NOVEL-APPROACH TO OPTICALLY-ACTIVE ENONE IRON CARBONYL-COMPLEXES - CORRELATION BETWEEN THEIR ABSOLUTE-CONFIGURATION AND CIRCULAR-DICHROISM

Enantiomerically enriched (eta4-benzylideneacetone)Fe(CO)2(L) complexes (L = trimethoxyphosphine, tributylphosphine) have been obtained by decarbonylation of racemic (eta2-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 P2(1)2(1)2(1) with a = 15.165 (1) angstrom, b = 15.558 (2) angstrom, c = 7.174 (2) angstrom, and Z = 4, and (-)-7 crystallized in the same space group with a = 12.036 (1) angstrom, b = 24.087 (2) angstrom, c = 8.609 (1) angstrom, and Z = 4. Several other enantiomerically enriched compounds of this type have been obtained by the same method. Moreover, four configurationally pure (eta4-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 (eta4-enone)Fe(CO)2(L) and (eta4-enone)Ru(CO)2(L) complexes is presented.