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Fe(CO)4 and Related Compounds as Isolobal Fragments

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journal contribution
posted on 16.05.2011, 00:00 by Lisa S. Cunden, R. G. Linck
The M(CO)4 fragment can be assigned to be isolobal with both CH3+ and CH2. In order to investigate this ambiguous isolobal assignment, we report calculations on compounds of the type M(CO)4Ln, where M is Fe (n = 0), Mn (n = −1), and Co (n = +1) and L is an η2 ligand with a π bond, generally an alkene. The L’s are varied in electron-withdrawing ability, and patterns in computed structural parameters are investigated. We report that the equatorial OC–M–CO angle is sensitive to the electron-withdrawing ability of the alkene just as the isolobal prediction suggests. Other structural parameters that vary monotonically with electron-withdrawing ability of the alkene are the “bending back” of the alkene, the metal–ligand bond distances, and carbon–oxygen bond distances. Changing the metal from neutral Fe to a negatively charged Mn or positively charged Co has the result of increasing and decreasing, respectively, the OC–M–CO angle. Several compounds of Ni(CO)3L are also investigated as a further example of the ability of the isolobal concept to yield chemically useful information.