Publications
175 results found
Kong RY, Crimmin MR, 2021, Chemoselective C−C σ‐Bond Activation of the Most Stable Ring in Biphenylene**, Angewandte Chemie, Vol: 133, Pages: 2651-2655, ISSN: 0044-8249
<jats:title>Abstract</jats:title><jats:p>The chemoselective cleavage of a six‐membered aromatic ring in biphenylene is reported using an aluminum(I) complex. This type of selectivity is unprecedented. In every example of transition metal mediated C−C σ‐bond activation reported to date, the reaction occurs at the central four‐membered ring of biphenylene. Insight into the origin of chemoselectivity was obtained through a detailed mechanistic analysis (isolation of an intermediate, DFT studies, activation strain analysis). In conclusion, the divergent reactivity can be attributed to differences in both the symmetry and radial extension of the frontier molecular orbitals of the aluminum(I) fragment compared to that of common transition metal fragments.</jats:p>
Kong RY, Crimmin MR, 2020, Cooperative strategies for CO homologation, DALTON TRANSACTIONS, Vol: 49, ISSN: 1477-9226
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- Citations: 30
Mulryan D, White AJP, Crimmin MR, 2020, Organocatalyzed fluoride metathesis, Organic Letters, Vol: 22, Pages: 9351-9355, ISSN: 1523-7060
A new organocatalyzed fluoride metathesis reaction between fluoroarenes and carbonyl derivatives is reported. The reaction exchanges fluoride (F–) and alternate nucleophiles (OAc–, OCO2R–, SR–, Cl–, CN–, NCS–). The approach provides a conceptually novel route to manipulate the fluorine content of organic molecules. When the fluorination and defluorination steps are combined into a single catalytic cycle, a byproduct free and 100% atom-efficient reaction can be achieved.
Sheldon DJ, Coates G, Crimmin MR, 2020, Defluorosilylation of trifluoromethane: upgrading an environmentally damaging fluorocarbon, CHEMICAL COMMUNICATIONS, Vol: 56, Pages: 12929-12932, ISSN: 1359-7345
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- Citations: 7
Kong RY, Crimmin M, 2020, Chemoselective C–C σ-Bond Activation of Biphenylene
<jats:p>The chemoselective cleavage of an arene ring in biphenylene is reported using an aluminium(I) complex. The reaction proceeds with complete integrity of the central 4-membered ring despite this ring containing the weakest C–C σ-bond in the hydrocarbon scaffold. A reaction intermediate derived from the (4+1) cycloaddition of the aluminium(I) complex to the p-system of biphenylene was isolated. Further experiments and DFT calculations suggest that this intermediate is involved in breaking of the C–C σ-bond. Activation strain analysis was used to understand the origins of the remarkable chemoselectivity of this system. Both the symmetry and diffuseness of the frontier molecular orbitals of the aluminium(I) fragment are implicated in its unusual reactivity with biphenylene.</jats:p>
Crimmin M, Mulryan D, White AJP, 2020, Organocatalyzed Fluoride Metathesis
<jats:p>A new organocatalyzed fluoride metathesis reaction between fluoroarenes and carbonyl derivatives is reported. The reaction exchanges fluoride (F–) and alternate nucleophiles (OAc–, CO2R–, SR–, Cl–, CN–, NCS–). The approach provides a conceptually novel route to manipulate the fluorine content of organic molecules. By combining fluorination and defluorination steps into a single catalytic cycle, a byproduct free and 100% atom-efficient reaction can be achieved.</jats:p>
Kong RY, Crimmin M, 2020, The Chemoselective C–C σ-Bond Activation of the Arene Ring of Biphenylene
<jats:p>The chemoselective cleavage of an arene ring in biphenylene is reported using an aluminium(I) complex. The reaction proceeds with complete integrity of the central 4-membered ring despite this ring containing the weakest C–C σ-bond in the hydrocarbon scaffold. A reaction intermediate derived from the (4+1) cycloaddition of the aluminium(I) complex to the p-system of biphenylene was isolated. Further experiments and DFT calculations suggest that this intermediate is involved in breaking of the C–C σ-bond. Activation strain analysis was used to understand the origins of the remarkable chemoselectivity of this system. Both the symmetry and diffuseness of the frontier molecular orbitals of the aluminium(I) fragment are implicated in its unusual reactivity with biphenylene.</jats:p>
Sheldon D, Coates G, Crimmin M, 2020, Defluorosilylation of Trifluoromethane: Upgrading an Environmentally Damaging Fluorocarbon
<jats:p>The rapid, room-temperature defluorosilylation of trifluoromethane, a highly potent greenhouse gas, has been achieved using a simple silyl lithium reagent. An extensive computational mechanistic analysis provides a viable reaction pathway and demonstrates the unexpected electrophilic nature of LiCF<jats:sub>3</jats:sub>. The reaction generates a bench stable fluorinated building block that shows promise as an easy-to-use difluoromethylating agent. The difluoromethyl group is an increasingly important bioisostere in active pharmaceutical ingredients, and therefore our methodology creates value from waste. The potential scalability of the process has been demonstrated by achieving the reaction on a gram-scale.</jats:p>
Rekhroukh F, Chen W, Brown RK, et al., 2020, Palladium-catalysed C-F alumination of fluorobenzenes: mechanistic diversity and origin of selectivity, CHEMICAL SCIENCE, Vol: 11, Pages: 7842-7849, ISSN: 2041-6520
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- Citations: 15
Hooper TN, Brown RK, Rekhroukh F, et al., 2020, Catalyst control of selectivity in the C-O bond alumination of biomass derived furans, CHEMICAL SCIENCE, Vol: 11, Pages: 7850-7857, ISSN: 2041-6520
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- Citations: 10
Kong RY, Crimmin MR, 2020, Activation and functionalization of C–C σ-Bonds of alkylidene cyclopropanes at main group centers, Journal of the American Chemical Society, Vol: 142, Pages: 11967-11971, ISSN: 0002-7863
Aluminum(I) and magnesium(I) compounds are reported for the C–C σ-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C–C σ-bond to main group center either at a single site (Al) or across a metal–metal bond (Mg–Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to α- or β-alkyl migration steps that break the C–C σ-bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C–C σ-bonds of alkylidene cyclopropanes.
hooper TN, Brown R, Rekhroukh F, et al., 2020, Catalyst Control of Selectivity in the C–O Bond Alumination of Biomass Derived Furans
<jats:p>Non-catalysed and catalysed reactions of aluminium reagents with furans, dihydrofurans and dihydropyrans were investigated and lead to the ring-expanded products due to the formal insertion of the aluminium reagent into a C–O bond of the heterocycle. Specifically, the reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with furan, 2-methylfuran, 2,3-dimethylfuran and 2-methoxyfuran proceeded between 25 and 80 ºC leading to ring-expanded and dearomatised products due to the net transformation of a sp2 C–O bond into a sp2 C–Al bond. The kinetics of the reaction of 1 with furan were found to be 1st order with respect to 1 with activation parameters ΔH‡ = +19.7 (± 2.7) kcal mol-1, ΔS‡ = –18.8 (± 7.8) cal K-1 mol-1 and ΔG‡298 K = +25.3 (± 0.5) kcal mol-1 and a KIE of 1.0 ± 0.1. DFT calculations support a stepwise mechanism involving an initial (4+1) cycloaddition of 1 with furan to form a bicyclic intermediate that rearranges by an a-migration. The selectivity of ring-expansion is influenced by factors that weaken the sp2 C–O bond through population of the s*-orbital. Inclusion of [Pd(PCy3)2] as a catalyst in these reactions results in expansion of the substrate scope to include 2,3-dihydrofurans and 3,4-dihydropyrans but also improves the selectivity. Under catalysed conditions, the C–O bond that breaks is that adjacent to C–H bond. The aluminium(III) dihydride reagent [{(MesNCMe)2CH}AlH2] (Mes = 2,4,6-trimethylphenyl, 2) can also be used under catalytic conditions to effect a dehydrogenative ring-expansion of furans. Further mechanistic analysis of the Pd-catalysed reaction of 1 with furan shows that C–O bond functionalisation occurs via an initial C–H bond alumination. Kinetic products can be isolated that are derived from installation of the aluminium reagent at the 2-position of the heterocycle. C–H alumination
Phillips NA, Coates GJ, White AJP, et al., 2020, Defluoroalkylation of sp(3) C-F bonds of industrially relevant hydrofluoroolefins, Chemistry: A European Journal, Vol: 26, Pages: 5365-5368, ISSN: 0947-6539
A simple, one‐pot procedure is reported for the selective defluoroalkylation of trifluoromethyl alkene derivatives with aldehydes and ketones. The reaction sequence allows construction of a new C−C bond in a highly selective manner from a single sp3 C−F bond of a CF3 group in the presence of sp2 C−F bonds. The scope incorporates industrially relevant fluorocarbons including HFO‐1234yf and HFO‐1234ze. No catalyst, additives or transition metals are required, rather the methodology relies on a recently developed boron reagent. Remarkably, the boron site of this reagent plays a dual role in the reaction sequence, being nucleophilic at boron in the C−F cleavage step (SN2’) but electrophilic at boron en route to the carbon–carbon bond‐forming step (SE2’). The duplicitous behaviour is underpinned by a hydrogen atom migration from boron to the carbon atom of a carbene ligand.
hooper TN, Brown R, Rekhroukh F, et al., 2020, Catalyst Control of Selectivity in the C–O Bond Alumination of Biomass Derived Furans
<jats:p>Non-catalysed and catalysed reactions of aluminium reagents with furans, dihydrofurans and dihydropyrans were investigated and lead to the ring-expanded products due to the formal insertion of the aluminium reagent into a C–O bond of the heterocycle. Specifically, the reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with furan, 2-methylfuran, 2,3-dimethylfuran and 2-methoxyfuran proceeded between 25 and 80 ºC leading to ring-expanded and dearomatised products due to the net transformation of a sp2 C–O bond into a sp2 C–Al bond. The kinetics of the reaction of 1 with furan were found to be 1st order with respect to 1 with activation parameters ΔH‡ = +19.7 (± 2.7) kcal mol-1, ΔS‡ = –18.8 (± 7.8) cal K-1 mol-1 and ΔG‡298 K = +25.3 (± 0.5) kcal mol-1 and a KIE of 1.0 ± 0.1. DFT calculations support a stepwise mechanism involving an initial (4+1) cycloaddition of 1 with furan to form a bicyclic intermediate that rearranges by an a-migration. The selectivity of ring-expansion is influenced by factors that weaken the sp2 C–O bond through population of the s*-orbital. Inclusion of [Pd(PCy3)2] as a catalyst in these reactions results in expansion of the substrate scope to include 2,3-dihydrofurans and 3,4-dihydropyrans but also improves the selectivity. Under catalysed conditions, the C–O bond that breaks is that adjacent to C–H bond. The aluminium(III) dihydride reagent [{(MesNCMe)2CH}AlH2] (Mes = 2,4,6-trimethylphenyl, 2) can also be used under catalytic conditions to effect a dehydrogenative ring-expansion of furans. Further mechanistic analysis of the Pd-catalysed reaction of 1 with furan shows that C–O bond functionalisation occurs via an initial C–H bond alumination. Kinetic products can be isolated that are derived from installation of the aluminium reagent at the 2-position of the heterocycle. C–H alumination
Crimmin M, Kong RY, 2020, Activation and Functionalization of C–C σ-Bonds of Alkylidene Cyclopropanes at Main Group Centers
<jats:p>Aluminum(I) and magnesium(I) compounds are reported for the C–C s-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C–C s-bond to main group center either at a single site (Al) or across a metal–metal bond (Mg–Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to a- or b-alkyl migration steps that break the C–C s-bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C–C s-bonds of alkylidene cyclopropanes.</jats:p>
Bakewell C, Garçon M, Kong RY, et al., 2020, Reactions of an aluminum(I) reagent with 1,2-, 1,3-, and 1,5-dienes: dearomatization, reversibility, and a pericyclic mechanism, Inorganic Chemistry, Vol: 59, ISSN: 0020-1669
Addition of the aluminum(I) reagent [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) to a series of cyclic and acyclic 1,2-, 1,3-, and 1,5-dienes is reported. In the case of 1,3-dienes, the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene-containing products. This mechanism has been examined by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4 + 1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4 + 1) cycloaddition includes styene, 1,1-diphenylethylene, and anthracene. In these cases, the diene motif is either in part, or entirely, contained within an aromatic ring and reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2-cyclononadiene or 1,5-cyclooctadiene, complementary reactivity is observed; the orthogonal nature of the C═C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavor a (4 + 1) cycloaddition. Rather, reaction pathways are determined by an initial (2 + 1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C═C π-bond, leading to complex organometallic products that incorporate fused hydrocarbon rings.
hooper TN, Brown R, Rekroukh F, et al., 2020, Catalyst Control of Selectivity in the C–O Bond Alumination of Biomass Derived Furans
<jats:p>Non-catalysed and catalysed reactions of aluminium reagents with furans, dihydrofurans and dihydropyrans were investigated and lead to the ring-expanded products due to the formal insertion of the aluminium reagent into a C–O bond of the heterocycle. Specifically, the reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with furan, 2-methylfuran, 2,3-dimethylfuran and 2-methoxyfuran proceeded between 25 and 80 ºC leading to ring-expanded and dearomatised products due to the net transformation of a sp2 C–O bond into a sp2 C–Al bond. The kinetics of the reaction of 1 with furan were found to be 1st order with respect to 1 with activation parameters ΔH‡ = +19.7 (± 2.7) kcal mol-1, ΔS‡ = –18.8 (± 7.8) cal K-1 mol-1 and ΔG‡298 K = +25.3 (± 0.5) kcal mol-1 and a KIE of 1.0 ± 0.1. DFT calculations support a stepwise mechanism involving an initial (4+1) cycloaddition of 1 with furan to form a bicyclic intermediate that rearranges by an a-migration. The selectivity of ring-expansion is influenced by factors that weaken the sp2 C–O bond through population of the s*-orbital. Inclusion of [Pd(PCy3)2] as a catalyst in these reactions results in expansion of the substrate scope to include 2,3-dihydrofurans and 3,4-dihydropyrans but also improves the selectivity. Under catalysed conditions, the C–O bond that breaks is that adjacent to C–H bond. The aluminium(III) dihydride reagent [{(MesNCMe)2CH}AlH2] (Mes = 2,4,6-trimethylphenyl, 2) can also be used under catalytic conditions to effect a dehydrogenative ring-expansion of furans. Further mechanistic analysis of the Pd-catalysed reaction of 1 with furan shows that C–O bond functionalisation occurs via an initial C–H bond alumination. Kinetic products can be isolated that are derived from installation of the aluminium reagent at the 2-position of the heterocycle. C–H alumination
Rekhroukh F, Chen W, Brown R, et al., 2020, Palladium-Catalysed C–F Alumination of Fluorobenzenes: Mechanistic Diversity and Origin of Selectivity
<jats:p>A palladium pre-catalyst, [Pd(PCy<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub>] is reported for the efficient and selective C–F alumination of fluorobenzenes with the aluminium(I) reagent [{(ArNCMe)<jats:sub>2</jats:sub>CH}Al] (<jats:bold>1</jats:bold>, Ar = 2,6-di-iso-propylphenyl). The catalytic protocol results in the transformation of sp<jats:sup>2</jats:sup> C–F bonds to sp<jats:sup>2</jats:sup> C–Al bonds and provides a route into reactive organoaluminium complexes (<jats:bold>2a-h</jats:bold>) from fluorocarbons. The catalyst is highly active. Reactions proceed within 5 minutes at 25 ºC (and at appreciable rates at even –50 ºC) and the scope includes low-fluorine-content substrates such as fluorobenzene, difluorobenzenes and trifluorobenzenes. The reaction proceeds with complete chemoselectivity (C–F vs C–H) and high regioselectivities ( >90% for C–F bonds adjacent to the most acidic C–H sites). The heterometallic complex [Pd(PCy<jats:sub>3</jats:sub>)(<jats:bold>1</jats:bold>)<jats:sub>2</jats:sub>] was shown to be catalytically competent. Catalytic C–F alumination proceeds with a KIE of 1.1–1.3. DFT calculations have been used to model potential mechanisms for C–F bond activation. These calculations suggest that two competing mechanisms may be in operation. Pathway 1 involves a ligand-assisted oxidative addition to [Pd(<jats:bold>1</jats:bold>)<jats:sub>2</jats:sub>] and leads directly to the product. Pathway 2 involves a stepwise C–H to C–F functionalisation mechanism in which the C–H bond is broken and reformed along the reaction coordinate, allowing it to act as a directing group for the adjacent C–F site. This second mechanism explains the experimentally observed regioselectivity. Experimental
Crimmin M, Kong RY, 2020, Activation and Functionalization of C–C σ-Bonds of Alkylidene Cyclopropanes at Main Group Centers
<jats:p>Aluminum(I) and magnesium(I) compounds are reported for the C–C s-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C–C s-bond to main group center either at a single site (Al) or across a metal–metal bond (Mg–Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to a- or b-alkyl migration steps that break the C–C s-bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C–C s-bonds of alkylidene cyclopropanes.</jats:p>
Bakewell C, Garçon M, Kong RY, et al., 2019, Reactions of an Aluminium(I) Reagent with 1,2-, 1,3- and 1,5-Dienes: Dearomatisation, Reversibility, and a Pericyclic Mechanism
<jats:p>The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.</jats:p>
Coates G, Rekhroukh F, Crimmin MR, 2019, Breaking carbon–fluorine bonds with main group nucleophiles, Synlett, Vol: 30, Pages: A-N, ISSN: 0936-5214
In this Account we describe a series of new reactions that we, and others, have reported that involve the transformation of C–F bonds into C–Mg, C–Al, C–Si, C–Fe and C–Zn bonds. We focus on the use of highly reactive main group nucleophiles and discuss aspects of reaction scope, selectivity and mechanism.
Garçon M, George S, Clare B, et al., 2019, A hexagonal planar transition-metal complex, Nature, Vol: 574, Pages: 390-393, ISSN: 0028-0836
Transition metal complexes are widely applied in the physical and biological sciences. They play pivotal roles in aspects of catalysis, synthesis,materials science, photophysics and bioinorganic chemistry.Our understanding of transition metal complexes originates from Alfred Werner’s realisation that their three-dimensional shape influences their properties and reactivity.1The intrinsic link between shape and electronic structure is now firmly underpinned by molecular orbital theory.2-5Despite over a century of advances in this field, transition metal complexes remain limited to a handful of well understood geometries. Archetypal geometriesfor six-coordinate transition metals are octahedral andtrigonal prismatic. Although deviations from idealbond angles and lengths are common,6alternativeparent geometries are staggeringly rare.7Hexagonal planar transition metalsare restricted to those found in condensed metallic phases,8the hexagonal pores of coordination polymers,9orclusters containing more than one transition metal in close proximity.10,11Although [Ni(PtBu)6] could beassignedas a hexagonal planar complex,12,13a molecular orbital analysis ultimately led to the conclusion that it is best described as a 16-electron complex with a trigonal planar geometry.14Here we report the isolation and structural characterisation of the first simple coordination complex in which six ligands form bonds with a central transition metal in a hexagonal planar arrangement.The discovery has the potential to open up new design principles and new ways of thinking about transition metal complexes which could impact multiple fields of science.
Hooper TN, Lau S, Chen W, et al., 2019, The partial dehydrogenation of aluminium dihydrides, Chemical Science, Vol: 10, Pages: 8083-8093, ISSN: 2041-6520
The reactions of a series of β-diketiminate stabilised aluminium dihydrides with ruthenium bis(phosphine), palladium bis(phosphine) and palladium cyclopentadienyl complexes is reported. In the case of ruthenium, alane coordination occurs with no evidence for hydrogen loss resulting in the formation of ruthenium complexes with a pseudo–octahedral geometry and cis-relation of phosphine ligands. These new ruthenium complexes have been characterised by multinuclear and variable temperature NMR spectroscopy, IR spectroscopy and single crystal X-ray diffraction. In the case of palladium, a series of structural snapshots of alane dehydrogenation have been isolated and crystallographically characterised. Variation of the palladium precursor and ligand on aluminium allows kinetic control over reactivity and isolation of intermetallic complexes that contain new Pd–Al and Pd–Pd interactions. These complexes differ by the ratio of H : Al (2 : 1, 1.5 : 1 and 1 : 1) with lower hydride content species forming with dihydrogen loss. A combination of X-ray and neutron diffraction studies have been used to interrogate the structures and provide confidence in the assignment of the number and position of hydride ligands. 27Al MAS NMR spectroscopy and calculations (DFT, QTAIM) have been used to gain an understanding of the dehydrogenation processes. The latter provide evidence for dehydrogenation being accompanied by metal–metal bond formation and an increased negative charge on Al due to the covalency of the new metal–metal bonds. To the best of our knowledge, we present the first structural information for intermediate species in alane dehydrogenation including a rare neutron diffraction study of a palladium–aluminium hydride complex. Furthermore, as part of these studies we have obtained the first SS 27Al NMR data on an aluminium(I) complex. Our findings are relevant to hydrogen storage, materials chemistry and catalysis.
Phillips NA, O'Hanlon J, Hooper TN, et al., 2019, Dihydridoboranes: Selective Reagents for Hydroboration and Hydrodefluorination, ORGANIC LETTERS, Vol: 21, Pages: 7289-7293, ISSN: 1523-7060
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- Citations: 11
Coates G, Tan HY, Kalff C, et al., 2019, Defluorosilylation of Industrially Relevant Fluoroolefins Using Nucleophilic Silicon Reagents, Angewandte Chemie, Vol: 131, Pages: 12644-12648, ISSN: 0044-8249
<jats:title>Abstract</jats:title><jats:p>A number of new magnesium and lithium silyl reagents were prepared and shown to be outstanding nucleophiles in reactions with industrially relevant fluoroolefins. These reactions result in a net transformation of either sp<jats:sup>2</jats:sup> or sp<jats:sup>3</jats:sup> C−F bonds into C−Si bonds by two modes of nucleophilic attack (S<jats:sub>N</jats:sub>V or S<jats:sub>N</jats:sub>2′). The methods are mild, proceeding with high chemo‐ and regioselectivity. Mechanistic pathways are described that lead to new substitution patterns from HFO‐1234yf, HFO‐1234ze, and HFO‐1336mzz, previously inaccessible by transition metal catalyzed difluorosilylation routes.</jats:p>
Coates G, Tan HY, Kalff C, et al., 2019, Defluorosilylation of industrially relevant fluoroolefins using nucleophilic silicon reagents, Angewandte Chemie - International Edition, Vol: 58, Pages: 12514-12518, ISSN: 1433-7851
A number of new magnesium and lithium silyl reagents were prepared and shown to be outstanding nucleophiles in reactions with industrially relevant fluoroolefins. These reactions result in a net transformation of either sp2 or sp3 C-F bonds into C-Si bonds by two modes of nucleophilic attack (SNV or SN2'). The methods are mild, proceeding with high chemo- and regioselectivity. Mechanistic pathways are described that lead to new substitution patterns from HFO-1234yf, HFO-1234ze and HFO-1336mzz, previously inaccessible by transition metal catalysed defluorosilylation routes.
Phillips N, White A, Crimmin M, 2019, Selective hydrodefluorination of hexafluoropropene to industrially relevant hydrofluoroolefins, Advanced Synthesis & Catalysis, Vol: 361, Pages: 3351-3358, ISSN: 1615-4150
The selective hydrodefluorination of hexafluoropropene to HFO‐1234ze and HFO‐1234yf can be achieved by reaction with simple group 13 hydrides of the form EH3 ⋅ L (E=B, Al; L=SMe2, NMe3). The chemoselectivity varies depending on the nature of the group 13 element. A combination of experiments and DFT calculations show that competitive nucleophilic vinylic substitution and addition‐elimination mechanisms involving hydroborated intermediates lead to complementary selectivities.
Kong RY, Crimmin M, 2019, Reversible Insertion of CO into an Aluminium–Carbon Bond
<jats:p>While reversible main-group mediated processes involving H2 and alkenes have been reported and studied for over a decade, no such reversible processes involving CO have been reported. In this paper, we show that a [2.2.1] aluminium metallobicycle is capable of reversibly inserting CO to form a [2.2.2] metallobicycle at 100 °C. Eyring analysis allowed determination of the Gibbs activation energy of the back-reaction, CO elimination reaction with G‡298K = 26.6 ±3.0 kcal mol-1. Computational studies reveal a highly asynchronous, but concerted, transition state for CO insertion. The coordination of CO to aluminium precedes C–C bond formation. The reversible migratory insertion reaction mimics that known for transition-metal and marks an important step forward for main group systems.</jats:p>
Crimmin M, White AJP, Phillips NA, 2019, Selective Hydrodefluorination of Hexafluoropropene to Industrially Relevant Hydrofluoroolefins
<jats:p>The selective hydrodefluorination of hexafluoropropene to HFO-1234ze and HFO-1234yf can be achieved by reaction with simple group 13 hydrides of the form EH3L (E = B, Al; L = SMe2, NMe3). The chemoselectivity varies depending on the nature of the group 13 element. A combination of experiments and DFT calculations show that competitive nucleophilic vinylic substitution and addition-elimination mechanisms involving hydroborated intermediates lead to complementary selectivities.</jats:p><jats:p />
Garcon M, Bakewell C, White AJP, et al., 2019, Unravelling nucleophilic aromatic substitution pathways with bimetallic nucleophiles, Chemical Communications, Vol: 55, Pages: 1805-1808, ISSN: 1359-7345
The reaction of a metal complex containing a polar Fe–Mg bond with 2-(pentafluorophenyl)pyridine leads to selective C–F bond activation. A stepwise SNAr mechanism involving attack of the bimetallic nucleophile on the electron-deficient aromatic ring has been identified by DFT calculations. Despite the long and rich history of metal anions in organic synthesis, this is the first time the SNAr mechanism has been elucidated in detail for metal-based nucleophiles.
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