Multinuclear (¹H,³¹P and¹⁹⁵Pt) NMR study and dynamical analysis of binuclear µ-hydrido µ-carbonyl Pt(i) cations with chelating diphosphines

Abstract

The dynamic behaviour of the binuclear µ-hydrido µ-carbonyl cations with chelating diphosphines, [Pt 2 (P-P) 2 -(µ-H)(µ-CO)]ϩ [P-P = dppe, 1, dppp, 2, and dppb H results are consistent with intramolecular mutual exchange of the P atoms with respect to the bridging ligands in all of the complexes 1-3. A detailed dynamical analysis carried out on complexes 2 and 3 shows that the dynamical process exchanges the P atoms within a single diphosphino ligand, and excludes the simultaneous P atom exchange in both ligands. The bite of the diphosphino ligands affects the rate of this process in the order 3 > 2 > 1. The process follows an activation law with ∆H ‡ = 67 and 60 kJ mol Ϫ1 for 2 and 3, respectively, so that P-Pt bond breaking should not be involved. The positive activation entropy (17-19 J K Ϫ1 mol Ϫ1 ) hints at a mechanism where the intermediate(s) have a less ordered structure than that of the stable complex. In accordance with the NMR results, two reactivity experiments provided further evidence of the intramolecular nature of the observed dynamics and exclude any equilibration path via Pt-P and/or Pt-Pt bond breaking. On these grounds, a mechanism involving rotation about a Pt-Pt bond could be proposed.

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

“…[26] The structural information obtained from NMR data for 2 is consistent with the ESI MS spectrum with a major peak at m/z = 1248.3, which corresponds to the molecular weight of the […”

“…[26] Comparison of the 1 JA C H T U N G T R E N N U N G (P'',Pt) values in the three complexes is consistent with the following order of trans influence for the bridging ligands: CO > S 2À > H À , as the 1 JA C H T U N G T R E N N U N G (P'',Pt) value in 2 is greater than in the CO analogue. The presence of the hydride bridge in 2 is confirmed in the 195 Pt spectrum and corroborated by X-ray data in the solid phase.…”

“…It is worth noting the similarity between the chemical shift values found for complexes 4 (À4370.5 ppm) and 5 (À4315.5 ppm) despite the different oxidation state of www.chemeurj.org the platinum atoms, which is consistent with values in the literature. [10,26] …”

“…However, full interpretation of this spectrum requires consideration of J-A C H T U N G T R E N N U N G (P,Pt) and JA C H T U N G T R E N N U N G (P,P) couplings through the platinum-platinum axis. [26] On this basis, the values…”

“…+ (P\P = dppe, dppp, dppb; dppb = 1,4-bis(diphenylphosphanyl)butane), [26] the latter at low temperature. The (Figure 1b) each of these signals is split into a triplet of triplets, owing to the coupling of this hydrogen atom with the phosphorus nuclei located in trans (P') and cis (P'') positions ( JA C H T U N G T R E N N U N G (P'',Pt) = 2702 Hz), respectively, and observed as an apparent doublet of doublets.…”