Revealing Coordination Patterns in C₅-Cyclic Lithium Organics

Lithium organics with a C₅ perimeter are the most prominent class of compounds in s-block metal organic chemistry to introduce bulky haptotropic bound substituents in organometallic complexes. In this paper we present some coordination patterns. (η⁵-Cp)Li(PMDETA) (1), (η⁵-Cp)Li(TMEDA) (2), and (η⁵-Cp)Li(DME) (3) reveal the electron-releasing capacity of the donor base: The better the density supply from the base, the longer the Li···Cp_center distance. The donor base DIGLYME gives the solvent-separated ion pair (SSIP) [(DIGLYME)₂Li][(η⁵-Cp)₂Li] (4). The contact ion pair (η²-Ind)Li(PMDETA) (5) shows an unprecedented strong C–H···π interaction of a PMDETA methyl group to the center of the C₆ perimeter of an indenyl anion. {(η⁵-Ind)Li(μ-DME)Li(η⁵-Ind)} (6) is a unique DME-bridged dimer, while [(DIGLYME)₂Li][Ind] (7) crystallizes as a SSIP.