Formation of niobium and tantalum ylide complexes

The reactions of tri(bis(ethyl)amino)phosphorus ylide (Et2N)3Pdouble bond; length as m-dashCH2 with cyclopentadienyl (Cp) metal (V) tetrachloride CpMCl4 (M = Nb 1; Ta 3) and pentamethylcycopentadienyl (Cp∗) metal (V) tetrachloride Cp∗MCl4 (M = Nb 2; Ta 4) were investigated. The hexa-coordinate ylide adducts complexes 5 (CpNbCl4(H2Cdouble bond; length as m-dashP(NEt2)3)), 6 (Cp∗NbCl4(H2Cdouble bond; length as m-dashP(NEt2)3)) and 8 (Cp∗TaCl4(H2Cdouble bond; length as m-dashP(NEt2)3)) with pseudo-octahedral geometry were structurally analyzed with X-ray diffraction. Compound 4 (Cp∗TaCl4) reacted with three molar equivalent of phosphorus ylide to form one ionic complex 9 ([H3C-P(NEt2)3][Cp∗TaCl5]) which was also structurally analyzed with X-ray diffraction. The possible formation mechanism of compound 9 has been discussed.