Niobium−Carbon Functionalities Supported by meso-Octaethylporphyrinogen and Derived Macrocycles

This report concerns the organometallic chemistry of niobium based on a macrocyclic ligand. To this purpose, the (meso-octaalkylporphyrinogen)niobium(V) complex [(η5151-Et8N4)NbCl], 2, has been used as an appropriate starting material. The ionization of the Nb−Cl bond by the use of AgSO3CF3 gave a bifunctional acid−base system with an increased acidity of the metal center in [(η5111-Et8N4)Nb(THF)(O3SCF3)], 3. The alkylation of 2 with LiMe gave a quite stable Nb(V) organometallic derivative [(η5111-Et8N4)Nb−Me], 4, which undergoes a migratory insertion reaction with ButNC leading to an η2-iminoacyl derivative [(η5111-Et8N4)Nb(ButNC)(η2-C(Me)NBut)], 6CN, 2217 and 1736 cm-1). Two steps of the reaction have been identified. An attempt to functionalize the NbO in [(η5111-Et8(C4H2N)3(p-MeC5H2N)NbO], 7, by the use of LiMe led, on the contrary, to [(η1111-Et7(CH-Me)(C4H2N)3(p-MeC5H2N)NbOLi(THF)3], derived from the metalation of one of the meso-ethyl groups in 9. While X-ray analysis provided information on the solid state structures of 3, 4, 6, and 9, NMR studies allowed us to establish a relationship between the bonding mode of the porphyrinogen in the solid state and in solution.