Simple synthesis and structure characterization of a phosphoniomethylidyne tantalum(V) complex

A high-valent phosphoniomethylidyne tantalum complex [(C5Me4H)Ta(triple bond; length of mdashC-PPh3)(double bond; length as m-dashCH-PPh3)Cl] (3) was obtained via transylidation reactions of (C5Me4H)TaCl4 with 5 equivalents of the phosphorus ylide Ph3P = CH2. The addition of strong base Li(N(SiMe3)2 is beneficial to the transylidation reaction and improves the yield of complex 3. The ylide adduct complex [(C5Me4H)TaCl4(CH2PPh3)] (4) as the reaction intermediate was isolated through the reaction of (C5Me4H)TaCl4 with one equivalent of the phosphorus ylide Ph3P = CH2. Both complexes 3 and 4 were structurally characterized by X-ray single crystal diffraction. A comparison on the preparation and properties of the phosphoniomethylidyne tantalum complexes with different supporting ligands, [CpTa(triple bond; length of mdashC-PPh3)(double bond; length as m-dashCH-PPh3)Cl] (1) (Cp = cyclopentadieneyl ligand), [(C5Me4H)Ta(triple bond; length of mdashC-PPh3)(double bond; length as m-dashCH-PPh3)Cl] (3) (C5Me4H = tetramethylcyclopentadienyl ligand) (3) and [Cp⁎Ta(triple bond; length of mdashC-PPh3)(double bond; length as m-dashCH-PPh3)Cl] (2) (Cp⁎ = pentamethylcyclopentadienyl ligand) was discussed.