Mechanism of stereoselective epoxidation of alkenes by oxo-iron porphyrins

Conference · Wed Feb 04 04:00:00 EST 1987 · J. Am. Chem. Soc.; (United States)

OSTI ID:6613816

Joergensen, K A

The structure of oxo-iron porphyrins and their stereoselective epoxidation properties of alkenes are analyzed from a theoretical point of view. It is found that the most stable structure of oxo-iron porphyrin is one in which oxygen is inserted into the iron-nitrogen bond. This structure is equivalent to some of the carbene analogues, and the bond lengths for Fe-O (1.9 A) and N-O (1.4 A) are in good agreement with those found in the nickel analogue of 6. The insertion of oxygen into the iron-nitrogen bond makes some of the d orbitals on iron available for interaction with the alkene; this type of complex is supported by recent experimental observations. The alkene can be coordinated in a perpendicular or parallel orientation at the iron atom (relative to the iron-oxygen bond), and the perpendicular orientation is found to be the most favorable. This binding of the alkene can then cause the stereoselective epoxidation properties, as the trans substituents will interact repulsively with the iron-porphyrin moiety. It is then suggested that the next step in the reaction mechanism is a slipping motion of the alkene toward the oxygen. This motion is controlled by a favorable interaction between the ..pi..* orbital of the alkene and the lone pair on the oxygen which is antisymmetric with respect to the iron-oxygen-nitrogen plane. Aspects of this type of mechanism in relation to the experimental results as well as other transition metal catalyzed epoxidation reactions are discussed.

• Research Organization: Aarhus Univ., Denmark
• OSTI ID: 6613816
• Conference Information: Journal Name: J. Am. Chem. Soc.; (United States) Journal Volume: 109:3
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKENES
BOND LENGTHS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
COMPLEXES
DATA
DIMENSIONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
INFORMATION
IRON COMPLEXES
LENGTH
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPLEXES
PORPHYRINS
STEREOCHEMISTRY
THEORETICAL DATA
TRANSITION ELEMENT COMPLEXES