b-Aryl Eliminations from Rh(I) Iminyl Complexes
β-Aryl eliminations from a series of iminyl complexes to form rhodium aryl complexes and free nitriles are reported. Iminyl complexes [Rh(PEt3)3(NCArAr‘)] were prepared from [Rh(COE)Cl]2, PEt3, LiN(SiMe3)2, and the imines HNCArAr‘. One example of these complexes was characterized by X-ray diffraction. Heating of these complexes in cyclohexane generated the rhodium aryl complexes and free nitriles in high yields; heating in benzene formed the same products in slightly lower yields. Complexes with varied aryl groups on the imine were studied to assess the migratory aptitudes of the aryl groups. Migration of the o-anisyl group occurred much faster than migration of a phenyl group; migration of a phenyl group occurred slightly faster than migration of the more electron-rich p-anisyl group; and migration of a phenyl group occurred slightly faster than migration of the more hindered o-tolyl group. Kinetic studies showed that the reaction was inverse first-order in the concentration of added phosphine and zero-order in added nitrile. These results show that the β-aryl elimination most likely occurs by dissociation of phosphine from the starting complex and carbon−carbon bond cleavage of the resulting 14-electron intermediate.
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