RhCl 3 -Assisted C-H and C-S Bond Scissions: Isomeric Self-Association of Organorhodium(III) Thiolato Complex. Synthesis, Structure, and Electrochemistry Kausikisankar Pramanik,* ,† Ujjwal Das, † Basab Adhikari, † Deepak Chopra, ‡ and Helen Stoeckli-Evans § Department of Chemistry, Inorganic Chemistry Section, JadaVpur UniVersity, Kolkata 700032, India, Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India, and Institut de Chemie, UniVersite ´ de Neucha ˆ tel, AV. de BelleVaux 51, 2000, Neucha ˆ tel, Switzerland Received August 11, 2007 The ligating properties of alkyl 2-(phenylazo)phenyl thioether 1 (HL R ;R ) Me, CH 2 Ph) 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 2 O 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 2 O 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 •+ by electrochemical oxidation was scrutinized by EPR spectroscopy. Introduction Platinum group metals display efficacy in various organic transformations via activation of C-H and C-S bonds; the latter process is less common. 1-7 In this context, suitable multidentate ligands incorporating both phenyl and thioether functions are good candidates for providing organothiolates of noble metals via C-H and C-S bond cleavages, respectively. In pursuing our search for alkyl 2-(phenylazo)- phenyl thioether 1, a typical ligand of this kind, we found that no metal-assisted S-dealkylation occurred with noble metal halides and only chelation modes of types 2 and 3 (Scheme 1) are cited in the literature. 5 Great attention has been paid to metal-assisted C-S bond activation from the standpoint of synthetic, catalytic, bioinorganic, and theoretical chemistry. 1-4 Interestingly, such S-dealkylation strategy (chelation mode 4) has indeed materialized success- fully with RhCl 3 ‚3H 2 O in the presence of excess PPh 3 , affording organorhodium(III) thiolato complexes. Recently, rhodium thiolato and organorhodium compounds have been found to exhibit various bioactivities, including anticancer activity. 8 * To whom correspondence should be addressed. E-mail: kpramanik@ hotmail.com. † Jadavpur University. ‡ Indian Institute of Science. § Universite ´ de Neucha ˆtel. (1) Transition Metal Sulfur Chemistry; Stiefel, E. I., Matsumoto, K., Eds.; ACS Symposium Series 653; American Chemical Society: Washing- ton, DC, 1996. Inorg. Chem. 2008, 47, 429-438 10.1021/ic7016006 CCC: $40.75 © 2008 American Chemical Society Inorganic Chemistry, Vol. 47, No. 2, 2008 429 Published on Web 12/28/2007