STEREOCHEMICAL NONRIGIDITY IN IRON CARBONYL FLUOROPHOSPHINE COMPOUNDS

Compositions of the formula Fe(CO)x(PF3)5-x, obtained through the substitution of phosphorus trifluoride into iron pentacarbonyl, have been clearly shown to contain more than one isomer. The isomers of these compositions, which are presumably trigonal bipyramidal, have now been demonstrated to be stereochemically nonrigid and in facile equilibrium. The Fe(CO)x(PF3)5-x compositions are originally basically random mixtures of isomers. Rapid isomerization results during alcoholic solvolysis reactions through which the lower phosphines are converted into products containing primarily one isomer. These isomerizations are brought about as the ligand is changed by an in situ replacement of F atoms by -OCH3 groups. The isomeric composition of the higher phosphines is also changed through these reactions but to a lesser degree. The new ligands of the general composition PFx(OCH3)3-x, show a strong preference for axial positions. When phosphines of the type PFx(CF3)3-x are substituted into iron pentacarbonyl, equatorial sites are favored by this ligand and the isomeric composition shifts toward the corresponding structures. © 1969, American Chemical Society. All rights reserved.