Novel approach to optically active enone-iron carbonyl complexes. Correlation between their absolute configuration and circular dichroism

Article abstract of DOI:10.1021/om00060a052

Enantiomerically enriched (η⁴-benzylideneacetone)Fe(CO)₂(L) complexes (L = trimethoxyphosphine, tributylphosphine) have been obtained by decarbonylation of racemic (η²-benzylideneacetone)Fe(CO)₃(L) with brucine N-oxide as the decarbonylating agent. Single-crystal X-ray diffraction has been used to confirm the absolute configuration of (pR)-[Fe(CO)₂((MeO)₃P)((E)-4-phenylbut-3-en-2-one)] ((-)-3) and (pR)-[Fe(CO)₂((Bu₃P)((E)-4-phenylbut-3-en-2-one)] ((-)-7). (-)-3 crystallized in the orthorhombic space group P2₁2₁2₁ with a = 15.165 (1) A?, b = 15.558 (2) A?, c = 7.174 (2) A?, and Z = 4 and (-)-7 crystallized in the same space group with a = 12.036 (1) A?, 6 = 24.087 (2) A?, c = 8.609 (1) A?, and Z = 4. Several other enantiomerically enriched compounds of this type have been obtained by the same method. Moreover, four configurationally pure (η⁴-enone)Ru(CO)₂(L) complexes have been prepared either by use of a chiral enone or by substitution via an optically active phosphine. Circular dichroism (CD) spectra of the complexes have been measured, and a general rule for predicting the absolute configuration of (η⁴-enone)Fe(CO)₂(L) and (η⁴-enone)Ru(CO)₂(L) complexes is presented.