Isoprene polymerization mediated by vanadium-[ONNO] complexes

Catalytic Behavior of Cobalt Complexes Bearing Pyridine-Oxime Ligands in Isoprene Polymerization

Several cobalt(II) complexes Co1-Co3 bearing pyridine-oxime ligands (L1 = pyridine-2-aldoxime for Co1; L2 = 6-methylpyridine-2-aldoxime for Co2; L3 = phenyl-2-pyridylketoxime for Co3) and picolinaldehyde O-methyl oxime (L4)-supported Co4 were synthesized and well characterized by FT-IR, mass spectrum and elemental analysis. The single-crystal X-ray diffraction of complex Co2 reveals that the cobalt center of CoCl2 is coordinated with two 6-methylpyridine-2-aldoxime ligands binding with Npyridine and Noxime atoms, which feature a distorted octahedral structure. These Co complexes Co1-Co4 displayed extremely high activity toward isoprene polymerization upon activation with small amount of AlClEt2 in toluene, giving polyisoprene with high activity up to 16.3 × 105 (mol of Co)-1(h)-1. And, the generated polyisoprene displayed high molecular weights and narrow molecular distribution with a cis-1,4-enriched selectivity. The type of cobalt complexes, cocatalyst and reaction temperature all have effects on the polymerization activity but not on the microstructure of polymer.

One-pot synthesis of cobalt complexes with 2,6-bis(arylimino)phenoxyl/phenthioxyl ligands and catalysis on isoprene polymerization

Several cobalt complexes supported by 2,6-bis(arylimino)phenoxyl/phenthioxyl ligands κ2N,X-Ar[NXN]CoCl(THF) (1a, X = O, Ar = 2,6-Me2C6H3; 1b, X = O, Ar = 2,6-iPr2C6H3; 2a, X = S, Ar = 2,6-Me2C6H3; 2b, X = S, Ar = 2,6-iPr2C6H3) were synthesized by direct oxygen(sulfur) insertion into the C-Co bond of the mixed-valence cobalt complexes {κ2C,N,η6-Ar[NCN]Co-κN-CoCl(μ-Cl)}2. Crystallization of 1b in the presence of water gave the hydrolysis product 1b'. Treatment of Ar[NCN]Li with dioxygen followed by the addition of CoCl2 afforded the heteroatomic complexes {κ2N,O-Ar[NON]Co(μ-Cl)2Li}2 (3a, Ar = 2,6-Me2C6H3; 3b, Ar = 2,6-iPr2C6H3) or κ2N,O-Ar[NON]Co2Cl2(μ-Cl)2Li(THF)2 (4a, Ar = 2,6-Me2C6H3; 4b, Ar = 2,6-iPr2C6H3) depending on the amount of CoCl2 used. The Co(iii)/Li heterometallic complex 3b' with imino-phenoxyl-amino ligands was formed probably via a redox reaction of 3b. The reactions of Ar[NCN]Li with elemental sulfur and CoCl2 gave κ2N,S-Ar[NSN]Co2Cl2(μ-Cl)2Li(THF)2 (5a, Ar = 2,6-Me2C6H3; 5b, Ar = 2,6-iPr2C6H3) respectively. These complexes were well characterized by FT-IR and elemental analyses, and the molecular structures of 1b', 3b', 4a, and 4b were confirmed by X-ray crystallography. Upon activation with Al2Et3Cl3 in toluene, these complexes showed high activities in isoprene polymerization affording cis-1,4 enriched polymers with a moderate molecular weight (0.85-4.72 × 104 Da).

An unsymmetrical binuclear iminopyridine-iron complex and its catalytic isoprene polymerization

A series of chloride-bridged unsymmetrical mixed Fe(ii)-HS/Fe(ii)-LS binuclear structures has been prepared and characterized. Upon activation with MAO, highly efficient catalytic polymerization of isoprene was achieved, delivering an ultra-high molecular weight (catalyst loading = 2.5 ppm, Mn = 1.8 × 106 g mol-1, Mw/Mn = 1.4).

Isoprene Polymerization: Catalytic Performance of Iminopyridine Vanadium(III) Chloride versus Vanadium(III) Chloride

A series of vanadium complexes bearing iminopyridine bidentate ligands with various electronic and steric properties: V1 [CH₂Ph], V2 [CMe₂CH₂CMe₃], V3 [Ph] and V4 [2,6-ⁱPr₂Ph] were prepared and characterized by IR spectroscopy and microanalytical analysis. The catalytic capacity of all the complexes has been investigated for isoprene polymerization and was controlled by tuning the ligand structure with different N-alkyl and N-aryl groups. Activated by methylaluminoxane (MAO), the aryl-substituted complex V3 [Ph] exhibited high cis-1,4 selectivity (75%), and the resultant polymers had high molecular weights (M_n = 6.6 × 10⁴) and narrow molecular weight distributions (PDI = 2.3). This catalyst showed high activity up to 734.4 kg polymer (mol V)⁻¹ h⁻¹ with excellent thermostability even stable at 70 °C. Compared to the traditional VCl₃/MAO catalytic system, iminopyridine-supported V(III) catalysts displayed higher catalytic activities and changed the selectivity of monomer enchainment from trans-1,4 to cis-1,4.

Coupling Reactions of Carbon Dioxide with Epoxides Catalyzed by Vanadium Aminophenolate Complexes

A series of vanadium compounds supported by tetradentate aminobis(phenolate) ligands were screened for catalytic reactivity in the reaction of propylene oxide (PO) with CO₂ : [VO(OMe)(O₂ NO^BuMeMeth )], [VO(OMe)(ON₂ O^BuMe )], [VO(OMe)(O₂ NN^BuBuPy )], and [VO(OMe)(O₂ NO^BuBuFurf )]. They showed similar reactivities, but reaction rates were higher for [VO(OMe)(ON₂ O^BuMe )], which was studied in more detail. Turnover frequencies for conversion of PO over 500 h^-1 were observed. Activation energies were determined experimentally through in situ IR spectroscopy for propylene carbonate (48.2 kJ mol^-1 ), styrene carbonate (45.6 kJ mol^-1 ), and cyclohexene carbonate (54.7 kJ mol^-1 ) formation.

Regio- and stereo-selective polymerization of 1,3-butadiene catalyzed by phosphorus–nitrogen PN3-pincer cobalt(ii) complexes

A new family of cobalt complexes (CoCl2-H, CoCl2-Me, CoCl2-iPr, CoBr2-H, CoBr2-Me, CoBr2-iPr, CoI2-H, CoI2-Me, and CoI2-iPr) supported by a PN³ ligand (6-(N,N′-di-t-butylphosphino)-2-pyrazol-yl-aminopyridine) have been prepared and fully characterized by FT-IR, elemental analysis, and X-ray analysis.