Reaction chemistry of complexes containing Pt-H, Pt-SH, or Pt-S fragments: From their apparent simplicity to the maze of reactions underlying their interconversion

The relevance of platinum in the reaction of thiophene and derivatives with homogeneous transition-metal complexes as models for hydrodesulfurization has led us to the study of the reaction chemistry of complexes containing Pt-H, Pt~SH, and Pt-S fragments. Exploration of the reactions triggered by addition of controlled amounts of Na 2 S or NaSH to [Pt 2 (H) 2 -(μ-H)(dppp) 2 ]ClO 4 (1) has provided evidence of the formation of complexes [Pt 2 (μ-H)(μ-S)(dppp) 2 ]ClO 4 (2), [Pt(H)(SH)(dppp)] (3), [Pt 2 (μ-S) 2 -(dppp) 2 ] (4), [Pt 2 (μ-S)(dppp) 2 ] (5) and [Pt(SH) 2 (dppp)], in which dppp denotes 1,3- bis(diphenylphosphanyl)propane. Consequently, complexes 1, 2, and 5 as well as the already reported 3, 4, and [Pt(SH) 2 (dppp)] have been obtained and fully characterized spectroscopically. Also the crystal structures of 1 and 2 have been solved. Complexes 1-5 constitute the main framework of the network of reactions that account for the evolution of 1 under various experimental conditions as shown in Scheme 1. Apparently, this network has complexes 2 and 4 as dead-ends. However, their reciprocal interconversion by means of the replacement of one bridging hydride or sulfide ligand in the respective {Pt(μ-H)(μ-S)Pt} and {Pt(μ-S) 2 Pt} cores enables the closure of the reaction cycle involving complexes 1-5. Theoretical calculations support the existence of the undetected intermediates proposed for conversion from 1 to 2 and from 3 to 2 and also account for the fluxional behavior of 1 in solution. The intermediates proposed are consistent with the experimental results obtained in comparable reactions carried out with labeled reagents, which have provided evidence that complex 1 is the source of the hydride ligands in complexes 2 and 3. Overall, our results show the strong dependence on the experimental conditions for the formation of complexes 1-5 as well as for their further conversion in solution. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.