Toward Metal-Capped One-Dimensional Carbon Allotropes:  Wirelike C₆−C₂₀Polyynediyl Chains That Span Two Redox-Active (η⁵-C₅Me₅)Re(NO)(PPh₃) Endgroups

Abstract

Reaction of the butadiynyl complex (η5-C5Me5)Re(NO)(PPh3)(C⋮CC⋮CH) (ReC 4 H) with Cu(OAc)2 (pyridine, 80 °C) gives the μ-octatetraynediyl complex ReC 8 Re (70%). Analogous cross-coupling of ReC 4 H and ReC 2 H gives (after chromatography) ReC 4 Re (14%), ReC 6 Re (44%), and ReC 8 Re (15%). Longer sp carbon chains are accessed by reactions of ReC 4 H with n-BuLi and CuI, which give ReC 4 Cu. This isolable species is treated in situ with BrC⋮CSiEt3 or BrC⋮CC⋮CSiMe3 (excess EtNH2, THF) to give ReC 6 SiEt 3 or ReC 8 SiMe 3 (84−77%). Desilylations (wet n-Bu4N+F-) yield ReC 6 H or ReC 8 H (88−73%). Then Cu(OAc)2 (pyridine, 50 °C) gives ReC 12 Re or ReC 16 Re (71−67%). The former is also available from ReC 4 Cu and BrC⋮CC⋮CBr (45%), and ReC 10 Re can be accessed by cross-coupling. ReC 6 H and ReC 8 H are similarly converted to ReC 10 SiR 3 (R = Me, Et; 51−26%) and ReC 12 SiMe 3 (43%). Desilylation of ReC 10 SiR 3 gives labile ReC 10 H, but only black powder is obtained from ReC 12 SiMe 3 . In situ coupling of ReC 10 H gives ReC 20 Re (52−34%), which unlike lower homologues is not obtained in analytically pure form. The effects of chain length upon visible spectra (progressively red-shifted and more intense bands; ε >190 000 M-1 cm-1), IR/Raman νC ⋮ C patterns (progressively more bands), 13C NMR chemical shifts (asymptotic limit of 64−67 ppm for ReC⋮C( C ⋮ C ) n ), cyclic voltammetry (decreased reversibility of two oxidations; a gradual shift of the first to thermodynamically less favorable potentials, so that only a single oxidation is observed for ReC 20 Re), and thermal stabilities (solid-state decompositions at 155 °C, ReC 20 Re, and 178−217 °C, lower homologues) are studied in detail.

Synthesis, Structure, and Reactivity of sp Carbon Chains with Bis(phosphine) Pentafluorophenylplatinum Endgroups: Butadiynediyl (C4) through Hexadecaoctaynediyl (C16) Bridges, and Beyond

“…Cyclic voltammograms sometimes show reversible couples, [2,7,8] and several such C 4 complexes have been isolated. However, the C 8 analogues are distinctly less stable, and have not yet proved spectroscopically observable.…”

“…One diiron C 8 cation radical, representing the intermediate oxidation state II, has proved isolable. [2a] As illustrated in Scheme 1, three classes of complexes with longer chains have been reported: chiral dirhenium C 12 , C 16 , and C 20 complexes of the type 1, the properties of which have been summarized in a detailed full paper; [7] Akita×s diiron C 12 complex 2;…”

Metall‐Alkinyl‐σ‐Komplexe: Synthesen und Materialien

“…[195] Zum besseren Verständnis der elektronischen Kommunikationsprozesse wurden Heterodimetallsysteme unter anderem mit Cyclovoltammetrie sowie magnetischen und optischen Messungen detailliert untersucht. [195][196][197][198] Rechnungen und physikalische Eigenschaften der Dirheniumverbindungen lassen darauf schließen, dass die HOMOs der längerkettigen Polymere merklichen Metall-dCharakter und Alkinyl-p-Charakter haben. Cyclovoltammogramme der kürzeren Oligomere zeigen unter geeigneten Bedingungen zwei chemisch reversible Einelektronenoxidationen.…”

Stereochemisch definierte Osmium‐Zentren durch asymmetrische Diaminierung von Olefinen: Konsequenzen für den Mechanismus Osmium‐vermittelter Acrylester‐Oxidationen

“…[1] Derartige Verbindungen, die bisweilen als "Chiral-at-Metal-Komplexe" bezeichnet werden, [2] haben in der organischen Synthese, [3] bei enantioselektiven Erkennungsprozessen, [4] in der Materialwissenschaft [5] und der Grundlagenforschung [6] bedeutende Anwendungen gefunden. Zum Beispiel beruht mit Noyoris asymmetrischer Transferhydrierung eines der herausragenden Konzepte der enantioselektiven Katalyse auf der kontinuierlichen Regenerierung eines stereogenen Rutheniumzentrums.…”