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

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2 Pentaborane Bsh Is An Important Precursor For Higher Boranes It Is Prepared By The Thermal Degradation Of Even Low 1 (52.46 KiB) Viewed 29 times

2. Pentaborane, BsH, is an important precursor for higher boranes. It is prepared by the thermal degradation of even lower boranes, as shown below: Na[BH] + HCI Na[B,HCI+HStep 1 Na[BH.CH BHNaci Hz Stop 2 a. Provide a balanced equation for step 2. [1 mark] b. Using Wade's Rules, predict the structure of B:He, [2 marks] c Bsh, can be reduced by elemental sodium to give the salt NazBsHo - what happens to the cage in this process and why? [3 marks) d. Reaction of Na:BHe with silicochloroform (HSC)) at high temperature results in the formation of a new cluster. NaSiB-H.. Using Wade's rules predict the structure of the cluster. How many environments will it possess in the Hand "B('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, "P:B, is a stronger Lewis acid than tris(dimethylamino)borane, (Me:N):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 BFs, two equivalents of pyridine, and (Et-Si][BA!" (where [BAT - [B(C.F.:], 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 miz=207. The "B{"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)