Homonuclear PdII and PtII and heteronuclear PdII-AuI and PtII-AuI complexes of a tripod triphosphine ligand: synthesis, characterization and reactions with molecules of biological relevance

Abstract

Complexes of the type Pd(tripod)X₂ [tripod = MeC(CH₂PPh₂)₃; X = Cl (1), Br (2), I (3)] and Pt(tripod)X₂ [X = Cl (4), Br (5), I (6)] have been synthesized. In these complexes tripod acts as a bidentate chelating ligand. The uncoordinated phosphorus atom can bind to Au^I to form the bimetallic complexes PdAu(tripod)X₃ [X = Cl (7), Br (8), I (9)] and PtAu(tripod)X₃ [X = Cl (10), Br (11), I (12)]. Complexes (1)–(12) have been characterized by microanalysis, f.a.b. mass spectrometry, i.r. spectroscopy, ³¹P and ¹⁹⁵Pt n.m.r. spectroscopies, and conductivity measurements. The structures of complexes (1), (4) and (11), as well as that of the unusual complex Cl₂Pt(tripod)AuBr_0.5Cl_0.5 (13), isolated from reaction of Pt(tripod)Br₂ (5), and [Au(thiodiglycol)Cl], have been determined. All complexes show square-planar geometry for Pd^II or Pt^II and linear geometry for Au^I. The X-ray crystal structure of (1) showed partial oxidation of the dangling phosphorus of the ligand in 50% of the molecule distributed randomly over the lattice. Reactions of complex (4), Pt(tripod)Cl₂, with the tripeptide glutathione (GSH) showed the formation of [Pt₂(tripod)₂(GS-µ–S)₂]²⁺ (15a). No reaction with N-acetyl-L-methionine (AcMet) or guanosine 5´-monophosphate (5´-GMP) was observed. Reactions of [Pt(tripod–O)(ONO₂)₂] (14) with GSH resulted in the formation of [Pt₂(tripod–O)₂(GS-µ-S)₂]²⁺ (15b). Displacement of the S-containing molecules by 5´-GMP in the presence of Au^I, via Pt–S bond cleavage, was observed for complex (15b). PtAu(tripod)Cl₃ (10) reacted with GSH, with initial attack on the Au^I centre.