Four-Center Interactions

Schlenk intermediates and the addition path have been made so far. However, our results seem to provide simple and realistic pathways. The Grignard addition occurs in a dimeric dichlorine-bridged form. A vicinal-magnesium bonding alkyl and C=0 interaction causes C—C bond formation via a four-center interaction as shown in Scheme 20 (polar mechanism). When the interaction is improbable owing to the steric effect, the Mg—0=C bond formation precedes the C—C bond formation and the Mg—C bond is ruptured (SET). 

Pino suggested that HCo(CO)4, favored under high CO partial pressures, could directly react with l-aUcenes to form the cobalt-aUcyl species RCo(CO)4. The direct reaction of the 18e saturated HCo(CO)4 with an alkene is somewhat unusual, but not unprecedented. A four-center interaction of the alkene double bond with the Co H bond leading to direct alkene insertion to the alkyl species was suggested (equation 4). 

Abstract Taking a binuclear copper complex as model system, the isotropic magnetic coupling is decomposed into different contributions. Perturbative expressions of the main contributions are derived and illustrated with numerical examples. An effective Hamiltonian is constructed that incorporates all important electron correlation effects and establishes a connection between the complex A-electron wave functions and the simpler qualitative methods discussed in the previous chapter. Subsequently an outline is given of the analysis of the coupling with a single determinant approach and the biquadratic and four-center interactions are decomposed. The chapter closes with the recently proposed method to extract DFT estimates for these complex interactions. 

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