Selectivity in propene polymerization with metallocene catalysts.

Theoretical studies on reactions of transition-metal complexes.

The abundance of solar thermal energy and the widespread demands for waste heat recovery make thermoelectric generators (TEGs) very attractive in harvesting low-cost energy resources. Meanwhile, thermoelectric refrigeration is promising for local cooling and niche applications. In this context there is currently a growing interest in developing organic thermoelectric materials which are flexible, cost-effective, eco-friendly and potentially energy-efficient. In particular, the past several years have witnessed remarkable progress in organic thermoelectric materials and devices. In this review, thermoelectric properties of conducting polymers and small molecules are summarized, with recent progresses in materials, measurements and devices highlighted. Prospects and suggestions for future research efforts are also presented. The organic thermoelectric materials are emerging candidates for green energy conversion.

Organic Thermoelectric Materials: Emerging Green Energy Materials Converting Heat to Electricity Directly and Efficiently

Cationic alkyl complexes of Group 4 metallocenes of the type [MCp2R]+(M = Ti, Zr or Hf, Cp = C5H5) have been recognised as the catalytically active species in metallocene-based olefin polymerisation catalysts. These highly electrophilic 14-electron species possess a very complex chemistry in which the formation of temporarily dormant stabilised adducts plays a dominant role. Cationic metal alkyls of this kind are found to be extremely active polymerisation catalysts, with high stereoselectivities and the potential to produce numerous previously inaccessible polymeric materials. A detailed understanding of the chemistry of these species promises to lead to a new generation of well defined polymerisation catalysts. Metallocene-based catalysts already play an increasing role in major industrial polymerisation processes.

Cationic Group 4 metallocene complexes and their role in polymerisation catalysis: the chemistry of well defined Ziegler catalysts

Stereospezifische Olefinpolymerisation mit chiralen Metallocenkatalysatoren

The direct insertion mechanism has been studied using PRDDO and ab initio electronic structure calculations. The calculated barrier for the direct insertion reaction Cp 2 TiCH 3 + +C 2 H 4 →Cp 2 TiC 3 H 7 + is +9.8 kcal/mol at the MP2 level. This is in excellent agreement with the experimental barrier of 6-12 kcal/mol. The calculated ΔE for the overall reaction is-12.4 kcal/mol. The geometries of several structures along the reaction pathway including the transition state are presented. The structure of the transition state was found to resemble a metallocyclobutane ring as is generally assumed for the direct insertion mechanism

The direct insertion mechanism in Ziegler-Natta polymerization: a theoretical study of Cp2TiCH3+ + C2H4 .fwdarw. Cp2TiC3H7+

We have calculated the ground-state geometries for a series of d 0 titanium and scandium complexes. The hydrides, as well as Ti(CH 3 ) 3 + , were found to be nonplanar (or bent), while the halides had planar structures. These results, along with the d-orbital populations for the complexes, show that when no π-bonding ligands are present, simple d 0 complexes adopt geometries in which the maximum amount of d-orbital participation to bonding is possible. However, when π-bonding ligands are available, such as in the fluorides and chlorides, the complexes will adopt the planar geometries

Cynthia A. Jolly

Papers

The direct insertion mechanism in Ziegler-Natta polymerization: a theoretical study of Cp2TiCH3+ + C2H4 .fwdarw. Cp2TiC3H7+

Ground-state geometries and inversion barriers for simple complexes of early transition metals

Poly (metal tetrathiooxalates): A structural and charge-transport study

Calculated inversion barriers and proton affinities for P(CH3)3 and P(C6H5)3

Conductive amorphous metal-tetrathiolato polymers: Synthesis of a new precursor C6O2S8 and its derived polymers and laxs structural studies