Alkene Polymerization Catalysts Bearing Tridentate Phenoxyamine Ligands with sp³ C Donors

Abstract

The reaction of vinyl‐appended phenoxyamine 2 with tetrabenzyltitanium provided the phenoxyaminetitanium(II) alkene complex [rac‐Lig2TiBn], arising from intramolecular vinyl‐group insertion followed by toluene elimination. Whereas [rac‐Lig2TiBn] was inactive for olefin polymerization upon benzyl abstraction, treatment with ethylene led to the formation of stable titanacyclopentane complex [rac‐Lig2(CH2)2TiBn]. Alternatively, six‐membered metallacyclic complexes [rac‐Lig1ZrBn2‐a/b] and [rac‐Lig1HfBn2‐a/b] were obtained from reaction of vinyl‐appended phenoxyamine 1 with tetrabenzylzirconium or tetrabenzylhafnium in a further rare example of intramolecular vinyl‐group insertion into neutral tribenzyl group IV precursors. Living and isoselective polymerization of 1‐hexene was promoted by [rac‐Lig1HfBn2‐a/b]/B(C6F5)3 at 0 °C, whereas [rac‐Lig1ZrBn2‐a/b]/B(C6F5)3 catalyzed the living and isoselective polymerization of propylene ([m4]=0.76) at 0 °C. This catalyst system was employed for the synthesis of a diblock copolymer featuring an isotactic polypropylene semicrystalline block and poly(ethylene‐co‐propylene) amorphous block.

Olefin Polymerization Reactivity of Group 4 Post‐Metallocene Catalysts Bearing a Four‐Membered C(sp3)‐Donor Chelate Ring

“…The Zr−C12 distance of 2.399(2) Å is longer than the Zr−C(benzyl) bonds, while the total internal angles for the four‐membered chelate ring equals 354.0°, thus implying that the metallacycle is close to planarity. Attention is drawn to the O1−Zr1−C12 bite angle of 137.07(5)°, which as expected is substantially smaller than that found in Zr‐[O,N,C(σ‐aryl)] (148–150°), and Zr‐[O,N(amine),CH(CH 2 CH 2 Ph)‐aryl] (158.2(1)°) derivatives, and hence one may envisage highly accessible active sites if similar bite angles are assumed for the corresponding cationic species (predicted to be 134.5–140.6° for benzyl cations of 1 – 6 ; DFT calculations). The molecular structure of 7‐Zr exhibits distorted trigonal‐bipyramidal geometry (τ=0.66) .…”

“…Hence the reaction of H 2 L 1–6 with M(CH 2 Ph) 4 (M=Ti, Zr, Hf) in a pentane/diethyl ether mixture at −78 °C, followed by stirring at 20 °C for 12 hours, proceeded cleanly and the racemic [O,N,CH(Ar)] complexes 1 (and ‐Zr/‐Hf ) and 2–6 were isolated as dark red (Ti), yellow‐orange (Zr) and yellow (Hf) crystalline solids in moderate to high yields (58–95 %; Scheme ). The metal‐C(methine) [M−CH(Ar)] moiety in the resultant four‐membered chelate is reminiscent of those in the following six‐membered metallacycles: (1) the previously reported [M–CH(CH 2 R)‐aryl] (R=methyl, benzyl) complexes;, (2) the benzylic‐type [Ti−CH(Me)‐aryl] species, the formation of which was predicted by DFT calculations from isomerization of the ethylene‐assimilated [Ti−CH 2 CH 2 ‐aryl] fragment . In contrast, treatment of the bis‐pyridine H 2 L 7 with M(CH 2 Ph) 4 (M=Ti, Zr) resulted in the formation of [O,N CH N] complexes 7 and 7‐Zr as black and dark red solids respectively, which contain a six‐membered partially delocalized N,N‐donor chelate (see crystal structure).…”

“…Hence the reaction of H 2 L 1-6 with M(CH 2 Ph) 4 (M = Ti, Zr, Hf) in a pentane/diethyl ether mixture at À 78°C, followed by stirring at 20°C for 12 hours, proceeded cleanly and the racemic [O,N,CH-(Ar)] complexes 1 (and -Zr/-Hf) and 2-6 were isolated as dark red (Ti), yellow-orange (Zr) and yellow (Hf) crystalline solids in moderate to high yields (58-95 %; Scheme 1). The metal-C (methine) [MÀ CH(Ar)] moiety in the resultant four-membered chelate is reminiscent of those in the following six-membered metallacycles: (1) the previously reported [M-CH(CH 2 R)-aryl] (R = methyl, benzyl) complexes; [23,24] (2) the benzylic-type [TiÀ CH(Me)-aryl] species, the formation of which was predicted Scheme 1. Synthesis of complexes (* racemic; only one stereoisomer shown).…”

“…Inspired by this monomer‐inserted process to develop ligand frameworks containing chelating C(sp 3 ) donors, Coates described the formation of a neutral Hf trimethyl derivative supported by a pyridylamido ligand bearing a pendant vinyl unit, which was found to undergo intramolecular vinyl insertion to generate diastereomeric complexes containing the [Hf−CH(Et)−naphthyl] moiety . Furthermore, metalation of a vinyl‐appended phenolate‐amine ligand with Zr‐ and Hf(CH 2 Ph) 4 was accompanied by benzyl migration to afford analogous [M−CH(CH 2 CH 2 Ph)‐aryl] moieties . In both cases, the corresponding catalysts featuring a six‐membered C(sp 3 )‐donor chelate can mediate the living, isoselective polymerization of α‐olefins.…”

“…[23] Furthermore, metalation of a vinylappended phenolate-amine ligand with Zr-and Hf(CH 2 Ph) 4 was accompanied by benzyl migration to afford analogous [MÀ CH-(CH 2 CH 2 Ph)-aryl] moieties. [24] In both cases, the corresponding catalysts featuring a six-membered C(sp 3 )-donor chelate can mediate the living, isoselective polymerization of α-olefins. As an aside, our treatment of phenolate-pyridine ligands bearing a pendant vinyl group with M(CH 2 Ph) 4 (TiÀ Hf) proceeded by an unprecedented vinylic dimerization reaction to yield binuclear complexes bearing a delocalized μ-C 4 R 2 H 2 core structure, which is sufficiently robust to support interesting catalytic reactivity at the bimetallic centers.…”