Niobium−Carbon Functionalities Supported by <i>meso</i>-Octaethylporphyrinogen and Derived Macrocycles

This report concerns the organometallic chemistry of niobium based on a macrocyclic ligand. To this purpose, the (<i>meso-</i>octaalkylporphyrinogen)niobium(V) complex [(η<sup>5</sup>:η<sup>1</sup>:η<sup>5</sup>:η<sup>1</sup>-Et<sub>8</sub>N<sub>4</sub>)NbCl], <b>2</b>, has been used as an appropriate starting material. The ionization of the Nb−Cl bond by the use of AgSO<sub>3</sub>CF<sub>3</sub> gave a bifunctional acid−base system with an increased acidity of the metal center in [(η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>-Et<sub>8</sub>N<sub>4</sub>)Nb(THF)(O<sub>3</sub>SCF<sub>3</sub>)], <b>3</b>. The alkylation of <b>2</b> with LiMe gave a quite stable Nb(V) organometallic derivative [(η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>-Et<sub>8</sub>N<sub>4</sub>)Nb−Me], <b>4</b>, which undergoes a migratory insertion reaction with Bu<sup>t</sup>NC leading to an η<sup>2</sup>-iminoacyl derivative [(η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>-Et<sub>8</sub>N<sub>4</sub>)Nb(Bu<sup>t</sup>NC)(η<sup>2</sup>-C(Me)NBu<sup>t</sup>)], <b>6</b> (ν<sub>C</sub><sub></sub><sub>N</sub>, 2217 and 1736 cm<sup>-1</sup>). Two steps of the reaction have been identified. An attempt to functionalize the NbO in [(η<sup>5</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>-Et<sub>8</sub>(C<sub>4</sub>H<sub>2</sub>N)<sub>3</sub>(<i>p</i>-MeC<sub>5</sub>H<sub>2</sub>N)NbO], <b>7</b>, by the use of LiMe led, on the contrary, to [(η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>:η<sup>1</sup>-Et<sub>7</sub>(CH-Me)(C<sub>4</sub>H<sub>2</sub>N)<sub>3</sub>(<i>p</i>-MeC<sub>5</sub>H<sub>2</sub>N)NbOLi(THF)<sub>3</sub>], derived from the metalation of one of the <i>meso</i>-ethyl groups in <b>9</b>. While X-ray analysis provided information on the solid state structures of <b>3</b>, <b>4</b>, <b>6</b>, and <b>9</b>, NMR studies allowed us to establish a relationship between the bonding mode of the porphyrinogen in the solid state and in solution.