Polar addition metals

From the results discussed above, it appears that the main influence of phosphines in controlling the course of propene dimerization consists in hindering, through steric interference, the second insertion step from proceeding according to Ni — C2 type addition. An explanation for the predominant Ni — C2 type addition in the absence of steric hindrance in terms of the polarity of metal-carbon, metal-H. and C=C bonds has been recently presented (104). The extremely bulky phosphine (t-C4H9)2P-i-C3H7 is even able to reverse the direction of Ni—H addition to propene, a step which is obviously less sensitive toward steric hindrance. 

Unfunctionalized alkenes have posed more of a problem, as they have no polar moiety which can coordinate to the catalyst. Such an additional metal binding site next to the C = C bond has proven to be crucial for directing coordination to the catalyst and, therefore, rhodium and ruthenium complexes, which are highly selective for functionalized alkenes, generally provide only low enan-tioselectivity for this class of substrates. 

Diazaphospholes 4 and 5 are colorless to pale yellow distillable liquids or crystalline solids that are stable to oxidation by air and do not react with elemental sulfur. They are readily hydrolyzed to give the hydrazone from which they originate and phosphorus acid. While only a few reactions of 1/7-1,2,3-diazaphospholes 4 are reported, the chemistry of the 2//-isomers 5 is well studied. In CHEC-II(1996), the following reactions of 1,2,3-diazaphos-pholes are described in detail N-protonation and alkylation, polar addition to the P=C bond and substitution at C-4, cycloaddition reactions, substituent reactions, and the formation of transition metal complexes <1996CHEC-II(4)771>. 

The prediction of a threshold current above which a leveler is unable to stabilize growth has also been identified in a recent linear stability study that includes two additional terms not previously considered, namely (a) complex formation between the additive and the metal cation and (b) interaction between the polar additives and... 

Duvdevani(40) have been directed at modification of ionomer properties by employing polar additives to specifically interact or plasticize the ionic interactions. This plasticization process is necessary to achieve the processability of thermoplastic elastomers based on S-EPDM. Crystalline polar plasticizers such as zinc stearate can markedly affect ionic associations in S-EPDM. For example, low levels of metal stearate can enhance the melt flow of S-EPDM at elevated temperatures and yet improve the tensile properties of this ionomer at ambient temperatures. Above its crystalline melting point, ca. 120°C, zinc stearate is effective at solvating the ionic groups, thus lowering the melt viscosity of the ionomer. At ambient temperatures the crystalline additive acts as a reinforcing filler. 

Chem. Descrip. Propylene carbonate CAS m32-7 EINECS/ELINCS 20S 572-1 Uses Solvent, reactant, plastidzer for fibers, textiles, dyeing, plastics and resins, gas treating, aromatic hydrocarbon extraction, metal extraction, surf, coatings (paints, varnishes, adhesives, plastics, epoxies, mastics), foundry sand binder, lubricants, electrolytes, cosmetics (polar additive for montmorillonite or bentonite clay gellants) fire extinguishing compds. antifoam for antifreeze hydraulic brake fluids as plating medium... 

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