The synthesis and identification of half-titanocenes containing an aryloxide ligand supported at the chain end (surface) of soluble star-shaped polymers, by adopting sequential one-pot living ring-opening metathesis polymerizations (ROMP) of norbornene (NBE) and a cross-linking reagent using a molybdenum alkylidene catalyst, have been explored. The Ti Kedge XANES spectra (in toluene at 25 °C) indicate that the basic geometry and electronic nature of the original complex, Cp*TiMe 2 (O-i Pr 2 C 6 H 3 ) (1), were preserved in the supported catalyst on the star-shaped ROMP polymers. The supported catalyst showed high catalytic activities for ethylene polymerization, which are lower than that by 1 but higher than that by the supported catalyst at the linear ROMP polymer chain end; efficient 1-hexene incorporation in the ethylene/1-hexene copolymerization has also been demonstrated in this star-shaped supported catalyst.

Mechanistic studies through Ti K-edge XANES and EXAFS spectra of the catalyst solution for 1-hexene polymerization using Cp*TiX2(O-2,6- i Pr2C6H3) [X = Cl (1), Me (2)]–MAO catalysts and for syndiospecific styrene polymerization using ( t BuC5H4)­TiCl2(O-2,6- i Pr2C6H3) (3)–MAO catalyst have been explored. Significant changes in the XANES spectrum (low energy shift in the edge peak, in addition to decrease in intensities of two pre-edge peaks) were observed when styrene (200 equiv) was added into a toluene solution containing 3 and MAO, strongly suggesting that the complex 3 [Ti­(IV)] was reduced to Ti­(III) by addition of styrene under these conditions. The EXAFS analysis suggests that the Ti–O bond (corresponding to coordination of phenoxide) was preserved along with dissociation of Ti–Cl bonds by treating with MAO. These XAS analysis data thus suggest that neutral Ti­(III) species, ( t BuC5H4)­Ti­(R)­(OAr), play a role as the active species. The DFT-based computational analysis on the syndiospecific styrene insertion reaction also revealed that the neutral Ti­(III) catalyst exhibits the lower activation energy than the others, strongly supporting the above mechanism. In contrast, no significant changes (in the oxidation state, basic structure) in the XANES spectra were observed when the toluene solution containing 1 (or 2) was added MAO and 1-hexene, whereas preservation of the Ti–O bond along with dissociation of the Ti–Cl by treating with MAO was suggested through the EXAFS analysis.

Ethylene copolymerization with 2-vinylnaphthalene (VN) by ( t BuC 5 H 4 )TiCl 2 (O-2,6-i Pr 2 C 6 H 3 ) (1)−MAO catalyst system afforded high-molecular-weight amorphous copolymers with unimodal molecular weight distributions as well as uniform compositions (M n = 18 100−39 900, M w /M n = 1.23−1.47, T g = 24−75 °C, VN 21.6−44.8 mol %). Copolymerization with 4vinylbiphenyl (VB) using 1− and (1,2,4-Me 3 C 5 H 2 )TiCl 2 (O-2,6-i Pr 2 C 6 H 3 ) (2)−MAO catalyst systems also yielded highmolecular-weight copolymers (M n = 96 200−222 000, M w /M n = 1.33−2.06), and synthesis of the copolymers with high VB contents (>50 mol %) has been demonstrated. These copolymerizations in the presence of a [Me 2 Si(C 5 Me 4 )(N t Bu)]TiCl 2 (4)−MAO catalyst system afforded semicrystalline polymers (possessing melting temperatures of 91−103 °C). Linear relationships between the glass transition temperature (T g ) and the comonomer (VN, VB) content have been demonstrated. The T g values in the same comonomer content increased in the order VN > VB > styrene, suggesting that introduction of an aromatic substituent to the side pendent group affects the thermal properties (T g values). These copolymers possess resonances ascribed to repeated VN (VB) incorporations on the basis of microstructural analysis of poly(ethylene-co-VN)s and poly(ethylene-co-VB)s through 13 C nuclear magnetic resonance (NMR) spectra, and the regioselectivity as well as the degree of the head-to-tail repeated insertions is affected by the cyclopentadienyl fragment and the comonomer (VN, VB, styrene) employed. Synthesis of high-molecular-weight amorphous poly(ethylene-co-VB) with high VB content, which possesses high T g with a uniform composition (M n = 130 000, M w /M n = 1.51, T g = 156 °C, VB 87.5 mol %), has thus been attained by copolymerization using the 2−MAO catalyst system.

V K-edge XANES (XANES = X-ray Absorption Near Edge Structure) spectra of the reaction solution of V(NAr)Cl2(OAr) (1, Ar = 2,6-Me2C6H3) with halogenated Al alkyls (Me2AlCl, Et2AlCl, EtAlCl2, 50 equiv) in toluene showed low energy shifts (2.6–3.6 eV on the basis of inflection point in the photon energy) in the edge absorption accompanying slight shift to low photon energy in the pre-edge peak (λmax values); a similar spectrum was observed when the reaction of 1 with Me2AlCl was conducted in n-hexane. These results strongly suggest a formation of similar vanadium(III) species irrespective of kind of Al alkyls and solvent (toluene or n-hexane). Significant low-energy shifts in the edge absorption accompanied with diminishing the strong pre-edge absorption were also observed when VOCl3 or VO(OiPr)3 was treated with Me2AlCl (10 equiv) in toluene, clearly indicating a formation of low oxidation state vanadium species accompanied with certain structural changes (from tetrahedral to octahedral) in solution.