The preparation of [M2Cp2(CO)4(n-T]2-PE) (E = as or Sb), the first complexes with naked heterodiatomic Group 15 ligands, and of their adducts with W(CO)5

Addition of one equivalent of the Group 15 trichlorides EC13 (E = P, As, or Sb) to the phosphido-bridged dimetallic anions [M2Cp2(CO)4(u-PH2)]- (M = Mo or \V) afforded moderate yields of the complexes [M2Cp2(CO)4(n-n2-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(u-n2-PAs)] to give a 2:1 adduct is reversible at room temperature on dissolution in solvents such as CH2C12 and THF; similar co-ordination to the Sb atom in [M2Cp2(CO)4(u-r|:-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{uV-AsPW(CO)5}] (2.217(5) A) and that in [Mo2Cp2(CO)4(u-ii2-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{u-n2-SbP\V(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.