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Abstract The overarching goal of this study is to effect the elimination of platinum from adducts withcis–C≡C−Pt−C≡C‐ linkages, thereby generating novel conjugated polyynes. Thus, the bis(hexatriynyl) complextrans‐(p‐tol₃P)₂Pt((C≡C)₃H)₂is treated with 1,3‐diphosphines R₂C(CH₂PPh₂)₂to generate (R₂C(CH₂PPh₂)₂)₂Pt((C≡C)₃H)₂(14; R=c,n‐Bu;e,p‐tolCH₂). These condense with the diiodide complexes R₂C(CH₂PPh₂)₂PtI₂(9 a,c) in the presence of CuI (cat.) and excess HNEt₂to give the title macrocycles [(R₂C(CH₂PPh₂)₂)Pt(C≡C)₃]₄(16 c,e) as adducts of the byproduct [H₂NEt₂]⁺I⁻(30–66 %). DOSY NMR experiments establish that this association is maintained in solution, but NaOAc removes the ammonium salt. The bis(triethylsilylpolyynyl) complexes (n‐Bu₂C(CH₂PPh₂)₂)Pt((C≡C)_nSiEt₃)₂(n=2, 3) are synthesized analogously to14 c. They react with I₂at rt to give mainly the diiodide complex9 cand the coupling product Et₃Si(C≡CC≡C)_nSiEt₃. The possibility of competing reactions giving IC≡C species is investigated. Analogous reactions of the Pt₄C₂₄macrocycle16 calso give9 c, but no sp¹³C NMR signals or mass spectrometric C_x^z+ions (x=24–100) could be detected. It is proposed that some cyclo[24]carbon is generated, but then rapidly converts to other forms of elemental carbon. No cyclotetracosane (C₂₄H₄₈) is detected when this sequence is carried out in the presence of PtO₂and H₂. 

Abstract The dialkyl malonate derived 1,3‐diphosphines R₂C(CH₂PPh₂)₂(R=a, Me;b, Et;c,n‐Bu;d,n‐Dec;e, Bn;f,p‐tolCH₂) are combined with (p‐tol₃P)₂PtCl₂ortrans‐(p‐tol₃P)₂Pt((C≡C)₂H)₂to give the chelatescis‐(R₂C(CH₂PPh₂)₂)PtCl₂(2 a–f, 94–69 %) orcis‐(R₂C(CH₂PPh₂)₂)Pt((C≡C)₂H)₂(3 a–f, 97–54 %). Complexes3 a–dare also available from2 a–dand excess 1,3‐butadiyne in the presence of CuI (cat.) and excess HNEt₂(87–65 %). Under similar conditions,2and3react to give the title compounds [(R₂C(CH₂PPh₂)₂)[Pt(C≡C)₂]₄(4 a–f; 89–14 % (64 % avg)), from which ammonium salts such as the co‐product [H₂NEt₂]⁺Cl⁻are challenging to remove. Crystal structures of4 a,bshow skew rhombus as opposed to square Pt₄geometries. The NMR and IR properties of4 a–fare similar to those of mono‐ or diplatinum model compounds. However, cyclic voltammetry gives only irreversible oxidations. As compared to mono‐platinum or Pt(C≡C)₂Pt species, the UV‐visible spectra show much more intense and red‐shifted bands. Time dependent DFT calculations define the transitions and principal orbitals involved. Electrostatic potential surface maps reveal strongly negative Pt₄C₁₆cores that likely facilitate ammonium cation binding. Analogous electronic properties of Pt₃C₁₂and Pt₅C₂₀homologs and selected equilibria are explored computationally.