Syntheses of Halogenated Polyhedral Phosphaboranes: Crystal Structure of conjuncto‐3,3′‐(closo‐1,2‐P₂B₄Br₃)₂

Abstract

Co‐pyrolysis of B2Br4 with PBr3 at 480 °C gave, in addition to the main product closo‐1,2‐P2B4Br4, conjuncto‐3,3′‐(1,2‐P2B4Br3)2 (1) and the twelve‐vertex closo‐1,7‐P2B10Br10 (2), both in low yields. X‐ray structure determination for 1 [triclinic, space‐group P1 with a = 7.220(2) Å, b = 7.232(2) Å, c = 8.5839(15) Å, α = 97.213(15)°, β = 96.81(2)°, γ = 94.07(2)° and Z = 1] confirmed that 1 adopts a structure consisting of two symmetrically boron–boron linked distorted octahedra with the bridging boron atoms in the 3,3′‐positions and the phosphorus atoms in the 1,2‐positions. The intercluster 2e/2c B–B bond length is 1.61(3) Å. The shortest boron–boron bond within the cluster framework is 1.68(2) Å located between the boron atoms antipodal to the phosphorus atoms. The icosahedral phosphaborane 2 was characterized by 11B‐11B COSY NMR spectroscopy showing cross peaks indicative for the isomer with the phosphorus atoms in 1,7‐positions. Both the X‐ray data of 1 and the NMR spectroscopic data of 1 and 2 give further evidence for the influence of an antipodal effect of heteroatoms to cross‐cage boron atoms and, vice versa, of an additional shielding of the phosphorus atoms caused by B‐Hal substitution at the boron positions trans to phosphorus.

Beyond the Limits of Perbromo‐Substituted Octahedral Pnictogenaboranes: A Spectroscopic and Computational Study

“…The pre-latter compound was identified as the 3,3'-isomer and the 11 B and 31 P NMR signals in the mixture were assigned through the evaluation of the spectra, giving À 0.3 ppm (the value in our earlier report in parentheses: 0.2 ppm) for B(3,3'), 8.9 ppm (9.2 ppm) for B(5,5') and 18.4 ppm (20.0 ppm) for B(4,4',6,6'); 31 P: À 142.1 ppm (À 142.0 ppm); evidently, the values are in good agreement with those found and also computed earlier. [7,8] In the 11 B and 31 P NMR and mass spectra of the mixture recorded after the 140 °C heating step, there are additional signals of product(s), which we, unfortunately, have not been able to identify (see Figures S1-S3). It is very unlikely that these unidentified signals originate from the 3-THT-P 2 isomer, because in the 31 P NMR spectrum, we could not find two signals of equal intensity in the calculated region between À 136 ppm and À 144 ppm (see Figures S2 and Figure 1).…”

“…The co-pyrolysis of B 2 Br 4 with PBr 3 has produced closo-1,2-P 2 B 4 Br 4 as well as conjuncto-3,3'-(1,2-P 2 B 4 Br 3 ) 2 under appropriate conditions. [8] In contrast to the above outlined reaction of the closo system with THF, the reaction of closo-1,2-P 2 B 4 Br 4 with Idip (3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene) in a strictly nonpolar solvent such as n-pentane, the conjuncto assembly has also been detected by EI-MS. [9] In order to gain a deeper insight into the reactivity of pnictogenaboranes with bases, we have now explored reactions analogous to that mentioned above and substituted THF by tetrahydrothiophene (THT). In addition, the experimental conditions during the ESI-MS experiments surprisingly yielded molecular ion peaks which indicate also the involvement of the σ-holes on the phosphorus and arsenic atoms as alternative electron acceptors besides bromine of the BÀ Br bonds (see Scheme 1 and Figure 2).…”

Chlorinated polyhedral selenaboranes revisited by joint experimental/computational efforts: the formation of closo-1-SeB9Cl9 and the crystal structure of closo-SeB11Cl11

“…It has been shown in all previous formations of heteroboranes via co-pyrolysis of B 2 X 4 with elemental halides in vacuo that the incorporation of heteroatoms can only occur in the gas phase, 10,12 and therefore the temperature during pyrolysis has to be high enough to vaporize both starting components, but not too high to cause the thermal degradation of the prospected heteroborane products ( e.g. as a reverse reaction of eqn (4)).…”

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

“…Additionally performed computations using the BP86 functional in the ZORA computations resulted in slightly worse results. Interestingly, the contribution of the SO coupling in the case of conjuncto- 3,3′-( closo -1,2-P 2 B 4 Br 3 ) 2 for the boron atoms B­(3,3′) that connect both octahedral units is even negative at the ZORA level, i.e., −0.9 ppm.…”