Unusual Nitrile–Nitrile and Nitrile–Alkyne Coupling of FcCN and FcCCCN

Abstract

The reactions of the Group 4 metallocene alkyne complexes, [Cp*2M(η2-Me3SiC2SiMe3)] (1 a: M=Ti, 1 b: M=Zr, Cp*=η5-pentamethylcyclopentadienyl), with the ferrocenyl nitriles, Fc-CN and Fc-C≡C-C≡N (Fc=Fe(η5-C5H5)(η5-C5H4)), is described. In case of Fc-C≡N an unusual nitrile–nitrile C-C homocoupling was observed and 1-metalla-2,5-diaza-cyclopenta-2,4-dienes (3 a, b) were obtained. As the first step of the reaction with 1 b, the nitrile was coordinated to give [Cp*2Zr(η2-Me3SiC2SiMe3)(N≡C-Fc)] (2 b). The reactions with the 3-ferrocenyl-2-propyne-nitrile FcC≡C-C≡N lead to an alkyne–nitrile C-C coupling of two substrates and the formation of 1-metalla-2-aza-cyclopenta-2,4-dienes (4 a, b). For M=Zr, the compound is stabilized by dimerization as evidenced by single-crystal X-ray structure analysis. The electrochemical behavior of 3 a, b and 4 a, b was investigated, showing decomposition after oxidation, leading to different redox-active products.

Reactivity Study of Pyridyl‐Substituted 1‐Metalla‐2,5‐diaza‐cyclopenta‐2,4‐dienes of Group 4 Metallocenes

“…To the best of our knowledge, solely three such group 4 metallocene compounds were obtained by a C−C coupling of two nitriles and an H‐transfer. The first one was established by warming Cp* 2 Ti(N=C(Fc)−C(Fc)=N) [Fc=‐(η 5 ‐C 5 H 4 )Fe(η 5 ‐C 5 H 5 )] to 80 °C, the second, a trinuclear compound, was obtained upon addition of adiponitrile to Cp* 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 ) and the third was achieved in the reaction of Cp* 2 Zr(η 2 ‐Me 3 SiC 2 SiMe 3 ) with PhCH 2 −C≡N . In case of the zirconocene complex the source of the additional H atoms is supposed to be the deprotonation of further PhCH 2 −C≡N.…”

Reactivity of a Seven‐Membered Zirconacyclocumulene towards CN Multiple Bonds – Formation of Metallaheterocycles by Insertion of C≡N and C=N Groups

“…Additionally, there were hints for the formation of the corresponding five‐membered 1‐metalla‐2‐aza‐cyclopenta‐2,4‐dienes E (Scheme ), established by an alkyne–nitrile C–C coupling, which were assumed as intermediates in the synthesis of heteroaromatic compounds 8. To the best of our knowledge, only in the case of 3‐ferrocenyl‐2‐propyne–nitrile and zirconocene7b and for an aluminum complex6a has the corresponding metallacyclopentadiene E been isolated by alkyne–nitrile coupling.…”

Bildung drei‐ und vierkerniger Titanacyclen durch [Cp*2Ti]‐vermittelte intermolekulare C‐C‐Kupplung von Dinitrilen

“…Bei der Zugabe von 1,3‐Dicyanbenzol ( 2 a ) zu [Cp* 2 Ti(η 2 ‐Me 3 SiC 2 SiMe 3 )] ( 1 ) erfolgte eine intermolekulare Nitril‐Nitril‐C‐C‐Kupplung zu 3 a (Schema ), wie sie bereits für Arylnitrile beobachtet worden war 5a,b. Wegen der Bifunktionalität von 2 a ist das Produkt ein hochsymmetrischer Makrocyclus.…”

“…Die Bevorzugung der dreikernigen Struktur ist bemerkenswert. In Übereinstimmung mit den einkernigen Komplexen [Cp* 2 Ti(‐NC(R)‐C(R)N‐)] (R=Phenyl, p ‐Tolyl, o ‐Tolyl, Ferrocenyl)5a,b liegen die C‐N‐Abstände im Bereich von Doppelbindungen. Die neu gebildeten C‐C‐Bindungen entsprechen verlängerten C‐C‐Einfachbindungen.…”

“…Die Bildung analoger einkerniger 1,4‐Diazabuta‐1,3‐dien‐Komplexe des Titans erfolgte meist durch die Kupplung von Isonitrilen14 oder die Koordinierung von 1,4‐Diazadienen 15. Beispiele für die Kupplung von Nitrilen zu derartigen Komplexen sind selten 5b. 16 Von besonderem Interesse ist in diesem Zusammenhang die Herkunft der Wasserstoffatome, die für die Protonierung der Stickstoffatome benötigt werden.…”