Polymerization of substituted acetylenes by various rhodium catalysts: Comparison of catalyst activity and effect of additives

This research deals with comparison of the activity of various Rh catalysts in the polymerization of monosubstituted acetylenes and the effect of various amines used in conjunction with [Rh(nbd)Cl]₂ in the polymerization of phenylacetylene. A zwitterionic Rh complex, Rh⁺(nbd)[(η⁶‐C₆H₅)B^?(C₆H₅)₃] ( 3 ), was able to polymerize phenylacetylene ( 5a ), t‐butylacetylene ( 5b ), N‐propargylhexanamide ( 5c ) and n‐hexyl propiolate ( 5d ), and displayed higher activity than the other catalysts examined, that is [Rh(nbd)Cl]₂ ( 1 ), [Rh(cod)(O‐o‐cresol)]₂ ( 2 ), and Rh‐vinyl complex ( 4 ). Monomers 5a and 5c polymerized virtually quantitatively or in fair yields with all these catalysts, while monomer 5b was polymerizable only with catalyts 3 and 4 . Monomer 5d did not polymerize in high yields with these Rh complexes. The catalytic activity tended to decrease in the order of 3 > 4 > 2 > 1 . Although polymerization of 5a did not proceed at all in toluene with [Rh(nbd)Cl]₂ alone, it smoothly polymerized in the presence of various amines as cocatalysts. The polymerization rate as well as the molecular weight of polymer depended on the basicity and steric bulkiness of amines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4530–4536, 2005     

A new class of ruthenium complexes containing Schiff base ligands as promising catalysts for atom transfer radical polymerization and ring opening metathesis polymerization

A novel series of Schiff base ruthenium complexes that are active catalysts in the field of atom transfer radical polymerization (ATRP), have been prepared. Moreover, when activated with trimethylsilyldiazomethane (TMSD), these species exhibit good catalytic activity in the ring opening metathesis polymerization (ROMP) of norbornene and cyclooctene. The activity for both the ROMP and ATRP reaction is dependent on the steric bulk and electron donating ability of the Schiff base ligand. The control over polymerization in ATRP was verified for the two substrates that exhibit the highest activity, namely MMA and styrene. The results show that the optimal ATRP equilibrium leading to a controlled polymerization, can be established by adjusting the steric and electronic properties of the Schiff base ligand.     

Unusually facil cis to trans isomerization of a polypropiolate bearing a long alkyl chain polymerized using a [Rh(norbornadiene)Cl]2 catalyst: An ESR study

Alkylpropiolate having n-hexadecyl moiety in the ester group was stereospecifically polymerized with a [Rh(norbornadiene)Cl]₂ complex catalyst in alcohol to give rise to cis-transoid polyacetylenes in high yields. The unusually facile cis to trans isomerization for the polymer was found to be induced when the polymer was warmed to even less than ca. 57°C. Under these conditions ESR spectra bearing hyperfine structures due to the radicals generated by the rotational scission in the cis–π bond were observed. This isomerization induced a large g value shift in the ESR spectra together with an increase of the radical concentration during the isomerization, indicating formation of planar conjugated trans sequences that stabilize mobile unpaired electrons as solitons. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2457–2461, 1998     

Transition metal complexes of tetradentate and bidentate Schiff bases as catalysts for ethylene polymerization: Effect of transition metal and cocatalyst

This article compares catalytic performance of ethylene polymerization in similar polymerization conditions of transition metal complexes having two ligands [O,N] (phenoxy‐imine) and having one tetradentate ligand [O,N,N,O] (salphen or salen). It is shown that the activity of both complex types as well as the product properties depend in the same way on the type of central metal in the complex and on the cocatalyst used. Although the type of ligand has some effect on the catalyst activity, yet it does not control the properties of the obtained products. The vanadium and zirconium complexes, irrespective of the cocatalyst used, yield linear polyethylene with high molecular weight (a few hundred thousand g/mol). Similar products are formed when titanium complexes activated with MAO are employed. On the other hand, the same titanium complexes in conjunction with Et₂AlCl, yield low molecular weight polyethylene (of a few thousand) and additionally a mixture of oligomers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 565–575, 2009     

New coordination catalysts based on rare earth compounds for polymerization of 1-octene

The study of rare earth coordination catalysts for polymerization of 1-octene has been successfully carried out for the first time. Some features and kinetic behavior of polymerization of 1-octene by Nd(naph)₃–AIEt₃ catalyst system in tetrachloro-methane are described. The overall polymerization activation energy E_a measured was 74.5 kJ/mol and the rate equation could be expressed as R_p = k_p [Nd] [M] (k_p = 3.21 × 10^?3 L/mol s, at 50°C). The catalytic activity of various rare earth elements in Ln (naph)₃ and ligands in NdL₃ for the polymerization was compared. A 1-octene oligomer with double bonds was obtained. It is either a white or pale yellow waxy semi-solid. Its number-average molecular weight is about 10³ and the molecular weight distribution is less than 2.     

Cationic η-benzyl nickel compounds with diphosphine ligands as catalyst precursors for ethylene oligomerization/polymerization: influence of the diphosphine bite angle

The oligomerization and/or polymerization of ethylene catalyzed by the cationic η³-benzylcomplexes [Ni(η³-CH₂C₆H₄-p-CF₃)(P-P)]⁺ BPh₄⁻ (P-P=ⁱPr₂P(CH₂)_nPⁱPr₂, n=1-3) have been studied. The activity of these single component catalysts depends on the length of the (CH₂)_n bridge of the diphosphine ligand. Thus, the dippm derivative (n=1) displays higher activity than compounds of the dippe (n=2) or dippp (n=3) ligands. The molecular weight of the products is also a function of n, and varies in the order dippm > dippe > dippp, with the former two catalysts giving rise to low molecular weight polyethylenes and the latter to oligomers.     

2-Benzoimidazol-8-alkylquinolinylnickel(II) complexes as efficient catalysts for ethylene oligomerization and vinyl polymerization of norbornene

A series of nickel complexes LNiCl₂ (C1–C16), where L represents 2-benzoimidazol-8-alkylquinoline and its derivatives, were prepared as potential catalysts for the oligomerization of ethylene. The molecular structure of a representative complex C2·CH₃CH₂OH was determined by single-crystal X-ray diffraction. Upon treatment with diethylaluminium chloride (Et₂AlCl), all nickel complex pre-catalysts exhibited good activities in the oligomerization of ethylene. Furthermore, in the presence of methylaluminoxane (MAO), the nickel pre-catalysts were suitable for vinyl polymerization of norbornene.     

Pressure-induced cis to trans isomerization of aromatic polyacetylenes prepared using a Rh complex catalyst: A control of π-conjugation length

This study reports that stereospecific polymerization of aromatic acetylenes, e.g., p-methoxyphenylacetylene (pMOPA) and p-ethoxyphenylacetylene (pEOPA)was successfully performed to give polyacetylene selectively bearing cis-transoid forms in high yield when a Rh complex catalyst, [Rh(norbornadiene)Cl]₂ was used in the presence of triethylamine as the polymerization solvent together with a detailed characterization of the resulting polymers, before and after compression. Compression of these polymers induced a cis-trans isomerization at room temperature under vacuum even in the solid state. Based on data collected before and after compression it is estimated that the trans conjugated length, (CC)_n, produced as a result of the compression is n = 26 for PpMOPA and n = 40 for PpEOPA polymers, respectively. We further found that g values in the ESR spectra of the pristine polymer were shifted to higher magnetic field by compression, indicating that unpaired electrons called solitons are stabilized in the trans conjugation length as mobile electrons, although in the pristine polymers the unpaired electrons are stabilized in the less conjugated chain, showing large g value, suggesting a magnetic interaction between oxygen in the alkoxy group of phenyl moiety and unpaired electrons in the cis form. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 217–223, 1998     

Dinuclear metal complexes of Schiff base ligands as catalysts for oxidation and epoxidation reactions

Dinuclear copper(II) complexes (Cu₂ L_nCl₃), nickel(II) complexes (Ni₂ L_nCl₃) and cobalt(II) complexes (Co₂L ₂ ⁿ Cl₂) from Schiff base ligands are synthesised, characterised and used as catalysts for oxidation of 3,5-DTBC to 3,5-DTBQ. (Cu₂L_nCl₃) are found to be more efficient than the other complexes. Dinuclear iron(III) complexes of composition (Fe₂L₂Cl₂) and ruthenium (III) complexes of composition Ru₂L ₂ ⁿ Cl₆(PPh₃)₂ and Ru₂L ₂ ⁿ Cl₂(PPh₃)₂ catalyse epoxidation of styrene and cyclohexene. Catalytic activities of ruthenium(III) complexes are much greater than those of analogous iron(III) complexes.     

Ruthenium complexes bearing bidentate Schiff base ligands as efficient catalysts for organic and polymer syntheses

A concise overview is given on mononuclear and dinuclear, bidentate Schiff base ruthenium complexes with different additional ligands and on their applications in various chemical transformations such as Kharasch addition, enol-ester synthesis, alkyne dimerization, olefin metathesis and atom transfer radical polymerization. These new ruthenium complexes, conveniently prepared from commonly available ruthenium compounds, are very stable, exhibit a good tolerance towards organic functionalities, air and moisture and display high activity and chemoselectivity in chemical transformations. Relevant features of coordination chemistry connected with the reaction mechanism and chemoselectivity are also fully described. Since the nature of Schiff bases can be changed in a variety of ways, appealing routes for designing and preparing novel ruthenium complexes can be foreseen in the future.     

The Design and Development of a High-Heating-Rate Thermogravimetric Analyzer Suitable for Use With Ablative Plastics

Abstract

The development of a high-heating-rate thermogravimetric analyzer for use with ablative plastics is described. Data are presented for the decomposition of a nylon-phenolic ablator.     

Tri-nuclear phthalocyanine complexes carrying N/O donor ligands as hydrogen peroxide catalysts,and their bleaching activity measurements by an online spectrophotometric method

A phthalocyanine (4) with four salicylhydrazone ligating groups that are directly linked through oxygen bridges to the macrocyclic core has been synthesized by condensation of tetrakis(4-formylphenoxy)phthalocyaninato zinc(II) (3) with salicylhydrazine. Salicylhydrazine was crystallized in methanol during the synthetic procedure. The crystal structure has triclinic space group P-1 with a = 5.8292(6) Å, b = 7.3039(7) Å, c = 17.9798(18) Å, α = 84.272(8)°, β = 89.184(8)°, γ = 81.469(8)°, and Z = 4. Intramolecular O–H?O and intermolecular O–H?O, N–H?N, N–H?O hydrogen bonds were determined in the crystal structure. In addition, there is a weak C–H?π interaction. Complexation on the periphery to yield tri-nuclear Zn(II)Pcs (5–7) was performed through the reaction of a Schiff base-substituted phthalocyanine (4) with MnCl₂·4H₂O, CoCl₂·6H₂O, or Ni(OAc)₂ salts. Fourier transform infrared, ¹H NMR, ¹³C NMR, UV–Vis, ICP-OES (inductively coupled plasma optical emission spectroscopy), mass spectroscopies, and elemental analyses were applied to characterize the prepared compounds. Bleach catalyst activity of the prepared phthalocyanine complexes (5–7) was examined by the degradation of morin and curcumin, respectively. The catalysts had better activity for color removing in solutions at ambient temperature than to that of tetraacetylethylenediamine (TAED).     

Schiff base as a novel kind of catalyst for reversible complexation‐mediated radical polymerization of methyl methacrylate

Two kinds of Schiff base, N,N′‐dibenzylidene‐1,2‐diaminoethane (NDBE) and N,N′‐disalicylidene‐1,2‐diaminoethane, have been found as efficient organic catalyst for reversible complexation‐mediated radical polymerization (RCMP) of methyl methacrylate (MMA) for the first time. The polymerization results show obvious features of “living”/controlled radical polymerization. Well‐defined and low‐polydispersity polymers (M_w/M_n = 1.20–1.40) are obtained in RCMP of MMA catalyzed by Schiff base at mild temperature (65–80°C). Moreover, Schiff base also exhibits a particularly high reactivity for RCMP of MMA with in situ formed alkyl iodide initiator. The polymer molecular weight and its polydispersity (M_w/M_n is around 1.20) are well controlled even with high monomer conversion. Notably, when the dosage of azo initiator is same as the dosage of iodine, the polymerization could also be realized in the presence of NDBE. The living feature of synthesized polymer is confirmed through the chain extension experiment. In short, Schiff base is a kind of high‐efficient catalyst for RCMP and reverse RCMP of MMA, which can be one of the most powerful and robust techniques for polymer synthesis. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1653–1663     

Heptane-soluble homogeneous zirconocene catalyst: Synthesis of a single diastereomer,polymerization catalysis,and effect of silica supports

Bis(1-indenyl)-di[1′S, 2′R, 5′S)-methoxy]silane ( 1 ) was converted into a mixture of corresponding ansa-diastereomeric zirconocenes. Further purification afforded a single dia-stereomer, di[(1′S, 2′R, 5′S)-methoxy] silylene-bis[η⁵-1(R, R)-(+)-indenyl] dichlorozirconium ( 2 ), which is optically active and hydrocarbon soluble. Extremely rapid ethylene, propylene, and ethylene-hexene polymerizations were observed both in toluene and n-heptane solutions; for instance, at 50°C, activity for ethylene polymerization reaches ～ 1.5×10¹⁰ (g of PE/((mol of Zr) · [C₂H₄] · h). The “bare” zirconocenium ion generated from 2/TIBA/Ph₃CB(C₆F₅)₄ exhibits unusual polymerization behaviors; the polymerization activity increases monotonically with temperature of polymerization (T_p) up to a conventional polymerization condition (50–70°C), and the ¹³C NMR study shows that the isotactic poly-propylene obtained has fairly high [mmmm] methyl pentad distributions at high T_p (?25°C with [mmmm] ～ 0.93–0.75) and a perfect stereoregularity at low T_p (?0°C with [mmmm] > 0.99). The catalyst precursors 2 and Et(Ind)₂ZrCl₂ ( 3 ) supported on silica by different approaches produced poly(olefins) of different molecular weights and stereoregularities, and a methylaluminokane and Ph₃CB(C₆F₅)₄ free silica-supported zirconocene system was found to be activated by triisobutylaluminum. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of novel neutral nickel complexes bearing fluorinated salicylaldiminato ligands and their catalytic behavior for vinylic polymerization of norbornene

A series of salicylaldimine‐based neutral Ni(II) complexes (3a–j) [ArN = CH(C₆H₄O)]Ni(PPh₃)Ph [3a, Ar = C₆H₅; 3b, Ar = C₆H₄F(o); 3c, Ar = C₆H₄F(m); 3d, Ar = C₆H₄F(p); 3e, Ar = C₆H₃F₂(2,4); 3f, Ar = C₆H₃F₂(2,5); 3g, Ar = C₆H₃F₂(2,6); 3h, Ar = C₆H₃F₂(3,5); 3i, Ar = C₆H₂F₃(3,4,5); 3j, Ar = C₆F₅] have been synthesized in good yield, and the structures of complexes 3a and 3i have been confirmed by X‐ray crystallographic analysis. Using modified methylaluminoxane as a cocatalyst, these neutral Ni(II) complexes exhibited high catalytic activities for the vinylic polymerization of norbornene. It was observed that the strong electron‐withdrawing effect of the fluorinated salicylaldiminato ligand was able to significantly increase the catalyst activity for vinylic polymerization of norbornenes. In addition, catalyst activity, polymer yield and polymer molecular weight can also be controlled over a wide range by the variation of reaction parameters such as Al:Ni ratio, norbornene:catalyst ratio, monomer concentration, polymerization temperature and time. Copyright © 2008 John Wiley & Sons, Ltd.     

ESR study on styrene polymerization with CpTiCl3/MMAO: Effect of monomer addition on catalyst activity

An on-line electron spin resonance (ESR) technique was applied to investigate the syndiospecific polymerization of styrene activated by the catalyst system CpTiCl₃/MMAO. The measurements included trivalent titanocene concentration and monomer conversion. The activation procedure was found to have a dramatic effect on catalyst activity. Adding the reactants in the order of (MMAO + CpTiCl₃) + St gave a much higher trivalent titanocene concentration and catalyst activity than the order of (MMAO + St) + CpTiCl₃. The catalyst deactivation behaviors in the temperature range of 25–70°C were followed as a function of time during polymerization. At high Al/Ti ratios (500–1000), the decay rates of trivalent titanocene in the presence of styrene were much faster than those of the pure catalyst system. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3385–3390, 1999     

Versatile reactivity of half-sandwich Ir and Rh complexes toward carboranylamidinates and their derivatives: synthesis, structure, and catalytic activity for norbornene polymerization

Synthesis, structure, and reactivity of carboranylamidinate‐based half‐sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ‐Cl)Cl}₂] (M=Ir, Rh; Cp*=η⁵‐C₅Me₅) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18‐electron complexes [Cp*IrCl(Cab^N‐DIC)] ( 1 a ; Cab^N‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHiPr)]), [Cp*RhCl(Cab^N‐DIC)] ( 1 b ), and [Cp*RhCl(Cab^N‐DCC)] ( 1 c ; Cab^N‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHCy)]). A series of 16‐electron half‐sandwich Ir and Rh complexes [Cp*Ir(Cab^N′‐DIC)] ( 2 a ; Cab^N′‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NiPr)]), [Cp*Ir(Cab^N′‐DCC)] ( 2 b , Cab^N′‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NCy)]), and [Cp*Rh(Cab^N′‐DIC)] ( 2 c ) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab^N,S‐DIC)], [Cp*M(Cab^N,S‐DCC)] (M=Ir 3 a , 3 b ; Rh 3 c , 3 d ), formed through BH activation, are obtained by reaction of [{Cp*MCl₂}₂] with carboranylamidinate sulfides [RN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHR)]S^? (R=iPr, Cy), which can be prepared by inserting sulfur into the C? Li bond of lithium carboranylamidinates. Iridium complex 1 a shows catalytic activities of up to 2.69×10⁶ g_PNB ${{\rm{mol}}_{{\rm{Ir}}}^{ - {\rm{1}}} }Synthesis, structure, and reactivity of carboranylamidinate-based half-sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ-Cl)Cl}(2)] (M = Ir, Rh; Cp* = η(5)-C(5)Me(5)) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18-electron complexes [Cp*IrCl(Cab(N)-DIC)] (1?a; Cab(N)-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NHiPr)]), [Cp*RhCl(Cab(N)-DIC)] (1?b), and [Cp*RhCl(Cab(N)-DCC)] (1?c; Cab(N)-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10))(NHCy)]). A series of 16-electron half-sandwich Ir and Rh complexes [Cp*Ir(Cab(N')-DIC)] (2?a; Cab(N')-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NiPr)]), [Cp*Ir(Cab(N')-DCC)] (2?b, Cab(N')-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10)(NCy)]), and [Cp*Rh(Cab(N')-DIC)] (2?c) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab(N,S)-DIC)], [Cp*M(Cab(N,S)-DCC)] (M = Ir 3?a, 3?b; Rh 3?c, 3?d), formed through BH activation, are obtained by reaction of [{Cp*MCl(2)}(2)] with carboranylamidinate sulfides [RN=C(closo-1,2-C(2)B(10)H(10))(NHR)]S(-) (R = iPr, Cy), which can be prepared by inserting sulfur into the C-Li bond of lithium carboranylamidinates. Iridium complex 1?a shows catalytic activities of up to 2.69×10(6) g(PNB) mol(Ir)(-1) h(-1) for the polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. Catalytic activities and the molecular weight of polynorbornene (PNB) were investigated under various reaction conditions. All complexes were fully characterized by elemental analysis and IR and NMR spectroscopy; the structures of 1?a-c, 2?a, b; and 3?a, b, d were further confirmed by single crystal X-ray diffraction.     

Synthesis of double silylene‐bridged binuclear zirconium complexes and their use as catalysts for olefin polymerization

New double silylene‐bridged binuclear zirconium complexes [(η⁵‐RC₅H₄)ZrCl₂]₂[μ,μ‐(SiMe₂)₂(η⁵‐C₅H₃)₂] [R = H ( 1 ), Me ( 2 ), ⁿPr ( 3 ), ⁱPr ( 4 ), ⁿBu ( 5 ), allyl ( 6 ), 3‐butenyl ( 7 ), benzyl ( 8 ), PhCH₂CH₂ ( 9 ), MeOCH₂CH₂ ( 10 )] were synthesized by the reaction of (η⁵‐RC₅H₄)ZrCl₃·DME with [μ,μ‐(SiMe₂)₂(η⁵‐C₅H₃)₂]^2? ( L^2? ) in THF, and they were all well characterized by ¹H NMR, MS, IR, and EA. The binuclear structure of Complex 3 was further confirmed by X‐ray diffraction, where the two zirconium centers are located trans relative to the bridging [μ,μ‐(SiMe₂)₂(η⁵‐C₅H₃)₂] moiety. When activated with methylaluminoxane (MAO), this series of zirconium complexes are highly active catalysts for the polymerization of ethylene even under very low molar ratio of Al/Zr (Complex 7 , 5.41 × 10⁵ g‐PE/mol‐Zr·h, Al/Zr = 50) and linear polyethylenes (PEs) with broad molecular weight distribution (MWD, M_w/M_n = 7.31–27.6) was obtained. The copolymerization experiments indicate that these complexes are also very efficient in the incorporation of 1‐hexene into the growing PE chain in the presence of MAO (Complex 6 , 3.59 × 10⁶ g‐PE/mol‐Zr·h; 1‐hexene content, 3.65%). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4901–4913, 2007     

Synthesis and application of pendant phenyl cyclopentadienyl lanthanide chlorides as catalyst precursors for methyl methacrylate polymerization

The synthesis and characterization of a series of new pendant phenyl substituted cyclopentadienyl lanthanide chlorides are reported. The analytical data of 3a–3e point to the formation of monomeric and unsolvated complexes, (PhCMe₂C₅H₄)₂LnCl (Ln = Er (3a), Sm (3b), Gd (3c), Y (3d), Nd (3e)); and the analytical data of 4a–4d point to the formation of the dimeric and unsolvated complexes, [(PhCH₂CMe₂C₅H₄)₂LnCl]₂ (Ln = Gd (4a), Y (4b), Sm (4c), Er (4d)). The X‐ray crystallographic structure of 4d indicates that the pendant phenyl substituent is not coordinated to the central metal. The nine complexes are efficient catalysts for the polymerization of methyl methacrylate in conjunction with Al(Et)₃ or NaH. As NaH was used as a new co‐catalyst, the catalytic systems show highly catalytic activity at room temperature. In the [(PhCH₂CMe₂C₅H₄)₂ErCl]₂/Al(Et)₃ catalyst system, the effects of the concentration of catalyst, and the temperature and time of polymerization were studied. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of (adamantylimido)vanadium(V)-alkyl complexes containing aryloxo ligands and their use as the catalyst precursors for ring-opening metathesis polymerization of norbornene, and ring-opening polymerization of tetrahydrofuran

Various (adamantylimido)vanadium(V) dialkyl complexes containing aryloxo ligands, V(NAd)(CH₂SiMe₃)₂(OAr) [Ad = 1-adamantyl (1); Ar = Ph (a), 4-FC₆H₄ (b), 2,6-F₂C₆H₃ (c), 2,6-Me₂C₆H₃ (d), C₆F₅ (e)], have been prepared and identified. These complexes were employed as the catalyst precursors for ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of PMe₃ at 80 °C. The activity was strongly affected by the aryloxo substituent and increased in the order: C₆H₅ < 4-FC₆H₄ < 2,6-Me₂C₆H₃ << 2,6-F₂C₆H₃, C₆F₅. The same trend was observed in the ROMPs by the arylimido-aryloxo analogues, V(NAr′)(CH₂SiMe₃)₂(OAr) (2a-e; Ar′ = 2,6-Me₂C₆H₃), under the same conditions, and the activities by the arylimido analogues were generally higher than the adamantylimido analogues in most case. The (imido)vanadium(V) complexes containing O-2,6-F₂C₆H₃ (1,2c) or OC₆F₅ (1,2e) exhibited high catalytic activities, and these results strongly suggest that electronic as well as steric factors play a role. Living ring-opening polymerization of THF proceeded in the presence of V(NAd) (CH₂SiMe₃)(OAr)₂ (Ar = 2,6-Me₂C₆H₃, C₆F₅) and [Ph₃C][B(C₆F₅)₄], affording high molecular weight polymers with narrow molecular weight distributions (ex. M_n = 2.11 × 10⁵, M_w/M_n = 1.18).