Interconversion of Molybdenum Imido and Amido Complexes by Proton‐Coupled Electron Transfer

Interconversion of the molybdenum amido [( Ph Tpy)(PPh 2 Me) 2 Mo(NH t BuAr)][BArF 24 ] ( Ph Tpy=4′‐Ph‐2,2′,6′,2“‐terpyridine; t BuAr=4‐ tert ‐butyl‐C 6 H 4 ; ArF 24 =(C 6 H 3 ‐3,5‐(CF 3 ) 2 ) 4 ) and imido [( Ph Tpy)(PPh 2 Me) 2 Mo(N t BuAr)][BArF 24 ] complexes has been accomplished by proton‐coupled electron transfer. The 2,4,6‐tri‐ tert ‐butylphenoxyl radical was used as an oxidant and the non‐classical ammine complex [( Ph Tpy)(PPh 2 Me) 2 Mo(NH 3 )][BArF 24 ] as the reductant. The N−H bond dissociation free energy (BDFE) of the amido N−H bond formed and cleaved in the sequence was experimentally bracketed between 45.8 and 52.3 kcal mol −1 , in agreement with a DFT‐computed value of 48 kcal mol −1 . The N−H BDFE in combination with electrochemical data eliminate proton transfer as the first step in the N−H bond‐forming sequence and favor initial electron transfer or concerted pathways.