Structural diversity in pyridine and polypyridine adducts of ring slipped manganocene: correlating ligand steric bulk with quantified deviation from ideal hapticity

Abstract

We have synthesized several new manganocene-adduct ([Cp₂Mn(L)] = 1–L) complexes using pyridine and polypyridine ligands and report their molecular structures and characterization data. Consistent with other molecules in this class [(η^x-Cp)₂MnL_n] or [(η^x-Cp)₂Mn(L–L)] (n = 1, 2; x = 1, 3, or 5), the manganese-cyclopentadienide interaction deviates from the classical η^x interactions (x = 3 or 5). Such deviations have been ascribed to steric factors and often called non-ideal hapticity. However, there is no quantification of this non-ideal hapticity and thus it is difficult to evaluate the extent of ring slippage or assign hapticity. Furthermore, the hypothesis that non-ideal hapticity in high-spin Mn^II complexes is induced by steric interactions has not been systematically evaluated. Therefore, we report herein a quantified scale for deviation from ideal hapticity between zero (ideal η⁵ interaction) and one (“η¹” interaction). This quantified deviation from ideal hapticity has an empirical relationship with the ligand's steric properties, which strongly supports the premise that steric interactions cause the deviations in ionic M–Cp interactions.