Catalysts For Hydrosilylation Of Alkynes Research Articles

Cover Picture: Quaternary Ammonium Salts: Catalysts for Hydrosilylation of Alkynes with Hydrosilanes (Adv. Synth. Catal. 24/2023)

Cover Picture: Quaternary Ammonium Salts: Catalysts for Hydrosilylation of Alkynes with Hydrosilanes (Adv. Synth. Catal. 24/2023)

Quaternary Ammonium Salts: Catalysts for Hydrosilylation of Alkynes with Hydrosilanes

AbstractMixing i‐PrI and DABCO in solvent EtCN gave two quaternary ammonium salts (QASs) quantitatively, one of which is monocationic (QAS‐1) and the other is dicationic (QAS‐2). These QASs were found to catalyze hydrosilylation of alkynes with hydrosilanes (HAH) without the aid of metal and metalloid catalysts. This organocatalysis can be applied to a variety of alkynes: terminal/internal aryl and alkyl alkynes with/without a functional group. With dihydrosilanes (H2Si), the HAH occurred with high E‐selectivity through syn addition, which was exclusively observed when using terminal alkyl alkynes, irrespective of a hydrosilane used. A scalable HAH is also feasible. The H−Si unit remaining in alkenylsilanes derived from H2Si is available for dehydrogenative alkynylation and N‐heteroarylation under zinc–pyridine catalysis. This synthetic application delivers unique silicon compounds that have, for instance, alkyl, aryl, alkenyl, and alkynyl groups in a single molecule. Mechanistic studies suggested that alkynes activated by QASs irreversibly react with hydrosilanes that become more nucleophilic by the coordination of EtCN. A radical pathway is unlikely. The QAS catalysts can be recovered and reused at least 5 times.

Low‐coordinate cobalt(0) N‐heterocyclic carbene complexes as catalysts for hydrosilylation of alkynes

AbstractAmong the great efforts of developing cobalt‐based catalysts for hydrosilylation reactions, cobalt (II) and cobalt(I) complexes are the extensively studied ones. In contrast, explorations on cobalt(0) complexes are relatively rare. Presented herein is the investigation on the catalytic performance of low‐coordinate cobalt(0) N‐heterocyclic carbene (NHC) complexes in the hydrosilylation reaction of alkynes, which disclosed the fine performance of [(CyIDep)Co(η2‐CH2CHSiMe3)2] (CyIDep denotes for a 1,3‐bis(2′,6′‐diethylphenyl)imidazole‐2‐ylidene that bears fused cyclohexyl group on the imidazole backbone) in catalyzing the syn‐addition of a series of symmetric and unsymmetric internal alkynes with H2SiPh2, producing vinylsilanes with high regio‐selectivity. Mechanistic study indicates that the catalytic reaction likely proceeds on a cobalt(0)/cobalt(II) cycle and that the high selectivity is governed by the steric nature of the NHC ligand.

Caged Iridium Catalyst for Hydrosilylation of Alkynes with High Site Selectivity

AbstractThe proximity and orientation of the reacting groups can be different in organic cages from in free solution, thus affecting the selectivity of the reaction. Herein, we reported a synthetic strategy to encapsulate iridium nanoparticles (Ir‐NP@COP1‐T) within organic cages in the homogeneous solution. Ir‐NP@COP1‐T showed good selectivity in the hydrosilylation reaction of alkynes. Our work provides a new perspective to the catalysis field by using soluble microporous cages as support for inorganic nano particles.

Platinum Complexes with Chelating Acyclic Aminocarbene Ligands Work as Catalysts for Hydrosilylation of Alkynes.

This work describes the preparation of a series of platinum–aminocarbene complexes [PtCl{C(N=Ca(C6R2R3R4R5CONb))=N(H)R1}(CNR1)]a–b (8–19, 65–75% isolated yield) via the reaction of cis-[PtCl2(CNR1)2] (R1 = Cy 1, t-Bu 2, Xyl 3, 2-Cl-6-MeC6H34) with 3-iminoisoindolin-1-ones HN=Ca(C6R2R3R4R5CONbH) (R2–R5 = H 5; R3 = Me, R2, R4, R5 = H 6; R3, R4 = Cl, R2, R5 = H 7). New complexes 17–19 were characterized by elemental analyses (C, H, N), ESI+-MS, Fourier transform infrared spectroscopy (FT-IR), one-dimensional (1H, 13C{1H}), and two-dimensional (1H,1H correlation spectroscopy (COSY), 1H,13C heteronuclear multiple quantum correlation (HMQC)/1H,13C heteronuclear single quantum coherence (HSQC), 1H,13C heteronuclear multiple bond correlation (HMBC)) NMR spectroscopy, and authenticity of known species 8–16 was confirmed by FT-IR and 1H and 13C{1H} NMR. Complexes 8–19 were assessed as catalysts for hydrosilylation of terminal alkynes with hydrosilanes to give vinyl silanes, and complex [PtCl{C(N=Ca(C6H3(5-Me)CONb))=N(H)(2-Cl-6-MeC6H3)}{CN(2-Cl-6-MeC6H3)}]a−b (18) showed the highest catalytic activity. The catalytic system proposed operates at 80–100 °C for 4–6 h in toluene and with catalyst loading of 0.1 mol %, enabling the reaction of a number of terminal alkynes (PhC≡CH, t-BuC≡CH, and 4-(t-Bu)C6H4C≡CH) with hydrosilanes (Et3SiH, Pr3SiH, i-Pr3SiH, and PhMe2SiH). Target vinyl silanes were prepared in 48–95% yields (as a mixture of α/β isomers) and with maximum turnover number of 8.4 × 103. Hydrosilylation of internal alkynes (PhC≡CPh, Me(CH2)2C≡C(CH2)2Me, and PhC≡CMe) with hydrosilanes (Et3SiH, PhMe2SiH) led to the corresponding trisubstituted silylated alkenes in 86–94% yields. Initial observations on the mechanism of the catalytic action of platinum–ADC catalysts 8–19 suggested a molecular catalytic cycle.

Recoverable platinum bis(fluoro-ponytailed) bipyridine complex as catalyst for hydrosilylation of alkynes under thermomorphic condition

The fluorous PtCl2[5,5′-bis-(n-C11F23CH2OCH2)-2,2′-bpy] complex (2) was prepared and employed as recoverable catalyst for the hydrosilylation of alkynes. Pt-catalyst 2 with F-content 0.53 was recovered under the thermomorphic method by design and the catalyst was demonstrated capable of re-usage for 8 times without loss of activity. The leaching of Pt in product mixture was monitored, with ICP-MS, to be at as low as 10−6 level per cycle in the 5-decyne reactions and at 10−3 level per cycle in the (HO)CMe2CCH reaction. The reaction-catalyst fulfills the principle of green chemistry, and with its addition nature the hydrosilylation delivers 100% atom economy. The easily prepared polyfluorinated (2,2′-bpy)Pt complex 2 is the robust and thermally stable catalyst, which doesn't require specific handling for utilization and storage in laboratory.

Rhodium(I) and iridium(I) imidazo[1,5-a]pyridine-1-ylalkylalkoxy complexes: Synthesis, characterization and application as catalysts for hydrosilylation of alkynes

Rh(I) and Ir(I) complexes bearing imidazo[1,5-a]pyridine-1-ylalkyl alcohol as chelating NˆO-monoanionic ligands were prepared as thermally stable compounds. Their spectroscopic properties and structures were determined based on IR and NMR spectra and X-ray analyses. The Rh(I) complexes were used as catalysts for the hydrosilylation of alkynes. The catalytic activities of the complexes were highly influenced by the substituents on their aromatic rings. Highly E-selective formation of vinylsilanes was achieved at higher temperatures for longer reaction times.

A Palladium Nanoparticles Catalyst for Hydrosilylation of Alkynes

Key words alkynes - hydrosilylation - imidazolium salts - palladium nanoparticles - transfer hydrogenation

ADC-metal complexes as effective catalysts for hydrosilylation of alkynes

Aminocarbene complexes cis-[PtCl2{C(N(H)N=CR2R3)=N(H)R1}(CNR1)](7–15) prepared via the nucleophilic addition of hydrazones H2N–N=CR2R3 [R2, R3=Ph 4; R2/R3=9H-fluorenyl 5; R2=H, R3=2-(OH)C6H46] to cis-[PtCl2(CNR1)2] [R1=cyclohexyl (Cy) 1, 2,6-Me2C6H3 (Xyl) 2, 2-Cl-6-MeC6H33] were evaluated as catalysts for the hydrosilylation of terminal alkynes with trisubstituted silanes giving vinyl silanes. The optimized catalytic system runs at 80–100°C in dry toluene for 3–6h with a typical catalyst loading of 0.1mol%. A range of substrates with different steric hindrance and activity (Et3SiH, Pr3SiH, iPr3SiH, and PhMe2SiH as silanes; PhCCH, tBuCCH, and 4-(tBu)C6H4CCH as alkynes) were successfully transformed into the target silylated products in 83–99% yields attesting the versatility of our catalytic system. Decreasing the catalysts loading to 10−3 mol% guaranteed the maximum TONs of 4.0×104 and TOFs of 1.7×103 (h−1) that were accomplished within 24h of the reaction.