NMR study of the oxidation of several Mo(II) precatalysts [CpMo(CO)(3)R] (R = CH2COOC2H5 1, CH(2)COOBornyl 5, CH3 6, CH2C6H5 7, CH2C6F5 8) with tert-butylhydroperoxide (TBHP) in CDCl3 at 22 degrees C shows the formation of complexes [CpMoO2R] (I), [CpMo(O)(eta(2)-O-2)R] (II) and transient species assigned as A and B. v(Mo-O-Mo) at 678 and 655 cm(-1) are identified during oxidation of 5 monitored by in situ IR. DFT calculations for R = CH2COOCH3 indicate that the involvement of [CpMoIv(O)R], I-o and [(CpMov(O)R)(2)(mu-O)(1,2)], (M-ox1,M-2) species in various oxidative transformations is energetically feasible. Oxidative decarbonylation of 5 at different reaction temperatures and oxidant and precatalyst concentrations has also been studied. IR and mass spectroscopic analysis of the precipitate obtained from oxidation of 5 suggests that it is an oxomolybdenum species without ligand R. NMR study of catalytic epoxidation of cis-cyclooctene using 1 illustrates the inhibitory effect of the substrate on oxidative transformations of the precatalyst. (C) 2015 Elsevier Inc. All rights reserved.