· Copper(II) Hexafluoroacetylacetonate
· (MW 477.66)
(catalyzes diazo compound decomposition and ylide formation;3 carbene additions4)
Alternate Names: cupric hexafluoroacetylacetonate; bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato-O,O´)copper.
Physical Data: green solid, mp 130-135 °C (hydrated forms),2 114-116 °C (anhyd).1
Solubility: sol EtOH, dioxane, CCl4, polar solvents; insol H2O.2
Form Supplied in: commercially available as a hydrated solid.
Preparative Methods: the dihydrate can be prepared from reaction of Copper(II) Acetate and hexafluoroacetylacetone dihydrate in aq NaOH, or by directly heating Cu(OAc)2.H2O and anhydrous hexafluoroacetylacetone.2
Purification: recryst from 50% EtOH or CCl4.2
Handling, Storage, and Precautions: irritant.
Unusual Heteroatomic Ylides.
Copper(II) hexafluoroacetylacetonate is an effective catalyst for the preparation of ylides from diazo compounds under mild conditions. This reagent is more effective than Copper(I) Acetylacetonate and Copper(II) Acetylacetonate, two examples of many transition metal chelates available for decomposition of diazo compounds. Lower reaction temperatures result in a purer product, but reaction times are greatly increased. The heat-sensitive arsonium, stibonium, bismuthonium, sulfonium, telluronium, and thiouronium ylides have been prepared in 20-78% yield under the catalysis of this reagent (eqs 1-3).3 Copper Bronze and other copper salts are effective, but give lower yields.
Carbene Additions to Vinyl Ethers.
The addition of Dimethyl Diazomalonate to the cyclic vinyl ether (1) was studied using several transition metal catalysts (eq 4).4 The intermediate zwitterionic species (2) was rationalized from the formation of rearrangement products (4a) and (4b). Although Cu(hfa)2 significantly reduces reaction times, as does the widely used catalyst Rh2(OAc)4, both result in significant skeletal fragmentation of the carbenium ion. However, Copper(II) Trifluoromethanesulfonate, Cu(acac)2, and other copper(II) acetonato chelates give little or no rearranged product while providing (3) in 74-80% yield.
- 1. Beilstein's Handbuch der Organischen Chemie, 4th ed.; Richter, F., Ed.; Springer: Berlin, 1918; 3rd Suppl. Vol. 1, Part 3, p 3124.
- 2. Belford, R. L.; Martell, A. E.; Calvin, M. J. Inorg. Nucl. Chem. 1956, 2, 11.
- 3. Glidewell, C.; Lloyd, D.; Metcalfe, S. S 1988, 319.
- 4. Alonso, M. E.; Fernández, R. T 1989, 45, 3313.
Edward J. Parish & Shengrong Li
Auburn University, AL, USA
Copyright © 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.