Variable Coordination Modes of Benzaldehyde Thiosemicarbazones – Synthesis, Structure, and Electrochemical Properties of Some Ruthenium Complexes

Abstract

Reaction of benzaldehyde thiosemicarbazones [H2LR, where H2 stands for the two protons, the hydrazinic proton, and the phenyl proton at the ortho position, with respect to the imine function and R (R = OCH3, CH3, H, Cl, and NO2) for the para substituent] with [Ru(PPh3)2(CO)2Cl2], carried out in refluxing ethanol, afforded monomeric complexes of type [Ru(PPh3)2(CO)(HLR)(H)]. The crystal structure of the [Ru(PPh3)2(CO)(HLNO2)(H)] complex was determined. The thiosemicarbazone ligand is coordinated to the ruthenium center as a bidentate N,S‐donor ligand forming a four‐membered chelate ring. When the reaction of the thiosemicarbazones with [Ru(PPh3)2(CO)2Cl2] was carried out in refluxing toluene, a family of dimeric complexes of type [Ru2(PPh3)2(CO)2(LR)2] were obtained. The crystal structure of [Ru2(PPh3)2(CO)2(LCl)2] was determined. Each thiosemicarbazone ligand is coordinated to one ruthenium atom, by dissociation of the two protons, as a dianionic tridentate C,N,S‐donor ligand, and at the same time the sulfur atom is also bonded to the second ruthenium center. 1H NMR spectra of the complexes of both types are in excellent agreement with their compositions. All the dimeric and monomeric complexes are diamagnetic (low‐spin d6, S = 0) and show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry of the [Ru(PPh3)2(CO)(HLR)(H)] and [Ru2(PPh3)2(CO)2(LR)2] complexes show the ruthenium(II)–ruthenium(III) oxidation within 0.48–0.73 V vs. SCE followed by a ruthenium(III)–ruthenium(IV) oxidation within 1.09–1.47 V vs. SCE. Potentials of both the oxidations are found to correlate linearly with the electron‐withdrawing character of the substituent R. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Cyclometallated ruthenium(II) carbonyl complexes with 1-pyrenaldehyde 4-R-3-thiosemicarbazones: Regioselective ruthenation of the 1-pyrenyl group

“…25 The carbonyl-C occupies the fourth equatorial coordination site and forms a C 2 NS square plane around the metal centre. As generally expected for hexacoordinated complexes containing {Ru(PPh 3 ) 2 } unit, the two bulky PPh 3 molecules occupy the two axial sites 19,20,24,25,[28][29][30][31][32]48,51 and completes a distorted octahedral C 2 NSP 2 coordination environment around the ruthenium(II) centre. The N(2)−C (19) and C(19)−S(1) (C(19) is the thioamidate-C) bond lengths in 1 (1.300(9) and 1.751(8) Å) as well as in 3 (1.290(11) and 1.731(11) Å) are consistent with the deprotonation of the thioamide functionality in the coordinated thiosemicarbazonate ligands (L 1 ) 2− and (L 3 ) 2− .…”

“…28,[48][49][50] The typical strong band for the terminally coordinated carbonyl group in 1−6 is observed in the range 1918-1956 cm −1 . 29,32,48,50 Three strong bands displayed by all the complexes at ∼520, ∼695 and ∼745 cm −1 are attributed to the metal coordinated EPh 3 ligands. 19,20,24,25,29,32 The 1 H-NMR spectra of 1−6 were recorded in CDCl 3 and compared to the spectra of H 2 L n recorded in (CD 3 ) 2 SO.…”

“…29,32,48,50 Three strong bands displayed by all the complexes at ∼520, ∼695 and ∼745 cm −1 are attributed to the metal coordinated EPh 3 ligands. 19,20,24,25,29,32 The 1 H-NMR spectra of 1−6 were recorded in CDCl 3 and compared to the spectra of H 2 L n recorded in (CD 3 ) 2 SO. A singlet observed at δ ∼11.7 ppm for the free H 2 L n is assigned to the thioamide −NH−C(=S)− proton.…”

“…Interestingly, analogous monocyclic aromatic aldehyde thiosemicarbazones are known to provide ortho-ruthenated complexes having 5,5-membered fused chelate rings, where the ligands act as CNS-donor. [28][29][30][31][32] It may be noted that among various Schiff bases containing nitrogen and sulphur donor atoms, thiosemicarbazones are quite unique with respect to their selectivity, sensitivity and the ability to adopt a variety of coordination modes towards various metal ions. 32,33 In view of the above facts, we have invesigated the ruthenium(II) coordination chemistry with 1-pyrenaldehyde 4-R-3-thiosemicarbazones (H 2 L n , where the two H's represent the dissociable thioamide and pyrenyl protons) (scheme 1).…”

Stabilization of CuII–I Bonds Using 2‐Benzoylpyridine Thiosemicarbazones – Synthesis, Structure, Spectroscopy, Fluo­rescence, and Cyclic Voltammetry

“…The oxidative and reductive responses of thiosemicarbazones coordinated to Ru, Rh, Pd, and Ir have also been reported. [37][38][39][40] …”