Developing a Highly Active Catalytic System Based on Cobalt Nanoparticles for Terminal and Internal Alkene Hydrosilylation

Easy preparation of small crystalline Pd2Sn nanoparticles in solution at room temperature

We describe here a simple protocol yielding small (<2 nm) crystalline Pd₂Sn nanoparticles (NPs) along with Pd homologues for sake of comparison. These NPs were obtained via an organometallic approach using Pd₂(dba)₃·dba (dba = dibenzylideneacetone) in THF with 2 equivalents of tributyltin hydride under 4 bars of H₂ at room temperature. The Pd NP homologues were prepared similarly, using Pd₂(dba)₃·dba with 2 equivalents of n-octylsilane. These NPs were found to be crystalline and very small with a similar mean size (ca. 1.5 nm). These NPs were finally used as nanocatalysts in solution for a benchmark Suzuki-Miyaura cross-coupling reaction. The Pd₂Sn NPs were found to be more active than Pd NPs analogues, exhibiting remarkable performances with Pd loading as low as 13 ppb. This result demonstrates a beneficial effect of tin on palladium in catalysis.

Borane-Protecting Strategy for Hydrosilylation of Phosphorus-Containing Olefins

Ir-catalyzed hydrosilylation of the alkenyl phosphine borane complex 1 was achieved to give the corresponding products 2. Because the phosphino group coordinates with metals and is unstable under aerobic conditions, the formation of the corresponding borane adduct was effective not only to promote the target hydrosilylation but also to keep 1 stable under aerobic conditions. The removal of coordinated borane from 2 was readily performed with the treatment by 1,4-diazabicyclo[2.2.2]octane to apply to further transformations. The immobilization and following deprotection of 2 on the surface of mesoporous silica were also examined.

Synthesis of Benzimidazo[2,1-a]isoquinoline and Indolo[2,1-a]isoquinoline Derivatives via Copper-Catalyzed Silylation/Methylation of 2-Arylindoles and 2-Arylbenzimidazoles

A one-pot method for the synthesis of silylsubstituted/methylsubstituted indolo[2,1-a]isoquinolin-6(5H)-ones and benzimidazo[2,1-a]isoquinoline-6(5H)-ones via copper(II)-initiated silylation/methylation of 2-arylindoles and 2-arylbenzimidazoles was developed. In this procedure, the C-Si bond and C-C bond were constructed by radical addition and cyclization. A series of 2-arylindole and 2-arylbenzimidazole derivatives were facilely transformed to indolo[2,1-a]isoquinolines and benzimidazo[2,1-a]isoquinolines in 39-83% yields.

Remote Site-Selective Asymmetric Protoboration of Unactivated Alkenes Enabled by Bimetallic Relay Catalysis

A remote C(sp³ )-H bond asymmetric borylation of unactivated alkenes was achieved by bimetallic relay catalysis. The reaction proceeded through reversible and consecutive β-H elimination/olefin insertion promoted by CoH species generated in situ, followed by copper-catalyzed asymmetric protoboration. The use of this synergistic Co/Cu catalysis protocol allowed the enantioselective protoboration of various unactivated terminal alkenes and internal alkenes, as well as an unrefined mixture of olefin isomers, at the distal less-reactive β-position to a functional group, leading to chiral organoboronates.

Mn2(CO)10 and UV light: a promising combination for regioselective alkene hydrosilylation at low temperature

The low temperature regioselective hydrosilylation of various alkenes with (1,1,1,3,5,5,5-heptamethyltrisiloxane) MD^HM is described using Mn₂(CO)₁₀ under UV irradiation with Mn loadings as low as 1 mol%, in the absence of additives and with excellent selectivity and yields. The generation of a manganese radical allowed the anti-Markovnikov hydrosilylation products to be selectively obtained in yields up to 99%.

14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes

Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh(iii) devoid of agostic interactions. The complexes [X-Rh(κ³(P,Si,Si)PhP(o-C₆H₄CH₂SiⁱPr₂)₂], where X = Cl (Rh-1), Br (Rh-2), I (Rh-3), OTf (Rh-4), Cl·GaCl₃ (Rh-5); derive from a bis(silyl)-o-tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl-Ir(κ³(P,Si,Si)PhP(o-C₆H₄CH₂SiⁱPr₂)₂], Ir-1, in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et₃SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et₃SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomers by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M(iii) complexes.

(Z)-Selective Hydrosilylation and Hydroboration of Terminal Alkynes Enabled by Ruthenium Complexes with an N-Heterocyclic Carbene Ligand

Metal-catalyzed trans-1,2-hydrosilylations and hydroborations of terminal alkynes that generate synthetically valuable (Z)-alkenylsilanes and (Z)-alkenylboranes remain challenging due to the (E)-selective nature of the reactions and the formation of the thermodynamically unfavorable (Z)-isomer. The development of new, efficient catalytic systems for the (Z)-selective hydrosilylation and hydroboration of terminal alkynes is thus highly desirable from a fundamental perspective as it would deepen our understanding of the metal-catalyzed (Z)-selective hydrosilylation and hydroboration of terminal alkynes. This personal account describes our research for developing a ruthenium complex that can efficiently catalyze the hydrosilylation and hydroboration of terminal alkynes, and for exploring the factors controlling (Z)-selectivity of the reactions. Our effort into the activation of B-protected boronic acids, R-B(dan) (dan=naphthalene-1,8-diaminato), that was believed not to participate in Suzuki-Miyaura cross-coupling, is also discussed.

Hydrosilylation of carbonyls over electron-enriched Ni sites of intermetallic compound Ni3Ga heterogeneous catalyst

Nanoparticulate intermetallic compound Ni3Ga supported on SiO2 has emerged as a highly efficient catalyst for the hydrosilylation of carbonyls, such as aldehydes and ketones, at room temperature. Formation of electron-enriched Ni via alloying with Ga is the key to the catalytic performance.

Nickel-Catalyzed Hydrosilylation of Terminal Alkenes with Primary Silanes via Electrophilic Silicon-Hydrogen Bond Activation

We report a simple and effective nickel-based catalytic system, NiCl₂·6H₂O/^tBuOK, for the electrophilically activated hydrosilylation of terminal alkenes with primary silanes. This protocol provides excellent performance under mild reaction conditions: exclusive anti-Markovnikov selectivity, broad functional group tolerance (36 examples), and good scalability (TON = 5500). However, the secondary and tertiary silanes are not suitable. Mechanistic studies revealed that this homogeneous catalytic hydrosilylation includes an electrophilically activated Si-H bond process without the generation of nickel hydrides.

Co2(CO)8 and unsaturated epoxides as unexpected partners in generating functionalized siloxane oils and cross-linked materials

The unexpected formation of cross-linked silicon materials was observed via hydrosilylation of unsaturated epoxides with polymethylhydrosiloxane using Co₂(CO)₈ as a catalyst.

Ni(ii) and Co(ii) bis(acetylacetonato) complexes for alkene/vinylsilane silylation and silicone crosslinking

Commercially available Ni(ii) and Co(ii) complexes – M(acac)₂ and M(tmhd)₂ – exhibit catalytic activity for alkene/vinylsilane dehydrogenative silylation (DS) and hydrosilylation (HS) with tertiary silanes without using any external reducing agents.

Co2(CO)8 as an efficient catalyst for the synthesis of functionalized polymethylhydrosiloxane oils and unconventional cross-linked materials

Co₂(CO)₈ was found to be an effective and structurally simple catalyst for the functionalization of polymethylhydrosiloxane into functional silicone fluids using terminal alkenes and into cross-linked silicone materials using unconventional tethers.

A family of rhodium(i) NHC chelates featuring O-containing tethers for catalytic tandem alkene isomerization-hydrosilylation

The rhodium complex Rh(HL)(COD)Cl, 1, L being a functionalized N-heterocyclic carbene (NHC) ligand with an oxygen-containing pendant arm, has been used as the entry point to synthesize a series of neutral and cationic Rh(i) O,C chelates. While the Rh-carbene interaction is similar in all these 16-electron complexes, structural analysis reveals that the strength of the Rh-O bond is greatly affected by the nature of the O-donor: R-O^- > R-OH > R-OBF₃. These subtle changes in the nature of the O-containing tether are found to be responsible for large differences in the alkene hydrosilylation catalytic activity of these compounds: the stronger the Rh-O interaction, the better the catalytic performances. The most active catalyst, [Rh(L)(COD)], 2, demonstrated good catalytic activity under mild reaction conditions for the hydrosilylation of a range of alkene substrates with the industrially relevant non-activated tertiary silane, 1,1,1,3,5,5,5-heptamethyltrisiloxane (MD^HM). Furthermore, this complex is an effective catalyst for the selective remote functionalization of internal olefins at room temperature via tandem alkene isomerization-hydrosilylation.