Reaction of (σ-alkynyl) Group 4 metallocene cation complexes with alkyl- and arylisocyanides

The cations [(RCp)(2)M(-C=C-CH3)(THF)(+)] (2a-d) [(RCp)(2)M = Cp2Ti, Cp2Zr, (MeCp)(2)Zr, and Cp2Hf] were generated in situ by treatment of the respective bis(propynyl) Group 4 metallocenes (RCp)(2)M(-C=C-CH3)(2) (1a-d) with N,N-dimethylanilinium tetraphenylborate. Addition of excess tert-butylisocyanide gave the isonitrile insertion/addition products [(RCp)(2)M(eta(2)-Me3C-NC-C=C-CH3)(kappa-C=N-CMe3) +] (8a-d). Complex 8b was characterized by X-ray diffraction. It contains a eta(2)-iminoacyl ligand with N-inside orientation and there is a kappa-tert-butylisocyanide coordinated to the cationic metallocene framework. Complex 8b exhibits the typical structural characteristics of a d degrees-configurated isonitrile complex (bond lengths 2.350(4) and 1.148(4) Angstrom for the Zr-C=N-R unit). Insertion of 2,6-dimethylphenylisocyanide into the Zr-C(sp) sigma-bond of in situ generated [Cp2Hf-C-=C-CH3+] cation td leads to the formation of the analogous cationic hafnocene complex Se. (C) 1998 Elsevier Science S.A. All rights reserved.