It is notable that the HNTf2 mediated borylation methodology gives high yielding formation of BN- [5]/ [6]-helicenes from the respective aminoboranes, even at room temperature. In contrast the use of only BBr3 resulted in low yielding (at best) formation of BN- [5]/ [6]helicenes under a range of conditions (including forcing conditions). DFT calculations were performed at the M06-2X/6-311+G(d,p) level with a polarisable continuum model (PCM) DCM (this level has provided accurate thermodynamic data in previous calculations on directed electrophilic C-H borylation) to provide insight into this disparity. Note, herein we discuss just the [5]helicene system, but analogous results were found with the parent 2-amino-biphenyl system, suggesting the outcomes are general for this type of aminoborane. Both borylation routes involving [NTf2] -lead to an aminoborane and HNTf2 being present in solution, with the hypothesis being that protonation of the aminoborane with HNTf2 proceeds, but only to a small extent (thus is not observed by NMR spectroscopy). Consistent with this, the reaction of an aminoborane with HNTf2 was found to be slightly endergonic (Scheme 6), thus borenium equivalents will be accessible in solution from aminoboranes and HNTf2. The coordination of BBr3 at N to form Lewis acid F is significantly less endergonic than borinium cation formation (Scheme 7, bottom), thus it is more feasible. However, while compound F is a functional borenium equivalent 12b it is significantly less electrophilic than bona-fide boreniums, e.g.