The preparation of [M2Cp2(CO)4(μ-η2-PE)] (E = As or Sb), the first complexes with naked heterodiatomic Group 15 ligands, and of their adducts with W(CO)5

Abstract

Addition of one equivalent of the Group 15 trichlorides ECl3 (E = P, As, or Sb) to the phosphido-bridged dimetallic anions [M2Cp2(CO)4(μ-PH2)]− (M = Mo or W) afforded moderate yields of the complexes [M2Cp2(CO)4(μ-η2-PE)], which feature a pseudo-tetrahedral M2PE core. Treatment of the new complexes with [W(CO)5(THF)] led to preferential co-ordination of this Lewis acid to the phosphorus atom. The additional co-ordination of a W(CO)5 fragment to the As atom in [M2Cp2(CO)4(μ-η2-PAs)] to give a 2∶1 adduct is reversible at room temperature on dissolution in solvents such as CH2Cl2 and THF; similar co-ordination to the Sb atom in [M2Cp2(CO)4(μ-η2-PSb)] is not observed. The crystal structures of the 1∶1 adducts and of one 2∶1 adduct have been determined. The P–As distances in [W2Cp2(CO)4{μ-η2-AsPW(CO)5}] (2.217(5) A) and that in [Mo2Cp2(CO)4(μ-η2-AsP{W(CO)5}2)], in which the As and P atoms are disordered (2.223(3) A), are intermediate between the P–P and As–As distances in homodiatomic E2 complexes. Similarly, the P–Sb distances in the two crystallographically independent molecules of [Mo2Cp2(CO)4{μ-η2-SbPW(CO)5}] (2.401(2), 2.410(2) A) are intermediate in length between the P–P and Sb-Sb distances in related homodiatomic E2 complexes.