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Issue 18, 2015
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Iridium-mediated C–S bond activation and transformation: organoiridium(iii) thioether, thiolato, sulfinato and thiyl radical compounds. Synthesis, mechanistic, spectral, electrochemical and theoretical aspects

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Abstract

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 [IrIII(LS)Cl(PPh3)2] 3 from precursor thioether complexes [IrIII(LSR)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 S3p. 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 (S3p 24% + Phπ 43% + dyz 15%) and spin density (ρS = +0.543, ρPh = +0.315, ρIr = +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 [IrIII(LSO2)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 [IrIII(LSR′)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.

Graphical abstract: Iridium-mediated C–S bond activation and transformation: organoiridium(iii) thioether, thiolato, sulfinato and thiyl radical compounds. Synthesis, mechanistic, spectral, electrochemical and theoretical aspects

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Supplementary files

Article information


Submitted
01 Feb 2015
Accepted
25 Mar 2015
First published
27 Mar 2015

Dalton Trans., 2015,44, 8625-8639
Article type
Paper
Author version available

Iridium-mediated C–S bond activation and transformation: organoiridium(III) thioether, thiolato, sulfinato and thiyl radical compounds. Synthesis, mechanistic, spectral, electrochemical and theoretical aspects

U. Das, T. Ghorui, B. Adhikari, S. Roy, S. Pramanik and K. Pramanik, Dalton Trans., 2015, 44, 8625 DOI: 10.1039/C5DT00448A

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