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‐ (C 6 F 5 )( p ‐tol 3 P) 2 Pt(C≡C) n SiEt 3 ( PtC 2 n Si ; n =5, 7, 9) and excess PtCl in the presence of wet n ‐Bu 4 N + F − (to effect protodesilylation) under Sonogashira‐type conditions (CuCl, base, other additives) afford the title compounds PtC 10 Pt , PtC 14 Pt , and PtC 18 Pt in 42–32 % yields. A four‐fold substitution of the phosphine ligands in PtC 10 Pt by PEt 3 affords Pt'C 10 Pt’ (78 %), and a Sonogashira reaction of Pt'C 2 H and Pt'Cl affords Pt'C 2 Pt’ (68 %). The analogous reaction with PtC 2 Si and PtCl is unsuccessful, presumably for steric reasons. The crystal structures of PtC 10 Pt , PtC 14 Pt , Pt'C 10 Pt′ , and Pt'C 2 Pt’ exhibit a number of interesting trends and features. Certain sp chain extension reactions that lead to or employ the precursors PtC 10 Si , PtC 12 Si , PtC 14 Si , and PtC 18 Si sometimes give byproducts derived from C 2 loss, and possible origins are discussed. Related phenomena have been reported by others in the course of synthesizing extended conjugated polyynes.