The ethylene polymerization and copolymerization of olefins catalyzed by dinuclear transition-metal complexes have recently attracted recent attention. [1] Both early-and latetransition-metal complexes with a dinuclear structure lead to an increase in the molecular weight in ethylene polymerization and in the co-monomer content for the copolymerization of ethylene with various co-monomers. [2] The stabilization of the growing polymer end and coordination of the comonomer are efficient in the bimetallic system. [3] Marks and co-workers synthesized a planar dinickel complex, which is supported by an aromatic bis(salicylaldimine) ligand (Scheme 1 a), [4] and found that copolymerization of ethylene with functionalized norbornenes and acrylates resulted in greater incorporation of the co-monomers than that with a mononuclear catalyst. [5] The catalysts, composed of the two nickel salicylaldimine centers and a spacer to join them, have been reported by several research groups independently (Scheme 1 b). [6] The polymer properties are influenced by the distance between nickel centers. Agapie and co-workers investigated olefin polymerization using their dinuclear complexes and revealed a dimer effect in inhibition of the catalysis by amine additives. [7] Lee and-co-workers reported the dinickel complex supported by a macrocyclic salicylaldimine ligand with a Ni···Ni separation of 8.869 (Scheme 1 c) and a moderate catalytic activity for ethylene polymerization. [8] We designed a dinuclear nickel catalyst supported by a rigid macrocyclic ligand, which forces the two nickel centers into close proximity, closer than reported for other catalysts so far. The catalyst is expected to show unique properties not only in ethylene polymerization but also in copolymerization with functionalized monomers, such as terminal dienes, [9] owing to the synergistic effects of the two metal centers. Herein, we show the synthesis of a new dinickel catalyst as well as its application in olefin polymerization.The dinuclear nickel complex 1 and its mononuclear analogue 2 are obtained from the reaction of deprotonated ligand precursors with [(Me 3 P) 2 NiMeCl]. [10] The molecular structure of 1, determined by X-ray crystallography (Figure 1), indicates that the methyl and PMe 3 ligands bonded to the two metal centers are positioned on the same side of the xanthene planes. The two nickel centers of 1 are separated by 4.73 , which is shorter than that in the previously reported dinuclear salicylaldimine nickel complexes (5.80-8.9 ). [5c, 6d, 7, 8] Both 1 and 2 catalyze ethylene polymerization in the presence of a [Ni(cod) 2 ] (cod = cyclo-1,5-octadiene) co-catalyst, which serves as a phosphine scavenger. The two complexes, however, differ significantly in the catalytic activity (2.1 g mmol Ni À1 h À1 atm À1 for 1 and 0.37 g mmol Scheme 1. Three classes of dinuclear salicylaldimine nickel catalyst for olefin polymerization. Figure 1. Structure of 1 determined by X-ray crystallography. Hydrogen atoms are omitted for clarity.

Introducing substituents onto SWNT sidewalls increases their solubility and tunes their properties. Controlling the degree of functionalization is important because the addition of numerous functional groups on the sidewall degrades their intrinsic useful electronic properties. We examined the synthesis and characterization of sidewall-functionalized SWNTs in this study. The functionalized SWNTs ((1)R-SWNTs-(2)R) were prepared in a one-pot reaction of SWNTs with alkyllithium ((1)RLi) followed by alkyl bromide ((2)RBr). The functionalized SWNTs were characterized by the absorption and Raman spectroscopy and thermogravimetric analysis. Not only the total number of functional groups introduced on the SWNT sidewall (formula mass: (1)R = (2)R) but also the ratio of (2)R to (1)R in the functionalized SWNTs (formula mass: (1)R ≠ (2)R) having two different substituents were clarified using the relation between results of Raman spectroscopy and thermogravimetric analysis. Results show that the degree of functionalization of (2)R to (1)R in (1)R-SWNTs-(2)R can be well controlled by the bulkiness of the alkyl groups of (1)RLi and (2)RBr. Moreover, substituent effects of reductive alkylation and reductive silylation of SWNTs via Birch reduction were investigated.

Doppeldecker: Ein Nickel‐Zweikernkomplex mit Doppeldeckerstruktur (siehe Schema) und kleinem Ni‐Ni‐Abstand vermittelt die Copolymerisation von Ethylen mit funktionalisierten Monomeren. Das Abstimmen des Ni‐Ni‐Abstands auf die Comonomerstruktur ergibt Polymere mit hohen Comonomerdichten.

Double-decker dinickel catalysts, even without any substituent on an ortho-position, afforded high molecular weight polyethylene with high crystallinity and less branching.