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

An η 2 -bound cyclooctatetraenediyl lanthanide complex of an η 5:η 1:η 5:η 1 -bound modified porphyrinogen has been prepared, owing to the limited coordination site space at the Sm III center. In contrast, when the auxiliary ligand is the smaller cyclopentadienyl ligand, η 5 binding is achieved through distortion of the macrocycle, leading to a reduction in its hapticity to η 5:η 1:η 1:η 1 binding.