Synthesis and Characterization of Tetraphenylphosphonium Tetraazidoborate

The chemistry of boron azides, first reported by E. Wiberg et al. in 1954 [1], was further investigated by P. I. Paetzold [2 4], and the field has been reviewed [5, 6]. Structural and spectroscopic data for boron dichloride azide (trimeric) [7, 8] and dimethylboron azide have been reported in the literature [9]. Quite recently, additional boron azides have been reported and structurally characterized [10 12] Calculated structures and gas-phase syntheses of boron triazide, boron chloride diazide, and boron dichloride azide are known; however, B(N3)3 has not been characterized in the condensed phase [13 15]. An isoelectronic analogue of boron triazide, the triazidocarbenium cation, has lately been reexamined with experimental and theoretical studies [16]. In 2001, we reported the first crystal structures of the highly energetic tetraazidoborate anion and boron triazide adducts with quinoline and pyrazine as well as of tetramethylpiperidinium azide [17]. Quantum chemical calculations were performed for B(N3)4 and B(N3)3 at HF, MP2, and B3-LYP levels of theory. The structure of tetraazidoborate was optimized to S4 symmetry although the X-ray diffraction analysis due to severe disorder problems did not show ideal S4 symmetry [17]. In this work we present the synthesis and structural characterization of tetraphenylphosphonium tetraazidoborate, [P(C6H5)4][B(N3)4], which