Orbital Concept for Methane Activation
Kazunari Yoshizawa and Mayuko Miyanishi
Abstract Theoretical thinking on methane C–H bond activation and hydroxylation by soluble and particulate methane monooxygenase (iron and copper enzyme
species) and related metal-oxo species such as FeO
+ is developed. The tetrahedral T d
structure of methane can be deformed into a C 3v or D 2d structure and bound at a coordinatively unsaturated metal-oxo site of a soluble methane monooxygenase model
from extended Hückel calculations. Mechanistic aspects about methane hydroxylation by the bare transition-metal oxide ion FeO
+ are analyzed by using density functional theory calculations. An important feature in the reaction is the spin crossover
between the high-spin and low-spin potential energy surfaces in particular in the
C–H activation process, the energy barrier of which is significantly decreased by the
spin inversion. The hydroxylation mechanisms of soluble and particulate methane
monooxygenase are considered. These mechanistic insights are reasonably extended
to methane activation by metal-exchanged zeolites and IrO 2 (110) surface.
Keywords C–H activation · Density functional theory · Extended Hückel
method · Metal oxides · Methane hydroxylation · Methane monooxygenase ·
Orbital interaction · Zeolites
1 Introduction
Methane and benzene are the most interesting saturated and unsaturated hydrocarbons, respectively. Table 1 lists various properties of methane and benzene. In particular, their C–H bond dissociation energies (BDEs) are extremely large. Benzene’s C–
H BDE of 110 kcal/mol is slightly larger than methane’s C–H BDE of 105 kcal/mol
(103 kcal/mol in density functional theory (DFT) calculations). Many important
chemical processes starting from benzene are widely used by replacing one of its
hydrogen atoms with another functional group. Examples of simple benzene derivatives are phenol, toluene, and aniline that involve OH, CH 3 , and NH 2 groups in
K. Yoshizawa (B) · M. Miyanishi
Institute for Materials Chemistry and Engineering, Kyushu University, Motooka 744, Nishi-ku,
Fukuoka 819-0395, Japan
e-mail: kazunari@ms.ifoc.kyushu-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
K. Yoshizawa (ed.), Direct Hydroxylation of Methane,
https://doi.org/10.1007/978-981-15-6986-9_1
1
Kazunari Yoshizawa and Mayuko Miyanishi
Abstract Theoretical thinking on methane C–H bond activation and hydroxylation by soluble and particulate methane monooxygenase (iron and copper enzyme
species) and related metal-oxo species such as FeO
+ is developed. The tetrahedral T d
structure of methane can be deformed into a C 3v or D 2d structure and bound at a coordinatively unsaturated metal-oxo site of a soluble methane monooxygenase model
from extended Hückel calculations. Mechanistic aspects about methane hydroxylation by the bare transition-metal oxide ion FeO
+ are analyzed by using density functional theory calculations. An important feature in the reaction is the spin crossover
between the high-spin and low-spin potential energy surfaces in particular in the
C–H activation process, the energy barrier of which is significantly decreased by the
spin inversion. The hydroxylation mechanisms of soluble and particulate methane
monooxygenase are considered. These mechanistic insights are reasonably extended
to methane activation by metal-exchanged zeolites and IrO 2 (110) surface.
Keywords C–H activation · Density functional theory · Extended Hückel
method · Metal oxides · Methane hydroxylation · Methane monooxygenase ·
Orbital interaction · Zeolites
1 Introduction
Methane and benzene are the most interesting saturated and unsaturated hydrocarbons, respectively. Table 1 lists various properties of methane and benzene. In particular, their C–H bond dissociation energies (BDEs) are extremely large. Benzene’s C–
H BDE of 110 kcal/mol is slightly larger than methane’s C–H BDE of 105 kcal/mol
(103 kcal/mol in density functional theory (DFT) calculations). Many important
chemical processes starting from benzene are widely used by replacing one of its
hydrogen atoms with another functional group. Examples of simple benzene derivatives are phenol, toluene, and aniline that involve OH, CH 3 , and NH 2 groups in
K. Yoshizawa (B) · M. Miyanishi
Institute for Materials Chemistry and Engineering, Kyushu University, Motooka 744, Nishi-ku,
Fukuoka 819-0395, Japan
e-mail: kazunari@ms.ifoc.kyushu-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
K. Yoshizawa (ed.), Direct Hydroxylation of Methane,
https://doi.org/10.1007/978-981-15-6986-9_1
1