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e. Explain why tris(isopropyl)borane, iPr3B, 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][BArF ] (where [BArF ] - = [B(C6F5)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{1H} NMR for A shows two
environments, one singlet and one triplet, whilst the 1H NMR shows
a single pyridine environment. What is A? Justify your answer
Answer parts e to h
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, (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 [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{'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]