Unusual kinetic and thermodynamic control in the formation of Pt(II)-complexes of a new C1-symmetric phosphine–phosphite

Versatile synthetic routes have been applied to prepare the new asymmetric phosphine–phosphite ligands 8 and 12. The chiral ligands have been designed so that the corresponding ligating groups have similar electronic properties and steric bulk, but 8 forms 6-, while 12 forms 7-membered chelate rings in their coordination compounds. The chelate size variation results in a markedly different coordination behavior towards Pt(II). In their reactions with Pt(PhCN)2Cl2 at 1:1 stoichiometry 12 forms the expected Pt(12)Cl2 complex, while 8 gives the Pt(8)22+ cation quantitatively. In the kinetically controlled reaction Pt(8)22+ is the major product even at a 8:Pt(PhCN)2Cl2 = 1:2 ratio. Most interestingly, at 1:1 ligand to precursor ratio, Pt(8)22+ cation rearranges to Pt(8)Cl2 within one day, indicating that the neutral complex is thermodynamically more favorable.

Graphical abstractIn the kinetically controlled reaction Pt(phosphine–phosphite)22+is the major product even at a phosphine–phosphite:Pt(PhCN)2Cl2 = 1:2 ratio. At 1:1 ligand (L) to precursor ratio, Pt(L)22+ cation rearranges to Pt(L)Cl2 within one day, indicating that the neutral complex is thermodynamically more favorable.Figure optionsDownload full-size imageDownload as PowerPoint slide