Four-Centre, Multi-Electron Bonding in Rare-Earth Germole Sandwich Complexes

Abstract

Abstract

Reduction of the germole-ligated sandwich complexes [(η5-CpGe)M(η5-Cpttt)]2 (1M, M = Y, Gd, Dy) with one or two equivalents of KC8/2.2.2-cryptand produces [{(η5-CpGe)M(η5-Cpttt)}2]− (2M) and [{(η5-CpGe)M(η5-Cpttt)}2]2− (3M), respectively, as salts of [K(2.2.2-cryptand)]+ (CpGe = [GeC4-2,5-(SiMe3)2–3,4-Me2]2−, Cpttt = 1,2,4-C5tBu3H2. X-ray crystallography shows that the bond lengths within the central {M2Ge2} rings contract markedly with each reduction. Computational analysis reveals the presence of unusual four-center, multielectron {M2Ge2} bonds, with the reduction increasing the germanium–germanium and metal–germanium bond orders while reducing the metal-Cpttt bond order. Analysis of 2Y by EPR spectroscopy reveals delocalization of the unpaired spin across both yttrium centers. Magnetic measurements on radical-bridged 2Gd show a large exchange coupling constant of −95 cm−1 (−2 J formalism). Single-molecule magnet behavior is found for the dysprosium–germole complexes. Complexes 1Y, 2Y, and 3Y can be interconverted by one-electron oxidation or reduction reactions of 2Y, which itself can also be formed by comproportionation of 1Y and 3Y. The masked divalent reactivity of 3Y is demonstrated through one-electron reduction of 2,2′-bipyridyl to give [(η5-CpGe)Y(η5-Cpttt)(2,2′-bipy)]− (4Y) and activation of Ph2Se2 to give [(η5-CpGe)Y(η5-Cpttt)(SePh)]− (5Y).