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 [(eta(5): eta(1):eta(5):eta(1)-Et(8)N(4))-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 [(eta(5):eta(1):eta(1):eta(1)-Et(8)N(4))Nb(THF)O3SCF3)], 3. The alkylation of 2 with LiMe gave a quite stable Nb(V) organometallic derivative [(eta(5):eta(1):eta(1):eta(1)-Et(8)N(4))Nb-Me] 4, which undergoes a migratory insertion reaction with Bu(t)NC leading to an eta(2)-iminoacyl derivative [(eta(5):eta(1):eta(1):eta(1)-Et(8)N(4))Nb(Bu(t)NC)(eta(2)-C(Me)=NBu(t))], 6 (nu(C=N)) 2217 and 1736 cm(-1)). Two steps. of the reaction have been identified. An attempt to functionalize the Nb=O in [(eta(5):eta(1):eta(1):eta(1)-Et(8)(C4H2N)(3)(p-MeC(5)H(2)N)Nb=O], 7, by the use of LiMe led, on the contrary, to [(eta(1):eta(1):eta(1):eta(1)- Et(7)(CH-Me)(C4H2N)(3)(p-MeC(5)H(2)N)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.