Preliminary communication

Übergangsmetall—carben-komplexe : LXX. Über die abreaktion von pentacarbonyl-phosphin(methoxymethylmethylen)-metall-komplexen☆

The electrochemical behaviour of a series of sixteen novel Fischer ethoxy- and aminocarbene complexes of the type [(CO)₄(PPh₃)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (1-4), [(CO)₃(dppe)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (5-8) (dppe = 1,2-bis(diphenylphosphino)ethane) and [(CO)₄P(OPh)₃W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (9-12) is investigated by means of cyclic voltammetry. The complexes all exhibit a two-electron oxidation process that is W-based and a one-electron reduction that is mainly localized on the carbene ligand. Complexes 1-4 and 9-12 are considerably more difficult to oxidize than 5-8 due to the better π-acceptor ability of the (CO)₄(PR′₃) (R′ = Ph or OPh) ligand combination than that of (CO)₃(dppe). Density functional theory calculations on the neutral, reduced and oxidized complexes confirmed the role of the frontier orbitals in the oxidation and reduction processes and enabled formulation of mathematical relationships that can be used to predict experimental measured potentials. X-ray crystal structures of 2cis, 3 and 5 are discussed.

The compound (butadiene)zirconocene reacts readily at room temperature with iron carbonyl complexes under CC coupling of the conjugated diene ligand with a carbonyl carbon atom. Starting from Fe(CO)₅ and (C₄H₆)ZrCp₂ the metallacyclic (π-allylzirconoxy)carbene iron complex is obtained in good yield. From the (butadiene)zirconocene equilibrium mixture ($\text{12a}\text{14a}$ = $\text{45}\text{55}$) the preferred reaction of the (s-trans-η⁴-diene)metallocene isomer with Fe(CO)₅ or Fe(CO)₄PPh₃ takes place. (s-cis-Butadiene)ZrCp₂ (14a), which is a stronger nucleophile than its isomer (12a), appears to be inert towards these metal carbonyls under kinetically controlled reaction conditions. This suggests a novel mechanism for the M-carbonyl → M-carbene transformation.

(Butadien)zirconocen reagiert mit Eisencarbonyl-Komplexen bei Raumtemperatur rasch unter CC-Verknüpfung des konjugierten Dienliganden mit einem Carbonylkohlenstoff. Mit Fe(CO)₅ wird so in guter Ausbeute der metallacyclische (π-Allylzirconoxycarben)-Eisenkomplex erhalten. Aus dem (Butadien)zirconocen-Gleichgewichtsgemisch ($\text{12a}\text{14a}$ = $\text{45}\text{55}$) reagiert ganz bevorzugt das (s-trans-η⁴-Dien)metallocen-Isomer mit Fe(CO)₅ bzw. Fe(CO)₄PPh₃. Das gegenüber 12a wesentlich nucleophilere (s-cis-Butadien)ZrCp₂ (14a) erweist sich in der kinetisch kontrolliert geführten Reaktion als inert gegenüber diesen Metallcarbonylen. Dies deutet auf einen neuartigen Mechanismus der M-Carbonyl → M-Carben Umwandlung

We report the chemical behavior of cobalt-stabilized carbenes, R₃M(CO)₃CoC(OEt)R′, and their parent anions, R₃M(CO)₃CoC(O⁻)R′, where M = Si or Ge. The anions where M = Si, R′ = Ph decompose thermally into the corresponding benzoylsilanes; when the silicon atom is chiral (R₃ = MePh-1-Np) optically active R₃SiCOPh is obtained with complete retention of configuration.