Cascade C-H Activation and Two C-C Bond Forming in Reaction of Azalutetacyclopentadiene with 2-Methylbenzonitriles

Azametallacyclopentadienes are an important class of metallacycles as the key intermediates in metal-promoted or catalyzed carbon-carbon coupling reaction of nitriles and alkynes. Rare-earth azametallacyclopentadienes have shown various reactivity toward nitriles, depending on the substituents of nitriles. The reaction of azalutetacyclopentadienes toward 2-methylbenzonitriles has been investigated in this work, which selectively affords the fused 7-5-6-membered azalutetacycles as products. Computational studies reveal that the reaction of azalutetacyclopentadienes toward 2-methylbenzonitriles selectively initiates with the remote activation of the benzylic C-H bond by the Lu-N bond, followed by the intramolecular nucleophilic attack from the deprotonated benzylic carbon to form a C-C bond. Subsequently, the high ring strain promoted the generation of the uncoordinated carbanion dissociated from the lutetium center, which then undergoes intramolecular nucleophilic attack toward C=N triple bond to give the final product containing fused 7-5-6-membered azalutetacycle. This work not only achieves highly selective three-step cascade reaction to form a unique class of rare-earth metallacycle, but also provides a new idea for the transformation of unsaturated substrates with C-H bonds that can be activated. The reaction of azalutetacyclopentadiene toward 2-methylbenzonitriles provides a series of fused 7-5-6-membered azalutetacycle products. Mechanistic studies reveal that the reaction proceeds through three steps: the activation of the benzylic C-H bond, followed by the first intramolecular nucleophilic attack to form the first new C-C bond, and then the intramolecular nucleophilic attack of uncoordinated carbanion toward C=N triple bond. Two new C-C bonds are formed in the highly selective three-step cascade transformation. image