Basuli, Falguni ; Peng, Shie-Ming ; Bhattacharya, Samaresh (2001) Chemical control on the coordination mode of benzaldehyde semicarbazone ligands. Synthesis, structure, and redox properties of ruthenium complexes Inorganic Chemistry, 40 (6). pp. 1126-1133. ISSN 0020-1669
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Official URL: http://pubs.acs.org/doi/abs/10.1021/ic000915e
Related URL: http://dx.doi.org/10.1021/ic000915e
Abstract
Reaction of benzaldehyde semicarbazone (HL-R, where H is a dissociable proton and R is a substituent (R = OMe, Me, H, Cl, NO2) at the para position of the phenyl ring) with [Ru(PPh3)3Cl2] and [Ru(PPh3)2(CO)2Cl2] has afforded complexes of different types. When HL-NO2 and [Ru(PPh3)3Cl2] react in solution at ambient temperature, trans-[Ru(PPh3)2(L-NO2)Cl] is obtained. Its structure determination by X-ray crystallography shows that L-NO2 is coordinated as a tridentate C,N,O-donor ligand. When reaction between HL-NO2 and [Ru(PPh3)3Cl2] is carried out in refluxing ethanol, a more stable cis isomer of [Ru(PPh3)2(L-NO2)Cl] is obtained. The trans isomer can be converted to the cis isomer simply by providing appropriate thermal energy. Slow reaction of HL-R with [Ru(PPh3)2(CO)2Cl2] in solution at ambient temperature yields 5-[Ru(PPh3)2(L-R)(CO)Cl] complexes. A structure determination of 5-[Ru(PPh3)2(L-NO2)(CO)Cl] shows that the semicarbazone ligand is coordinated as a bidentate N,O-donor, forming a five-membered chelate ring. When reaction between HL-R and [Ru(PPh3)2(CO)2Cl2] is carried out in refluxing ethanol, the 4-[Ru(PPh3)2(L-R)(CO)Cl] complexes are obtained. A structure determination of 4-[Ru(PPh3)2(L-NO2)(CO)Cl] shows that a semicarbazone ligand is bound to ruthenium as a bidentate N,O-donor, forming a four-membered chelate ring. All the complexes are diamagnetic (low-spin d6, S = 0 ). The trans- and cis-[Ru(PPh3)2(L-NO2)Cl] complexes undergo chemical transformation in solution. The 5- and 4-[Ru(PPh3)2(L-R)(CO)Cl] complexes show sharp NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry of the 5-[Ru(PPh3)2(L-R)(CO)Cl] and 4-[Ru(PPh3)2(L-R)(CO)Cl] complexes show the Ru(II)-Ru(III) oxidation to be within 0.66-1.07 V. This oxidation potential is found to linearly correlate with the Hammett constant of the substituent R.
| Item Type: | Article |
|---|---|
| Source: | Copyright of this article belongs to American Chemical Society. |
| ID Code: | 1889 |
| Deposited On: | 08 Oct 2010 11:40 |
| Last Modified: | 21 Jan 2011 11:03 |
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