Investigations of reactions between chiral molybdenum imido alkylidene complexes and ethylene: Observation of unsolvated base-free methylene complexes, metalacyclobutane and metalacyclopentane complexes, and molybdenum(IV) olefin complexes

In this paper we explore reactions between 13CH213CH2 and the imido alkylidene complexes, Mo(NAr)(CHCMe2Ph)[(S)-Biphen] (3a; NAr = N-2,6-i-Pr2C6H3), Mo(NArCl)(CHCMe3)[(S)-Biphen] (3b; NArCl = N-2,6-Cl2C6H3), Mo(NAd)(CHCMe2Ph)[(S)-Biphen] (3c; NAd = N-1-adamantyl), Mo(NAr)(CHCMe2Ph)[(R)-Benz2Bitet] (3d), and Mo(NArCl)(CHCMe2Ph)[(R)-Benz2Bitet] (3e). (See text for a description of Biphen and Benz2Bitet.) Under a variety of conditions and for various combinations of imido, alkylidene, and diolate ligands, we have observed α-substituted molybdacyclobutanes Mo(NR)(*CH2*CH2CHCMe2Ph)[diolate] (*C = 13C), unsubstituted molybdacyclobutanes Mo(NR)(*CH2*CH2*CH2)[diolate], olefin complexes Mo(NR)(*CH2CHR)[diolate] (R = H or CMe2Ph), molybdacyclopentane complexes Mo(NR)(*CH2*CH2*CH2*CH2)[diolate], and base-free methylene complexes Mo(NR)(*CH2)[diolate]. We also have crystallographically characterized a molybdenum ethylene complex derived from a biphenolate complex, Mo(N-2,6-Cl2C6H3)(CH2CH2)[rac-Biphen](Et2O).