Chemical Control on the Coordination Mode of Benzaldehyde Semicarbazone Ligands. Synthesis, Structure, and Redox Properties of Ruthenium Complexes
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- 作者：Falguni Basuli ; Shie-Ming Peng ; and Samaresh Bhattacharya
- 刊名：Inorganic Chemistry
- 出版年：2001
- 出版时间：March 12, 2001
- 年：2001
- 卷：40
- 期：6
- 页码：1126 - 1133
- 全文大小：122K
- 年卷期：v.40,no.6(March 12, 2001)
- ISSN：1520-510X
文摘
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] hasafforded 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-NO2is coordinated as a tridentate C,N,O-donor ligand. When reaction between HL-NO2 and [Ru(PPh3)3Cl2] is carriedout in refluxing ethanol, a more stable cis isomer of [Ru(PPh3)2(L-NO2)Cl] is obtained. The trans isomer can beconverted 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 structuredetermination of 5-[Ru(PPh3)2(L-NO2)(CO)Cl] shows that the semicarbazone ligand is coordinated as a bidentateN,O-donor, forming a five-membered chelate ring. When reaction between HL-R and [Ru(PPh3)2(CO)2Cl2] iscarried out in refluxing ethanol, the 4-[Ru(PPh3)2(L-R)(CO)Cl] complexes are obtained. A structure determinationof 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). Thetrans- 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 theHammett constant of the substituent R.