ChemInform Abstract: Vibrational Spectra and Normal Coordinate Analysis of the Tetrahalogeno‐closo‐1,2‐diphosphahexaboranes P2B4X4, X: Cl, Br.

Lorenzen, Volker; Preetz, W.; Keller, W.; Haubold, W.

doi:10.1002/chin.199952015

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“…In the first class, some dephospha-, dearsa-, or deboronation reactions followed by metalation − and also partial halogenation reactions have been reported. However, the chemistry of the second type remains so far under-researched, and previous reports have been limited to their preparation, − spectroscopy, − and quantum chemical computations. , Such closo -species of the type Pn 2 B x Hal x (Pn = P, As; Hal = Cl, Br; x = 4, 8, 10) are particularly interesting electronic systems due to the unique configuration involving the presence of P and/or As. Each one bears a lone pair of electrons directed away from the polyhedral surface, and it is not yet known whether these heteroatoms behave as Lewis bases, acids, or neutrals.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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Reactions of the perhalogenated polyhedral pnictogenaboranes closo-1,2-Pn2B4Hal4 (Pn = P, As; Hal = Cl, Br) with Lewis bases are presently being studied with a focus on rationalizing the sites of nucleophilic attacks on clusters bearing σ-holes. These σ-holes are localized both on pnictogens and, for Hal = Br, on bromine atoms, as revealed by electrostatic potential (ESP) and intrinsic bond orbital (IBO) analyses. Surprisingly, the attack of the cyclic ether THF on closo-1,2-Pn2B4Br4 does not occur on the site with the largest positive partial charge, centered in the middle of the pnictogen–pnictogen vector. Instead, presumably promoted by the positivated bromine substituents, THF inserts into the boron–bromine bonds of the negatively charged boron atoms opposite to the pnictogen atoms to form 4-(4-bromobut-1-oxy)-closo-1,2-Pn2B4Br3 (1-PB and 1-AsB) and 4,6-(4-bromobut-1-oxy)2-closo-1,2-Pn2B4Br2 (2-PB and 2-AsB). 11B and 31P chemical shift computations at various levels support the assignments of the signals, which reflect the correctness of the molecular geometries in solutions. The Lewis-acidic perchlorinated analogues closo-1,2-P2B4Cl4, closo-1,2-As2B4Cl4, and the mixed closo-1,2-AsPB4Cl4 bear negative charges. These negative charges are revealed by the V s,max values when computing the electrostatic potentials both on the boron and the chlorine atoms. Due to this negative charge, the analogues do not react with THF unless they are heated above 66 °C, where they slowly decompose to borate esters B(OR)3 without the formation of concrete intermediates. The evaluation of 31P NMR data of 1-PB has allowed the experimental determination of the coupling constant 1 J(31P(1), 31P(2)) = |143| Hz in a closo-diphosphaborane for the first time, which agrees well with the computed value of −178 Hz. The pioneering joint experimental vs computational interpretation of 31P NMR spectra in the area of boron cluster chemistry was decisive for the structural characterization of 1-PB and 2-PB.

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