Synthesis and structure of new carborane-substituted cyclotriphosphazenes

The reactions of [N3P3Cl6] with one, two, or three equivalents of the difunctional 1,2-closo-carborane C2B10H10{CH2OH}(2) and K2CO3 in acetone have been investigated. These reactions led to the new spiro-closo-carboranylphosphazenes gem-[N3P3Cl6-2n{(OCH2)(2)C2B10H10}(n)] (n = 1 (1), 2 (2)) and the first fully carborane-substituted phosphazene gem-[N3P3{(OCH2)(2)C2B10H10}(3)] (3). A bridged product, non-gem[N3P3Cl4{OCH2)(2)C2B10H10}] (4), was also detected. The reaction of the well-known spiro derivatives [N3P3Cl2(O2C12H8)(2)] and [N3P3Cl4(O2C12H8)] with the same carborane-diol and K2CO3 in acetone gave the new compounds gem-[N3P3(O2C12H8)(3-n){(OCH2)(2)C2B10H10}(n)] (n=1 (5) or 2 (6), respectively), without signs of intra- or intermolecularly bridged species. Upon treatment with NEt3 in acetone, compound 5 was converted into the corresponding nido-carboranylphosphazene. However, the reaction of gem-[N3P3(O2C12H8)(2){(OCH2)(2)C2B10H10}] (5) with NEt3 in ethanol instead of acetone proceeded in a different manner to give the new compound (NHEt3)(2)[N3P3(O2C12H8)(2)(O){OCH2C2B10H10CH2- OCH2CH3}] (7). For compounds with two 2,2'-dioxybiphenyl units, gem-[N3P3(O2C12H8)(2){(OCH2)(2)C2B10H10}] (5), (NHEt3)[N3P3(O2C12H8)(2){(OCH2)(2)C2B9H10}] (8), and (NHEt3)(2)[N3P3(O2C12H8)(2)(O){OCH2C2B9H10CH2- OCH2CH3}] (7), a mixture of different stereoisomers may be expected. However, for 5 and 7 only the meso compounds seem to be formed, with the same (R,S)-configuration as in the precursor [N3P3C12O2C12H8)(2)]. The reaction of 5 to give 8 seems to proceed with a change of configuration at one phosphorus center, giving a racemic mixture. The crystal structures of the nido-carboranylphosphazenes 7 and 8 have been confirmed by X-ray diffraction methods.