No abstract

No abstract

The synthesis and properties of two soluble, weakly coordinating derivatives of the tetrakis(perfluoroaryl)borate anion B(4-C6F4TBS)4 - and B(4-C6F4TIPS)4 - (TBS = tert-butyldimethylsilyl and TIPS = triisopropylsilyl) are reported. Reaction of the trityl salts of the above anions with a variety of zirconium and thorium L2MMe2 complexes in benzene or toluene affords the cationic ion-paired methyl complexes L2MMe+X- or the corresponding hydrido complexes L2MH+X- (L2 = bis(cyclopentadienyl)- or cyclopentadienylamido-type ligand) when the reaction is carried out under dihydrogen. The solid state structure of the complex (Me5Cp)2ThMe+B(C6F5)4 - has been characterized by X-ray diffraction. The B(C6F5)4 --based zirconocenium methyl complexes L2MMe+ are unstable at room temperature with respect to, among other factors, intramolecular C−H activation of the ligand framework. In general, the thermal stabilities of the B(C6F4TBS)4 -- and B(C6F4TIPS)4 --derived complexes are greater than those of the corresponding B(C6F5)4 -- and MeB(C6F5)3 --derived analogues. The relative coordinative tendencies of MeB(C6F5)3 -, B(C6F5)4 -, B(C6F4TBS)4 -, and B(C6F4TIPS)4 - are estimated from the solution spectroscopic information and the structural dynamics of the ion-pairs and follow the order MeB(C6F5)3 - > B(C6F4TBS)4 - ≈ B(C6F4TIPS)4 - > B(C6F5)4 -. The coordination of the neutral metallocene precursors to the cationic metallocenes is found to compete with counteranion coordination. Arene solvent coordination to the zirconium constrained geometry cation [(Me4Cp)SiMe2(NtBu)]ZrMe+ is also observed when B(C6F5)4 - is the counteranion. (1,2-Me2Cp)2ZrMe+B(C6F4TBS)4 - undergoes slow decomposition under an inert atmosphere to afford [(1,2-Me2Cp)2ZrF]2(μ-F)+B(C6F4TBS)4 -, which has been characterized by X-ray diffraction. The olefin polymerization activity and thermal stability of the zirconocene catalysts reaches a maximum when B(C6F4TBS)4 - and B(C6F4TIPS)4 - are used as counteranions. The polymerization activity of the zirconium constrained geometry complex also reaches a maximum in aromatic solvents when B(C6F5)4 - is used as the counteranion, apparently due to solvent coordination.

No abstract

No abstract

The functionalized (fZuoroary1)borate salts Ph3CiB(C84TBS)4-and Ph3C+B(C84TIPS)4-(TBS = tBuMe2Si; TIPS = iPr3Si) are prepared in three steps from 1,4-HCg&. Reaction with zirconocene dimethyls yields crystalline, thermally stable, soluble L2ZrCH3+B-(C$&iR&-and LfzZrH+B(C84SiR&-salts (L = q5-C a 5 ; $-1,Z-MezCSH3; L ' = rf-MesCS, which function as highly active ethylene polymerization catalysts.

A series of zirconium and lanthanide metallocene catalysts are active in the regioselective ring-opening polymerization of strained exo-methylenecycloalkanes to yield exo-methylene-functionalized polyethylenes. MCB (methylenecyclobutane) affords the polymer [CH2CH2CH2C(CH2)] n under the catalytic action of (1,2-Me2Cp)2ZrMe+MeB(C6F5)3 -, and MCP (methylenecyclopropane) affords the polymer [CH2CH2C(CH2)] n under the catalytic action of [(Me5Cp)2LuH]2. Reversible deactivation of the [(Me5Cp)2LuH]2 catalyst is observed in the MCP polymerization reaction and is ascribed to formation of a Lu-allyl species based on D2O quenching experiments. In contrast, the catalysts [(Me5Cp)2SmH]2 and [(Me5Cp)2LaH]2 yield the dimer 1,2-dimethylene-3-methylcyclopentane (DMP) from MCP with high chemoselectivity. The mechanism of dimerization is proposed to involve the intermediacy of 3-methylene-1,6-heptadiene (MHD) and is supported by the observation that independently synthesized MHD is smoothly converted to DMP under catalytic conditions. (Me5Cp)2ZrMe+MeB(C6F5)3 - catalyzes the polymerization of MCP to a polyspirane consisting of 1,3-interlocked five-membered rings (poly(1,4:2,2-butanetetrayl), (C4H6) n ). From end group analysis, the reaction pathway is proposed to consist of β-alkyl shift-based ring-opening followed by an intramolecular insertive, ring-closing “zipping-up” process. AM1-level computations indicate that the zipping-up reaction is exothermic by ∼16 kcal/(mol of ring closure). Under the same catalytic conditions, the monomers methylenecyclopentane, methylenecyclohexane, and 2-methylenenorbornane undergo double bond migration (to the adjacent internal position) rather than polymerization. In contrast to the relatively restrictive requirements for homopolymerization, MCB-ethylene copolymerization is catalyzed by a wide variety of zirconocenium catalysts, including those generated conveniently from MAO, to afford high molecular weight {[CH2CH2] x [CH2CH2CH2C(CH2)] y } n copolymers with the incorporated MCB having an exclusively ring-opened microstructure. The activity of the catalysts in incorporating MCB into the polymer chain follows the order:  Cp2ZrMe+ > (1,2-Me2Cp)2ZrMe+ ≫ (Me5Cp)2ZrMe+, regardless of the counteranion identity. Labeling experiments with 13CH213CH2 confirm that MCB ring-opening occurs with C2−C3, C2−C5 bond scission. MCP-ethylene copolymerization to yield high molecular weight {[CH2CH2] x [CH2CH2C(CH2)] y } having an exclusively ring-opened microstructure is catalyzed by [(Me5Cp)2LuH]2 and [(Me5Cp)2SmH]2. When [(Me5Cp)2LaH]2 is used as the catalyst, more than 50% of the MCP is located at the chain ends in a dienyl structure. The only zirconium polymerization catalyst which incorporates MCP in the ring-opened form in a moderate percentage is [(Me4CpSiMe2(NtBu)]ZrMe+ B(C6F5)4 -. The activity of d0/fn catalysts in incorporating MCP into the polymer follows the order:  [(Me4CpSiMe2(NtBu)]ZrMe+B(C6F5)4 - > [(Me5Cp)2LuH]2 > [(Me5Cp)2SmH]2 > [(Me5Cp)2LaH]2.

No abstract