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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 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 PtO2and H2.
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Bench‐Stable Dinuclear Mn(I) Catalysts in E ‐Selective Alkyne Semihydrogenation: A Mechanistic Investigation**
Abstract Dinuclear manganese hydride complexes of the form [Mn2(CO)8(μ‐H)(μ‐PR2)] (R=Ph,1; R=iPr,2) were used inE‐selective alkyne semi‐hydrogenation (E‐SASH) catalysis. Catalyst speciation studies revealed rich coordination chemistry and the complexes thus formed were isolated and in turn tested as catalysts; the results underscore the importance of dinuclearity in engendering the observedE‐selectivity and provide insights into the nature of the active catalyst. The insertion product obtained from treating2with (cyclopropylethynyl)benzene contains acis‐alkenyl bridging ligand with the cyclopropyl ring being intact. Treatment of this complex with H2affords exclusivelytrans‐(2‐cyclopropylvinyl)benzene. These results, in addition to other control experiments, indicate a non‐radical mechanism forE‐SASH, which is highly unusual for Mn−H catalysts. The catalytically active species are virtually inactive towardscistotransalkene isomerization indicating that theE‐selective process is intrinsic and dinuclear complexes play a critical role. A reaction mechanism is proposed accounting for the observed reactivity which is fully consistent with a kinetic analysis of the rate limiting step and is further supported by DFT computations.
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- Award ID(s):
- 1919594
- PAR ID:
- 10372502
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 28
- Issue:
- 53
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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