Experimental and Theoretical Studies on the Mechanism of the C–S Bond Activation of Pd^II Thiolate/Thioether Complexes

Abstract

Two equivalents of L (L = 4-methylthio-2-thioxo-1,3-dithiole-5-thiolate or Medmit) react with cis-Pd­(PR3)2Cl2 (R = Ph and Et) to afford Pd­(PR3)­(η1-L)­(η2-L) (R = Et: 1 ; R = Ph: 2) complexes, which have been characterized by X-ray crystallography. These compounds are dynamic in solution due to an exchange of the thiomethyl groups on palladium. Variable-temperature 1H NMR spectroscopy reveals a low coalescence temperature (173 K). Treatment of Pd­(diphos)­Cl2 (diphos = dppe or dppm) with 2 equiv of L affords thiolato complexes Pd­(dppe)­(η1-L)2 (3) and Pd­(dppm)­(η1-L)2 (4). Whereas 3 is rigid in solution with firm η2-coordination of dppe and η1-coordination of the thiolate, two linkage isomers Pd­(η2-dppm)­(η1-L)2 and Pd­(η1-dppm)­(η1-L)­(η2-L) coexist in a solution of 4. L coordinated on PdII undergoes a S-demethylation reaction leading to dithiolene complexes and MeL. This transformation requires high temperature, and its efficiency depends on the nature of the phosphines as well as the nature of the metal (Pd vs Pt). DFT calculations reveal that the most likely mechanism depends on the lability of phosphines. Starting from M­(PR3)2(η1-L)2 (M= Pd and Pt; R = Ph and Et), the favored sequence implies decoordination of one triethyl phosphine (M­(PEt3)­(η1-L)­(η2-L)2 as intermediate) or two triphenylphosphines (Pd­(η2-L)2 as intermediate) followed by oxidative addition and reductive elimination (OA/RE) reactions. In the case of PEt3, this OA/RE sequence can also compete with an intramolecular nucleophilic addition ( AN ), which can be described as an attack of a thiolate sulfur atom on a CH3 + carbocation. An intramolecular SN2 process was found to be the most feasible, starting from M­(dppe)­(η1-L)2 (M= Pd and Pt), with the nucleophile approaching the thiomethyl group at an angle of 180° with respect to the CCH3 –S bond. The influence of the coligand has also been studied experimentally. Structurally characterized disulfide L–L dimer has been isolated upon reaction of 2 equiv of L with MCl2 (M = Pd and Pt).

Iron-SNS and -CNS Complexes: Selective Caryl–S Bond Cleavage and Amine-Borane Dehydrogenation Catalysis

“…Thus Fe-mediated cleavage of the C aryl –S bond in L1 was unexpected. While examples of C–S bond oxidative addition have been reported previously, the reluctance of iron to access the tetravalent oxidation state leads presumably to formation of the ·SMe radical . The electron-rich Fe­(II) center likely transfers an electron to the C–S antibonding orbital, inducing C–S bond homolysis and Fe–C bond formation.…”

Crystal structures of 4,4′-(disulfane-1,2-diyl)bis(5-methyl-2H-1,3-dithiol-2-one) and 4,4′-(diselanane-1,2-diyl)bis(5-methyl-2H-1,3-dithiol-2-one)

“…Wardell and coworkers carried out the controlled oxidation of cesium 4-benzoylthio-1,3-dithiole-2-thione-5-thiolate using iodine as oxidant and obtained bis(4-benzoylthio-1,3-dithiole-2-thione)-5,5-disulfide, in two polymorphic forms (Comerlato et al, 2010). Recently the formation of a disulfide with a 4-(methylsulfanyl)-2H-1,3-dithiole-2-thione unit was reported from the reaction of a Cs complex with MCl 2 (M = Pt, Pd) by Kumar et al (2017). Notably, such compounds predominantly constitute unanticipated side products and the focus of the respective characterization lies in crystallographic analyses with respect to solid-state intermolecular interactions and packing motifs.…”

Synthesis of Organosilicon‐Based Thioether Ligand Class Showing Defined S‐Stereogenic Coordination in Crystalline Palladium(II) Complexes

“…[4] Other studies on similar topics are known as well. [14,27,28] Additionally, thioethers are often used as ligands in copper(I) halide complexations as metal-enriched coordination polymers of these compounds often exhibit luminescent properties. [29][30][31][32][33][34][35][36][37][38][39][40] In this work, we wanted to investigate the influence of the substituent on the configurational stability of the sulphur atom by modifying the aromatic system and investigating the corresponding Pd(II) complexes by SCXRD and NMR experiments at varying temperatures.…”

“…Also, we analysed the inversion of sulphur stereogenic centres in cis ‐platinum(II) complexes by temperature dependent 195 Pt‐NMR [4] . Other studies on similar topics are known as well [14,27,28] . Additionally, thioethers are often used as ligands in copper(I) halide complexations as metal‐enriched coordination polymers of these compounds often exhibit luminescent properties [29–40] …”