Ring-Size-Modulated Reactivity of Putative Dicobalt-Bridging Nitrides: C-H Activation versus Phosphinimide Formation.

Dicobalt complexes supported by flexible macrocyclic ligands were used to target the generation of the bridging nitrido species [(n PDI2 )Co2 (μ-N)(PMe3 )2 ]3+ (PDI=2,6-pyridyldiimine; n=2, 3, corresponding to the number of catenated methylene units between imino nitrogen atoms). Depending on the size of the macrocycle and the reaction conditions (solution versus solid-state), the thermolysis of azide precursors yielded bridging phosphinimido [(2 PDI2 )Co2 (μ-NPMe3 )(PMe3 )2 ]3+ , amido [(n PDI2 )Co2 (μ-NH2 )(PMe3 )2 ]3+ (n=2, 3), and C-H amination [(3 PDI2 *-μ-NH)Co2 (PMe3 )2 ]3+ products. All results are consistent with the initial formation of [(n PDI2 )Co2 (μ-N)(PMe3 )2 ]3+ , followed by 1) PMe3 attack on the nitride, 2) net hydrogen-atom transfer to form N-H bonds, or 3) C-H amination of the alkyl linker of the n PDI2 ligand.