Electronically flexible

Combination of the electronically flexible ligands and transition metals... 

Examples of non-symmetric and electronically flexible ligands are shown in Fig. 7, including neutral monoanionic as well as dianionic ligands. The ligands possess HOMO/LUMO energy gap values of <8.5 eV for neutral ligands and <7.0 eV for anionic ligands, at the MNDO-PM3 level calculations. 

A large number of transition metal complexes whose cationic complexes are 10- to 16-electron species (including those with the ligands summarized in Fig. 7) were investigated to determine their potential as ethylene polymerization catalysts with methyaluminoxane (MAO) activation at 25 °C under atmospheric pressure. As a result, we discovered a number of high-activity catalysts for ethylene polymerization that contain electronically flexible ligands [11]. 

The interest in these ligands has stemmed largely from their proven involvement in the chemistry of coordinated dinitrogen. However, they are of considerable intrinsic interest as their electronic flexibility permits them to bind to transition metals with a wide variety of bonding modes. 

Barriers of 12.5-15.5 kcal/mol for neutral CpMo(CO)(MeC=CMe)-(SR) complexes are quite similar to rotational barriers in cationic complexes (74). Given the 7r acidity of CO and the tt basicity of SR-, these barriers are surprisingly small. Sulfur donor ligands tend to be electronically flexible, and the soft thiolate may facilitate alkyne rotation by simultaneous rotation of the thiolate substituent. 

In summary, the electronic flexibility of [M(S )] fragments gives rise to very diverse complexes, structures, and reactivities. 

Processing PCTFE is by the conventional methods (extrusion, injection, etc.) processing temperatures are high, and any degradation of PCTFE can cause severe corrosion and environmental problems. Applications include wire and cable insulation, electronic flexible printed circuits, packaging material (transparent film and sheet), pharmaceutical industry in particular strip and blister packs for tablets and capsules, etc. In the chemical industry, used as gaskets, 0-rings, valve seats, chemical tank liners, etc. 

The conversion of one- to two-electron transfer is an essential feature of this model. It is made possible by the electronic flexibility of haem iron and by the presence of two metals in the centre. The input of electrons shown is thought to arise from haem a, or possibly Cu [99]. For further details and discussion, see Refs. 29, 97-100, 129-133. 

It required a decade of study to develop a clear understanding of the principles and outcome of pterin reactions to molybdenum. The results summarized here tell the story of non-innocent ligand behavior of pterin and pteridine ligands. During this period the first crystal structure of molybdenum enzymes emerged from which the dithiolene chelation of molyb-dopterin was proved. While protein structures unequivocally confirmed the dithiolene coordination to molybdenum, the alternative coordination mode described in this section underscores the electronic flexibility of the pterin system partnered with molybdenum. 

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