Olefin and CO Competition Equilibria for Bis(cyclopentadienyl)vanadium(II)

Abstract

The substitution reactions of VCp 2 (CO) with some selected olefins have been studied. Tetracyanoethylene (tcne) and fumaronitrile (fn), containing electron-withdrawing substituents, promptly react with VCp 2 (CO) with quantitative formation of VCp 2 (tcne) and VCp 2 (fn), respectively, while acrylonitrile and diethyl fumarate (defu) gave partial displacement of coordinated carbon monoxide under a CO atmosphere. No CO displacement from VCp 2 (CO) was observed with cyclooctene and norbornene. The carbonylation of VCp 2 (defu) (VCp 2 (defu) + CO a VCp 2 (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 VCp 2 (VCp 2 + defu a Cp 2 (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 VCp 2 (VCp 2 + CO a VCp 2 (CO)) has been calculated to be K a ) (8.2 ( 0.4) × 10 3 : i.e., about 2 orders of magnitude higher than that for the complexation of defu. The present data for the 3d 3 system of vanadium(II) (ν ˜CO in toluene 1881 cm -1 ) are compared with those exhibited by the 5d 10 system of AuCl(CO) (ν ˜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.

Competition between Carbon Monoxide and Alkenes in Chloro Complexes of Platinum(II)

“…The nature of the metal−olefin bond is a subject of great interest, particularly in comparison with the competitive metal−CO interaction. For early transition metals, quantitative studies show that alkenes are unable to displace coordinated carbon monoxide . However, alkenes containing electron-withdrawing substituents (tetracyanoethylene, fumaronitrile) give complete displacement of carbon monoxide from VCp 2 (CO) 7d…”

“…For early transition metals, quantitative studies show that alkenes are unable to displace coordinated carbon monoxide . However, alkenes containing electron-withdrawing substituents (tetracyanoethylene, fumaronitrile) give complete displacement of carbon monoxide from VCp 2 (CO) 7d…”

B(C6F5)3 Adducts of TCNE− and TCNQ−Vanadium Complexes as New Building Blocks for Molecule-Based Magnets

“…To our knowledge, and although the structure has been only partially solved (X = Br), this represents the only example of a structurally characterized vanadium−TCNE complex supported by Cp ligands. TCNE was also reported to substitute carbon monoxide in Cp 2 V(CO) to afford a complex formulated as “Cp 2 V(TCNE)” on the basis of analytical and spectroscopic (IR) evidence . In a somewhat related vein, we have recently demonstrated that Cp 2 V reacts with simple nitriles (RCN) when they are activated with a Lewis acid L (L = BCl 3 , B(C 6 F 5 ) 3 , AlCl 3 ) to give Lewis acid adducts of vanada(IV)azirine complexes, [Cp 2 V(η 2 -RCN·L)] .…”

Adventures in Vanadocene Chemistry

“…Turning now to another source of vanadocene, carbonylbis(cyclopentadienyl)vanadium(ii) [Cp 2 VCO] is easily obtained by treatment of 1 with CO. [30] A few reactivity studies have been conducted with olefins [31] and dinitrogen oxides [32] in which, in the absence of X-ray analysis, IR spectroscopy plays an important role in the characterization of the resulting compounds.…”