SYNTHESIS AND X-RAY STRUCTURE OF AN (OXODIMETHYLIDENEMETHANE)IRON DIMER, [(CH2COCH2)(CO)3FE]2

An iron carbonyl π-complex of the oxyallyl species was synthesized in two steps by complexation of a silylenol ether of α-bromoacetone and subsequent dehydrohalogenation by pyridine/AgBF4. The isolated intermediate, bromotricarbonyl(F73-2-hydroxy-2-propenyl)iron, shows an unexpectedly high acidity (piCa= 5.2). The tricarbonyl(oxyallyl)iron complex exists as [(CH2COCH2)(CO)3Fe]2 only, a head-to-tail dimer, as revealed by Ή and13C NMR spectroscopy as well as by X-ray diffraction analysis. This complex shows a butterfly like bent skeleton of C2 symmetry which inverts on the NMR time scale with an activation energy of 72 kJ/mol at room temperature. It crystallizes as orange hexagonal plates in the orthorhombic space group Pbc2l with α = 11.658 (2) Â, b = 6.192 (1) Â, c = 20.311 (4) Â, and Ζ = 4. According to the analytical and chemical observations, this complex exhibits a structure halfway between a 2-substituted π-allylic complex and a metallacyclobutanone compound. © 1990, American Chemical Society. All rights reserved.