STERIC AND ELECTRONIC EFFECTS ON PT-195 NMR CHEMICAL-SHIFTS OF PLATINUM(II) PHOSPHINE COMPLEXES

Platinum‐195 chemical shift measurements for cis‐PtCl2(PCy3)2 and trans‐PtXCl(PCy3)2 (X = H, Cl, SnCl2Ph and SnCl3) in methylene chloride solution are reported. A comparison of these shifts with those from analogous complexes containing less bulky phosphine ligands indicates significant steric effects on the 195Pt shift of the PCy3 complexes. For cis‐PtCl2(PCy3)2 a downfleld shift of over 200 ppm is obtained. For the cis‐PtCl2(PCy3)2 complexes the deshielding of 195Pt is found to increase in the order X = H < Cl < SnCl3, SnCl2Ph, which corresponds to the change in the bulk of X. The observed downfield shifts in the bulky 2Ph complexes are rationalized in terms of steric crowding, lengthening of the PPt bond and deshielding of the Pt nucleus. Copyright © 1990 John Wiley & Sons, Ltd.