Oxidation of [CpMo(CO)3R] olefin epoxidation precatalysts with tert-butylhydroperoxide

• NMR and in situ IR study of oxidation of [CpMo(CO)3R] complexes with TBHP.
• Mo(IV) and Mo(V) intermediates are presented/proposed.
• Catalyst robustness with respect to side reactions has been evaluated.

NMR study of the oxidation of several Mo(II) precatalysts [CpMo(CO)3R] (R = CH2COOC2H51, CH2COOBornyl 5, CH36, CH2C6H57, CH2C6F58) with tert-butylhydroperoxide (TBHP) in CDCl3 at 22 °C shows the formation of complexes [CpMoO2R] (I), [CpMo(O)(η2-O2)R] (II) and transient species assigned as A and B. ν(MoOMo) 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], I0 and [(CpMoV(O)R)2(μ-O)1,2], (Mox1,2) 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.

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