Publications
175 results found
Bakewell C, White AJP, Crimmin MR, 2019, Reversible alkene binding and allylic C–H activation with an aluminium(i) complex, Chemical Science, Vol: 8, Pages: 2452-2458, ISSN: 2041-6520
The monomeric molecular aluminium(I) complex 1 [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) reacts with a series of terminal and strained alkenes including ethylene, propylene, allylbenzene and norbornene to form alkene bound products. Remarkably all these reactions are reversible under mild conditions (298–353 K) with alkene binding being disfavoured at higher temperatures due to the positive reaction entropy. Van't Hoff analyses have allowed quantification of the binding events with Image ID:c8sc04865g-t1.gif. Calculations and single crystal X-ray diffraction studies are consistent with the alkene bound species being metallocyclopropane complexes. Alkene binding involves a reversible redox process with changes from the +1 to +3 aluminium oxidation state. Under more forcing conditions the metallocyclopropane complexes undergo non-reversible allylic C–H bond activation to generate aluminium(III) allyl hydride complexes. This represents a rare example of redox-based main group reactivity in which reversible substrate binding is followed by a further productive bond breaking event. Analysis of the mechanism reveals a reaction network in which alkene dissociation and reformation of 1 is required for allylic C–H activation, a realisation that has important implications for the long-term goal of developing redox-based catalytic cycles with main group compounds.
Kong RY, Crimmin MR, 2019, Reversible insertion of CO into an aluminium–carbon bond, Chem. Commun., Vol: 55, Pages: 6181-6184
A [2.2.1] aluminium metallobicycle is capable of reversibly inserting CO to form a [2.2.2] metallobicycle at 100 °C. 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 of CO at aluminium thus mimics well-established transition-metal reactivity.
Lau S, White A, Casely I, et al., 2018, Tunable binding of dinitrogen to a series of heterobimetallic hydride complexes, Organometallics, Vol: 37, Pages: 4521-4526, ISSN: 0276-7333
The reaction of [Ru(H)2(N2)2(PCy3)2] (1) with β-diketiminate stabilized hydrides of Al, Zn, and Mg generates a series of new heterobimetallic complexes with either H2 or N2 ligated to the ruthenium center. Changing the main-group fragment of the M·Ru-N2 (M = Al, Zn, Mg) complexes can subtly alter the degree of binding, and therefore activation, of the diatomic ligand, as evidenced by the νN≡N absorptions in the infrared data. Experimental and computational data rationalize this tunable binding; decreasing the electronegativity of the main group in the order Al > Zn > Mg infers greater ionic character of these M·Ru-N2 complexes, and this in turn results in greater destabilization of the frontier molecular orbitals of ruthenium and therefore greater Ru(4d) → π*(N2) back-donation.
Crimmin MR, Coates G, Bakewell C, et al., 2018, Reactions of fluoroalkanes with Mg-Mg bonds: scope, sp3C-F / sp2C-F coupling and mechanism, Chemistry - A European Journal, Vol: 24, Pages: 16282-16286, ISSN: 0947-6539
sp3C-F bonds of fluoroalkanes (7 examples; 1o, 2o and 3o) undergo addition to a low-valent Mg-Mg species generating reactive organomagnesium reagents. Further reactions with a series of electrophiles results in a net C-F to C-B, C-Si, C-Sn or C-C bond transformation (11 examples, diversity). The new reactivity has been exploited in an unprecedented one-pot magnesium-mediated coupling of sp3C-F and sp2C-F bonds. Calculations suggest that the sp3C-F bond activation step occurs by frontside nucleophilic attack of the Mg-Mg reagent on the fluoroalkane.
Garçon M, White AJP, Crimmin MR, 2018, Palladium-catalysed magnesiation of benzene, Chemical Communications, Vol: 54, Pages: 12326-12328, ISSN: 1359-7345
In the presence of a catalytic quantity of [Pd(PCy3)2], a reagent containing a Mg-Mg bond effects the C-H functionalisation of benzene resulting in a 100% atom efficient transformation to generate an unprecedented aryl magnesium hydride.
Bakewell C, White AJP, Crimmin M, 2018, Reversible Alkene Binding and Allylic C–H Activation with an Aluminum(I) Complex
<jats:p>Reversible alkene binding to a low-valent main group complex is documented. The reaction involves an aluminium(I) reagent and includes both terminal and strained alkenes. This reversible binding event is just a forerunner to non-reversible C–H activation of the allylic position of the alkene. Mechanistic analysis shows that in contrast to common transition metal systems, the C–H activation does not proceed from a metal bound alkene complex. Dissociation of the alkene and reformation of the aluminium(I) fragment is required to liberate the active site and frontier molecular orbitals involved in C–H activation.</jats:p>
Kong RY, Crimmin MR, 2018, Carbon chain growth by sequential reactions of CO and CO2 with [W(CO)6] and an aluminum(I) reductant, Journal of the American Chemical Society, Vol: 140, Pages: 13614-13617, ISSN: 0002-7863
The formation of carbon chains by the coupling of COx (x = 1 or 2) units on transition metals is a fundamental step relevant to Fischer–Tropsch catalysis. Fischer–Tropsch catalysis produces energy dense liquid hydrocarbons from synthesis gas (CO and H2) and has been a mainstay of the energy economy since its discovery nearly a century ago. Despite detailed studies aimed at elucidating the steps of catalysis, experimental evidence for chain growth (Cn → Cn+1; n ≥ 2) from the coupling of CO units on metal complexes is, to the best of our knowledge, unprecedented. In this paper, we show that carbon chains can be grown from sequential reactions of CO or CO2 with a transition metal carbonyl complex. By exploiting the cooperative effect of transition and main group metals, we document the first example of chain propagation from sequential coupling of CO units (C1 → C3 → C4), along with the first example of incorporation of CO2 into the growing carbon chain.
Bakewell C, White AJP, Crimmin M, 2018, Reversible Alkene Binding and Allylic C–H Activation with an Aluminum(I) Complex
<jats:p>Reversible alkene binding to a low-valent main group complex is documented. The reaction involves an aluminium(I) reagent and includes both terminal and strained alkenes. This reversible binding event is just a forerunner to non-reversible C–H activation of the allylic position of the alkene. Mechanistic analysis shows that in contact to common transition metal systems, the C–H activation does not proceed from a metal bound alkene complex. Dissociation of the alkene and reformation of the aluminium(I) fragment is required to liberate the active site and frontier molecular orbitals involved in C–H activation.</jats:p>
Garçon M, White AJP, Crimmin M, 2018, Palladium–Catalysed Magnesiation of Benzene
<jats:p>In the presence of a catalytic quantity of a palladium bis(phosphine) complex, a reagent containing a Mg-Mg bond effects the C-H functionalisation of benzene. The resulting 100% atom efficient transformation generates an unprecedented aryl magnesium hydride.</jats:p>
Kong R, Crimmin M, 2018, Carbon Chain Growth by Sequential Reactions of CO and CO2 with a Transition Metal Carbonyl Complex
<jats:p><jats:italic>The formation of carbon chains by the coupling of COx (X = 1 or 2) units on transition metals is a fundamental step relevant to Fischer-Tropsch catalysis. Fischer-Tropsch catalysis produces energy dense liquid hydrocarbons from synthesis gas (CO and H2) and has been a mainstay of the energy economy since its discovery nearly a century ago. Despite detailed studies aimed at elucidating the steps of catalysis, experimental evidence for chain growth (Cn to Cn+1 ; n > 2) from the reaction of CO with metal complexes is unprecedented. In this paper, we show that carbon chains can be grown from sequential reactions of CO or CO2 with a transition metal carbonyl complex. By exploiting the cooperative effect of transition and main group metals, we document the first example of chain propagation from sequential coupling of CO units (C1 to C3 to C4), along with the first example of incorporation of CO2 into the growing carbon chain.</jats:italic></jats:p><jats:p />
Hicken A, White AJP, Crimmin MR, 2018, Preparation and characterisation of heterobimetallic copper-tungsten hydride complexes, Dalton Transactions, Vol: 47, Pages: 10595-10600, ISSN: 1477-9234
The preparation and structural characterisation of three new heterobimetallic hydride complexes containing 3-centre,2-electron W-H-Cu bonds is reported. These complexes have been characterised by single crystal X-ray crystallography and multinuclear NMR spectroscopy. The bonding in these complexes has been analysed by DFT calculations.
Hooper TN, Garcon M, White AJP, et al., 2018, Room temperature catalytic carbon-hydrogen bond alumination of unactivated arenes: mechanism and selectivity, CHEMICAL SCIENCE, Vol: 9, Pages: 5435-5440, ISSN: 2041-6520
We report the first catalytic methods for the transformation of C–H bonds of unactivated arenes into C–Al bonds. The catalytic reactions occur at 25 °C (benzene, toluene and xylenes) with palladium loadings as low as 0.1 mol%. Remarkably, the C–H activation of toluene and xylenes proceeds with ortho- and meta-selectivity. This selectivity is highly unusual and complementary to both Friedel–Crafts and the majority of C–H borylation methods. Through a detailed mechanistic analysis (Eyring analysis, KIE, DFT, QTAIM) we show that unusual Pd–Al intermetallic complexes are on the catalytic cycle and that the selectivity is determined by weak attractive dispersion forces in the transition state for C–H bond breaking.
Bakewell C, White AJP, Crimmin MR, 2018, Reactions of fluoroalkenes with an aluminium(I) complex, Angewandte Chemie International Edition, Vol: 57, Pages: 6638-6642, ISSN: 1521-3757
A series of industrially relevant fluoroalkenes react with a monomeric AlI complex. These reactions break strong sp2 and sp3 C-F bonds, and result in the formation of a diverse array of organoaluminium compounds. Mechanistic studies show that two mechanisms are likely in operation: 1) direct oxidative addition of the C-F bond to AlI occurs with retention of alkene stereochemistry, and 2) stepwise formation and decomposition of a metallocyclopropane intermediate occurs with inversion of alkene stereochemistry. As part of this mechanistic analysis, we have isolated the first aluminium metallocyclopropane complex from oxidative addition of an alkene to AlI . Remarkably this reaction is reversible and reductive elimination of the alkene occurs at higher temperature reforming AlI . Furthermore, in selected cases the organoaluminium products are susceptible toward β-fluoride elimination to yield a double C-F activation pathway.
Bakewell C, White AJP, Crimmin MR, 2018, Reactions of Fluoroalkenes with an Aluminium(I) Complex, Angewandte Chemie, Vol: 130, Pages: 6748-6752, ISSN: 0044-8249
<jats:title>Abstract</jats:title><jats:p>A series of industrially relevant fluoroalkenes react with a monomeric Al<jats:sup>I</jats:sup> complex. These reactions break strong sp<jats:sup>2</jats:sup> and sp<jats:sup>3</jats:sup> C−F bonds, and result in the formation of a diverse array of organoaluminium compounds. Mechanistic studies show that two mechanisms are likely in operation: 1) direct oxidative addition of the C−F bond to Al<jats:sup>I</jats:sup> occurs with retention of alkene stereochemistry, and 2) stepwise formation and decomposition of a metallocyclopropane intermediate occurs with inversion of alkene stereochemistry. As part of this mechanistic analysis, we have isolated the first aluminium metallocyclopropane complex from oxidative addition of an alkene to Al<jats:sup>I</jats:sup>. Remarkably this reaction is reversible and reductive elimination of the alkene occurs at higher temperature reforming Al<jats:sup>I</jats:sup>. Furthermore, in selected cases the organoaluminium products are susceptible toward β‐fluoride elimination to yield a double C−F activation pathway.</jats:p>
Butler MJ, White AJP, Crimmin MR, 2018, Heterobimetallic rebound: a mechanism for diene-to-alkyne isomerization with M-Zr hydride complexes (M = Al, Zn, and Mg), Organometallics, Vol: 37, Pages: 949-956, ISSN: 0276-7333
The reaction of a series of M·Zr heterobimetallic hydride complexes withdienes and alkynes has been investigated (M = Al, Zn, and Mg). Reaction of M·Zr with1,5-cyclooctadiene led to diene isomerization to 1,3-cyclooctadiene, but for M = Zn alsoresult in an on-metal diene-to-alkyne isomerization. The resulting cyclooctyne fragment istrapped between Zr and Zn metals in a heterobimetallic species that does not form for M= Mg or Al. The scope of diene isomerization and alkyne trapping has been exploredleading to the isolation of three new heterobimetallic slipped metallocyclopropenecomplexes. The mechanism of diene-to-alkyne isomerization was investigated throughkinetics. While the reaction is first-order in Zn·Zr at high diene concentration andproceeds with ΔH‡ = +33.6 ± 0.7 kcal mol−1, ΔS‡ = +23.2 ± 1.7 cal mol−1 K−1, and ΔG⧧298 K = +26.7 ± 1.2 kcal mol−1, the rateis dependent on the nature of the diene. The positive activation entropy is suggestive of involvement of a dissociative step. Onthe basis of DFT calculations, a heterobimetallic rebound mechanism for diene-to-alkyne isomerization has been proposed. Thismechanism explains the origin of heterobimetallic control over selectivity: Mg---Zr complexes are too strongly bound to generatereactive fragments, while Al---Zr complexes are too weakly bound to compensate for the contrathermodynamic isomerizationprocess. Zn---Zr complexes have favorable energetics for both dissociation and trapping steps.
Zhurakovskyi O, Türkmen YE, Löffler LE, et al., 2018, Enantioselective Synthesis of the Cyclopiazonic Acid Family Using Sulfur Ylides, Angewandte Chemie, Vol: 130, Pages: 1360-1364, ISSN: 0044-8249
<jats:title>Abstract</jats:title><jats:p>A convergent, nine‐step (LLS), enantioselective synthesis of α‐cyclopiazonic acid and related natural products is reported. The route features a) an enantioselective aziridination of an imine with a chiral sulfur ylide; b) a bioinspired (3+2)‐cycloaddition of the aziridine onto an alkene; and c) installation of the acetyltetramic acid by an unprecedented tandem carbonylative lactamization/N−O cleavage of a bromoisoxazole.</jats:p>
Bakewell C, Ward BJ, White AJP, et al., 2018, A combined experimental and computational study on the reaction of fluoroarenes with Mg-Mg, Mg-Zn, Mg-Al and Al-Zn bonds, Chemical Science, Vol: 9, Pages: 2348-2356, ISSN: 2041-6520
Through a combined experimental and computational (DFT) approach, the reaction mechanism of theaddition of fluoroarenes to Mg–Mg bonds has been determined as a concerted SNAr-like pathway inwhich one Mg centre acts as a nucleophile and the other an electrophile. The experimentally determinedGibbs activation energy for the addition of C6F6 to a Mg–Mg bond of a molecular complex,DG‡298 K(experiment) ¼ 21.3 kcal mol1 is modelled by DFT with the uB97X functional, DG‡298 K(DFT) ¼25.7 kcal mol1. The transition state for C–F activation involves a polarisation of the Mg–Mg bond andsignificant negative charge localisation on the fluoroarene moiety. This transition state is augmented bystabilising closed-shell Mg/Fortho interactions that, in combination with the known trends in C–F andC–M bond strengths in fluoroarenes, provide an explanation for the experimentally determinedpreference for C–F bond activation to occur at sites flanked by ortho-fluorine atoms. The effect ofmodification of both the ligand coordination sphere and the nature and polarity of the M–M bond (M ¼Mg, Zn, Al) on C–F activation has been investigated. A series of highly novel b-diketiminate stabilisedcomplexes containing Zn–Mg, Zn–Zn–Zn, Zn–Al and Mg–Al bonds has been prepared, including thefirst crystallographic characterisation of a Mg–Al bond. Reactions of these new M–M containingcomplexes with perfluoroarenes were conducted and modelled by DFT. C–F bond activation is dictatedby the steric accessibility, and not the polarity, of the M–M bond. The more open coordinationcomplexes lead to enhanced Mg/Fortho interactions which in turn lower the energy of the transitionstates for C–F bond activation.
Zhurakovskyi O, Tuerkmen YE, Loeffler LE, et al., 2018, Enantioselective synthesis of the Cyclopiazonic acid family using sulfur ylides, Angewandte Chemie International Edition, Vol: 57, Pages: 1346-1350, ISSN: 1521-3757
A convergent, nine‐step (LLS), enantioselective synthesis of α‐cyclopiazonic acid and related natural products is reported. The route features a) an enantioselective aziridination of an imine with a chiral sulfur ylide; b) a bioinspired (3+2)‐cycloaddition of the aziridine onto an alkene; and c) installation of the acetyltetramic acid by an unprecedented tandem carbonylative lactamization/N−O cleavage of a bromoisoxazole.
Crimmin MR, Hicken A, White AJP, 2017, Selective Reduction of CO2 to a Formate Equivalent with Heterobimetallic Gold---Copper Hydride Complexes., Angewandte Chemie International Edition, Vol: 56, Pages: 15127-15130, ISSN: 1521-3757
A series of heterobimetallic complexes containing 3-center,2-electron Au-H-Cu bonds have been prepared from addition of a parent gold hydride to a bent d10 copper(I) fragment. These highly unusual heterobimetallic complexes represent a missing link in the widely investigated series of neutral and cationic coinage metal hydride complexes containing Cu-H-Cu and M-H-M+ moieties (M = Cu, Ag). The well-defined heterobimetallic hydride complexes act as pre-catalysts for the conversion of CO2 to HCO2Bpin using HBpin as a reductant. The selectivity of the heterobimetallic complexes for the catalytic production of a formate equivalent surpasses that of the parent monomeric group 11 complexes.
Chen W, Hooper TN, Ng J, et al., 2017, Palladium-Catalyzed Carbon-Fluorine and Carbon-Hydrogen Bond Alumination of Fluoroarenes and Heteroarenes, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 56, Pages: 12687-12691, ISSN: 1433-7851
Through serendipitous discovery, a palladium bis(phosphine) complex was identified as a catalyst for the selective transformation of sp2C−F and sp2C−H bonds of fluoroarenes and heteroarenes to sp2C−Al bonds (19 examples, 1 mol % Pd loading). The carbon–fluorine bond functionalization reaction is highly selective for the formation of organoaluminium products in preference to hydrodefluorination products (selectivity=4.4:1 to 27:1). Evidence is presented for a tandem catalytic process in which hydrodefluorination is followed by sp2C−H alumination.
Crimmin MR, Lau S, Ward B, et al., 2017, Mild sp2Carbon-Oxygen Bond Activation by an Isolable Ruthenium(II) bis(Dinitrogen) Complex: Experiment and Theory, Organometallics, Vol: 36, Pages: 3654-3663, ISSN: 0276-7333
The isolable ruthenium(II) bis(dinitrogen) complex [Ru(H)2(N2)2(PCy3)2] (1) reacts with aryl ethers (Ar–OR, R = Me and Ar) containing a ketone directing group to effect sp2C–O bond activation at temperatures below 40 °C. DFT studies support a low-energy Ru(II)/Ru(IV) pathway for C–O bond activation: oxidative addition of the C–O bond to Ru(II) occurs in an asynchronous manner with Ru–C bond formation preceding C–O bond breaking. Alternative pathways based on a Ru(0)/Ru(II) couple are competitive but less accessible due to the high energy of the Ru(0) precursors. Both experimentally and by DFT calculations, sp2C–H bond activation is shown to be more facile than sp2C–O bond activation. The kinetic preference for C–H bond activation over C–O activation is attributed to unfavorable approach of the C–O bond toward the metal in the selectivity determining step of the reaction pathway.
Crimmin MR, Chen W, Hooper TN, et al., 2017, Palladium-Catalysed Carbon-Fluorine and Carbon-Hydrogen Bond Alumination of Fluoroarenes and Heteroarenes, Angewandte Chemie, Vol: 129, Pages: 12861-12865, ISSN: 1521-3757
Through serendipitous discovery, a palladium bis(phosphine) complex was identified as a catalyst for the selective transformation of sp2C−F and sp2C−H bonds of fluoroarenes and heteroarenes to sp2C−Al bonds (19 examples, 1 mol % Pd loading). The carbon–fluorine bond functionalization reaction is highly selective for the formation of organoaluminium products in preference to hydrodefluorination products (selectivity=4.4:1 to 27:1). Evidence is presented for a tandem catalytic process in which hydrodefluorination is followed by sp2C−H alumination.
Crimmin MR, hicken A, White AJP, 2017, Reversible Coordination of Boron-, Aluminum-, Zinc-, Magnesium- and Calcium-Hydrogen bonds to bent {CuL2} fragments: Heavy sigma-Complexes of the Lightest Coinage Metal, Inorganic Chemistry, Vol: 56, Pages: 8669-8682, ISSN: 0020-1669
A series of copper(I) complexes bearing electron-deficient β-diketiminate ligands have been prepared. The study includes [{{ArNC(CR3)}2CH}Cu(η2-toluene)n] (Ar = Mes, R = F, n = 0.5, [12·tol]; Ar = C6F5, R = Me, n = 1, [2·tol]; Ar = 2,6-Cl2C6H3, R = H, n = 0.5, [32·tol]). Reactions of [1–3n·tol] with boranes, alanes, a zinc hydride, a magnesium hydride, and a calcium hydride generate the corresponding σ complexes ([1–3·B], [3·B′], [3·Al], [3·Al′], [1–3·Zn], [1·Mg], and [1·Ca]). These species all form reversibly, being in equilibrium with the arene solvates in solution. With the exception of the calcium complex, the complexes have all been characterized by single-crystal X-ray diffraction studies. In solution, the σ-hydride of the aluminum, zinc, magnesium, and calcium derivatives resonates between −0.12 and −1.77 ppm (C6D6 or toluene-d8, 193–298 K). For the σ-borane complexes, the hydrides are observed as a single resonance between 2 and 3.5 ppm (C6D6, 298 K) and bridging and terminal hydrides rapidly exchange on the NMR time scale even at 193 K. Quantification of the solution dynamics by van’t Hoff analysis yields expectedly small values of ΔH° and negative values of ΔS° consistent with weak binding and a reversible process that does not involve aggregation of the copper species. The donor–acceptor complexes can be rationalized in terms of the Dewar–Chatt–Duncanson model. Density functional theory calculations show that the donation of σ-M–H (or E–H) electrons into the 4s-based orbital (LUMO or LUMO+1) of the copper fragment is accompanied by weak back-donation from a dxz-based orbital (HOMO or HOMO–1) into the σ*-M–H (or E–H) orbital.
Ekkert O, White AJP, Crimmin MR, 2017, Stereoisomerism of bis(sigma-Zincane) complexes: evidence for an intramolecular pathway, Chemistry-A European Journal, Vol: 23, Pages: 5682-5686, ISSN: 1521-3765
The first bis(σ-zincane) complexes, heterotri- metallic species [M(CO)4(η2-HZnBDI)2], have been prepared (BDI=κ2-{2,6-(iPr)2C6H3NCMe}2CH). For M=Cr, a single stereoisomer is observed in solution and the solid-state. For M=Mo and W, cis and trans isomers were found to reversibly interconvert at 297 K. Despite the huge steric demands of the ligand on zinc, the cis isomer was found to be the most thermodynamically stable in all cases. The activation parameters for the isomerisation when M=Mo are ΔH≠=20.8 kcal mol−1 and ΔS≠=−12.8 cal K−1 mol−1. In combination with DFT calculations, the negative activation entropy suggests an intramolecular rotation mechanism for isomerisation.
Pike SD, Crimmin MR, Chaplin AB, 2017, Organometallic chemistry using partially fluorinated benzenes, Chemical Communications, Vol: 53, Pages: 3615-3633, ISSN: 1364-548X
Fluorobenzenes, in particular fluorobenzene (FB) and 1,2-difluorobenzene (1,2-DiFB), are increasingly becoming recognised as versatile solvents for conducting organometallic chemistry and transition-metal-based catalysis. The presence of fluorine substituents reduces the available π-electron density and consequently fluorobenzenes generally bind weakly to metal centres, allowing them to be used as essentially non-coordinating solvents or as readily displaced ligands. In this context, examples of well-defined complexes of fluorobenzenes are discussed, including trends in binding strength with increasing fluorination and different substitution patterns. Compared to more highly fluorinated benzenes, FB and 1,2-DiFB typically demonstrate greater chemical inertness, however, C–H and C–F bond activation reactions can be induced using appropriately reactive transition metal complexes. Such reactions are surveyed, including catalytic examples, not only to provide perspective for the use of FB and 1,2-DiFB as innocent solvent media, but also to highlight opportunities for their exploitation in contemporary organic synthesis.
Phanopoulos A, Leung AHM, Yow S, et al., 2017, Binuclear β-diketiminate complexes of copper(I), Dalton Transactions, Vol: 46, Pages: 2081-2090, ISSN: 1477-9226
The reaction of a series of dinucleating bis(β-diketiminate) pro-ligands with mesitylcopper in the presence and absence of mono and diphosphines has allowed the isolation of a new series of dicopper(I) complexes. Inclusion of trans-1,2-cyclohexyl (1), 2,6-pyridyl (2), and 2,2′-oxydiaryl (3) spacers between the β-diketiminate units has been studied. The isolation of three new copper(I) phosphine complexes [1·Cu2(PPh3)2], [2·Cu2(PPh3)2] and [3·Cu2(PPh3)2] is reported. While these compounds display large Cu⋯Cu separations of 5.4–7.9 Å in the solid state, solution data are consistent with a large degree of conformational freedom. Modification of the monophosphine to a diphosphine, DPPE, allowed the isolation of the novel 11-membered bimetallic macrocycle [2·Cu2(DPPE)] containing both a binucleating nitrogen based ligand and a chelating diphosphine. While acetonitrile adducts of this series could also be generated in situ, under forcing conditions reaction of the 2,6-pyridyl bridged ligand with mesityl copper led to the formation [2·Cu2]2. This latter complex is a dimer of dicopper(I) units in which the bis(β-diketiminate) ligand now binds four copper(I) centers through not only the expected κ2-N,N′-chelation but also κ1- and η2-binding of the central pyridine through orthogonal Cu–N and Cu–arene interactions. Reversible coordination of alkenes, pyridine and quinoline to the copper cluster was identified allowing the isolation and structural characterisation of a further series of dinuclear complexes [2·Cu2(pyridine)2], [2·Cu2(cyclopentene)2] and [2·Cu2(norbornene)2]. Solution studies allow quantification of the reversible binding event through a van't Hoff analysis. Both solution and the solid state data suggest a weak anagostic interaction exists in the latter two alkene complexes of copper(I). The new complexes have been characterized by X-ray dif
Butler MJ, Crimmin MR, 2017, Magnesium, zinc, aluminium and gallium hydride complexes of the transition metals., Chemical Communications, Vol: 53, Pages: 1348-1365, ISSN: 1364-548X
The preparation and applications of heterobimetallic complexes continue to occupy researchers in the fields of organometallic, main group, and coordination chemistry. This interest stems from the promise these complexes hold as precursors to materials, reagents in synthesis and as new catalysis. Here we survey and organise the state-of-the-art understanding of the TM-H-M linkage (M = Mg, Zn, Al, Ga). We discuss the structure and bonding in these complexes, their known reactivity, and their largely unrealised potential in catalysis.
chen W, Bakewell C, Crimmin MR, 2016, Functionalisation of Carbon-Fluorine Bonds with Main Group Reagents, SYNTHESIS, Vol: 49, Pages: 810-821, ISSN: 0039-7881
Synthetic approaches to produce reactive chemical building blocks from fluorinated molecules by the functionalization of carbon–fluorine bonds with main group reagents are reviewed. The reaction types can be categorized as: (i) the formal 1,2-addition of C–F bonds across Si–Si, B–B, or Mg–Mg bonds; (ii) the oxidative addition of C–F bonds to Si(II), Ge(II), and Al(I) centres; and (iii) the dehydrogenative coupling of C–F bonds with Al–H or B–H bonds. Many of the advances have emerged between 2015–2016 and are largely focused upon aromatic substrates that contain sp2 C–F bonds.
Ekkert O, White AJ, Crimmin MR, 2016, Trajectory of approach of a zinc-hydrogen bond to transition metals, Angewandte Chemie - International Edition, Vol: 55, Pages: 16031-16034, ISSN: 1433-7851
Through a dramatic advance in the coordination chemistry of the zinc-hydride bond, we describe the trajectory for the approach of this bond to transition metals. The dynamic reaction coordinate was interrogated through analysis of a series of solid state structures and is one in which the TM-H-Zn angle becomes increasingly acute as the TM-Zn distance decreases. Parallels may be drawn with the oxidative addition of boron-hydrogen and silicon-hydrogen bonds to transition metal centers.
Bakewell C, White AJ, Crimmin MR, 2016, Addition of carbon-fluorine bonds to a Mg(I)-Mg(I) bond: an equivalent of Grignard formation in solution, Journal of the American Chemical Society, Vol: 138, Pages: 12763-12766, ISSN: 1520-5126
Addition of the carbon-fluorine bond of a series of perfluorinated and polyfluorinated arenes across the Mg-Mg bond of a simple coordination complex proceeds rapidly in solution. The reaction results in the formation of a new carbon-magnesium bond and a new fluorine-magnesium bond and is analogous to Grignard formation in homogeneous solution.
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