1,3,2‐Dioxaphospholanes with an Annelated 1,2‐Dicarba‐ closo ‐dodecaborane(12) Unit: Formation and Dimerization

By using 1,2-hydroxy-1,2-dicarba-closo-dodecaborane(12) and the corresponding dilithium salt [1,2-(LiO)2-1,2-C2B10H10] for the synthesis of 1,3,2-dioxaphospholanes, it was shown that these species are short-lived with few exceptions. The phosphorus halides undergo disproportionation reactions towards phosphite derivatives, whereas the P-organo-substituted five-membered rings dimerize to give ten-membered rings. Even the P-diethylamino and the P-ethoxy compounds dimerize slowly. Dimerization is the favored process when using the dilithium salt together with ether. The reactions were monitored by multinuclear magnetic resonance spectroscopy (1H, 11B, 13C, 31P NMR). The gas-phase structures were optimized by DFT methods [B3LYP/6-311+G(d,p) level of theory], and NMR spectroscopic parameters were calculated. One dimer was characterized by X-ray analysis. All products were found to be sensitive to hydrolysis and oxidation. Thus, crystals of 1-[(1,1-dimethylethyl)hydroxyphosphinyl]oxy-2-hydroxy-1,2-dicarba-closo-dodecaborane(12) could be isolated and characterized by X-ray analysis, as well as the starting material 1,2-hydroxy-1,2-dicarba-closo-dodecaborane(12) (with HNEt2/HCl). In all three solid-state structures, the C–C(carborane) bond lengths are elongated with respect to all other neutral ortho-carborane derivatives bearing second-row substituents at one or both carbon atoms.