Cath Weetman

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23 Mar 07:55

[ASAP] Cooperative Bond Activation and Catalytic CO2 Functionalization with a Geometrically Constrained Bis(silylene)-Stabilized Borylene

by Xi Chen, Yin Yang, Hao Wang, and Zhenbo Mo

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Journal of the American Chemical Society
DOI: 10.1021/jacs.3c00949
23 Mar 07:54

[ASAP] Synthesis and Reactivity of an Anti-van’t Hoff/Le Bel Compound with a Planar Tetracoordinate Silicon(II) Atom

by Changkai Shan, Shicheng Dong, Shenglai Yao, Jun Zhu, and Matthias Driess

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Journal of the American Chemical Society
DOI: 10.1021/jacs.3c00722
10 Mar 07:18

Trapping of a Transient Base‐Stabilised Alumylene and Alumylene‐Type Reactivity of a Self‐Stabilising Dialumene towards Organic Azides

by Debabrata Dhara, Arumugam Jayaraman, Marcel Härterich, Merle Arrowsmith, Malte Jürgensen, Maximilian Michel, Holger Braunschweig
Trapping of a Transient Base-Stabilised Alumylene and Alumylene-Type Reactivity of a Self-Stabilising Dialumene towards Organic Azides

An NHC-stabilised aluminium(III) terphenyl dihalide was reduced in the presence of alkynes to trap the in-situ-formed alumylene [NHC(Ter)Al:]. In the absence of an alkyne the reduction yielded a self-stabilised dialumene, which showed alumylene-like reactivity towards organic azides.


Abstract

The reduction of a carbene-coordinated, sterically encumbered terphenyl-substituted aluminium diiodide, (LRAlI2), yielded a “masked” dialumene (LRAl=AlRL), self-stabilised through [2+2] cycloaddition with a peripheral aromatic group. During the course of the reaction, a carbene-stabilised arylalumylene (LRAl:) was generated in situ, which was trapped using an alkyne, generating an aluminacyclopropene or a C−H activated product thereof, depending on the steric bulk of the alkyne. The masked dialumene also underwent intramolecular cycloreversion and dissociation into alumylene fragments, which reacted with various organic azides to yield monomeric or dimeric iminoalanes depending on the sterics of the azide substituent. The thermodynamics of monomeric and dimeric iminoalane formation were probed by theoretical calculations.

10 Mar 07:17

[ASAP] Li vs Na: Divergent Reaction Patterns between Organolithium and Organosodium Complexes and Ligand-Catalyzed Ketone/Aldehyde Methylenation

by Nathan Davison, Claire L. McMullin, Lu Zhang, Shu-Xian Hu, Paul G. Waddell, Corinne Wills, Casey Dixon, and Erli Lu

TOC Graphic

Journal of the American Chemical Society
DOI: 10.1021/jacs.3c01033
06 Mar 08:10

Linear and Bent Cp*2Si: Reversible Phase Transition of a Key Molecule

by Paul Niklas Ruth, Julijan Sarcevic, Regine Herbst-Irmer, Christian P. Sindlinger, Dietmar Stalke
Linear and Bent Cp*2Si: Reversible Phase Transition of a Key Molecule

The organometallic lighthouse molecule Cp*2SiII was always the odd one out of the heavier homologues. In the solid-state counterintuitively there is a linear molecule next to two bent ones. While the latter is more stable, the linear conformer was mainly attributed to fuzzy packing effects. Now it is clear that the linearity has to be attributed to entropy in the room temperature phase while the bending is due to dispersion of the rings in the 80 K phase.


Abstract

The solid-state structure of decamethylsilicocene Cp*2Si with a bent and a linear molecule in the same unit cell was so far considered an exception in relation to the structures of its all-bent heavier analogues Cp*2E with E=Ge, Sn, Pb. Here, we present the solution to this conundrum by reporting a low-temperature phase, where all three symmetrically independent molecules are present in a bent formation. This reversible enantiotropic phase transition occurs in the temperature range between 80 K and 130 K and provides a rationale for the unexpected linear molecule based in entropy beyond hand-waving explanations such as electronic reasons or packing effects.

11 Nov 17:43

Reversible Dihydrogen Activation and Catalytic H/D Exchange with Group 10 Heterometallic Complexes

by Martí Garçon, Andreas Phanopoulos, Andrew White, Mark Richard Crimmin
Reversible Dihydrogen Activation and Catalytic H/D Exchange with Group 10 Heterometallic Complexes**

Reaction of a hexagonal planar palladium complex having a [PdMg3H3] core with H2 is reversible and leads to the formation of a new [PdMg2H4] tetrahydride species. 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.


Abstract

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.

09 Nov 16:22

Anionic Magnesium and Calcium Hydrides: Transforming CO into Unsaturated Disilyl Ethers

by Jacob S. McMullen, Ryan Huo, Petra Vasko, Alison J. Edwards, Jamie Hicks
Anionic Magnesium and Calcium Hydrides: Transforming CO into Unsaturated Disilyl Ethers

CO has directly been transformed into small organic starting materials using earth-abundant, anionic group 2 hydride reagents.


Abstract

The synthesis, characterisation and reactivity of two isostructural anionic magnesium and calcium complexes is reported. By X-ray and neutron diffraction techniques, the anionic hydrides are shown to exist as dimers, held together by a range of interactions between the two anions and two bridging potassium cations. Unlike the vast proportion of previously reported dimeric group 2 hydrides, which have hydrides that bridge two group 2 centres, here the hydrides are shown to be “terminal”, but stabilised by interactions with the potassium cations. Both anionic hydrides were found to insert and couple CO under mild reaction conditions to give the corresponding group 2 cis-ethenediolate complexes. These cis-ethenediolate complexes were found to undergo salt elimination reactions with silyl chlorides, allowing access to small unsaturated disilyl ethers with a high percentage of their mass originating from the C1 source CO.

27 Oct 18:09

A Germapyramidane Switches Between 3D Cluster and 2D Cyclic Structures in Single‐Electron Steps

by Peter Coburger, Fabio Masero, Jonas Bösken, Victor Mougel, Hansjörg Grützmacher
A Germapyramidane Switches Between 3D Cluster and 2D Cyclic Structures in Single-Electron Steps

The mutual redox-isomerisation of a cationic nido-germapyramidane into a planar aromatic germole-diide is reported. The mechanism was elucidated using electrochemical and theoretical studies.


Abstract

Reaction of the imidazolium-substituted iphosphate-diide, (Ipr)2C2P2 (IDP), with GeCl2 ⋅ dioxane and KBArF24 [(BarF24)−=tetrakis[(3,5-trifluoromethyl)phenyl]borate)] afforded the dicationic spherical-aromatic nido-cluster [Ge(η4-IDP)]2+ ([1]2+) (Ipr=1,3-bis(2,6-diisopropylphenyl)imidazolium-2-ylidene). This complex is a rare heavy analogue of the elusive pyramidane [C(η4-C4H4)]. [1]2+ undergoes two reversible one-electron reductions, which yield the radical cation [2]⋅ + and the neutral GeII species 3. Both [2]⋅ + and 3 rearrange in solution forming the 2D aromatic and planar imidazolium-substituted digermolide [4]2+ and germole-diide 5, respectively. Both planar species can be oxidized back to [1]2+ using AgSbF6. These redox-isomerizations correspond to the fundamental transformation of a 3D aromatic cluster into a 2D aromatic ring compound upon reduction and vice versa. The mechanism of these reactions was elucidated using DFT calculations and cyclic voltammetry experiments.

26 Oct 07:03

Towards Substrate–Reagent Interaction of Lochmann–Schlosser Bases in THF: Bridging THF Hides Potential Reaction Site of a Chiral Superbase

by Lukas Brieger, Tobias Schrimpf, Rebecca Scheel, Christian Unkelbach, Carsten Strohmann
Towards Substrate–Reagent Interaction of Lochmann–Schlosser Bases in THF: Bridging THF Hides Potential Reaction Site of a Chiral Superbase

The isolation of a new THF-solvated, ferrocene-based Lochmann–Schlosser base with all four components lithium, potassium, carbanion, and alkoxide led to the observation of new structural motifs with respect to these superbasic reagents. The “kick out” of a THF leads to the detachment, providing the typical Li/K reaction site, whereas the “smart pass” leads to the favorable THF-displacement and the K/K reaction site provided for substrates.


Abstract

The metalation of N,N-dimethylaminomethylferrocene in THF by the superbasic mixture of n BuLi/KO t Bu proceeds readily at low temperatures to afford a bimetallic Li2K2 aggregate containing ferrocenyl anions and tert-butoxide. Starting from an enantiomerically enriched ortho-lithiated aminomethylferrocene, an enantiomerically pure superbase can be prepared. The molecular compound exhibits superbasic behavior deprotonating N,N-dimethylbenzylamine in the α-position and is also capable of deprotonating toluene. Quantum chemical calculations provide insight into the role of the bridging THF molecule to the possible substrate–reagent interaction. In addition, a benzylpotassium alkoxide adduct gives a closer look into the corresponding reaction site of the Lochmann–Schlosser base that is reported herein.

26 Oct 07:02

Coordination of Pnictogenylboranes Towards Tl(I) Salts and a Tl‐ Mediated P−P Coupling

by Robert Szlosek, Matthias Ackermann, Christian Marquardt, Michael Seidl, Alexey Timoshkin, Manfred Scheer
Coordination of Pnictogenylboranes Towards Tl(I) Salts and a Tl- Mediated P−P Coupling

Reactions of NMe3-stabilized pnictogenylboranes with Tl(I) salts of weakly coordinating anions led to rare examples of Tl coordination compounds [Tl(EH2BH2⋅NMe3) n ]+ (n=1, 3; E=P, As) featuring mono and threefold coordination of pnictogenylboranes. In addition, by using CH2Cl2 as a solvent, an unprecedented, Tl-promoted P−P coupling was observed, leading to [Me3N⋅BH2PH2-PHBH2⋅NMe3]+. During these investigations, novel Tl[WCA] salts were prepared and the synthesis of EH2BH2⋅NMe3 was improved towards greater accessibility.


Abstract

The coordination chemistry of only Lewis-base (LB)-stabilized pnictogenylboranes EH2BH2⋅NMe 3 (E=P, As) towards Tl(I) salts has been studied. The reaction of Tl[BArCl] (BArCl=[B(3,5-C6H3Cl2)4]−) with the corresponding pnictogenylborane results in the formation of [Tl(EH2BH2⋅NMe3)][BArCl] (1 a: E=P; 1 b: E=As). Whereas the Tl ion in 1 a/b is monocoordinated, the exchange of the weakly coordinating anion (WCA) in the Tl(I) salt leads to the formation of a trigonal pyramidal coordination mode at the Tl atom by coordination of three equivalents of EH2BH2 ⋅ NMe3 in [Tl(EH2BH2 ⋅ NMe3)3][WCA] (2 a: E=P, WCA=TEFCl; 2 b: E=As, WCA=TEF) (TEF=[Al{OC(CF3)3}4]−, TEFCl=[Al{(OC(CF3)2(CCl3)}4]−). Furthermore, by using two equivalents of PH2BH2⋅NMe 3 , a Tl(I)-mediated P−P coupling takes place in CH2Cl2 as solvent resulting in [Me3N⋅BH2PH2PHBH2⋅NMe3][WCA] (WCA=TEF, 3 a; BArCl, 3 b; TEFCl, 3 c). In contrast, for the arsenic derivatives 1 b and 2 b, no coupling reaction is observed. The underlying chemical processes are elucidated by quantum chemical computations.

26 Oct 06:58

Noncovalent Interactions in Halogenated Pyridinium Salts of the Weakly Coordinating Anion [Al(OTeF5)4]−

by S. Kotsyuda, Ahmet Nadi Toraman, Patrick Voßnacker, Mathias A. Ellwanger, Simon Steinhauer, Carsten Müller, Sebastian Hasenstab-Riedel
Noncovalent Interactions in Halogenated Pyridinium Salts of the Weakly Coordinating Anion [Al(OTeF5)4]−

The synthesis and structural characterization of the perhalogenated pyridinium cations [C5F5NH]+ and [C5F4ClNH]+ and the dimeric cations [(C5F5N)2H]+ and [(C5Cl5N)2H]+ as [Al(OTeF5)4]− salts are presented. These cations show noncovalent interactions with the weakly coordinating anion [Al(OTeF5)4]− such as strong fluorine specific interactions as well as σ-hole and anion-π interactions.


Abstract

The synthesis and the first structural characterization of the halogenated pyridinium salts [C5F5NH]+, [C5F4ClNH]+, [(C5F5N)2H]+, [(C5Cl5N)2H]+ of the weakly coordinating anion (WCA) [Al(OTeF5)4]−, showing noncovalent interactions in the solid state, are presented. The salts were characterized by the multinuclear NMR and IR spectroscopy as well as X-ray diffraction. Hirshfeld surface analysis and solid state structures reveal various intermolecular anion-π and σ-hole interactions between the corresponding halogenated pyridinium cations and the anion [Al(OTeF5)4]−.

26 Oct 06:57

Quantifying the Influence of Covalent Metal‐Ligand Bonding on Differing Reactivity of Trivalent Uranium and Lanthanide Complexes

by Taylor V. Fetrow, Joshua Zgrabik, Rina Bhowmick, Francesca D. Eckstrom, George Crull, Bess Vlaisavljevich, Scott R. Daly
Quantifying the Influence of Covalent Metal-Ligand Bonding on Differing Reactivity of Trivalent Uranium and Lanthanide Complexes

Here we report experimental and computational studies that quantify the measured effect of variations in metal-ligand covalency on the reactivity of phosphinodiboranate complexes with trivalent uranium and similarly sized lanthanides.


Abstract

Qualitative differences in the reactivity of trivalent lanthanide and actinide complexes have long been attributed to differences in covalent metal-ligand bonding, but there are few examples where thermodynamic aspects of this relationship have been quantified, especially with U3+ and in the absence of competing variables. Here we report a series of dimeric phosphinodiboranate complexes with trivalent f-metals that show how shorter-than-expected U−B distances indicative of increased covalency give rise to measurable differences in solution deoligomerization reactivity when compared to isostructural complexes with similarly sized lanthanides. These results, which are in excellent agreement with supporting DFT and QTAIM calculations, afford rare experimental evidence concerning the measured effect of variations in metal-ligand covalency on the reactivity of trivalent uranium and lanthanide complexes.

26 Oct 06:55

Bimetallic Aluminum‐ and Niobium‐Doped MCM‐41 for Efficient Conversion of Biomass‐Derived 2‐Methyltetrahydrofuran to Pentadienes

by Mengtian Fan, Shaojun Xu, Bing An, Alena M Sheveleva, Alexander Betts, Joseph Hurd, Zhaodong Zhu, Meng He, Dinu Iuga, Longfei Lin, Xinchen Kang, Christopher M A Parlett, Floriana Tuna, Eric JL McInnes, Luke L Keenan, Daniel Lee, Martin P Attfield, Sihai Yang
Bimetallic Aluminum- and Niobium-Doped MCM-41 for Efficient Conversion of Biomass-Derived 2-Methyltetrahydrofuran to Pentadienes

The highly selective conversion of biomass-derived 2-methyltetrahydrofuran (2-MTHF) into pentadienes has been achieved over an aluminum and niobium bimetallic atomically doped MCM-41. The NbV sites enhance the catalytic performance by binding 2-MTHF.


Abstract

The production of conjugated C4–C5 dienes from biomass can enable the sustainable synthesis of many important polymers and liquid fuels. Here, we report the first example of bimetallic (Nb, Al)-atomically doped mesoporous silica, denoted as AlNb-MCM-41, which affords quantitative conversion of 2-methyltetrahydrofuran (2-MTHF) to pentadienes with a high selectivity of 91 %. The incorporation of AlIII and NbV sites into the framework of AlNb-MCM-41 has effectively tuned the nature and distribution of Lewis and Brønsted acid sites within the structure. Operando X-ray absorption, diffuse reflectance infrared and solid-state NMR spectroscopy collectively reveal the molecular mechanism of the conversion of adsorbed 2-MTHF over AlNb-MCM-41. Specifically, the atomically-dispersed NbV sites play an important role in binding 2-MTHF to drive the conversion. Overall, this study highlights the potential of hetero-atomic mesoporous solids for the manufacture of renewable materials.

26 Oct 06:53

Facile Synthesis of Uranium Complexes with a Pendant Borane Lewis Acid and 1,2‐Insertion of CO into a U−N Bond

by Wei Su, Thayalan Rajeshkumar, Libo Xiang, Laurent Maron, Qing Ye
Facile Synthesis of Uranium Complexes with a Pendant Borane Lewis Acid and 1,2-Insertion of CO into a U−N Bond

Reactions between the highly strained uranacycle I with various boranes afford unprecedented uranium complexes bearing either a pendant borate or a pendant borane Lewis acid. The latter promotes the 1,2-insertion of CO into a UIV-N bond.


Abstract

In this contribution, we illustrate uranium complexes bearing a pendant borate (i.e. 1 and 2) or a pendant borane (i.e. 3 and 4) moiety via reaction of the highly strained uranacycle I with various 3-coordinate boranes. Complexes 3 and 4 represent the first examples of uranium complexes with a pendant borane Lewis acid. Moreover, complex 3 was capable of activation of CO, delivering a new CO activation mode, and an abnormal CO 1,2-insertion pathway into a U−N bond. The importance of the pendant borane moiety was confirmed by the controlled experiments.

10 Oct 07:36

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)‐Centre: Labile Mono‐ and Bis(hydridogallyl)zinc Complexes

by Louis J. Morris, Thayalan Rajeshkumar, Laurent Maron, Jun Okuda
Cath Weetman

reversible oxidative addition

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)-Centre: Labile Mono- and Bis(hydridogallyl)zinc Complexes

Zinc dihydride reacts with a gallium(I) reagent by reversible oxidative addition to provide di- and trimetallic hydridogallyl zinc complexes. The position of oxidative addition-reductive elimination equilibria can be controlled by coordination/decoordination of TMEDA.


Abstract

In the presence of TMEDA (N,N,N’,N’-tetramethylethylenediamine), partially deaggregated zinc dihydride as hydrocarbon suspensions react with the gallium(I) compound [(BDI)Ga] (I, BDI={HC(C(CH3)N(2,6-iPr2-C6H3))2}−) by formal oxidative addition of a Zn−H bond to the gallium(I) centre. Dissociation of the labile TMEDA ligand in the resulting complex [(BDI)Ga(H)−(H)Zn(tmeda)] (1) facilitates insertion of a second equiv. of I into the remaining Zn−H to form a thermally sensitive trinuclear species [{(BDI)Ga(H)}2Zn] (2). Compound 1 exchanges with polymeric zinc dideuteride [ZnD2]n in the presence of TMEDA, and with compounds I and 2 via sequential and reversible ligand dissociation and gallium(I) insertion. Spectroscopic and computational studies demonstrate the reversibility of oxidative addition of each Zn−H bond to the gallium(I) centres.

05 Oct 06:54

[ASAP] Synthesis, Structure, and Reactivity of a Superbulky Low-Valent β‑Diketiminate Al(I) Complex

by Samuel Grams, Jonathan Mai, Jens Langer, and Sjoerd Harder
Cath Weetman

Aluminium Big nacnac

TOC Graphic

Organometallics
DOI: 10.1021/acs.organomet.2c00427