Catalysts For Hydrosilylation Research Articles

ChemInform Abstract: Hydrosilylation Reaction of Olefins: Recent Advances and Perspectives

AbstractReview: recent developments of efficient, selective, and cheaper hydrosilylation catalyst systems appearing in the last decade; 79 refs.

Synthesis and Reactivity of a Hydrido CNC Pincer Cobalt(III) Complex and Its Application in Hydrosilylation of Aldehydes and Ketones

Reaction of the N-benzylidene-1-naphthylamine with CoMe(PMe3)4 afforded the hydrido CNC pincer cobalt complex CoH(PMe3)2[(C6H4)CH═N(C10H6)] (1) via double C–H bond activation. In the 1H NMR spectrum, a triplet at −18.98 ppm is the typical signal of the hydrido ligand (Co–H). Complex 1 reacted with haloalkane (CH3I and EtBr) to deliver CoX(PMe3)2((C6H4)CH═N(C10H6)) (X = I (2); Br (3)). However, the reactions of complex 1 with HCl and trifluoroacetic acid (TFA) delivered HCoCl(PMe3)2((C6H4)CH═N(C10H7)) (4) and HCo(OCOCF3)(PMe3)2((C6H4)CH═N(C10H7)) (5) with the cleavage of the Co–C(naphthyl) bond. In the 1H NMR spectra, the signals of the hydrido ligands were found at −21.31 (4) and −18.71 (5) ppm. A reaction of complex 1 with DCl was carried out to prove that the hydrogen atom eliminated to the naphthyl carbon comes from HCl. Complex 1 reacted with acetylacetone, resulting in the formation of Co(acac)(PMe3)2((C6H5)CHNH(C10H6)) (7). Complex 1 was found to be an efficient catalyst for hydrosilylation of aldehydes and ketones. The molecular structures of complex 1, 2, 4, and 7 were determined by X-ray single-crystal diffraction.

Preparation, Characterization, and Catalytic Reactions of NCN Pincer Iron Complexes Containing Stannyl, Silyl, Methyl, and Phenyl Ligands

Preparation and reactivity of chiral and achiral NCN pincer Fe complexes containing bis(oxazolinyl)phenyl (abbreviated as phebox) ligands with SnMe3, SiMe3, Me, and Ph ligands were investigated. Irradiation of (phebox)SnMe3 (2) with 1 equiv of Fe(CO)5 led to oxidative addition to give NCN pincer stannyl complex (phebox)Fe(CO)2(SnMe3) (3). Similarly, oxidative addition of (phebox)SiMe3 (4) with Fe(CO)5 resulted in the formation of silyl complex (phebox)Fe(CO)2SiMe3 (5). Me and Ph complexes (phebox)Fe(CO)2R (7, R = Me; 8, R = Ph) were synthesized by transmetalation of the bromide complex (phebox)Fe(CO)2Br (1) with ZnMe2 and ZnPh2, respectively. These phebox Fe complexes served as catalysts for hydrosilylation of a ketone and C–H silylation of N-methylindole.

Stable and Easily Handled FeIII Catalysts for Hydrosilylation of Ketones and Aldehydes

AbstractThe amine–bis(phenolate) iron(III)‐catalysed reduction of ketones and aldehydes to the corresponding secondary and primary alcohols by a consecutive hydrosilylation/hydrolysis process is reported. The amine–bis(phenolate) iron(III) catalyst is easily accessible, stable towards moisture and air and has a broad substrate scope.

Room temperature organocatalyzed reductive depolymerization of waste polyethers, polyesters, and polycarbonates.

The reductive depolymerization of a variety of polymeric materials based on polyethers, polyesters, and polycarbonates is described using hydrosilanes as reductants and metal-free catalysts. This strategy enables the selective depolymerization of waste polymers as well as bio-based polyesters to functional chemicals such as alcohols and phenols at room temperature. Commercially available B(C6 F5)3 and [Ph3 C(+),B(C6 F5)4(-)] catalysts are active hydrosilylation catalysts in this procedure and they are compatible with the use of inexpensive and air-stable polymethylhydrosiloxane and tetramethyldisiloxane as reductants. A significant advantage of this recycling method is derived from its tolerance to the additives present in waste plastics and its ability to selectively depolymerize mixtures of polymers.

ChemInform Abstract: Enantioselective Hydrosilylation of Ketones Catalyzed by a Readily Accessible N‐Heterocyclic Carbene—Ir Complex at Room Temperature.

AbstractNovel types of air‐stable Ir NHC‐complexes containing a hydroxy‐amide functionalized azolium ligand are developed and used as catalyst for the asymmetric hydrosilylation of ketones in the presence of (EtO)2MeSiH under mild reaction conditions.

Bipyridine- and phenanthroline-based metal-organic frameworks for highly efficient and tandem catalytic organic transformations via directed C-H activation.

We report here the synthesis of a series of robust and porous bipyridyl- and phenanthryl-based metal-organic frameworks (MOFs) of UiO topology (BPV-MOF, mBPV-MOF, and mPT-MOF) and their postsynthetic metalation to afford highly active single-site solid catalysts. While BPV-MOF was constructed from only bipyridyl-functionalized dicarboxylate linker, both mBPV- and mPT-MOF were built with a mixture of bipyridyl- or phenanthryl-functionalized and unfunctionalized dicarboxylate linkers. The postsynthetic metalation of these MOFs with [Ir(COD)(OMe)]2 provided Ir-functionalized MOFs (BPV-MOF-Ir, mBPV-MOF-Ir, and mPT-MOF-Ir), which are highly active catalysts for tandem hydrosilylation of aryl ketones and aldehydes followed by dehydrogenative ortho-silylation of benzylicsilyl ethers as well as C-H borylation of arenes using B2pin2. Both mBPV-MOF-Ir and mPT-MOF-Ir catalysts displayed superior activities compared to BPV-MOF-Ir due to the presence of larger open channels in the mixed-linker MOFs. Impressively, mBPV-MOF-Ir exhibited high TONs of up to 17,000 for C-H borylation reactions and was recycled more than 15 times. The mPT-MOF-Ir system is also active in catalyzing tandem dehydrosilylation/dehydrogenative cyclization of N-methylbenzyl amines to azasilolanes in the absence of a hydrogen acceptor. Importantly, MOF-Ir catalysts are significantly more active (up to 95 times) and stable than their homogeneous counterparts for all three reactions, strongly supporting the beneficial effects of active site isolation within MOFs. This work illustrates the ability to increase MOF open channel sizes by using the mixed linker approach and shows the enormous potential of developing highly active and robust single-site solid catalysts based on MOFs containing nitrogen-donor ligands for important organic transformations.

Linear and star architecture methacrylate-functionalised PDMS

Methacrylate-terminated poly(dimethylsiloxane)s in both linear and star architectures have been produced through a time-efficient 1 pot, 2 stage reaction which involved hydrosilylation of small molecule silanes with allyl methacrylate and subsequent equilibration of the product with octamethylcyclotetrasiloxane (D4) in the presence of an acid catalyst. This synthetic route required only one work-up procedure and the products were comparable to those produced by 2 step processes typically reported in literature. All methacrylate-terminated products were approximately double the molar masses anticipated based on reagent loadings. This is thought to be due to redistribution of siloxane bonds in the presence of the platinum hydrosilylation catalyst accompanied by a loss of silicon from the reaction by evaporation of dimethylsilane. It is believed that this is the first report of such siloxane equilibration occurring at room temperature.

Hydrosilylation reaction of olefins: recent advances and perspectives

This review focuses on the recent development of efficient, selective, and cheaper hydrosilylation catalyst systems appearing in the last decade.

Rhodium Nanoflowers Stabilized by a Nitrogen‐Rich PEG‐Tagged Substrate as Recyclable Catalyst for the Stereoselective Hydrosilylation of Internal Alkynes

AbstractMorphology and size controllable rhodium nanoparticles stabilized by a nitrogen‐rich polyoxyethylenated derivative have been prepared by reduction of RhCl3 with NaBH4 in water at room temperature and fully characterized. The flower‐like Rh NPs are effective and recyclable catalysts for the stereoselective hydrosilylation of challenging internal alkynes and diynes, affording the (E)‐vinylsilanes in quantitative yields for a wide range of substrates. The insolubility of the nanocatalyst in diethyl ether allows its easy separation and recycling.magnified image

ChemInform Abstract: Comparing Well‐Defined Manganese, Iron, Cobalt, and Nickel Ketone Hydrosilylation Catalysts

AbstractReview: [34 refs.

1 H and 29Si NMR Spectroscopy as a Powerful Analytical Tool to Evaluate the Activity of Various Platinum-Based Catalysts in Model Olefin Hydrosilylation

The structure of polysiloxane copolymers obtained by hydrosilylation of 1-octene with polymethylhydrosiloxane (PMHS) was analyzed by 29Si NMR spectroscopy and revealed a tendency to form block copolymers. Although all the platinum catalysts that were used showed a tendency to form some block structures, only Karstedt catalyst led to well defined block copolymers. However, the tacticity of these copolymers could not be determined using Heteronuclear Multiple Bond Correlation (HMBC) 2D (1H/ 29Si) NMR technique. The following criteria were found to affect the structure of the hydrosilylation product: low SiH conversion, the “age” of the Karstedt catalyst (low TON) and high octene/SiH ratios.

Solid Supported Palladium(0) Nanoparticles: An Efficient Heterogeneous Catalyst for Regioselective Hydrosilylation of Alkynes and Suzuki Coupling of β-Arylvinyl Iodides

The solid supported palladium(0) nanoparticles (NPs) were found as an active heterogeneous catalyst for regioselective hydrosilylation of alkynes with organosilanes in the presence of NaI as additive. Aliphatic as well as aromatic terminal/substituted alkynes with both electron releasing and withdrawing functionalities similarly participated in the hydrosilylation to produce regioselective β-isomers of vinylsilanes under mild reaction conditions. Reducible functional groups such as nitrile, ester, halide, alkene and alkyne were also found to be tolerated under this condition. Furthermore, the triethylsilylstyrene was applied for consecutive iododesilylation followed by Suzuki coupling reaction to produce stilbenes. The air/moisture stable SS–Pd catalyst was recycled for hydrosilylation reaction up to ten runs without significant loss of its catalytic activity. Solid Supported Palladium(0) Nanoparticles: An Efficient Heterogeneous Catalyst for Regioselective Hydrosilylation of Alkynes and Suzuki Coupling of β-Arylvinyl Iodides

Comparing Well-Defined Manganese, Iron, Cobalt, and Nickel Ketone Hydrosilylation Catalysts

A brief review of manganese-catalyzed hydrosilylation is presented along with a personal account of how the design for the highly active catalyst, (^Ph2PPrPDI)Mn, was conceived. The reductive transformations achieved using this catalyst are described and put into further context by comparing the observed activities with those attained for leading late first-row transition-metal catalysts.

ChemInform Abstract: Cobalt Carbonyl‐Based Catalyst for Hydrosilylation of Carboxamides.

AbstractCommercially available octacarbonyldicobalt can be used in low catalytic loading for the chemoselective reduction of tertiary amides in the presence of silane reagents.

A Palladium Nanoparticles Catalyst for Hydrosilylation of Alkynes

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

Polysiloxane-based core-shell microspheres for toughening of epoxy resins

We present a simple procedure for preparation of core shell poly(dimethylsiloxane)–epoxy microspheres (CPR) by suspension polymerisation route and demonstrate its potential as effective toughener for thermosetting epoxy resin. The curing of siloxane macromonomer was performed in the presence of platinum based hydrosilylation catalyst and the effect of reaction parameters on the dimensions of the polydimethylesiloxane (PDMS) based elastomeric microspheres was quantified, which could be varied from 90 to 216 μ. CPR were prepared by coating the PDMS core with epoxy resin in an additional step. Composites containing varying amounts of microspheres (3–10 % w/w) were prepared and the effect of their incorporation on quasi-static as well as dynamic properties of epoxy resin was evaluated. The glass transition temperature of the unmodified epoxy was unaltered on blending with elastomeric microspheres, which indicated its existence in a well separated phase. The presence of an epoxy coating on the silicone core led to improved dispersion in the epoxy matrix, which was evident from higher impact strength and fracture energies(GIC) as compared to its uncoated analogues. The charpy impact strength and GIC increased by 148 % and 70 % respectively on introduction of 5 % CPR. This was however accompanied with a reduction in the tensile modulus and strength of the base epoxy. Excellent agreement was found between the experimentally measured modulae and the predictions made on the basis of Halpin Tsai and Lewis-Neilson models. Post-mortem morphological studies of the fracture surfaces revealed the presence of spherical cavities which substantiate the role of rubber cavitation as the primary toughening mechanism in microsphere toughened epoxy composites.

Phosphinite-Iminopyridine Iron Catalysts for Chemoselective Alkene Hydrosilylation

A series of new pincer iron complexes with electron-donating phosphinite-iminopyridine (PNN) ligands has been prepared and characterized. These iron compounds are efficient and selective catalysts for the anti-Markovnikov alkene hydrosilylation of primary, secondary, and tertiary silanes. More importantly, the system exhibits unprecedented functional group tolerance with reactive groups such as ketones, esters, and amides. Furthermore, the iron-catalyzed alkene hydrosilylation was successfully applied to the synthesis of a valuable insecticide, silafluofen. The electronic properties and structures of the iron complexes have been studied by spectroscopies and computational methods. Overall, the iron catalysts may provide a low-cost and environmentally benign alternative to currently employed precious metal systems for alkene hydrosilylation.

Cobalt Carbonyl‐Based Catalyst for Hydrosilylation of Carboxamides

AbstractThe cobalt carbonyl [Co2(CO)8] complex is employed as a useful catalyst for the reduction of tertiary amides to the corresponding tertiary amines using 1,1,3,3‐tetramethyldisiloxane (TMDS) and poly(methylhydrosiloxane) (PMHS) as silane reagents under thermal (100 °C) or photo‐assisted conditions (UV, 350 nm at room temperature). Of particular interest, a low catalytic amount (0.5 mol%) of [Co2(CO)8] is used to perform the reaction with 2.2 equiv. of PMHS at 100 °C for 3 h. This reaction is the first example of a cobalt‐catalyzed hydrosilylation of amides.magnified image

Homobimetallic Rhodium NHC Complexes as Versatile Catalysts for Hydrosilylation of a Multitude of Substrates in the Presence of Ambient Air

Two recently reported air- and water-stable di-Rh complexes based on 1,3-bis(3′-butylbenzimidazol-2′-ylidene)benzene were utilized as catalysts for hydrosilylation. Among the substrates investigated were aldehydes, ketones, α,β-unsaturated carbonyls, acyl chlorides, nitriles, alkenes, nitro groups, isocyanates, and tertiary amides. Additionally, carbon dioxide underwent hydrosilylation to produce dimethylphenylsilylformate. The catalysts compared well to other previously reported hydrosilylation catalysts, and the Rh–Cl catalyst was found to be faster and more selective than the Rh–I complex in each case.