The development of transition-metal-catalyzed transformations that employ molecular oxygen (O 2 ), carbon dioxide (CO 2 ), and nitrous oxide (N 2 O) as inexpensive and chemically benign "green" oxidants for the industrial-scale production of specialty and commodity chemicals is of significant scientific, commercial, and environmental interest. [2] To achieve this goal, a fine thermodynamic balance must be established for reaction pathways involving oxygen atom transfer (OAT) to, and from, a given metal center in a fashion that favors productive substrate oxidation. [4] Herein, we report a new class of low-valent Group 6 metal complex that, in the case of molybdenum, can mediate the direct oxidation of tert-butyl isocyanide, tBuNC, to the corresponding isocyanate, tBuNCO, through nondegenerate OAT utilizing N 2 O as a chemical oxidant according to: RNC + N 2 O!RN=C=O + N 2 . We further detail the ability of this same class of metal complex to serve as a photocatalyst for the reversible degenerate OAT between CO and CO 2 in the case of molybdenum and tungsten. For both nondegenerate and degenerate OAT processes, which proceed at near ambient conditions, key intermediates have been isolated and structurally characterized, including midvalent terminal oxo metal complexes, the first unequivocal examples of h 2 -(OCNR) metal complexes that are supported by a k 2 -O,C bonding motif, and finally, a rare example of a h 2 -CO 2 tungsten complex that can engage in elimination of either CO or CO 2 . Collectively, these results serve to establish catalytically competent OAT cycles that are based on a Group 6 metal M II /M IV formal oxidation state couple. [6] By way of contrast, all biological molybdenum-and tungsten-dependent oxotransferase enzymes investigated to date appear to favor thermal OAT mechanisms based on a M IV /M VI couple. [4] We have previously reported that the Group 6 dinuclear "end-on-bridged" dinitrogen complexes, [{Cp*M[N(iPr)-C(Me)N(iPr)]} 2 (m-h 1 :h 1 -N 2 )] (Cp* = h 5 -C 5 Me 5 ), for M = Mo (1) and W (2), can function as convenient M II synthons for [Cp*M{N(iPr)C(Me)N(iPr)}(L) 2 ], where L = CO for M = Mo (3) and W (4), and L = CN(2,6-Me 2 C 6 H 3 ) for M = Mo (5) and W ( ), according to Scheme 1. In keeping with known