Polymerization of α-Olefins and Butadiene and Catalytic Cyclotrimerization of 1-Alkynes by a New Class of Group IV Catalysts. Control of Molecular Weight and Polymer Microstructure via Ligand Tuning in Sterically Hindered Chelating Phenoxide Titanium an

摘要

A new class of homogeneous catalysts for olefin oligo-polymerization is reported. These titanium or zirconium sterically hindered chelating alkoxide complexes were prepared by reaction of M(CH_2Ph)_4 (M = Ti, Zr) or Zr(CH_2Ph)_2Cl_2(OEt_2)_2 with the appropriate biphenol or binaphthol, or by reaction of TiCl_4 with the diol. Using these methodologies, a range of binaphthoxide and biphenoxide catalysts with varying steric hindrance have been prepared: {1,1′-(2,2′,3,3′-OC_(10)H_5SiR_3)}_2ZrCl_2 {R_3 = Me_3 (1); R_3 = MePh_2 (2); R_3 = Ph_3 (3)}, {1,1′-(2,2′,3,3′-OC_(10)H_5SiMe_3)}_2Ti(CH_2Ph)_2 (4), {1,1′-(2,2′,3,3′-OC_(10)H_5SiMePh_2)}_2Zr(CH_2Ph)_2 (5), (1,1′-(2,2′,3,3′-OC_(10)H_5-SiPh_3)}_2M(CH_2Ph)_2 (M = Ti (7), M = Zr (8)}, 2,2′-S(4-Me,6-~tBuC_6H_2O)_2MX_2 {MX_2 = TiCl_2 (10); MX_2 = ZrCl_2 (11); MX_2 = Ti(CH_2Ph)_2 (12)}, {2,2′-S(4-Me,6-~tBuC_6H_2O)_2}_2Ti (13), 2,2′-(4,6-~tBu_2C_6H_2O)_2MX_2 {MX_2 = Ti(CH_2-Ph)_2 (14); MX_2 = ZrCl_2(THF)_2 (15)}, {2,2′-(4-OMe,6-~tBuC_6H_2O)_2}_2Ti (16), 2,2′-(4-OMe,6-~tBuC_6H_2O)_2Ti(CH_2Ph)_2 (17)}, 2,2′-CH_2(4-Et,6-~tBuC_6H_2O)_2TiX_2 {X = CH_2Ph (18), X = Cl (19), and {2,2′-CH_2(4-Et,6-~tBuC_6H_2O)_2}_2Ti (20). This class of L_2MCl_2 systems can be regarded as being analogous to the well-documented range of Group IV metallocenes. Alkylation of (O—O)ZrCl_2 ((O-O = chelating phenoxide) allowed access to other alkyl species. Therefore, reaction of 3 with MeLi or Me_3SiCH_2Li afforded {1,1′-{2,2′,3,3′-OC_(10)H_5SiPh_3}_2ZrX_2 {X = Me (6); X = CH_2SiMe_3 (9)}, respectively. The X-ray crystal structure of 17 is reported. At 213 K, 17·1/2OEt_2 has space group P1 and unit cell dimensions a = 8.737(9) A, b= 11.840(10) A, c = 17.135(17) A, α = 98.28(7)°, β = 90.53(8)°, γ = 101.38(7)°, μ(Mo Kα) = 2.88 cm~(-1). Attempts to prepare analogous sterically hindered binaphthiolates were thwarted by the absence of known sterically hindered chelating binaphthiols. Synthetic routes to such ligands were attempted albeit without success. The chelating phenoxide and binaphthoxide titanium and zirconium species, in the presence of an aluminum cocatalyst are active for the oligo-polymerization of α-olefins. For the polymerization of ethylene, rates of up to 4740 kg of PE/mol of catalyst·h (100 kg/g of Ti·h) were obtained. They are active for the polymerization of butadiene and the catalytic cyclotrimerization of terminal acetylenes to 1,2,4- and 1,3,5-trisubstituted benzenes. This ratio of benzenes is dependent on the steric bulk of the ancillary binaphthol ligands. Steric modifications also have a clear influence on the degree of 1-hexene polymerization as well as the tacticity of poly-(1-hexene). In particular, the chelating alkoxide ligand framework can induce stereoregularity. For 1 and 2, with methylaluminoxane as cocatalyst, regioregular and stereospecific polymerization of 1-hexene is observed to give high molecular weight isotactic polyhexene. Related ligand-dependent differences in polymer microstructure are observed in the polymerization of butadiene. Cationic complexes have been synthesized. [(C_(10)H_5SiPh_3O)_2Zr(CH_2-Ph)]BPh_4 (21), and zwitterionic (C_(10)H_5SiPh_3O)_2Zr(CH_2Ph)(η~6-PhCH_2)B(C_6F_5)_3 (22) were made by treatment of 8 with [PhNMe_2H]BPh_4 and B(C_6F_5)_3, respectively. They are active for the polymerization of ethylene.