Acid-catalyzed isomerization of rhenium alkyne complexes to rhenium allene complexes via 1-metallacyclopropene intermediates
- Univ. of Wisconsin, Madison, WI (United States). Dept. of Chemistry
The alkyne complexes C{sub 5}Me{sub 5}(CO){sub 2}Re({eta}{sup 2}-MeC{triple_bond}CMe) (1) and C{sub 5}H{sub 5}(CO){sub 2}Re({eta}{sup 2}-MeC{triple_bond}CMe) (6) underwent acid-catalyzed isomerization by way of 1-metallacyclopropene intermediates to form the allene complexes C{sub 5}Me{sub 5}(CO){sub 2}Re({eta}{sup 2}-2,3-MeHC{double_bond}C{double_bond}CH{sub 2}) (5) and C{sub 5}H{sub 5}(CO){sub 2}Re({eta}{sup 2}-2,3-MeHC{double_bond}C{double_bond}CH{sub 2}) (7). Stoichiometric reaction of 1 with CF{sub 3}CO{sub 2}H initially produced the kinetic addition product C{sub 5}Me{sub 5}(CO){sub 2}Re[{eta}{sup 2}-(Z)-MeHC{double_bond}CMeO{sub 2}CCF{sub 3}] (8-Z), which slowly isomerized to the thermodynamically more stable E isomer 8-E. The reaction of 6 with CF{sub 3}CO{sub 2}H at {minus}73 C produced only C{sub 5}H{sub 5}(CO){sub 2}Re[{eta}{sup 2}-(E)-MeHC{double_bond}CMeO{sub 2}CCF{sub 3}] (9-E), which isomerized at -60 C to a 80:20 equilibrium mixture of 9-E and 9-Z. Treatment of 9-E and 9-Z with base led to formation of allene complex 7. The rate of this elimination was independent of base concentration. Labeling studies showed that the 1-metallacyclopropene intermediate C{sub 5}H{sub 5}(CO){sub 2}({eta}{sup 2}-CMeCHMe){sup +}CF{sub 3}CO{sub 2}{sup {minus}} (12-CF{sub 3}CO{sub 2}) undergoes a number of important reactions which include, in order of decreasing relative rates: (1) addition of trifluoroacetate to give enol trifluoroacetate complexes, (2) deprotonation to give complexed allenes, (3) degenerate 1,2-hydride migrations, (4) hydride migrations to give {eta}{sup 3}-allyl complexes, and (5) deprotonation to give complexed alkynes.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 315970
- Journal Information:
- Organometallics, Vol. 17, Issue 21; Other Information: PBD: 12 Oct 1998
- Country of Publication:
- United States
- Language:
- English
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