The chiral thallium amidinium cyclopentadiene-N-ylide complexes [C-5(CO2Me)(4){ArNC(Ar ' )NAr}]Tl were synthesized and structurally characterized by X-ray diffraction analysis and NMR spectroscopy. In these complexes, an unusual mode of coordination of the thallium atom was found, viz., the thallium atom is coordinated by both the side-chain nitrogen atom (N-Tl, 2.833(6) Angstrom) and the pi system of the cyclopentadienyl ring (Tl-Cp, 2.887(4) Angstrom; eta (5)-bonding).