Activator-free single-component Co(<scp>i</scp>)-catalysts for regio- and enantioselective heterodimerization and hydroacylation reactions of 1,3-dienes. New reduction procedures for synthesis of [L]Co(<scp>i</scp>)-complexes and comparison to <i>in situ</i> generated catalysts

Parsutkar, Mahesh M.; Moore, Curtis E.; RajanBabu, T. V.

doi:10.1039/d2dt01484j

Cited by 7 publications

(12 citation statements)

References 61 publications

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“…We started the optimization studies with hydroboration of a prototypical 1,3-diene, ( E )-2-methyl 1,3-octadiene ( 1a ), using pinacolborane (HBPin) under conditions known to generate a cationic Co(I)-catalyst ( L CoBr 2 /Zn/NaBARF). , This reaction gave varying amounts of products corresponding to [4,3]-( 2a ), [4,1]-( 2b ), [1,4]-( 2c ), and [1,2]-( 2d ) addition of the borane (Table ). In a systematic examination of ligand effects, more than 40 ligands were explored, and the most significant results are shown in Table .…”

Section: Resultsmentioning

confidence: 99%

“…Systematic examination of solvents revealed that although methylene chloride and diethyl ether were acceptable, the latter was found to be the solvent of choice with minimal side reactions, especially for the formation of the [4,1]-adduct 2b with some of the ligands (vide infra). Among the activators, NaBARF was found to be the best choice for the generation of a cationic Co(I) intermediate, which is presumed to be the active catalyst in these reactions (SI(I), Tables S2–S3 (p S39)). , Examination of the results in Table reveals that unlike the phosphinooxazoline ligands that gave mostly the [1,2]-hydroboration product ( 2d ) irrespective of the substitution pattern of the phosphine on the oxazoline ring, chelating bis -phosphines have a dramatic effect on the regioselectivity of the hydroboration process depending on the backbone scaffolding. Most common achiral 1, n - bis -diarylphosphinoalkanes (dppm, dppe, dppp) and ligands like dpppbz, DPEPhos, and XantPhos gave the [1,2]-hydroboration product ( 2d ) in greater than 90% selectivity over other regioisomers (Table , entry 1).…”

Section: Resultsmentioning

confidence: 99%

“…The starting cobalt complex, [ P ∼ P ]CoBr 2 , when reduced by Zn in the presence of NaBARF makes a 12-electron cationic Co(I) complex, which is presumed to be the active catalyst in this reaction. The diene is a good candidate for binding with cobalt as it makes a stable 16-electron complex (Figure A) . Once this complex is formed, there is a possibility of an oxidative cyclization of the diene with the cobalt-bound catalyst [( P ∼ P )Co] + , thereby producing a five-membered cobaltacycle intermediate (Figure A).…”

Section: Resultsmentioning

confidence: 99%

“…The diene is a good candidate for binding with cobalt as it makes a stable 16-electron complex (Figure 7A). 37 Once this complex is formed, there is a possibility of an oxidative cyclization of the diene with the cobalt-bound catalyst [(P∼P)Co] + , thereby producing a five-membered cobaltacycle intermediate (Figure 7A). The formation of this complex could be followed by HBPin addition to form the products.…”

Section: Journal Of Thementioning

confidence: 99%

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Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes

et al. 2023

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Enantiopure homoallylic boronate esters are versatile intermediates because the C–B bond in these compounds can be stereospecifically transformed into C–C, C–O, and C–N bonds. Regio- and enantioselective synthesis of these precursors from 1,3-dienes has few precedents in the literature. We have identified reaction conditions and ligands for the synthesis of nearly enantiopure (er >97:3 to >99:1) homoallylic boronate esters via a rarely seen cobalt-catalyzed [4,3]-hydroboration of 1,3-dienes. Monosubstituted or 2,4-disubstituted linear dienes undergo highly efficient regio- and enantioselective hydroboration with HBPin catalyzed by [(L*)Co]+[BARF]−, where L* is typically a chiral bis-phosphine ligand with a narrow bite angle. Several such ligands (e.g., i-PrDuPhos, QuinoxP*, Duanphos, and BenzP*) that give high enantioselectivities for the [4,3]-hydroboration product have been identified. In addition, the equally challenging problem of regioselectivity is uniquely solved with a dibenzooxaphosphole ligand, (R,R)-MeO-BIBOP. A cationic cobalt(I) complex of this ligand is a very efficient (TON >960) catalyst while also providing excellent regioselectivities (rr >98:2) and enantioselectivities (er >98:2) for a broad range of substrates. A detailed computational investigation of the reactions using Co complexes from two widely different ligands (BenzP* and MeO-BIBOP) employing the B3LYP-D3 density functional theory provides key insights into the mechanism and the origins of selectivities. The computational results are in full agreement with the experiments. For the complexes we have examined thus far, the relative stabilities of the diastereomeric diene-bound complexes [(L*)Co(η4-diene)]+ lead to the initial diastereofacial selectivity, which in turn is retained in the subsequent steps, providing exceptional enantioselectivity for the reactions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Journal Of Thementioning

confidence: 99%

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Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes

et al. 2023

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“…All SCXRD structures associated with this work have been deposited with the CCDC [66] . Details of computational investigations and associated additional references are cited within the Supporting Information [74–102] …”

Section: Supporting Informationmentioning

confidence: 99%

P^I and P^III Ions Supported by BZIMPY Ligands

LaFortune,

Swidan,

Ovens

et al. 2023

Chemistry A European J

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We report a class of compounds in which both PIII‐X and PI forms featuring the same ligand are stable and readily cycled with each other. A series of PIII‐X (X = Cl, Br, I) dicationic triflate salts supported by benzyl‐ and allyl‐substituted 2,6‐bis(benzimidazole‐2‐yl)pyridine (BZIMPY) ligands is synthesized. Surprisingly, treatment of these with R3PO (R = Et, Oct) results in reduction to BZIMPY‐ligated PI monocationic triflate salts while treatment with Ph3P reduces but also substitutes the compound to produce Ph3P‐BZIMPY‐ligated PI dicationic triflate salts. The mechanisms of these surprising reductions are probed experimentally and rationalized computationally. The PIII‐X dications are shown to be strong Lewis acids both experimentally and computationally and to readily behave as X+, PX, and P+ transfer agents in reactions with phosphines, NHCs, and diazabutadienes. The PI mono‐ and dications are shown to be very effective P+ transfer agents when treated similarly. Oxidation from a monocationic PI salt back to the dicationic PIII‐X (X = Cl, Br) salt was achieved by treatment with N‐chlorosuccinimide (NCS) or N‐bromosuccinimide (NBS). Full characterization is reported using multinuclear nuclear magnetic resonance spectroscopy, elemental analysis, and single crystal X‐ray diffractometry where suitable crystals were isolated.

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Experimental and Computational Studies on Cobalt(I)‐Catalyzed Regioselective Allylic Alkylation Reactions

Andreetta,

Martin,

Souilah

et al. 2023

Angewandte Chemie

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Here, we report the development of cobalt(I)‐catalyzed regioselective allylic alkylation reactions of tertiary allyl carbonates with 1,3‐dicarbonyl compounds. A family of well‐defined tetrahedral cobalt(I) complexes bearing commercially available bidentate bis(phosphine) ligands [(P,P)Co(PPh3)Cl] are synthesized and explored as catalysts in allylic alkylation reactions. The catalyst [(dppp)Co(PPh3)Cl] (dppp = 1,3‐Bis(diphenylphosphino)propane) enables the alkylation of a large variety of tertiary allyl carbonates with high yields and excellent regioselectivity for the branched product. Remarkably, this methodology is selective for the activation of tertiary allyl carbonates even in the presence of secondary allyl carbonates. This contrasts with the selectivity observed in cobalt‐catalyzed allylic alkylations enabled by visible light photocatalysis. Mechanistic insights by means of experimental and computational investigations support a Co(I)/Co(III) catalytic cycle.

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Activator-free single-component Co(i)-catalysts for regio- and enantioselective heterodimerization and hydroacylation reactions of 1,3-dienes. New reduction procedures for synthesis of [L]Co(i)-complexes and comparison to in situ generated catalysts

Abstract: New synthesis of (L)[CoIX]-complexes from (L)CoX2 and Mashima's reagent.

Cited by 7 publications

References 61 publications

Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes

Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes

P^I and P^III Ions Supported by BZIMPY Ligands

Experimental and Computational Studies on Cobalt(I)‐Catalyzed Regioselective Allylic Alkylation Reactions

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Activator-free single-component Co(i)-catalysts for regio- and enantioselective heterodimerization and hydroacylation reactions of 1,3-dienes. New reduction procedures for synthesis of [L]Co(i)-complexes and comparison to in situ generated catalysts

Abstract: New synthesis of (L)[CoIX]-complexes from (L)CoX2 and Mashima's reagent.

Cited by 7 publications

References 61 publications

Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes

Ligand Control in Co-Catalyzed Regio- and Enantioselective Hydroboration: Homoallyl Secondary Boronates via Uncommon 4,3-Hydroboration of 1,3-Dienes

PI and PIII Ions Supported by BZIMPY Ligands

Experimental and Computational Studies on Cobalt(I)‐Catalyzed Regioselective Allylic Alkylation Reactions

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P^I and P^III Ions Supported by BZIMPY Ligands