Preparation and nuclear magnetic resonance study of salts of the platinum(I) anions [Pt2X4(CO)2]2–(X = Cl, Br, or I)

Abstract

Reactions of the anions [PtX₃(CO)]^–(X = Cl, Br, or I) with controlled amounts of formic acid and tri-n-propylamine in tetrahydrofuran lead to high yields of salts of [Pt₂X₄(CO)₂]^2– if appropriate cations are chosen. For Cl and Br derivatives with ¹³C-enriched CO (75%)¹⁹⁵Pt and ¹³C n.m.r. studies are reported and values of ¹J(PtPt) established. At 300 K there is exchange of CO between adjacent platinum atoms. Studies of ¹⁹⁵Pt Fourier-transform n.m.r. spectra of the mixed halide species [Pt₂X_nY_4–n(CO)₂]^2–(X,Y = Cl,Br; Cl,I; or Br,I) are interpreted on the basis of a marked preference for isomers with the higher atomic number halide on the Pt–Pt axis. For the Cl,Br system comparison between spectra obtained at 220 and at 300 K shows that at the higher temperature halide site exchange occurs on a given Pt atom, but is synchronised between both Pt atoms in the anion; this is interpreted in terms of the interplatinum atom exchange of the CO groups via CO bridging. Studies of the mixed halide species derived from [PtX₃(CO)]^– establish ¹⁹⁵Pt shifts for fourteen of the eighteen possible species, and show that species with lower atomic number halide trans to CO are preferred.