Hydrogen bonding interaction of CpCo(Dithiolene) complex with monocyclic 2-pyridonyl substituent and unexpected formation of dithiolene-fused tricyclic pyridone derivative

One-pot reaction of [CpCo(CO)2], elemental sulfur with some heterocycle-substituted alkynes (R–Ctriple bond; length of mdashC–HET) produced [CpCo(dithiolene)] complexes with 2PyOBn (2), with both 2PyOBn and 2-hydroxy-2-propyl groups (C(OH)Me2) (5), both 2Py and C(OH)Me2 (8), both 4Py and C(OH)Me2 (11), and with 4Py substituent (13). A deprotection of benzyl group (Bn) from 2 with trimethylsilyl iodide formed [CpCo(dithiolene)] with 2-pyridonyl substituent (3). Heating reaction of 8 without any base resulted in the C(OH)Me2 group elimination to form the 2-pyridylethylenedithiolate complex (9), but 11 underwent only dehydration at the C(OH)Me2 under heating. While the preparation of 5, the benzyl free complex (6) was obtained as a main product. 6 has a dithiolene-fused tricyclic pyridone skeleton. The structures of 3, 5, 6, 8, and 11 were determined by X-ray diffraction studies. Intramolecular OH⋯N(2Py) hydrogen bondings are found in 5 and 8, and an intermolecular OH⋯N(4Py) one is found in 11 at solid state. In the 2-pyridonyl complex 3, intermolecular NH⋯O and CH(dithiolene)⋯O hydrogen bondings are observed. 8 showed an intermolecular Cp⋯Cp face-to-face interaction. The tricyclic complex 6 exhibited lower energy electronic absorption (λmax = 668 nm) compared with the others (λmax = 562–614 nm), due to an extended π-conjugation of aromatic cobaltadithiolene ring.