(attempts to form mono-borylated N-Me-pyrrole resulted in mono and diborylated products). From the reactions producing 3i and 3j a small quantity of crystals suitable for X-ray diffraction analysis were formed. Notably, this analysis showed these were not 3i/3j but instead were the H-BBN adducts of 3i and 3j, termed 3i-(H-BBN) and 3j-(H-BBN) (Fig. ). In-situ analysis of the Zn/Al catalyzed reactions that form 3i/3j revealed that while the major resonance is due to 3i/3j (11B ≈ 72), an additional minor 11 B resonance at ca. 5 ppm was present consistent with 3i/3j-(H-BBN). Indeed, dissolution of crystals of 3i-(H-BBN) or 3j-(H-BBN) led to formation of 3i/3j and (H-BBN)2 as the major product (by NMR spectroscopy), indicating a solution equilibrium favoring 3i/3j and (H-BBN)2. Note, no resonances for thienyl analogues of 3i-/3j-(H-BBN) were observed in any of the reactions, presumably due to the lower nucleophilicity of thiophenes relative to indoles/pyrroles and consistent with the computed trend observed in our DFT calculations (see Table ). The formation of 3i/3j-(H-BBN) is related to the reaction of Et2N-C≡C-BBN with (H-BBN)2 which forms a compound also containing a cyclic CB2H unit (Fig. inset, compound B). With the mono-borylation scope assessed, our attention turned to the diborylation of thiophenes given the importance of diborylated precursors in accessing organic materials. Note, to date the catalytic C-H diborylation of thiophenes via an SEAr type process (i.e. transition metal free) is limited to only the most highly nucleophilic thiophenes, such as 3,4dialkoxy-substituted thiophenes. Diborylated thienyl products 5b-5f proved accessible through zinc catalysis simply by increasing the equivalents of (H-BBN)2 used (Chart 3).