N-methyl naphthalimide can be readily cyclomanganated at the 2-position, directed by the adjacent amide O atom. Di-cyclomanganation also occurs readily to attach Mn(CO)₄ groups at both 2, 7 positions. An X-ray structure determination of the mono-substituted example confirmed the five-membered metallocyclic ring. Cleavage of the Mn–C bond by HgCl₂ or ICl generates 2-substituted HgCl or I derivatives respectively. Reaction of the mono-cyclomanganated N-methyl naphthalimide with phenylacetylene gives an (η⁵-cyclohexadienyl)Mn(CO)₃ complex where the cyclohexadienyl ring has formed by two PhCCH adding in a formal [2 + 2 + 2] process across the C(1)–C(2) bond of the naphthalimide, breaking the aromaticity of the naphthalene ring as shown by a single crystal structure determination.