Bonding in transition metal-ether complexes: The spectroscopy and reactivity of the Zr atom-dimethyl ether system

The reactivity and bonding of neutral Zr metal atoms with dimethyl ether have been thoroughly characterized using flow tube reactor, PFI-ZEKE, and DFT techniques. Between 275 and 371 K, these species forro an association complex with the Zr bound to the ether O atom. Using a flow tube reactor, the equilibrium constant for the association reaction has been found to be 6 ± 2 × 10^-14 cm³ at 361 ± 10 K. From this measure the Zr-dimethyl ether bond energy is estimated to be 80 ± 2 kJ mo1^-1. The ZEKE spectrum of the association complex is reproduced very well by DFT calculations. The calculations indicate that the Zr-dimethyl ether complex is bound by dative bonding involving donation of electron density from the highest occupied dimethyl ether orbital of a₁ symmetry to the Zr 4d orbital of σ symmetry directed along the Zr-dimethyl ether bond axis. Dative bonding interactions are much stronger than donor-acceptor bonding as the vacant dimethyl ether antibonding orbital lies roo high in energy for back-donation of electron density from Zr to be efficient. This finding is likely a general characterisfic of neutral transition metal-ether complexes. To our knowledge, these results constitute the most detailed investigation, to date, of neutral transition metal-ether bonding and reactivity.