Publications
159 results found
Stadler B, Gorgas N, White AJP, et al., 2023, Double Deprotonation of CH3 CN by an Iron-Aluminium Complex., Angew Chem Int Ed Engl
Herein we present the first double deprotonation of acetonitrile (CH3 CN) using two equivalents of a bimetallic iron-aluminium complex. The products of this reaction contain an exceeding simple yet rare [CHCN]2- dianion moiety that bridges two metal fragments. DFT calculations suggest that the bonding to the metal centres occurs through heavily polarised covalent interactions. Mechanistic studies reveal the intermediacy of a monomeric [CH2 CN]- complex, which has been characterised in situ. Our findings provide an important example in which a bimetallic metal complex achieves a new type of reactivity not previously encountered with monometallic counterparts.[1, 2] The isolation of a [CHCN]2- dianion through simple deprotonation of CH3 CN also offers the possibility of establishing a broader chemistry of this motif.
Parr JM, Crimmin MR, 2023, Carbon-Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates., Angew Chem Int Ed Engl
Current examples of carbon chain production from metal formyl intermediates with homogeneous metal complexes are described in this Minireview. Mechanistic aspects of these reactions as well as the challenges and opportunities in using this understanding to develop new reactions of CO and H2 are also discussed.
Parr JMM, Phanopoulos A, Vickneswaran A, et al., 2023, Understanding the role of ring strain in beta-alkyl migration at Mg and Zn centres, CHEMICAL SCIENCE, ISSN: 2041-6520
Garcon M, Phanopoulos A, White AJP, et al., 2022, Reversible Dihydrogen Activation and Catalytic H/D Exchange with Group 10 Heterometallic Complexes, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, ISSN: 1433-7851
Garçon M, Phanopoulos A, Sackman GA, et al., 2022, The Continuum Between Hexagonal Planar and Trigonal Planar Geometries**, Angewandte Chemie, Vol: 134, ISSN: 0044-8249
Mies T, Schurmann C, Ito S, et al., 2022, Synthesis and Characterization of a Calcium-Pyrazolonato Complex. Observation of In-Situ Desolvation During Micro-Electron Diffraction, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, ISSN: 0044-2313
Garcon M, Phanopoulos A, Sackman GA, et al., 2022, The Continuum Between Hexagonal Planar and Trigonal Planar Geometries, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 61, ISSN: 1433-7851
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- Citations: 1
Gorgas N, White AJP, Crimmin MR, 2022, Diverse reactivity of an iron-aluminium complex with substituted pyridines, CHEMICAL COMMUNICATIONS, Vol: 58, Pages: 10849-10852, ISSN: 1359-7345
Rekhroukh F, Zhang L, Kong RY, et al., 2022, Stereoselective insertion of cyclopropenes into Mg-Mg bonds, CHEMICAL COMMUNICATIONS, Vol: 58, Pages: 8282-8285, ISSN: 1359-7345
Sheldon DJ, Crimmin MR, 2022, Repurposing of F-gases: challenges and opportunities in fluorine chemistry, CHEMICAL SOCIETY REVIEWS, Vol: 51, Pages: 4977-4995, ISSN: 0306-0012
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- Citations: 3
Gorgas N, White AJP, Crimmin MR, 2022, Cooperative C-H Bond Activation by a Low-Spin d(6) Iron-Aluminum Complex, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 144, Pages: 8770-8777, ISSN: 0002-7863
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- Citations: 4
Parr JM, White AJP, Crimmin MR, 2022, Magnesium-stabilised transition metal formyl complexes: structures, bonding, and ethenediolate formation, CHEMICAL SCIENCE, Vol: 13, Pages: 6592-6598, ISSN: 2041-6520
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- Citations: 2
Mulryan D, Rodwell J, Phillips NA, et al., 2022, Au(I) Catalyzed HF Transfer: Tandem Alkyne Hydrofluorination and Perfluoroarene Functionalization, ACS CATALYSIS, Vol: 12, Pages: 3411-3419, ISSN: 2155-5435
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- Citations: 1
Batuecas M, Kong RY, White AJP, et al., 2022, Functionalization and hydrogenation of carbon chains derived from CO, Angewandte Chemie International Edition, Vol: 61, ISSN: 1433-7851
Selective reactions that combine H 2 , CO and organic electrophiles (aldehyde, ketones, isocyanide) to form hydrogenated C 3 and C 4 carbon chains are reported. These reactions proceed by CO homologation mediated by [W(CO) 6 ] and an aluminum(I) reductant, followed by functionalization and hydrogenation of the chain ends. A combination of kinetics (rates, KIEs) and DFT calculations has been used to gain insight into a key step which involves hydrogenation of a metallocarbene intermediate. These findings expand the extremely small scope of systems that combine H 2 and CO to make well-defined products with complete control over chain length and functionality.
Gorgas N, White A, Crimmin M, 2022, Cooperative C–H Bond Activation by a Low-Spin d6 Iron–Aluminium Complex
<jats:p>The reactions of transition metal complexes underpin numerous synthetic processes and catalytic transformations. Typically, this reactivity involves the participation of empty and filled molecular orbitals centred on the transition metal. Kinetically stabilised species, such as octahedral low-spin d6 transition metal complexes, are not expected to participate directly in these reactions. However, novel approaches that exploit metal ligand-cooperativity offer an opportunity to challenge these preconceptions. Here we show that inclusion of an aluminium-based ligand into the coordination sphere of neutral low-spin d6 iron complex leads to unexpected reactivity. Complexes featuring an unsupported Fe–Al bond are capable of the intermolecular C–H bond activation of pyridines. Mechanistic analysis suggests that C–H activation proceeds through a reductive deprotonation in which the two metal centres (Fe and Al) act like a frustrated Lewis-pair. Key to this behaviour is a ground state destabilisation of the d6 iron complex, brought about by the inclusion of the electropositive aluminium-based ligand. These findings have immediate implications for the design of reagents and catalysts based on 1st row transition metals.</jats:p>
Gorgas N, White A, Crimmmin M, 2022, Cooperative C–H Bond Activation by a Low-Spin d6 Iron–Aluminium Complex
<jats:p>The reactions of transition metal complexes underpin numerous synthetic processes and catalytic transformations. Typically, this reactivity involves the participation of empty and filled molecular orbitals centred on the transition metal. Kinetically stabilised species, such as octahedral low-spin d6 transition metal complexes, are not expected to participate directly in these reactions. However, novel approaches that exploit metal ligand-cooperativity offer an opportunity to challenge these preconceptions. Here we show that inclusion of an aluminium-based ligand into the coordination sphere of neutral low-spin d6 iron complex leads to unexpected reactivity. Complexes featuring an unsupported Fe–Al bond are capable of the intermolecular C–H bond activation of pyridines. Mechanistic analysis suggests that C–H activation proceeds through a reductive deprotonation in which the two metal centres (Fe and Al) act like a frustrated Lewis-pair. Key to this behaviour is a ground state destabilisation of the d6 iron complex, brought about by the inclusion of the electropositive aluminium-based ligand. These findings have immediate implications for the design of reagents and catalysts based on 1st row transition metals.</jats:p>
Zhang L, Kaukver S, McMullen J, et al., 2022, Catalytic C-H Alumination of Thiophenes: DFT Predictions and Experimental Verification, Organometallics, ISSN: 0276-7333
A computational model for the palladium-catalyzed C-H functionalization of thiophenes with aluminum hydride reagents has been developed. This model predicts that metalation should occur exclusively at the 2-position of the heterocycle. While related 2-metalated furans are known to undergo a ring-expansion reaction, further calculations suggest that the thiophene-derived organoaluminum compounds should be both kinetically and thermodynamically stable with respect to ring opening. This model is supported by experimental data. Selective C-H alumination of thiophene, 2-methylthiophene, 2-methoxythiophene, and benzothiophene was achieved using [Pd(PCy3)2] as a catalyst with loadings as low as 0.02 mol %. Even under extremely forcing conditions (200 °C) there was no evidence for a ring-opening event. The differences in selectivity between furan and thiophene systems are rationalized in terms of the stabilization of a key intermediate (and transition state) in the pathway for furan ring opening by a strong dative O→Al interaction.
Batuecas M, Kong R, White A, et al., 2021, Functionalization and Hydrogenation of Carbon Chains Derived from CO
<jats:p>Selective reactions that combine H2, CO and organic electrophiles (aldehyde, ketones, isocyanide) to form hydrogenated C3 and C4 carbon chains are reported. These reactions proceed by CO homologation mediated by [W(CO)6] and an aluminum(I) reductant, followed by functionalization and hydrogenation of the chain ends. A combination of kinetics (rates, KIEs) and DFT calculations has been used to gain insight into a key step which involves hydrogenation of a metallocarbene intermediate. These findings expand the extremely small scope of systems that combine H2 and CO to make well-defined products with complete control over chain length and functionality.</jats:p>
Mulryan D, Rodwell J, Phillips N, et al., 2021, Au(I) Catalyzed HF Transfer: Tandem Alkyne Hydrofluorination and Perfluoroarene Functionalisation
<jats:p>HF transfer reactions between organic substrates are an incredibly rare class of transformation. Such reactions require the development of new catalytic systems that can promote both defluorination and fluorination steps in a single reaction sequence. Herein, we report a novel catalytic protocol in which an equivalent of HF is generated from a perfluoroarene | nucleophile pair and transferred directly to an alkyne. The reaction is catalysed by [Au(IPr)NiPr2] (IPr = N,N’-1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and is 100 % atom efficient. HF transfer generates two useful products in the form of functionalised fluoroarenes and fluoroalkenes. Mechanistic studies (rate laws, KIEs, DFT calculations, competition experiments) are consistent with the Au(I) catalyst facilitating a catalytic network involving both concerted SNAr and hydrofluorination steps. The nature of the nucleophile impacts the turnover-limiting step. The cSNAr step is turnover-limiting for phenol-based nucleophiles while proteodeauration likely becomes turnover-limiting for aniline-based nucleophiles. The new approach removes the need for direct handling of HF reagents in hydrofluorination and offers new possibilities to manipulate the fluorine content of organic molecules through catalysis.</jats:p>
Kong RY, Batuecas M, Crimmin MR, 2021, Reactions of aluminium(i) with transition metal carbonyls: scope, mechanism and selectivity of CO homologation, CHEMICAL SCIENCE, Vol: 12, Pages: 14845-14854, ISSN: 2041-6520
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- Citations: 7
Parr J, White AJP, Crimmin M, 2021, Magnesium-Stabilised Transition Metal Formyl Complexes: Structures, Bonding, and Ethenediolate Formation
<jats:p>Herein we report the first comprehensive series of crystallographically characterised transition metal formyl complexes. In these complexes, the formyl ligand is trapped as part of a chelating structure between a transition metal (Cr, Mn, Fe, Co, Rh, W, and Ir) and a magnesium (Mg) cation. Calculations suggest that this bonding mode results in significant oxycarbene-character of the formyl ligand. Electron-rich late-transition metal complexes have the highest oxycarbene-character to the bonding and are the most stable in solution. Further reaction of a heterometallic Cr---Mg formyl complex results in a rare example of C–C coupling and formation of an ethenediolate complex. These results show that well-defined transition metal formyl complexes are potential intermediates in the homologation of carbon monoxide.</jats:p>
Parr J, White AJP, Crimmin M, 2021, Magnesium-Stabilised Transition Metal Formyl Complexes: Structures, Bonding, and Ethenediolate Formation
<jats:p>Herein we report the first comprehensive series of crystallographically characterised transition metal formyl complexes. In these complexes, the formyl ligand is trapped as part of a chelating structure between a transition metal (Cr, Mn, Fe, Co, Rh, W, and Ir) and a magnesium (Mg) cation. Calculations suggest that this bonding mode results in significant oxycarbene-character of the formyl ligand. Electron-rich late-transition metal complexes have the highest oxycarbene-character to the bonding and are the most stable in solution. Further reaction of a heterometallic Cr---Mg formyl complex results in a rare example of C–C coupling and formation of an ethenediolate complex. These results show that well-defined transition metal formyl complexes are potential intermediates in the homologation of carbon monoxide.</jats:p>
Brown R, Hooper TN, Rekhroukh F, et al., 2021, Alumination of aryl methyl ethers: switching between sp 2 and sp 3 C–O bond functionalisation with Pd-catalysis, Chemical Communications, Vol: -, Pages: 1-4, ISSN: 1359-7345
The reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) with aryl methyl ethers proceeded with alumination of the sp3 C–O bond. The selectivity of this reaction could be switched by inclusion of a catalyst. In the presence of [Pd(PCy3)2], chemoselective sp2 C–O bond functionalisation was observed. Kinetic isotope experiments and DFT calculations support a catalytic pathway involving the ligand-assisted oxidative addition of the sp2 C–O bond to a Pd–Al intermetallic complex.
Crimmin MR, 2021, Benzene rings reach their breaking point, NATURE, Vol: 597, Pages: 33-34, ISSN: 0028-0836
Kong R, Batuecas M, Crimmin M, 2021, Reactions of Aluminium(I) with Transition Metal Carbonyls: Scope, Mechanism and Selectivity of CO Homologation
<jats:p>Over the past few decades, numerous model systems have been discovered that create carbon–carbon bonds from CO. These reactions are of potential relevance to the Fischer-Tropsch (F-T) process, a technology that converts syngas mixtures (H2/CO) into mixtures of hydrocarbons. In this paper, a new homogeneous model system that constructs carbon chains from CO is reported. The system exploits the cooperative effect of a transition metal complex and main group reductant. An entire reaction sequence from C1 to C2 to C3 to C4 has been synthetically verified. The scope of reactivity is broad and includes a variety of transition metals (M = Cr, Mo, W, Mn, Re, Co), including those found in industrial heterogeneous F-T catalysts. Variation of the transition metal fragment impacts the relative rate of the steps of chain growth, allowing isolation and structural characterisation of a rare C2 intermediate. The selectivity of carbon chain growth is also impacted by this variable; two distinct isomers of the C3 carbon chain were observed to form in different ratios with different transition metal reagents. Based on a combination of experiments (isotope labelling studies, study of intermediates) and calculations (DFT, NBO, ETS-NOCV) we propose a complete mechanism for chain growth that involves defined reactivity at both transition metal and main group centres.</jats:p>
Sheldon DJ, Crimmin MR, 2021, Complete deconstruction of SF6 by an aluminium(i) compound, CHEMICAL COMMUNICATIONS, Vol: 57, Pages: 7096-7099, ISSN: 1359-7345
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- Citations: 9
Sheldon D, Crimmin M, 2021, Complete Deconstruction of SF6 by an Aluminium(I) Compound
<jats:p><jats:bold>The room-temperature activation of SF<jats:sub>6</jats:sub>, a potent greenhouse gas, is reported using a monovalent aluminium(I) reagent to form well-defined aluminium(III) fluoride and aluminium(III) sulfide products. New reactions have been developed to utilise the aluminium(III) fluoride and aluminium(III) sulfide as a nucleophilic source of F<jats:sup>–</jats:sup> and S<jats:sup>2– </jats:sup>for a range of electrophiles. The overall reaction sequence results in the net transfer of fluorine or sulfur atoms from an environmentally detrimental gas to useful organic products.</jats:bold></jats:p>
Brown R, hooper TN, Rekroukh F, et al., 2021, Alumination of Aryl Methyl Ethers: Switching Between Sp2 and Sp3 C–O Bond Functionalisation with Pd-Catalysis
<jats:p>The reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with aryl methyl ethers proceeded with alumination of the sp3 C–O bond by a presumed SN2 pathway. The selectivity of this reaction could be switched by inclusion of a catalyst. In the presence of [Pd(PCy3)2], chemoselective sp2 C–O bond functionalisation was observed. Kinetic isotope experiments and DFT calculations support a catalytic pathway involving the ligand-assisted oxidative addition of the sp2 C–O bond to a Pd---Al intermetallic complex. The net result of both non-catalysed and catalytic pathways is the generation of polar organoaluminium complexes from aryl methyl ethers with complete atom-efficiency. Switches in selectivity yield isomeric products from a single starting material. The methodology (and mechanistic insight) holds promise as a means to functionalise aromatic molecules derived from lignin depolymerisation and we demonstrate an application to a derivative of vanillin.</jats:p>
Phillips N, Kong R, White A, et al., 2021, Slippage between η2 and η1 coordination in Group 11 borataalkene complexes: models for alkene activation, Angewandte Chemie International Edition, Vol: 60, Pages: 12013-12019, ISSN: 1433-7851
A series of linear late transition metal (M = Cu, Ag, Au and Zn) complexes featuring a side-on [B=C] - containing ligand have been isolated and characterised. The [B=C] - moiety is isoelectronic with the C=C system of an alkene. Comparison across the series shows that in the solid-state, deviation between the η 2 and η 1 coordination mode occurs. The degree of slippage is greatest for Au > Ag > Cu. A related zinc complex containing two [B=C] - ligands was prepared as a further point of comparison for the η 1 coordination mode. The bonding in these new complexes has been interrogated by computational techniques (QTAIM, NBO, ETS-NOCV) and rationalised in terms of the Dewar-Chatt-Duncanson model. The combined structural and computational data provide unique insight into catalytically relevant linear d 10 complexes of Cu, Ag and Au. Slippage is proposed to play a key role in catalytic reactions of alkenes through disruption and polarisation of the p -system. Through the preparation and analysis of a consistent series of group 11 complexes, we show that variation of the metal can impact the degree of slippage and hence substrate activation.
Phillips NA, Kong RY, White AJP, et al., 2021, Group 11 Borataalkene Complexes: Models for Alkene Activation, Angewandte Chemie, Vol: 133, Pages: 12120-12126, ISSN: 0044-8249
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