1,1′‐Ferrocenylene‐Bridged Bis(N‐Heterocyclic Olefin) Derivatives

Abstract

The 1,1'-ferrocenylene (fc)-bridged bis(N-heterocyclic olefin) compounds (IMes=CH) 2 fc (1, IMes = 1,3-dimesitylimidazolin-2ylidene) and (IPr=CH) 2 fc (2, IPr = 1,3-bis(2,6diisopropylphenyl)imidazolin-2-ylidene) were synthesised from (ICH 2 ) 2 fc (3) and the respective N-heterocyclic carbene IMes or IPr. Ligand substitution reactions of 1 and 2 with [BH 3 (THF)] afforded the complexes [1(BH 3 ) 2 ] and [2(BH 3 ) 2 ] as mixtures of the rac-and meso-diastereomers. The new ferrocene derivatives 1-3 and the complexes meso-[1(BH 3 ) 2 ], rac-[1(BH 3 ) 2 ] and rac-[2(BH 3 ) 2 ] were structurally characterised by single-crystal X-ray diffraction. 1 and 2 represent a new class of ferrocene-based, and hence redox-active, bidentate ligands. The presence of three redox-active moieties, viz. the ferrocene unit and the two NHO units, is reflected by three consecutive oxidations according to an electrochemical investigation exemplarily performed with 2 by cyclic voltammetry.

Synthetic Strategies of N‐Heterocyclic Olefin (NHOs) and Their Recent Application of Organocatalytic Reactions and Beyond

“…Recently, Nobel Prize winners in 2021, Benjamin List and David MacMillan apparently reported the synthetic significance of asymmetric organocatalysis [18–21] . Over the past two decades, N‐heterocyclic carbenes (NHCs) and N‐Heterocyclic Olefins (NHOs) often play a vital role in organocatalysis, asymmetric synthesis, ligand and organometallics [22–33] . Taking advantage of the inversion of the polarity of the umpolung concept, numerous carbene‐mediated wide‐ranging range of chemical conversions have been achieved via Breslow intermediates (Figure 1).…”

“…[18][19][20][21] Over the past two decades, N-heterocyclic carbenes (NHCs) and N-Heterocyclic Olefins (NHOs) often play a vital role in organocatalysis, asymmetric synthesis, ligand and organometallics. [22][23][24][25][26][27][28][29][30][31][32][33] Taking advantage of the inversion of the polarity of the umpolung concept, numerous carbene-mediated wide-ranging range of chemical conversions have been achieved via Breslow intermediates (Figure 1). [34][35][36][37] In recent days, N-heterocyclic Olefins (NHOs) are commonly used as donor-ligands and organocatalysts.…”