Reactivity of a Phosphido-Niobocene Derivative toward CS₂ and Alkyl Halides to Give Phosphinodithioformato- and Phosphino-Niobocene Complexes:  X-ray Crystal Structures of [Nb(η⁵-C₅H₄SiMe₃)₂(κ¹-S-SC(S)(PPh₂))(CO)] and [Nb(η⁵-C₅H₄SiMe₃)₂(P(I)Ph₂)(CO)]I₃

The reaction of the niobocene complex [Nb(η⁵-C₅H₄SiMe₃)₂(PHPh₂)(CO)]Cl (1) with NaOH yielded the corresponding phosphidoniobocene derivative [Nb(η⁵-C₅H₄SiMe₃)₂(PPh₂)(CO)] (2) 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(η⁵-C₅H₄SiMe₃)₂(κ¹-S-SC(S)(PPh₂))(CO)] (3) and [Nb(η⁵-C₅H₄SiMe₃)₂(κ²-S,S-SC(S)(PPh₂))] (4); the latter compound can also be prepared by the corresponding CO elimination of 3. The cationic d² species [Nb(η⁵-C₅H₄SiMe₃)₂(PRPh₂)(CO)]X (R = Me, X = I (5); CH₂Ph, X = Br (6); CH₂CH₂Ph, X = Br (7)) were prepared by the reaction of alkyl halides RX (R = Me, X = I; CH₂Ph, X = Br; CH₂CH₂Ph, X = Br) with 2 by electrophilic attack on the phosphorus atom present in the phosphido terminal ligand. In the same way, the reaction of 2 with ICH₂CH₂I yielded the complex [Nb(η⁵-C₅H₄SiMe₃)₂(P(I)Ph₂)(CO)]I₃ (8). The molecular structures of 3 and 8 were determined by single-crystal X-ray diffraction studies.