Synthesis, properties and complexation of (pS)-1-isocyano-2-methylferrocene, the first planar-chiral isocyanide ligand

Reaction of enantiomerically pure, planar-chiral (pS)-1-bromo-2-methylferrocene (1) with phthalimide in the presence of Cu2O produces (pS)-1-phthalimido-2-methylferrocene (2), quantitative reduction of which with hydrazine hydrate affords (pS)-1-amino-2-methylferrocene (3) with >99% ee. Formylation of amine 3 followed by dehydration of the resulting (pS)-1-formamido-2-methylferrocene (4) provides (pS)-1-isocyano-2-methylferrocene (5), the first example of a planar-chiral isocyanide ligand, in a good yield. Isocyanide 5 reacts with PdI2 to give the crystallographically characterized chiral complex trans-[PdI2{(pS)-1-isocyano-2-methylferrocene}2] (6). The redox behavior of 4, 5, and 6, accessed by cyclic voltammetry, is discussed.

Graphical abstractThe first example of a planar-chiral isocyanide has been synthesized in high enantiomeric purity. Upon complexation, this non-benzenoid aromatic isocyanide ligand exhibits robust redox activity.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Enantiomerically pure, planar-chiral (pS)-1-bromo-2-methylferrocene was synthesized. ► Adduct of the title isocyanide ligand with PdI2 was structurally characterized. ► Redox behavior of several new planar-chiral ferrocene-based compounds is discussed.