The anaerobic and aerobic decompositions of L2Mo(0)2R2 [L2 = 4,4′-dimethyl-2,2′-dipyridyl, R = CH2Ph, 1; R = CH2C6H4CH3-p, 2; R = (CH2)4CH:CH2, 3; R = CH2CHMe2, 4; R = CH2CMe3) 5; R = CH2CMe2Ph, 6] were studied. The anaerobic decomposition mode chosen by a given L2Mo(O)2R2 complex is a sensitive function of the hydrocarbyl group, R. If accessible β-hydrogens are present on R (as in 3 and 4), equal amounts of alkane and alkene are formed through a β-hydrogen abstraction pathway. In the case of 4, an additional pathway involving Mo-R bond homolysis accounts for 10% of the products formed. When β-hydrogens are absent from R (as in 1, 2, and 6), the free radical, R*, formed by Mo-R bond homolysis is the predominant product. However, in every case there is an additional minor pathway for the formation of the alkane, RH, that involves α-hydrogen abstraction from the neighboring hydrocarbyl group. Because of the expected low stability of the primary neopentyl radical, the α-hydrogen abstraction pathway, rather than Mo-R bond homolysis, predominates in the decomposition of 5. The reaction of the L2Mo(O)2R2 complexes with O2 appears to proceed almost exclusively through the intermediacy of the free radical, R*. In inert solvents, the principal organic product is the corresponding aldehyde, and the role of O2 in its formation from L2Mo(O)2R2 is 2-fold: (a) O2 promotes the homolysis of the Mo-R bond to form R*, and (b) O2 traps the resultant radical to yield the aldehyde. Labeling studies indicated that O2, rather than the Mo=O group, was the predominant source of oxygen for the aldehydes. Mechanistic implications of our observations for the heterogeneous oxidation of alkanes and alkenes by Mo(VI)- and V(V)-oxo species are discussed.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry