ARYLIMINODIMAGNESIUM REAGENTS .23. EFFICIENT FORMATION OF SOME AMIDINES BY THE REACTIONS OF ARYLIMINODIMAGNESIUM WITH WEAKLY ELECTRON-ACCEPTING BENZONITRILE, N,N-DIMETHYLFORMAMIDE AND RELATED-COMPOUNDS - FEATURES OF REACTIONS GOVERNED BY SIGMA-COMPLEXATION

In many reactions of magnesium reagents, including Grignard and arylim inodimagnesium [ArN(MgBr)2, IDMg], the formation of abnormal products via reactions such as radical dimerization, hydrogen abstraction and c onjugate 1,4-addition originating from efficient single electron trans fer (SET) is not excluded. In IDMg reactions with benzonitrile and N,N -dimethylformamide in tetrahydrofuran, however, clean reactions took p lace affording N-arylbenzamidine and N,N'-diarylformamidine vis exclus ive 1,2-addition and condensation plus replacement, respectively. Some alkyl and arylvinyl cyanides gave the corresponding amidines without 1,4-addition or hydrogen abstraction. These results are the first obse rvation of such reactions of magnesium reagents, and are attributed to a combination of the weak electron-donating ability (EDA) of IDMg wit h the weak electron-accepting ability (EAA) of nitriles. Although ESR is therefore inapplicable, factors governing the product yields were s tudied on the basis of effects caused by the addition of strongly coor dinating hexamethylphosphoramide and pyridine to the reagent solution, and by addition of nitrobenzenes having a strong EAA. From the result s, a large participation of sigma-complexation followed by implicit SE T in the inner sphere of the complex is proposed.