Isocyanide Insertion Reactions with Organometallic Group 4 Tropocoronand Complexes:  Formation of η²-Iminoacyl, Enediamido, η²-Imine, and μ-Imido Products

The reactivity of the tropocoronand complexes [M(TC-3, n )R 2 ] (M = Zr(IV), Hf(IV); n = 3, 5; R = CH 2 Ph, Ph) with aryl and alkyl isocyanides is described. Alkyl isocyanides induced migration of both benzyl groups to afford the bis(iminoacyl) species [Hf(TC-3, n ){η 2 -(R)N C(CH 2 Ph)} 2 ] ( n = 5, R = Cy ( 1 ), n -Bu ( 2 ); n = 3, R = Cy ( 3 )). Different products were isolated with aryl isocyanides, depending on the rate of substrate addition. Treatment of [M(TC-3, n )(CH 2 Ph) 2 ] with excess 2,6-dimethylphenyl isocyanide (ArNC) generated the enediamido = Zr ( 4 ), Hf ( 5 )) via coupling of two bis(iminoacyl) groups, whereas slow step-wise addition produced = Zr, n = 3 ( 6 ); M = Hf, n = 3 ( 7 ), n = 5 ( 8 )). The η 2 -imine an intermediate in the formation of 7, was isolated and characterized, but the corresponding zirconium species was unstable in solution, decomposing to form the imido-bridged compound {[Zr(TC-3,3)] 2 (μ-NAr) 2 } ( 10 ). Altering the nature of the carbon donor ligands also influenced the reactivity. Addition of both aryl and alkyl isocyanides to solutions of [Zr(TC-3,3)Ph 2 ] ( 11 ) afforded the η 2 -imine complexes R = Cy ( 12 ), Ar ( 13 )), the stability of which may be due in part to interactions between the metal center and a phenyl ring. Electron-withdrawing R substituents enhance this effect. All new compounds were characterized by X-ray crystallography, and plausible mechanisms for the migration reactions are outlined.