Rhodium complexes of 1,3-diaryltriazenes: Usual coordination, N-H bond activation and, N-N and C-N bond cleavage |
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Authors: | Chhandasi GuhaRoy Samaresh Bhattacharya |
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Institution: | a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India b Department of Chemistry, Howard University, Washington, DC 20059, USA |
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Abstract: | Reaction of 1,3-diaryltriazenes (R-C6H4-NN-(NH)-C6H4-R, R = OCH3, CH3, H, Cl, NO2 at the para position) with Rh(PPh3)3Cl] in ethanol in the presence of a base (NEt3) affords a family of yellow complexes (1-R) containing a PPh3, two de-protonated triazenes coordinated as bidentate N,N-donors, and an aryl (C6H4-R) fragment coordinated in the η1-fashion. A similar reaction in toluene yields a group of reddish-orange complexes (2-R) containing a PPh3, two N,N-coordinated triazenes, and a chloride. Structures of the 1-CH3 and 2-CH3 complexes have been determined by X-ray crystallography. All the 1-R and 2-R complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. The 1-R and 2-R complexes also fluoresce in the visible region under ambient condition while excited at around 400 nm. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation (within 0.76-1.68 vs. SCE), followed by an oxidation of the coordinated triazene ligand (except the R = NO2 complexes). An irreversible reduction of the coordinated triazene is also observed for all the complexes below −0.96 V vs. SCE. In the 1-R and 2-R complexes potential of the Rh(III)-Rh(IV) oxidation correlates linearly with the electron-withdrawing nature of the para-substituent (R). |
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Keywords: | 1 3-Diaryltriazenes Rhodium N-H bond activation N-N and C-N bond cleavage η1-Aryl complexes |
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