Synthesis and Electrochemical and Theoretical Studies of Fischer-Type Alkenyl−Carbyne Tungsten Complexes [(dppe)(CO)2(RNC)W{⋮CCHCCH2CH2(CH2)nCH2}][BF4] (R = Alkyl, Aryl)

The cationic isocyanide alkenyl-carbyne complexes [dppe = κ 2 -( P,P )-Ph 2 P(CH 2 ) 2 PPh 2; R = Bu n, n = 1 ( 2a ); R = Bu t, n = 1 ( 2b ), 4 ( 2c ); R = Cy, n = 1 ( 2d ), 4 ( 2e ); R = PhCH 2, n = 1 ( 2f ), 4 ( 2g ); R = 2,6-Me 2 C 6 H 3, n = 1 ( 2h ), 4 ( 2i )] were prepared by reactions of the corresponding acetonitrile complexes [ 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 trans - and cis -[(PH 3 ) 2 (CO) 2 (L)W(⋮C−CH CH 2 )] m + [L = Cl - ( m = 0), NCMe ( m = 1), CNMe ( m = 1), or CO ( m = 1)], which also comprise the related carbonyl and chloride species, allowing a comparison of the effects of the Cl -, NCMe, CNMe, and CO ligands, which are shown to follow their electron π-donor/acceptor properties. The electrochemical behavior of complexes 2a − i, as well as that of the related carbonyl, phosphine [L = CO; n = 1 ( 3a ), 4 ( 3b ); L = PMe 3, n = 1 ( 4a )] and phosphinodithiocarboxylate [ 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 π-electron acceptor minus σ-donor 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 (β) parameters for the binding metal fragments containing alkenyl-carbyne ligands, indicating they exhibit rather low electron-richness and polarizability, which are accounted for by the very strong π-electron acceptance of the coordinated alkenyl-carbyne groups. These ligands are activated toward proton loss by anodic oxidation of their complexes.