Hydrosilylation Of Alkenes Research Articles

Silylene [PSiP] Pincer Cobalt(II) Chloride–Catalyzed Alkene Hydrosilylation

ABSTRACTSilylene metal complexes exhibit excellent catalytic activity and selectivity in homogeneous catalysis. However, there are relatively few examples of silylene metal complexes as catalysts for the hydrosilylation of alkenes. In order to study the effect of a silylene ligand on the catalytic performance of [PSiP] pincer Co(II) chloride for alkene hydrosilylation, the PMe3 ligand in (MeSi(C6H4‐PPh2)2)Co (PMe3)Cl (1) was replaced by a silylene ligand, and a silylene [PSiP] pincer Co(II) chloride, (MeSi(C6H4‐PPh2)2)Co (PhC (NtBu)2Si)Cl (2), was used as catalyst to study its catalytic activity in alkene hydrosilylation. It was confirmed that silylene Complex 2 has excellent catalytic activity for alkene hydrosilylation with Ph2SiH2 as a hydrogen source. For alkene hydrosilylation, compared to phosphine Complex 1, silylene Complex 2 does not need NaBHEt3 as an additive. In addition, for aromatic alkenes, silylene Complex 2 has anti‐Markovnikov selectivity, while phosphine Complex 1 provides Markovnikov products in the presence of NaBHEt3.

Synthesis of Dinuclear Cobalt Silylene Complexes and Their Catalytic Activity for Alkene Hydrosilylation Reactions.

A novel dinuclear silylene cobalt complex [((Me3P)2Co)(PMe2)(CoCl(PMe3))(Si(NCH2PPh2)2C6H4)] (1) supported by the [PSi(silylene)P] ligand was prepared through the reaction of N-heterocyclic [PSiP] pincer ligand L1 (HSiCl(NCH2PPh2)2C6H4) with Co(PMe3)4. Complex [((Me3P)2Co)2(Si(NCH2PPh2)2C6H4)] (2) was formed through the reaction of complex 1 with MeLi. To the best of our knowledge, complexes 1 and 2 are the first examples of dinuclear silylene cobalt complexes supported by the [PSi(silylene)P] ligand. A new preligand L2 (SiCl2(NCH2PPh2)2C6H4) was synthesized, and the reaction of preligand L2 with Co(PMe3)4 afforded silyl cobalt complex [((Me3P)2Co)(SiCl(NCH2PPh2)2C6H4)] (3). The reaction of 3 with CO delivered cobalt carbonyl complex [((Me3P)(CO)Co)(Si(NCH2PPh2)2C6H4)]2O (4). The catalytic activity of cobalt complexes 1-4 on the hydrosilylation of alkenes was explored. Among the four complexes, complex 1 has the best catalytic activity. The catalytic process could be promoted with NaBHEt3 as an additive, and a complete conversion with an excellent selectivity of 98:2 (b/l) could be reached at 120 °C within 8 min for aryl alkenes. A possible catalytic cycle was proposed on the basis of the experimental results and literature reports, with a cobalt hydride complex as an active intermediate. The molecular structure of complexes 1-4 was determined by single-crystal X-ray diffraction analysis.

Visible‐Light‐Initiated Uranyl‐Catalyzed Hydrosilylation and Hydrosulfonylation of Alkenes and Alkynes

This study investigates the visible‐light‐initiated uranyl(VI)‐catalyzed activation of Si‐H bonds through direct hydrogen atom transfer, which facilitates the formation of silyl radicals from silanes. The silyl radical can abstract a chlorine atom from the sulfonyl chloride, leading to the generation of sulfonyl radicals. These silyl radicals and sulfonyl radicals could react with alkenes and alkynes, achieving the first example of uranyl‐catalyzed hydrosilylation and hydrosulfonylation of unsaturated C‐C bonds. This method features mild reaction conditions and a broad substrate scope, and exhibiting exceptional functional‐group tolerance. Consequently, it is suitable for the late‐stage functionalization of drug derivatives.

Methoxide‐Enabled Zirconium‐Catalyzed Migratory Alkene Hydrosilylation

A zirconocene dichloride‐catalyzed alkene hydrosilylation is reported that can be applied to non‐activated and conjugated terminal and internal alkenes. It involves a catalytic Zr‐walk process and leads to a selective conversion to the linear product. Lithium methoxide serves as mild catalyst activating agent, which significantly increases the applicability and operational simplicity in comparison to earlier zirconium(II)‐based protocols. Supported by additional experiments and calculations, a mechanism via zirconium(IV) intermediates is proposed. Due to the benign nature and ready‐availability of the zirconium catalyst, the reaction is an attractive alternative to established alkene hydrosilylation methods.

Methoxide-Enabled Zirconium-Catalyzed Migratory Alkene Hydrosilylation.

A zirconocene dichloride-catalyzed alkene hydrosilylation is reported that can be applied to non-activated and conjugated terminal and internal alkenes. It involves a catalytic Zr-walk process and leads to a selective conversion to the linear product. Lithium methoxide serves as mild catalyst activating agent, which significantly increases the applicability and operational simplicity in comparison to earlier zirconium(II)-based protocols. Supported by additional experiments and calculations, a mechanism via zirconium(IV) intermediates is proposed. Due to the benign nature and ready-availability of the zirconium catalyst, the reaction is an attractive alternative to established alkene hydrosilylation methods.

Efficient and stable NiMo alloy nanoparticles on ZSM-5 for alkene hydrosilylation

The hydrosilylation of alkene substrates bearing additional functionalities is difficult to achieve by heterogeneous non-noble catalysts and has not been extensively realized with heterogeneous earth-abundant transition metals. Herein, we report NiMo alloy nanoparticles (NPs) supported on ZSM-5 zeolite, which exhibits high activity and selectivity for the hydrosilylation of functionalized terminal and internal alkenes. Compared with the corresponding monometallic counterparts, the Ni3Mo/ZSM-5 catalyst shows a distinct enhancement in the hydrosilylation of alkene. The key to the catalytic performance is the formation of the NiMo alloy, where the electrons are transferred from Mo to Ni. The NiMo alloy NPs have been verified by XRD, XPS and TEM analysis, and further characterized by ICP, BET, NH3-TPD, and H2-TPR. In addition, the Ni3Mo/ZSM-5 catalyst exhibits good reusability for the hydrosilylation reaction with wide substrate scope.

Radical-Chain Hydrosilylation of Alkenes Enabled by Triplet Energy Transfer.

Development of mild, robust and metal-free catalytic approach for the hydrosilylation of alkenes is critical to the advancement of modern organosilicon chemistry given their powerful capacity in the construction of various C-Si bonds. Herein, we wish to disclose a visible light-triggered organophotocatalytic strategy, which proceeds via a triplet energy transfer (EnT)-enabled radical chain pathway. Notably, this redox-neutral protocol is capable of accommodating a broad spectrum of electron-deficient and -rich alkenes with excellent functional group compatibility. Electron-deficient alkenes are more reactive and the reaction could be finished within a couple of minutes even in PBS solution with extremely low concentration, which suggests its click-like potential in organic synthesis. The preparative power of the transformations has been further highlighted in a number of complex settings, including the late-stage functionalization and scale-up experiments. Furthermore, although only highly reactive (TMS)3SiH is suitable hydrosilane substrate, our studies revealed the great reactivity and versatility of (TMS)3Si- group in diverse C-Si and Si-Si bond cleavage-based transformations, enabling the rapid introduction of diverse functional groups and the facile construction of valuable quaternary silicon architectures.

Hydrosilylation of Olefins Activated on Highly Lewis-Acidic Calcium Cation.

The report introduces simple yet highly reactive calcium salt, Ca[Al(ORF)4]2 (RF=C(CF3)3), 1, which effectively catalyses olefin hydrosilylation through an unusual mechanism involving the activation of the alkene molecule. Upon dissolution in o-difluorobenzene (oDFB), 1 forms a highly Lewis acidic [Ca(oDFB)6]2+ complex. Our DFT calculations reveal that fluoride ion affinity is comparable to SbF5. Reactivity tests show that it effectively catalyses the hydrosilylation of olefins with high regioselectivity, also in reactions involving sterically demanding substrates like (iPr)3SiH or tetrasubstituted olefins. Experimental and computational results point to the mechanism where the olefin molecule forms a complex with Ca2+, which significantly facilitates the attack of H-SiR3 on the C=C double bond.

Radicals as Chiral Catalysts for Asymmetric Radical Cyclization Reactions

AbstractDue to the innate highly reactive properties and short life‐time, organic free radicals can often serve as promoters or intermediates to engage in various radical transformations, which are often otherwise difficult to access by ionic pathway‐based mechanisms. With the evolvement of radical chemistry, chiral radical catalyzed‐transformations have recently emerged as an attractive and robust platform for synthesis of chiral molecules of interest. Herein, we highlight several creative and strategic advances in chiral radical catalyst design, cyclization reaction achievements, and future challenges. Key ScientistsIn the 1980s, some pioneering studies by Feldman and Oshima revealed that the thiyl radical could catalyze cyclization of vinylcyclopropane with alkenes, providing access to racemic cyclopentanes. In 1996, Brian P. Roberts reported an interesting enantioselective hydrosilylation of prochiral alkenes by using thioglucose‐derived chiral thiyl radical catalysts. Since then, chiral radical catalysis has become an emerging and promising catalytic strategy in organic synthesis. However, this field has not been extensively explored further until the Maruoka group in 2014 achieved the asymmetric C—C bond formation by employing a newly designed indanol core‐based chiral thiyl radical catalyst. In this protocol, an enantioselective radical cyclization of vinylcyclopropanes with electron‐rich alkenes was developed. In 2020, Chen and Xiao disclosed a nitrogen radical‐catalyzed version of this reaction. Later, this strategy was further expanded to metalloradical catalyzed asymmetric radical cascade cyclization reactions by Zhang in 2021. Later on, Wang, Fu and Zhang et al. described a novel class of boryl radical‐catalyzed asymmetric radical cycloisomerization reactions, further showcasing enormous synthetic potential of chiral radical catalysis. This Emerging Topic has focused on asymmetric radical cyclization reactions involving diverse chiral radical catalysts.

Electrophilic Hydrosilylation of Electron-Rich Alkenes Derived from Enamines.

The low-electron count, air-stable, platinum complexes [Pt(ItBu')(ItBu)][BArF] (C1) (ItBu=1,3-di-tert-butylimidazol-2-ylidene), [Pt(SiPh)3(ItBuiPr)2][BArF] (C2) (ItBuiPr=1-tert-butyl-3-iso-propylimidazol-2-ylidene), [Pt(SiPh)3(ItBuMe)2][BArF] (C3), [Pt(GePh3)(ItBuiPr)2][BArF] (C4), [Pt(GePh)3(ItBuMe)2][BArF] (C5) and [Pt(GeEt)3(ItBuMe)2][BArF] (C6) (ItBuMe=1-tert-butyl-3-methylimidazol-2-ylidene) are efficient catalysts (particularly the germyl derivatives) in both the silylative dehydrocoupling and hydrosilylation of electron rich alkenes derived from enamines. The steric hindrance exerted by the NHC ligand plays an important role in the selectivity of the reaction. Thus, bulky ligands are selective towards the silylative dehydrocoupling process whereas less sterically hindered promote the selective hydrosilylation reaction. The latter is, in addition, regioselective towards the β-carbon atom of both internal and terminal enamines, leading to β-aminosilanes. Moreover, the syn stereochemistry of the amino and silyl groups implies an anti Si-H bond addition across the double bond. All these facts point to a mechanistic picture that, according to experimental and computational studies, involves a non-classical hydrosilylation process through an outer-sphere mechanism in which a formal nucleophilic addition of the enamine to the silicon atom of a platinum σ-SiH complex is the key step. This is in sharp contrast with the classical Chalk-Harrod mechanism prevalent in platinum chemistry.

Iridium-Catalyzed Hydrosilylation of Polymeric Olefins: Moving beyond Platinum-Based Catalysts for Surfactants

Iridium-Catalyzed Hydrosilylation of Polymeric Olefins: Moving beyond Platinum-Based Catalysts for Surfactants

Supported bimetallic PtNi-vinyl complex for hydrosilylation of straight-chain terminal alkenes with tertiary silanes: Effect of Ni promoter on catalytic performance

A bimetallic PtNi-vinyl complex as catalytic active center was created on modified rice straw biochar by introducing an appropriate amount of cheap Ni component as a catalytic promoter. The constructed bimetallic catalyst (PtNi-VTES-RSOC) was used to catalyze hydrosilylation of terminal alkenes with tertiary silanes to produce alkylsilanes with high commercial application value. The experimental results proved that the conversion of 1-octene 96.5 % and selectivity for target product 97.1 % were obtained in hydrosilylation of 1-octene with triethoxysilane catalyzed by PtNi-VTES-RSOC with mass ratio of Pt/Ni = 1.5:1 (molar ratio of Pt/Ni≈1:2) under mild conditions (atmospheric pressure, solvent-free, 50 ℃ and 3 h). It also possessed higher catalytic ability and regioselectivity for hydrosilyation of long-chain alkenes (1-octadecene) with tertiary silanes compared to the counterpart monometallic catalysts. The characterization and theoretical calculation results demonstrated that the introduced suitable amount of Ni(II) could affect the structure of original Pt(II)-vinyl complexes and form a stable and unique bimetallic vinyl coordination microstructure by using a shared vinyl group, thereby affecting morphology, structure, and catalytic performance of the as-prepared bimetallic catalyst with mass ratio of Pt/Ni = 1.5:1. Changing the introduction order and introducing excessive or insufficient of Ni(II) would both disrupt the formation of this special structure and affect the catalytic performance. Additionally, the formed stable complex structure with vinyl groups could well maintain the catalytic stability. The study results exposed that the as-prepared bimetallic catalyst would possess a great industrial application potential in the hydrosilylation of alkenes by efficiently increasing the product quality and reducing operation cost.

Heterometallic Mg‐Ni‐Mg Complex Promoted Hydrosilylation of Alkenes: Catalytic Performance and Intermediates Characterization†

Comprehensive SummaryHeteronuclear metal complexes have played an increasingly important role in both small molecules activation and catalytic transformation due to the potential metal‐metal synergies. In this work, we reported that the well‐defined Mg‐Ni‐Mg complex [(LMg)2Ni(C2H4)2] {L = [(DippNCMe)2CH]−, Dipp = 2,6‐iPr2C6H3} was capable of catalyzing the conversion of a diverse array of terminal alkenes to hydrosilylated products in anti‐Markovnikov fashion using PhSiH3 as the silicon source. The stoichiometric reaction of heterometallic Mg‐Ni‐Mg complex with one equivalent PhSiH3 obtained a silyl‐nickel‐monohydride complex [(LMg)2NiH(C2H4)(SiHPhEt)] featuring a Ni‐Si‐H‐Mg interaction. Moreover, treatment of heterometallic Mg‐Ni‐Mg complex with three equivalents PhSiH3 provided the silyl‐nickel‐trihydride complex [(LMg)2NiH3(SiHPhEt)] with three hydride‐bridged at Mg‐Ni‐Mg fragment. Further reactions of the resultant silyl‐nickel complexes with alkenes, e.g., ethylene and styrene, yielded the corresponding alkene‐coordinated Mg‐Ni‐Mg complexes [(LMg)2Ni(C2H4)2], [(LMg)2NiH2(C2H4)] and [(LMg)2NiH2(CH2CHPh)], respectively, with the elimination of PhEtSiH2. Based on the control experiments, both silyl‐nickel‐monohydride and silyl‐nickel‐trihydride complexes were considered as active intermediates in the catalytic hydrosilylation reaction.

Stabilizing Few‐Atom Platinum Clusters by Zinc Single‐Atom‐Glue for Efficient Anti‐Markovnikov Alkene Hydrosilylation

Few‐atom metal clusters (FAMCs) exhibit superior performance in catalyzing complex molecular transformations due to their special spatial environments and electronic states, compared to single‐atom catalysts (SACs). However, achieving the efficient and accurate synthesis of FAMCs while avoiding the formation of other species, such as nanoparticles and SACs, still remains challenges. Herein, we report a two‐step strategy for synthesis of few‐atom platinum (Pt) clusters by predeposition of zinc single‐atom‐glue (Zn1) on MgO nanosheets (Ptn‐Zn1/MgO), where FAMCs can be obtained over a wide range of Pt contents (0.09 to 1.45 wt%). Zn atoms can act as Lewis acidic sites to allow electron transfer between Zn and Pt through bridging O atoms, which play a crucial role in the formation and stabilization of few‐atom Pt clusters. Ptn‐Zn1/MgO exhibited a high selectivity of 93% for anti‐Markovnikov alkene hydrosilylation. Moreover, an excellent activity with a turnover frequency of up to 1.6 ×104 h−1 can be achieved, exceeding most of the reported Pt SACs. Further theoretical studies revealed that the Pt atoms in Ptn‐Zn1/MgO possess moderate steric hindrance, which enables high selectivity and activity for hydrosilylation. This work presents some guidelines for utilizing atomic‐scale species to increase the synthesis efficiency and precision of FAMCs.

Stabilizing Few-Atom Platinum Clusters by Zinc Single-Atom-Glue for Efficient Anti-Markovnikov Alkene Hydrosilylation.

Few-atom metal clusters (FAMCs) exhibit superior performance in catalyzing complex molecular transformations due to their special spatial environments and electronic states, compared to single-atom catalysts (SACs). However, achieving the efficient and accurate synthesis of FAMCs while avoiding the formation of other species, such as nanoparticles and SACs, still remains challenges. Herein, we report a two-step strategy for synthesis of few-atom platinum (Pt) clusters by predeposition of zinc single-atom-glue (Zn1) on MgO nanosheets (Ptn-Zn1/MgO), where FAMCs can be obtained over a wide range of Pt contents (0.09 to 1.45 wt %). Zn atoms can act as Lewis acidic sites to allow electron transfer between Zn and Pt through bridging O atoms, which play a crucial role in the formation and stabilization of few-atom Pt clusters. Ptn-Zn1/MgO exhibited a high selectivity of 93 % for anti-Markovnikov alkene hydrosilylation. Moreover, an excellent activity with a turnover frequency of up to 1.6×104 h-1 can be achieved, exceeding most of the reported Pt SACs. Further theoretical studies revealed that the Pt atoms in Ptn-Zn1/MgO possess moderate steric hindrance, which enables high selectivity and activity for hydrosilylation. This work presents some guidelines for utilizing atomic-scale species to increase the synthesis efficiency and precision of FAMCs.

Platinum(II) Phenylpyridyl Schiff Base Complexes as Latent, Photoactivated, Alkene Hydrosilylation Catalysts.

Photoactivated catalysts for the hydrosilylation of alkenes with silanes offer temporal control in manufacturing processes that require silicone curing. We report the development of a range of air-stable Pt(II) (salicylaldimine)(phenylpyridyl), [Pt(sal)(ppy)], complexes as photoinitiated hydrosilylation catalysts. Some of these catalysts show appreciable latency in thermal catalysis and can also be rapidly (10 s) activated by a LED UV-light source (365 nm), to give systems that selectively couple trimethylvinylsilane and hexamethylsiloxymethylsilane to give the linear hydrosilylation product. Although an undetectable (by NMR spectroscopy) amount of precatalyst is converted to the active form under UV-irradiation in the timescale required to initiate hydrosilylation, clean and reliable kinetics can be measured for these systems that allow for a detailed mechanism to be developed for Pt(sal)(ppy)-based photoactivated hydrosilylation. The suggested mechanism is shown to have close parallels with, but also subtle differences from, those previously proposed for thermally-activated Karstedt-type Pt(0) systems.

Catalytic Properties of [PSiP] Pincer Cobalt(II) Chlorides Supported by Trimethylphosphine for Alkene Hydrosilylation Reactions.

In this paper, six silyl [PSiP] pincer cobalt(II) chlorides 1-6 [(2-Ph2PC6H4)2MeSiCo(Cl)(PMe3)] (1), [(2-Ph2PC6H4)2HSiCo(Cl)(PMe3)] (2), [(2-Ph2PC6H4)2PhSiCo(Cl)(PMe3)] (3), [(2-iPr2PC6H4)2HSiCo(Cl)(PMe3)] (4), [(2-iPr2PC6H4)2MeSiCo(Cl)(PMe3)] (5), and [(2-iPr2PC6H4)2PhSiCo(Cl)(PMe3)] (6)) were prepared from the corresponding [PSiP] pincer preligands (L1-L6), CoCl2 and PMe3 by Si-H bond activation. The catalytic activity of complexes 1-6 for alkene hyrdosilylation was studied. It was confirmed that complex 1 is the best catalyst with excellent regioselectivity among the six complexes. Using 1 as the catalyst, the catalytic reaction was completed within 1 h at 50 °C, predominantly affording Markovnikov products for aryl alkenes and anti-Markovnikov products for aliphatic alkene substrates. During the investigation of the catalytic mechanism, the Co(II) hydrides [(2-Ph2PC6H4)2MeSiCo(H)(PMe3)] (8) and [(2-iPr2PC6H4)2MeSiCo(H)(PMe3)] (9) were obtained from the stoichiometric reactions of complex 1 and 5 with NaBHEt3, respectively. Complexes 8 and 9 could also be obtained by the reactions of preligands L1 and L5 with Co(PMe3)4 via Si-H bond cleavage. More experiments corroborated that complex 8 is the real catalyst for this catalytic system. Under the same catalytic conditions as complex 1, using complex 8 as a catalyst, complete conversion of styrene was also achieved in 1 h, and the selectivity remained unchanged. Based on the experimental results, we propose a plausible mechanism for this catalytic reaction. The addition of B(C6F5)3 to catalyst 1 can reverse the selectivity of styrene hydrosilylation from the Markovnikov product as the main product (b/l = 99:1) to the anti-Markovnikov product as the main product (b/l = 40:60). Further study indicated that using the (CoCl2 + L1) system instead of complex 1, the selectivity was changed from Markovnikov to anti-Markovnikov product (b/l = 1:99.7). Therefore, the selectivity for the substrate styrene is influenced by the presence of a PMe3 ligand. The different selectivities may be caused by different active species. For the system of complex 1, a cobalt(II) hydride is the real catalyst, but for the (CoCl2 + L1) system, a cobalt(I) complex is proposed as active species. The molecular structures of Co(II) compounds 5 and 9 were resolved by single-crystal X-ray diffraction.

Synthesis of organosilicon‐containing phosphinyl ligands and application in the iron catalyzed hydrosilylation of olefins

Synthesis of organosilicon‐containing phosphinyl ligands and application in the iron catalyzed hydrosilylation of olefins

Precise immobilization of metal single atoms into a porphyrinic metal-organic framework for an efficient alkene hydrosilylation

Precise immobilization of metal single atoms into a porphyrinic metal-organic framework for an efficient alkene hydrosilylation

Pt(II) complexes bearing P,N-donor ligands as catalysts in chemoselective hydrosilylation, hydrogermylation, and hydroboration of terminal alkenes

In this report, we present the synthesis of six novel neutral platinum complexes employing readily available P,N-donor ligands through a straightforward two-step procedure. Subsequently, we investigated their catalytic activity in the hydroelementation of terminal olefins, highlighting their versatile utility in material and natural product chemistry. The efficient addition of silicon, germanium, and boron hydrides to the CC bond at low catalyst loading occurred exclusively in an anti-Markovnikov manner. Furthermore, our substrate scope encompasses a wide range of aliphatic and aromatic alkenes, featuring substituents with varying electronic properties. In contrast to many previous Pt-complexes, our catalytic system displayed exceptional chemoselectivity towards other unsaturated functional groups, such as carbonyl and internal CC bonds. Notably, it also exhibited remarkable tolerance to hydroxyl, alkoxyl, silyl, and thioether moieties. Additionally, we accentuated the prowess of our catalyst, showcasing its capability to sustain consistent activity and selectivity throughout numerous catalytic cycles.