Studies of Chelation. Part 9. Cobalt Complexes of 1--2-naphthol and 1--2-naphthol Ligands. Tautomerism and Reactivity

DOI: 10.1039/DT9810000559

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 559 - 566 (1981)

Update date:2022-09-26

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Authors:

Connor, Joseph A.

Fine, David J.

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Article abstract of DOI:10.1039/DT9810000559

Spectroscopic characterisation (1H and 13C n.m.r., i.r., Raman, and u.v.-visible) of various 1-<(substituted phenyl)azo>-2-naphthols, R-Haz (R = 4'-Me, 4'-OMe, 4'-Cl, H, 2'-OMe, 2'-Me, 2'-Cl, and 2'-Br), and 1-<(substituted phenylimino)methyl>-2-naphthols, R-Hsb (R = 4'-OMe, 4'-Me, 4'-Cl, H, 4'-Br, 4'-CF3, 4'-CN, 4'-NO2, 2'-OMe, 2'-Me, 2'-CHMe2, 2'-Cl, 2'-CN, and 2'-NO2), in the solid state and in solution in both polar and non-polar solvents has shown that the hydrogen-bonded keto-tautomer is dominant in polar solvents.Reaction of cobalt(II) salts with R-Haz and with R-Hsb in ethanol produces , cis-, and fac- (L=R-az or R-sb).The tautomeric form of the ligand in these complexes is established by vibrational spetroscopy and shown to be predominantly keto (hydrazone, ketoenamine) in , in , and (X = Cl or Br) but predominantly enolimine in .The interconversion of and is established generally: the intermediate, five-co-ordinate is identified in certain cases (R = 4-OMe, 4'-Me, or H).In the chelation process, proton loss follows ring closure and is succeeded by tautomerisation where this occurs.The facility with which the chelating ligand deviates from coplanarity of the benzene and naphthalene rings is a critical feature of the chelation process.The formation of from and from in the presence of air occurs easily and is acid catalysed. is formed only under vigorously oxidising conditions.The isoelectronic ligands R-Haz and R-Hsb should not be regarded as identical in their reactivity towards cobalt(II).