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

Interconversion of the molybdenum amido [( Tpy)(PPh Me) Mo(NHtBuAr)][BArF ] ( Tpy=4'-Ph-2,2',6',2"-terpyridine; tBuAr=4-tert-butyl-C H ; ArF =(C H -3,5-(CF ) ) ) and imido [( Tpy)(PPh Me) Mo(NtBuAr)][BArF ] 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 [( Tpy)(PPh Me) Mo(NH )][BArF ] 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 , in agreement with a DFT-computed value of 48 kcal mol . 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.