The substitution reactions of VCp2(CO) with some selected olefins have been studied. Tetracyanoethylene (tcne) and fumaronitrile (fn), containing electron-withdrawing substituents, promptly react with VCp2(CO) with quantitative formation of VCp2(tcne) and VCp2(fn), respectively, while acrylonitrile and diethyl fumarate (defu) gave partial displacement of coordinated carbon monoxide under a CO atmosphere. No CO displacement from VCp2(CO) was observed with cyclooctene and norbornene. The carbonylation of VCp2(defu) (VCp2(defu) + CO a VCp2(CO) + defu) has been studied gas volumetrically from both sides, and the equilibrium constant for the displacement of coordinated defu by carbon monoxide was estimated to be 55 ( 8 at 298.5 K. Variable-temperature experiments between 298.5 and 327.7 K have shown the enthalpy change to be -2.4 kcal mol-1. The equilibrium constant for the addition of defu to VCp2 (VCp2 + defu a Cp2(defu)) has been evaluated spectroscopically to be 150 ( 11 at 298.5 K. From the available data, the equilibrium constant for the addition of carbon monoxide to VCp2 (VCp2 + CO a VCp2(CO)) has been calculated to be Ka ) (8.2 ( 0.4) 103: i.e., about 2 orders of magnitude higher than that for the complexation of defu. The present data for the 3d3 system of vanadium(II) (î˜CO in toluene 1881 cm-1) are compared with those exhibited by the 5d10 system of AuCl(CO) (î˜CO in toluene 2153 cm-1), whose behavior consistently shows an opposite dependence, as far as the olefin/ CO competition is concerned, on the nature of the olefin.
|Autori:||CALDERAZZO F; M. GUELFI; G. PAMPALONI|
|Titolo:||Olefin and CO competition equilibria for bis(cyclopentadienyl)vanadium(II)|
|Anno del prodotto:||2004|
|Appare nelle tipologie:||1.1 Articolo in rivista|