Azulene (bicyclo[5.3.0]decapentaene) is a polar non-alternant aromatic hydrocarbon featuring a highly polarizable π-system. In this investigation, the electron richness of low-valent (OC)5Cr(CNR) (e.g., Figure 1) and Cr(CNR)6 moieties were remotely tuned using 2-isocyanoazulene ligands. These azulenes were substituted at the 1,3-positions to probe electronic inhomogeneity along its scaffold. The electron rich chromium complexes serve as convenient electronic reporters for discerning even minute differences in the π-acceptor/σ-donor characteristics of isocyanide ligands. Employing 13C NMR, FTIR, UV-Visible spectroscopic, X-Ray crystallographic, and electrochemical studies, the π-acceptor/σ-donor ratio was quantitatively assessed for these 2-isocyanazulene ligands. The magnitude of the π-acceptor/σ-donor ratio for the 1,3-dicyano-2-isocyanoazulene ligand is comparable to that of both trifluorovinyl isocyanide and pentafluorophenyl isocyanide.

Probing the π-acceptor/σ-donor ratio of 2-isocyanoazulene ligands as possible rivals of polyfluorinated organic isocyanides

253rd National Meeting (2017)

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