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Title: Alternative modes of bonding of C 4 F 8 units in mononuclear and binuclear iron carbonyl complexes
Density functional theory studies show that the lowest energy C 4 F 8 Fe(CO) 4 structure is not the very stable experimentally known ferracyclopentane isomer (CF 2 CF 2 CF 2 CF 2 )Fe(CO) 4 obtained from Fe(CO) 12 and tetrafluoroethylene. Instead isomeric (perfluoroolefin)Fe(CO) 4 structures derived from perfluoro-2-butene, perfluoro-1-butene, and perfluoro-2-methylpropene are significantly lower energy structures by up to ∼17 kcal mol −1 . However, the activation energies for the required fluorine shifts from one carbon to an adjacent carbon atom to form these (perfluoroolefin)Fe(CO) 4 complexes from tetrafluoroethylene are very high ( e.g. , ∼70 kcal mol −1 ). Therefore the ferracyclopentane isomer (CF 2 CF 2 CF 2 CF 2 )Fe(CO) 4 , which does not require a fluorine shift to form from Fe 3 (CO) 12 and tetrafluoroethylene, is the kinetically favored product. The lowest energy structures of the binuclear (C 4 F 8 ) 2 Fe 2 (CO) n ( n = 7, 6) derivatives have bridging perfluorocarbene ligands and terminal perfluoroolefin ligands.
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New Journal of Chemistry
Page Range or eLocation-ID:
6932 to 6942
Sponsoring Org:
National Science Foundation
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