Buckling under Strain: Relief of Steric Pressure Occurs Differently for Samarium(III) Porphyrinogen Complexes of the π-Bound Auxiliary Ligands Cyclopentadienyl and Cyclooctatetraenediyl

An η2-bound cyclooctatetraenediyl lanthanide complex of an η5:η1:η5:η1-bound modified porphyrinogen has been prepared, owing to the limited coordination site space at the SmIII center. In contrast, when the auxiliary ligand is the smaller cyclopentadienyl ligand, η5 binding is achieved through distortion of the macrocycle, leading to a reduction in its hapticity to η5:η1:η1:η1 binding.