The synthesis and characterization of (tBuPBP)Ni(OAc) (
- NSF-PAR ID:
- 10316910
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 12
- Issue:
- 27
- ISSN:
- 2041-6520
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 5 ) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe (1 ) is presented. An unexpected CO2cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (tBuPBOP)2Ni4(μ‐CO)2(6 ). Mechanistic investigation of this reaction indicates a reductive scission of CO2by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO2activation reaction produces a three‐coordinate (tBuP2BO)Ni‐acyl intermediate (A ) that leads to a (tBuP2BO)−NiIcomplex (B ) via a likely radical pathway. The NiIspecies is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (tBuP2BO)NiII(η2‐TEMPO) (7 ). Additionally,13C and1H NMR spectroscopy analysis using13C‐enriched CO2provides information about the species involved in the CO2activation process. -
Abstract The synthesis and characterization of (tBuPBP)Ni(OAc) (
5 ) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe (1 ) is presented. An unexpected CO2cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (tBuPBOP)2Ni4(μ‐CO)2(6 ). Mechanistic investigation of this reaction indicates a reductive scission of CO2by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO2activation reaction produces a three‐coordinate (tBuP2BO)Ni‐acyl intermediate (A ) that leads to a (tBuP2BO)−NiIcomplex (B ) via a likely radical pathway. The NiIspecies is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (tBuP2BO)NiII(η2‐TEMPO) (7 ). Additionally,13C and1H NMR spectroscopy analysis using13C‐enriched CO2provides information about the species involved in the CO2activation process. -
Abstract Allylation of nucleophiles with highly reactive electrophiles like allyl halides can be conducted without metal catalysts. Less reactive electrophiles, such as allyl esters and carbonates, usually require a transition metal catalyst to facilitate the allylation. Herein, we report a unique transition-metal-free allylation strategy with allyl ether electrophiles. Reaction of a host of allyl ethers with 2-azaallyl anions delivers valuable homoallylic amine derivatives (up to 92%), which are significant in the pharmaceutical industry. Interestingly, no deprotonative isomerization or cyclization of the products were observed. The potential synthetic utility and ease of operation is demonstrated by a gram scale telescoped preparation of a homoallylic amine. In addition, mechanistic studies provide insight into these C(sp 3 )–C(sp 3 ) bond-forming reactions.more » « less
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Abstract Allylation and conjunctive cross‐coupling represent two useful, yet largely distinct, reactivity paradigms in catalysis. The union of these two processes would offer exciting possibilities in organic synthesis but remains largely unknown. Herein, we report the use of allyl electrophiles in nickel‐catalyzed conjunctive cross‐coupling with a non‐conjugated alkene and dimethylzinc. The transformation is enabled by weakly coordinating, monodentate aza‐heterocycle directing groups that are useful building blocks in synthesis, including saccharin, pyridones, pyrazoles, and triazoles. The reaction occurs under mild conditions and is compatible with a wide range of allyl electrophiles. High chemoselectivity through substrate directivity is demonstrated by the facile reactivity of the β‐γ alkene of the starting material, whereas the ϵ‐ζ alkene of the product is preserved. The generality of this approach is further illustrated through the development of an analogous method with alkyne substrates. Mechanistic studies reveal the importance of the dissociation of the weakly coordinating directing group to allow the allyl moiety to bind and facilitate C(sp3)−C(sp3) reductive elimination.
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