1,8-Bis(dimethylamino)-2-(4-methoxyphenyl)naphthalene (1) was synthesized for use as an η 6 -coordinating ligand with a chargeable tag for ESI-MS analysis. The pK a of the proton sponge moiety was essentially unaffected by addition of the anisole group (pK a = 18.2 ± 0.7 at 297 K in CD 3 CN). Cr(η 6 -1)(CO) 3 (2) was prepared to demonstrate the utility of (1) as an ESI tag and 2 was easily visible by ESI(+)-MS. A single crystal structure of the complex showed η 6 -binding of the ligand as expected with the charged moiety being far removed from the metal centre. The gas-phase reactivity of 2 was found to match that of the analogous uncharged chromium carbonyl complex Cr(C 6 H 5 OCH 3 )(CO) 3 indicating that 1 has potential as a chargeable tag for the study of organometallic complexes and their reactions by ESI-MS.