Synthesis of (Bromo-η4-2-pyrone)tricarbonyliron complexes

The addition of the tricarbonyliron 'Fe(CO)(3)' unit to several bromo-substituted 2-pyrones has been investigated. Direct reaction with Fe-2(CO)(9) in benzene at 80 degreesC results in poor yields and hydrodebromination. Switching the solvent to n-Bu2O, sequential addition of Fe-2(CO)(9) and slow passage of N-2 through the solution improves the yields of the tricarbonyliron complexed 2-pyrones. Direct 'Fe(CO)(3)' transfer reagents such as (eta(4)-benzylidene-acetone)tricarbonyliron or generic (eta(4)-1-azabuta-1,3-diene)tricarbonyliron complexes, under both stoichiometric and catalytic conditions, fails to give the desired complexes. Surprisingly, the unstable bis(eta(2)-cis-cyclooctene)Fe(CO)(3) (Grevels' reagent) did serve as a useful transfer reagent.