Hydrosilylation Of Terminal Alkynes Research Articles

Novel Pt(II) Mono- and Biscarbene Complexes: Synthesis, Structural Characterization and Application in Hydrosilylation Catalysis

Reactions of imidazolium and benzimidazolium halides with PtBr2 and PtI2 in DMSO afford cis-Pt(II) heterocyclic carbene DMSO mixed ligand complexes 1−3 and biscarbene complexes 4−6. The reaction between 1,3-dibenzylbenzimidazolium bromide and PtBr2 in CH3CN gives no carbene complex but a benzimidazolium hexabromoplatinate(IV) salt 7. All the products have been fully characterized by NMR and ESI-MS spectroscopy as well as X-ray single-crystal diffraction study. Both intramolecular γ-hydride interactions with metal or its coordinated bromide and intermolecular H-bonding between heterocyclic proton with bromide are evident in some of these structures. These complexes are active in the hydrosilylation of terminal alkynes (phenylacetylene and trimethylsilylacetylene) with triethylsilane and bis(trimethylsiloxy)methylsilane. When phenylacetylene is used, the monocarbene complexes (1−3) show higher catalytic activity than chelating biscarbene analogues (5 and 6). Non-chelating biscarbene complex 4 gives a different selectivity pattern favoring the β(Z) and dehydrogenative silylation products when compared to 1−3, 5 and 6, and 7. In contrast, 4 and 5 are more active than 1 and 2 toward trimethylsilylacetylene. In general, monocarbene complexes give higher conversions over a short duration in the hydrosilylation of phenylacetylene with triethylsilane and bis(trimethylsiloxy)methylsilane, whereas in the hydrosilylation of trimethylsilylacetylene with triethylsilane, the chelating and biscarbene tend to be more active.

Recent advances in organothorium and organouranium catalysis

In this critical review we summarize the latest results obtained during the last decade concerning the catalytic activities of organoactinide complexes. We begin with a brief summary of the synthesis and characterization of uranium and thorium complexes that later will be used as catalysts for demanding chemical transformations. Hydroamination, hydrosilylation of terminal alkynes, coupling of terminal alkynes with isonitriles, catalytic reduction of azides and hydrazines, ring opening polymerization of cyclic esters and polymerization of alpha-olefins are covered in this review (118 references). The topics covered in this review regarding organoactinide chemistry will be of interest to inorganic, organic and organometallic chemists, material and catalytic scientists due to its unique mode of activation as compared to late transition-metals. In addition, the field of organoactinide complexes in catalysis is steadily growing, because of the complementary reactivity of organoactinides as compared to other early or late transition complexes, in demanding chemical transformations.

Alkenyl-functionalized NHC iridium-based catalysts for hydrosilylation

A family of alkenyl-functionalized N-heterocyclic-carbene–iridium(I) complexes has been synthesized, providing a series of mono-coordinated, bis-chelate and pinceralkenyl-NHC species. Olefin coordination is highly influenced by the nature of the substituents on the NHC ring, and on the length of the alkenyl branch. A fluxional process involving coordination/decoordination of the olefin in bis-allyl-NHC complexes has been studied, and the activation parameters have been determined by means of VT-NMR spectroscopy. The mono-coordinated complexes are highly active in the hydrosilylation of terminal alkynes, showing high selectivity for the Z-isomers, with no α-isomers or dehydrogenative silylation processes being observed. The molecular structures reported that are representative of the species have been determined by means of X-ray crystallography.

A One‐Pot Synthesis of (E)‐Disubstituted Alkenes by a Bimetallic [Rh–Pd]‐Catalyzed Hydrosilylation/Hiyama Cross‐Coupling Sequence

A bimetallic [Rh-Pd] catalyst was prepared by soaking into an iodide ionic gel an equimolar solution of [RhCl(PPh(3))(3)] and Pd(OAc)(2) in CH(2)Cl(2). Its catalytic activity was evaluated by rhodium-catalyzed hydrosilylation (H), palladium-catalyzed Hiyama coupling (C), and in the one-pot hydrosilylation/Hiyama coupling sequence (H/C). It was found that the homogeneous combination [RhCl(PPh(3))(3)]/NaI was a superior system compared to the polyionic mono- and bimetallic rhodium catalysts in the hydrosilylation of terminal alkynes. Interestingly, the most effective catalyst in terms of stereo- and chemoselectivities was observed to be the bimetallic ionic gel [Rh-Pd] in the one-pot process leading to (E)-alkenes with good yields. The remarkable stereocontrol is ascribed to a beneficial Pd-catalyzed isomerization from the mixture of stereoisomeric vinylsilanes obtained in the initial hydrosilylation step into the more stable (E)-adduct. The [Rh-Pd] heterogeneous catalyst also showed a higher chemoselectivity than the homogeneous catalytic combination, and no detrimental formation of Sonogashira side product was observed due to an ionic-gel-mediated kinetic modulation. To illustrate its scope and limitations, the described one-pot bimetallic catalytic sequence was extended to functionalized terminal alkynes and various iodide substrates. Conjugated systems, such as hydroxycinnamaldehyde, dienes, and trienes, were synthesized in good overall yields. To avoid deactivation of the Rh species, N-heterocyclic iodides had to be added sequentially after completion of hydrosilylation.

Hydrosilylation of Terminal Alkynes with Alkylidene Ruthenium Complexes and Silanes.

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Hydrosilylation of Alkynes Mediated by N-Heterocyclic Carbene Platinum(0) Complexes

The hydrosilylation of terminal alkynes by silanes catalyzed by N-heterocyclic carbene platinum(0) complexes has been investigated. The alkynes included 1-octyne and phenylacetylene. The silanes investigated were bis(trimethylsilyloxy)methylsilane, (trimethylsilyloxy)dimethylsilane, tert-butyldimethylsilane, triphenylsilane, phenyldimethylsilane, triethylsilane, and triethoxysilane. X-ray crystal structures for [Pt(N,N‘-dicyclohexylimidazol-2-ylidene)(η2-dimethylacetylenedicarboxylate)2] (8) and [Pt{C(E)C(E)−C(E)C(E)}(N,N‘-dimethylbenzimidazol-2-ylidene)(σ-NCCH3)] (10) (E = CO2Me) have been obtained. A selectivity model, based on structural parameters of the N-heterocyclic carbene, has been devised in order to rationalize the observed regioselectivity obtained. By a judicious choice of catalyst, alkyne, and silane, the regioselectivity of the addition can be controlled.

Hydrosilylation of Terminal Alkynes with Alkylidene Ruthenium Complexes and Silanes

[reaction: see text] Ruthenium alkylidene complexes 1-3 mediate hydrosilylation of alkynes with silanes. When triethoxy- or triphenylsilanes are used as silylating agents, the reaction affords alpha-substituted vinylsilanes as major products.

Hydrosilylation of Alkynes Catalyzed by Ruthenium Carbene Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Hydrosilylation of alkynes catalyzed by ruthenium carbene complexes

Hydrosilylation of terminal alkynes with a variety of silanes catalyzed by Cl 2(PCy 3) 2Ru CHPh ( 1 ) affords mainly the Z-isomer via trans addition in excellent yields. The presence of a hydroxyl group in close proximity to the triple bond was observed to exert a strong directing effect, resulting in the highly selective formation of the α-isomer. Intramolecular hydrosilylation of a homopropargylic silyl ether was demonstrated to give the cis addition product.

Organoactinides-New Type of Catalysts For Carbon-Silicon Bond Formation

Organoactinide complexes of the type Cp2*AnMe2 (An = Th, U) have been found to be efficient catalysts for the hydrosilylation of terminal alkynes. The chemoselectivily and regiospecificity of the reactions depend strongly on the nature of the catalyst, the nature of the alkyne, the silane substituents, the ratio between the silane and alkyne, the solvent and the reaction temperature. The hydrosilylation reaction of the terminal alkynes with PhSiH3 at room temperature produces the trans-vinylsilane as the major product along with the silylalkyne and the corresponding alkene. At higher temperatures the cis-vinylsilane and the double hydrosifylated alkene, in which the two silicon moieties are connected at the same carbon atom, are also obtained. Replacing the pentamethylcyclopentadienyl ligand by the bridge ligation [Me2SiCp"2]2- 2[Li]+ (Cp" = C5Me4) affords the synthesis of ansa-Me2SiCp"2ThBu2, which was found to react extremely fast for the hydrosilylation of terminal alkynes or alkenes with PhSiH3. Besides the rapidity of the processes using the bridge organoactinide, as compared to Cp*2ThMe2 the chemo- and regio-selectivity of the products were increased allowing the production of only the trans-vinylsilane and the 1-silylated alkane for the hydrosilylation of alkyne and alkene, respectively.

Organoactinides—novel catalysts for demanding chemical transformations

The catalytic effect obtained by opening the coordination sphere of the organoactinide complex is presented. Replacing the pentamethylcyclopentadienyl ligand in Cp 2*ThCl 2 (Cp*=C 5Me 5) by the bridge ligation [Me 2SiCp 2″] 2− 2[Li] + (Cp″=C 5Me 4) affords the synthesis of ansa-Me 2SiCp 2″ThCl 2, which reacts with two equiv of BuLi affording the corresponding dibutyl complex ansa-Me 2SiCp 2″Th″Bu 2. This latter complex was found to be an active catalyst for the dimerization of terminal alkynes, and in the hydrosilylation of terminal alkynes with PhSiH 3. In both processes a large chemoselectivity and regioselectivity are achieved due to the hindered equatorial plane, attributed to the disposition of the methyl groups in the bridge ligation, forcing the incoming substrates to react with a specific regiochemistry.

The Catalytic Effect in Opening an Organoactinide Metal Coordination Sphere: Regioselective Dimerization of Terminal Alkynes and Hydrosilylation of Alkynes and Alkenes with PhSiH3 Promoted by Me2SiCp‘ ‘2ThnBu2

This contribution describes the catalytic effect observed by opening the coordination sphere at an organoactinide complex. Replacing the pentamethylcyclopentadienyl ligand in Cp*2ThCl2 (Cp* = C5Me5) by the bridge ligation [Me2SiCp‘ ‘2]2-2[Li]+ (Cp‘ ‘ = C5Me4) affords the synthesis of ansa-Me2SiCp‘ ‘2ThCl2. The X-ray structure of this bridged complex coordinated to LiCl salt and solvent is presented, indicating the large coordinative unsaturation of the bridge organoactinides. This dichloro complex reacts with 2 equiv of BuLi, affording the corresponding dibutyl complex ansa-Me2SiCp‘ ‘2Th(CH2CH2CH2CH3)2, which was found to react extremely fast for the dimerization of terminal alkynes and also in the hydrosilylation of terminal alkynes or alkenes with PhSiH3. Besides the rapidity of the processes using the bridge organoactinide, as compared to Cp*2ThMe2, the chemo- and regioselectivity of the products were increased, allowing the production of only the gem-dimer, the trans-vinylsilane, and the 1-silylated a...

ChemInform Abstract: Highly Stereoselective and Efficient Hydrosilylation of Terminal Alkynes Catalyzed by [RuCl2(p-cymene)]2.

With [RuCl2(p-cymene)]2 as a catalyst, extremely high regio- and stereoselectivity was observed in the hydrosilylation reaction of various terminal alkynes under mild conditions to afford β-(Z)-vinylsilanes in excellent yields. A dramatic directing effect was also observed when alkynes having a hydroxyl group at the β position to the triple bond were employed as a substrate, and in these cases regioisomeric α-vinylsilanes were generated with excellent selectivity.