A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands, [TiX2{2,2‘-Te(4-Me-6- t Bu-C6H2O)2}]2 (5:  X = Cl; 6:  X = O i Pr), catalyzed the ring-opening polymerization of cyclic esters such as ε-caprolactone, δ-valerolactone, and l-lactide. The strong dependence of polymerizations on the solvent was observed in this catalytic system. When the polymerizations of ε-caprolactone and l-lactide were carried out in toluene at 100 °C, tellurium-bridged bis(aryloxo)titanium complex 5 was found to give polymers with rather broad molecular weight distribution due to back-biting. When the polymerizations of ε-caprolactone and l-lactide was carried out in anisole or in dioxane at 100 °C, complex 5 was found to initiate the controlled polymerization, to result in quantitative polymer yields and narrow molecular weight distributions (living nature). The diblock copolymers of l-lactide and ε-caprolactone were also obtained with the catalyst system 5 in anisole. The diblock copolymers showed two melting endothermic at 44.7−53.5 °C derived from the ploy(ε-caprolactone) block and at 155.2−156.8 °C derived from the ploy(l-lactide) block.

A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands,), were prepared. 5b and 6b were determined by X-ray crystallography to have chloro-and isopropoxo-bridged dimeric structures. The structural data for these complexes indicated that the Ti-Te coordination bonds were stronger than the similar Ti-S coordination bonds in the corresponding sulfur-bridged complexes. The reaction of (C 5 R 5 )TiCl 3 (R ) H, Me) with 2,2′-Te(4-R-6-R′-C 6 H 2 OLi) 2 gave monocyclopentadienyl derivatives, (C 5 R 5 )TiCl{2,2′-Te(4-Me-6-t Bu-C 6 H 2 O) 2 } (7, R ) H; 8, R ) Me). The monomeric four-legged piano-stool geometry of 8 was revealed by X-ray analysis. Upon addition of methylaluminoxane (MAO), these complexes catalyzed the polymerization of ethylene. The activities of the tellurium-bridged complexes were found to be significantly higher than those of the corresponding methylene-bridged complex.

We demonstrate that highly surface-sensitive supersonic rare-gas (He, Ar, and Xe) atom scattering, in both the quantum and classical regimes, can probe and quantify the interlayer interactions between graphene monolayers and metal substrates in terms of the Debye temperature corresponding to the surface normal vibration, and the surface effective mass. As models of the strongly and weakly interacting graphene, we investigated two systems, graphene on Ru(0001) and Pt (111), respectively. The experimental data for Ar and Xe are compared with the results from theoretical simulations based on the classical smooth surface model. For gr/Pt(111) we find that the scattering pattern of the rare-gas beam, including the Debye-Waller attenuation of the He beam, are quite similar to that from highly oriented pyrolytic graphite (HOPG); this suggests that the graphene-Pt (111) interaction is much like a van der Waals interaction. On the contrary, for the gr/Ru(0001) system, we find a smaller Debye-Waller attenuation and a larger surface effective mass, indicating that graphene on Ru(0001) is tightly bonded to the substrate. Furthermore, asymmetrical spectral shapes in the Ar and Xe scattering spectra from gr/Ru(0001) are interpreted as a result of the lateral distribution of the interlayer interaction corresponding to the moiré pattern. It is found that the "valley" region of the moiré pattern has high effective mass reflecting stronger bonding to the substrate, contributing to the high reflectivity of the He beam reported for this system. On the other hand, the effective mass of the "hill" region is found to be similar to that of HOPG, indicating that this region is well decoupled from the substrate. These results demonstrate a unique capability of atom scattering to probe and evaluate the molecule-substrate interaction and its spatial distributions.

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