hydrodefluorination has emerged as a potential alternative disposal method for perfluoroalkyl compounds. Although the transformation of trifluoromethyl arenes into the corresponding methyl arenes has been studied by several research groups, hydrodefluorination reactions of longer perfluoroalkyl chains remain rare. Herein, we report exhaustive hydrodefluorination reactions of pentafluoroethyl arenes and longer-chain analogues using molecular nickel catalysis. Despite the cleavage of multiple C(sp³)-F bonds, the reaction already proceeds upon gentle heating (60 °C). A mechanistic investigation indicated that the reaction proceeds via benzylic hydrodefluorination reactions followed by homobenzylic ones. We reveal the multiple roles of the Ni catalyst, which include C-F bond cleavage, promotion of HF elimination, and hydrosilylation.

Research on inorganic activators of dibromo Co-terpyridine complex precatalyst for hydrosilylation

The search for a stable, inexpensive, and easy-to-handle activator toward the catalyst precursor [Co(tpy)Br₂] in the hydrosilylation of olefins with hydrosilane revealed that K₂CO₃ is an effective activator. This inorganic salt is available on substrates with some functional groups and can be readily removed by simple filtration or centrifugation after the reaction. After examining and comparing the activator abilities of various salts, it was proposed that low MX lattice energy, high X-nucleophilicity, and a strong Si-X bond are necessary for an inorganic salt (MX) to be an excellent activator.