Synthesis and Reactivity of 16-Electron Cycloheptatrienyl-Molybdenum(0) Complexes with Bis(imidazolin-2-imine) Ligands

The reaction of the ligands 1,2-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-imino)ethane (BL i Pr ) and 1,2-bis(1,3,4,5-tetramethylimidazolin-2-imino)ethane (BL Me ) with the cycloheptatrienyl-molybdenum complex [(η 7 -C 7 H 7 )Mo(CH 3 CN) 3 ]X (X = BF 4, PF 6 ) leads to acetonitrile substitution and formation of stable 16-electron half-sandwich complexes (η 7 -C 7 H 7 )Mo(BL i Pr )]BF 4, [ 1 ]BF 4, and [(η 7 -C 7 H 7 )Mo(BL Me )]X, [ 2 ]X (X = BF 4, PF 6 ), two of which could be crystallographically characterized to reveal undistorted two-legged piano stool geometries. Cyclovoltammetric studies exhibit very negative redox potentials of E ° = −1.095 V and E ° = −1.138 V versus the ferrocene/ferrocenium couple (0 V), indicative of very electron-rich metal complexes. Oxidation of [ 2 ]X with (η 7 -C 7 H 7 )BF 4 or [Fe(η 5 -C 5 H 5 ) 2 ]PF 6 furnished the Mo(I) complexes of general formula [(η 7 -C 7 H 7 )Mo(BL Me )(CH 3 CN)]X 2, [ 3 ]X 2 (X = BF 4, PF 6 ), which display a three-legged piano stool geometry in the solid state by coordination of one additional acetonitrile molecule to molybdenum. The same geometry is observed upon reaction of [ 1 ]BF 4 and [ 2 ]PF 6 with 2,6-dimethylphenyl isocyanide (XyNC) to afford the isocyanide complexes [ 1 (CNXy)]BF 4 and [ 2 (CNXy)]PF 6 . Their CN stretching vibrations are observed at 2041 and 2030 cm −1, confirming the electron richness and strong π-electron-releasing capability of the molybdenum-imine moiety.