Strained bicyclo[6.1.0]nonyne (BCN) is a well-established bioorthogonal reagent which can be used as dienophile in IEDDA reactions. We had chosen BCN in our studies because the product of the IEDDA reaction with 1,2,4-triazine is an aromatic pyridine. The pyridine is part of the conjugated system of the metal complex and is beneficial to the luminescent properties. While there are several studies using TCO derivatives, to the best of our knowledge, there are only two reports evaluating kinetics of the reaction of 1,2,4-triaizine with BCN. In 2015 Webb et al. reported the second-order rate constant of 3.8x10 -4 M -1 s -1 for the reaction of 3-substituted-1,2,4-triazine with benzoyl-protected BCN. We previously reported that coordination of the 1,2,4-triazine to Ir(III) significantly boosts the reaction rates. For example, the second order rate constant of ligand 6 was determined to be 0.059 M -1 s -1 , whereas the corresponding iridium complex 2 reacts with BCN two orders of magnitude faster, with a rate constant of 7.87 M -1 s -1 . (Figure ).