Equilibria metallotropic

The products are in metallotropic equilibrium between the 0-bonded (enol) and C-bonded (keto) isomers, and the topic has been reviewed (194). 

These phosphinous amide anions are presumably responsible for the formation of the by-products AT-phosphino phosphinous amides 11 and mono-phosphazenes derived from diphosphanes 12 in the sequential treatment of primary amines with n-BuLi and chlorophosphanes for preparing NH phosphinous amides [75,88] (Scheme 14). Compounds 11 and 12 are presumably derived from anions 9 and 10, respectively, generated by deprotonation of the newly formed phosphinous amide with the lithiated amine R NHLi. In solution, 9 can establish a metallotropic equilibrium with 10. 

Another option for the preparation of allenyllithium reagents involves the carbolithia-tion of activated conjugated enynes15. Thus, addition of BuLi to the enyne 281 led to an allenyllithium compound 282 (in metallotropic equilibrium with its propargylic counterpart). Subsequent addition of allylzinc bromide generated the allylic 1,1-dimetallic species... 

Allylic organozinc reagents display a unique reactivity towards alkenyl-, allenyl- and alkynylmetals. Allenic organozinc reagents which are in metallotropic equilibrium with their propargylic counterparts (equation 150) also share some similarities with allylic organozinc reagents in their behavior towards alkenes and alkynes. 

The value of the silicon substituent in promoting the carbolithiation is illustrated by comparing the reactions of hex-l-en-3-yne 42 and l-(trimethylsilyl)but-3-en-l-yne 43 with u-BuLi in ether, as shown in Scheme 7-33. However, to be synthetically useful, the metallotropic equilibrium between the lithioallene and the lithioalkyne should be displaced by reaction with an electrophile in favor of only one derivative. Thus, the addition of zinc salts to a mixture of propargyl-allenyllithium derivatives quantitatively leads to the allenylzinc bromide intermediate (Scheme 7-34) and reaction of the latter with electrophiles, via an 8 2 process [34], only gives the propargyl derivative (Scheme 7-34). 

Chemistry of Small Carbohydrates - Equilibrium Solution Properties, Pure Appl. Chem. 59, 1189 (1987) and references dted therein. [160] L. A. Fedorov, D. N. Kravtsov, and A. S. Peregudov Metallotropic Tautomeric Transformations of the a, a-Type in Organometallic and Complex Compounds, Usp. Khim. 50, 1304 (1981) Russ. Chem. Rev. 50, 682 (1981). 

A novel type of metallotropic tautomerism, that is, reversible and equilibrium isomerization of 5-bis(Me3Si-fluorenyl)-rare earth metal complexes to 776-bis(Me3Si-fluorene-AlR3)-rare earth metal complexes, has been reported. 

A useful method for the generation of 1-alkenyllithiums is founded on the N,C-lithiation of A -tosylhydrazones. The intermediate 260a enters into an equilibrium with the metallotropic species 260b from which lithium p-toluenesulfmate and nitrogen are eliminated. Applied to P-ionone, the Shapiro approach opens a convenient entry to 3-(2,6,6-trimethylcyclohex-l-enyl)-l-methylene-2-propenyllithium (Scheme 1-207). ... 

---