Organotantalum Phosphaketene and Phosphaazaallene Complexes

The first tantalum phosphaketene and phosphaazaallene complexes [Cp*Ta{1,2‐(NSiMe 3 ) 2 C 6 H 4 }{P(R)CX}] {Cp* = C 5 Me 5 ; X = O; R = cyclohexyl (Cy, 3 ), i Pr ( 4 ); X = NCy, R = Cy ( 5 ), i Pr ( 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‐(NSiMe 3 ) 2 C 6 H 4 }(PR)] {R = Cy ( 1 ), i Pr ( 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.