- 2 Pentaborane Bshg Is An Important Precursor For Higher Boranes It Is Prepared By The Thermal Degradation Of Even Lo 1 (213.73 KiB) Viewed 9 times
boranes. It is prepared by the thermal degradation of even lower
boranes, as shown below: a. Provide a balanced equation for step 2.
[1 mark] b. Using Wade’s Rules, predict the structure of B5H9. [2
marks] c. B5H9 can be reduced by elemental sodium to give the salt
Na2B5H9 – what happens to the cage in this process and why? [3
marks] d. Reaction of Na2B5H9 with silicochloroform (HSiCl3) at
high temperature results in the formation of a new cluster,
NaSiB5H6. Using Wade’s rules, predict the structure of the cluster.
How many environments will it possess in the 1H and 11B{1H} NMR
spectra?
Please answer question 2
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[B3H8] + HCI Na[B3H4Cl] + H2 Step 1 Δ Na[B3H,CI] BGH, + NaCl + H2 Step 2 a. Provide a balanced equation for step 2. [1 mark] b. Using Wade's Rules, predict the structure of BsHy. [2 marks] C. B3H, can be reduced by elemental sodium to give the salt Na2B3H9 – what happens to the cage in this process and why? [3 marks] d. Reaction of Na2BsHwith silicochloroform (HSiCl) 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 '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)3B. [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][BAr*] (where [BAr+] = [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{"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]