Reactivity of a Phosphido-Niobocene Derivative toward CS<sub>2</sub> and Alkyl Halides to Give Phosphinodithioformato- and Phosphino-Niobocene Complexes:  X-ray Crystal Structures of [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(κ<sup>1</sup>-S-SC(S)(PPh<sub>2</sub>))(CO)] and [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(P(I)Ph<sub>2</sub>)(CO)]I<sub>3</sub>

The reaction of the niobocene complex [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(PHPh<sub>2</sub>)(CO)]Cl (<b>1</b>) with NaOH yielded the corresponding phosphidoniobocene derivative [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(PPh<sub>2</sub>)(CO)] (<b>2</b>) by deprotonation of the P−H bond. The subsequent insertion reaction of carbon disulfide into the Nb−P bond yielded the first examples of a diphenylphosphinodithioformato ligand coordinated to the niobocene system by giving [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(κ<sup>1</sup>-S-SC(S)(PPh<sub>2</sub>))(CO)] (<b>3</b>) and [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(κ<sup>2</sup>-S,S-SC(S)(PPh<sub>2</sub>))] (<b>4</b>); the latter compound can also be prepared by the corresponding CO elimination of <b>3</b>. The cationic d<sup>2</sup> species [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(PRPh<sub>2</sub>)(CO)]X (R = Me, X = I (<b>5</b>); CH<sub>2</sub>Ph, X = Br (<b>6</b>); CH<sub>2</sub>CH<sub>2</sub>Ph, X = Br (<b>7</b>)) were prepared by the reaction of alkyl halides RX (R = Me, X = I; CH<sub>2</sub>Ph, X = Br; CH<sub>2</sub>CH<sub>2</sub>Ph, X = Br) with <b>2</b> by electrophilic attack on the phosphorus atom present in the phosphido terminal ligand. In the same way, the reaction of <b>2</b> with ICH<sub>2</sub>CH<sub>2</sub>I yielded the complex [Nb(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>SiMe<sub>3</sub>)<sub>2</sub>(P(I)Ph<sub>2</sub>)(CO)]I<sub>3</sub> (<b>8</b>). The molecular structures of <b>3</b> and <b>8</b> were determined by single-crystal X-ray diffraction studies.