CHARGE AND ELECTRON-TRANSFER FROM METAL-TO-CARBON BONDS OF MAIN-GROUPORGANOMETALLICS MR(N) (M=AL, GA, ZN) TO AROMATIC N-HETEROCYCLES - COLORED PRECURSOR COMPOUNDS AND RADICAL COMPLEX-FORMATION

The coordinatively unsaturated compounds AlR(3), GaR(3) and ZnR(2), R = isopropyl, were reacted with linearly bridging pyrazine, terramethyl pyrazine or 4,4'-bipyridine ligands and with potentially chelating 2,2 '-bipyridine. The primary reaction products are diamagnetic dinuclear complexes ('bis-adducts') which are characterized by intense long-wave length ligand-to-ligand charge transfer (LLCT) transitions sigma(M-R)- ->pi(L) and which may yield radical complexes after loss of R(.). The latter reaction is assumed to have a strong single electron transfer (SET) component. An isolable 'Al(II)' species (bpy)Al[CH(SiMe(3))(2)]( 2) has been characterized unambiguously by ESR, W-Vis and cyclic volta mmetry as an Al(III) complex of the bpy radical anion. Irradiation int o the fairly intense LLCT absorption bands (epsilon > 3000 M(-1) cm(-1 )) of the dinuclear complexes between pyrazine and (AlPr3)-Pr-i or (Ga Pr3)-Pr-i resulted in bleaching and formation of a mixture of non-arom atic products. Attempts are made to correlate charge transfer properti es and radical formation with the geometrical and electronic structure s of the precursor complexes.