Chloride abstraction from [(
Chloride abstraction from [(
- NSF-PAR ID:
- 10102568
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 131
- Issue:
- 27
- ISSN:
- 0044-8249
- Page Range / eLocation ID:
- p. 9292-9296
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract R ,R )‐(iPrDuPhos)Co(μ‐Cl)]2with NaBArF4(BArF4=B[(3,5‐(CF3)2)C6H3]4) in the presence of dienes, such as 1,5‐cyclooctadiene (COD) or norbornadiene (NBD), yielded long sought‐after cationic bis(phosphine) cobalt complexes, [(R ,R )‐(iPrDuPhos)Co(η2,η2‐diene)][BArF4]. The COD complex proved substitutionally labile undergoing diene substitution with tetrahydrofuran, NBD, or arenes. The resulting 18‐electron, cationic cobalt(I) arene complexes, as well as the [(R ,R )‐(iPrDuPhos)Co(diene)][BArF4] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt–substrate complex, [(R ,R )‐(iPrDuPhos)Co(MAA)][BArF4] (MAA=methyl 2‐acetamidoacrylate) was crystallographically characterized as the opposite diastereomer to that expected for productive hydrogenation demonstrating a Curtin–Hammett kinetic regime similar to rhodium catalysis. -
null (Ed.)Diene self-exchange reactions of the 17-electron, formally cobalt(0) cyclooctadienyl precatalyst, (R,R)-(iPrDuPhos)Co(COD) (P2CoCOD, (R,R)-iPrDuPhos = 1,2-bis((2R,5R)-2,5-diisopropylphospholano)benzene, COD = 1,5-cyclooctadiene) were studied using natural abundance and deuterated 1,5-cyclooctadiene. Exchange of free and coordinated diene was observed at ambient temperature in benzene-d6 solution and kinetic studies support a dissociative process. Both neutral P2CoCOD and the 16-electron, cationic cobalt(I) complex, [(R,R)-(iPrDuPhos)Co(COD)][BArF4] (BArF4 = B[(3,5-(CF3)2)C6H3]4) underwent instantaneous displacement of the 1,5-cyclooctadiene ligand by carbon monoxide and generated the corresponding carbonyl derivatives. The solid-state parameters, DFT-computed Mulliken spin density and analysis of molecular orbitals suggest an alternative description of P2CoCOD as low-spin cobalt(II) with the 1,5-cyclooctadiene acting as a LX2-type ligand. This view of the electronic structure provides insight into the nature of the ligand substitution process and the remarkable stability of the neutral cobalt complexes toward protic solvents observed during catalytic alkene hydrogenation.more » « less
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Abstract Intermediates relevant to cobalt‐catalyzed alkene hydroformylation have been isolated and evaluated in fundamental organometallic transformations relevant to aldehyde formation. The 18‐electron (
R ,R )‐(iPrDuPhos)Co(CO)2H has been structurally characterized, and it promotes exclusive hydrogenation of styrene in the presence of 50 bar of H2/CO gas (1:1) at 100 °C. Deuterium‐labeling studies established reversible 2,1‐insertion of styrene into the Co−D bond of (R ,R )‐(iPrDuPhos)Co(CO)2D. Whereas rapid β‐hydrogen elimination from cobalt alkyls occurred under an N2atmosphere, alkylation of (R ,R )‐(iPrDuPhos)Co(CO)2Cl in the presence of CO enabled the interception of (R ,R )‐(iPrDuPhos)Co(CO)2C(O)CH2CH2Ph, which upon hydrogenolysis under 4 atm H2produced the corresponding aldehyde and cobalt hydride, demonstrating the feasibility of elementary steps in hydroformylation. Both the hydride and chloride derivatives, (X=H−, Cl−), underwent exchange with free13CO. Under reduced pressure, (R ,R )‐(iPrDuPhos)Co(CO)2Cl underwent CO dissociation to form (R ,R )‐(iPrDuPhos)Co(CO)Cl. -
Abstract Intermediates relevant to cobalt‐catalyzed alkene hydroformylation have been isolated and evaluated in fundamental organometallic transformations relevant to aldehyde formation. The 18‐electron (
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