Platinum Elimination from Bis(triethylsilylpolyynyl) Complexes (n‐Bu₂C(CH₂PPh₂)₂)Pt((C≡C)_nSiEt₃)₂ (n=2, 3) and Macrocycles Comprised of Four L₂Pt Corners and Four C≡CC≡CC≡C Linkers; An Approach to Cyclo[24]carbon

The overarching goal of this study is to effect the elimination of platinum from adducts with cis –C≡C−Pt−C≡C‐ linkages, thereby generating novel conjugated polyynes. Thus, the bis(hexatriynyl) complex trans‐(p‐tol3P)2Pt((C≡C)3H)2 is treated with 1,3‐diphosphines R2C(CH2PPh2)2 to 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 HNEt2 to 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 to 14 c. They react with I2 at rt to give mainly the diiodide complex 9 c and the coupling product Et3Si(C≡CC≡C)nSiEt3. The possibility of competing reactions giving IC≡C species is investigated. Analogous reactions of the Pt4C24 macrocycle 16 c also give 9 c, but no sp 13C NMR signals or mass spectrometric Cxz+ 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 PtO2 and H2. [ABSTRACT FROM AUTHOR]