202412-93-9Relevant academic research and scientific papers
Isocyanide insertion reactions with organometallic group 4 tropocoronand complexes: Formation of η2-iminoacyl, enediamido, η2-imine, and μ-imido products
Scott, Michael J.,Lippard, Stephen J.
, p. 5857 - 5868 (2008/10/08)
The reactivity of the tropocoronand complexes [M(TC-3,n)R2] (M = Zr(IV), Hf(IV); n = 3, 5; R = CH2Ph, 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){n2-(R)N=C(CH2Ph)}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)(CH2Ph)2] with excess 2,6-dimethylphenyl isocyanide (ArNC) generated the enediamido compounds [(TC-3,3)MN(Ar)C(CH2Ph)=C(CH2Ph)N(Ar)] (M = Zr (4), Hf (5)) via coupling of two bis(iminoacyl) groups, whereas slow step-wise addition produced [(TC-3,n)-MN(Ar)C(CH2Ph)2C(=NAr)] (M = Zr, n = 3 (6); M = Hf, n = 3 (7), n = 5 (8)). The η2-imine complex [(TC-3,5)HfN(Ar)C(CH2Ph)2] (9), 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)Ph2] (11) afforded the η2-imine complexes [(TC-3,3)ZrN(R)C(Ph)2] 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.
