Synthesis and electrochemical and theoretical studies of Fischer-type alkenyl-carbyne tungsten complexes [(dppe)(CO)2(RNC)W{CCH=CCH2CH2(CH2)nCH2}][BF4] (R = alkyl, aryl)

The cationic isocyanide alkenyl-carbyne complexes cis-[(dppe)(CO)(2)(RNC)W{dropC-CH=CCH2CH2(CH2)(n)CH2}][BF4] [dppe = kappa (2-)(P,P)-Ph2P(CH2)(2)PPh2; R = Bu-n, n = 1 (2f), 4 (2g); R = 2,6-Me2C6H3, n = 1 (2h), 4 (2i)] were prepared by reactions of the corresponding acetonitrile complexes trans-[(dppe)(CO)(2)(NCMe)W{dropC-CH=CCH2CH2(CH)(n)CH2}][BF4][n = 1 (1a), 4 (1b)] with the appropriate isocyanide. Ab initio quantum-chemical methods at the RHF and single-point MP2 levels of theory were applied to the investigation of the structure, bonding, oxidation potential, and relative isomeric stability at the model complexes 2a-i, as well as that of the related carboxyl, phosphine [(dppe)(CO)(2)(L)W{dropC-CH=CCH2-CH2(CH2)(n)CH2}][BF4] [L = CO; n = 1 (3a), 4 (3b); L = PMe3, n = 1 (4a)] and phosphino-dithiocarboxylate [(dppe)(kappa 3-S2CPCy3)W{dropC-CH=CCH2CH2(CH2)nCH(2)}[BF4] [n = 1 (5a), 4 (5b)] compounds, was investigated by cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt electrode. The oxidation potential follows the order of the net pi -electron acceptor minus sigma -donar character of the ligands, and from the observed linear dependence on the electrochemical P-L ligand parameter it was possible to estimate the values of the electron-richness (E-S) and polarizability (beta) parameters for the binding metal fragments containing alkenyl-carbyne ligands, {(dppe)(CO)(2)W(dropC-CH=CCH2CH2(CH2)nCH(2))}(+), indicating they exhibit rather low electron-richness and polarizability, which are accounted for by very strong pi -electron acceptance of the coordinated alkenyl-carbyne groups. These ligands are activated toward proton loss by anodic oxidation of thier complexes.