Platinum Elimination from Bis(triethylsilylpolyynyl) Complexes (n-BuC(CHPPh))Pt((C≡C)SiEt) (n=2, 3) and Macrocycles Comprised of Four LPt 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-tolP)Pt((C≡C)H) is treated with 1,3-diphosphines RC(CHPPh) to generate (RC(CHPPh))Pt((C≡C)H) (14; R=c, n-Bu; e, p-tolCH). These condense with the diiodide complexes RC(CHPPh)PtI (9 a,c) in the presence of CuI (cat.) and excess HNEt to give the title macrocycles [(RC(CHPPh))Pt(C≡C)] (16 c,e) as adducts of the byproduct [HNEt] 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-BuC(CHPPh))Pt((C≡C)SiEt) (n=2, 3) are synthesized analogously to 14 c. They react with I at rt to give mainly the diiodide complex 9 c and the coupling product EtSi(C≡CC≡C)SiEt. The possibility of competing reactions giving IC≡C species is investigated. Analogous reactions of the PtC macrocycle 16 c also give 9 c, but no sp C NMR signals or mass spectrometric C 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 (CH) is detected when this sequence is carried out in the presence of PtO and H.