Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains, and Crystallographic Studies

Abstract

The silylated hexatriynyl complex trans-(C₆ F₅ )(p-tol₃ P)₂ Pt(C≡C)₃ SiEt₃ (PtC₆ TES) is converted in situ to PtC₆ H (wet n-Bu₄ N⁺ F^- , THF) and cross coupled with the diyne H(C≡C)₂ SiEt₃ (HC₄ TES; CuCl/TMEDA, O₂ ) to give PtC₁₀ TES (71 %). This sequence is repeated twice to afford PtC₁₄ TES (65 %) and then PtC₁₈ TES (27 %). An analogous series of reactions starting with PtC₈ TES gives PtC₁₂ TES (60 %), then PtC₁₆ TES (43 %), and then PtC₂₀ TES (17 %). Similar cross couplings with H(C≡C)₂ Si(i-Pr)₃ (HC₄ TIPS) give PtC₁₂ TIPS (68 %), PtC₁₄ TIPS (68 %), and PtC₁₆ TIPS (34 %). The trialkylsilyl species (up to PtC₁₈ TES) are converted to 3+2 "click" cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C₆ F₅ )(p-tol₃ P)₂ Pt(C≡C)_n-1 C=CHN(CH₂ C₆ H₅ )N=N (29-92 % after workups). The most general procedure involves generating the terminal polyynes PtC_x H (wet n-Bu₄ N⁺ F^- , THF) in the presence of benzyl azide in DMF and aqueous CuSO₄ /ascorbic acid. All of the preceding complexes are crystallographically characterized and the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopolymorphs of PtC₂₀ TES are obtained, both of which feature molecules with parallel sp carbon chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.

Keywords: alkyne cross-coupling; click reaction; crystal structures; platinum; polyyne; protodesilylation.