C-O and C-S bond cleavage in chelating diethers and thioethers promoted by η9,η5-bis(indenyl)zirconium sandwich complexes:: A combined experimental and computational study

Gently warming the eta(6),eta(5)-bis(indenyl)zirconium dimethoxyethane compound (eta(6)-C9H5-1,3-(SiMe3)(2))(eta(5)-C9H5-1,3-(SiMe3)(2))Zr(DME) (1-DME) to 45 degrees C resulted in C-O bond scission to yield an equimolar mixture of the zirconocene ethylene compound (eta(5)-C9H5-1,3-(SiMe3)(2))(2)Zr(eta(2)-CH2CH2) and the corresponding zirconium bis(methoxide) complex (eta(5)-C9H5-1,3-(SiMe3)(2))(2)Zr(OMe)(2). Monitoring the relative rates of 1-DME versus 1-DME-d(10) cleavage by H-1 NMR spectroscopy established no kinetic isotope effect (k(H)/k(D) = 1.0(1)), eliminating the possibility of C-H activation in or prior to the rate-determining step. Computational studies support a pathway involving rate-determining DME dissociation from the eta(6),eta(5)-bis(indenyl)zirconium complex followed by facile eta(6) to eta(5) indenyl haptotropic rearrangement and C-O bond scission. Corresponding C-S bond cleavage chemistry has been investigated for three thioethers and the mechanism of bond activation compared to the oxygen congeners.