Abstract
Silica-supported bis(alkyl) complexes of Cr(IV) and V(IV), (⋮SiO)2M(CH2R)2, undergo surprisingly clean thermal transformations to generate supported alkylidene complexes, (⋮SiO)2MCHR, with concurrent liberation of RCH3. The reactions are quantitative and kinetically first order, suggesting that all surface organometallic complexes possess or can access very similar coordination environments. Isotope-labeling and kinetics experiments support a mechanistic assignment of intramolecular α-H elimination. In the case of the Cr complexes, the temperature dependences of the first-order rate constants give nonlinear Eyring plots that are concave downward. A two-step mechanism of reversible (alkyl)(alkylidene)CrVI hydride formation followed by reductive elimination of alkane is proposed. This mechanism is not accessible for V(IV), therefore concerted α-H elimination is considered more likely. The activation parameters for the thermolysis of (⋮SiO)2V(CH2SiMe3)2, obtained from the linear Eyring plot, are ΔH⧧ = (11.0 ...
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call