Preparation and Conformational Properties of Several 1,8-Diarylnaphthalenes

Six new 1,8-diarylnaphthalenes, each having closely held parallel aromatic rings, were synthesized by a Kharash-type Grignard cross-coupling of arylmagnesium iodide and 1,8-diiodonaphthalene in the presence of N,N′-bis(1-methyl-3-oxobutylidene)ethylenediaminatonickel(II) as a catalyst. Among them, 1,8-di(1-naphthyl) naphthalene was obtained as cis and trans rotamers, caused by the restricted rotation at the 1,8-position. Interconversion between the rotamers on heating above their melting points was confirmed by differential scanning calorimetry. The proton magnetic resonance spectral studies of the 1,8-diarylnaphthalenes indicated the presence of a face-to-face arrangement of aromatic rings in the peri-position. Two new 8,8′-diaryl-1,1′-binaphthyls, each having two sets of closely held parallel aromatic rings, were isolated as minor coupling products. Trans-trans conformations were proposed for them on the basis of their thermal behavior. Several nickel(II) complexes were found to be effective catalysts for preparative Grignard cross-coupling reaction involving closely crowded geometry.