Reactivity of a dihydroboron species: synthesis of a hydroborenium complex and an expedient entry into stable thioxo- and selenoxo-boranes†
The reaction of a recently synthesized dihydroboron species complexed with bis(phosphinimino)amide, LBH2 (1), (L = [N(Ph2PN(2,4,6-Me3C6H2))2]−) with 3 equivalents of BH2Cl·SMe2 or one equivalent of BCl3 affords the first stable monohydridoborenium ion, [LBH]+[HBCl3]− (2) that is stable without a weakly coordinating bulky anion. Compound 2 can also be prepared directly by refluxing LH with 3 equivalents of BH2Cl·SMe2. Interestingly, reaction of LBH2 (1) with elemental sulfur and selenium involves oxidative addition of S and Se into B–H bonds and subsequent release of H2S (or H2Se) from the intermediate LB(SH)2 (or LB(SeH)2) species forming stable compounds with terminal boron–chalcogen double bonds LBS (3) and LBSe (4). The electronic structures of compounds 2, 3 and 4 were elucidated by high resolution mass spectrometry, multi-nuclear NMR and single crystal X-ray diffraction studies. Ab initio calculations on 3 are in excellent agreement with its experimental structure and clearly support the existence of the boron–sulfur double bond.