η¹-Bound 2-Pyrone Complexes of Molybdenum and Iron: A Synthetic and Structural Study

Oxidative cleavage of the [Mo(CO)3(η5-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 and 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(η5-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 and 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 reacts with PhC⋮CPh to give [Mo(CO)(η2-PhC⋮CPh)2(η5-C5H5)][BF4].