Structure, bonding, and reactivity of molybdenum eta(3)-cyclohexenone complexes in comparison with their cyclopentenone analogues: eta(3)-allyl/eta(4)-diene conversionстатья
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Аннотация:The neutral eta(3)-cyclohexenone complexes [Mo(eta(3)-C6H7O)(CO)(2)(MeCN)(2)Br] 1, [Mo(eta(3)-C6H7O)(CO)(2){HB(pz)(3)}] 2, [Mo(eta(3)-C6H7O)(CO)(2)(bipy)Br] 3 (bipy = 2,2'-bipyridine) and [Mo(eta(3)-C6H7O)(CO)(2)(dppm)Br] 4 (dppm = Ph2PCH2PPh2) have been synthesized. The structure of 2 has been determined by X-ray crystallography. All these complexes resist hydride abstraction using Ph3C+PF6-, in sharp contrast to the eta(3)-cyclopentenone analogues where eta(3)-allyl/eta(4)-diene conversion is a facile process. A rationale for this different behaviour is provided by extended-Huckel calculations combined with a Walsh analysis of hydrogen abstraction. Thus, while in the eta(3)-C5H5O --> eta(4)-C5H4O conversion a Mobius system is formed upon release of hydride via electrophilic attack, this is not possible in the hypothetical eta(3)-C6H7O --> eta(4)-C6H6O process. Therefore, eta(3)-C6H7O is a C-H acid. Also, the occurrence of different conformations, exo for allyl and endo for diene complexes, is rationalized.