Synthetic Approaches to and Structures of Diplatinum Polyynediyl Complexes trans,trans-[(C6F5)(R3P)2Pt(C≡C)nPt(PR3)2(C6F5)] With Odd Numbers of Triple Bonds; Avoiding Complicating Ethynediyl Extrusions

Reactions of trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)_nSiEt₃ (PtC_2nSi; n=5, 7, 9) and excess PtCl in the presence of wet n-Bu₄N⁺ F⁻ (to effect protodesilylation) under Sonogashira-type conditions (CuCl, base, other additives) afford the title compounds PtC₁₀Pt, PtC₁₄Pt, and PtC₁₈Pt in 42–32 % yields. A four-fold substitution of the phosphine ligands in PtC₁₀Pt by PEt₃ affords Pt'C₁₀Pt’ (78 %), and a Sonogashira reaction of Pt'C₂H and Pt'Cl affords Pt'C₂Pt’ (68 %). The analogous reaction with PtC₂Si and PtCl is unsuccessful, presumably for steric reasons. The crystal structures of PtC₁₀Pt, PtC₁₄Pt, Pt'C₁₀Pt′, and Pt'C₂Pt’ exhibit a number of interesting trends and features. Certain sp chain extension reactions that lead to or employ the precursors PtC₁₀Si, PtC₁₂Si, PtC₁₄Si, and PtC₁₈Si sometimes give byproducts derived from C₂ loss, and possible origins are discussed. Related phenomena have been reported by others in the course of synthesizing extended conjugated polyynes.