Synthesis and structural characterization of isomeric ‘lantern-shaped’ platinum(III) complexes of formula [Pt 2(PPh 3)X{ N(H)C(R) O} 4](NO 3) 2 (X=PPh 3, H 2O)

Abstract

The platinum(III) lantern type complexes [Pt 2(PPh 3) 2{ N(H)C(R) O} 4](NO 3) 2 [R=Me ( 1), Bu t ( 2)], and [Pt 2(H 2O)(PPh 3){ N(H)C(Bu t) O} 4](NO 3) 2 ( 3) were synthesized and characterized by 1H NMR and X-ray crystallography ( 2 and 3). The compounds can give rise to formation of isomers differing for the sets of equatorial donor atoms around each platinum, N 3O/NO 3 or N 2O 2, and, in the case of N 2O 2, for the cis or trans geometry. The effect of the anion upon the chemical shifts of NH protons was studied for NO 3 − , BF 4 − , and ClO 4 − . The stability of phosphine axial ligands in the complexes N 3O/NO 3–[Pt 2(PPh 3) 2{ N(H)C(R) O} 4](NO 3) 2 as a function of the set of donor atoms was also studied. The complex N 3O/NO 3– 3 is the fist non-symmetric lantern-type platinum dimer to be characterized by X-ray diffraction. Comparison of the platinum/axial ligand bond distances in different complexes of this type allows to conclude that two factors contribute to the lengthening of axial bonds: the strong trans labilizing effect of the intermetallic bond and the trans-influence of the axial ligand on the second platinum unit.