Coordination-driven self-assembly, structures, and dynamic properties of diplatinum hexatriynediyl and butadiynediyl complexes in which the sp carbon chains are shielded by sp³ carbon chains: Towards endgroup-endgroup interactions

Sequential reactions of trans(C₆F₅)(p-tol ₃P)₂Pt(C≡C)₃SiEt₃ (PtC ₆-SiEt₃) with nBu₄N⁺ F^- (THF/methanol), PtCl, KPF₆/tBuOK, and CuCl give trans,trans-[(C ₆F₅){(p-tol₃P)₂}Pt(C≡ C) ₃Pt{(Pp-tol₃)₂}(C₆F₅)] (PtC₆Pt) in 95% yield on multigram scales. Reactions of PtC ₆Pt and Ar₂P(CH₂)_mPAr₂ afford substitution products trans,trans-[(C₆F₅){(Ar ₂P(CH₂)_mPAr₂)}Pt(C≡C) ₃Pt{(Ar₂P(CH₂)_mPAr ₂)}(C₆F₅)] (PtC₆Pt-m/Ar; m/Ar = 8/p-tol, 78%; 10/Ph, 82%; 11/Ph, 69%; 12/Ph, 57%; 14/p-tol, 57%; 14/p-C ₆H₄-tBu, 71%), in which the diphosphines span the square planar platinum endgroups. An analogous reaction with PEt₃ gives a tetrakis PEt₃ complex Pt′C₆Pt′ (72%). The crystal structures of PtC₆Pt, Pt′C₆Pt′, PtC₆Pt-10/Ph, PtC₆Pt-11/Ph, and PtC₆Pt-14/p-tol or solvates thereof are compared. In PtC₆Pt, the endgroups can avoid van der Waals contact, and define angles of 0°. In PtC₆Pt-14/p- tol, the sp³ chains twist around the sp chain in a chiral double-helical motif, with an endgroup/endgroup angle of 189°. The sp ³ chains are too short to adopt analogous conformations in the other complexes, but laterally shield the sp chain. NMR spectroscopy shows that the helical enantiomers of PtC₆Pt-14/p-tol rapidly interconvert in solution at low temperature. A crystal structure of PtC₄Pt shows endgroups that are in van der Waals contact and define an angle of 41°. Reactions with Ar₂P-(CH₂)₈PAr₂ give PtC₄Pt-8/Ar (Ar = Ph, 53%; p-tol, 87%). Low-temperature NMR spectroscopy establish non-helical chiral conformations. Electrochemical oxidations of the diplatinum complexes are analyzed, the reversibilities of which decrease with increasing sp chain length.