Imperial College London

Professor Mark R. Crimmin

Faculty of Natural SciencesDepartment of Chemistry

Professor of Organometallic Chemistry
 
 
 
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Contact

 

+44 (0)20 7594 2846m.crimmin Website

 
 
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Location

 

501NMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

175 results found

Sheldon DJ, Parr JM, Crimmin MR, 2024, Defluorination of HFCs by a magnesium reagent., Dalton Trans, Vol: 53, Pages: 6524-6528

Reaction of a series of HFCs with a main group reagent containing a Mg-Mg bond results in defluorination to form the corresponding magnesium fluoride complex. In the case of 1,1,1,2-tetrafluoroethane (HFC-134a) generation of the fluoride occurs alongside selective formation of 1,1-difluoroethene. DFT calculations have been carried out to better understand the selectivity and compare the barriers for sp3 C-F bond activation with sp3 C-H bond activation in this system.

Journal article

Yang W, White AJP, Crimmin MR, 2024, Deoxygenative Coupling of CO with a Tetrametallic Magnesium Hydride Complex, Angewandte Chemie, Vol: 136, ISSN: 0044-8249

<jats:title>Abstract</jats:title><jats:p>Addition of CO to a tetrametallic magnesium hydride cluster results in both carbon‐carbon bond formation and deoxygenation to generate an acetaldehyde enolate [C<jats:sub>2</jats:sub>OH<jats:sub>3</jats:sub>]<jats:sup>−</jats:sup> which remains coordinated to the cluster. To the best of our knowledge, this is the first example of formation of an isolable complex containing an [C<jats:sub>2</jats:sub>OH<jats:sub>3</jats:sub>]<jats:sup>−</jats:sup> fragment from reaction of CO with a metal hydride, and the first example of CO homologation and deoxygenation at a main group metal. DFT studies suggest that key steps in the mechanism involve nucleophilic attack of an oxymethylene on a formyl ligand to generate an unstable [C<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>H<jats:sub>3</jats:sub>]<jats:sup>3−</jats:sup> fragment, which undergoes subsequent deoxygenation.</jats:p>

Journal article

Yang W, White AJP, Crimmin MR, 2024, Deoxygenative coupling of CO with a tetrametallic magnesium hydride complex, Angewandte Chemie International Edition, Vol: 63, ISSN: 1433-7851

Addition of CO to a tetrametallic magnesium hydride cluster results in both carbon-carbon bond formation and deoxygenation to generate an acetaldehyde enolate [C2 OH3 ]- which remains coordinated to the cluster. To the best of our knowledge, this is the first example of formation of an isolable complex containing an [C2 OH3 ]- fragment from reaction of CO with a metal hydride, and the first example of CO homologation and deoxygenation at a main group metal. DFT studies suggest that key steps in the mechanism involve nucleophilic attack of an oxymethylene on a formyl ligand to generate an unstable [C2 O2 H3 ]3- fragment, which undergoes subsequent deoxygenation.

Journal article

Gorgas N, Stadler B, White AJP, Crimmin MRet al., 2024, Vinylic C-H Activation of Styrenes by an Iron-Aluminum Complex., J Am Chem Soc, Vol: 146, Pages: 4252-4259

The oxidative addition of sp2 C-H bonds of alkenes to single-site transition-metal complexes is complicated by the competing π-coordination of the C═C double bond, limiting the examples of this type of reactivity and onward applications. Here, we report the C-H activation of styrenes by a well-defined bimetallic Fe-Al complex. These reactions are highly selective, resulting in the (E)-β-metalation of the alkene. For this bimetallic system, alkene binding appears to be essential for the reaction to occur. Experimental and computational insights suggest an unusual reaction pathway in which a (2 + 2) cycloaddition intermediate is directly converted into the hydrido vinyl product via an intramolecular sp2 C-H bond activation across the two metals. The key C-H cleavage step proceeds through a highly asynchronous transition state near the boundary between a concerted and a stepwise mechanism influenced by the resonance stabilization ability of the aryl substituent. The metalated alkenes can be further functionalized, which has been demonstrated by the (E)-selective phosphination of the employed styrenes.

Journal article

Farley SES, Mulryan D, Rekhroukh F, Phanopoulos A, Crimmin MRet al., 2024, Catalytic HF Shuttling between Fluoroalkanes and Alkynes., Angewandte Chemie International Edition, Vol: 63, ISSN: 1433-7851

In this paper, we report BF3  ⋅ OEt2 as a catalyst to shuttle equivalents of HF from a fluoroalkane to an alkyne. Reactions of terminal and internal aliphatic alkynes led to formation of difluoroalkane products, while diarylalkynes can be selectively converted into fluoroalkenes. The method tolerates numerous sensitive functional groups including halogen, protected amine, ester and thiophene substituents. Mechanistic studies (DFT, probe experiments) suggest the catalyst is involved in both the defluorination and fluorination steps, with BF3 acting as a Lewis acid and OEt2 a weak Lewis base that mediates proton transfer. In certain cases, the interconversion of fluoroalkene and difluoroalkane products was found to be reversible. The new catalytic system was applied to demonstrate proof-of-concept recycling of poly(vinylidene difluoride).

Journal article

Perez-Jimenez M, Crimmin MR, 2024, Photochemical H2 activation by an Zn-Fe heterometallic: a mechanistic investigation., Chem Sci, Vol: 15, Pages: 1424-1430, ISSN: 2041-6520

Addition of H2 to a Zn-Fe complex was observed to occur under photochemical conditions (390 or 428 nm LED) and leads to the formation of a heterometallic dihydride complex. The reaction does not occur under thermal conditions and DFT calculations suggest this is an endergonic, light driven process. Through a combined experimental and computational approach, the plausible mechanisms for H2 activation were investigated. Inhibition experiments, double-label cross-over experiments, radical trapping experiments, EPR spectroscopy and DFT calculations were used to gain insight into this system. The combined data are consistent with two plausible mechanisms, the first involving ligand dissociation followed by oxidative addition of H2 at the Fe centre, the second involving homolytic fragmentation of the Zn-Fe heterometallic and formation of radical intermediates.

Journal article

McMullen JS, White AJP, Crimmin MR, 2023, Ring-expansion and desulfurisation of thiophenes with an aluminium(I) reagent., Chem Commun (Camb), Vol: 59, Pages: 14681-14684

Reactions of thiophene, 2-methylthiophene, 2-methoxythiophene, 2,3-dimethylthiophene, and benzothiophene with the aluminium(I) complex [{ArNC(Me)2H}Al] (Ar = 2,6-di-isopropylphenyl) are reported. In all cases, carbon-sulfur bond activation and ring-expansion of the heterocycle is observed. For thiophene, we identify a reaction network for desulfurisation that includes an unusual second carbon-sulfur bond activation step.

Journal article

Parr JM, Crimmin MR, 2023, Carbon-carbon bond activation by Mg, Al, and Zn complexes., Chem Sci, Vol: 14, Pages: 11012-11021, ISSN: 2041-6520

Examples of carbon-carbon bond activation reactions at Mg, Al, and Zn are described in this review. Several distinct mechanisms for C-C bond activation at these metals have been proposed, with the key C-C bond activation step occurring by (i) α-alkyl elimination, (ii) β-alkyl elimination, (iii) oxidative addition, or (iv) an electrocyclic reaction. Many of the known pathways involve an overall 2-electron redox process. Despite this, the direct oxidative addition of C-C bonds to these metals is relatively rare, instead most reactions occur through initial installation of the metal on a hydrocarbon scaffold (e.g. by a cycloaddition reaction or hydrometallation) followed by an α-alkyl or β-alkyl elimination step. Emerging applications of Mg, Al, and Zn complexes as catalysts for the functionalisation of C-C bonds are also discussed.

Journal article

Parr JM, Crimmin MR, 2023, Carbon-carbon bond activation by Mg, Al, and Zn complexes, CHEMICAL SCIENCE, ISSN: 2041-6520

Journal article

Parr JM, White AJP, Crimmin MR, 2023, Calcium-stabilised transition metal bis(formyl) complexes: structure and bonding, CHEMICAL COMMUNICATIONS, Vol: 59, Pages: 9840-9843, ISSN: 1359-7345

Journal article

Sheldon DJ, Parr JM, Crimmin MR, 2023, Room Temperature Defluorination of Poly(tetrafluoroethylene) by a Magnesium Reagent, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 145, Pages: 10486-10490, ISSN: 0002-7863

Journal article

Parr JM, Crimmin MR, 2023, Carbon‐Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates**, Angewandte Chemie, Vol: 135, ISSN: 0044-8249

<jats:title>Abstract</jats:title><jats:p>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 H<jats:sub>2</jats:sub> are also discussed.</jats:p>

Journal article

Stadler B, Gorgas N, White AJP, Crimmin MRet al., 2023, Double Deprotonation of CH3CN by an Iron-Aluminium Complex., Angew Chem Weinheim Bergstr Ger, Vol: 135, ISSN: 0044-8249

Herein we present the first double deprotonation of acetonitrile (CH3CN) 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 [CH2CN]- 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 CH3CN also offers the possibility of establishing a broader chemistry of this motif.

Journal article

Baker GJ, White AJP, Casely IJ, Grainger D, Crimmin MRet al., 2023, Catalytic, Z-Selective, Semi-Hydrogenation of Alkynes with a Zinc-Anilide Complex, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 145, Pages: 7667-7674, ISSN: 0002-7863

Journal article

Stadler B, Gorgas N, White AJP, Crimmin MRet al., 2023, Double Deprotonation of CH<sub>3</sub>CN by an Iron-Aluminium Complex, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, ISSN: 1433-7851

Journal article

Parr JM, Crimmin MR, 2023, Carbon-Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, ISSN: 1433-7851

Journal article

Zhang L, Kaukver S, McMullen J, White AJP, Crimmin MRet al., 2023, Catalytic C-H Alumination of Thiophenes: DFT Predictions and Experimental Verification, ORGANOMETALLICS, Vol: 42, Pages: 1711-1716, ISSN: 0276-7333

Journal article

Mies T, Schurmann C, Ito S, White AJP, Crimmin MR, Barrett AGMet al., 2023, Synthesis and Characterization of a Calcium-Pyrazolonato Complex. Observation of <i>In-Situ</i> Desolvation During Micro-Electron Diffraction, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, Vol: 649, ISSN: 0044-2313

Journal article

Mies T, Schürmann C, Ito S, White AJP, Crimmin MR, Barrett AGMet al., 2023, Front Cover: Synthesis and Characterization of a Calcium‐Pyrazolonato Complex. Observation of <i>In‐Situ</i> Desolvation During Micro‐Electron Diffraction (Z. Anorg. Allg. Chem. 5/2023), Zeitschrift für anorganische und allgemeine Chemie, Vol: 649, ISSN: 0044-2313

Journal article

Parr JMM, Phanopoulos A, Vickneswaran A, Crimmin MRRet al., 2023, Understanding the role of ring strain in β-alkyl migration at Mg and Zn centres, Chemical Science, Vol: 14, Pages: 1590-1597, ISSN: 2041-6520

The activation of C–C σ-bonds within strained three- and four-membered hydrocarbons at electrophilic Mg and Zn centres is reported. This was achieved in a two-step process involving (i) hydrometallation of a methylidene cycloalkane followed by (ii) intramolecular C–C bond activation. While hydrometallation of methylidene cyclopropane, cyclobutane, cyclopentane and cyclohexane occurs for both Mg and Zn reagents, the C–C bond activation step is sensitive to ring size. For Mg, both cyclopropane and cyclobutane rings participate in C–C bond activation. For Zn, only the smallest cyclopropane ring reacts. These findings were used to expand the scope of catalytic hydrosilylation of C–C σ-bonds to include cyclobutane rings. The mechanism of C–C σ-bond activation was investigated through kinetic analysis (Eyring), spectroscopic observation of intermediates, and a comprehensive series of DFT calculations, including activation strain analysis. Based on our current understanding, C–C bond activation is proposed to occur by a β-alkyl migration step. β-Alkyl migration is more facile for more strained rings and occurs with lower barriers for Mg compared to Zn. Relief of ring strain is a key factor in determining the thermodynamics of C–C bond activation, but not in stabilising the transition state for β-alkyl migration. Rather, we ascribe the differences in reactivity to the stabilising interaction between the metal centre and the hydrocarbon ring-system, with the smaller rings and more electropositive metal (Mg) leading to a smaller destabilisation interaction energy as the transition state is approached. Our findings represent the first example of C–C bond activation at Zn and provide detailed new insight into the factors at play in β-alkyl migration at main group centres.

Journal article

Garcon M, Phanopoulos A, White AJP, Crimmin MRet al., 2023, Reversible dihydrogen activation and catalytic H/D exchange with group 10 heterometallic complexes, Angewandte Chemie International Edition, Vol: 62, ISSN: 1433-7851

Reaction of a hexagonal planar palladium complex featuring a [PdMg3H3] core with H2 is reversible and leads to the formation of a new [PdMg2H4] tetrahydride species alongside an equivalent of a magnesium hydride co-product [MgH]. While the reversibility of this process prevented isolation of [PdMg2H4], analogous [PtMg2H4] and [PtZn2H4] complexes could be isolated and characterised through independent syntheses. Computational analysis (DFT, AIM, NCIPlot) of the bonding in a series of heterometallic tetrahydride compounds (Ni–Pt; Mg and Zn) suggests that these complexes are best described as square planar with marginal metal-metal interactions; the strength of which increases slightly as group 10 is descended and increases from Mg to Zn. DFT calculations support a mechanism for H2 activation involving a ligand-assisted oxidative addition to Pd. These findings were exploited to develop a catalytic protocol for H/D exchange into magnesium hydride and zinc hydride bonds.

Journal article

Garçon M, Phanopoulos A, White AJP, Crimmin MRet al., 2023, Reversible Dihydrogen Activation and Catalytic H/D Exchange with Group 10 Heterometallic Complexes**, Angewandte Chemie, Vol: 135, ISSN: 0044-8249

<jats:title>Abstract</jats:title><jats:p>Reaction of a hexagonal planar palladium complex featuring a [PdMg<jats:sub>3</jats:sub>H<jats:sub>3</jats:sub>] core with H<jats:sub>2</jats:sub>is reversible and leads to the formation of a new [PdMg<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>] tetrahydride species alongside an equivalent of a magnesium hydride co‐product [MgH]. While the reversibility of this process prevented isolation of [PdMg<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>], analogous [PtMg<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>] and [PtZn<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>] complexes could be isolated and characterised through independent syntheses. Computational analysis (DFT, AIM, NCIPlot) of the bonding in a series of heterometallic tetrahydride compounds (Ni–Pt; Mg and Zn) suggests that these complexes are best described as square planar with marginal metal‐metal interactions; the strength of which increases slightly as group 10 is descended and increases from Mg to Zn. DFT calculations support a mechanism for H<jats:sub>2</jats:sub>activation involving a ligand‐assisted oxidative addition to Pd. These findings were exploited to develop a catalytic protocol for H/D exchange into magnesium hydride and zinc hydride bonds.</jats:p>

Journal article

Garcon M, Phanopoulos A, Sackman GA, Richardson C, White AJP, Cooper R, Edwards AJ, Crimmin MRet al., 2022, The Continuum Between Hexagonal Planar and Trigonal Planar Geometries, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 61, ISSN: 1433-7851

Journal article

Garçon M, Phanopoulos A, Sackman GA, Richardson C, White AJP, Cooper RI, Edwards AJ, Crimmin MRet al., 2022, The Continuum Between Hexagonal Planar and Trigonal Planar Geometries**, Angewandte Chemie, Vol: 134, ISSN: 0044-8249

<jats:title>Abstract</jats:title><jats:p>New heterometallic hydride complexes that involve the addition of {Mg−H} and {Zn−H} bonds to group 10 transition metals (Pd, Pt) are reported. The side‐on coordination of a single {Mg−H} to Pd forms a well‐defined σ‐complex. In contrast, addition of three {Mg−H} or {Zn−H} bonds to Pd or Pt results in the formation of planar complexes with subtly different geometries. We compare their structures through experiment (X‐ray diffraction, neutron diffraction, multinuclear NMR), computational methods (DFT, QTAIM, NCIPlot), and theoretical analysis (MO diagram, Walsh diagram). These species can be described as snapshots along a continuum of bonding between ideal trigonal planar and hexagonal planar geometries.</jats:p>

Journal article

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

Journal article

Garçon M, Phanopoulos A, White A, Crimmin Met al., 2022, Reversible Dihydrogen Activation and Catalytic H/D Exchange with Group 10 Heterometallic Complexes

<jats:p>Reaction of a hexagonal planar palladium complex with a [PdMg3H3] core with H2 is reversible and leads to the formation of a new [PdMg2H4] tetrahydride species alongside an equivalent of a magnesium hydride co-product [MgH]. While the reversibility of this process prevented isolation and structural characterisation of [PdMg2H4], analogous [PtMg2H4] and [PdZn2H4] complexes could be isolated and characterised through independent syntheses. Computational analysis (DFT, AIM, NCIPlot) of the bonding in a series of heterometallic tetrahydride compounds (Ni-Pt; Mg and Zn) suggests that these complexes are best described as square planar with marginal metal–metal interactions; the strength of which increases as group 10 is descended and increases from Mg to Zn. DFT calculations support a mechanism for H2 activation involving a ligand-assisted oxidative addition to Pd. These findings were exploited to develop a catalytic protocol for H/D exchange into magnesium hydride and zinc hydride bonds.</jats:p>

Journal article

Gorgas N, White A, Crimmin M, 2022, Diverse Reactivity of an Iron–Aluminium Complex with Substituted Pyridines

<jats:p>The reaction of an Fe–Al complex with an array of substituted pyridines is reported. Depending on the substitution pattern of the substrate site-selective sp2 or sp3 C–H bond activation is observed. A series of reaction products are observed based on (i) C–Al bond formation, (ii) C–C bond formation by nucleophilic addition or (iii) deprotonation of the β-diketiminate ligand. A divergent set of mechanisms involving a common intermediate is proposed.</jats:p>

Journal article

Rekhroukh F, Zhang L, Kong RY, White AJP, Crimmin MRet al., 2022, Stereoselective insertion of cyclopropenes into Mg-Mg bonds, CHEMICAL COMMUNICATIONS, Vol: 58, Pages: 8282-8285, ISSN: 1359-7345

Journal article

Baker G, White A, Casely I, Grainger D, Crimmin Met al., 2022, Catalytic, Z-Selective, Semi-Hydrogenation of Alkynes with a Zinc–Anilide Complex

<jats:p>The reversible activation of dihydrogen with a molecular zinc anilide complex is reported. The mechanism of this reaction has been probed through stoichiometric experiments and DFT calculations. The combined evidence suggests that H2 activation occurs by addition across the Zn–N bond via a four-membered transition state in which the Zn and N atoms play a dual role of Lewis acid and Lewis base. The zinc hydride complex that results from H2 addition, has been shown to be remarkably effective for the hydrozincation of C=C bonds at modest temperatures. The scope of hy-drozincation includes alkynes, alkenes, and a 1,3-butadiyne. For alkynes, the hydrozincation step is stereospecific leading exclusively to the syn-isomer. Competition experiments show that the hydrozincation of alkynes is faster than the equivalent alkene substrates. These new discoveries have been used to develop an unprecedented catalytic sys-tem for the semi-hydrogenation of alkynes. The catalytic scope includes both aryl and alkyl substituted internal al-kynes and proceeds with high alkene : alkane (96 : 4) and Z : E ratios (&gt;91 : 9). This work offers a first example of selective hydrogenation catalysis using zinc complexes.</jats:p>

Journal article

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

Journal article

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