Imido Vanadium Research Articles

Vanadium-Catalyzed Terpolymerization of α,ω-Dienes with Ethylene and Cyclic Olefins: Ready Access to Polar-Functionalized Polyolefins

α,ω-Dienes are an important class of monomers due to their utility in the synthesis of cyclopolyolefins and reactive polyolefin intermediates. In this contribution, the terpolymerization of two α,ω-dienes (i.e., 1,5-hexadiene and 1,7-octadiene) with ethylene and various cyclic olefins [i.e., norbornene (NB), 5-ethylidene-2-norbornene (ENB), and dicyclopentadiene (DCPD)] catalyzed by a chelated imido vanadium complex has been examined. The ENB and DCPD diene termonomers provide additional sites for post-polymerization functionalization. Vanadium-catalyzed terpolymerization of the investigated α,ω-dienes yields polyolefins with a high molecular weight (Mw up to 200 × 103 g mol–1), unimodal and narrow molecular weight distribution, subambient glass transition temperatures (−30 < Tg °C < −3), and a proper content of C═C bonds. Comprehensive NMR investigation of the obtained polymers revealed that subtle changes in the α,ω-diene size have important effects on the numerous combinations of insertion paths (ring closure vs ring opening), from which different repeating units with a C═C bond in the side or main polymer chain and cyclic units are installed. Finally, the poly(ethylene-ter-1,5-hexadiene-ter-NB) was subjected to thiol-ene addition using thioglycolic acid, methyl thioglycolate, and N-acetyl-l-cysteine to access polar-functionalized polyolefins with a degree of functionalization and properties dependent on the thiol substitution.

Vanadium(V) imido chlorides and n-propoxides — Towards a rational design of vanadium imido precatalysts for ethylene polymerization

Vanadium(V) imido complexes are widely used in olefin polymerization and oligomerization. In this report we present the synthesis and the results of ethylene polymerization studies for a series of vanadium(V) imido complexes with various substituents at the imido fragment. All complexes have been prepared in nearly quantitative yields by the interaction of N-sulfinylamines with VOCl3 or VO(OnPr)3 and characterized using 1H, 13C, 51V NMR and elemental analysis. The solid-state structure of complex V(=NArOMe)(OnPr)3 was established using X-ray. Vanadium(V) imido chlorides and n-propoxides exhibited similar moderate catalytic activities (320–547 kgPE·mol(V)−1·h−1·atm−1). The maximum catalytic activity (547 kgPE·mol(V)−1·h−1·atm−1) was achieved for (adamantylimido)vanadium(V) n-propoxide. The molecular weights of the resulting polyethylenes were higher (Mv = 3.7–6.5·105 Da) for imido n-propoxide complexes as compared to the corresponding imido chlorides (Mv = 2.1–5.5·105 Da). The localization of DFT calculated HOMO on imide nitrogen was proposed to favor the reaction between imide ligand and Et2AlCl used as activator.

Semibatch Terpolymerization of Ethylene, Propylene, and 5-Ethylidene-2-norbornene: Heterogeneous High-Ethylene EPDM Thermoplastic Elastomers

Thermoplastic elastomers (TPEs) are materials combining the processability of thermoplastics and the elasticity of rubbers. The global value and demand of TPEs are expected to grow in the coming years, and advancement in synthetic chemistry is the key driving force. This contribution provides a simple synthesis of high-ethylene EPDMs with high molecular weight, narrow molecular weight distribution (1.9 < Mw/Mn < 2.3), and properties which can be adjusted from soft thermoplastic to elastomer. EPDMs are prepared through the terpolymerization of ethylene with propylene and 5-ethylidene-2-norbornene (ENB), where ethylene is continuously supplied to the reaction bath, while propylene and ENB are added only at the beginning. Polymerizations are catalyzed by three known imido vanadium­(IV) complexes, differing in the imido substituent and coligand, in combination with Et2AlCl and Cl3CCO2Et. The obtained EPDMs are a mixture of macromolecules, each of them featuring a nonrandom comonomer distribution and nonuniform composition. Each chain likely contains multiblocks where the comonomers are segmented, i.e., blocks with high ethylene content that may crystallize and blocks with high propylene and ENB content that may not crystallize. This broad chemical composition distribution is due to time drift that occurs during the polymerization, which in turn depends on the experimental conditions and ligand set. Composition drift causes variation in the instantaneous feed comonomer ratio and hence in the chemical composition of the terpolymer over the period of conversion. In proper experimental conditions, EPDMs behave as TPEs without the need of vulcanization, polymer blending, and reinforcement through the addition of fillers. They exhibit high elongation at break, strain hardening at large deformation, remarkable shape retention properties (up to 76% recovery after 10 cycles at 300% and about 90% at 410% strain), and remelting processability with no fall in properties for recycle and reuse.

Bis(imido)vanadium(V)-Catalyzed [2+2+1] Coupling of Alkynes and Azobenzenes Giving Multisubstituted Pyrroles.

The combination of VCl3(THF)3 and N, N-bis(trimethylsilyl)aniline (1a) is an efficient catalyst for the [2+2+1] coupling reaction of alkynes and azobenzenes, giving multisubstituted pyrroles. A plausible reaction mechanism involves the generation of a mono(imido)vanadium(III) species as an initiation step, where 1a served as an imido source with concomitant release of 2 equiv of ClSiMe3, followed by a reaction with azobenzene to form a catalytically active bis(imido)vanadium(V) species via N═N bond cleavage.

Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes

The synthesis and the characterization of a series of phosphine adducts of (imido)vanadium(IV) dichloride complexes of the type V(═NR)Cl2(PMe2Ph)2 [R = 2,6-Cl2-Ph (1), 2,6-iPr2-Ph (2), and tBu (3)] and V(═NtBu)Cl2(PMe3)2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N–V–C bond. Complexes 1–3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et2AlCl (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1–3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly(ethylene)s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform c...

Synthesis of Disentangled Ultra‐High Molecular Weight Polyethylene using Vanadium(V)‐Based Catalysts

Two known imido vanadium(V) trichloride complexes, [Cl3V=N–C6H3‐2,6‐Me2] (1) and [Cl3V=N–C6H3‐2,6‐iPr2] (2), both of which have escaped testing as ethylene polymerization catalyst precursors, were synthesized and their capacity to polymerize ethylene in the presence of the co‐catalyst MAO (methylaluminoxane) (Al:V ratio: 1000:1) at 10 °C is reported. The resulting polymers, from both catalysts, have molecular weights exceeding 1–2 million g/mol as suggested by the insolubility at high temperature and rheological measurements. According to the rheological and DSC annealing characterizations the synthesized Ultra‐High Molecular Weight PolyEthylene from both 1 and 2 show features of a high degree of disentanglement.

Novel SiO2‐Supported Silyl‐Chromate(Cr)/Imido‐Vanadium(V) Bimetallic Catalysts Producing Polyethylene and Ethylene/1‐Hexene Copolymers with Bimodal Molecular‐Weight Distribution

Novel SiO2‐supported silyl‐chromate(Cr)/imido‐vanadium(V) (Cr‐imidoV) bimetallic catalysts for ethylene and ethylene/α‐olefin polymerization are investigated. These catalysts are prepared using the residual surface hydroxyl groups in SiO2‐supported imido‐vanadium catalysts to further support bis(triphenylsilyl) chromate (BC) in order to get the merits from both the SiO2‐supported imido vanadium catalyst and the SiO2‐supported silyl chromate S‐2 catalyst. By investigation of the polymerization behavior and the microstructures of their polymers, several vital factors such as the addition amount of imido vanadium active centers and the dosage of 1‐hexene in the ethylene homopolymerization and ethylene/1‐hexene copolymerization are systematically investigated. Compared with the traditional S‐2 catalyst and our previously reported SiO2‐supported silyl‐chromate(Cr)/vanadium(V)‐oxide (Cr‐V) bimetallic catalyst, the novel Cr‐imidoV bimetallic catalysts show even higher activity and better 1‐hexene incorporation ability, together with higher molecular weight (MW) and bimodal molecular‐weight distribution (MWD). image

Thermolysis of Half-Sandwich Vanadium(V) Imido Complexes to Generate Vanadium(III) Imido Species via a Vanadium(IV) Intermediate

Thermolysis of half-sandwich vanadium imido complexes Cp(RN)V(i-Pr(2)N)Me (R = p-Tol, 1a; R = t-Bu, 1b) results in a mixture of products, including vanadium(IV) dimers [CpVMe](2)(mu-RN)(2), i-Pr(2)NH, i-PrNCMe(2), CH(4), and one or more paramagnetic species. In the presence of dmpe (dmpe = bis(dimethylphosphino)ethane), PMe(3), or PhSSPh, the initially formed paramagnetic species can be trapped, providing Cp(RN)VL(2)(R = p-Tol, L(2) = dmpe, 2a; R = t-Bu, L(2) = dmpe, 2b; R = p-Tol, L = PMe(3), 3a; R = t-Bu, L = PMe(3), 3b; R = t-Bu, L = SPh,4b). This suggests that the initially formed species is [Cp(RN)V]. When generated in situ, [Cp(RN)V] is active in the [2+2+2] cyclotrimerization of PhCCH (R = p-Tol, t-Bu) and PhCCPh (R = t-Bu). Furthermore, the data presented indicate a mechanism in which both [CpVMe](2)(mu-RN)(2) and [Cp(RN)V] originate from a common intermediate, vanadium(IV) imido species [Cp(RN)VMe].

Separation of Petroporphyrins from Asphaltenes by Chemical Modification and Selective Affinity Chromatography

Part of the metalloporphyrin fraction was separated from asphaltenes by a combination of reactive modification and affinity chromatography. The targeted vanadyl porphyrin complexes were modified by reaction with oxalyl chloride followed by a long chain alkylamine or perfluoroalkylaniline to produce an imido vanadium(IV) derivative bearing an octadecyl or perfluoroctyl side chain. This derivatized asphaltene was then chromatographed on C18-silica gel or perfluorous (-C8F17) silica gel to remove the tagged metalloporphyrins from the remaining asphaltene. With the C18-tagging and reverse-phase chromatography method, from 15 to 40% of the total vanadium content together with comparable percentages of nickel was removed, with less than 5% mass loss from the asphaltene fraction. The fluorous tagging process gave better removal of metals on one sample but was limited by the lower recovery of asphaltenes on other samples. This approach requires further optimization for quantitative selective separation of metal c...

Influence of supported vanadium catalyst on ethylene polymerization reactions

AbstractBACKGROUND: In the research area of homogeneous Ziegler–Natta olefin polymerization, classic vanadium catalyst systems have shown a number of favourable performances. These catalysts are useful for (i) the preparation of high molecular weight polymers with narrow molecular weight distributions, (ii) the preparation of ethylene/R‐olefin copolymers with high R‐olefin incorporation and (iii) the preparation of syndiotactic polypropylenes. In view of the above merits of vanadium‐based catalysts for polymerization reactions, the development of well‐defined single‐site vanadium catalysts for polymerization reactions is presently an extremely important industrial goal. The main aim of this work was the synthesis and characterization of a heterogeneous low‐coordinate non‐metallocene (phenyl)imido vanadium catalyst, V(NAr)Cl3, and its utility for ethylene polymerization.RESULTS: Imido vanadium complex V(NAr)Cl3 was synthesized and immobilized onto a series of inorganic supports: SiO2, methylaluminoxane (MAO)‐modified SiO2 (4.5 and 23 wt% Al/SiO2), SiO2 Al2O3, MgCl2, MCM‐41 and MgO. Metal contents on the supported catalysts determined by X‐ray fluorescence spectroscopy remained between 0.050 and 0.100 mmol V g−1 support. Thermal stability of the catalysts was determined by differential scanning calorimetry (DSC). Characterization of polyethylene was done by gel permeation chromatography and DSC. All catalyst systems were found to be active in ethylene polymerization in the presence of MAO or triisobutylaluminium/MAO mixture (Al/V = 1000). Catalyst activity was found to depend on the support nature, being between 7.5 and 80.0 kg PE (mol V)−1 h−1. Finally, all catalyst systems were found to be reusable for up to three cycles.CONCLUSION: Best results were observed in the case of silica as support. Acid or basic supports afforded less active systems. In situ immobilization led to higher catalyst activity. The resulting polyethylenes in all experiments had ultrahigh molecular weight. Finally, this work explains the synthesis and characterization of reusable supported novel vanadium catalysts, which are useful in the synthesis of very high molecular weight ethylene polymers. Copyright © 2007 Society of Chemical Industry

Use of Vanadium Complexes as Catalysts in the Synthesis of Guanidines: New Experimental Data and DFT Analysis of the Carbodiimide Interaction with the Catalyst

The activity of several imido vanadium complexes as catalysts of the guanylation reaction was studied. Complex V(N-2,6-iPr2C6H3)Cl3, 1, was found to be an efficient precatalyst for the reaction between carbodiimides and both primary and secondary aryl amines to give the corresponding guanidines 2−6. Two possible pathways for the reaction were considered for a DFT study: (i) [2+2] carbodiimide addition to the vanadium−imido bond, a mechanism previously ascertained by Richeson and co-workers for the synthesis of guanidines catalyzed by titanium imido compounds (J. Am. Chem. Soc. 2003, 125, 8100); and, alternatively, (ii) carbodiimide insertion into the vanadium−amido bond, which would be formed in situ by the interaction of the amine reagent with 1. First, the titanium-catalyzed reaction, using {(Me2N)C(NMe)2}2Ti(NMe) (A) as a model complex, was studied. Second, two different vanadium model complexes, V(NMe)Cl3 (B) and V(NMe)(NMe2)Cl2 (C), were considered for the guanylation. Noticeably, whereas for model A the [2+2] carbodiimide addition to the metal−imido bond was an exergonic process, for model B the same pathway was not exergonic and gave a much higher activation barrier than that computed for A. Finally, the two pathways were investigated with model C, containing both imido and amido functionalities. The results show that for vanadium-catalyzed guanylation reactions the carbodiimide insertion into the metal−amido bond is favorable with respect to the carbodiimide addition to the metal−imido bond, which is the mechanism operative for titanium.

Guanylation of Aromatic Amines Catalyzed by Vanadium Imido Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Guanylation of aromatic amines catalyzed by vanadium imido complexes

The reaction of formation of guanidines by coupling of carbodiimides and aromatic amines using imido vanadium complexes as catalyst have been investigated. Results demonstrate that the complex V(N-2,6- i Pr 2C 6H 3)Cl 3 is an effective catalyst for this process.

Tris(pyrazolyl)borate imido vanadium (V) compound immobilized on inorganic supports and its use in ethylene polymerization

Abstract Tris(pyrazolyl)borate imido vanadium (V) was immobilized onto a series of inorganic supports: SiO 2 , MAO-modified SiO 2 (4.5 and 23 wt.% Al/SiO 2 ), SiO 2 –Al 2 O 3 , MgCl 2 , MCM-41 and MgO. Immobilized metal content determined by XRF remained between 0.045 and 0.098 mmol V/g support. The highest metal content were observed in the case of supports bearing large surface area (SiO 2 –Al 2 O 3 and MCM-41). All the systems were shown to be active in ethylene polymerization in the presence of MAO or TiBA/MAO mixture (Al/V=1000). Catalyst activity was shown to depend on the support nature, being between 8.1 and 88.0 kg PE/(mol V h). Best results were observed in the case of silica as support. Acid or basic supports afforded less active systems. In situ immobilization led to higher catalyst activity, even in the presence of common alkylaluminum co-catalyst (TiBA). Resulting polyethylenes showed M w higher than 2.7×10 6 Da, suggesting the production of ultra-high molecular weight polymers.

Synthesis and crystal structure of unprecedented phosphine adducts of d(1)-aryl imido-vanadium(IV) complexes.

The reaction of the imido precursor [V(NAr)Cl(2)](n)() (1) (Ar = 2,6-i-Pr(2)C(6)H(3)) with 3 equiv of PMe(2)Ph yields the monomeric complex [V(=NAr)Cl(2)(PMe(2)Ph)(2)] (2). Reacting 1 with 1.5 equiv of dmpe or 1 equiv of dppm affords the dimeric complexes [V(=NAr)Cl(2)(dmpe)](2)(mu-P,P'-dmpe) (3) and [V(=NAr)Cl(2)(dppm)](2) (4), respectively. Complexes 2-4 have been fully characterized by spectroscopic methods, magnetism studies, and X-ray crystallography.

Synthesis and structure of a series of new d(1)-Aryl imido-vanadium(IV) complexes stabilized by n-donor ligands.

A family of new coordination vanadium(IV) compounds supported by a terminal or bridged aryl imido ligand are reported. Reaction of V(NMe(2))(4) with anilines ArNH(2), where Ar = 2,6-i-Pr(2)-C(6)H(3), 2,6-Me(2)-C(6)H(3), Ph, 2,6-Cl(2)-C(6)H(3), and C(6)F(5), afforded the diamagnetic imido-bridged complexes [V(NAr)(NMe(2))(2)](2) (1a-e). Chlorination of 1a-e with trimethylchlorosilane afforded complexes 2a-e formulated as [V(=NAr)Cl(2)(NHMe(2))(x)()](n)(). One-pot reaction of V(NMe(2))(4) with ArNH(2) in the presence of an excess of trimethylchlorosilane gave the five-coordinate compound [V(=NAr)Cl(2)(NHMe(2))(2)] (3a-e). Reaction of 3a-e with pyridine, bipyridine (bipy), or N,N,N',N'-tetramethylethylenediamine (tmeda) gave respectively the six-coordinate tris- or bis(pyridine) adducts [V(=NAr)Cl(2)(Py)(3)] (4a-e) or [V(=NAr)Cl(2)(Py)(2)(NHMe(2))] (5a), bipyridine complexes [V(=NAr)Cl(2)(bipy)(NHMe(2))] (5a-e) and [V(=NAr)Cl(2)(bipy)(Py)] (9a), and tmeda adduct [V(=NAr)Cl(2)(tmeda)(NHMe(2))] (10a). Moreover, five-coordinate complexes free of NHMe(2) ligands, such as [V(=NAr)Cl(2)(Py)(2)] (5a), [V(=NAr)Cl(2)(bipy)] (8a), and [V(=NAr)Cl(2)(tmeda)] (11a), were directly prepared starting from precursors 2a-e. All compounds were totally characterized by spectroscopic methods (IR, (1)H NMR for diamagnetic complexes, and EPR for paramagnetic complexes), elemental analysis, magnetism, and single-crystal X-ray diffraction studies for 1b, 3a, 3d, 4b, 4d, 7c, 10a, and 11a.

Synthesis, Structural Characterization, and MO Calculations of Vanadium Imido Complexes Containing Bidentate Phosphine Coligands.

Treatment of complex V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3) with 1,2-dimethoxyethane (dme) gives in quasi-quantitative yield the adduct V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3)(dme) (1). Interaction of 1 with bidentate phosphines gives V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3)(P-P) (P-P = depe, 2a; dppe, 2b) compounds. An X-ray analysis (monoclinic, space group P2(1)/c, a = 14.7387(14) Å, b = 10.6738(10) Å, c = 16.999(3) Å, beta = 90.954(2) degrees, Z = 4, R = 0.0544), carried out on complex 2a, shows a mer arrangement of the chloride ligands and a nonsymmetrical coordination of the diphosphine ligand. One of the phosphorus atoms occupies the trans position with respect to the organoimido ligand. MO calculations on the models V(NR)Cl(3)(H(2)PCH(2)CH(2)PH(2)) (R = H, C(6)H(5)) of complex 2a were performed. The mer isomer, which is more stable than the fac isomer, shows good agreement with the experimental data.

Alkylation and reductive dimerization of half-sandwich imido vanadium dichlorides

The vanadium imido complex ArNVCl 3 ( 2) (Ar = 2,6-C 6H 3( 1Pr) 2) can be converted to the half-sandwich imido vanadium complex CpV(NAr)Cl 2 ( 3) by reaction with CpSiMe 3. Reaction of 3 and of CpV(N- p-tolyl)Cl 2 ( 1) with alkylating reagents did not allow the isolation of the pure dialkyl complexes but showed extensive reduction of vanadium. Reaction of 1 with AlMe 3 leads to the formation of a mixture of diamagnetic dimeric, imido-bridged complexes (CpV) 2( μ-N- p-tolyl) 2MeR (R = Me or Cl), which can be converted to the pure chloro compound [CpV( μ-N- p-tolyl)Cl] 2 ( 4) by reaction with HCl. Dimerization is prevented when the more bulky ArN ligand is used. Alkylation of 4 with MeLi proceeds cleanly to give the methyl compound [CpV( μ-N- p-tolyl)Me] 2 ( 5). The molecular structures of the formally vanadium(IV) complexes 4 and 5 have been obtained, showing a planar cyclovanadazene core with a vanadium-vanadium single bond and VCl and VC Me bond lengths that are characteristic of V(V) compounds. Compound 5 reacts with CO by insertion in the VC bond, but no reaction is observed with other small unsaturated molecules or Brønsted acids. The 51V NMR chemical shifts of the new complexes are reported and compared with the chemical shifts of known imido vanadium complexes.