Four‐Centre, Multielectron Bonding in Rare‐Earth Germole Sandwich Complexes

Abstract Reduction of the germole‐ligated sandwich complexes [(η 5 ‐Cp Ge )M(η 5 ‐Cp ttt )] 2 ( 1 M , M = Y, Gd, Dy) with one or two equivalents of KC 8 /2.2.2‐cryptand produces [{(η 5 ‐Cp Ge )M(η 5 ‐Cp ttt )} 2 ] − ( 2 M ) and [{(η 5 ‐Cp Ge )M(η 5 ‐Cp ttt )} 2 ] 2− ( 3 M ), respectively, as salts of [K(2.2.2‐cryptand)] + (Cp Ge  = [GeC 4 ‐2,5‐(SiMe 3 ) 2 –3,4‐Me 2 ] 2− , Cp ttt  = 1,2,4‐C 5 t Bu 3 H 2 . X‐ray crystallography shows that the bond lengths within the central {M 2 Ge 2 } rings contract markedly with each reduction. Computational analysis reveals the presence of unusual four‐center, multielectron {M 2 Ge 2 } bonds, with the reduction increasing the germanium–germanium and metal–germanium bond orders while reducing the metal‐Cp ttt bond order. Analysis of 2 Y by EPR spectroscopy reveals delocalization of the unpaired spin across both yttrium centers. Magnetic measurements on radical‐bridged 2 Gd 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 1 Y , 2 Y, and 3 Y can be interconverted by one‐electron oxidation or reduction reactions of 2 Y , which itself can also be formed by comproportionation of 1 Y and 3 Y . The masked divalent reactivity of 3 Y is demonstrated through one‐electron reduction of 2,2′‐bipyridyl to give [(η 5 ‐Cp Ge )Y(η 5 ‐Cp ttt )(2,2′‐bipy)] − ( 4 Y ) and activation of Ph 2 Se 2 to give [(η 5 ‐Cp Ge )Y(η 5 ‐Cp ttt )(SePh)] − ( 5 Y ).