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(PPh3)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).3H2O 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 PPh3 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.

An attractive methodology, single-electron transfer (SET) reductive cleavage of the C-S bond mediated by a metal in the presence of the external stimuli PPh3, has been applied to the kinetically inert IrCl3 in order to synthesize the thiolato complex [Ir(III)(L(S))Cl(PPh3)2] 3 from precursor thioether complexes [Ir(III)(L(SR))Cl2(PPh3)] (R = alkyl) 2. The aforesaid cleavage process in association with (arene)C-H activation furnishes a new class of organosulfur compounds of iridium(III). The thiolato chelate 3 displays a reversible oxidative wave at 0.75 V vs. Ag/AgCl signifying its remarkable nucleophilic character. The high electron density on the thiolato-S vis-à-vis superior nucleophilicity can be envisaged through the formation of a number of S-centered derivatives. This observation has been corroborated with the nature of HOMO in 3, which assumes 49% of S(3p). Notably, the facile oxidative nature of 3 makes it an apposite precursor for metal-stabilized thiyl radical species. Indeed, iridium(III)-stabilized 3˙(+) can be generated by chemical/electrochemical means. The axial EPR spectra with g ∼ 2.0 along with theoretical analysis of SOMO (S(3p) 24% + Ph(π) 43% + d(yz) 15%) and spin density (ρ(S) = +0.543, ρ(Ph) = +0.315, ρ(Ir) = +0.151) of one-electron oxidized 3˙(+) validate the iridium-stabilized thiyl radical description. This observation suggests that the CNS coordination mode in thiophenolato complex 3 is redox-active. Complex 3 is very prone to S-centered oxidation under normal aerobic conditions to yield metallosulfoxide [Ir(III)(L(SO2))Cl(PPh3)2] 4. The enhanced nucleophilicity of thiolato-S can also be manifested via the smooth S-C bond making process with alkyl halides (R'X, R' = Me and allyl; X = Br, I) and subsequent formation of thioether complexes of type [Ir(III)(L(SR'))ClX(PPh3)] 5. The organosulfur compounds of iridium(III) exhibit rich spectral properties including luminescence and the origin of these transitions is scrutinized with DFT and TD-DFT methods.

Herein, we report the effects of different electronwithdrawing groups (EWG) (−F) and electron-donating groups (EDG) (−OMe and −NH 2 ) on main ligands (ppy) and ancillary (acac) of [Ir(ppy) 2 (acac)] [ppy = 2-phenylpyridine; acac = acetylacetonato] using seven complexes by DFT and TDDFT calculations. We find that irrespective of the substituents, absorption of ppy-substituted complexes is blue-shifted, while for the acac-substituted complexes, it is red-shifted. The calculations also show that the substitution of EWGs causes an overall drop in the frontier molecular orbital energy levels; however, we observed a reverse effect for EDGs. To calculate the radiative rate k r , we considered the spin−orbit coupling matrix element (SOCME) (⟨T 1 |H SOC |S n ⟩) between S n (n = 1, 2, etc.) excited state and T 1 , transition dipole moment (μ(S n )), and the energy difference between excited singlet states S n and T 1 state (ΔE(S n − T 1 )). To compare the temperature-independent nonradiative process, we considered SOC between T 1 and S 0 (⟨T 1 |H SOC |S 0 ⟩) and the energy gap between optimized T 1 and S 0 states. Furthermore, to formulate the temperature-dependent nonradiative rate, we computed the activation barrier (E 1 ) for the metal-to-ligand state ( 3 MLCT) to a metal-centered state ( 3 MC) conversion. The emission peaks show that the changes of triplet state T 1 from 3 MLCT → 3 MC via transition states ( 3 TS) and 3 MLCT → 1 GS (GS = ground state) via the 3 MC/ 1 GS minimum energy crossing point are not much affected by the nature of substituents in the ancillary and the main ligand. The order of E 1 for the investigated complexes indicates that electron-donating substituents −OMe at both ppy and acac ligands can cause a decrease in nonradiative rate constants. Natural transition orbitals of the complexes show that they are mainly localized on the main ligand ppy and the Ir atoms and hardly on the ancillary ligand acac.