Highly Active Immobilized Catalyst for Ethylene Polymerization: Neutral Single Site Y(III) Complex Bearing Bulky Silylallyl Ligand.

Exploring the surface organometallic chemistry on silica of highly electrophilic yttrium complexes is a relatively uncommon endeavor, particularly when focusing on tris-alkyl complexes characterized by Y-C σ-alkyl bonds. A drawback with this class of complexes once grafted on silica, is the frequent occurrence of alkyl transfer by ring opening of siloxane groups, resulting in a mixture of species. Herein, we employed a more stable homoleptic yttrium allyl complex bearing bulky η-1,3-bis(trimethylsilyl)allyl ligand to limit this transfer reaction.

Well-defined silica supported bipodal molybdenum oxo alkyl complexes: a model of the active sites of industrial olefin metathesis catalysts.

A well-defined, silica-supported molybdenum oxo alkyl species, ([triple bond, length as m-dash]SiO-)Mo([double bond, length as m-dash]O)(CHBu), was prepared by the selective grafting of Mo([double bond, length as m-dash]O)(CHBu)Cl onto a silica partially dehydroxylated at 200 °C using a rigorous surface organometallic chemistry approach. The immobilized bipodal surface species, partly resembling the active species of industrial MoO/SiO olefin metathesis catalysts, exhibited excellent functional group tolerance in conjunction with its high activity in homocoupling, self and ring closing olefin metathesis.

Well-Defined Molybdenum Oxo Alkyl Complex Supported on Silica by Surface Organometallic Chemistry: A Highly Active Olefin Metathesis Precatalyst.

The well-defined silica-supported molybdenum oxo alkyl species (≡SiO-)MoO(CHBu) was selectively prepared by grafting of MoO(CHBu)Cl onto partially dehydroxylated silica (silica) using the surface organometallic chemistry approach. This surface species was fully characterized by elemental analysis and DRIFT, solid-state NMR, and EXAFS spectroscopy. This new material is related to the active species of industrial supported MoO/SiO olefin metathesis catalysts.

Solvent-Free Ring-Opening Metathesis Polymerization of Norbornene over Silica-Supported Tungsten-Oxo Perhydrocarbyl Catalysts.

Ring opening metathesis polymerization (ROMP) of bicyclo[2.2.1]hept-2-ene (norbornene) is carried out over silica-supported catalysts based on tungsten complexes bearing an oxo ligand (1: [(SiO)W(O)(CH SiMe ) , 2: [(SiO)W(O)(CHCMe Ph)(dAdPO)], dAdPO  2,6 diadamantyl-4-methylphenoxide, 3: [(SiO) W(O)(CH SiMe ) ]).

On the track to silica-supported tungsten oxo metathesis catalysts: input from 17O solid-state NMR.

The grafting of an oxo chloro trisalkyl tungsten derivative on silica dehydroxylated at 700 °C was studied by several techniques that showed reaction via W-Cl cleavage, to afford a well-defined precatalyst for alkene metathesis. This was further confirmed by DFT calculations on the grafting process. (17)O labeling of the oxo moiety of a series of related molecular and supported tungsten oxo derivatives was achieved, and the corresponding (17)O MAS NMR spectra were recorded.

Nickel-silicide colloid prepared under mild conditions as a versatile Ni precursor for more efficient CO2 reforming of CH4 catalysts.

Preparing highly active and stable non-noble-metal-based dry reforming catalysts remains a challenge today. In this context, supported nickel nanoparticles with sizes of 1.3 ± 0.

Small changes have consequences: lessons from tetrabenzyltitanium and -zirconium surface organometallic chemistry.

Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi-grafted and mono-grafted single-site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono- versus bi-grafted species for the same surface concentration of silanol species.

Shifting from Ziegler-Natta to Philips-type catalyst? A simple and safe access to reduced titanium systems for ethylene polymerization.

Silica-supported titanium(IV) chloride is readily reduced by Mashima and co-workers' reagent (1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene) to afford materials active in ethylene polymerisation without need of aluminum alkyl cocatalyst.

Development of the first well-defined tungsten oxo alkyl derivatives supported on silica by SOMC: towards a model of WO3/SiO2 olefin metathesis catalyst.

A well-defined, silica-supported tungsten oxo alkyl species prepared by the surface organometallic chemistry approach displays high and sustained activity in propene metathesis. Remarkably, its catalytic performances outpace those of the parent imido derivative, underlining the importance of the oxo ligand in the design of robust catalysts.

Grafting reaction of organotin complexes on silica catalyzed by tungstic heteropolyacids.

The grafting reaction of tetramethyltin on silica is catalyzed by H(4)SiW(12)O(40) preliminary impregnated on the support. While the reaction proceeds at temperatures higher than 150 degrees C on silica alone, the presence of the polyacid allows the grafting at room temperature. A study as a function of the polyacid coverage has shown that there is a direct correlation between the reaction rate and the number of highly acidic sites on the support, probing that there is a reaction of the tetraalkyltin with them (limiting step) followed by a migration of the grafted fragment on the silica surface.

Access to well-defined isolated Fe(II) centers on silica and their use in oxidation.

Well-defined Fe(II) isolated sites are obtained by reaction of diaryl-N,N'-diazadiene bis(neosilyl) iron (1) with an aerosil silica, SiO(2-(700)). This system can be used as a precursor for the catalytic oxidation of cyclohexene into cyclohexene oxide, cyclohexenol and cyclohexenone in the presence of H(2)O(2).

Synthesis, characterization and propane metathesis activity of a tantalum-hydride prepared on high surface area "silica supported zirconium hydroxide".

A new tantalum-hydride supported on zirconium hydroxide [(triple bond SiO)(2)Zr(H)-O-Ta(H)(x)-(OSi triple bond)] (x = 1 or 3) was prepared using surface organometallic chemistry and its catalytic properties in the propane metathesis reaction were assessed showing improved activity and selectivities in comparison to the tantalum-hydride supported on silica.

Well-defined surface imido amido tantalum(v) species from ammonia and silica-supported tantalum hydrides.

The MCM-41 supported hydrides [([triple bond]SiO)(2)TaH(3)], 1a, and [([triple bond]SiO)(2)TaH(3)], 1b, cleave N-H bonds of ammonia at room temperature to yield the well-defined imido amido surface complexes [([triple bond]SiO)(2)Ta(NH)(NH(2))], 2, and 2xNH(3). Additionally, the surface silanes [[triple bond]Si-H] that exist in close proximity to 1a and 1b also react with ammonia at room temperature to give the surface silylamido [Si-NH(2)]. Such reaction is tantalum assisted: surface silanes were synthesized independently and in absence of tantalum by reaction of highly strained silica, SiO(2-1000), with SiH(4) and no reaction with ammonia was observed.

Detailed structural investigation of the grafting of [Ta(=CHtBu)(CH2tBu)3] and [Cp*TaMe4] on silica partially dehydroxylated at 700 degrees C and the activity of the grafted complexes toward alkane metathesis.

The reaction of [Ta(=CHtBu)(CH2tBu)3] or [Cp*Ta(CH3)4] with a silica partially dehydroxylated at 700 degrees C gives the corresponding monosiloxy surface complexes [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2] and [([triple bond]SiO)Ta(CH3)3Cp*] by eliminating a sigma-bonded ligand as the corresponding alkane (H-CH2tBu or H-CH3). EXAFS data show that an adjacent siloxane bridge of the surface plays the role of an extra surface ligand, which most likely stabilizes these complexes as in [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])] (1a') and [([triple bond]SiO)Ta(CH3)3Cp*([triple bond]SiOSi[triple bond])] (2a'). In the case of [(SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])], the structure is further stabilized by an additional interaction: a C-H agostic bond as evidenced by the small J coupling constant for the carbenic C-H (JC-H = 80 Hz), which was measured by J-resolved 2D solid-state NMR spectroscopy.

Hydrogenolysis of cycloalkanes on a tantalum hydride complex supported on silica and insight into the deactivation pathway by the combined use of 1D solid-state NMR and EXAFS spectroscopies.

Hydrogenolysis of cyclic alkanes is catalysed by [(triple bond)SiO)(2)Ta-H] (1) at 160 degrees C and leads to lower alkanes and cyclic alkanes including cyclopentane. The turnover number is correlated with the number of carbon atoms of the cyclic alkanes, and therefore while cycloheptane is readily transformed, cyclopentane does not give any product (<1 %). The mechanism of ring contraction probably involves carbene de-insertion as a key carbon-carbon bond-cleavage step.