2. Pentaborane, BsHg, is an important precursor for higher boranes. It is prepared by the thermal degradation of even lo

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2 Pentaborane Bshg Is An Important Precursor For Higher Boranes It Is Prepared By The Thermal Degradation Of Even Lo 1 (18.17 KiB) Viewed 8 times

2 Pentaborane Bshg Is An Important Precursor For Higher Boranes It Is Prepared By The Thermal Degradation Of Even Lo 2 (77.25 KiB) Viewed 8 times

2. Pentaborane, BsHg, is an important precursor for higher boranes. It is prepared by the thermal degradation of even lower boranes, as shown below: Na[B3Hal + HCI Na(B3HCl) + H2 Step 1 Na(B3HCI) B.Hg + NaCl + H2 Step 2

C. B:He can be reduced by elemental sodium to give the salt Na2B-H9 - what happens to the cage in this process and why? [3 marks] d. Reaction of Na2BsH, with silicochloroform (HSiC) at high temperature results in the formation of a new cluster, NaSiBsH.. Using Wade's rules, predict the structure of the cluster. How many environments will it possess in the 'H and 11B{"H} NMR spectra? [4 marks) As well as being useful precursors for cluster synthesis, lower boranes are important as Lewis acids and in organometallic catalysis. e. Explain why tris(isopropyl)borane, 'PrzB, is a stronger Lewis acid than tris(dimethylamino)borane, (MezN)B. [2 marks] f. Explain why heating phenylboronic acid in the absence of water leads to the formation of triphenylboroxime. [2 marks] g. Explain why heating phenylboronic acid in the presence of water leads to the formation of benzene. [2 marks] h. The reaction of BF3, two equivalents of pyridine, and [Et3Si]BArf) (where [BAr'] = [B(C.Fs)4], a weakly coordinating anion) results in the formation of a new boron-containing compound, A, whose positive mass spectrum shows a molecular ion peak at m/z=207. The 11B{'H} NMR for A shows two environments, one singlet and one triplet, whilst the 'H NMR shows a single pyridine environment. What is A? Justify your answer. [4 marks]