Cyclopalladation of azobenzenes and their reactivity towards N-substituted imidazolidine-2-thiones and allied ligands: Synthesis, structures, spectroscopy and ESI-mass studies

Abstract

Reactions of palladium(II) chloride with azobenzene (azbH), p-methoxyazobenzene (mazbH) and 4, 4′-diethoxyazobenzene (deazbH) in methanol yielded halogen bridged dinuclear precursors [Pd2(κ2:C,N-L)2(μ-Cl)2] (here L = azb−, mazb− and deazb−). These precursors were further reacted with a series of N, S- donor thio-ligands, namely, 1,3-imidazolidine-2-thiones (imdzSH-NR; R = H, Me, Et, Prn, Bun, Ph), N-methyl-imidazoline-2-thione (imzSH-NMe), 1,3-benzimidazoline-2-thione (bzimSH-NH) and 1, 3- thiazolidine-2-thione (tzdSH). Nineteen dinuclear organometallic compounds synthesized are listed as follows: (a) [Pd2(κ2:C, N-azb)2(μ-N, S-imdzS-NR)2] (R = H, 1; Me, 2; Et 3; Prn4; Bun5; Ph 6), (b) [Pd2(κ2:C, N-mazb)2(N, S-imdzS-NR)2] (R = Me, 7; Et, 8; Prn9; Bun10), (c) [Pd2(κ2:C, N-deazb)2(N, S-imdzS-NR)2] (R = Et, 11; Prn12; Bun13; Ph 14), (d) [Pd2(κ2:C, N-azb)2(μ-N, S-L)2] (L = bzimS-NH 15; imzS-NMe 16; tzdS 17), and (e) [Pd2(κ2:C, N-deazb)2(N, S-L)2] (L = bzimS-NH 18; imzS-NMe 19). All these compounds have been characterized with the help of analytical data, electron absorption, NMR and fluoresecence spectroscopy, ESI-mass spectrometry and single crystal X-ray crystallography. The loss of one C-H proton of an azobenzene and one N-H proton of a thio-ligand occurred per palladium metal center in dinuclear complexes synthesized, which have C, N-chelating azobenzenes and N, S-bridging heterocyclic thiolates.