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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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Sustainable Pd(OAc) 2 /Hydroquinone Cocatalyst System for Cis ‐Selective Dibenzoyloxylation of 1,3‐Cyclohexadiene
Abstract The 1,4‐diacyloxylation of 1,3‐cyclohexadiene (CHD) affords valuable stereochemically defined scaffolds for natural product and pharmaceutical synthesis. Existingcis‐selective diacyloxylation protocols require superstoichiometric quantities of benzoquinone (BQ) or MnO2, which limit process sustainability and large‐scale application. In this report, reaction development and mechanistic studies are described that overcome these limitations by pairing catalytic BQ withtert‐butyl hydroperoxide as the stoichiometric oxidant. Catalytic quantities of bromide enable a switch fromtranstocisdiastereoselectivity. A catalyst with a 1:2 Pd:Br ratio supports highcisselectivity while retaining good rate and product yield. Further studies enable replacement of BQ with hydroquinone (HQ) as a source of cocatalyst, avoiding the handling of volatile and toxic BQ in large‐scale applications.
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- Award ID(s):
- 1953926
- PAR ID:
- 10306968
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 43
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 23182-23186
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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