High spin-Manganocene mit sperrigen, alkylierten Cyclopentadienyl-Liganden

Octaisopropylmanganocene and hexa(tert.-butyl)manganocene show high spin behaviour whereas 1,1',2,2',4,4'-hexaisopropyl-3,3',5,5'-tetramethylmanganocene exhibits spin crossover from high spin to low spin configuration on cooling below -106 degrees C. 1,1'-Diisopropyl-octamethyl-manganocene is low spin at 36 degrees C in solution. The electronic influence of ring alkylation favouring low spin manganocenes is superseded by the steric effect of metal-ring expansion weakening the ligand field and evoking high spin behaviour.