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Keywords:

  • Ylides;
  • Phosphorus;
  • Sulfur;
  • Palladium;
  • Conformational preferences

Abstract

The coordination properties of the ylide–sulfonium salts [Ph3P=C(H)COCH2S(R1)R2]X [R1 = R2 = Et, X = Br (2); R1 = Me, R2 = Ph, X = ClO4 (5)], the phosphonium–sulfide salt [Ph3PCH2COCH2SEt]Br (3) and the neutral ylide–sulfide [Ph3P=C(H)COCH2SPh] (4) towards PdII have been studied. Four different bonding modes have been characterized. The reactions of the ylide–sulfonium salts 2 and 5 with PdCl2(NCMe)2 and NEt3 afford the chelating bis(ylide) complexes cis-[PdCl2{Ph3PC(H)COC(H)S(R1)R2C,C}] [R1 = R2 = Et (6); R1 = Me, R2 = Ph (7)], which are obtained selectively in the meso form (RS/SR). This bonding mode is characterized, including by X-ray crystallography, in the acetylacetonate (acac) complexes [Pd(acac-O,O′){Ph3PC(H)COC(H)S(R1)R2C,C}]ClO4 [R1 = R2 = Et (8); R1 = Me, R2 = Ph (9)], which were obtained by reaction of the respective precursor 6 or 7 with AgClO4 and Tl(acac). On the other hand, the C,S-chelating bonding mode has been characterized in [PdCl2{Ph3PC(H)COCH2SR-κC,S}] [R = Et (10); R = Ph (11)], obtained by reaction of the phosphonium–sulfide salt 3 with PdCl2(NCMe)2 and NEt3 or by reaction of the ylide–sulfide 4 with PdCl2(NCMe)2, respectively. Furthermore, the tridentate bonding mode μ-SC,C,S has been determined in the dinuclear derivative [PdCl{Ph3PC(H)COC(H)SPh-μ-SC,C,S}]2 (13), synthesized by reaction of the ylide–sulfide 4 with PdCl2(NCMe)2 and NEt3. Compound 13 reacts with PPh3 to afford the κC,C-chelate [PdCl{Ph3PC(H)COC(H)SPh-κC,C}PPh3] (14) after cleavage of the sulfide bridge. Compound 14 was obtained as a single diastereoisomer, which was characterized as the D,L form (RR/SS).