C−H Bond Activation of Hydrocarbons by an Imidozirconocene Complex

Monomeric imidozirconocene complexes of the type Cp₂(L)ZrNCMe₃ (Cp = cyclopentadienyl, L = Lewis base) have been shown to activate the carbon−hydrogen bonds of benzene, but not the C−H bonds of saturated hydrocarbons. To our knowledge, this singularly important class of C−H activation reactions has heretofore not been observed in imidometallocene systems. The MNR bond formed on heating the racemic ethylenebis(tetrahydro)indenyl methyl tert-butyl amide complex, however, cleanly and quantitatively activates a wide range of n-alkane, alkene, and arene C−H bonds. Mechanistic experiments support the proposal of intramolecular elimination of methane followed by a concerted addition of the hydrocarbon C−H bond. Products formed by activation of sp² C−H bonds are generally more thermodynamically stable than those formed by activation of sp³ C−H bonds, and those resulting from reaction at primary C−H bonds are preferred over secondary sp³ C−H activation products. There is also evidence that thermodynamic selectivity among C−H bonds is sterically rather than electronically controlled.