ИСТИНА

Previously, we demonstrated that heteroarylamido hafnium postmetallocene catalysts developed by Symyx1 and featuring [C,N,N]-ligands with 5-membered imidazolyl or thiazolyl donor heterocycle were able to insert nitriles into Hf–CAr bond forming [N,N,N]-complexes with imide moiety, which were also shown be active in olefin polymerization.2 For the extensively studied pyridylamides of zirconium and hafnium,3 however, the reactivity appeared to be different. Here, we report that these complexes with [C,N,N]-ligand insert nitriles into M–CAr bond reversibly forming an equilibria between the starting [C,N,N]-complexes and newly formed [N,N,N]-complexes with ketimide moiety in a 7-membered metallacycle. The discovered reverse reaction of the nitrile insertion into M–CAr bond represents an unprecedented example of β-aryl elimination from a ketimide ligand in early transition metals complexes. Further experimental and computational studies suggest thermodynamic and electronic grounds for this reactivity. Weak orbital overlap between the ketimide nitrogen and the metal, and unfavorable 7-membered metallacycle destabilize the product of insertion into the M–CAr bond, while the pyridylamide moiety acts as a directing group making the reverse process viable. Exploiting β-carbon elimination in complexes of early transition metals may extend the range of catalysts that are accessible for C–C activation processes in the future.