Preparation of buta-1,3-diynyl complexes of platinum(II) and their use in the construction of neutral molecular squares: synthesis, structural and theoretical characterisation of cyclo-{Pt(μ-C≡CC≡C)(dppe)}₄ and related chemistry

Abstract

Copper(I)-catalysed reactions of cis-PtCl₂(L)₂ (L = PEt₃, L₂ = dppe, dppp) with buta-1,3-diyne have given the corresponding diynyl complexes, cis-Pt(C≡CC≡CH)₂(L)₂ (L = PEt₃ 1, L₂ = dppe 2, dppp 3) whose solid-state structures have been determined from single crystal X-ray diffraction studies. Theoretical calculations were carried out to probe the electronic structure of these diynyl complexes. Complex 2 reacts with Co₂(CO)₈ to give a bis-adduct 5 and with Ru₃(μ-dppm)(CO)₁₀ to give a mono-adduct 6; in both, the least hindered C≡C triple bond(s) is(are) coordinated. Lithiation (LiBut) of 2 gives a dilithio derivative, which has been converted to dimethyl 7 or mono-SiMe₃ 8 or -Au(PPh₃) 9 complexes. Cu(I) and Ag(I) (MI) adducts (“tweezer” complexes) have been obtained from reactions of 2 with MISCN or [MI(NCMe)₄]⁺. An ES mass spectrometric study of the interactions of 2 with Group 1 cations and with Tl⁺ is also described; comparative experiments with {W(CO)₃Cp}₂(μ-C₈), in which the four C≡C triple bonds do not have a “tweezer” conformation, have also been carried out. The degree of association is determined by the competitive solvation of the Group 1 cation. Coupling of the buta-1,3-diynyl complexes with Pt(OTf )₂(L’)₂ gives homo- or mixed-ligand molecular squares cyclo-{(L)₂Pt(μ-C≡CC≡C)₂Pt(L’)₂}₂ (L, L’ = PEt₃, L₂, L’₂ = dppe, dppp; not all combinations), of which the molecular structure of cyclo-{Pt(μ-C≡CC≡C)(dppe)}₄ 17 is described (as solvates containing dmso). The molecular squares form adducts with substituted ammonium triflates [NH₂R₂][OTf] (R = Et, Pri, Cy; NH₂R₂ = dbuH) and with Group 11 cations [MI(NCMe)]⁺.