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$RhCl_3$-Assisted C-H and C-S Bond Scissions: Isomeric Self-Association of Organorhodium(III) Thiolato Complex. Synthesis, Structure, and Electrochemistry

Kausikisankar, Pramanik and Ujjwal, Das and Basab, Adhikari and Deepak, Chopra and Helen, Stoeckli-Evans (2008) $RhCl_3$-Assisted C-H and C-S Bond Scissions: Isomeric Self-Association of Organorhodium(III) Thiolato Complex. Synthesis, Structure, and Electrochemistry. In: Inorganic Chemistry, 47 (2). pp. 429-438.

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The ligating properties of alkyl 2-(phenylazo)phenyl thioether 1 $(HL^R$; R = Me, $CH_2Ph)$ toward Rh(III) have been examined. A novel hexacoordinated orthometalated rhodium(III) thiolato complex trans-[Rh(L)Cl$(PPh_3)_2]$ 5 has been synthesized from 1 and $RhCl_3$·$3H_2O$ in the presence of excess $PPh_3$ via in situ C$(sp^2)$-H and C$(sp^3)$-S bond scissions, which is the first example for a coordination compound of $[L]^2^-$. We were also able to isolate the intermediate organothioether rhodium(III) compound trans-$[Rh(L^R)Cl_2(PPh_3)]$ 6 with 1 equiv of $PPh_3$ relative to both 1 and $RhCl_3$·$3H_2O$ in the course of the synthesis of the S-dealkylated product. $PPh_3$ plays a crucial role in the C$(sp^3)$-S cleavage process. A plausible mechanistic pathway is presented for C-S bond cleavage, and reductive cleavage by single-electron transfer mechanism is likely to be operative. The electronically and coordinatively saturated thiolato complex 5, indefinitely stable in the solid state, undergoes spontaneous self-dimerization in solution via dissociation of one coordinated $PPh_3$ molecule to afford edge-shared bioctahedral anti-$[Rh(L)Cl(PPh_3)]_2$ 7 and syn-$[Rh(L)Cl(PPh_3)]_2$ 8 isomers. All the synthesized organosulfur rhodium(III) compounds were isolated as both air- and moisture-stable solids and spectroscopically characterized in both solution and solid states. In addition, all the representative members have been authenticated by single-crystal X-ray structure analyses. Availability of the isomeric dimers provides an opportunity to recognize the presence of noncovalent intramolecular "metallochelate-metallochelate" interaction in the sterically encumbered syn isomer. Unlike other organosulfur rhodium complexes, the monomeric thiolato complex 5 exhibits a fully reversible oxidative wave at 0.82 V vs Ag/AgCl, which is supposed to be primarily centered on the thiolato sulfur atom, and such perception is consistent with the DFT study. Formation of rhodium-bound thiyl radical cation $5^\bullet^+$ by electrochemical oxidation was scrutinized by EPR spectroscopy.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to American Chemical Society
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 25 Feb 2008
Last Modified: 19 Sep 2010 04:42
URI: http://eprints.iisc.ernet.in/id/eprint/13087

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