Synthesis and structural characterization of isomeric 'lantern-shaped' platinum(III) complexes of formula [Pt2(PPh3)X{N(H)C(R)O}4](NO3)2 (X = PPh3, H2O)

The platinum(III) lantern type complexes [Pt-2(PPh3)(2){N(H)C(R)O}(4)](NO3)(2) [R =Me (1), Bu-t (2)], and [Pt-2(H2O)(PPh3)- {N(H)C(Bu-t)O}(4)](NO3)(2) (3) were synthesized and characterized by H-1 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, (NO)-O-3/NO3 orN(2)O(2), and, in the case of N2O2, for the cis or trans geometry. The effect of the anion upon the chemical shifts of NH protons was studied for NO3-, BF4-, and ClO4-. The stability of phosphine axial ligands in the complexes (NO)-O-3/NO3-[Pt-2(PPh3)(2){N(H)C(R)O}(4)](NO3)(2) as a function of the set of donor atoms was also studied. The complex (NO)-O-3/NO3-3 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. (C) 2002 Elsevier Science B.V. All rights reserved.