Chemistry of Metal Oxo Alkyl Complexes. Mechanistic Studies on the Anaerobic and Aerobic Decompositions of Molybdenum(VI) Dioxo Dialkyl Complexes

William M. Vetter, Ayusman Sen

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)244-250
Number of pages7
JournalOrganometallics
Volume10
Issue number1
DOIs
StatePublished - Jan 1 1991

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Molybdenum
molybdenum
Hydrogen
Metals
Alkanes
chemistry
Decomposition
decomposition
aldehydes
Aldehydes
alkanes
hydrogen
metals
Alkenes
free radicals
alkenes
Free Radicals
products
Labeling
marking

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Cite this

@article{3100cf53dd53498f8b7647e6cd4464d3,
title = "Chemistry of Metal Oxo Alkyl Complexes. Mechanistic Studies on the Anaerobic and Aerobic Decompositions of Molybdenum(VI) Dioxo Dialkyl Complexes",
abstract = "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.",
author = "Vetter, {William M.} and Ayusman Sen",
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Chemistry of Metal Oxo Alkyl Complexes. Mechanistic Studies on the Anaerobic and Aerobic Decompositions of Molybdenum(VI) Dioxo Dialkyl Complexes. / Vetter, William M.; Sen, Ayusman.

In: Organometallics, Vol. 10, No. 1, 01.01.1991, p. 244-250.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Chemistry of Metal Oxo Alkyl Complexes. Mechanistic Studies on the Anaerobic and Aerobic Decompositions of Molybdenum(VI) Dioxo Dialkyl Complexes

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N2 - 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.

AB - 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.

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