Vanadium(v) tetra-phenolate complexes: synthesis, structural studies and ethylene homo-(co-) polymerization capability

Reaction of the ligand α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xylene (p-L1H4) with two equivalents of [VO(OR)3] (R = nPr, tBu) in refluxing toluene afforded, after work-up, the complexes {[VO(OnPr)(THF)]2(-p-L1)}·2(THF) (1·2(THF)) or {[VO(OtBu)]2(-p-L1)}·2MeCN (2·2MeCN), respectively in moderate to good yield. A similar reaction using the meta ligand, namely α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-m-xylene (m-L2H4) afforded the complex {[VO(OnPr)(THF)]2(-p-L2)} (3). Use of [V(Np-R1C6H4)(tBuO)3] (R1 = Me, CF3) with p-L1H4 led to the isolation of the oxo-imido complexes {[VO(tBuO)][V(Np-R1C6H4)(tBuO)](-p-L1)} (R1 = Me, 4·CH2Cl2; CF3, 5·CH2Cl2), whereas use of [V(Np-R1C6H4)Cl3] (R1 = Me, CF3) in combination with Et3N/p-L1H4 or p-L1Na4 afforded the diimido complexes {[V(Np-MeC6H4)(THF)Cl]2(-p-L1)}·4toluene (6·4toluene) or {[V(Np-CF3C6H4)(THF)Cl]2(-p-L1)} (7). For comparative studies, the complex [(VO)(μ-OnPr)L3]2 (8) has also been prepared via the interaction of [VO(nPrO)3] and 2-(α-(2-hydroxy-3,5-di-tert-butylphenyl)benzyl)-4,6-di-tert-butylphenol (L3H2). The crystal structures of 1·2THF, 2·2MeCN, 3, 4·CH2Cl2, 5·CH2Cl2, 6·4toluene·thf, 7 and 8 have been determined. Complexes 1 – 3 and 5 - 8 have been screened as pre-catalysts for the polymerization of ethylene in the presence of a variety of co-catalysts (with and without a re-activator), including DMAC (dimethylaluminium chloride), DEAC (diethylaluminium chloride), EADC (ethylaluminium dichloride) and EASC (ethylaluminium sesquichloride) at various temperatures and for the co-polymerization of ethylene with propylene; results are compared versus the benchmark catalyst [VO(OEt)Cl2]. In some cases, activities as high as 243,400 g/mmolV.h (30.43 Kg PE/mmolV.h.bar) were achievable, whilst it also proved possible to obtain higher molecular weight polymers (in comparable yields to the use of [VO(OEt)Cl2]). In all cases with dimethylaluminium chloride (DMAC)/ethyltrichloroacetate (ETA) activation, the activities achieved surpassed those of the benchmark catalyst. In the case of the co-polymerization of ethylene with propylene, Complexes 1 – 3 and 5 - 8 showed comparable or higher molecular weight than [VO(OEt)Cl2] with comparable catalytic activities or higher in the case of the imido complexes 6 and 7

Multimetallic lithium complexes derived from the acids Ph 2 C(X)CO 2 H (X=OH, NH 2 ): Synthesis, structure and ring opening polymerization of lactides and lactones

Reaction of LiOR (R = t-Bu, Ph) with the acids 2,2/-Ph2C(X)(CO2H), X = OH (benzH), NH2 (pdgH) was investigated. For benzH, one equivalent LiOt-Bu in THF afforded [Li(benz)(THF)]2·2THF (1·2THF), which adopts a 1D chain structure. If acetonitrile is used (mild conditions), another solvate of 1 is isolated; LiOPh also led to 1. Robust work-up afforded [Li7(benz)7(MeCN)] (2·2MeCN·THF). Use of LiOt-Bu (2 equivalents) led to {Li8(Ot-Bu)2[(benz)](OCPh2CO2CPh2CO2t-Bu)2(THF)4} (3), the core of which comprises two open cubes linked by benz ligands. For dpgH, two equivalents of LiOt-Bu in THF afforded [Li6(Ot-Bu)2(dpg)2(THF)2] (4), which contains an Li2O2 6-step ladder. Similar reaction of LiOPh afforded [Li8(PhO)4(dpg)4(MeCN)4] (5). Complexes 1 - 5 were screened for their potential as catalysts for ring opening polymerization (ROP) of ε-caprolactone (ε-CL), rac-lactide (rac-LA) and δ-valerolactone (δ-VL). For ROP of ε-CL, conversions > 70% were achievable at 110 oC with good control. For rac-LA and δ-VL, temperatures of at least 110 oC over 12h were necessary for activity (conversions > 60%). Systems employing 2 were inactive

Organoaluminium complexes derived from anilines or Schiff bases for the ring-opening polymerization of ε-Caprolactone, δ-Valerolactone and rac-Lactide

Reaction of R1R2CHN=CH(3,5-tBu2C6H2-OH-2) (R1 = R2 = Me L1H; R1 = Me, R2 = Ph L2H; R1 = R2 = Ph L3H) with slightly greater than one equivalent of R33Al (R3 = Me, Et) afforded the complexes [(L1–3)AlR32] (L1, R3 = Me 1, R3 = Et 2; L2, R3 = Me 3, R3 = Et 4; L3 R3 = Me 5, R3 = Et 6); complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2′-diphenylglycine afforded either 5 or the byproduct [Ph2NCH2(3,5-tBu2C6H2-O-2)AlMe2] (7). The known Schiff base complex [2-Ph2PC6H4CH2(3,5-tBu2C6H2-O-2)AlMe2] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH2,2-PPh2C6H4 with Me3Al, namely {Ph2PC6H4N[(Me2Al)2µ-Me](µ-Me2Al)} (9), were also isolated. For structural and catalytic comparisons, complexes resulting from the interaction of Me3Al with diphenylamine (or benzhydrylamine), namely {Ph2N[(Me2Al)2µ-Me]} (10) and [Ph2CHNH(µ-Me2Al)]2·MeCN (11), were prepared. The molecular structures of the Schiff proligands derived from Ph2CHNH2 and 2,2′-Ph2C(CO2H)(NH2), together with those of complexes 5, 7 and 9–11·MeCN were determined; 5 contains a chelating imino/phenoxide ligand, whereas 7 contains the imino function outside of the metallocyclic ring. Complex 9 contains three nitrogen-bound Al centres, two of which are linked by a methyl bridge, whilst the third bridges the N and P centres. In 10, the structure resembles 9 with a bridging methyl group, whereas the introduction of the extra carbon in 11 results in the formation of a dimer. All complexes have been screened for their ability to promote the ring-opening polymerization (ROP) ε-caprolactone, δ-valerolactone or rac-lactide, in the presence of benzyl alcohol, with or without solvent present. Reasonable conversions were achievable at room temperature for ε-caprolactone when using complexes 7, 9 and 12, whilst at higher temperatures (80–110 °C), all complexes produced good (> 65 %) to quantitative conversions over periods as short as 3 min, albeit with poor control. In the absence of solvent, conversions were nearly quantitative at 80 °C in 5 min with better agreement between observed and calculated molecular weight (Mn). For rac-lactide, conversions were typically in the range 71–86 % at 110 °C in 12 h, with poor control affording atactic polylactide (PLA), whilst for δ-valerolactone more forcing conditions (12–24 h at 110 °C) were required for high conversion. Co-polymerization of ε-caprolactone with rac-lactide afforded co-polymers with appreciable lactide content (35–62.5 %); the reverse addition was ineffective, affording only (polycaprolactone) PCL

Mono- and tetra-nuclear copper complexes bearing bis(imino)phenoxide derived ligands: catalytic evaluation for benzene oxidation and ROP of epsilon-caprolactone

Complexes of the type [Cu(L)2] (1) and [Cu4L2(μ4−O)(OAc)4] (2) have been obtained from the reaction of the phenoxydiimine 1,3-(2,6-R22C6H3N=CH)2-5-R1C6H2OH-2 (LH) (where R1 = Me, tBu, Cl; R2 = Me, iPr) with copper(II) acetate [Cu(OAc)2]; changing the molar ratio of the reactants affords 10 differing amounts of 1 or 2. Reaction of the parent dialdehyde [1,3-(CHO)2-5-MeC6H2OH-2] with [Cu(OAc)2] in the presence of Et3N afforded, following work-up, a polymeric chain (3) comprising {[Cu2(OAc)4]OAc}n, HNEt3 and MeCN. The crystal structures of 1 (R1 = Me, R2 = iPr 1a; R1 = Cl, R2 = iPr 1b), 2 (R1 = Me, R2 = Me 2a; R1 = Me, R2 = iPr 2b; R1 = tBu, R2 = Me 2c; R1 = Cl, R2 = Me 2d; R1 = Cl, R2 = iPr 2e; R1 = tBu, R2 =iPr 2f) and 3 are reported (synchrotron radiation was necessary for 3). The 15 magnetic properties of the cluster 2b are presented. Complexes of type 2 and 3 were screened for the ring opening polymerization (ROP) of ε-caprolactone, with or without benzyl alcohol present, under a variety of conditions, however only trace polymer was isolated. The electrochemistry of all complexes was also investigated, together with their ability to catalyze benzene oxidation (using hydrogen peroxide); although low conversions were observed, the tetra-nuclear complexes exhibited excellent selectivity

Vanadyl sulfates: molecular structure, magnetism and electrochemical activity

Reaction of differing amounts of vanadyl sulfate with p-tert-butylthiacalix[4]areneH4 and base allows access to the vanadyl-sulfate species [NEt4]4[(VO)4(μ3-OH)4(SO4)4]·½H2O (1), [HNEt3]5[(VO)5(μ3-O)4(SO4)4]·4MeCN (2·4MeCN) and [NEt4]2[(VO)6(O)2(SO4)4(OMe)(OH2)]·MeCN (3·MeCN). Similar use of p-tert-butylsulfonylcalix[4]areneH4, p-tert-butylcalix[8]areneH8 or p-tert-butylhexahomotrioxacalix[3]areneH3 led to the isolation of [HNEt3]2[H2NEt2]2{[VO(OMe)]2p-tert-butylcalix[8-SO2]areneH2} (4), [HNEt3]2[V(O)2p-tert-butylcalix[8]areneH5] (5) and [HNEt3]2[VIV2VV4O11(OMe)8] (6), respectively. Dc magnetic susceptibility measurements were performed on powdered microcrystalline samples of 1–3 in the T = 300–2 K temperature range. Preliminary screening for electrochemical water oxidation revealed some activity for 2 with turnover frequency (TOF) and number (TON) of 2.2 × 10−4 s−1 and 6.44 × 10−6 (mmol O2/mmol cat.), respectively. The compound 3 showed an improved electrochemical activity in the presence of water. This is related to the increased number and the rate of electrons exchanged during oxidation of V4+ species, facilitated by protons generated in the water discharge process

Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of epsilon-caprolactone

Reaction of the pro-ligand α,α,α’,α’-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L1H4) with two equivalents of [NbCl5] in refluxing toluene afforded, after work-up, the complex {[NbCl3(NCMe)]2(μ-p-L1)}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl2(OEt)(NCMe)]2(μ-p-L1)}·312 MeCN·0.614toluene (2·312 MeCN·0.614toluene) was formed. A similar reaction using [TaCl5] afforded the yellow complex {[TaCl2(OEt)(NCMe)]2(μ-p-L1)}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α’,α’tetra (3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L2H4) only the use of [Nb(O)- Cl3(NCMe)3] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb-(NCMe)Cl(m-L2H2)2]}·312 MeCN (4·312MeCN) or {[Nb(NCMe)Cl(m-z2H2)2]}·5MeCN (4·5MeCN). The molecular structures of 1–4 and the tetraphenols L1H4 and m-L2H4·2MeCN have been determined. Complexes 1–4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat)

Influence of secondary ligand on structures and topologies of lanthanide coordination polymers with 1,3,5-triazine-2,4,6-triamine hexaacetic acid

<div><p>A series of new lanthanide coordination polymers has been synthesized and structurally characterized; [Ln₄(TTHA)₂(pzac)(H₃O)₂(H₂O)]·5H₂O (Ln = Pr (<b>1a</b>) and Nd (<b>1b</b>)), [Sm₈(TTHA)₄(pzac)_0.5(H₃O)(H₂O)_7.5]·4H₂O (<b>2</b>), [Ln₄(HTTHA)₂(SO₄)(H₂O)₄]·5H₂O (Ln = Pr (<b>3a</b>) and Nd (<b>3b</b>)), where H₆TTHA = 1,3,5-triazine-2,4,6-triamine hexaacetic acid, and H₂pzac = 2,5-dioxo-piperazine-1,4-diacetic acid. The compounds feature 3-D frameworks comprising the deprotonated H₆TTHA as the primary ligand and either the <i>in situ</i> generated pzac²⁻ or sulfate as the secondary ligands. The influence of the deprotonated H₆TTHA in directing the framework structures through preferential coordination modes and molecular conformation is described. The effect of the secondary ligands in increasing the compactness of the frameworks and in the alternation of the framework topologies based on the four-connected <b>pts</b> type is described.</p></div

Vanadium(V) phenolate complexes for ring opening homo- and co-polymerisation of [epsilon]-caprolactone, L-lactide and rac-lactide

The vanadyl complexes [VO(OtBu)L1] (1) and {[VO(OiPr)]2(m-p-L2p)} (2) {[VO(OR)]2(m-p-L2m)} (R ¼ iPr 3, tBu 4) have been prepared from [VO(OR)3] (R ¼ nPr, iPr or tBu) and the respective phenol, namely 2,20- ethylidenebis(4,6-di-tert-butylphenol) (L1H2) or a,a,a 0 ,a 0-tetra(3,5-di-tert-butyl-2-hydroxyphenyl–p/m-) xylene-para-tetraphenol (L2p/mH4). For comparative studies, the known complexes [VO(m-OnPr)L1]2 (I), [VOL3]2 (II) (L3 H3 ¼ 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-tert-butylphenol) were prepared. An imido complex {[VCl(Np-tolyl)(NCMe)]2(m-p-L2p)} (5) has been prepared following work-up from [V(Np-tolyl)Cl3], L2pH4 and Et3N. The molecular structures of complexes 1–5 are reported. Complexes 1–5 and I and II have been screened for their ability to ring open polymerise 3-caprolactone, L-lactide or rac-lactide with and without solvent present. The co-polymerization of 3-caprolactone with L-lactide or rac-lactide afforded co-polymers with low lactide content; the reverse addition was ineffective

Organoaluminium complexes of ortho-, meta-, para-anisidines: synthesis, structural studies and ROP of epsilon-caprolactone (and rac-lactide)

Organoaluminium complexes of ortho-, meta-, para-anisidines: synthesis, structural studies and ROP of epsilon-caprolactone (and rac-lactide

Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: synthesis, characterization and ROP of epsilon-caprolactone

Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: synthesis, characterization and ROP of epsilon-caprolacton