Organic synthesis by means of noble metal complexes—XCIV : Palladium catalyzed hydrosilylation of monoenes and conjugated dienes

Palladium compounds and metallic palladium combined with phosphine are active catalysts of selective hydrosilylation of terminal olefins. Butadiene and trichlorosilane give a 1:1 adduct and trimethylsilane affords a 1:2 adduct. Special features of the palladium catalyzed hydrosilylation reactions are presented.     

Silicon hydrides and nickel complexes : II. Mechanism of the hydrosilylation catalyzed by nickel-phosphine complexes

Two ethylene-nickel(0) complexes, viz., [1,2-bis(diphenylphosphino)ethane]-(ethylene)nickel(0) and bis(triphenylphosphine)(ethylene)nickel(0) have been used in a comparison of their catalytic activities in hydrosilylation reactions with those of the corresponding nickel(II) complexes, viz., dichloro [1,2-bis(diphenylphosphino)-ethane]nickel(II) and dichlorobis(triphenylphosphine)nickel(II). The reaction profiles are similar, apart from a significant difference in the induction period; the nickel(II) catalysts requiring a substantially longer time. A mechanism involving a nickel(0) species is proposed for the hydrosilylation.The interchange of hydrogen and chlorine on silicon accompanying the hydrosilylation is related to a high electron density at the nickel atom bearing the phosphine, olefin, and silicon hydride ligands.     

Synthesis of novel poly(ethylene glycol)‐containing imidazolium‐functionalized phosphine ligands and their application in the hydrosilylation of olefins

A series of polyethylene glycol‐containing imidazolium‐functionalized phosphine ligands (mPEG‐im‐PPh₂) were successfully synthesized and used in the rhodium‐catalyzed hydrosilylation of olefins. The results indicate that the RhCl₃/mPEG‐im‐PPh₂ catalytic system exhibits both excellent activity and selectivity for the β‐adduct. In addition, the catalytic system may be recycled at least six times.     

Hydroformylation of nitrogen-containing cyclic olefins via “in-situ” rhodium-phosphine catalysts

Hydroformylation of nitrogen-containing cyclic olefins (N-substituted nortropidines, N-methyl-1,2,3,6-tetrahydropyridine (THP) with rhodium-PR₃ catalysts prepared “in situ” is reported. The nortropidines reacted rapidly when either trialkyl- or triaryl-type phosphines were used, and the regioselectivities were not significantly influenced by the nature of the phosphine. With the less basic THP the rates and selectivities were generally lower, and were influenced by the phosphine ligand and by the presence of added bases such as Et₃N.     

DFT study on mechanism of carbonyl hydrosilylation catalyzed by high-valent molybdenum (IV) hydrides

Density functional theory (DFT) calculations have been employed to investigate hydrosilylation of carbonyl compounds catalyzed by three high-valent molybdenum (VI) hydrides: Mo(NAr)H(Cp)(PMe₃) (1A), Mo(NAr)H(PMe₃)₃ (1B), and Mo(NAr)H (Tp)(PMe₃) (Tp?=?tris(pyrazolyl) borate) (1C). Three independent mechanisms have been explored. The first mechanism is “carbonyl insertion pathway”, in which the carbonyls insert into Mo?H bond to give a metal alkoxide complex. The second mechanism is the “ionic hydrosilylation pathway”, in which the carbonyls nucleophilically attacks η¹-silane molybdenum adduct. The third mechanism is [2 + 2] addition mechanism which was proposed to be favorable for the high-valent di-oxo molybdenum complex MoO₂Cl₂ catalyzing the hydrosilylation. Our studies have identified the “carbonyl insertion pathway” to be the preferable pathway for three molybdenum hydrides catalyzing hydrosilylation of carbonyls. For Mo(NAr)H (Tp)(PMe₃) (Tp?=?tris(pyrazolyl) borate), the proposed nonhydride mechanism experimentally is calculated to be more than 32.6?kcal/mol higher than the “carbonyl insertion pathway”. Our calculation results have derived meaningful mechanistic insights for the high-valent transition metal complexes catalyzing the reduction reaction.     

Frustrated Lewis Pair Chelation as a Vehicle for Low‐Temperature Semiconductor Element and Polymer Deposition

The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB , ⁱPr₂P(C₆H₄)BCy₂ (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH₂}] and [PB{GeH₂}] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine‐borane ligand ( PB ) after element deposition, and 2) the single‐source precursor [PB{SiH₂}] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe₂}] was also prepared, and shown to release poly(dimethylsilane) [SiMe₂]_n upon heating. Overall, this study introduces a “closed loop” deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.     

以N-杂环卡宾为配体的金属络合物催化有机合成的反应

综述了近几年来以N-杂环卡宾为配体的金属络合物催化有机合成的反应。     

Effect of catalysts on the reaction of allyl esters with hydrosilanes

The reaction of hydrosilylation of allyl esters XOCH₂CH=CH₂ (X = MeCO, CF₃CO, C₃F₇CO) and PhOCH₂CH=CH₂ with hydrosilanes HSiY₃ (Y = Cl, OEt) in the presence of the Speier catalyst, the Speier catalyst with additives, and of various nickel complexes was studied. The catalytic hydrosilylation reaction in the presence of the Speier catalyst is accompanied by the reduction. Additives to the Speier catalyst (vinyltriethoxysilane and some ethers) allow to suppress considerably the reduction reaction. In the presence of the studied nickel complexes mainly reduction and isomerization reactions occurred. The best nickel catalysts of hydrosilylation were the mixtures of NiCl₂ or Ni(acac)₂ with phosphine oxides. In contrast to allyl esters, the hydrosilylation of simple olefins proceeds easier, the content of the product of hydrosilylation in the reaction mixture reaches 94.3%.     

Cobalt bis(2‐ethylhexanoate) and terpyridine derivatives as catalysts for the hydrosilylation of olefins

A simple method for the hydrosilylation of olefins by using air‐stable cobalt catalysts is developed. The catalyst system is composed of simple, cheap, and readily available cobalt(II) salts and well‐defined terpyridine derivatives as cocatalysts or ligands, and the hydrosilylation processes can be processed smoothly under mild conditions without either Grignard reagents or NaHBEt₃ as activator.     

Carbonylation of Olefins under Mild Temperature Conditions in the Presence of Palladium Complexes

During a search for catalysts that allow carbonylation reactions on olefins to proceed below 100 °C, complex palladium(II ) compounds having the formula L_mPdX_n were found to be catalytically active. L denotes a ligand such as a phosphine, nitrile, amine, or olefin, X is an acid residue, and m+n is 3 or 4. The catalysts permit the carbonylation of heat-sensitive compounds, as well as selective carbonylation of polyunsaturated olefins. The new process can also be carried out on the industrial scale, as is shown by the carbonylation of cyclododecatriene     

The catalytic activity of alkali metal alkoxides and titanium alkoxides in the hydrosilylation of unfunctionalized olefins

The catalytic activities of titanium alkoxides and alkali metal alkoxides for hydrosilylation of unfunctionalized olefins have been studied. Titanium(IV) alkoxides showed excellent catalytic activity, while alkali metal alkoxides have low catalytic activity for the hydrosilylation of olefins. However, by using titanocene dichloride as an additive, alkali metal alkoxides showed also excellent catalytic property for hydrosilylation. In comparison with titanium alkoxides, no α-adduct was obtained by using alkali metal alkoxides/Cp₂TiCl₂ as catalysts.     

Study on the anti‐sulfur‐poisoning characteristics of platinum–acetylide–phosphine complexes as catalysts for hydrosilylation reactions

A series of platinum–acetylide–phosphine complexes were synthesized and their anti‐sulfur‐poisoning characteristics investigated. In comparison with Speier's and Karstedt's catalysts, the platinum–acetylide–phosphine complexes exhibited both higher catalytic activity and selectivity for the β‐adduct for the hydrosilylation reactions under the same conditions. Furthermore, the complexes also exhibited a strong ability to resist to sulfur‐poisoning. This indicated that the alkyne ligands containing the silyl group had a strong impact on the hydrosilylation reaction. Copyright © 2014 John Wiley & Sons, Ltd.     

Molecular Structure and Spectral Characteristics of the Complex [Ni(Bu3P)2(NCS)2], and Its Catalytic Properties in Hydrosilylation Reaction

According to X-ray diffraction data, the nickel complex [Ni(Bu₃P)₂(NCS)₂] has a square-planar structure with the two phosphine ligands trans to each other and the thiocyanate ligand coordinated by the nitrogen atom. The IR and ¹H, ^{1 3}C, and ^{3 1}P NMR data show that the same structure is preserved in solutions. The catalytic activity of the complex in hydrosilylation of 1-hexene with chlorohydrosilanes HSiMe_{3 - n} Cl _n varies in the series HSiCl₃ > HSiMeCl₂ > HSiMe₂Cl. The reactions of the complex with hydrosilanes involve substitution of the anionic ligand and formation of silyl complexes.     

Hydroformylation of alkenes with paraformaldehyde catalyzed by rhodium-phosphine complexes

The hydroformylation of medium-chain C6 olefins and of allyl alcohol was achieved with paraformaldehyde in dioxane solution using rhodium catalysts with mono-, bi-, and tri-dentate phosphine ligands. The highest activities with n/i ratios around 2, were obtained for a system derived from [Rh(dppe)₂]⁺, prepared in situ by reaction of Rh(acac)(CO)₂ with 2 eq of dppe.     

Mechanistic investigation on hydrogenation and hydrosilylation of ethylene catalyzed by rhenium nitrosyl complex

The mechanistic study for hydrogenation and hydrosilylation of ethylene catalyzed by a rhenium nitrosyl complex is carried out with the aid of density functional theory computations. The hydrogenation of ethylene is found to be available kinetically in which the oxidative addition of H₂ plays a role in decreasing the reaction barrier. For the case of hydrosilylation of ethylene, it is found the oxidative addition of HSiMe₃ cannot occur due to steric reasons, instead, a σ-bond metathesis process for reductive elimination of C₂H₅SiMe₃ is proposed. The major reason for the inaccessibility for the hydrosilylation is resulted from the fact that the oxidative addition of HSiMe₃ cannot give a more stable intermediate.     

Electroanalytical investigation on the stability of tetracoordinate nickel(I) complexes

The stability of tetracoordinate nickel(I) complexes, of the type [Ni(CN)₂P₂]^? (P=substituted phosphine), generated by cathodic reduction of the parent nickel(II) complexes, has been studied by cyclic voltammetry and double potential step techniques. Evidence has been obtained that nickel(I) complexes decay to the dimeric species Ni₂(CN)₂P₄ via a first order chemical reaction the rate determining step being the release of a cyanide ion leading to the radical species [Ni(CN)P₂]. The experimental trend obtained for the first order kinetic constants has been explained on the basis of the different “trans-effect” induced by a cyanide ligand in comparison with that induced by a phosphine group and taking into account the different basic character of the phosphine ligands.     

Chiral organochlorosilanes derived from terpenes: diastereoselective hydrosilylation of methylene bicyclo[2.2.1]heptanes with HSiMenCln − 2 (n=0-2)

The H₂PtCl₆ catalysed hydrosilylation of the terpenes (+)-α-fenchene (XI), (−)-2-methylene bornane (XII), (+)-camphene (XIII) and (−)-3-methylene fenchane (XIV) using HSiMe₂Cl or HSiMeCl₂ proceeds with high regioselectively and in some cases, with high diastereoselectivity. KF-assisted oxidation of the hydrosilylation products gives predominately endo-terpene alcohols. The alcohols have inverted endo/exo ratios to those formed by oxidative hydroboration. Reaction of XIV with HSiMe₂Cl or HSiMeCl₂ is accompanied by a clean rearrangement of the isocamphane skeleton into (+)-2-methylene bornane (XII) prior to hydrosilylation.     

Catalysis of hydrosilylation XIII. Gas-phase hydrosilylation of acetylene by trichlorosilane on functionalised silica supported rhodium and ruthenium phosphine complexes

Gas-phase hydrosilylation of acetylene by tri-chlorosilane catalyzed in a continuous flow apparatus by rhodium and ruthenium phosphine complexes immobilized on the silica via mercapto, phosphine, amine and nitrile ligands has been studied. GLC analysis of the reaction products showed vinyltrichlorosilane to be accompanied by products of double hydrosilylation of acetylene and the redistribution of trichlorosilane followed by the hydrosilylation and hydrogenative hydrosilylation of acetylene with dichlorosilane. A scheme for this complex competitive–consecutive reaction was proposed. The yield and selectivity of vinyltrichlorosilane can be much improved under special reaction conditions, e.g. rate flow of the particular substrates, temperature, given catalyst and others. Kinetic measurements carried out in the range of 115–140°C allowed us to evaluate the activation energy, E_a, for the vinyltrichlorosilane synthesis, which varied between 20.5 and 27.6 kJ mol^?1 for the selected rhodium and ruthenium supported complexes.     

Effect of triarylphosphane ligands on the rhodium‐catalyzed hydrosilylation of alkene

A series of triarylphosphanes ( 1a , 2a , 3a , 4a , 5a , 6a , 7a , 8a , 9a , 10a , 11a ) have been synthesized. An X‐ray crystal structure analysis of (2‐bromophenyl)diphenylphosphane ( 1a ) unambiguously confirmed the constitution of the functionalized phosphane. The hydrosilylation reaction of styrene with triethoxysilane catalyzed with RhCl₃/triarylphosphane was studied. In comparison with the classic Wilkinson's catalyst, rhodium complexes with functionalized triarylphosphane ligands are characterized by a very high catalytic effectiveness for the hydrosilylation of alkene. Among these catalysts tested, RhCl₃/diphenyl(2‐(trimethylsilyl)phenyl)phosphane ( 8a ) exhibited excellent catalytic properties. Using this silicon‐containing phosphane ligand for the rhodium‐catalyzed hydrosilylation of styrene, both higher conversion of alkene and higher β‐adduct selectivity were obtained than with Wilkinson's catalyst. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly Active and Selective Catalysis of Copper Diphosphine Complexes for the Transformation of Carbon Dioxide into Silyl Formate

Copper diphosphine complexes have been found to be highly active and selective homogeneous catalysts for the hydrosilylation of CO₂. The structure of the phosphine ligands strongly affects their catalytic activity. Turnover number (TON) reaches 70 000 after 24 hours with 1,2‐bis(diisopropylphosphino)benzene as a ligand under 1 atmosphere of CO₂. ¹H and ¹³C NMR spectra, carried out under the reaction conditions, showed the reaction mechanism through insertion of CO₂ into Cu? H to afford Cu/formate species.