A Redox‐Active Heterobimetallic N‐Heterocyclic Carbene Based on a Bis(imino)pyrazine Ligand Scaffold

Abstract

An ew redox-active N-heterocyclic carbene (NHC) architecture is obtained using N-methylated pyrazinediimine iron complexes as precursors.The new species exhibit strong paccepting/s-donating properties and are able to ligate two metal centres simultaneously.T he redox activity was demonstrated by the reversible chemicalo xidation of ah eterobimetallic Fe 0 /Rh I example,w hich affords an isolable ligand-based radical cation. The reversible redox process was then applied in the catalytic hydrosilylation of 4,4'-difluorobenzophenone, where the reaction rate could be reversibly controlled as af unction of the catalyst oxidation state.T he new NHC exhibits high electrophilicity and nucleophilicity,w hich was demonstrated in the reversible activation of alcohols and amines.The electronic structure of the resulting complexes was investigated through various spectroscopic and computational methods.

Redox Activity of Iron Diazine-Diimine Carbonyl and Dinitrogen Complexes: A Comparative Study of the Influence of the Heterocyclic Ring

“…Similar to the redox chemistry of 7 , the oxidized and reduced states of pyrazine analogue (P Pz DI)­Fe­(CO) 2 ( 12 ) could also be chemically accessed under similar conditions as described above. The oxidation of 12 in the presence of [Fc]­[BAr F 24 ] to give 13 is metal-centered, as previously reported, while reduction mediated by KC 8 /18-crown-6 yields a transient ligand-based radical. Nevertheless, this radical rapidly dimerizes to give a diamagnetic C–C coupled dimer 14 (Scheme ).…”

“…In the case of 10 , a Δ g = 0.112 (Table ) also suggests significant metalloradical character, consistent with an ls -Fe­(I) complex. The metal-based oxidation of 7 mirrors that of the pyridine and pyrazine analogue. , X-ray diffractometry (Figure , left) on single crystals of 10 shows that the geometry around the iron center is preserved as square pyramidal (τ = 0.06), similar to that of 7 .…”

“…Through the increased π-acidity, pyrimidine­diimine iron complexes can facilitate fast alkyne trimerization reactions, where the uncommon 1,3,5-substituted arene is the major reaction product . On the other hand, the presence of a functionalization-accessible nitrogen atom in pyrazine­diimine iron complexes opens access to a new class of heterobimetallic NHCs that can function as redox switches in catalysts . Because diazine-based PDI iron systems can facilitate new reactivity patterns, a deeper understanding of their electronic structure in relation to the established pyridine-based analogues would provide a better rationalization of their different reactivity.…”

Applications of iron pincer complexes in hydrosilylation reactions

“…A novel NHC with redox activity, which acts as excellent pacceptors and s-donors was used to form a catalytic Fe/Rh complex by Ros ¸ca and co-workers. 36 Simultaneous ligation of two metal centres is possible for the NHC. The catalyst 30 was obtained in 90% yield from the reaction of unstable NHC intermediate 29 using 0.5 equiv.…”

Ein redoxaktives, heterobimetallisches N‐heterocyclisches Carben auf Basis eines Bis(imino)pyrazin‐Liganden

“…[20] Die molekularen Strukturen von 7 und 8 konnten durch Einkristallrçntgenstrukturanalyse aufgeklärt werden (Abbildung 1). [21] Die Struktur von 7 zeigt, dass der Pyrazinring seine Aromatizitätb ehält [22] und eine planare Struktur aufweist.Der N-Ca-C Winkel ist dennoch verkleinert (]114.29-(14)8 8 in 7,v erglichen mit 119.03(18) in 1•[I] [8] ). Das Ausmaß der Winkelverkleinerung ist vergleichbar mit analogen Isochinolin-1-ylidin-Rhodium(I)-Komplexen.…”