ChemInform Abstract: Twelve‐Vertex Heteroborane Clusters by Copyrolysis of Tetrachlorodiborane(4) and Element Halides.

Abstract

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Reactivity of Perhalogenated Octahedral Phospha- and Arsaboranes toward THF: A Joint Experimental/Computational Study

“…In comparison, samples of closo-1,2-As 2 B 4 Br 4 dissolved in neat THF were heated to reflux. After 5 min of heating, the 11 B NMR spectra revealed a ratio of (still unreacted) Pn 2 B 4 Br 4 /1-Pn-THF/2-Pn-THF in % of 50:45:5 in the case of P-reaction and of 90:10:0 in the case of the As-reaction. Whereas the phosphaborane reaction ended up after 2 h 45 min with the formation of 2-PB, the Asreaction showed only a ratio of 30:65:5.…”

“…As expected, 2-AsB exhibited two signals at −3.7 ppm and 30.8 ppm in a 1:1 ratio. For the experimental 11 B NMR spectra of the reaction of closo-1,2-As 2 B 4 Br 4 with THF, see Figures S12 and S13. Interestingly, the GIAOcomputed 13 C NMR spectra of 1-AsB and 2-AsB are nearly the same as those for 1-PB and 2-PB, respectively, which further supports the fact that no substantial influence of carbon atoms toward the octahedral moieties is apparent.…”

“…On that basis and guided by an earlier observation, we used "activated" THF (represented by OBuBr − ) as reported. 16 At first, when this chain was added to P(2) and 11 B NMR chemical shifts of this monoanionic were computed at the GIAO-PBE1PBE/6−311+G**// B3LYP/6−311+G** level within the GIAO/NMR approach, 33 reasonably good agreement with the experimental data was obtained (14.7, 0.7, and 26.5 ppm with respect to experimental values of 15.0, −5.0, and 26.0 ppm, respectively). However, the computed 31 P NMR chemical shifts (P(2) −47 ppm, P(1) −136 ppm) are far from the experimental data (−294 and −148 ppm).…”

“…At this point, it must be mentioned that in the case of boron atoms to which a heavier halogen is bonded, the computed 11 B chemical shift is usually influenced by the socalled spin−orbit (SO) coupling. 45 Employing the twocomponent relativistic zeroth-order regular approximation (ZORA) method within the ADF code (well established for accounting for the SO corrections) to the 11 B shifts in all of the boron positions in closo-1,2-Pn 2 B 4 X 4 (X = Cl, Br) revealed the necessity of considering such a correction in the case of the bromine derivative, in which SO amounts to up to 9 ppm. These results are in contradiction to the chlorine derivative with SO of ca.…”

“…It continues to react with another equivalent of THF upon warm-up. The reaction is completed after repeated heating with neat THF to 66°C or THF dissolved in C 6 D 6 to 80 °C monitored by11 B and31 PNMR spectroscopy, the latter showing only two11 B signals of equal intensity (−11 and 26 ppm) and one 31 P signal (−294 ppm); see Scheme 2. Further reaction of THF with respect to the defined products was not observed.…”