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.     

On the reactivity of supported zirconium organic catalysts in the polymerization of ethylene

The ethylene polymerization with tetrabenzyl zirconium displays a higher concentration of active centres on catalysts obtained by supporting of the organometallic compound on alumina or silica-alumina carriers than by activation without supporting. The active centres of the supported catalysts possess different polymerization reactivity. At the beginning of the polymerization in the presence of monomer, these active centres are formed from a small amount of the stable surface compounds originated in the carrier impregnation. The maximum polymerization rate depends on the pretreatment, the loading and the porosity of the carrier. The more active these centres, the quicker they lose their activity. A relation was found between a chemical deactivation reaction and the concentration of the hydroxyl groups remaining on the catalyst after impregnation. Addition of hydrogen or butyllithium can change the polymerization in a different manner. The addition of butyllithium causes an increase in the number and the reactivity of the active centres and a suppression of the chemical deactivation.     

Synthesis, structure and reactivity of samarium complexes supported by Schiff-base ligands

Three tris(salicyladiminato) samarium complexes were synthesized by the reaction of anhydrous SmCl₃ with the sodium salts of the Schiff-bases in THF in 3:1 molar ratio. X-ray diffraction studies revealed that the coordination geometry around samarium atom could be best described as a distorted pentagonal bipyramidal for complexes 1 and 2 and as a distorted tricapped trigonal prism for complex 3. It was found that the coordination environment around samarium atom has significant effect on the catalytic activity of homoleptic Schiff-base complexes of lanthanide. The increasing order of the catalytic activity for the ring-opening polymerization of ε-caprolactone, as well as guanylation of aniline with N,N-diisopropylcarbodiimide is 3 < 2 < 1.     

Nucleophilic reactivity of a series of peroxomanganese(III) complexes supported by tetradentate aminopyridyl ligands

Peroxomanganese(iii) adducts have been postulated as important intermediates in manganese-containing enzymes and small molecule oxidation catalysts. Synthetic peroxomanganese(iii) complexes are known to be nucleophilic and facilitate aldehyde deformylation, offering a convenient way to compare relative reactivities of complexes supported by different ligands. In this work, tetradentate dipyridyldiazacycloalkane ligands with systematically perturbed steric and electronic properties were used to generate a series of manganese(ii) and peroxomanganese(iii) complexes. X-Ray crystal structures of five manganese(ii) complexes all show the ligands bound to give trans complexes. Treatment of these Mn(II) precursors with H(2)O(2) and Et(3)N in MeCN at -40 °C results in the formation of peroxomanganese(iii) complexes that differ only in the identity of the pyridine ring substituent and/or the number of carbons in the diazacycloalkane backbone. To determine the effects of small ligand perturbations on the reactivity of the peroxo group, the more thermally stable peroxomanganese(iii) complexes were reacted with cyclohexanecarboxaldehyde. For these complexes, the rate of deformylation does not correlate with the expected nucleophilicity of the peroxomanganese(iii) unit, as the inclusion of methyl substituents on the pyridines affords slower deformylation rates. It is proposed that adding methyl-substituents to the pyridines, or increasing the number of carbons on the diazacycloalkane, sterically hinders nucleophilic attack of the peroxo ligand on the carbonyl carbon of the aldehyde.     

Characterization of the structure and reactivity of monocopper-oxygen complexes supported by beta-diketiminate and anilido-imine ligands

Copper-oxygen complexes supported by beta-diketiminate and anilido-imine ligands have recently been reported (Aboelella et al., J Am Chem Soc 2004, 126, 16896; Reynolds et al., Inorg Chem 2005, 44, 6989) as potential biomimetic models for dopamine beta-monooxygenase (DbetaM) and peptidylglycine alpha-hydroxylating monooxygenase (PHM). However, in contrast to the enzymatic systems, these complexes fail to exhibit C--H hydroxylation activity (Reynolds et al., Chem Commun 2005, 2014). Quantum chemical characterization of the 1:1 Cu-O(2) model adducts and related species (Cu(III)-hydroperoxide, Cu(III)-oxo, and Cu(III)-hydroxide) indicates that the 1:1 Cu-O(2) adducts are unreactive toward substrates because of the weakness of the O--H bond that would be formed upon hydrogen-atom abstraction. This in turn is ascribed to the 1:1 adducts having both low reduction potentials and basicities. Cu(III)-oxo species on the other hand, determined to be intermediate between Cu(III)-oxo and Cu(II)-oxyl in character, are shown to be far more reactive toward substrates. Based on these results, design strategies for new DbetaM and PHM biomimetic ligands are proposed: new ligands should be made less electron rich so as to favor end-on dioxygen coordination in the 1:1 Cu-O(2) adducts. Comparison of the relative reactivities of the various copper-oxygen complexes as hydroxylating agents provides support for a Cu(II)-superoxide species as the intermediate responsible for substrate hydroxylation in DbetaM and PHM, and suggests that a Cu(III)-oxo intermediate would be competent in this process as well.     

Synthesis and characterization of mononuclear zinc aryloxide complexes supported by nitrogen/sulfur ligands possessing an internal hydrogen bond donor

Treatment of a dinuclear zinc hydroxide complex ([(bmnpaZn)(2)(mu-OH)(2)](ClO(4))(2) (1) or [(benpaZn)(2)(mu-OH)(2)](ClO(4))(2) (2)) with excess equivalents of an aryl alcohol derivative (p-HOC(6)H(4)X; X = NO(2), CHO, CN, COCH(3), Br, H, OCH(3)) yielded the nitrogen/sulfur-ligated zinc aryloxide complexes [(bmnpa)Zn(p-OC(6)H(4)NO(2))](ClO(4)) (3), [(benpa)Zn(p-OC(6)H(4)NO(2))](ClO(4)) (4), [(benpa)Zn(p-OC(6)H(4)CHO)](ClO(4)) (5), [(benpa)Zn(p-OC(6)H(4)CN)](ClO(4)) (6), [(benpa)Zn(p-OC(6)H(4)COCH(3))](ClO(4)) x 0.5H(2)O (7), [(benpa)Zn(p-OC(6)H(4)Br)](ClO(4)) (8), [(benpa)Zn(p-OC(6)H(5))](ClO(4)) (9), and [(benpa)Zn(p-OC(6)H(5)OCH(3))](ClO(4)) (10). The solid state structures of 2, 3, 5, and 6 have been determined by X-ray crystallography. While 3 and 6 exhibit a mononuclear zinc ion possessing a distorted five-coordinate trigonal bipyramidal geometry, in 5 each zinc center exhibits a distorted six-coordinate octahedral geometry resulting from coordination of the aldehyde carbonyl oxygen of another zinc-bound aryloxide ligand, yielding a chain-type structure. Zinc coordination of the aldehyde carbonyl of 5 is indicated by a large shift (>40 cm(-)(1)) to lower energy of the carbonyl stretching vibration (nu(C[double bond]O) in solid state FTIR spectra of the complex. In the solid state structures of 3, 5, and 6, a hydrogen-bonding interaction is found between N(3)-H of the supporting bmnpa/benpa ligand and the zinc-bound oxygen atom of the aryloxide ligand (N(3)...O(1) approximately 2.78 A). Solution (1)H and (13)C NMR spectra of 3-10 in CD(3)CN and FTIR spectra in CH(3)CN are consistent with all of the aryloxide complexes having a similar solution structure, with retention of the hydrogen-bonding interaction involving N(3)-H and the oxygen atom of the zinc-coordinated aryloxide ligand. For this family of zinc aryloxide complexes, a correlation was discovered between the chemical shift position of the N(3)-H proton resonance and the pK(a) of the parent aryl alcohol. This correlation indicates that the strength of the hydrogen-bonding interaction involving the zinc-bound aryloxide oxygen is increasing as the aryloxide moiety increases in basicity.     

Synthesis, reactivity, and computational analysis of halophosphines supported by dianionic guanidinate ligands

The reported chemistry and reactivity of guanidinate supported group 15 elements in the +3 oxidation state, particularly phosphorus, is limited when compared to their ubiquity in supporting metallic elements across the periodic table. We have synthesized a series of chlorophosphines utilizing homo- and heteroleptic (dianionic)guanidinates and have completed a comprehensive study of their reactivity. Most notable is the reluctancy of these four-membered rings to form the corresponding N-heterocyclic phosphenium cations, the tendency to chemically and thermally eliminate carbodiimide, and the scarcely observed ring expansion by insertion of a chloro(imino)phosphine into a P-N bond of the P-N-C-N framework. Computational analysis has provided corroborating evidence for the unwillingness of the halide abstraction reaction by demonstrating the exceptional electron acceptor properties of the target phosphenium cations and the underscoring strength of the P-X bond.     

Use of alkyl 2,4,6-triisopropylbenzoates in the asymmetric homologation of challenging boronic esters

(-)-Sparteine induced lithiation of primary 2,4,6-triisopropylbenzoates and subsequent homologation of boronic esters is reported. A comparative study with lithiated N,N-diisopropylcarbamates has demonstrated the superiority of the hindered benzoate.     

Investigations on the silica gel supported form of microcrystalline zirconium phosphate ion exchanger and its applications in chemical separations

The ion exchanger Si-ZrP in the form of particles of high mechanical stability and good ion exchange performance was prepared by precipitating silicic acid in the slurry of crystalline zirconium phosphate. The conditions of preparation were optimally chosen. The stability of Si-ZrP ion exchanger particles in acidic and basic solutions, the ion exchange properties and kinetics of Si-ZrP were investigated.     

Uranium complexes supported by an aryloxide functionalised triazacyclononane macrocycle: synthesis and characterisation of a six-coordinate U(III) species and insights into its reactivity

A reactive low-valent uranium(III) complex supported by an aryloxide functionalised triazacyclononane has been synthesised and provides a platform for enhanced uranium reactivity.     

Synthesis and reactivity of rare earth metal alkyl complexes stabilized by anilido phosphinimine and amino phosphine ligands

Anilido phosphinimino ancillary ligand H(2)L(1) reacted with one equivalent of rare earth metal trialkyl [Ln{CH(2)Si(CH(3))(3)}(3)(thf)(2)] (Ln=Y, Lu) to afford rare earth metal monoalkyl complexes [L(1)LnCH(2)Si(CH(3))(3)(THF)] (1 a: Ln=Y; 1 b: Ln=Lu). In this process, deprotonation of H(2)L(1) by one metal alkyl species was followed by intramolecular C--H activation of the phenyl group of the phosphine moiety to generate dianionic species L(1) with release of two equivalnts of tetramethylsilane. Ligand L(1) coordinates to Ln(3+) ions in a rare C,N,N tridentate mode. Complex l a reacted readily with two equivalents of 2,6-diisopropylaniline to give the corresponding bis-amido complex [(HL(1))LnY(NHC(6)H(3)iPr(2)-2,6)(2)] (2) selectively, that is, the C--H activation of the phenyl group is reversible. When 1 a was exposed to moisture, the hydrolyzed dimeric complex [{(HL(1))Y(OH)}(2)](OH)(2) (3) was isolated. Treatment of [Ln{CH(2)Si(CH(3))(3)}(3)(thf)(2)] with amino phosphine ligands HL(2-R) gave stable rare earth metal bis-alkyl complexes [(L(2-R))Ln{CH(2)Si(CH(3))(3)}(2)(thf)] (4 a: Ln=Y, R=Me; 4 b: Ln=Lu, R=Me; 4 c: Ln=Y, R=iPr; 4 d: Ln=Y, R=iPr) in high yields. No proton abstraction from the ligand was observed. Amination of 4 a and 4 c with 2,6-diisopropylaniline afforded the bis-amido counterparts [(L(2-R))Y(NHC(6)H(3)iPr(2)-2,6)(2)(thf)] (5 a: R=Me; 5 b: R=iPr). Complexes 1 a,b and 4 a-d initiated the ring-opening polymerization of d,l-lactide with high activity to give atactic polylactides.     

New side-on bound dinitrogen complexes of zirconium supported by an arene-bridged diamidophosphine ligand and their reactivity with dihydrogen

A new dinitrogen complex, deep blue-green {[NPN]*Zr(THF)}(2)(mu-eta(2):eta(2)-N(2)) ([NPN]* = {[N-(2,4,6-Me(3)C(6)H(2))(2-N-5-MeC(6)H(3))](2)PPh}), was prepared in high yield by the reduction of [NPN]*ZrCl(2) with 2.2 equiv of KC(8) in THF under N(2). The solid-state molecular structure shows that N(2) is strongly activated (N-N bond length: 1.503(6) A) and bound side-on to two Zr atoms. Coordinated THF can be readily replaced by adding pyridine (py) or PMe(2)R (R = Me, Ph) to the complex to obtain {[NPN]*Zr(py)}(2)(mu-eta(2):eta(2)-N(2)) or {[NPN]*Zr(PMe(2)R)}(mu-eta(2):eta(2)-N(2)){Zr[NPN]*} in high yield. X-ray diffraction experiments show that the N(2) moiety is strongly activated and remains side-on bound to Zr for the py and PMe(2)Ph adducts; interestingly, only one PMe(2)Ph coordinates to the Zr(2)N(2) unit. {[NPN]*Zr(PMe(2)R)}(mu-eta(2):eta(2)-N(2)){Zr[NPN]*} reacts slowly with H(2) to provide {[NPN]*Zr(PMe(2)R)}(mu-H)(mu-eta(2):eta(2)-N(2)H){Zr[NPN]*}, as determined by isotopic labeling, and multinuclear NMR spectroscopy. The THF adduct does not react with H(2) even after an extended period, whereas the pyridine adduct does undergo a reaction with H(2), but to a mixture of products.     

Synthesis, characterization, and activity in ethylene polymerization of silica supported cationic cyclopentadienyl zirconium complexes

Cp*ZrMe3 reacts with silica pretreated at 800 degrees C, SiO(2-(800)) through two pathways: (a) protolysis of a Zr-Me group by surface silanols and (b) transfer of a methyl group to the surface by opening of strained siloxane bridges, in a relative proportion of ca. 9/1, respectively, affording a well-defined surface species [([triple bond]SiO)ZrCp*(Me)2], 3, but with two different local environments 3a, [([triple bond]SiO)ZrCp*(Me)2][[triple bond]Si-O-Si[triple bond]], and the other with 3b, [structure: see text]. The reaction of the species 3 with B(C6F5)3 is controlled by this local environment and gives three surface species [([triple bond]SiO)ZrCp*(Me)](+)[MeB(C6F5)3]- [[triple bond]Si-O-Si[triple bond]], 4a (20%), [([triple bond]SiO)ZrCp*(Me)](+)[(Me)B(C6F5)3]- [[triple bond]Si-Me], 4b (10%), and [([triple bond]SiO)2ZrCp*](+)[(Me)B(C6F5)(3)](-)[[triple bond]Si-O-Si[triple bond]], 5 (70%). On the contrary, the reaction of Cp*Zr(Me)3, Cp2Zr(Me)2 with [[triple bond]SiO-B(C6F5)3](-)[HNEt2Ph]+, 6, leads to a unique species [([triple bond]SiO)B(C6F5)3](-)[Cp*Zr(Me)2.NEt2Ph]+, 7, and [([triple bond]SiO)ZrCp2](+)[(Me)B(C6F5)3]-, 9 respectively. The complexes 4 and 7 are active catalysts in ethylene polymerization at room temperature, 93 and 67 kg PE mol Zr1- atm(-1) bar(-1), respectively, indicating that covalently bounded Zr catalyst 4 is slightly more active than the "floating" cationic catalyst 7.     

Investigation on catalytic systems containing nickel supported on silica and bonded with organic ligands and complexed by lewis acids

The catalytic properties of the

(n = 0–3) system, resulting from the reaction of (C₃H₅)₂Ni with hydroxide groups of silica gel and complexation with a Lewis acid, MeAlCl₂, have been studied in the oligomerization of propylene. It has been ascertained that when n > 3 the excess of MeAlCl₂ is carried out from the catalyst bed by the products. The yield of the product is influenced by the rate of propylene flow and the composition of the catalyst. The yield of products increases with the rise in the propylene flow rate. The highest yield was obtained for n = 1 and the flow of propylene = 360 ml/min g. The elimination by the olefin of the allyl group from the complex in the initial stages of oligomerization was ascertained. This testifies to the formation of new forms of the surface nickel complex that should contain catalytically active NiH or NiR bonds. The EPR studies determined the valence of nickel in this system (n = 1) to be +2 and thus made it possible to propose its structure.     

Investigation of the silica gel supported form of a microcrystalline zirconium phosphate ion-exchanger Si−ZrP and its application in chemical separations

Structural investigations were carried out using X-ray diffraction and infrared spectroscopy. The bonds acting on the interface between the microcrystalline zirconium phosphate particles and the silica gel spheroids were characterized. The specific surface, the porosity, the pore volume distribution and other physical features of Si–ZrP were determined.     

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.     

Synthesis, structures and reactivity of group 4 hydrazido complexes supported by calix[4]arene ligands

Reaction of TiCl(2)(Me(2)Calix) with 2 equiv of LiNHNRR' afforded the corresponding terminal hydrazido(2-) complexes Ti(NNRR')(Me(2)Calix) (R = Ph, R' = Ph (1) or Me; R = R' = Me (3)) which were all structurally characterized. The X-ray structure of Ph(2)NNH(2) is reported for comparison. Compound 1 was also prepared from Na(2)[Me(2)Calix] and Ti(NNPh(2))Cl(2)(py)(3). Reaction of ZrCl(2)(Me(2)Calix) with 2 equiv of LiNHNR(2) afforded only the bis(hydrazido(1-)) complexes Zr(NHNR(2))(2)(Me(2)Calix) (R = Ph or Me). Treatment of Ti(NNMe(2))(Me(2)Calix) (3) with MeI gave the zwitterionic hydrazidium species Ti(NNMe(3))(MeCalix) (6) via a net isomerization reaction which was found to be catalytic in MeI. The corresponding reaction of 3 with CD(3)I gave Ti(NNMe(2)CD(3))(MeCalix) (6-d(3)) with concomitant elimination of MeI. Reaction of 3 with 1 equiv of MeOTf gave [Ti(NNMe(3))(Me(2)Calix)][OTf] (7-OTf) which in turn reacted with (n)Bu(4)NI to form 6 and MeI. Addition of PhCHO to 3 gave the mu-oxo dimer [Ti(mu-O)(Me(2)Calix)](2) and benzaldehyde-dimethylhydrazone. Reaction of either 3 or 6 with (t)BuNCO gave the zwitterionic species Ti{(t)BuNC(NNMe(3))O}(MeCalix) (10) which has been crystallographically characterized. Compound 10 is the formal product of insertion of an isocyanate into the Ti=N(alpha) bond of a titanium hydrazide or hydrazidium species (Me(2)Calix or MeCalix = dianion or trianion of the di- or monomethyl ether of p-tert-butyl calix[4]arene, respectively).     

Oxidation of alcohols by metal nitrates supported on silica gel

Many metal nitrates, especially zinc(II) and copper(II) nitrates, supported on silica gel, oxidized secondary and benzylic alcohols to the corresponding ketones and aldehydes efficiently.