Reduktion von (Cyclobutadien)(cyclopentadienyl)‐ und (1,5‐Cyclooctadien)‐ (cyclopentadienyl)nickel‐Kationen

Abstract

Cyclic voltammetry of the four cationic Ni sandwich com-characterized analytically and by an X-ray structure deterplexes [Ni(C5R5)(C4R$)]+ (2: R = H, R = Ph; 3 R = H, mination as the dimer 6 of 3, linked through cyclobutenyl R' = Me; 4 R = Me, R = Ph; 5: R = R = Me) shows re-rings, the first example for a dimerization of an electron-rich versible one-electron reductions for the phenyl derivatives 2 sandwich complex at a substituted C atom. EPR spectra of the and 4 and a peak pattern characteristic of reductive dimerineutral complexes 2 and 4 are compared to those of (1,5-cyzation/oxidative monomerization for the methyl derivatives 3 clooctadiene)(cyclopentadienyl)nickel (7) and are interpreted and 5. The product of the reduction of 3 was isolated and in terms of a substantial static Jahn-Teller distortion, Unter den potentiellen ElektroneniiberschuB-Sandwich-Komplexen verdient das System NiCp(CBD) (Cp = q5-C5R5, CBD = q4-C4R4) besonderes Interesse. In den letzten Jahren sind eine Reihe von metallorganischen Ni(1)-Komplexen der Konstitution NiCpL, rnit L2 = Diolefin'), Bi-pyridin3t4) und Diphosphan4) bekannt geworden, deren Existenz die besondere Fahigkeit des Nickels zur Stabilisierung eines radikalischen Grundzustandes belegt. Daher sollte Nickel(1) am ehesten in der Lage sein, als Zentralmetall auch fiir einen paramagnetischen Cyclobutadien-Komplex zu fungieren.Als Ausgangsverbindungen fur die Erzeugung, eventuell kurzlebiger, neutraler 19-Elektronen-Komplexe NiCp(CBD) bieten sich die betreffenden Kationen an, deren elektrochemische Reduktion Hinweise auf die Existenz und Lebensdauer der Neutralverbindung liefert.AufschluD iiber die Elektronenverteilung im Neutralkomplex kann uber die ESR-Spektren der paramagnetischen Cyclobutadien-Komplexe, insbesondere im Vergleich mit denen der neutralen Diolefinkomplexe NiCp(diolefin), von denen wir das Cyclooctadienderivat in Substanz isoliert haben, erhalten werden. Ergebnisse S y nt hesenAls Ni(CBD)-Bausteine kommen die Halogeno-Komplexe fNi(C4Ph4)Br2Iz5) und [Ni(C4Me4)Cl2Iz6) in Betracht. Die Cyclopentadienylierung gelingt in beiden Fallen durch Umsetzung mit FeCp(C0)'Br bzw. [FeCp(C0)2]2 in siedendem Toluol" nach G1. (1). Fur die Einfiihrung eines Cp*-Liganden (Cp* = q5-C5Me5) in 1 a kann Cp*Li dienen. Mit der Methylverbindung 1 b trat die gewiinschte Reaktion nicht ein. Sie lieD sich schlieDlich mit SnCp*Me3 oder Cp*Tl cyclopentadienylieren. Es wurden so die im Cp-und im CBD-Ring verschieden substituierten Derivate [2 -5]X erhalten.

Electronic Spectra of the Tetraphenylcyclobutadienecyclopentadienylnickel(II) Cation and Radical

“…The parent 1 is known to be reversibly reduced to a 19-electron neutral radical at −740 mV vs NHE in DMF and −730 mV vs NHE in CH 2 Cl 2 . Our measurement yielded a similar half-wave reduction potential vs NHE for the bromide salt in CH 3 CN/0.1 M n -Bu 4 N + PF 6 – , −0.765 V. For the bromide of 1a in CH 3 CN/0.1 M n -Bu 4 N + PF 6 – , the value was −0.662 V.…”

Isolated Cationic Organometallic Nickel(I) Arene Complexes

“…PF 6 – or CF 3 SO 3 – ) . The only organometallic formal 19 VE complex including Ni I is the scarcely characterized CpNi(cod) …”

“…phosphines, carbenes,, β‐diketiminates or Cp – (Cyclopentadienyl), , Only a few examples of Ni I arene complexes are known, all of which are molecular compounds. Wolf and Kölle, for example, reported on Ni I ‐Cp complexes. Isolated structures, in which Ni I is coordinated by neutral aromatic ligands, are just known in nacnac complexes: Thus, the compounds [(L Me Ni I ) 2 (toluene)] with η 3 ‐coordination of toluene to each Ni atom, or in the bulkier mononuclear [L t Bu Ni I (toluene)] with just η 2 ‐coordination to the arene ligand were described {L R = [HC{C(R)NC 6 H 3 ( i Pr) 2 } 2 ] (R = Me, t Bu)}.…”

16-Electron through 19-Electron Complexes of the 1,5-COD and 1,3-COD Isomers of (η5-C5Ph5)Rh(η4-C8H12): Electrochemical Evidence for an Oxidatively Induced Agostic Interaction

“…Electron-transfer-induced isomerizations have been studied in depth for cyclooctatetraene (COT) complexes of Co , and, to a lesser extent, Ni and Pd . Cyclooctadiene (COD) complexes of the later transition metals have also received some attention, , but the metal−1,5-COD bond has generally been found to be unisomerized in the electron-transfer products. A possible exception is the 19-electron anion [CpCo(1,5-COD)] - , which has been reported to isomerize to the 1,3-isomer .…”