Xphos ligand and platinum catalysts: A versatile catalyst for the synthesis of functionalized β-(E)-vinylsilanes from terminal alkynes

Hydrosilylation of functionalized terminal arylalkynes with a variety of silanes catalyzed by PtCl₂ or PtO₂ in the presence of the air-stable and bulky Xphos ligand was investigated. Regardless of the electronic nature (electron withdrawing or donating group) and the position (o, m, p) of the substituents on the aromatic ring, a single β-(E)-styrylsilanes was obtained in good to excellent yields. The regioselectivity of the H-Si bond addition was found to be governed by steric effects induced by the bulky Xphos ligand. A dramatic regioselectivity was also observed when functionalized terminal aliphatic alkynes were employed as a substrate and in these cases regioisomeric β-(E)-vinylsilanes were generated with excellent selectivity.     

C60乙二胺衍生物铂配合物的合成及其催化硅氢化性能

C₆₀与乙二胺反应,再与氯亚铂酸钾配位,得到了一种以C₆₀衍生物为基的Pt(Ⅱ)配合物,并研究了其在烯烃与三乙氧基硅烷的硅氢加成反应中的催化性能。结果表明,该配合物为硅氢加成反应的高效催化剂,并对苯乙烯有独特的催化性能,以近100%的区域选择性得到α-加成产物。     

Tri(t-butyl)phosphine-assisted selective hydrosilylation of terminal alkynes

<正>A highly efficient and regio-/stereoselective method of hydrosilylating terminal alkynes was developed using Pt(DVDS)-tri(t-butyl) phosphine catalyst system at room temperature.Trans-products or alpha-products were obtained almost exclusively depending on the alkynes and silanes employed.     

Regioselective hydrostannation of highly hindered arylalkynes under ortho-directing effects

Palladium-catalyzed hydrostannation reactions of ortho-disubstituted arylalkynes were achieved with total stereo- and regio-selectivity in THF at room temperature. The regioselectivity was found to be under the control of the ortho-substituents (ortho-directing effects, ODE) and pure α-vinylstannanes are produced in good yields and as single isomers regardless of the substituents’ nature. These hydrostannation α-products are precursors of choice for the preparation of stereo-defined triarylolefins.     

Synthesis of 2-methylidene-1-silacyclohexanes by intramolecular hydrosilylation

The preparation of various (hex-5-ynyl)silanes was achieved following two different synthetic approaches from readily available materials such as 4-bromobutene, 6-iodohexyne and chlorosilanes. Different reaction conditions for intramolecular hydrosilylation were tested to prepare the corresponding 2-methylidene-1-silacyclohexanes. Notably, the use of Speier’s catalyst allowed the regioselective formation of the desired products in moderate yields.     

Expanded ring N-heterocyclic carbene complexes of zero valent platinum dvtms (divinyltetramethyldisiloxane): Highly efficient hydrosilylation catalysts

The synthesis and characterisation of a series of new 6- and 7-membered NHC (N-heterocyclic carbene) complexes 7-12 of zero valent platinum dvtms (divinyltetramethyldisiloxane), [Pt(NHC)(dvtms)] are reported. A number of the complexes were investigated as catalyst precursors in the hydrosilylation of a range of unsaturated substrates, including alkynes, alkenes and a ketone with triethylsilane and bis(trimethylsiloxy)methylsilane (MD’M), at low catalyst loading (0.005 mol %); in general, the activity, and the selectivity for 1-functionalised product was found to be high.     

负载型铂催化剂催化苯乙烯硅氢加成反应

分别研究了硅胶、γ-Al2O3和5分子筛负载聚乙二醇络合铂催化剂催化苯乙烯与甲基二氯硅烷的硅氢加成反应,发现这三种催化剂对β-加成产物的选择性为100%,不生成α-加成产物。而用Speier催化剂对β-加成产物的选择性为55%,产生α-加成产物。在这三种催化剂中,分子筛作载体的催化剂重复使用性较差,Al2O3作载体的催化剂诱导期较长,而硅胶作载体的催化剂比其它两种催化剂重复使用性好,且诱导期也较短,因此具有明显的优越性。文中还初步探讨了这三种催化剂出现高选择性的原因。     

Hydrosilylation of alkynes catalysed by platinum on titania

The heterogeneous hydrosilylation of alkynes catalysed by platinum on titania is reported. A variety of hydrosilanes react with both terminal and internal alkynes to furnish the corresponding vinyl silanes in high yields and short reaction times as well as in a regio- and stereoselective manner. The catalyst can be easily recovered and reused in several consecutive cycles.     

Regiocontrol in the palladium-catalyzed hydrophosphinylation of terminal alkynes

The regioselectivity of the palladium-catalyzed hydrophosphinylation of terminal alkynes was investigated. Complementary conditions to achieve the predominant formation of either the linear or the branched alkenyl-H-phosphinate products were identified. With Pd/xantphos in acetonitrile, the linear isomer is generally obtained with good to excellent selectivity, and E-stereospecificity. On the other hand, by using Pd/dppf in the non-polar solvent toluene, good selectivity for the branched alkenyl-H-phosphinate is typically observed. The role of various reaction parameters is studied.     

Regio- and stereoselective hydrosilylation of immobilized terminal alkynes

Regio- and stereoselective hydrosilylation of terminal alkynes on solid support using diisopropyl hydrosilanes yielding β-(E)-vinyl silanes with excellent selectivity is reported. The hydrosilylation is catalyzed by Pt(DVDS)/P(ⁱBuNCH₂CH₂)₃N (DVDS = 1,3-divinyl-1,1,3,3-tetramethyl-disiloxane), in which the bulky proazaphosphatrane ligand plays a key role for the selectivity. The immobilized products are characterized with gel phase¹³C NMR and ¹H high resolution magic angle spinning NMR.     

Platinum(II)-bis-(N-heterocyclic carbene) complexes: synthesis, structure and catalytic activity in the hydrosilylation of alkenes

Chelating biscarbene ligands increase the stability of metal-organic catalyst systems. The catalytic activities of seven structurally different platinum(II)-bis-NHC-complexes in the hydrosilylation of alkenes have been investigated and compared with the catalytic activity of the Karstedt catalyst and of a highly active platinum(0)-NHC-complex. It is shown that a fine-tuning of the catalytic activity of the platinum(II)-bis-NHC-complexes is possible. The synthesis of a platinum(II)-bis-NHC-complex with similar activity, but additional advantages compared to the Karstedt catalyst, is reported. The solid state structure of 1,1-[Bis(3,3′-(4-methoxyphenyl)-1,1′-1H-imidazolium-2,2′-ylidene)methanediyl]platinum(II)-dichloride is presented.     

Platinum-catalyzed intermolecular hydroamination of terminal alkynes

The hydroamination of terminal alkyl- and arylacetylenes with aniline is catalyzed by platinum(II) bromide, yielding the corresponding imines. Contrary to what has been previously demonstrated for the platinum(II)-catalyzed hydroamination of -olefins, the presence of n-Bu₄PBr has a detrimental effect on the course of the reaction. The hydroamination of 1-hexyne is highly regioselective (Markovnikov) at 60 °C, but the regioselectivity decreases upon increasing the temperature. The hydroamination of phenylacetylene is fully regioselective (Markovnikov) at 100 °C. TON up to 146 were obtained in the presence of a catalytic source of protons.     

Double Insertion of Coordinated Phosphanylalkyne Ligands into a Pt−C6F5 Bond

Enhanced reactivity is shown by uncoordinated C≡C bonds in the proximity of a metal in phosphanylacetylene complexes. cis-[Pt(C₆F₅)₂(thf)₂] reacts with [M(C₆F₅)₂(PPh₂C≡CPh)₂] (M=Pt, Pd) to form binuclear complexes containing the novel 2,3-bis(diphenylphosphanyl)-1,3-butadien-1-yl bridging ligand. Substitution of the solvent ligands with, for example, PPh₂H (see picture) provides species that could be characterized by X-ray crystallography.     

p-Toluenesulfonic acid-promoted selective functionalization of unsymmetrical arylalkynes: a regioselective access to various arylketones and heterocycles

Regioselective hydration of a wide range of internal alkynes has been afforded in high to good yields by using PTSA in EtOH. The scope of the reaction of alkynes has been delineated. Arylaliphatic alkynes and diarylalkynes were regioselectively hydrated in good to excellent yields and short reaction times when the reaction was achieved under microwave irradiation. Moreover, diarylalkynes, arylenynes as well as diaryldiynes bearing a methoxy- or a thiomethyl substituent on the ortho position underwent a regioselective 5-endo-dig-cyclization to give a variety of 2-aryl- and 2-styrylbenzofuran or benzothiphene derivatives. We believe that, this new environmentally metal-free procedure combined to microwave irradiation would be in importance in the search of green laboratory-scale synthesis.     

Rapid microwave assisted hydration of internal arylalkynes in the presence of PTSA: an efficient regioselective access to carbonyl compounds

A metal-free procedure for the regioselective hydration of internal arylalkynes under microwave irradiation is described. The reaction promoted by PTSA takes place rapidly in EtOH and regioselectively afforded in good yields various carbonyl compounds 2.     

Selective hydrosilylation of styrene using an in situ formed platinum(1,3-dimesityl-dihydroimidazol-2-ylidene) catalyst

A highly active and selective in situ formed platinum(N-heterocyclic carbene) catalyst for the hydrosilylation of styrene with triethylsilane is described, which unlike all other known hydrosilylation catalysts, selectively yields hydrosilylation products, but (almost) no dehydrogenative silylation products.     

Synthesis of a novel functional polymer immobilized platinum complex and its application in the catalytic hydrosilylation of 3,3,3-trifluoropropene with triethoxysilane

A novel polymer has been synthesized using 2-vinylpyridine as a functional monomer and allyl polyethylene glycol as a cross-linking agent, and platinum has been immobilized on this synthesized polymer. The resulting immobilized catalyst showed superior catalytic performance for the hydrosilylation of 3,3,3-trifluoropropene with triethoxysilane as compared to homogenous platinum catalyst, polystyrene-immobilized platinum or other hydrosilylation catalysts. The conversion of silane is about 100% and the maximum yield of β-adduct is 92.3% with slightly α-adduct. Furthermore, the catalyst showed sufficient stability that it could be reused three times without noticeable inactivation.     

Calix[4]dithiacrown-6 and Its Platinum Complex

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Atroposelective Synthesis of Axially Chiral Styrenes by Platinum- Catalyzed Stereoselective Hydrosilylation of Internal Alkynes

Hydrofunctionalization of alkynes is one of the most efficient ways to access axially chiral styrenes with open-chained olefins. While great advances have been achieved for 1-alkynylnaphthalen-2-ols and analogues, atroposelective hydrofunctionalization of unactivated internal alkynes lags. Herein we reported a platinum-catalyzed atroposelective hydrosilylation of unactivated internal alkynes for the first time. With monodentate TADDOL-derived phosphonite L1 used as a chiral ligand, various axially chiral styrenes were achieved in excellent enantioselectivities with high E-selectivities. Control experiments showed that the NH-arylamide groups have significant effects on both the yields and enantioselectivities and could act as directing groups. The potential utilities of the products were shown by the transformations of the amide motifs of the products.     

Nickel-catalyzed regioselective hydrocyanation of terminal alkynes by assistance of a tosyl group

Nickel-catalyzed regioselective hydrocyanation of terminal alkynes is described. A tosylamide functionality at the propargyl position was the most suitable group for controlling the regiochemistry for CCN bond formation as well as rate enhancement. A gram-scale synthesis was achieved by minimizing the catalyst loading to 2?mol%. The major HCN adduct could be transformed to the corresponding indoline through construction of a benzylic quaternary carbon under iron catalysis.