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
S. Hasenzahl et al., 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, Inorganica Chimica Acta, 225(1-2), 1994, pp. 23-34
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.