Boron and Carbon Lewis Acids in FLPs for the Activation of sigma and pie bonds

Abstract

In the presence of B(C6F5)3 five-membered heteroarenes undergo dehydrosilylation and hydrosilylation with silanes. The former, favoured on addition of a weak base, produces H2 as a by-product making the process catalytic in B(C6F5)3 but also enabling competitive heteroarene hydrogenation. The dehydrosilylation of 2-(SiR2H)-biphenyls catalysed by B(C6F5)3 and a weak base forms silafluorenes with H2 as the only byproduct. Attempts to extend this approach to synthesize siloles derived from 2,2'-bithiophenes and N-Me-2-Ph-indole resulted in competing reactivity, including protodesilylation. B(C6F5)3 also catalysed the one-pot, two-step formation of silaindenes from aryl-alkynes by alkyne trans-hydrosilylation, followed by an intramolecular Sila-Friedel-Crafts reaction facilitated by a weak base. A range of benzothiazolium salts were produced and their Lewis acidity was assessed relative to B(C6F5)3. A number of FLPs were tested as hydrogenation catalysts. Further work was carried out on N-methylacridinium salts resulting in the discovery of a surprising solvent dependence of a solution of [N-methylacridinium][BArCl] and 2,6-lutidine in THF, which resulted in the activation of the methyl group whereas previously in DCM this FLP is capable of activating H2 and shows no sign of activation of the methyl group. Investigations into intramolecular carbon FLPs, tethering 2,6-lutidine to either a N-methylbenzothiazolium or N-methylacridinium scaffold, resulted in no H2 activation. Investigations into the reactivity of N¬-methylacridinium salts with terminal alkynes resulted in the second example of a hydrocarbation reaction, with structure of the thermodynamic and kinetic products isolated.

Date of Award	1 Aug 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Alan Brisdon (Supervisor) & Michael Ingleson (Supervisor)