Arylmetal-IB, aryllithium, and arylmetal-IB-lithium compounds have polynuclear structures consisting of a metal core to which each of the aryl groups is bound via C(1) to two metals by a three-center two-electron (3c-2e) bond. When the metals are unlike and aryl is dissymmetrically substituted C( 1) is a center of chirality. Rotation of the aryl group around the C(1)…C(4) axis causes a continuous inversion of configuration at C(1). Dynamic 1H and 13C NMR studies revealed that the prochiral methylene group in 2-(Me2NCH2)C6H4-metal compounds Ar4M2Li2 (M = Cu, Ag, or Au) is an excellent probe for the monitoring of the configuration at C(1) in each of the 2-(Me2NCH2)C6H4MLi units. In this way the rotation of 3c-2e bonded aryl groups around the C(1)…C(4) axis has been established for the first time. Introduction of a second center of chirality of which the configuration cannot invert allows the detection of the stereochemistry of the Ar4M2Li2 aggregates. The use of the chiral 2-Me2NCH(Me) rather than the prochiral 2-Me2NCH2 group as a built-in ligand provided unambiguous proof for the occurrence of Cu-N coordination in the Ar4Cu4 compounds at low temperature. Formation of Cu-N coordination bonds in the Ar4Cu4 cluster having C2 symmetry constitutes a second element of chirality which in combination with the chirality at the benzylic C atoms gives rise to two distinguishable stereoisomers of Ar4Cu4. Li-N coordination in [5-Me-2-(Me2NCH2)C6H4]4Li4, which likewise constitutes an element of chirality, could be detected by 1H and 13C NMR. The novel results concerning the dy namics of 3c-2e bonded aryl groups at the same time provide a rationale for the kinetic stability order of the ortho-substituted arylmetal-1B clusters: 2-Me2NC(Z)HC6H4 (Z = H or Me) ≈ 2-Me2CHCH2C6H4 ≈ 2-Me2NC6H4 ≈ 2,6-(MeO)2C6H3 ≈ 2,6-Me2C6H3 > 2-MeC6H4 > 4-MeC6H4 ≈ unsubstituted phenyl-M cluster. © 1979, American Chemical Society. All rights reserved.
