Chelating diamide complexes of titanium, zirconium and scandium : new polymerization catalysts based on non-cp ligand environments
Creators: name: Scollard, John D.
Publisher: name: University of British Columbia
Year: 2009

description: The reaction of RHN(CH₂)₃NHR (2.3a,b) ( a, R = 2,6-Me₂C₆H₃ ; b, R = 2,6- [sup i]Pr₂C₆H₃ ) with two equivalents of butyl lithium (BuLi) followed by two equivalents of ClSiMe₃ yields the silylated diamines R(Me₃Si)N(CH₂)₃N(SiMe₃)R (2.9a,b). The reaction of 2.9a,b with TiCl₄ yields the dichloride complexes [RN(CH₂)₃NR]TiCl₂ (2.10a,b) and two equivalents of ClSiMe₃ . An X-ray study of 2.10b (P2₁/n, a = 9.771(1) Å, b = 14.189(1) Å , c = 21.081(2) Å , β = 96.27(1)°, V = 2905.2(5) Å³ , Z = 4, T = 25°C, R = 0.0701, R[sub w] = 0.1495) revealed a distorted tetrahedral geometry about titanium with the aryl groups lying perpendicular to the TiN₂-plane. Complexes 2.10a,b react with two equivalents of MeMgBr to give the dimethyl derivatives [RN(CH₂)₃NR]TiMe₂ (2.11a,b). An X-ray study of 2.11a (P2₁2₁2₁, a = 8.0955(10) Å , b = 15.288(4) Å , c = 16.909(3) Å , V = 2092.8(7) Å³, Z = 4, T = 23°C, R = 0.0759, R[sub w] = 0.1458) again revealed a distorted tetrahedral geometry about titanium with titanium-methyl bond lengths of 2.100(9) Å and 2.077(9) Å . These titanium dimethyl complexes are active catalyst precursors for the polymerization of α-olefins, when activated with methylaluminoxane (MAO). Activities up to 350,000 g of poly(1-hexene)/ mmol catalyst•h were obtained in neat 1-hexene at 68 °C. These systems actively engage in chain transfer to aluminum. Equimolar amounts of 2.11a or 2.11b and B(C₆F₅)₃ catalyze the living polymerization a-olefins. Polydispersities (M[sub w]/M[sub n]) as low as 1.05 were measured. Highly active living systems are obtained when 2.11a is activated with {Ph₃C}⁺[B(C₆F₅)₄]⁻. A primary insertion mode (1,2 insertion) has been assigned based on isotopically labeling the initiator and purposeful termination of the polymer chain with iodine. The addition of a pentane solution of complexes 2.11a,b to a pentane solution of B(C₆F₅)₃ at 23°C yields an insoluble yellow-orange solid (2.52a,b) in nearly quantitative yield. Complexes 2.52a,b are catalysts for the living polymerization of 1-hexene at 23°C. In the absence of monomer, complex 2.52b slowly evolves methane over the course of several hours to give a new pentane soluble derivative [RN(CH₂)₃NR]Ti[CH₂B(C₆F₅)₂](C₆F₅) (2.54b) in quantitative yield as indicated by NMR spectroscopy. The molecular structure of 2.54b was confirmed by X-ray crystallography (P2₁/n, a = 20.292(2) Å, b = 11.253(2) Å, c = 23.459(2) Å, β = 114.967(7)°, V = 4856(1) Å³ , Z = 4, T = 21°C, R = 0.041, R[sub w] = 0.034). Complex 2.54b is inactive for the polymerization of α-olefins. The reaction of diamines 2.3b with Zr(NMe₂)₄ yields the complex, [RN(CH₂)₃NR]Zr(NMe₂)₂ (4.1b), and two equivalents of NHMe₂ . Compound 4.1b reacts with two equivalents of [Me₂NH₂]Cl to yield the complex [RN(CH₂)₃NR]ZrCl₂CNHMe₂)₂ (4.5b) and in the presence of excess pyridine affords the complex [RN(CH₂)₃NR]ZrCl₂py₂ (4.6b). The base-free dichloride complex[RN(CH₂)₃NR]ZrCl₂ (4.7b) can be prepared from 4.1b and excess ClSiMe₃. The alkylation of compound 4.6b or 4.7b with two equivalents of MeMgBr, two equivalents of PhCH₂MgCl, and one equivalent of NaCp(DME) yields the alkyl derivatives [RN(CH₂)₃NR]ZrR₂ (4.12a, R = Me; 4.13b, R = CH₂Ph) and [RN(CH₂)₃NR]Zr(ri5-C5H5)Cl (4.26b), respectively. The reaction of two equivalents of PhMe₂CCH₂MgCl with complex 4.6b yields the π²-pyridyl complex [RN(CH₂)₃NR]Zr(ƞ²- N,C-NC₅H₄)(CH₂CMe₂Ph) (4.20b). An X-ray study of 4.20b (P1, a = 10.146(2) Å, b = 12.336(2) Å, c = 16.723(2) Å, a = 81.00(2)°, P = 74.99(2)°, y= 76.24(2), V = 1953.6(6) Å³, Z = 2, T = 25°C, R = 0.0951, R[sub w] = 0.2287) revealed an edge-capped tetrahedral geometry with the pyridyl nitrogen occupying the capping position. Complex 4.20b is likely formed via proton abstraction from coordinated pyridine. The catalyst system 4.12b/MAO polymerizes 1-hexene to a mixture of high polymer and oligomers. Activation with {Ph₃C}[B(C₆F₅)₄] yields only oligomers (n = 2-7). Rapid β-hydride elimination precludes polymer formation in these systems.