Synthesis and Reactivity of Molybdenum(IV) Complexes with Alkyl and Aryl Isocyanides

The synthesis and characterization of the bis(isocyanide) complexes (RNC)2Mo(NPh)(o-(Me3SiN)2C6H4) (2: 2a, R = tBuNC; 2b, R = 2,6-dimethylphenyl) and the subsequent reactivity of these complexes with excess isocyanide have been reported. An X-ray crystal structure of (RNC)2Mo(NPh)(o-(Me3SiN)2C6H4) (R = 2,6-dimethylphenyl) is reported. Treatment of 2a with excess tert-butyl isocyanide resulted in the formation of the tris(isocyanide) complex (tBuNC)3Mo(NPh)(o-(Me3SiN)2C6H4) (3). Complex 3 exists in solution in equilibrium with 2a. Using a two-site exchange mechanism the activation barrier for the dissociative exchange of tBuNC has been calculated. The X-ray crystal structure of (tBuNC)3Mo(NPh)(o-(Me3SiN)2C6H4) is reported. Computational studies (ONIOM) performed on 3 reveal that π conflicts in this complex results in the lengthening of the Mo−N(amido)cis bond relative to the Mo−N(amido)transbond. Treatment of 2b with excess 2,6-dimethylphenyl isocyanide results in the slow insertion of the isocyanide ligands into the Mo−N bond of the chelating diamide ligand, resulting in a novel chelating iminocarbamoyl bis(isocyanide) complex, 4. An X-ray crystal structure of 4 is reported.