Lewis base character of the phosphorus atom in phosphanido-niobocene complexes. Synthesis of new early–early homo- and heterobimetallic entities

Abstract

The reaction of phosphanido complexes [Nb(η⁵-C₅H₄SiMe₃)₂(L)(PPh₂)] [L = CO (1), CNXylyl (2)] with early transition metal halides in high oxidation states has been carried out. New bimetallic niobocene complexes [{Nb(η⁵-C₅H₄SiMe₃)₂(L)}(μ-PPh₂)(MCl₅)] [M = Nb, L = CO (3), L = CNXylyl (4); M = Ta, L = CO (5), L = CNXylyl (6)] have been successfully synthesized by the reaction with [MCl₅]₂ (M = Nb or Ta). In a similar way [{Nb(η⁵-C₅H₄SiMe₃)₂(L)}(μ-PPh₂)(MCl₄)] [M = Ti, L = CO (13), CNXylyl (14); M = Zr, L = CO (15), CNXylyl (16)] were synthesized using MCl₄ (M = Ti or Zr). Solutions of complexes 4–6 in chloroform produced new ionic derivatives [Nb(η⁵-C₅H₄SiMe₃)₂(P(H)Ph₂)(L)] [MCl₆] [M = Nb, L = CO (7), L = CNXylyl (8); M = Ta, L = CO (9), L = CNXylyl (10)]. Ionic complexes [Nb(η⁵-C₅H₄SiMe₃)₂(P(Cl)Ph₂)(L)] [NbCl₄O(thf)] [L = CO (11), CNXylyl (12)] were formed from solutions in thf – rapidly in the case of 3 but more slowly for 4. New heterometallic complexes [Nb(η⁵-C₅H₄SiMe₃)₂(L)(μ-PPh₂){(Ti(η⁵-C₅R₅)Cl₃}] [R = H, L = CO (17), CNXylyl (18); R = CH₃, L = CO (19), CNXylyl (20)] were synthesized by the reaction of 1 or 2 with [Ti(η⁵-C₅R₅)Cl₃] (R = H or CH₃). All of these compounds were characterized by IR and multinuclear NMR spectroscopy, and the molecular structures of 9 and 12 were determined by single-crystal X-ray diffraction.