Monodisperse Molecular Models for the sp Carbon Allotrope Carbyne; Syntheses, Structures, and Properties of Diplatinum Polyynediyl Complexes with PtC20Pt to PtC52Pt Linkages

Aayushi Arora; Sourajit Dey Baksi; Nancy Weisbach; Hashem Amini; Nattamai Bhuvanesh; John A Gladysz

doi:10.1021/acscentsci.3c01090

Monodisperse Molecular Models for the sp Carbon Allotrope Carbyne; Syntheses, Structures, and Properties of Diplatinum Polyynediyl Complexes with PtC₂₀Pt to PtC₅₂Pt Linkages

ACS Cent Sci. 2023 Nov 16;9(12):2225-2240. doi: 10.1021/acscentsci.3c01090. eCollection 2023 Dec 27.

Authors

Aayushi Arora¹, Sourajit Dey Baksi¹, Nancy Weisbach¹, Hashem Amini¹, Nattamai Bhuvanesh¹, John A Gladysz¹

Affiliation

¹ Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, United States.

Abstract

Extended conjugated polyynes provide models for the elusive sp carbon polymer carbyne, but progress has been hampered by numerous synthetic challenges. Stabilities appear to be enhanced by bulky, electropositive transition-metal endgroups. Reactions of trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)_nSiEt₃ (n = 4-6, PtC_xSi (x = 2n)) with n-Bu₄N⁺F^-/Me₃SiCl followed by excess tetrayne H(C≡C)₄SiEt₃ (HC₈Si) and then CuCl/TMEDA and O₂ give the heterocoupling products PtC_x+8Si, PtC_x+16Si, and sometimes higher homologues. The PtC_x+16Si species presumably arise via protodesilylation of PtC_x+8Si under the reaction conditions. Chromatography allows the separation of PtC₁₆Si, PtC₂₄Si, and PtC₃₂Si (from n = 4), PtC₁₈Si and PtC₂₆Si (n = 5), or PtC₂₀Si and PtC₂₈Si (n = 6). These and previously reported species are applied in similar oxidative homocouplings, affording the family of diplatinum polyynediyl complexes PtC_xPt (x = 20, 24, 28, 32, 36, 40 in 96-34% yields and x = 44, 48, 52 in 22-7% yields). These are carefully characterized by ¹³C NMR, UV-visible, and Raman spectroscopy and other techniques, with particular attention to behavior as the C_x chain approaches the macromolecular limit and endgroup effects diminish. The crystal structures of solvates of PtC₂₀Pt, PtC₂₄Pt, and PtC₂₆Si, which feature the longest sp chains structurally characterized to date, are analyzed in detail. All data support a polyyne electronic structure with a nonzero optical band gap and bond length alternation for carbyne.