Synthesis and reactivity of perhalogenated acyclic and metallacyclic tantalum(V) phosphoraniminato complexes: Discovery of an unexpected ligand coupling reaction to form the novel phosphazenium salt [N(PCl2NH2)(2)] [TaCl6]

The reaction of TaCl5 with a single equivalent of Cl3P=NSiMe3 resulted in t he isolation of the perhalogenated(phosphoraniminato) tantalum(V) complex T aCl4(N=PCl3) (1). Reaction of 1 with an excess of THF and subsequent coolin g produced crystals of TaCl4(N=PCl3)(THF) (1 THF), which possesses a distor ted octahedral Ta center with a THF molecule coordinated trans to the phosp horaniminato Ligand. The reaction of 1 with the aminophosphoranimine, (Me3S i)(2),NPCl2=NSiMe3, resulted in a [3 + 1] cyclocondensation reaction to for m the metallacyclic complex, TaCl3(N=PCl3)[N(SiMe3)PCl2N(SiMe3)] (2), which contains a TaNPN four-membered ring and a phosphoraniminato ligand (N=PC13 ). The analogous [3 + 1] cyclocondensation reaction between (Me3Si)(2)NPCl2 =NSiMe3 and TaCl5 led to the isolation of TaCl4[N(SiMe3)PCl2N(SiMe3)] (3). An attempt to cleave the NPN ligand from the Ta center in 2 via protonolysi s with HCl led to an unusual phosphoraniminato Ligand coupling reaction to yield the novel phosphazenium salt [N(PCl2NH2)(2)] [TaCl6] (4). All new com pounds (1 THF and complexes 1-4) were characterized by single-crystal X-ray diffraction.