Allyl complexes dynamic

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. 

Our calculations show that the isomerization of the silyl-alkyl complex to form a V-allyl complex affords a significant stabilization as summarized in Figure 11. TheiV toil3 isomerization of 9a to the anti silyl-allyi complex, 10a-anti, results in a 9.5 kcal/mol stabilization and isomerization to the syn isomer, lOa-syn, results in a 7.2 kcal/mol stabilization. Isomerization of 9b to the anti silyl-allyi complex, 10b-anti, results in a 6.1 kcal/mol stabilization and isomerization to the syn isomer, lOb-.vyn results in a 5.4 kcal/mol stabilization. High temperature (500 °C) molecular dynamics simulations initiated at the V complex, 9a, reveal that the rj1 to T 3 isomerization has a minimal barrier and occurs in the sub-pico time frame. The inter-conversion between the syn and anti isomers has not been examined since both isomers are stereochemically equivalent, however, we expect the barrier to be small. 

Allyl complexes (pseudo-rotations, dynamic NMR studies, 1, 416 with tungsten carbonyls and isocyanides, 5, 688-689 rc-Allyl complexes with Cr, 5, 305 with Cr(II), 5, 300 with Cr(III), 5, 300 and cyclodextrins, 12, 789 in enyne carbometallation, 10, 328 with rhodium, 7, 220-221 (j-Allyl complexes, with iron, 6, 98 5-Allyldiisopinocampheylboranes, in asymmetric allylboration, 9, 198... 

Japan. Allyl complexes classified by (135) symmetry, and discussions of NMR and solution dynamics 14 (44)... 

K. Vrieze, Fluxional allyl complexes, in Dynamic Nuclear Magnetic Resonance Spectroscopy (Eds. L. M. Jackman, F. A. Cotton), Academic Press, New York, 1975. 

Butadiene, which is bound in a n -manner to iron, reacts stoichio-metrically with carbon dioxide to form an allyl carboxylato complex in yields up to 75 % [38]. This allyl complex shows a dynamic behaviour Presumably three isomeric structures exist in solution, two of them with a n"-allyl bonding (Figure 16). Subsequent reactions of the allyl carboxylato complexes yield carboxylic acids. Acidic hydrolysis in methanol at -30°C gives methyl-3-pentenoate and methyl-4-pentenoate in a ratio of 10 1. If the iron allyl complex reacts with further carbon dioxide at 90 C, a second insertion of CO2 into the Fe-C-bond occurs after hydrolysis with hydrochloric acid in methanol the Z- and E-dimethyl esters of 3-hexenedioic acid are formed. 

One common dynamic process of metal-allyl complexes is the equilibration of s)m and anti substituents by a sequence of interconversions. The interconversion of one... 

The mechanism of the reactions catalyzed by complexes of these other metals is less well understood than the mechanism of the reactions catalyzed by complexes of palladium. This discrepancy in mechanistic understanding results, in part, from the accessibility of the allylpalladium intermediates and the detailed studies of the chemistry and dynamics " of these complexes. Fewer allyl complexes relevant to the allylations catalyzed by other metals have been isolated. ° ... 

The dynamics of the allyl intermediates can have a large effect on the regioselectivity and stereoselectivity of the catalytic reactions.The dynamics of allyl complexes have been studied extensively by variable-temperature NMR spectroscopy. Allyl complexes can undergo rearrangements by the... 

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... 

The spectrum of (f/ -C3H5)Mn(CO)4 conforms to the A B X pattern. Some allyl complexes show this pattern at low temperatures, but as the temperature is raised the resonances broaden, finally coalescing to an A X spectrum in which the syn and anti protons show an averaged signal. Such observations indicate that dynamic processes are proceeding at a rate comparable with the lifetime of the nuclear spin states. 

P. S. Pregosin and R. Salzmann, Coord. Chem. Rev., 1996, 155, 35-68. Structure and Dynamics of Chiral Allyl Complexes of Pd(II) NMR Spectroscopy and Enantioselective Allylic Alkylation. 

Apparent rotation of the allyl moiety describes the effect observed in certain dynamic 9 -allylic complexes but, when it is not associated with simultaneous ry - //-exchange, it is usually the result of a change in the auxiliary... 

As shown also by detailed NMR studies (18), the allyl complex in solution is binuclear (N.M.R. and cryosoopic data), and undergoes a dynamic rearrangement between the syitinetric (tail-to-tail) and 2 disymnetric (head-to-tail) isomers, under the temperature conditions viiere polymerization takes place. 

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