Theoretical studies on #pi#-complex formation of organocopper compounds with acetylene. The origin of nucleophilicity of organocuprates

摘要

Complexes between MeCu and Me_2Cu~- with acetylene have been examined with the aid of HF, MP2, and B3LYP methods. The structure of the MeCu/acetylene complex was not much affected by the choice of the theoretical methods, since the effects of electron-correlation are rather small in this complex. The structure of the Me_2Cu~-/acetylene complex, on the other hand, depends strongly on the method, since electron correlation plays the key role in back donation from the copper 3d_(xz) orbital to the acetylene #pi#~* orbital. As a result, the B3LYP and the MP2 methods, which take electron correlation effects into account, afforded a cupriocyclopropene #pi#-complex as observed experimentally, while the HF method predicted an electrostatic complex between Me_2Cu~- and the acidic acetylenic proton. Molecular orbital analysis indicated that the high nucleophilicity of organocuprates such as Me_2Cu~- is due to the back donation from the copper 3d_(xz) orbital, which necessitates the use of a theoretical method that appropriately evaluates the electron correlation effects. Similarly, a d-#pi#~* Me_2Au~-/acetylene complex was also located by the B3LYP calculations.