Pressure Modulates Stereoregularities in the Polymerization of Propylene Promoted by rac-Octahedral Heteroallylic Complexes

Abstract

This communication reports the synthesis and activity of four racemic mixtures of bis (benzamidinate) group-4 complexes, cis-[p-R′C 6 H 4 (4)) as precatalysts for the stereoregular polymerization of propylene. These complexes catalyze the stereoregular polymerization of propylene only under pressure in CH 2 Cl 2 , producing polypropylene with very large isotacticities (mmmm % ) ∼95-98), high melting points (140-154°C ).a Methylaluminoxane, solvent removed from a 20% solution in toluene (Schering) at 25°C /10 -6 Torr. b Grams of total polymer/mole of Zr‚h. c By viscosimeter technique in 1,2,4-trichlorobenzene at 130°C (K ) 1.37 × 10 -2 ; R ) 0.7). d An additional low molecular weight oily fraction was separated from the solid. e The polypropylene is obtained as an elastomer (Tg).

First‐Row Transition Metal Bis(amidinate) Complexes; Planar Four‐Coordination of FeII Enforced by Sterically Demanding Aryl Substituents

“…[1,2] Their steric and electronic properties are readily modified through variation of the substituents on the carbon and nitrogen atoms, and they have been employed as ancillary ligands in various catalytic conversions, e.g. oligomerisation [3,4] or polymerisation [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] of olefins or of cyclic esters. [21,22] Due to the geometric constraints of the NCN ligand backbone, amidinates have small N-M-N bite angles (typically 63-65°).…”

“…The room-temperature 1 H NMR spectrum of the diamagnetic Ni complex 5 in [D 6 ]benzene shows two septuplets for the isopropyl methine protons and four doublets for the isopropyl methyl protons. This is consistent with the approximate D 2 The rate constant for the interconversion of the enantiomers k = 2.25 (38) s -1 at 338 K was obtained by plotting the extent of exchange vs. the mixing time.…”

“…The solid was extracted with benzene (40 mL) until the extracts were colourless. The crude product was recrystallised from hot benzene, affording 6·C 6 [85] The ratio of the peak volumes of the cross-peaks and the diagonal peaks (I x / I d ) was plotted vs. mixing time τ. The rate constants k for the exchange process was determined by fitting the data to the equation [79] The free energy of activation ΔG ‡ at 338 K was calculated by substitution of k 338 according to the relation [80] Magnetic Measurements: Data were collected on crystalline samples (ca.…”

Olefin Polymerization with Non-metallocene Catalysts (Early Transition Metals)

“…This displacement reaction would afford the proposed catalytically active species 3 0 . Isospecific propylene polymerization took place if zirconium complexes containing bis(amidinate) complexes (4), bearing achiral substituents R, at higher propylene pressures [32]. As shown in Table 3.1, the stereo-regularity in the resultant polypropylene was modulated by the pressure (from atactic to isotactic through elastomers).…”

Stereospecific Olefin Polymerization Catalyzed by Metallocene Complexes

“…Benzamidinate complexes 65 and 66 also give isotactic polypropylene (66, [mmmm]=0.95-0.98) [196,197].…”