Syntheses and Structures of Dinuclear Double-Stranded Helicates of Divalent Manganese, Iron, Cobalt, and Zinc

The syntheses and solid-state and solution structures of a series of unusually volatile, charge neutral, [4 + 4]
double-stranded helical complexes of divalent manganese, iron, cobalt, and zinc are described. Deprotonation of
the N4-donor iminopyrrole ligand H2L by KH cleanly generates the salt K2(THF)2L, which displays both σ and π
interactions between K and iminopyrrolyl fragments in the X-ray crystal structure. Transamination, salt elimination,
and protonolysis reactions were found to be versatile and, in general, high-yielding routes to the dinuclear double
helicates [M2(L)2] (M = Mn, Fe, Co, and Zn). These compounds are isomorphous in the solid state by X-ray
crystallography and adopt dinuclear cleft motifs as a result of π stacking between opposing iminopyrrolyl fragments.
This motif was also observed in the solution structures of [Fe2(L)2] and [Zn2(L)2] below 230 and 200 K, respectively
(ΔG⧧ = ∼46 and 39.0 kJ mol-1, respectively).