Long-lived complex

Steel PG, Teasdale CWT. Polymer supported palladium A-heterocyclic carbene complexes long lived recyclable catalysts for cross coupling reactions. Tetrahedron Lett 2004 45 8977-8980. 

The success of a chiral separation depends upon the formation of diastereo-meric pair between each enantiomer and a chiral reagent. There are two types of diastereomeric complex long-lived and short-lived diastereomers. Short-lived diastereomers were discussed in the previous sections such diastereomers occur between a pair of enantiomers and a chiral environment. Long-lived diastereomers are formed by chemical reaction between a pair of enantiomers and a chiral reagent. 

That is, rapid IVR in the long lived intennediate is an essential step. We shall treat this important process in the next section, but mention here in passing the observation of so-called supercollisions transferring large average amounts of energy (AE) m one collision [ ], even if intennediate complex fonnation may not be important. 

Huang Z S, Jucks K W and Miiier R E 1986 The argon-hydrogen fluoride binary complex an example of a long lived... 

Finding snch acids (called snperacids ) turned out to be the key to obtaining stable, long-lived alkyl cations and, in general, carbocations. If any deprotonation were still to take place, the formed alkyl cation (a strong Lewis acid) would immediately react with the formed olefin (a good TT-base), leading to the mentioned complex reactions. 

If a triplet-state molecule (A ) meets a singlet-state molecule (B ), a short-lived complex can be formed (an exciplex). In the latter, the molecules exchange energy, returning to its singlet state (A ) and B raised to its triplet state (B ). If the new triplet state is relatively long-lived, it can serve to produce the population inversion needed for lasing, as in the He/Ne laser. 

The data also bear on the validity of the two models that have been proposed to describe the mechanism of ionic chain propagation in the gas phase. In review, Lampe, Franklin, and Field (23) have proposed that the polymerization proceeds through the reactions of long-lived, undissociated, intermediate reaction complexes,... 

The two factors F, and FJ are very complex and not known. It is virtually certain, however, that each contains several terms. For example, where long-lived radiation-produced species influence the yield, Fj must contain terms such as A 1 — (At + l)c (l — e ) which expresses the average age of the atoms produced. The subsequent thermal effects are often describable in terms of first-order reactions so that FJ must contain one or more terms of the form (1 — Up to the present, there has not been enough information available on any system to make careful statement of Eq. (5) worthwhile. 

In either case, abstraction mechanisms are direct (no long-lived collision complex is formed), have small entropy costs ( loose transition states), and typically deposit large amounts of vibrational energy in the newly formed bond while the other bonds in the system act largely as spectators. 

Because of the deep potential well and small exoergicity, conventional wisdom will then predict a long-lived complex being involved in the title reaction and the statistical behavior might be borne out.1,22 23... 

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