A Mo(VI) alkylidyne complex with polyhedral oligomeric silsesquioxane ligands: homogeneous analogue of a silica-supported alkyne metathesis catalyst

A highly active alkyne metathesis catalyst is realized by replacing the amide ligands of a molybdenum(VI) trisamide alkylidyne complex with silanol groups from incompletely condensed POSS (polyhedral oligomeric silsesquioxane) ligands. This catalyst serves as an effective homogeneous mimic of an amorphous silica-supported catalyst. Reactivities of various catalytic mixtures are reported along with an X-ray structure of the aniline-coordinated amidodisiloxymolybdenum(VI) alkylidyne complex.     

Highly active trialkoxymolybdenum(VI) alkylidyne catalysts synthesized by a reductive recycle strategy

A systematic study of alkyne metathesis catalyzed by trialkoxymolybdenum(VI) alkylidyne complexes is reported, in which substrate functional groups, alkynyl substituents, and catalyst ligands are varied. Sterically hindered trisamidomolybdenum(VI) propylidyne complex 5 was prepared conveniently through a previously communicated reductive recycle strategy. Alcoholysis of 5 with various phenols/alcohols provides a set of active catalysts for alkyne metathesis at room temperature, among which the catalyst with p-nitrophenol as ligand shows the highest catalytic activity and is compatible with a variety of functional groups and solvents. A key finding that enabled the use of highly active molybdenum(VI) catalysts is replacement of the commonly used propynyl substituents on the starting alkyne substrates with butynyl groups. Under reduced pressure using 1,2,4-trichlorobenzene as an involatile solvent, the alkyne metathesis of butynyl substituted compounds proceeds well at 30 degrees C providing high yields (83%-97%) of dimers. Rationalization of the special role played by butynyl substrates is discussed.     

A reductive recycle strategy for the facile synthesis of molybdenum(VI) alkylidyne catalysts for alkyne metathesis

A convenient synthesis of trisamido molybdenum(VI) alkylidyne complexes has been developed, in which the key step is the addition of a geminal dichloride to a trisamido molybdenum(III) complex in the presence of magnesium to continuously recycle unwanted side product 4, selectively generating the desired alkylidyne complexes in high yield.     

The polymerization of ethylene with a highly active Ziegler-Natta catalyst

A soluble ethylene catalyst were obtained by mixing a methylene dichloride solution of dichlorobis(γ-cyclopentadienyl) titanium (Cp₂TiCl₂) with a heptane solution of ethylaluminium sesquichloride (Al₂Et₃Cl₃) or of diethylaluminium chloride (AlEt₂Cl). Ethylene was polymerized using these catalysts; the solution was examined by electron spin resonance technique before the polymerization and during the reaction. The catalyst activity remained constant for a long period, and the polymerization went on at the same rate for 6–8 hr. The mechanism of the reaction is discussed.     

Synthesis and oxidation of d(6) tungsten pincer complexes: a complete series of tungsten(ii) hydridocarbonyl and halocarbonyl pincer complexes

Reaction of the neutral P(H)NP ligand [HN(SiMe(2)CH(2)PPh(2))(2)] with tungsten hexacarbonyl resulted in coordination of P(H)NP through both phosphorus donor atoms to form the tungsten complex [W(P(HN)P)(CO)(4)] (1). Reaction of P(H)NP with tris(acetonitrile)tricarbonyl tungsten gave both facial and meridional tridentate isomers [W(P(H)NP)(CO)(3)] (2-fac and 3-mer). These three d(6) tungsten complexes could be interconverted under appropriate conditions. The thermodynamically favored isomer 3 was protonated to form seven-coordinate [W(P(H)NP)(CO)(3)H][BF(4)] (4). A related series of cationic tungsten(ii) halide complexes was synthesized, [W(P(H)NP)(CO)(3)X](+) (6, X = I; 7, X = Br; 8, X = Cl; 9, X = F), by various routes. All of the tungsten(ii) complexes underwent deprotonation at the amine site of the P(H)NP ligand when triethylamine was added, resulting in neutral seven-coordinate complexes. Variable temperature (1)H, (31)P{(1)H}, and (13)C{(1)H} NMR spectroscopy showed fluxional behavior for all the seven-coordinate complexes reported here. Analysis of IR and NMR spectroscopic data showed trends through the series of coordinated halides. Crystal structures of tetracarbonyl 1, meridional tricarbonyl 3, and cationic hydride 4 were determined to confirm the coordination mode of the P(H)NP ligand.     

Cycloisomerization of omega-aryl-1-alkynes: GaCl3 as a highly electrophilic catalyst for alkyne activation

Cycloisomerization of a variety of omega-aryl-1-alkynes, where omega = 5 or 6, in the presence of a catalytic amount of GaCl3 provided dihydronaphthalene derivatives or dihydrobenzocycloheptenes, respectively, in high yields.     

A SeCSe-Pd(II) pincer complex as a highly efficient catalyst for allylation of aldehydes with allyltributyltin

An air- and moisture-stable SeCSe-Pd(II) pincer complex was synthesized and found to catalyze the nucleophilic allylation of aldehydes with allyltributyltin. The allylation of a variety of aromatic and aliphatic aldehydes to give the corresponding homoallyl alcohols was performed at room temperature to 60 degrees C in yields ranging from 50% (for typical aliphatic aldehydes) to up to 97% (for aromatic aldehydes) using 5 x 10(-3) to 1 mol % of the Pd catalyst. NMR spectroscopic study indicated that a sigma-allylpalladium intermediate was formed and possibly functions as the nucleophilic species that undergoes addition to the aldehydes.     

Iridium bis(phosphinite) p-XPCP pincer complexes: highly active catalysts for the transfer dehydrogenation of alkanes

A series of new bis(phosphinite) p-XPCPIrHCl pincer complexes ([PCP = eta(3)-5-X-C(6)H(2)[OP(tBu)(2)](2)-1,3], X = MeO (4a), Me (4b), H (4c), F (4d), C(6)F(5) (4e), and Ar(F) [=3,5-bis(trifluoromethyl)phenyl] (4f)) have been synthesized. Treatment of compounds 4a-f with NatOBu in cyclooctane (COA)/tert-butylethylene (TBE) mixtures generates species with unprecedented catalytic activity for the catalyzed transfer dehydrogenation of COA with TBE as acceptor to form cyclooctene (COE) and tert-butylethane (TBA). With substrate:precatalyst ratios of 3030COA:3030TBE:1p-XPCPIrHCl (4):1.1NaOtBu, turnover numbers (TONs) between 1400 and 2200 (up to 72% conversion in TBE) and initial turnover frequencies (TOFs) between 1.6 and 2.4 s(-1) have been observed at 200 degrees C.     

A family of highly active copper(I)-homoscorpionate catalysts for the alkyne cyclopropenation reaction

Equimolar mixtures of ethyl diazoacetate and alkynes can be converted into cyclopropenes in very high yields, at room temperature, through the intermediacy of readily available Cu(I) catalysts containing trispyrazolylborate ligands.     

Palladium(0) alkyne complexes as active species: a DFT investigation

Alkynes have been found to be excellent ligands for Pd(0); the stability of a range of alkyne-Pd(0) complexes, and their reactivity in oxidative addition, have been investigated by DFT methods.     

Pd(OH)2/C (Pearlman's catalyst): a highly active catalyst for Fukuyama,Sonogashira, and Suzuki coupling reactions

Treatment of thiol esters 1 with zinc reagent 2 in the presence of a small amount (相似文献   

Extractive spectrophotometric determination of tungsten(VI) using 3-hydroxy-2-(2'-thienyl)-4-oxo-4H-1-benzopyran

A simple, rapid, highly sensitive and selective spectrophotometric method for the determination of tungsten(VI) in trace amounts is developed using 3-hydroxy-2-(2'-thienyl)-4-oxo-4H-1-benzopyran (HTB) as a reagent for the complexation of metal ion and extracting the 1:2 (metal:ligand) complex into dichloromethane from 0.2 M HCl solution. It obeys Beer's law in the range 0-2.8 microg Wml(-1) with molar absorptivity and Sandell's sensitivity at 415 nm as 6.45 x 10(4) L mol(-1) cm(-1) and 0.0029 microg W(VI) cm(-2), respectively. The method is free from the interference of a large number (39) of elements and handles satisfactorily the analysis of various samples of varying complexity.     

5d early-transition-metal corroles: a trioxo-bridged binuclear tungsten(VI) derivative

The synthesis and full characterization of the first tungsten corrole reveal that it is a binuclear trioxo-bridged complex of tungsten(VI), a coordination motif without precedence for tungsten chelated by other ligands.     

Computational study-led organocatalyst design: a novel, highly active urea-based catalyst for addition reactions to epoxides

An in silico study examined the stabilities of hydrogen-bonded complexes between simple thiourea catalysts and three different electrophiles and identified a novel, highly active N-tosyl urea catalyst for the promotion of addition reactions to epoxide electrophiles. Synthesis and evaluation of 6 revealed it to be a powerful catalyst for the addition of 1,2-dimethylindole to styrene oxide under conditions in which simple N,N-bis-aryl ureas and thioureas (including 1) are inactive. Subsequent studies determined 6 to be compatible with a range of indole and epoxide substrates (including (E)-stilbene oxide) and found that relatively poor nucleophiles such as sterically and electronically deactivated anilines, thiophenol, and benzyl alcohol could be efficiently and regioselectively added to oxiranes under mild conditions.     

Studies of ziegler-type catalysts for the polymerization of ethylene and propylene—I a highly active catalyst for the polymerization of ethylene

The reaction product of an incompletely desolvated ethereal Grignard reagent and TiCl₄, when employed with a trialkylaluminium cocatalyst, possesses catalytic activity for the polymerization of ethylene, of some two orders of magnitude (on the basis of Ti) greater than that of traditional TiCl₃ catalysts. The yield of polyethylene increases linearly with increasing ⁱBu₃Al concentration, when a constant amount of Et,Zn is also present.     

Correlating Fe source with Fe-N-C active site construction:Guidance for rational design of high-performance ORR catalyst

Pyrolyzed Fe-N_X/C materials derived from Fe-doped ZIF-8 are recently emerged as promising alternatives to noble metal platinum-based catalysts towards oxygen reduction reaction(ORR) and elucidating the dependacne of Fe source on the active site structure and final ORR performance is highly desirbale for further development of these materials. Here, we designed and synthesized a series of Fe-N-C catalysts using ZIF-8 and various iron salts(Fe(acac)_3, FeCl_3, Fe(NO_3)_3) as precusors. We found that the iron precursors,mainly the molecular size, hydrolysis extent, do play a major role in determining the final morphology of Fe, namely forming the Fe-Nx coordination or Fe_3C nanoparticles, as well as the site density, therefore,significantly affecting the ORR activity. Among the three iron sources, Fe(acac)_3 is most advantageous to the preferential formation of single-atom Fe-Nx active sites and the derived catalyst demonstrated best ORR performance.