Intramolecular Oxidative Addition Triggered by One-Electron Oxidation of Molybdenum(iii) Tris(anilide): Generation of Molybdenum(v) Imido Aryl Bis(anilide) by Autocatalysis

One-electron oxidation of molybdenum(iii) tris(anilide) Mo(N[tBu]Ar)3 (Ar: ArMe = 3,5-Me2C6H3 and ArPh = 3,5-Ph2C6H3) led to intramolecular oxidative addition across the N–Cipso bond of a ligated anilide to form the cationic Mo(vi) imido/aryl bis(anilide) complexes [Mo(N[tBu]Ar)2(NtBu)(Ar)][B(C6F5)4]. One-electron reduction of [Mo(N[tBu]ArMe)2(NtBu)(ArMe)][B(C6F5)4] allowed access to the neutral Mo(v) species [Mo(N[tBu]ArMe)2(NtBu)(ArMe)]. The d1 electron configuration was confirmed through EPR spectroscopy and the Evans method. Compound [Mo(N[tBu]ArMe)2(NtBu)(ArMe)] was experimentally and theoretically shown to be stable against reductive elimination which would form the energetically less favorable Mo(N[tBu]Ar)3. The high activation barrier has so far prevented Mo(N[tBu]Ar)3 from isomerizing spontaneously to [Mo(N[tBu]ArMe)2(NtBu)(ArMe)]. An autocatalytic process was developed to access [Mo(N[tBu]ArMe)2(NtBu)(ArMe)] through reduction of [Mo(N[tBu]ArMe)2(NtBu)(ArMe)][B(C6F5)4] by Mo(N[tBu]Ar)3, which itself was converted into the oxidizing agent. Attempts to access stable Mo(iv) cations with 4,4′-bipyridine only resulted in labile binding of 4,4′-bipyridine to one or two molybdenum(iii) tris(anilide) complexes.