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)(2)Cl-2 at 1:1 stoichiometry 12 forms the expected Pt(12)Cl-2 complex, while 8 gives the Pt(8)(2)(2+) cation quantitatively. In the kinetically controlled reaction Pt(8)(2)(2+) is the major product even at a 8:Pt(PhCN)(2)Cl-2 = 1:2 ratio. Most interestingly, at 1:1 ligand to precursor ratio, Pt(8)(2)(2+) cation rearranges to Pt(8)Cl-2 within one day, indicating that the neutral complex is thermodynamically more favorable. (C) 2008 Elsevier B.V. All rights reserved.