“…Synthesis of the 13 C-labelled benzimidazole (1-1) and benzimidazolium salt (1-H)(I) proceeded via modified literature methods from commercially available 13 C-formyl labelled triethyl orthoformate in two steps (Scheme 1). 25 Synthesis of the gold complex (1-AuCl) is challenging, as a typical base used for these reactions, 6,20,23 potassium hexamethyldisilazane, generated an undesirable side product containing hexamethyldisilazane that could not be separated from the gold complex. Screening of alternative bases led to selection of potassium tertbutoxide, which, while slower to deprotonate (1-H)(I), cleanly generates the free carbene in THF at room temperature over two days.…”