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

Graphical Abstract

The platinum twist: These platinum complexes are accessed by reactions of trans,trans-[(C₆F₅){(p-tol₃P)₂}Pt(CC)_nPt{(Pp-tol₃)₂}(C₆F₅)] and Ar₂P(CH₂)_mPAr₂ (m/2n/Ar=8/6/p-tol, 10/6/Ph, 11/6/Ph, 12/6/Ph, 14/6/p-tol, 14/6/ p-C₆H₄-tBu, 8/4/Ph, 8/4/p-tol). Those with n=3 crystallize with coplanar endgroups in the limiting structures A (m=14; double-helical) and B (m=10, 11; non-helical); those with n=2 have endgroup–endgroup interactions that prohibit coplanarity, and exhibit dissymmetric non-helical conformations in solution.

Abstract

Sequential reactions of trans-(C₆F₅)(p-tol₃P)₂Pt(CC)₃SiEt₃ (PtC₆SiEt₃) with nBu₄N⁺ F⁻ (THF/methanol), PtCl, KPF₆/tBuOK, and CuCl give trans,trans-[(C₆F₅){(p-tol₃P)₂}Pt(CC)₃Pt{(Pp-tol₃)₂}(C₆F₅)] (PtC₆Pt) in 95 % yield on multigram scales. Reactions of PtC₆Pt and Ar₂P(CH₂)_mPAr₂ afford substitution products trans,trans-[(C₆F₅){(Ar₂P(CH₂)_mPAr₂)}Pt(CC)₃Pt{(Ar₂P(CH₂)_mPAr₂)}(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-C₆H₄-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 sp³ 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.