Metall-π-Komplexe von Benzolderivaten : XVII. Bis(η-aren)chrom(d5, d6, d7)-Komplexe des Trimethylsilylbenzols, 1,4-bis(trimethylsilyl)benzols und 1,3,5-tris(trimethylsilyl)benzols

Abstract By metal atom-ligand vapour cocondensation bis(trimethylsilyl-η-benzene)chromium (IV), bis[1,4-bis(trimethylsilyl)-η-benzene]chromium (V) and bis[1,3,5-tris(trimethylsilyl)-η-benzene]chromium (VI) have been prepared. 1 H and 13 C NMR as well as mass spectra of these new derivatives of bis(benzene)chromium are compared with those of the free ligands. The most conspicuous chemical property of IV–VI is the ease of desilylation which is effected by reagents as mild as absolute methanol at room temperature. The complexes IV, V and VI may be oxidized to the radical cations IV + , V + and VI + by means of pyridine-4-aldehyde and reduced to the radical anions IV − , V − and VI − at a potassium mirror. The species IV − –VI − represent the first paramagnetic bis(arene)metal anions. An ESR investigation reveals, that the hyperfine coupling constants a ( 1 H) and a ( 53 Cr) for the radical cations and their respective radical anion counterparts are quite similar although, presumably, the nature of the singly occupied molecular orbital is different in the two situations. The latter fact is, however, reflected in the different relative magnitude of g ∥ and g ⊥ . Whereas for the Cr( d 5 ) radical cations g ∥ ≈ 2.00 > g ⊥ pertains, the Cr( d 7 ) radical anions are characterized by g ⊥ ≈ 2.00 > g ∥ .