η1-Bound 2-pyrone complexes of molybdenum and iron:: A synthetic and structural study

Oxidative cleavage of the [Mo(CO)(3)(eta(5)-C5H5)](2) with AgBF4 in the presence of 4-methoxy-6-methyl-2-pyrone or 3-bromo-4-methoxy-6-methyl-2-pyrone results in the formation of [Mo(CO)(3)(eta(5)-C5H5){eta(1)(O)-O=COCMe=CHC(OMe)=CH}][BF4] and [Mo(CO)(3)(eta(5)-C5H5){eta(1)(O)-O=COCMe=CHC(OMe)=CBr}][BF4], respectively. Single-crystal X-ray diffraction studies have demonstrated that the orientation of the 2-pyrone ligands varies markedly within the two complexes. In the case of the 4-methoxy-6-methyl-2-pyrone complex the pyrone unit lies parallel to the Mo-CO axis, whereas the bromo-substituted pyrone lies in a perpendicular orientation. Similarly, reactions of [Fe(CO)(2)(eta(5)-C5H5)](2) with AgBF4 in the presence of 4-methoxy-6-methyl-2-pyrone or 3-bromo-4-methoxy-6-methyl-2-pyrone result in formation of [Fe(CO)(2)(eta(5)-C5H5){eta(1)(O)-COCMe=CHC(OMe)=CH}][BF4] and [Fe(CO)(2)(eta(5)-C5H5){eta(1)(O)-COCMe=CHC(OMe)=CBr}][BF4], respectively. Whereas the orientations of the pyrone ligands in the molybdenum and iron complexes containing the brominated 2-pyrone ligands are identical, the iron complex containing the 4-methoxy-6-methyl-2-pyrone contains three cations in the asymmetric unit, two of which have the 2-pyrone ligand perpendicular to the Cp(centroid)-Fe axis, whereas the third unit is parallel. The 2-pyrone ligands of these cations form a stack in which the parallel unit is sandwiched between the two with a perpendicular orientation. The pyrone ligands appear to be only weakly coordinated to the metals and solutions of the complexes rapidly decompose. The complex [Mo(CO)(3)(eta(5)-C5H5){eta(1)(O)-O=COCMe=CHC(OMe)=CH}][BF4] reacts with PhCdropCPh to give [Mo(CO)(eta(2)-PhCdropCPh)(2)(eta(5)-C5H5)][BF4]