Non-classical carbonyl complexes of zirconium: The syntheses, characterization, and reactivities of (η5-C5Me5)2Zr(η2-E2)(CO) (E S, Se, Te)

The non-classical zirconium carbonyl complexes Cp2∗Zr(η2-E2)(CO) (E  S, Se, Te) have been prepared by the reactions of Cp2∗Zr(CO)2 with the elemental chalcogens (ca. two equivalents) at ca. 80°C. Cp2∗Zr(η2-E2)(CO) are characterized by νCO stretching frequencies of 2057 cm−1 (E  S), 2037 cm−1 (E  Se) and 2006 cm−1 (E  Te), and the ditellurido derivative Cp2∗Zr(η2-Te2)(CO) has been structurally characterized by X-ray diffraction. The dichalcogenido-carbonyl complexes Cp2∗Zr(η2-E2)(CO) (E  S, Se, Te) react further with excess chalcogen to give the trichalcogenido complexes Cp2∗Zr(η2-E2), which have also been structurally characterized by X-ray diffraction. The formation of the tritellurido complex Cp2∗Zr(η2-Te3) is reversible, and addition of CO (1 atm) regenerates Cp2∗Zr(η2-Te)(CO). In the presence of pyridine, the dichalcogenido derivatives Cp2∗Zr(η2-E2)(CO) react with Cp2∗Zr(CO)2 to give the terminal chalcogenido complexes Cp2∗Zr(E)(NC5H5). Cp2∗Zr(η2-Te2)(CO) exists in both triclinic and tetragonal modifications. Interestingly, the derived ZrCO bond lengths for the two structures were significantly different, while the CO bond lengths for each structure were similar. The origin of the discrepancy was determined to be crystallographic disorder in the tetragonal modification, and appropriate modelling allowed the derivation of a reasonable ZrCO bond length for the tetragonal form.