Synthesis of planar chiral iridacycles by cationic metal π-coordination: Facial selectivity, and conformational and stereochemical consequences

Facial selectivity during the π-coordination of pseudo-tetrahedral iridacycles by neutral (Cr(CO) ₃), monocationic (Cp*Ru ⁺), and biscationic (Cp*Ir ²⁺) metal centers was directly influenced by the coulombic imbalance in the coordination sphere of the chelated Ir center. We also showed by using theoretical calculations that the feasibility of the related metallacycles that displayed metallocenic planar chirality was dependent to the presence of an electron-donating group, such as NMe ₂, which contributed to the overall stability of the complexes. When the π-bonded moiety was the strongly electron-withdrawing Cp*Ir ²⁺ group, the electron donation from NMe ₂ resulted in major conformational changes, with a barrier to rotation of about 17 kcal mol ^-1 for this group that became spectroscopically diastereotopic (high-field ¹H NMR spectroscopy). This peculiar property is proposed as a means to introduce a new type of constitutional chirality at the nitrogen center: planar chirality at tertiary aromatic amines.