Experimental and Theoretical Studies on the Mechanism of the C–S Bond Activation of PdII 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 P...