Iridium as a general catalyst for the decarbonylative addition of aldehydes to alkynes

A general catalytic system for the decarbonylative addition reaction of aldehydes with alkynes is developed by using an iridium catalyst system. Both aromatic and aliphatic aldehydes reacted with terminal alkynes efficiently to give the corresponding olefination products in high yields and up to 11:1 E/Z selectivity.     

Cobalt‐Catalyzed Z‐Selective Hydrosilylation of Terminal Alkynes

A cobalt‐catalyzed Z ‐selective hydrosilylation of alkynes has been developed relying on catalysts generated from bench‐stable Co(OAc)₂ and pyridine‐2,6‐diimine (PDI) ligands. A variety of functionalized aromatic and aliphatic alkynes undergo this transformation, yielding Z ‐vinylsilanes in high yields with excellent selectivities (Z /E ratio ranges from 90:10 to >99:1). The addition of a catalytic amount of phenol effectively suppressed the Z /E ‐isomerization of the Z ‐vinylsilanes that formed under catalytic conditions.     

Formation and properties of hydrogenation catalysts based on palladium bisacetylacetonate and sodium tetrahydroborate

Properties of the Pd(acac)₂-nNaBH₄ system in catalysis of the reactions of hydrogenation of alkenes, alkynes, and carbonyl and nitro groups were studied. A number of spectral methods (NMR, UV spectroscopy) and X-ray phase analysis were used to examine the main stages of formation of palladium hydrogenation catalysts produced in the interaction of Pd(acac)₂ with sodium tetrahydroborate, and reasons for the bimodal nature of the dependence of the catalytic activity on the B/Pd ratio were considered.     

Palladium-catalyzed hydrophosphinylation of alkenes and alkynes

Various palladium catalysts promote the addition of hypophosphorous derivatives ROP(O)H(2) to alkenes and alkynes in good yields and under mild conditions. Particularly, Cl(2)Pd(PPh(3))(2)/2 MeLi, and Pd(2)dba(3)/xantphos allow for phosphorus-carbon bond formation instead of transfer hydrogenation. Commercial aqueous solutions of hypophosphorous acid can be employed successfully at ambient temperature. With styrene and terminal alkynes, the regioselectivity (linear versus branched products) can be controlled to some extent with the catalytic system employed. The methodology considerably extends upon previous routes for the preparation of H-phosphinic acids and other organophosphorus compounds.     

Palladium-based bimetallic catalysts for highly selective semihydrogenation of alkynes using ex situ generated hydrogen

Semihydrogenation of alkynes to alkenes is an important and fundamental reaction in many industrial and synthetic applications and often suffers low selectivity because of the overhydrogenation. Here, highly selective semihydrogenation of alkynes is achieved by using H₂ ex situ generated from formic acid dehydrogenation with palladium (Pd)-based bimetallic catalysts through a two-chamber reactor in this work, realizing efficient utilization of H₂ and selective production of alkenes under mild reaction conditions. The Pd-based bimetallic catalysts show excellent catalytic performances for semihydrogenation of alkynes (PdZn bimetallic catalyst) and dehydrogenation of formic acid (PdAg bimetallic catalyst) in the two-chamber reactor.     

钯催化下(Z)-3-碘-3-三氟甲基-1-芳基烯丙醇与末端炔 烃的偶联反应

在Pd(PPh~3)~4/CuI催化下和使用1mol的NEt~3作碱和THF作溶剂,(Z)-3-碘-3-三氟甲基-1-芳基烯丙醇(1)与末端炔烃(3)反应得到正常的偶联产物5。当以NEt~3作碱和溶剂,Pd(PPh~3)~4/CuI催化1与3的交叉偶联反应生成化合物4。4为正常偶联化合物5在NEt~3存在下双键发生重排反应的产物。     

A Palladium Nanoparticle–Nanomicelle Combination for the Stereoselective Semihydrogenation of Alkynes in Water at Room Temperature

The addition of NaBH₄ to Pd(OAc)₂ in water containing nanomicelles leads to the generation of H₂ and Pd nanoparticles. Subsequent reduction of disubstituted alkynes affords Z‐alkenes in high yields. These reactions are general, take place in water at ambient temperatures, and offer recycling of the aqueous reaction mixture along with low overall E Factors.     

Chemoselective hydrogenation using molecular sieves-supported Pd catalysts: Pd/MS3A and Pd/MS5A

Palladium catalysts embedded on molecular sieves (MS3A and MS5A) were prepared by the adsorption of Pd(OAc)₂ onto molecular sieves with its in situ reduction to Pd⁰ by MeOH as a reducing agent and solvent. 0.5% Pd/MS3A and 0.5% Pd/MS5A catalyzed the hydrogenation of alkynes, alkenes, and azides with a variety of coexisting reducible functionalities, such as nitro group, intact. It is noteworthy that terminal alkenes of styrene derivatives possessing electron-donating functionalities on the benzene nucleus were never hydrogenated under 0.5% Pd/MS5A-catalyzed conditions, while internal alkenes of 1-propenylbenzene derivatives were readily reduced to the corresponding alkanes.     

Fast and Selective Semihydrogenation of Alkynes by Palladium Nanoparticles Sandwiched in Metal–Organic Frameworks

The semihydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry. Unfortunately, state‐of‐the‐art heterogeneous catalysts hardly achieve high turnover frequencies (TOFs) simultaneously with almost full conversion, excellent selectivity, and good stability. Here, we used metal–organic frameworks (MOFs) containing Zr metal nodes (“UiO”) with tunable wettability and electron‐withdrawing ability as activity accelerators for the semihydrogenation of alkynes catalyzed by sandwiched palladium nanoparticles (Pd NPs). Impressively, the porous hydrophobic UiO support not only leads to an enrichment of phenylacetylene around the Pd NPs but also renders the Pd surfaces more electron‐deficient, which leads to a remarkable catalysis performance, including an exceptionally high TOF of 13835 h^?1, 100 % phenylacetylene conversion 93.1 % selectivity towards styrene, and no activity decay after successive catalytic cycles. The strategy of using molecularly tailored supports is universal for boosting the selective semihydrogenation of various terminal and internal alkynes.     

Fast and Selective Semihydrogenation of Alkynes by Palladium Nanoparticles Sandwiched in Metal–Organic Frameworks

The semihydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry. Unfortunately, state-of-the-art heterogeneous catalysts hardly achieve high turnover frequencies (TOFs) simultaneously with almost full conversion, excellent selectivity, and good stability. Here, we used metal–organic frameworks (MOFs) containing Zr metal nodes (“UiO”) with tunable wettability and electron-withdrawing ability as activity accelerators for the semihydrogenation of alkynes catalyzed by sandwiched palladium nanoparticles (Pd NPs). Impressively, the porous hydrophobic UiO support not only leads to an enrichment of phenylacetylene around the Pd NPs but also renders the Pd surfaces more electron-deficient, which leads to a remarkable catalysis performance, including an exceptionally high TOF of 13835 h⁻¹, 100 % phenylacetylene conversion 93.1 % selectivity towards styrene, and no activity decay after successive catalytic cycles. The strategy of using molecularly tailored supports is universal for boosting the selective semihydrogenation of various terminal and internal alkynes.     

Stereoselective Synthesis of Trisubstituted Alkenes through Sequential Iron‐Catalyzed Reductive anti‐Carbozincation of Terminal Alkynes and Base‐Metal‐Catalyzed Negishi Cross‐Coupling

The stereoselective synthesis of trisubstituted alkenes is challenging. Here, we show that an iron‐catalyzed anti‐selective carbozincation of terminal alkynes can be combined with a base‐metal‐catalyzed cross‐coupling to prepare trisubstituted alkenes in a one‐pot reaction and with high regio‐ and stereocontrol. Cu‐, Ni‐, and Co‐based catalytic systems are developed for the coupling of sp‐, sp²‐, and sp³‐hybridized carbon electrophiles, respectively. The method encompasses a large substrate scope, as various alkynyl, aryl, alkenyl, acyl, and alkyl halides are suitable coupling partners. Compared with conventional carbometalation reactions of alkynes, the current method avoids pre‐made organometallic reagents and has a distinct stereoselectivity.     

Copper (II)-catalyzed regio- and stereoselective addition of H/P(O)R2 to alkynes

Cu(acac)₂ is the new universal catalyst for β-E regio- and stereoselective syn-addition of the H–P(O)-bond of diphenylphosphine oxide, H-phosphinates, dialkylphosphites to various alkynes in the synthesis of P(O)-containing alkenes. Without additives and ligands Cu(II)-compounds showed better results than CuI or Ni(acac)₂. The catalytic system developed is tolerant to typical organic functional groups present in the alkynes and to the nature of different substituents in the H–P(O)-compounds.     

Palladium-catalyzed conjugate addition to electron-deficient alkynes with benzenesulfinic acid derived from 1,2-bis(phenylsulfonyl)ethane: selective synthesis of (E)-vinyl sulfones

A new, selective method for the synthesis of (E)-vinyl sulfones is presence by palladium-catalyzed C-S bond cleavage/conjugate addition. In the presence of Pd(OAc)(2) and DMEDA (N(1),N(2)-dimethylethane-1,2-diamine), 1,2-bis(phenylsulfonyl)ethane underwent the C-S bond cleavage, followed by conjugate addition to numerous electron-deficient alkynes afforded the corresponding (E)-vinyl sulfones in moderate to good yields.     

Monomeric Magnesium Catalyzed Alkene and Alkyne Hydroboration

In this work, two monomeric magnesium alkyl complexes ( 1 and 2 ) were prepared using bis(phosphino)carbazole framework and among them 1 has been used as a catalyst for hydroboration of alkenes and alkynes with pinacolborane (HBpin). A broad variety of aromatic and aliphatic alkenes and alkynes were efficiently reduced. Anti-Markovnikov regioselective hydroboration of alkenes and alkynes was achieved, which was confirmed by deuterium-labelling experiments. The work represents the first example of the use of magnesium in homogeneous catalytic hydroboration of alkene with broad substrate scope. Experimental mechanistic investigations and DFT calculations provided insights into the reaction mechanism. Finally, the hydroboration protocol was extended to terpenes.     

A DFT computational study of the bis-silylation reaction of acetylene catalyzed by palladium complexes

In this paper we have investigated at the DFT(B3LYP) level the catalytic cycle for the bis-silylation reaction of alkynes promoted by palladium complexes. A model-system formed by an acetylene molecule, a disilane molecule, and the Pd(PH(3))(2) complex has been used. The most relevant features of this catalytic cycle can be summarized as follows: (i) The first step of the cycle is an oxidative addition involving H(3)Si-SiH(3) and Pd(PH(3))(2). It occurs easily and leads to the cis (SiH(3))(2)Pd(PH(3))(2) complex that is 5.39 kcal mol(-1) lower in energy than reactants. (ii) The transfer of the two silyl groups to the C-C triple bond does not occur in a concerted way, but involves many steps. (iii) The cis (SiH(3))(2)Pd(PH(3))(2) complex, obtained from the oxidative addition, is involved in the formation of the first C-Si bond (activation barrier of 18.34 kcal mol(-1)). The two intermediates that form in this step cannot lead directly to the formation of the final bis(silyl)ethene product. However, they can isomerize rather easily (the two possible isomerizations have a barrier of 16.79 and 7.17 kcal mol(-1)) to new more stable species. In both these new intermediates the second silyl group is adjacent to the acetylene moiety and the formation of the second C-Si bond can occur rapidly leading to the (Z)-bis(silyl)ethene, as experimentally observed. (iv) The whole catalytic process is exothermic by 41.54 kcal mol(-1), in quite good agreement with the experimental estimate of this quantity (about 40 kcal mol(-1)).     

A facile preparation of 1-perflouroalkylalkenes and alkynes. Palladium catalyzed reaction of perfluoroalkyl iodides with organotin compounds

Alkenyl, allyl, and alkynylstannanes react with perfluoroalkyl iodides in the presence of a catalytic amount of Pd(PPh₃)₄ to give alkenes and alkynes bearing perfluoroalkyl group.     

A facile stereospecific synthesis of （Z）-2-sulfonyl-substituted 1,3-enynes via Sonogashira coupling of （E）-α-iodovinyl sulfones with 1-alkynes

(E)-a-Iodovinyl sulfones 1 underwent the Sonogashira coupling reactions with terminal alkynes 2 in piperidine at room temperature in the presence of 5 mol% of Pd(PPh3)4 and 10 mol% of CuI to stereospecifically afford the corresponding (Z)-2- sulfonyl-substituted 1,3-enynes 3 in high yields.     

Palladium-catalyzed convenient one-pot synthesis of multi-substituted 2-pyrones via transesterification and alkenylation of enynoates

An efficient one-pot protocol for the synthesis of multi-substituted 2-pyrone derivatives from internal alkynes and unactivated alkenes is reported. The methodology involves difunctionalization of internal alkynes by using Pd(II) as a catalyst alongwith X-Phos as ligand via 6-endo transesterification and subsequent alkenylation pathway. Notable features include simple and easily available starting materials, including a range of unactivated alkenes, reduced synthetic steps and mild reaction conditions with high efficiency.     

Palladium-catalyzed desulfitative Mizoroki-Heck couplings of sulfonyl chlorides with mono- and disubstituted olefins: rhodium-catalyzed desulfitative heck-type reactions under phosphine- and base-free conditions

New conditions have been found for the desulfitative Mizoroki-Heck arylation and trifluoromethylation of mono- and disubustituted olefins with arenesulfonyl and trifluoromethanesulfonyl chlorides. Thus (E)-1,2-disubstituted alkenes with high stereoselectivity and 1,1,2-disubstituted alkenes with 12:1 to 21:1 E/Z steroselectivity can be obtained. Herrmann's palladacycle at 0.1 mol % is sufficient to catalyze these reactions, for which electron-rich or electron-poor sulfonyl chlorides and alkenes are suitable. If phosphine- and base-free conditions are required, 1 mol % [RhCl(C(2)H(4))(2)] catalyzes the desulfitative cross-coupling reactions. Contrary to results reported for [RuCl(2)(PPh(3))(2)]-catalyzed coupling reactions with sulfonyl chlorides, the palladium and rhodium desulfitative Mizoroki-Heck coupling reactions are not inhibited by radical scavenging agents. Possible sulfones arising from the sulfonylation of alkenes at 60 degrees C are not desulfitated at higher temperatures in the presence of the Pd or Rh catalysts.     

Encapsulation of Palladium Carbide Subnanometric Species in Zeolite Boosts Highly Selective Semihydrogenation of Alkynes

The selective hydrogenation of alkynes to alkenes is a crucial step in the synthesis of fine chemicals. However, the widely utilized palladium (Pd)-based catalysts often suffer from poor selectivity. In this work, we demonstrate a carbonization-reduction method to create palladium carbide subnanometric species within pure silicate MFI zeolite. The carbon species can modify the electronic and steric characteristics of Pd species by forming the predominant Pd−C₄ structure and, meanwhile, facilitate the desorption of alkenes by forming the Si−O−C structure with zeolite framework, as validated by the state-of-the-art characterizations and theoretical calculations. The developed catalyst shows superior performance in the selective hydrogenation of alkynes over mild conditions (298 K, 2 bar H₂), with 99 % selectivity to styrene at a complete conversion of phenylacetylene. In contrast, the zeolite-encapsulated carbon-free Pd catalyst and the commercial Lindlar catalyst show only 15 % and 14 % selectivity to styrene, respectively, under identical reaction conditions. The zeolite-confined Pd-carbide subnanoclusters promise their superior properties in semihydrogenation of alkynes.