The Effects of Activators on Zirconium Phosphinimide Ethylene Polymerization Catalysts

Abstract

Synthetic routes to the species CpZr(NPt-Bu 3 ) 2 Cl, 7, Cp 2 Zr(NPt-Bu 3 )Cl, 8, CpZr(NPt-Bu 3 ) 2 -Me, 9, Cp 2 Zr(NPt-Bu 3 )Me, 10, and CpZr(NPt-Bu 3 ) 2 Bn, 11, were developed in a manner similar to that previously reported for zirconium phosphinimide complexes. Rather than employing metathesis routes, transamination was considered to synthesize bis-phosphinimide zirconium complexes. At ambient temperature, Zr(NPt-Bu 3 ) 3 (NMe 2 ), 15, was isolated in less than 5% yield, but could be obtained cleanly via reaction of Zr(NPt-Bu 3 ) 3 Cl, 14, with LiNMe 2 . However, thermolysis of Zr(NEt 2 ) 4 with HNPt-Bu 3 afforded Zr(NPt-Bu 3 ) 2 (NEt 2 ) 2 , 12, which was subsequently converted to Zr(NPt-Bu 3 ) 2 Cl 2 , 13, upon reaction with trimethylsilyl chloride. Cationic products were generated from the reaction of Lewis acids in the presence of a donor to provide the salts [CpZr(NPt-Bu 3 )Me( THF)][MeB(C 6 F 5 ) 3 ], 16, [Cp*Zr(NPt-Bu 3 )((i-PrN) 2 -CMe)][MeB(C 6 F 5 ) 3 ], 17, and [CpZr(NPt-Bu 3 )((i-PrN) 2 CMe)][MeB(C 6 F 5 ) 3 ], 18. Similarly, reaction of [HNMe 2 Ph][B(C 6 F 5 ) 4 ] with 4 generated the salt [CpZr(NPt-Bu 3 )Me(NMe 2 Ph)]-[B(C 6 F 5 ) 4 ], 19, while reaction of 11 with B(C 6 F 5 ) 3 gave the base-free product [CpZr(NPt-Bu 3) 2 ][BnB(C 6 F 5 ) 3 ], 20. Structural considerations and preliminary MO calculations support the reactivity studies that augur well for olefin polymerization activity. Experimentally, previously reported screening using MAO as a solvent scrubber/activator with 1-4 showed only moderate polymerization activities. However, use of 20 equiv of Al(i-Bu) 3 as scavenger and 2 equiv of B(C 6 F 5 ) 3 as cocatalyst resulted in a significant increase in activity relative to that observed upon activation with MAO. Use of [Ph 3 C][B(C 6 F 5 ) 4 ] as the cocatalyst led to even higher ethylene polymerization activities.

Neutral and Cationic N-Heterocyclic Carbene Zirconium and Hafnium Benzyl Complexes: Highly Regioselective Oligomerization of 1-Hexene with a Preference for Trimer Formation

“…The upfield resonance of the benzyl C ipso (δ 131.8 ppm) and the large 1 J CH coupling constant of the benzyl CH 2 group ( 1 J CH = 140 Hz) indicate that the benzyl group binds in a η 2 mode to Zr. − Though the 1 H NMR chemical shift of the N Me 2 Ph methyl groups is nearly identical with that of free NMe 2 Ph (δ 2.93 vs 2.90 ppm, respectively), the C ipso –NMe 2 Ph resonance is shifted upfield (δ 139.7 vs 150.7 ppm for free NMe 2 Ph) and the NMe 2 Ph 1 H NMR resonances are shifted downfield relative to those of free NMe 2 Ph. These data strongly suggest that NMe 2 Ph effectively coordinates the Zr center in cation 5a + . This is further substantiated by the presence of a NOE correlation between the N Me 2 Ph moiety and a t Bu group of the [ t Bu (OCO)]Zr chelate.…”

Homoleptic Imidophosphorane Stabilization of Tetravalent Cerium

“…They differ from siloxides in their degree of zwitterionic character and the energy and radial extent of the donor atom (N 2p vs O 2p; Scheme A). In contrast to the few previous studies of imidophosphorane chemistry employing alkyl or aryl substituents, − dialkylamide substituents (piperidine in this case) amplify this zwitterionic character by stabilizing the P cationic character and terminal nitrogen N 2– character (Scheme A). Spectroscopic, reactivity, and theoretical studies of homoleptic trivalent and tetravalent complexes of cerium supported by the tris­(piperidinyl)­imidophosphorane ligand, [NP­(pip) 3 ] − [pip = piperidinyl, a six-membered ring, N­(C 5 H 10 )], indicate that covalent interactions between the metal and ligand govern the most significant stabilization of tetravalent cerium observed to date. , The binding of a potassium ion in the inner coordination sphere of the trivalent complex contributes significantly to the thermodynamic driving force for complex oxidation.…”

Titanium and zirconium complexes with aminoiminophosphorane ligands

“…(2) 2.3640(9) 2.3162 (19) Bond angles N(Ph)(1)-Ti-N(Ph) (2) 93.78(14) -N(t-Bu)(1)-Ti-N(t-Bu) (2) 164.19 (15) 112.09(19) P(1)-Ti-P (2) 119.76(4) 94.66(7) Cl(1)-Ti-Cl (2) 86.90 (5) 93.19 (8) The two N(t-Bu) atoms are situated in 1.052 and −0.405 phosphinimide complexes were also observed by Stephan and coworkers. 22,23 We have also reported a series of titanium and zirconium phenoxy-phosphinimide complexes, 24 and these complexes were inactive for ethylene polymerization at atmospheric pressure, but were highly active under ca. 0.6 MPa ethylene pressure.…”