Nickel Catalyzed Vinylidene Insertions into O-H Bonds.
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ABSTRACT:
SUBMITTER: Kang H
PROVIDER: S-EPMC8115312 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:A nickel-catalyzed reductive cyclization of 1,1-dichloroalkenyl silanes is reported. The products of this reaction are unsaturated five- or six-membered silacycles. Intermolecular variants are also described, providing access to trisubstituted vinyl silanes that are not accessible by alkyne hydrosilylation or sila-Heck-type processes. A variety of silanes can be utilized, including those that serve as nucleophilic partners in Hiyama cross-coupling reactions. Mechanistic studies using deuterium-labelled silanes are described.
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Project description:While nickel catalysts have previously been shown to activate even the least reactive Csp2-O bonds, i.e. aryl ethers, in the context of C-C bond formation, little is known about the reactivity limits and molecular requirements for the introduction of valuable functional groups under homogeneous nickel catalysis. We identified that due to the high reactivity of Ni-catalysts, they are also prone to react with existing or installed functional groups, which ultimately causes catalyst deactivation. The scope of the Ni-catalyzed coupling protocol will therefore be dictated by the reactivity of the functional groups towards the catalyst. Herein, we showed that the application of computational tools allowed the identification of matching functional groups in terms of suitable leaving groups and tolerated functional groups. This allowed for the development of the first efficient protocol to trifluoromethylthiolate Csp2-O bonds, giving the mild and operationally simple C-SCF3 coupling of a range of aryl, vinyl triflates and nonaflates. The novel methodology was also applied to biologically active and pharmaceutical relevant targets, showcasing its robustness and wide applicability.
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Project description:We report the first catalytic method for activating the acyl C-O bonds of methyl esters through an oxidative-addition process. The oxidative-addition adducts, formed using nickel catalysis, undergo in?situ trapping to provide anilide products. DFT calculations are used to support the proposed reaction mechanism, to understand why decarbonylation does not occur competitively, and to elucidate the beneficial role of the substrate structure and the Al(OtBu)3 additive on the kinetics and thermodynamics of the reaction.
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Project description:Through the use of a catalyst formed in situ from NiBr(2)·diglyme and a pybox ligand (both of which are commercially available), we have achieved our first examples of coupling reactions of unactivated tertiary alkyl electrophiles, as well as our first success with nickel-catalyzed couplings that generate bonds other than C-C bonds. Specifically, we have determined that this catalyst accomplishes Miyaura-type borylations of unactivated tertiary, secondary, and primary alkyl halides with diboron reagents to furnish alkylboronates, a family of compounds with substantial (and expanding) utility, under mild conditions; indeed, the umpolung borylation of a tertiary alkyl bromide can be achieved at a temperature as low as -10 °C. The method exhibits good functional-group compatibility and is regiospecific, both of which can be issues with traditional approaches to the synthesis of alkylboronates. In contrast to seemingly related nickel-catalyzed C-C bond-forming processes, tertiary halides are more reactive than secondary or primary halides in this nickel-catalyzed C-B bond-forming reaction; this divergence is particularly noteworthy in view of the likelihood that both transformations follow an inner-sphere electron-transfer pathway for oxidative addition.
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Project description:The hydrogenolysis of the aromatic C-O bond in aryl ethers catalyzed by Ni was studied in decalin and water. Observations of a significant kinetic isotope effect (kH /kD =5.7) for the reactions of diphenyl ether under H2 and D2 atmosphere and a positive dependence of the rate on H2 chemical potential in decalin indicate that addition of H to the aromatic ring is involved in the rate-limiting step. All kinetic evidence points to the fact that H?addition occurs concerted with C-O bond scission. DFT calculations also suggest a route consistent with these observations involving hydrogen atom addition to the ipso position of the phenyl ring concerted with C-O scission. Hydrogenolysis initiated by H addition in water is more selective (ca. 75?%) than reactions in decalin (ca. 30?%).
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Project description:The first nickel bis-boryl complexes cis-[Ni( i Pr2ImMe)2(Bcat)2], cis-[Ni( i Pr2ImMe)2(Bpin)2] and cis-[Ni( i Pr2ImMe)2(Beg)2] are reported, which were prepared via the reaction of a source of [Ni( i Pr2ImMe)2] with the diboron(4) compounds B2cat2, B2pin2 and B2eg2 ( i Pr2ImMe = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene; B2cat2 = bis(catecholato)diboron; B2pin2 = bis(pinacolato)diboron; B2eg2 = bis(ethylene glycolato)diboron). X-ray diffraction and DFT calculations strongly suggest that a delocalized, multicenter bonding scheme dictates the bonding situation of the NiB2 moiety in these square planar complexes, reminiscent of the bonding situation of "non-classical" H2 complexes. [Ni( i Pr2ImMe)2] also efficiently catalyzes the diboration of alkynes using B2cat2 as the boron source under mild conditions. In contrast to the known platinum-catalyzed diboration, the nickel system follows a different mechanistic pathway, which not only provides the 1,2-borylation product in excellent yields, but also provides an efficient approach to other products such as C-C coupled borylation products or rare tetra-borylated compounds. The mechanism of the nickel-catalyzed alkyne borylation was examined by means of stoichiometric reactions and DFT calculations. Oxidative addition of the diboron reagent to nickel is not dominant; the first steps of the catalytic cycle are coordination of the alkyne to [Ni( i Pr2ImMe)2] and subsequent borylation at the coordinated and, thus, activated alkyne to yield complexes of the type [Ni(NHC)2(η2-cis-(Bcat)(R)C[double bond, length as m-dash]C(R)(Bcat))], exemplified by the isolation and structural characterization of [Ni( i Pr2ImMe)2(η2-cis-(Bcat)(Me)C[double bond, length as m-dash]C(Me)(Bcat))] and [Ni( i Pr2ImMe)2(η2-cis-(Bcat)(H7C3)C[double bond, length as m-dash]C(C3H7)(Bcat))].
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Project description:Poly(vinylidene fluoride) (PVDF) based ferroelectric polymers have attracted considerable attention both academically and industrially due to their tunable ferroelectric properties. By pinning the conformation of the polymer chain and the ferroelectric phase physically or chemically, the ferroelectric behaviors of PVDF based polymers could be finely turned from normal ferroelectric into relaxor ferroelectric, anti-ferroelectric like, and even linear dielectric. Besides high energy electron irradiation and chemical copolymerization with the bulky monomers, in this work, an alternative strategy is presented to regulate the dielectric and ferroelectric performances of PVDF based ferroelectric polymer for the first time. CH=CH bonds with the desired content are inserted by a controlled dehydrofluorination reaction into a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer (TrFE refers to trifluoroethylene) synthesized from the hydrogenation of P(VDF-CTFE) (CTFE refers to chlorothrifluoroethylene). The influence of the CH=CH bonds along with the fabrication conditions on the crystallization and ferroelectric relaxation of the resultant copolymers (referred to P(VDF-TrFE-DB)) was carefully characterized and discussed. The nonrotatable CH=CH bonds result in depressed dielectric and ferroelectric performances in the as-cast films by confining the orientation of ferroelectric grains in P(VDF-TrFE). The normal ferroelectric performance of P(VDF-TrFE) is turned into anti-ferroelectric like behavior in the resultant P(VDF-TrFE-DB). The cleavage of CH=CH bonds is responsible for the recovery of the ferroelectric behavior in the annealed samples. Uniaxial stretching favors the alignment of the polymer chain and ferroelectric domains, which may address the further regulated ferroelectric characters in the stretched samples.
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Project description:The development of Cu-catalyzed addition of carbon nucleophiles to vinylidene cyclopropanes was reported. The reactions with 1,1-bisborylmethane provided homopropargylic boronate products by forming a C-C bond at the terminal carbon atom of the allene moiety of vinylidene cyclopropanes. Alkynyl boronates are also suitable nucleophile precursors in reactions with vinylidene cyclopropanes, and skipped diynes were obtained in high yields. In addition, the Cu-enolate generated from the initial addition of nucleophilic copper species to vinylidene cyclopropanes can be intercepted by an external electrophile. As such, vinylidene cyclopropane serves as a linchpin to connect a nucleophile and an electrophile by forming two carbon-carbon bonds sequentially.
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