Catalyst For Hydrosilation Research Articles

Efficient and selective catalysis for hydrogenation and hydrosilation of alkenes and alkynes with PNP complexes of scandium and yttrium

Scandium and yttrium congeneric complexes, supported by a monoanionic PNP ligand, were studied as catalysts for alkene hydrogenation and hydrosilation, and alkyne semihydrogenation and semihydrosilation. The yttrium congener was found to be much more active in all cases, but this greater activity is accompanied by more rapid catalyst decomposition and therefore higher total yields for some of the reactions with the scandium catalyst. Calculations indicate that the reactions may proceed via σ-bond metathesis of the alkyl complexes to form metal hydride intermediates into which alkenes/alkynes insert.

Selective Hydrosilation of CO2 to a Bis(silylacetal) Using an Anilido Bipyridyl‐Ligated Organoscandium Catalyst

A rigid anilido bipyridyl ligand has been designed for use in an organoscandium-based carbon dioxide hydrosilation catalyst. Ligand attachment by alkane elimination results in metalation of an aryl C-H bond in a 3,5-di-tert-butylphenyl group installed on the pyridyl unit, thus rendering the ligand tetradentate. Insertion of CO2 into the newly formed Sc-C bond leads to a κ(1) carboxylate which, when treated with the borane B(C6F5)3, becomes hemilabile. In addition to activating the catalyst, the k(1) carboxylate effectively sequesters free B(C6F5)3 and the ensemble is able to effectively hydrosilate CO2, in the presence of excess Et3SiH, almost exclusively to R3SiOCH2OSiR3. A maximum turnover number of about 3400 (conversion of silane) is observed. Mechanistic experiments suggest that the sequestration of free B(C6F5)3 by the hemilabile carboxylate contributes to the selectivity observed and prevents over reduction to methane.

Anionic Synthesis of α‐Functionalized Polymers by Combination of 1,1‐Diphenylethylene and Hydrosilation Chemistry

AbstractA new general anionic functionalization method (GFM) for preparing α‐chain‐end functionalized polymers utilizes the initiator formed from sec‐butyllithium and dimethyl[4‐(1‐phenylvinyl)‐phenyl]silane (DPESiH) followed by hydrosilation with substituted alkenes. α‐(4‐dimethylsilyl hydride)phenyl‐functionalized polystyrene and poly(methyl methacrylate) were synthesized in quantitative yield by living anionic polymerization. These α‐silyl hydride‐functionalized polymers were further functionalized by reaction with tridecafluorooctene in the present of Karstedt's hydrosilation catalyst. These tridecafluorooctane‐functionalized polymers were characterized by SEC, FTIR, 1H‐, 13C‐ and 19F‐NMR spectroscopy.

Structural and mechanistic investigation of a cationic hydrogen-substituted ruthenium silylene catalyst for alkene hydrosilation

The cationic ruthenium silylene complex [Cp*(iPr3P)Ru(H)2(SiHMes)][CB11H6Br6], a catalyst for olefin hydrosilations with primary silanes, was isolated and characterized by X-ray crystallography. Relatively strong interactions between the silylene Si atom and Ru–H hydride ligands appear to reflect a highly electrophilic silicon center. The mechanism of olefin hydrosilation was examined by kinetics measurements and other experiments to provide the first experimentally determined mechanism for the catalytic cycle. This mechanism involves a fast, initial addition of the Si–H bond of the silylene complex to the olefin. Subsequent elimination of the product silane produces an unsaturated intermediate, which can be reversibly trapped by olefin or intercepted by the silane substrate. The latter reaction pathway involves activation of the reactant silane by Si–H oxidative addition and α-hydrogen migration to regenerate the key silylene intermediate.

Catalytic Activity and Inhibition of Platinum Complexes for Room Temperature Vulcanized Silicone Rubber

Platinum complexes of unsaturated siloxanes are useful as hydrosilation catalysts. In the process of room temperature vulcanized (RTV) silicone rubber, improved hydrosilation results are needed, however, a period of working time is also necessary in practice. Platinum at the zero oxidation state, like Karstedt catalyst is found active in parts per million levels in RTV silicon rubbers. Preferred addition cured silicone is formed by addition of an organohydrogenpolysiloxane (Si-H) across a π-bond to a vinyl-containing organopolysiloxane (C = C). The report reviews the preparation of platinum complexes from Speiers catalyst to Karstedt catalyst both of which are widely used in industry. Patents on the improvement of Karstedt catalyst and papers on the mechanism of hydrosilylation are also presented. The inhibitors for high temperature vulcanized (HTV) silicon rubber are reviewed as well as RTV silicon rubber. Keywords: Platinum complexes, inhibitor, room temperature vulcanized silicone rubber, hydrosilation, polysiloxane

Alkene Hydrosilation by a Cationic Hydrogen-Substituted Iridium Silylene Complex

A cationic hydrogen-substituted iridium silylene complex [(PNP)(H)Ir Si(Mes)H][B(C6F5)4] (2) was synthesized via hydride abstraction from the corresponding neutral iridium silyl hydride complex. DFT calculations for 2 indicate that the cationic charge is localized at the silicon center and depict a LUMO with predominant silicon p-orbital character. Notably, complex 2 reacts rapidly with unhindered alkenes at ambient temperatures to afford disubstituted silylene complexes via Si-C bond formation. Complex 2 is also the catalyst for alkene hydrosilation of primary silanes with a high degree of anti-Markovnikov selectivity.

Anionic Synthesis of Primary Amine Functionalized Polystyrenes via Hydrosilation of Allylamines with Silyl Hydride Functionalized Polystyrenes

A general anionic ω-chain-end functionalization methodology is described and illustrated by the synthesis of ω-primary amine functionalized polystyrenes. First, the quantitative ω-silyl hydride functionalization of well-defined poly(styryl)lithium (Mn = 2200 and 14 100 g/mol) was effected with dimethylchlorosilane in hydrocarbon solution at room temperature. In the second step, involving amination by hydrosilation, the silyl hydride functionalized polystyrene was added quantitatively to 3-[N,N-bis(trimethylsilylamino]-1-propene, a protected amine, using Karstedt's Pt(0) hydrosilation catalyst in benzene. One of the principal advantages of this method is the fact that it is not necessary to use protecting groups for many functional groups, as illustrated by the quantitative primary amine functionalization of ω-silyl hydride functionalized poly(styryl)lithium with allylamine using the Karstedt's hydrosilation catalyst. The silyl hydride and amine functionalized polystyrenes were characterized by SEC, FTIR, ...

The preparation of a new polysiloxane copolymer with glucosylthioureylene groups on the side chains

A new polysiloxane with pendent sugar units was prepared by a two-step method: the preparation of the polysiloxane with amino groups on the side chain and then the copolysiloxane reacted with glucosyl isothiocyanate. All polymers were characterized by FT-IR 1H-NMR, 1H–1H-COSY, 13C-NMR, and DEPT respectively. In the same time, Platinum oxide was found to be a versatile and powerful hydrosilation catalyst in the hydrosilylation reaction of aminotrimethylenepolysiloxanes with heptamethylcyclotetrasiloxane (D 4 H).

Synthesis, structures, and alkene hydrosilation activities of neutral tripodal amidozirconium alkyls

Aminolysis of Zr(CH2C6H5)4 with CH[(CH3)2SiNHAr]3 (Ar = para-tolyl and para-fluorophenyl) affords CH[(CH3)2SiNAr]3ZrCH2C6H51a and 1b (a: Ar = para-tolyl; b: Ar = para-fluorophenyl). Solution and solid state X-ray structural data suggest an η2-bonding mode for the benzyl group in 1a and 1b. Treating 1a and 1b with N,N-dimethylanilinium chloride or triphenylmethyl chloride yields CH[(CH3)2SiNAr]3ZrCl (2a and 2b). Complex 2a exhibits a fast dimer–monomer equilibrium in benzene. Single-crystal X-ray diffraction of 2a reveals a dimeric structure bridged by two μ-Cl atoms. Metathesis of 2a and 2b with n-butyllithium in toluene and then in hexane yields CH[(CH3)2SiNAr]3ZrnBu (3a and 3b). The crystal structures and the IR spectra of 3a and 3b in Nujol mulls reveal weak β-agostic interactions, but solution NMR spectra of 3a and 3b give no evidence for such a motif. Further, the larger Zr–Cα–Cβ angles and the longer Zr–Cβ distances suggest the β-agostic interactions in 3a and 3b are weaker than those in the previously reported cases of Group 4 metals. Complexes 1a, 1b, 3a, and 3b are active alkene hydrosilation catalysts. The catalytic activities exhibited by these complexes are in contrast to the inertness of the previously reported neutral molecules of the type X3MR (X = amide, alkoxide, or siloxide; M = Group 4 metal; R = alkyl or hydride). We attribute the improved activity to three factors: the small ancillary groups of the ligand, the accessibility of the coordination sites cis to the Zr-alkyl group due to the small “bite angle” of the ligand, and the weakened N(p) → Zr(d) π donation due to the coordination geometry imposed by the tripodal ligand.

ChemInform Abstract: Synthesis and Properties of a Stable, Cationic, Rhodium Lewis‐Acid Catalyst for Hydrosilation, Mukaiyama Aldol and Cyclopropanation Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hydrosilation of polyfluoroolefin in dense carbon dioxide

Abstract Ruthenium and rhodium phosphine complexes catalyze the hydrosilation of olefins in dense carbon dioxide. The incorporation of polyfluorinated phosphine ligands in the conventional hydrosilation catalysts provides enhanced solubility in dense carbon dioxide resulting in a higher catalytic activity and selectivity; the best result was obtained using RuCl2[P(C6H4-p-CF3)3]3. The reaction is applicable to the synthesis of a fluorous silane coupling agent.

Synthesis and properties of a stable, cationic, rhodium Lewis-acid catalyst for hydrosilation, Mukaiyama aldol and cyclopropanation reactions

The remarkably stable cationic, three-coordinate, 14-electron rhodium complex 1 has been synthesized, isolated and used as a catalyst for hydrosilation, Mukaiyama aldol and cyclopropanation reactions.

Pt 0 compounds bound in a silsesquioxane layer: active hydrosilation catalysts protected by the gel

Colloidal silica particles modified with a hydrosilane (SiH), triethoxysilane (TES), reacted with Karstedt's catalyst, Pt 6 (1,1,3,3-tetramethyl-1,3-divinyldisiloxane) y , to give a supported platinum catalyst. The silica-supported platinum nanoparticles were catalytically active in the hydrosilation reaction; the catalytic activity was maintained after recovering and recycling the catalyst through at least three further hydrosilation experiments. Differences between the supported catalyst and Karstedt's catalyst are noted. Upon drying, catalytically inactive surface-bound platinum nanoparticles with an average diameter of 2 nm were produced. Larger platinum aggregates, which typically form in solution from platinum compounds without a stabilizer or in the presence of silica particles surface modified with monofunctional SiH groups (Me 2SiHOEt), were not observed with the silica particles modified with TES. A hydridosilsesquioxane ( HSiO 3 2 ) layer grafted to the silica surface was believed to be critical in controlling the ultimate size of the supported platinum nanoparticles.

Photoactivated hydrosilation curing of a ceramic precursor: Crosslinking and pyrolysis of branched oligo[(methylsilylene) methylene

Abstract The complex bis(acetylacetonato)platinum(II) was activated by UV light in liquid mixtures of oligo[(methylsilylene)methylene](OMSM) leading to rapid solidification and the formation of polycarbosilane with a crosslinked structure. A hydrosilation catalyst is produced by irradiation of this complex which promotes chain extension at OMSM silicon hydride sites with the additive tetravinylsilane. Dihydridosilicon end groups on the oligomer are necessary for rapid photocuring. The crosslinked polymers were pyrolyzed under inert conditions giving 70% yields of β-silicon carbide ceramic char with an overall carbon to silicon ratio of 1.79 to 1. Films of OMSM resin were spin-coated onto silicon wafers, cured, and pyrolyzed. Images on the film surfaces were retained in shape and dimension after pyrolysis.

Rapid Photoactivated Hydrosilation Polymerization of Vinyldimethylsilane

The complex bis(acetylacetonato)platinum(II) is inactive in the dark but forms a highly reactive hydrosilation catalyst upon irradiation with near-UV light. Vinyldimethylsilane is polymerized with it. Poly[(dimethyl)vinylsilane] is the major product; minor components consist of the dimers 1,1,2,3,3-pentamethyl-1,3-disilacyclopentane and 1,1,4,4-tetramethyl-1,4-disilacyclohexane and oligomers. After photoactivation the catalyst remains reactive for an indefinite period of time with hydride and vinyl polymer end-groups, thus the molecular weight of the major product increased from 5500 g/mol (Mw) shortly after irradiation to 12300 g/mol in six months due to end-linking of polymer chains. Photoactivation of the catalyst and the subsequent step polymerization reaction are unaffected by dissolved air.

Platinum(II) Bis(.beta.-diketonates) as Photoactivated Hydrosilation Catalysts

Irradiation of platinum(II) bis({beta}-diketonates) in the presence of hydrosilanes and olefins results in olefin hydrosilation. The initial rate of hydrosilation is dependent upon the choice of {beta}-diketonate ligand, hydrosilane, and olefin. Formation of an active catalyst requires the presence of either triethylsilane or triethylvinylsilane during a brief period of irradiation. Addition of the second reactant results in hydrosilation without further irradiation. Substantial inhibition of hydrosilation is observed when dibenzocyclooctatetraene is added following irradiation and prior to addition of the second reactant, but not when mercury is added following irradiation. These results indicate that the active form of the photogenerated catalyst is homogeneous rather than heterogeneous. Correlation of hydrosilation reactivity with the spectroscopic changes which occur during irradiation suggests that the primary photoproduct is not catalyticaly active and that a secondary photochemical reaction results in the loss of one of the two {beta}-diketonate ligands and the formation of the active catalyst.

Simultaneous hydrosilation and ring‐opening polymerization as a route to novel polymer architectures

AbstractTypical platinum, rhodium and cobalt hydrosilation catalysts have been found to catalyze the ring‐opening polymerization of many different types of heterocyclic monomers. In particular, epoxide monomers undergo especially rapid polymerization with these catalysts. Investigations have shown that in the case of platinum and rhodium catalysts these polymerizations proceed at the surface of the metal colloids by means of a novel cationic mechanism. In contrast, polymerizations with octacarbonyldicobalt take place by a homogeneous cationic mechanism. In all cases, polymerization appears to proceed by the formal attack of a positively charged silicon species on the heteroatom with the formation of a silicon‐oxygen bond. Interesting comb, graft, block and network polymers can be prepared by carrying out simultaneous epoxide ring‐opening and hydrosilation reactions using these catalysts.

ChemInform Abstract: Discrete Chiral Rhodium Phosphine Complexes as Catalysts for Asymmetric Hydrosilation of Ketones

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reactivity of cobalt acetyl complexes (PR3)(CO)3CoCOCH3 toward monohydrosilanes

Monohydrosilanes HSiR[prime][sub 3] (SiR[prime][sub 3] = SiMe[sub 2]Ph, SiMeEt[sub 2], SiEt[sub 3], SiPh[sub 3]) cleave the cobalt acetyl complexes CH[sub 3]C(O)Co(CO)[sub 3](PR[sub 3]) (PR[sub 3] = PPh[sub 2]Me, PPh[sub 3]) in C[sub 6]D[sub 6] at room temperature to give the cobalt silyl compounds R[prime][sub 3]SiCo(CO)[sub 3](PR[sub 3]) and ethoxysilanes. Neither acetaldehyde nor the [alpha]siloxyethyl complexes CH[sub 3]CH(OSiR[prime][sub 3])Co(CO)[sub 3](PR[sub 3]) were detected by NMR spectral monitoring, irrespective of whether 1 or 2 equiv of HSiR[prime][sub 3] was used. Six cobalt silyl compounds were isolated in 85-95% yields and were fully characterized, including by [sup 1]H, [sup 13]C, [sup 31]P, and [sup 29]Si NMR spectroscopy. Further studies involving the reaction between CH[sub 3]C(O)Co(CO)[sub 3](PPh[sub 2]Me) and HSiMe[sub 2]Ph afforded the following observations. (1) The presence of CO (1 atm) or free phosphine (1 equiv) inhibits this reaction. (2) Wilkinsons's compound, RhCl(PPh[sub 3])[sub 3], has no effect. (3) Benzaldehyde (1 equiv) inhibits this reaction, whereas acetaldehyde undergoes hydrosilation to give EtOSiMe[sub 2]Ph. The cobalt acetyl also is an effective acetaldehyde hydrosilation catalyst. (4) The cobalt silyl compound PhMe[sub 2]SiCo(CO)[sub 3](PPh[sub 2]Me), in contrast, neither undergoes silyl exchange (with HSiEt[sub 3]) nor catalyzes hydrosilation of acetaldehyde under the standard reaction conditions. These resultsmore » are compared with those of previous studies involving reactions between CH[sub 3]C(O)Co(CO)[sub 3](PPh[sub 3]) and HSiEt[sub 3] or HSiPh[sub 3] in THF at 50[degrees]C/1 atm CO and between the manganese acetyl CH[sub 3]C(O)Mn(CO)[sub 5] and HSiR[prime][sub 3]. Mechanistic alternatives are outlined. 41 refs., 6 figs., 3 tabs.« less

Manganese carbonyl compounds as hydrosilation catalysts for organoiron acyl complexes

Manganese acyl complexes L(CO){sub 4}MnCOR (L = CO, R = CH{sub 3}, Ph; L = PPh{sub 3}, PEt{sub 3}, R = CH{sub 3}) are effective catalysts (2-5%) for hydrosilating FpCOR compounds (R = CH{sub 3}, Ph; Fp = Fe(CO){sub 2}({eta}{sup 5}-C{sub 5}H{sub 5})) with monohydro-, dihydro-, and trihydrosilanes. Fp({alpha}-siloxyalkyl) complexes FpCH(CH{sub 3})OSiR{prime}{sub 3} (SiR{prime}{sub 3} = SiEt{sub 3}, SiMe{sub 2}Ph, SiHPh{sub 2}, SiHEt{sub 2}), (FpCH(CH{sub 3})O){sub 2}SiR{prime}{sub 2} (R{prime} = Et, Ph), FpCH(Ph)OSiHPh{sub 2}, and (FpCH(CH{sub 3})O){sub 3}SiPh are isolated (after column chromatography on silica gel or on polystyrene (size-exclusion) beads) and fully characterized. Substituted manganese acetyl compounds L(CO){sub 4}MnCOCH{sub 3} are extremely active catalysts that quantitatively transform FpCOCH{sub 3} and dihydrosilanes R{prime}{sub 2}SiH{sub 2} (R{prime} = Et, Ph) to Fp({alpha}-siloxyalkyl) complexes FpCH(CH{sub 3})OSiHR{prime}{sub 2}. The manganese acetyl catalysts endure (within NMR spectral detection limits) until all of the organoiron acyl substrate is consumed; only then do they undergo rapid hydrosilation. Other manganese complexes, including (CO){sub 5}MnSiMe{sub 3}, Mn{sub 2}(CO){sub 10}, (CO){sub 5}MnCH{sub 3}, and (CO){sub 5}MnCHPh(OSiHR{prime}{sub 2}), also catalyze the hydrosilation of FpCOCH{sub 3}.