Synthesis and Structural Studies of Platinum Complexes Containing Monodentate, Bridging, and Chelating Formamidine Ligands

Abstract

The reactions of K2PtCl4 with N,N'-diphenylformamidine (HDPhF) and N.N'-di-p-tolylformamidine (HDTolF) produce the trans square-planar compounds PtCl2(HDPhF)2, 1a, and PtCl2(HDTolF)2, 1b. Compound la crystallizes as yellow parallelepipeds in the space group P21/c with two independent molecules in the asymmetric unit and unit cell dimensions a = 23.427(7) Å, b = 16.677(6) Å, c = 12.980(4) Å, and β= 96.10(2)°. These compounds are soluble in common organic solvents and have been used as starting materials for the preparation of diplatinum compounds. Treatment of 1a and 1b with NaOMe and the halide abstraction reagent TIPF6 produces the compounds Pt2(μ-DArF)2(η2-DArF)2, Ar = Ph (2a) and Tol (2b), respectively. Compound 2a crystallizes as yellow rods in the space group P1̄ with unit cell dimensions a = 12.296(3) Å, b = 12.310(4) Å, c = 15.374(4) Å, α = 90.75(2)°, β = 91.02(2)°, and γ = 110.20(2)°. Compound 2b crystallizes with a molecule of THF, as yellow rods in the space group P21/c with a = 17.883(3) Å, b = 14.517(3) Å, c = 22.581(3) Å, and β = 98.17(1)°. These compounds contain two cis bridging formamidinato ligands and two formamidinato ligands that are chelated to separate Pt centers. Upon heating, they further react to give the tetrabridged compounds Pt2(μ-DArF)4 Ar = Ph (3a), Tol (3b). Compound 3a crystallizes as orange cubes in the cubic space group I432 with a = 19.671(1) Å. On going from the bis-bridged, bis-chelate structure in 2a to the tetrabridged structure in 3a, the metal-metal separation decreases from 2.910(1) to 2.649(1) Å. Both 2b and 3b have been oxidized to give the PtII-PtIII compound Pt2(μ-DTolF)4(PF6), 4. Compound 4 crystallizes as cubes in the tetragonal space group P4/ncc with a = 14.392(1) ̊ and c = 14.436(1) Å. The Pt-Pt distance in 4 is 2.5304(6) Å.