Electrochemical reductive carbon-to-carbon coupling of σ-ethynyl complexes of transition metals

Abstract

The electrochemical properties of a-ethynyl complexes of chromium subgroup metals were studied by cyclic voltammetry and preparative-scale electrolysis. The redox cycle of CsHs(CO)3CrC~CPh was shown to give the bis-carbyne complex (qS-CsHs)(CO)2C~C--C(Ph)=C(Ph)--C,~Cr(CO)2(q5-CsHs) formed via the reduetive C1~--CI3 coupling of ethynyl moieties. The influence of the nature of the metal atom and the ligand environment on the course of this reaction was considered.

Synthesis, Redox Chemistry, and Electronic Structure of the Alkynyl Cyclopentadienyl Molybdenum Complexes [Mo(C≡CR)(CO)(L2)Cp′]n+ (n = 0 or 1; R = Ph or C6H4-4-Me, L2 = Ph2PCH2CH2PPh2 or 2PMe3, Cp′ = Cp or Cp*)

“…To commence investigations on the redox chemistry of [Mo(CCR)(CO)(L 2 )Cp′], the cyclic voltammetry of complexes 5b , 6a / b , 8a / b , and 9b at a glassy carbon electrode in CH 2 Cl 2 /0.2 M [Bu n 4 N] PF 6 was examined; previous electrochemical studies on cyclopentadienyl molybdenum alkynyl complexes are restricted to the tricarbonyl derivatives [Mo(CCPh)(CO) 3 Cp′] . The results are presented in Table , alongside data for the corresponding halide complexes [MoX(CO)(L 2 )Cp′], which have been included for comparison.…”

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

“…[106] In an interesting counterpoint, reduction of the group 6 alkynyl complexes [M(CϵCPh)(CO) 3 CpЈ] either chemically (Na/K, M = Cr, CpЈ = Cp) or electrochemically (M = Cr, CpЈ = Cp; M = Mo, W, CpЈ = Cp*) also affords bis-(carbyne) complexes [CpЈ(CO) 2 MϵC-C(Ph)=C(Ph)-CϵM(CO) 2 CpЈ], albeit in very low yields for the Mo and W examples, and is thought to occur by the sequence of reduction, CO elimination, C β -C β coupling and oxidation shown in Scheme 13. [107,108] The bis(carbyne) product undergoes two reversible reduction processes, separated by around 140 mV, although the electronic characteristics of the intermediate mono-anion have not been investigated in detail.…”

Metallacumulenes as Potential Electron Reservoir Devices

“…Our interest in this area focuses on the preparation of redox-active di- or polynuclear organometallic complexes containing manganese (end) groups, and we consequently sought to utilize the stability and electron richness of dmpe-substituted half-sandwich Mn I moieties for the buildup of molecular redox wires . A major route to dinuclear metal systems bearing cumulene bridges utilizes coupling processes of appropriate mononuclear species. ,,,,− On the basis of the promising results in the synthesis of mononuclear vinylidene complexes described in the preceding section, addition of acetylene derivatives to unsaturated metal complexes was the chosen route to prepare mononuclear half-sandwich manganese butatrienylidene complexes.…”