Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes center dot Cr(CO)(3)C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)(3)(C5R5)](2) have been investigated under CO, Ar, and N-2 atmospheres. Under an Ar or N-2 atmosphere the reaction is stoichiometric and produces the Cr Cr triply bonded complex [Cr(CO)(2)(C5R5)](2). Under a CO atmosphere regeneration of [Cr(CO)(3)(C5R5)](2) (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically, Two key intermediates in the reaction, center dot Cr(CO)(2)(ketene)(C5R5) and Cr-2(CO)(5)(C5R5)(2) have been detected spectroscopically. The complex center dot Cr((CO)-C-13)(2)(O=C-13=CHSiMe3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(Cr-53) = 125 MHz; A((CO)-C-13) = 22.5 MHz; A(O=C-13=CHSiMe3) = 12.0 MHz. The complex Cr-2(CO)(5)(C5H5)(2), generated in situ, does not show a signal in its H-1 NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from Cr-3(2)(CO)(5)-(C5H5)(2) producing (1)[Cr(CO)(2)(C5H5)](2) and CO addition to 3Cr(2)(CO)(5)(C5H5)(2) producing (1)[Cr(CO)(3)(C5H5)](2) have been measured by kinetics and show Delta H-double dagger congruent to 23 kcal mol(-1) for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of (Cr(CO)(n)(C5H5)](2) (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr Cr bond strength in (Cr(CO)(2)(C5H5)](2) as 72 kcal mol(-1). The complex [Cr(CO)(2)(C5H5)](2) does not readily undergo (CO)-C-13 exchange at room temperature or 50 degrees C implying that 3Cr(2)(CO)(5)(C5H5)(2) is not readily accessed from the thermodynamically stable complex [Cr(CO)(2)(C5H5)](2). A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N-2 is proposed on the basis of a combination of experimental and theoretical data.