Cooperation between cis and trans influences in cisPt(II)PPh3)2 complexes : structural, spectroscopic and computational studies

The relevance of cis and trans influences of some anionic ligands X and Y in cis-[PtX2(PPh3)2] and cis-[PtXY(PPh3)2] complexes have been studied by the X-ray crystal structures of several derivatives (X2 = (AcO)2 (3), (NO3)2 (5), Br2 (7), I2 (11); and XY = Cl(AcO) (2), Cl(NO3) (4) and Cl(NO2) (13)), DFT calculations, and one bond Pt-P coupling constants, 1JPtP. The latter have allowed an evaluation of the relative magnitude of both influences. It is concluded that such influences act in a cooperative way, and that the cis influence is not irrelevant when rationalising the 1JPtP values, as well as the experimental Pt-P bond distances. On the contrary, in the optimised geometries, evaluated through B3LYP/def2-SVP calculations, the cis influence was not observed, except for compounds ClPh (21), Ph2 (22), and in lesser extent, Cl(NO2) (13) and (NO2)2 (14). A Natural Bond Order analysis on the optimised structures, however, has shown how the cis influence can be related to the s-character of the Pt hybrid orbital involved in the Pt–P bonds and the net atomic charge on Pt. We have also found that in the X-ray structures of cis-[PtX2(PPh3)2] complexes the two Pt-X and the two Pt-P bond lengths are different each other, and are related to the conformation of the phosphine groups, rather than to the crystal packing, since this feature is observed also in the optimised geometries.