Dynamic allylic compounds

Butenyllithium and butenylmagnesium chloride were used as "dynamic allylic compounds. The former was selected because of the ability of lithium catalysts to provide high rates of diene polymerization and to give stereoregular polymers the latter was selected for its availability and simplicity of synthesis. 

The solutions are nonconducting, and the compounds display no tendency to undergo chemical reactions (hydrolysis, polymerization, etc.). However, as shown later, heating these compounds in the presence of donor reagents causes significant changes in most of their properties (NMR spectra, chemical activity, electrical conductivity, etc.), thus making them similar in properties to the typical dynamic allylic compounds. 

The fact that the transition of the spectrum from a 7r-allylic to a dynamic one is accompanied by a change in the properties of these compounds show that dynamic allylic compounds of Li, Mg, and Pd have the same nature. 

Various types of metal allylic compounds differ significantly in their physical and chemical properties. Dynamic allylic compounds exhibit the highest chemical activity. 

Dynamic allylic compounds are formed as a result of rapid exchange (intra- and intermolecular) between tautometric tr-, a-forms and an intermediate (ionic) form. 

Hydrolysis of dynamic allylic compounds proceeds through 7r-bond with 7r, [Pg.278]

The structure and chemical properties of metal-allyl compounds (ir-allylic, dynamic and a-allylic) which can be considered as models of a living polymer chain in butadiene polymerization have been studied. The polymerization of dienes proceeds only in dynamic allylic systems through the metal-ligand ir-bond in a-isomers. 

Tetraallyl- and tetrabutenyltin (a-allylic compounds) do not act as initiators of butadiene polymerization even under most favorable conditions (presence of donor additives, elevated temperature). In contrast, butenyllithium, which is considered to be a typical compound of dynamic structure, does initiate polymerization even at temperatures below zero. 

At higher temperatures, allyl complexes are no longer rigid they become dynamic, fluxional compounds. Therefore, AM2X2 spectra become AX4 spectra. Temperatures of such transitions for various compounds range from 200 to 450 K. The hafnium allyl compound [Hf( / -C3H5)4] exhibits an AX4-type spectrum even at 199 K. For dynamic... 

Titanium group allyl compounds are sensitive to air, water, and alcohols. Tetrallyl derivatives of zirconium and hafnium are dynamic compounds. The complex Hf(allyl)4 gives the AX4 type NMR spectrum even at very low temperatures (199 K). The Ti(III) complexes are paramagnetic magnetic moments correspond to one unpaired electron and, for various allyl groups, vary in the 1.47-1.75 BM range. The properties of allyl... 

Ally derivatives of the alkali metals and alkaline earth metals Dynamic nmr spectroscopy even at very low temperatures shows apparent symmetry for the allylmetal compounds [26] indicating either a very low barrier for the metalomeric equilibrium (33) between degenerate monohapto species [26a] and [26b] or the presence of a n-bridged species [26c] with time-independent symmetry. Deuterium isotope effects on terminal mono-and geminal-dideuteriated allyl compounds of the alkali and alkaline earth metals were investigated to allow distinction between these two possibilities... 

Calculations of alkali metal allyl derivatives involving all alkali metals (Li-Cs) indicate a preferred geometry with the metal symmetrically bound in a predominantly electrostatic manner to all three carbon atoms.143 Solution studies of allyllithium in ether indicate the compounds to be highly aggregated in THF complex dynamic behavior is observed. 

Inter-ring metal migrations, dynamic NMR studies, 1, 412 Intracyclic germanium-carbon bond formation large rings, 3, 706 small rings, 3, 703 Intramolecular Alder-ene reactions with metals, 10, 576 with palladium, 10, 568 with rhodium, 10, 575 with ruthenium, 10, 572 with transition metal catalysts, 10, 568 Intramolecular allylations, in cyclizations, with indium compounds, 9, 679... 

The synthesis of conformationally constrained bicyclic and tricyclic compounds, obtained via 5-Exo-Trig iodocyclisation of polybenzylated sugars with an allylic substituent at the anomeric position, is described. The conformation of these molecules has been studied by n.O.e. experiments and Molecular Dynamics calculations. The introduction of an amino and a carboxylic group resulted in the formation of conformationally constrained bicyclic glyco-aminoacids that mimic protein turn conformation. 

As stated above, for compounds having a 7r-allylic structure, reactions (including polymerization) occur after the compounds are transformed into the dynamic form. Polymerization in the presence of such compounds can be represented by Reaction 15. 

The second dynamic process involves C—Li exchange. Around and below 230 K, most of the internally solvated allylic lithium compounds exhibit one bond spin coupling between 13C and 7Li (/ = 3/2) and to 6Li (/ = 1). The 13C NMR of lithium bound carbon consists of equally spaced equal multiplets, an equal triplet for coupling to 6Li and an equal quartet for coupling to 7Li. The separation between adjacent lines are the coupling constants. 

TABLE 13. Quantitative and qualitative dynamic behavior of internally solvated allylic lithium compounds in diethyl ether-dio solution... 

Normant also reported a new extension of Gaudemar s original procedure, allowing the preparation of allylic 1,1- and 1,3-bis-metallic species of types 10 and 11 [Eq. (10) 23 -25]. The exact nature of these reagents is unknown, and a dynamic equilibrium between the two compounds 10 and 11 may take place. 

Compounds of Group 10. Dynamic NMR spectra for (192) and (193) gave measurements of barriers to n-a allyl conversion.946 Similar studies were made on (dippe)Ni(ri3-allyl)(CN), where dippe = bis(di-isopropylphosphino) ethane.947 All 4 diastereotropic isopropyl groups in the Z-conformer of (194) (Ar = 2,6-1Pr2C6H3) give separate resonances. TOCSY experiments gave evidence on ZjE isomerisation.948 Variable-temperature NMR spectra for [2-(r 2 r 2-... 

Extensive use of vicinal proton-proton couplings has been made by Fraenkel and Qiu in their studies on the structure and dynamic behaviour of several methyl substituted allylic lithium compounds, by Shestakova et who studied the structure of the complex between lanthanum(III) nitrate and 1,9 diaza-18-crown-6, and by Goto et whose subjects of interest have been square-planar ternary platinum(II) complexes with A -ethyl- or A -benzyl-1,2-ethanediamine and 2,2 -bipyridine or 1,10-phenanthroline. 

Frater quotes an interesting example 62 where NaBH4 reduction gave the all equatorial trans-61 (racemic of course) while baker s yeast reduction gives one enantiomer of the cis compound 61 evidently by reagent controlled dynamic kinetic resolution (chapter 28). Allylation of the enolate of d.v-61 goes with the expected anti selectivity.10... 

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