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Organotantalum Phosphaketene and Phosphaazaallene Complexes



The first tantalum phosphaketene and phosphaazaallene complexes [Cp*Ta{1,2-(NSiMe3)2C6H4}{P(R)CX}] {Cp* = C5Me5; X = O; R = cyclohexyl (Cy, 3), iPr (4); X = NCy, R = Cy (5), iPr (6)} were obtained by insertion of carbon monoxide or cyclohexyl isocyanide into the Ta–P bond of cyclohexyl- and (isopropylphosphanylidene)tantalum(V) complexes, [Cp*Ta{1,2-(NSiMe3)2C6H4}(PR)] {R = Cy (1), iPr (2)}. Phosphaazaallene complexes 5 and 6 occur as E and Z isomers. These isomers have different electronic structures according to NMR spectroscopic studies and DFT calculation. Both isomers of the cyclohexylphosphanyl derivative (i.e., 5a and 5b) and one isomer of the isopropylphosphanyl derivative (i.e., 6b) could be structurally characterized by X-ray crystallography.