Carbonyl complexes of noble metals with halide ligands: I. Platinum(II) / halide exchange, dimerization, isomerization, 13C NMR data and crystal and molecular structure of Pt 2I 4(CO) 2

Abstract

Room temperature and atmospheric pressure carbonylation of PtI 2 in toluene gave trans-PtI 2(CO) 2 as the predominant isomer, together with cis-PtI 2(CO) 2. Lowering of p(CO) resulted in conversion of PtI 2(CO) 2 into Pt 2I 4(CO) 2 both in solution and in the solid state. The iodide-bridged centrosymmetric Pt 2I 4(CO) 2 was studied by single crystal X-ray diffractometry. Monoclinic; space group C2/ c; a 10.772(2); b 9.077(1); c 13.001(3) Å; β 112.26(2)°; U 1176.5(5) Å 3; Z = 4; D calc 5.385 g cm −3; Mo- K α radiation (λ 0.71069 Å); μ(Mo-K α) 343.6 cm −1; F(000) = 1584. The structure consists of Pt 2I 2(μ-I) 2(CO) 2 units with tetracoordinated square planar platinum bonded to two bridging iodides, one terminal iodide and one terminal CO group. The PtPt nonbonding distance is 3.846(2) Å. A new preparative procedure for the monomeric halo carbonyls PtX 2(CO) 2 (X  Br, I) involves treatment of cis-PtCl 2(CO) 2 with dry HX in toluene. Addition of CO to Pt 2Br 4(CO) 2 occurs readily to give cis-PtBr 2(CO) 2 through the transient trans-PtBr 2(CO) 2. The 13C NMR spectra data for the platinum complexes show that: (a) values of J(PtC) decreases in the sequence Pt 2X 4(CO) 2 > [PtX 3(CO)] − > cis-PtX 2 (CO) 2 ⪆ trans-PtX 2(CO) 2 > [PtX 5(CO)] −; (b) within each series of compounds, values of J(PtC) decrease in the sequence Cl > Br > I.