Cyclohexa-1,4-dienes in transition-metal-free ionic transfer processes

Safe- and convenient-to-handle surrogates of hazardous chemicals are always in demand. Recently introduced cyclohexa-1,4-dienes with adequate substitution fulfil this role as El(+)/H- equivalents in B(C6F5)(3)-catalysed transfer reactions of El-H to pi- and sigma-donors (C=C/C equivalent to C and C=O/C=N). Surrogates of Si-H/Ge-H, H-H and even C-H bonds have been designed and successfully applied to ionic transfer hydrosilylation/hydrogermylation, hydrogenation and hydro-tert-butylation, respectively. These processes and their basic principles are summarised in this Minireview. The similarities and differences between these transfer reactions as well as the challenges associated with these transformations are discussed.