- 2 Pentaborane Bshy Is An Important Precursor For Higher Boranes It Is Prepared By The Thermal Degradation Of Even Lo 1 (80.66 KiB) Viewed 9 times
- 2 Pentaborane Bshy Is An Important Precursor For Higher Boranes It Is Prepared By The Thermal Degradation Of Even Lo 2 (57.75 KiB) Viewed 9 times
2. Pentaborane, BsHy, is an important precursor for higher boranes. It is prepared by the thermal degradation of even lower boranes, as shown below: Na[B3Hg] + HCI Na[B3H4Cl] + H2 Step 1 A Na[B3H-CI) B5H9 + NaCl + H2 Step 2 a. Provide a balanced equation for step 2. [1 mark] b. Using Wade's Rules, predict the structure of BsH. [2 marks] C. BsH, can be reduced by elemental sodium to give the salt Na2BsH9 - what happens to the cage in this process and why? [3 marks] d. Reaction of Na2BsH, with silicochloroform (HSiCl) at high temperature results in the formation of a new cluster, NaSiBsH6. Using Wade's rules, predict the structure of the cluster. How many environments will it possess in the 'Hand 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, 'Pr3B, is a stronger Lewis acid than tris(dimethylamino)borane, (Me2N)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 [BArF] = [B(C6Fs)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{TH} 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]