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 (BLiPr) and 1,2-bis(1,3,4,5-tetramethylimidazolin-2-imino)ethane (BLMe) with the cycloheptatrienyl-molybdenum complex [(eta(7)-C7H7)Mo(CH3CN)(3)]X (X = BF4, PF6) leads to acetonitrile substitution and formation of stable 16-electron half-sandwich complexes (eta(7)-C7H7)Mo(BLiPr)]BF4, [1]BF4, and [(eta(7)-C7H7)Mo(BLMe)]X, [2]X (X = BF4, PFA two of which could be crystallographically characterized to reveal undistorted two-legged piano stool geometries. Cyclovoltammetric studies exhibit very negative redox potentials of E degrees = -1.095 V and E degrees = -1.138 V versus the ferrocene/ferrocenium couple (0 V), indicative of very electron-rich metal complexes. Oxidation of [2]X with (eta(7)-C7H7)BF4 or [Fe(eta(5)-C5H5)(2)]PF6 furnished the Mo(I) complexes of general formula [(eta(7)-C7H7)Mo(BLMe)(CH3CN)]X-2, [3]X-2 (X = BF4, PF6), 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]BF4 and [2]PF6 with 2,6-dimethylphenyl isocyanide (XyNC) to afford the isocyanide complexes [1(CNXy)]BF4 and [2(CNXy)]PF6. Their CN stretching vibrations are observed at 2041 and 2030 cm(-1), confirming the electron richness and strong pi-electron-releasing capability of the molybdenum-imine moiety.