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Relevant academic research and scientific papers

Selectivity Reverse of Hydrosilylation of Aryl Alkenes Realized by Pyridine N-Oxide with [PSiP] Pincer Cobalt(III) Hydride as Catalyst

Six silyl cobalt(III) hydrides 1-6 with [PSiP] pincer ligands having different substituents at the P and Si atoms ([(2-Ph2PC6H4)2MeSiCo(H)(Cl)(PMe3)] (1), [(2-Ph2PC6H4)2HSiCo(H)(Cl)(PMe3)] (2), [(2-Ph2PC6H4)2PhSiCo(H)(Cl)(PMe3)] (3), [(2-iPr2PC6H4)2HSiCo(H)(Cl)(PMe3)] (4), [(2-iPr2PC6H4)2MeSiCo(H)(Cl)(PMe3)] (5), and [(2-iPr2PC6H4)2PhSiCo(H)(Cl)(PMe3)] (6)) were synthesized through the reactions of the ligands (L1-L6) with CoCl(PMe3)3 via Si-H bond cleavage. Compounds 1-6 have catalytic activity for alkene hydrosilylation, and among them, complex 3 is the best catalyst with excellent anti-Markovnikov regioselectivity. A silyl dihydrido cobalt(III) complex 7 from the reaction of 3 with Ph2SiH2 was isolated, and its catalytic activity is equivalent to that of complex 3. Complex 7 and its derivatives 10-12 could also be obtained through the reactions of complexes 3, 1, 4, and 5 with NaBHEt3. The molecular structure of 7 was indirectly verified by the structures of 10-12. To our delight, the addition of pyridine N-oxide reversed the selectivity of the reaction, from anti-Markovnikov to Markovnikov addition. At the same time, the reaction temperature was reduced from 70 to 30 °C on the premise of high yield and excellent selectivity. However, this catalytic system is only applicable to aromatic alkenes. On the basis of the experimental information, two reaction mechanisms are proposed. The molecular structures of cobalt(III) complexes 3-6 and 10-12 were determined by single crystal X-ray diffraction analysis.

-Chelate Cobalt(III) Hydride Catalyzed Hydrosilylation of Alkenes

Bidentate ligand 2-diphenylphosphinobenzaldehyde or 2-diisopropylphosphinobenzaldehyde reacted with CoCl(PMe3)3 to give [P,C]-chelate cobalt(III) hydrides [mer-(Me3P)3Co(H)(Cl)(o-Ph2P-C6H4-C═O)] (1) or [mer-(Me3P)3Co(H)(Cl)(o-iPr2P-C6H4-C═O)] (2), respectively. Complex 2 was new and characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. It was found that both complex 1 and 2 are active catalysts for hydrosilylation of alkenes. Although the catalytic activity of 1 is slightly higher, catalyst 1 and 2 have the same selectivity. The selectivity for aromatic alkenes is mainly of the Markovnikov type, while the selectivity for aliphatic alkenes is almost 100% anti-Markovnikov type. In the study of the reaction mechanism, a silyl cobalt dihydride [(Ph2ClSi)Co(H)2(PMe3)3] was isolated from the stoichiometric reaction of hydride 1 with Ph2SiH2. The catalytic mechanism for alkene hydrosilylation with [HCo(PMe3)3] as a real catalyst is proposed and discussed with the experimental results.

Solvent-Free Hydrosilylation of Alkenes Catalyzed by Well-Defined Low-Valent Cobalt Catalysts

A solvent-free cobalt-catalyzed highly selective hydrosilylation of alkenes has been developed. It was found that both Co(PMe3)4 and CoCl(PMe3)3 are highly active catalysts for hydrosilylation of alkenes. The former promoted Markovnikov-type hydrosilylation of the aryl alkenes, while the latter catalyzed anti-Markovnikov-type hydrosilylation of the alkyl alkenes. These two catalytic systems tolerate a variety of functional groups and provide high selectivity and medium to high yield. In the exploration of the reaction mechanism, a dinuclear silyl cobalt(I) complex [(PMe3)2Co(μ-?2-HSiPh2)2Co(PMe3)2] (4) from the Co(PMe3)4 system and a silyl cobalt dihydride [(PMe3)3Co(H)2SiClPh2] (5) from the CoCl(PMe3)3 system were obtained. It is proposed that the silyl cobalt(I) intermediate, [Co(PMe3)3(SiHPh2)], is the real catalyst for the Co(PMe3)4 system, while the hydrido cobalt(I) intermediate, [HCo(PMe3)3], is the real catalyst for the CoCl(PMe3)3 system. Complexes 4 and 5 were characterized by spectroscopic methods and single-crystal X-ray diffraction.

Synthesis and properties of [PCP] pincer silylene cobalt(i) complexes

In this study, two [PCP] pincer silylene cobalt(i) complexes [((Ph2POCH2)2CH)Co(PMe3)(SiCl((NtBu)2CAr))] (Ar = Ph (2) and 4-MePh (3)) were synthesized through the substitution reaction of t

The Effect of Substituents on the Formation of Silyl [PSiP] Pincer Cobalt(I) Complexes and Catalytic Application in Both Nitrogen Silylation and Alkene Hydrosilylation

Four different [PSiP]-pincer ligands L1-L4 ((2-Ph2PC6H4)2SiHR (R = H (L1) and Ph (L2)) and (2-iPr2PC6H4)2SiHR′ (R′ = Ph (L3) and H (L4)) were used to investigate the effect of substituents at P and/or Si atom of the [PSiP] pincer ligands on the formation of silyl cobalt(I) complexes by the reactions with CoMe(PMe3)4 via Si-H cleavage. Two penta-coordinated silyl cobalt(I) complexes, (2-Ph2PC6H4)2HSiCo(PMe3)2 (1) and (2-Ph2PC6H4)2PhSiCo(PMe3)2 (2), were obtained from the reactions of L1 and L2 with CoMe(PMe3)4, respectively. Under similar reaction conditions, a tetra-coordinated cobalt(I) complex (2-iPr2PC6H4)2PhSiCo(PMe3) (3) was isolated from the interaction of L3 with CoMe(PMe3)4. It was found that, only in the case of ligand L4, silyl dinitrogen cobalt(I) complex 4, [(2-iPr2PC6H4)2HSiCo(N2)(PMe3)], was formed. Our results indicate that the increasing of electron cloud density at the Co center is beneficial for the formation of a dinitrogen cobalt complex because the large electron density at Co center leads to the enhancement of the ?-backbonding from cobalt to the coordinated N2. It was found that silyl dinitrogen cobalt(I) complex 4 is an effective catalyst for catalytic transformation of dinitrogen into silylamine. Among these four silyl cobalt(I) complexes, complex 1 is the best catalyst for hydrosilylation of alkenes with excellent regioselectivity. For aromatic alkenes, catalyst 1 provided Markovnikov products, while for aliphatic alkenes, anti-Markovnikov products could be obtained. Both catalytic reaction mechanisms were proposed and discussed. The molecular structures of complexes 1-4 were confirmed by single-crystal X-ray diffraction.

Optimization preparation method for alkyl silicon compound based on addition reaction

The invention relates to an optimization preparation method for alkyl silicon compound based on addition reaction, wherein a bivalent nickel salt and an alkoxy metal compound are used as a catalytic system to catalyze the reverse Markov addition reaction of terminal aliphatic olefin and a silane reagent so as to realize the selective synthesis of alkyl silicon compounds. The method has the advantages of simple and easily available catalytic system, simple synthetic route, high efficiency, economy, mild conditions and wide applicability, and plays a great role in promoting the later industrialproduction of alkyl silicon compounds.

Visible-Light-Mediated Metal-Free Hydrosilylation of Alkenes through Selective Hydrogen Atom Transfer for Si?H Activation

Although there has been significant progress in the development of transition-metal-catalyzed hydrosilylations of alkenes over the past several decades, metal-free hydrosilylation is still rare and highly desirable. Herein, we report a convenient visible-