The structure of amorphous silicon is widely thought of as a fourfold-connected random network, and yet it is defective atoms, with fewer or more than four bonds, that make it particularly interesting. Despite many attempts to explain such "dangling-bond" and "floating-bond" defects, respectively, a unified understanding is still missing. Here, we show that atomistic machine-learning methods can reveal the complex structural and energetic landscape of defects in amorphous silicon. We study an ultra-large-scale, quantum-accurate structural model containing a million atoms, and more than ten thousand defects, allowing reliable defect-related statistics to be obtained. We combine structural descriptors and machine-learned local atomic energies to develop a universal classification of the different types of defects in amorphous silicon. The results suggest a revision of the established floating-bond model by showing that fivefold-coordinated atoms in amorphous silicon exhibit a wide range of local environments, and it is shown that fivefold (but not threefold) coordination defects tend to cluster together. Our study provides new insights into one of the most widely studied amorphous solids, and has general implications for modelling and understanding defects in disordered materials beyond silicon alone.

https://arxiv.org/abs/2308.16868

The homoleptic magnesium bis(aluminyl) compound Mg[Al(NON)]₂ (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) can be accessed from K₂[Al(NON)]₂ and MgI₂ and shown to possess a non-linear geometry (Al–Mg–Al = 164.8(1)) primarily due to the influence of dispersion interactions. This compound acts a four-electron reservoir in the reductive defluorination of SF₆, and reacts thermally with polar substrates such as MeI via nucleophilic attack through aluminium, consistent with the QT-AIM charges calculated for the metal centres, and a formal description as a Al(I)–Mg(II)–Al(I) trimetallic. On the other hand, under photolytic activation, the reaction with 1,5-cyclooctadiene leads to the stereoselective generation of transannular cycloaddition products consistent with radical based chemistry, emphasizing the covalent nature of the Mg–Al bonds and a description as a Al(II)–Mg(0)–Al(II) synthon.

https://doi.org/10.26434/chemrxiv-2022-s63x6

Polymer chemical recycling to monomers (CRM) is important to help achieve a circular plastic economy, but the “rules” governing catalyst design for such processes remain unclear. Here, carbon dioxide-derived polycarbonates undergo CRM to produce epoxides and carbon dioxide. A series of dinuclear catalysts, Mg(II)M(II) where M(II) = Mg, Mn, Fe, Co, Ni, Cu, and Zn, are compared for poly(cyclohexene carbonate) depolymerizations. The recycling is conducted in the solid state, at 140 °C monitored using thermal gravimetric analyses, or performed at larger-scale using laboratory glassware. The most active catalysts are, in order of decreasing rate, Mg(II)Co(II), Mg(II)Ni(II), and Mg(II)Zn(II), with the highest activity reaching 8100 h–1 and with >99% selectivity for cyclohexene oxide. Both the activity and selectivity values are the highest yet reported in this field, and the catalysts operate at low loadings and moderate temperatures (from 1:300 to 1:5000, 140 °C). For the best heterodinuclear catalysts, the depolymerization kinetics and activation barriers are determined. The rates in both reverse depolymerization and forward CHO/CO₂ polymerization catalysis show broadly similar trends, but the processes feature different intermediates; forward polymerization depends upon a metal–carbonate intermediate, while reverse depolymerization depends upon a metal-alkoxide intermediate. These dinuclear catalysts are attractive for the chemical recycling of carbon dioxide-derived plastics and should be prioritized for recycling of other oxygenated polymers and copolymers, including polyesters and polyethers. This work provides insights into the factors controlling depolymerization catalysis and steers future recycling catalyst design toward exploitation of lightweight and abundant s-block metals, such as Mg(II).

https://doi.org/10.1021/acscatal.3c04208#

Machine learning (ML) models for molecules and materials commonly rely on a decomposition of the global target quantity into local, atom-centered contributions. This approach is convenient from a computational perspective, enabling large-scale ML-driven simulations with a linear-scaling cost and also allows for the identification and posthoc interpretation of contributions from individual chemical environments and motifs to complicated macroscopic properties. However, even though practical justifications exist for the local decomposition, only the global quantity is rigorously defined. Thus, when the atom-centered contributions are used, their sensitivity to the training strategy or the model architecture should be carefully considered. To this end, we introduce a quantitative metric, which we call the local prediction rigidity (LPR), that allows one to assess how robust the locally decomposed predictions of ML models are. We investigate the dependence of the LPR on the aspects of model training, particularly the composition of training data set, for a range of different problems from simple toy models to real chemical systems. We present strategies to systematically enhance the LPR, which can be used to improve the robustness, interpretability, and transferability of atomistic ML models.

https://doi.org/10.1021/acs.jctc.3c00704

A tetraboryl digermene synthesized by the reaction between a dia- nionic digermanide nucleophile and a boron halide electrophile is dimeric both in the solid state and in hydrocarbon solution. It fea- tures both a planar ‘alkene-like’ geometry for the Ge2B4 core, and an exceptionally short GevGe double bond. These structural fea- tures are consistent with the known electronic properties of the boryl group, and with lowest energy (in silico) fragmentation into two triplet bis(boryl)germylene fragments.

https://doi.org/10.1039/D3DT03416J

We describe the facile synthesis of [(Me₃Si)₂CH]₂E=PMes* (E = Ge, Sn) from the reaction of the tetrylenes with the phospha-Wittig reagent, Me₃P–PMes*. Their reactivity towards a range of substrates with protic and hydridic E–H bonds (E = N, O, Si) is described. In addition to hydroelementation reactions of the E=P bonds, we show that these compounds, particularly [(Me₃Si)₂CH]₂Sn=PMes*, also act as base-stabilized phosphinidenes, allowing phosphinidene transfer to other nucleophiles.

https://doi.org/10.1002/chem.202301542

Understanding the chemistry underpinning intermetallic synergy and the discovery of generally applicable structure-performances relationships are major challenges in catalysis. Additionally, high-performance catalysts using earth-abundant, non-toxic and inexpensive elements must be prioritised. Here, a series of heterodinuclear catalysts of the form Co(III)M(I/II), where M(I/II) = Na(I), K(I), Ca(II), Sr(II), Ba(II) are evaluated for three different polymerizations, by assessment of rate constants, turn over frequencies, polymer selectivity and control. This allows for comparisons of performances both within and between catalysts containing Group I and II metals for CO₂/propene oxide ring-opening copolymerization (ROCOP), propene oxide/phthalic anhydride ROCOP and lactide ring-opening polymerization (ROP). The data reveal new structure-performance correlations that apply across all the different polymerizations: catalysts featuring s-block metals of lower Lewis acidity show higher rates and selectivity. The epoxide/heterocumulene ROCOPs both show exponential activity increases (vs. Lewis acidity, measured by the pKa of [M(OH₂)_m]ⁿ⁺), whilst the lactide ROP activity and CO₂/epoxide selectivity show linear increases. Such clear structure-activity/selectivity correlations are very unusual, yet are fully rationalised by the polymerization mechanisms and the chemistry of the catalytic intermediates. The general applicability across three different polymerizations is significant for future exploitation of catalytic synergy and provides a framework to improve other catalysts.

https://doi.org/10.1038/s41467-023-40284-z

Machine learning (ML) methods are of rapidly growing interest for materials modeling, and yet, the use of ML interatomic potentials for new systems is often more demanding than that of established density-functional theory (DFT) packages. Here, we describe computational methodology to combine the CASTEP first-principles simulation software with the on-the-fly fitting and evaluation of ML interatomic potential models. Our approach is based on regular checking against DFT reference data, which provides a direct measure of the accuracy of the evolving ML model. We discuss the general framework and the specific solutions implemented, and we present an example application to high-temperature molecular-dynamics simulations of carbon nanostructures. The code is freely available for academic research

https://doi.org/10.1063/5.0155621

All fluorochemicals—including elemental fluorine and nucleophilic, electrophilic, and radical fluorinating reagents—are prepared from hydrogen fluoride (HF). This highly toxic and corrosive gas is produced by the reaction of acid-grade fluorspar (>97% CaF₂) with sulfuric acid under harsh conditions. The use of fluorspar to produce fluorochemicals via a process that bypasses HF is highly desirable but remains an unsolved problem because of the prohibitive insolubility of CaF₂. Inspired by calcium phosphate biomineralization, we herein disclose a protocol of treating acid-grade fluorspar with dipotassium hydrogen phosphate (K₂HPO₄) under mechanochemical conditions. The process affords a solid composed of crystalline K₃(HPO₄)F and K_2-xCa_y(PO₃F)_a(PO₄)_b, which is found suitable for forging sulfur-fluorine and carbon-fluorine bonds.

https://doi.org/10.1126/science.adi1557

We describe a new synthetic methodology for the preparation of high quality, emission tuneable InP-based quantum dots (QDs) using a solid, air- and moisture-tolerant primary phosphine as a group-V precursor. This presents a significantly simpler synthetic pathway compared to the state-of-the-art precursors currently employed in phosphide quantum dot synthesis which are volatile, dangerous and air-sensitive, e.g. P(Si(CH₃)₃)₃.

https://doi.org/10.1039/D3NH00162H

We describe the use of the cyaphide-azide 1,3-dipolar cycloaddition reaction for the synthesis of a new class of inorganic rotaxanes containing gold(I) triazaphosphole stoppers. Electron-deficient bis-azides, which thread perethylated pillar[5]arene in aromatic solvents, readily react with two equivalents of Au(IDipp)(CP) (IDipp = 1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene) to afford interlocked molecules via an inorganic click reaction. These transformations proceed in good yields (ca. 65%) and in the absence of a catalyst. The resulting organometallic rotaxanes are air- and moisture-stable and can be purified by column chromatography under aerobic conditions. The targeted rotaxanes were characterized by multi-element nuclear magnetic resonance (NMR) spectroscopy, mass-spectrometry, and single-crystal X-ray diffraction.

https://doi.org/10.1002/ange.202309211

The complex diberyllocene, CpBeBeCp (Cp, cyclopentadienyl anion), has been the subject of numerous chemical investigations over the past five decades yet has eluded experimental characterization. We report the preparation and isolation of the compound by the reduction of beryllocene (BeCp₂) with a dimeric magnesium(I) complex and determination of its structure in the solid state by means of x-ray crystallography. Diberyllocene acts as a reductant in reactions that form beryllium-aluminum and beryllium-zinc bonds. Quantum chemical calculations indicate parallels between the electronic structure of diberyllocene and the simple homodiatomic species diberyllium (Be₂).

https://doi.org/10.1002/chem.202301648

The complex diberyllocene, CpBeBeCp (Cp, cyclopentadienyl anion), has been the subject of numerous chemical investigations over the past five decades yet has eluded experimental characterization. We report the preparation and isolation of the compound by the reduction of beryllocene (BeCp₂) with a dimeric magnesium(I) complex and determination of its structure in the solid state by means of x-ray crystallography. Diberyllocene acts as a reductant in reactions that form beryllium-aluminum and beryllium-zinc bonds. Quantum chemical calculations indicate parallels between the electronic structure of diberyllocene and the simple homodiatomic species diberyllium (Be₂).

https://doi.org/10.1126/science.adh4419

Utilizing carbon dioxide (CO₂) to make polycarbonates through the ring-opening copolymerization (ROCOP) of CO₂ and epoxides valorizes and recycles CO₂ and reduces pollution in polymer manufacturing. Recent developments in catalysis provide access to polycarbonates with well-defined structures and allow for copolymerization with biomass-derived monomers; however, the resulting material properties are under-investigated. Here, new types of CO₂-derived thermoplastic elastomers (TPEs) are described together with a generally applicable method to augment tensile mechanical strength and Young's modulus without requiring material re-design. These TPEs combine high glass transition temperature (T_g) amorphous blocks comprising CO₂-derived poly(carbonates) (A-block), with low Tg poly(ε-decalactone), from castor oil, (B-block) in ABA structures. The poly(carbonate) blocks are selectively functionalized with metal-carboxylates, where the metals are Na(I), Mg(II), Ca(II), Zn(II) and Al(III). The colorless polymers, featuring <1 wt% metal, show tunable thermal (T_g), and mechanical (elongation at break, elasticity, creep-resistance) properties. The best elastomers show >50-fold higher Young's modulus and 21-times greater tensile strength, without compromise to elastic recovery, compared with the starting block polymers. They have wide operating temperatures (-20 to 200 ˚C), high creep-resistance and yet remain recyclable. In future, these materials could substitute high-volume petrochemical elastomers and be utilized in high-growth fields like medicine, robotics and electronics.

https://doi.org/10.1002/adma.202302825

The steric tuning of a tridentate acridane-derived NNN pincer ligand allows for the isolation of a strictly T-shaped phosphine that exhibits ambiphilic reactivity. Well-defined phosphorus-centered reactivity towards nucleophiles and electrophiles is reported, contrasting with prior reports on this class of compounds. Reactions towards oxidants are also described. The latter result in the two-electron oxidation of the phosphorus atom from +III to +V, and are accompanied by a strong geometric distortion of the NNN pincer ligand. By contrast, cooperative activation of E–H (HCl, HBcat, HOMe) bonds proceeds with retention of the phosphorus redox state. When using H₂O as a substrate, the reaction results in the full disassembly of H₂O to its constituent atoms, highlighting the potential of this platform for small molecule activation reactions.

https://doi.org/10.1002/chem.202300818

The synthesis of group 9 pyridine-diimine complexes M(^DippPDI)X and [M(^DippPDI)L]⁺ (M = Co, Rh; ^DippPDI = 1,1’-(pyridine-2,6-diyl)bis(N-(2,6-diisopropylphenyl)ethan-1-imine; X = CP^-, CCH^-; L = CO, ^tBuNC) bearing a series of strong-field ligands, including the cyaphide ion (C≡P^-), is reported. A combined experimental and computational comparative study of the group 9 PDI cyaphide complexes Co(^DippPDI)(CP) and Rh(^DippPDI)(CP), as well as the N-heterocyclic carbene (NHC) gold(I) cyaphide complex Au(IDipp)(CP) (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), reveals the σ-donor and π-acceptor properties of the κC-cyaphido ligand, and allow us to suggest a position for this ion in the spectrochemical series.

https://doi.org/10.1039/D3SC01126G

A series of dynamic metalloporphyrin [2]rotaxane molecular shuttles comprising of bis-functionalised Zn(II) porphyrin axle and pyridyl functionalised macrocycle components are prepared in high yield via active metal template synthetic methodology. Extensive variable temperature 1H NMR and quantitative UV-Vis spectroscopic titration studies demonstrate dynamic macrocycle translocation is governed by an inter-component co-ordination interaction between the macrocycle pyridyl and axle Zn(II) metalloporphyrin, which serves to bias a ‘resting state’ co-conformation. The dynamic shuttling behaviour of the interlocked structures is dramatically inhibited by the addition of a neutral Lewis base such as pyridine, but can also be tuned via post-synthetic rotaxane demetallation of the porphyrin axle core to give free-base, or upon subsequent metallation, Ni(II) [2]rotaxane analogues. Importantly, the Lewis acidic Zn(II) porphyrin axle component is also capable of coordinating anions which induces mechanical bond shuttling behaviour resulting in a novel optical sensing response.

https://doi.org/10.1002/chem.202300608

Machine learning (ML) approaches enable large-scale atomistic simulations with near-quantum-mechanical accuracy. With the growing availability of these methods there arises a need for careful validation, particularly for physically agnostic models – that is, for potentials which extract the nature of atomic interactions from reference data. Here, we review the basic principles behind ML potentials and their validation for atomic-scale materials modeling. We discuss best practice in defining error metrics based on numerical performance as well as physically guided validation. We give specific recommendations that we hope will be useful for the wider community, including those researchers who intend to use ML potentials for materials “off the shelf”.

https://doi.org/10.1063/5.0139611

The reactions of anionic aluminium or gallium nucleophiles {K[E(NON)]}₂ (E = Al, 1; Ga, 2; NON = 4,5-bis(2,6- diisopropylanilido)-2,7-ditert-butyl-9,9-dimethylxanthene) with beryllocene (BeCp₂) led to the displacement of one cyclopentadienyl ligand at beryllium and the formation of compounds containing Be−Al or Be−Ga bonds (NON)EBeCp (E = Al, 3; Ga, 4). The Be−Al bond in the beryllium−aluminyl complex [2.310(4) Å] is much shorter than that found in the small number of previous examples [2.368(2) to 2.432(6) Å], and quantum chemical calculations suggest the existence of a non-nuclear attractor (NNA) for the Be−Al interaction. This represents the first example of a NNA for a heteroatomic interaction in an isolated molecular complex. As a result of this unusual electronic structure and the similarity in the Pauling electronegativities of beryllium and aluminium, the charge at the beryllium center (+1.39) in 3 is calculated to be less positive than that of the aluminium center (+1.88). This calculated charge distribution suggests the possibility for nucleophilic behavior at beryllium and correlates with the observed reactivity of the beryllium−aluminyl complex with N,N′-diisopropylcarbodiimide − the electrophilic carbon center of the carbodiimide undergoes nucleophilic attack by beryllium, thereby yielding a beryllium−diaminocarbene complex.

https://doi.org/10.1021/jacs.3c00480

The cyaphide anion, CP^-, is shown to undergo three distinct oligomerization reactions in the coordination sphere of metals. Reductive coupling of Au(IDipp)(CP) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) by Sm(Cp*)₂(OEt₂) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl), was found to afford a tetra-metallic complex containing a 2,3-diphosphabutadiene-1,1,4,4-tetraide fragment. By contrast, non-reductive dimerization of Ni(SIDipp)(Cp)(CP) (SIDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolidin-2-ylidene; Cp = cyclopentadienyl), gives rise to an asymmetric bimetallic complex containing a 1,3-diphosphacyclobutadiene-2,4-diide moiety. Spontaneous trimerization of Sc(Cp*)₂(CP) results in the formation of a trimetallic complex containing a 1,3,5-triphosphabenzene-2,4,6-triide fragment. These transformations show that while cyaphido transition metal complexes can be readily accessed using metathesis reactions, many such species are unstable to further oligomerization processes.

https://doi.org/10.1002/anie.202218047

A review about the known chemistry of the cyaphide ion, (C≡P)⁻. This remarkable diatomic anion has been the subject of study since the late nineteenth century, however its isolation and characterization eluded chemists for almost a hundred years. In this mini-review, we explore the pioneering synthetic experiments that first allowed for its isolation, as well as more recent developments demonstrating that cyaphide transfer is viable in well-established salt-metathesis protocols. The physical properties of the cyaphide ion are also explored in depth, allowing us to compare and contrast the chemistry of this ion with that of its lighter congener cyanide (an archetypal strong field ligand and important organic functional group). Recent studies show that the cyaphide ion has the potential to be used as a versatile chemical regent for the synthesis of novel molecules and materials, hinting at many interesting future avenues of investigation.

https://doi.org/10.1002/anie.202217749

The reduction of the boryl-substituted SnII bromide {(HCDippN)₂B}Sn(IPrMe)Br with 1.5 equivalents of potassium graphite leads to the generation of the cyclic tetratin tetraboryl system K₂[Sn₄{B(NDippCH)₂}₄], a homo-metallic heavier analogue of the cyclobutadiene dianion. This system is non-aromatic as determined by Nucleus Independent Chemical Shift Calculations (NICS(0) = 0.28, NICS(1) = 3.17), with the primary contributing resonance structures shown by Natural Resonance Theory (NRT) to involve a Sn=Sn double bond and 1,2-localized negative charges. Abstraction of the K⁺ cations or oxidation leads to contraction or cleavage of the Sn4 unit, respectively, while protonation generates the neutral dihydride 1,2-Sn₄{B(NDippCH)₂}₄H₂ (a heavier homo- logue of cyclobutene) in a manner consistent with the predicted charge distribution in the [Sn₄{B(NDippCH)₂}₄]₂ dianion.

https://doi.org/10.1002/chem.202300006

Boryltin compounds featuring the metal in the + 1 or 0 oxidation states can be synthesized from the carbene- stabilized tin(II) bromide (boryl)Sn(NHC)Br (boryl = {B(NDippCH)₂}; NHC=C{(NiPrCMe)₂}) by the use of strong reducing agents. The formation of the mono-carbene stabilized distannyne and donor-free distannide systems (boryl)SnSn(IPrMe)(boryl) (2) and K₂[Sn₂(boryl)₂] (3), using Mg(I) and K reducing agents mirrors related germanium chemistry. In contrast to their lighter congeners, however, systems of the type [Sn(boryl)]n are unstable with respect to disproportionation. Carbene abstraction from 2 using BPh₃, and two-electron oxidation of 3 both result in the formation of a 2 : 1 mixture of the Sn(II) compound Sn(boryl)₂, and the hexatin cluster, Sn₆(boryl)₄ (4). A viable mechanism for this rearrangement is shown by quantum chemical studies to involve a vinylidene intermediate (analogous to the isolable germanium compound, (boryl)2Ge=Ge), which undergoes facile atom transfer to generate Sn(boryl)₂ and trinuclear [Sn₃(boryl)₂]. The latter then dimerizes to give the observed hexametallic product 4, with independent studies showing that similar trigermanium species aggregate in analogous fashion.

https://doi.org/10.1002/chem.202203395

The reaction of TaMe₃Cl₂ with the rigid acridane- derived trisamine H₃NNN yields the tantalum(V) complex [TaCl₂(NNN^cat)]. Subsequent reaction with dioxygen results in the full four-electron reduction of O₂ yielding the oxido- bridged bimetallic complex [{TaCl₂(NNN^sq)}₂O]. This dinuclear complex features an open-shell ground state due to partial ligand oxidation and was comprehensively characterized by single crystal X-ray diffraction, LIFDI mass spectrometry, NMR, EPR, IR and UV/VIS/NIR spectroscopy. The mechanism of O₂ activation was investigated by DFT calculations revealing initial binding of O₂ to the tantalum(V) center followed by complete O₂ scission to produce a terminal oxido-complex.

https://doi.org/10.1002/chem.202203266

A systematic study to access stable stannaimines is reported, by combining different heteroleptic stannylenes with a range of organic azides. The reactions of terphenyl-/hypersilyl- substituted stannylenes yield the putative tin nitrogen double bond, but is directly followed by 1,2-silyl migration to give Sn(II) systems featuring bulky silylamido ligands. By contrast, the transition from a two σ donor ligand set to a mixed σ-donor / π-donor scaffold allows access to three new stannaimines which can be handled at room temperature. The reactivity profile of these Sn=N bonded species is crucially dependent on the substituent at the nitrogen atom. As such, the Sn=NMes (Mes = 2,4,6-Me₃C₆H₂) system is capable of activating a broad range of substrates under ambient conditions via 1,2-addition reactions, [2+2] and [4+2] cycloaddition reactions. Most interestingly, very rare examples of main group multiple bond metathesis reactions are also found to be viable.

https://doi.org/10.1002/anie.202211616

The development of sustainable plastic materials is an essential target of chemistry in the 21st century. Key objectives toward this goal include utilizing sustainable monomers and the development of polymers that can be chemically recycled/degraded. Polycarbonates synthesized from the ring-opening copolymerization (ROCOP) of epoxides and CO₂, and polyesters synthesized from the ROCOP of epoxides and anhydrides, meet these criteria. Despite this, designing efficient catalysts for these processes remains challenging. Typical issues include the requirement for high catalyst loading; low catalytic activities in comparison with other commercialized polymerizations; and the requirement of costly, toxic cocatalysts. The development of efficient catalysts for both types of ROCOP is highly desirable. This Account details our work on the development of catalysts for these two related polymerizations and, in particular, focuses on dinuclear complexes, which are typically applied without any cocatalyst. We have developed mechanistic hypotheses in tandem with our catalysts, and throughout the Account, we describe the kinetic, computational, and structure–activity studies that underpin the performance of these catalysts. Our initial research on homodinuclear M(II)M(II) complexes for cyclohexene oxide (CHO)/CO₂ ROCOP provided data to support a chain shuttling catalytic mechanism, which implied different roles for the two metals in the catalysis. This mechanistic hypothesis inspired the development of mixed-metal, heterodinuclear catalysts. The first of this class of catalysts was a heterodinuclear Zn(II)Mg(II) complex, which showed higher rates than either of the homodinuclear [Zn(II)Zn(II) and Mg(II)Mg(II)] analogues for CHO/CO₂ ROCOP. Expanding on this finding, we subsequently developed a Co(II)Mg(II) complex that showed field leading rates for CHO/CO₂ ROCOP and allowed for unique insight into the role of the two metals in this complex, where it was established that the Mg(II) center reduced transition state entropy and the Co(II) center reduced transition state enthalpy. Following these discoveries, we subsequently developed a range of heterodinuclear M(III)M(I) catalysts that were capable of catalyzing a broad range of copolymerizations, including the ring-opening copolymerization of CHO/CO₂, propylene oxide (PO)/CO₂, and CHO/phthalic anhydride (PA). Catalysts featuring Co(III)K(I) and Al(III)K(I) were found to be exceptionally effective for PO/CO₂ and CHO/PA ROCOP, respectively. Such M(III)M(I) complexes operate through a dinuclear metalate mechanism, where the M(III) binds and activates monomers while the M(I) species binds the polymer change in close proximity to allow for insertion into the activated monomer. Our research illustrates how careful catalyst design can yield highly efficient systems and how the development of mechanistic understanding aids this process. Avenues of future research are also discussed, including the applicability of these heterodinuclear catalysts in the synthesis of sustainable materials.

https://doi.org/10.1021/acs.accounts.2c00197

Homologation of carbon monoxide is central to the heterogeneous Fischer Tropsch Process for the production of hydrocarbon fuels. C–C bond formation has been modelled by homogeneous systems, with [C_nO_n]^2- fragments (n = 2-6) formed by two-electron reduction being commonly encountered. Here we show that four- or six-electron reduction of CO can be accomplished by the use of anionic aluminium(I) ('aluminyl') compounds, to give both topologically linear and branched C4/C6 chains. We show that the mechanism for homologation relies on the highly electron-rich nature of the aluminyl reagent, and on an unusual mode of interaction of the CO molecule, which behaves primarily as a Z-type ligand in initial adduct formation. The formation of [C₆O₆]^4- from [C₄O₄]^4- shows a solution-phase CO homologation process that brings about chain branching via complete C-O bond cleavage, while comparison of the linear [C₄O₄]^4- system with the [C₄O₄]^6- congener formed under more reducing conditions, models the net conversion of C–O bonds to C–C bonds in the presence of additional reductant.

https://doi.org/10.1021/jacs.2c05228

We report on the insertion of alkynes into heterometallic M–M' bonds, producing (aluminylalkenyl)copper compounds which possess differential reactivity at the two derived M–C functions. Uniquely, this system is capable of controlling access to isolable syn or anti dimetallated alkenes, by employing either kinetic or thermodynamic control. Variation of reaction time also allows regiocontrol to be exerted over the insertion of unsymmetrical alkynes. Subsequent derivatization with CO is both stereoselective (to syn systems) and regioselective (to Cu–C bonds), leading to the formation of the first structurally characterized examples of copper acyl compounds - aided by the cooperative reactivity of the proximal aluminium centre.

https://doi.org/10.1039/D2CC02578G

The synthesis of heterometallic transition metal complexes featuring bridging cyaphide ions (C≡P⁻) is reported. These are synthesized from reactions of Au(IDipp)(CP) (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with electron-rich, nucleophilic transition metal reagents, affording Au(IDipp)(μ₂-C≡P)Ni(^MeIⁱPr)₂ (^MeIⁱPr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) and Au(IDipp)(μ₂-C≡P)Rh(Cp*)(PMe₃). These studies reveal that, in contrast to the cyanide ion, bimetallic cyaphido complexes strongly favour a η¹:η² coordination mode that maximises the interaction of the second metal (Ni, Rh) with the π-manifold of the ion (and not the phosphorus atom lone pair). End-on bridging can be effectively unlocked by blocking the π-manifold, as demonstrated by reaction of Au(IDipp)(μ²-C≡P)Rh(Cp*)(PMe₃) with an electrophilic transition metal reagent, W(CO)₅(THF), which affords the heterotrimetallic compound Au(IDipp)(μ₃-C≡P)[Rh(Cp*)(PMe₃)][W(CO)₅].

https://doi.org/10.1002/anie.202206783

The reaction of amido-substituted stannylenes with phospha-Wittig reagents (Me₃PPR) results in release of hexamethyldisilazane and tethering of the resulting −CH₂PMe₂PR fragment to the tin center to give P-donor stabilized stannylenes featuring four-membered Sn,C,P,P heterocycles. Through systematic increases in steric loading, the structures of these systems in the solid state can be tuned, leading to successive P–P bond lengthening and Sn–P contraction and, in the most encumbered case, to complete P-to-Sn transfer of the phosphinidene fragment. The resulting stannaphosphene features a polar Sn=P double bond as determined by structural and computational studies. The reversibility of phosphinidene transfer can be established by solution phase measurements and reactivity studies.

https://doi.org/10.1021/jacs.2c03302

Machine learning (ML) based interatomic potentials are emerging tools for material simulations, but require a trade-off between accuracy and speed. Here, we show how one can use one ML potential model to train another: we use an accurate, but more computationally expensive model to generate reference data (locations and labels) for a series of much faster potentials. Without the need for quantum-mechanical reference computations at the secondary stage, extensive reference datasets can be easily generated, and we find that this improves the quality of fast potentials with less flexible functional forms. We apply the technique to disordered silicon, including a simulation of vitrification and polycrystalline grain formation under pressure with a system size of a million atoms. Our work provides conceptual insight into the ML of interatomic potential models and suggests a route toward accelerated simulations of condensed-phase systems.

https://doi.org/10.1063/5.0099929

The cyanide ion plays a key role in a number of industrially relevant chemical processes, such as the extraction of gold and silver from low grade ores. Metal cyanide compounds were arguably some of the earliest coordination complexes studied and can be traced back to the serendipitous discovery of Prussian blue by Diesbach in 1706. By contrast, heavier cyanide analogues, such as the cyaphide ion, C≡P–, are virtually unexplored despite the enormous potential of such ions as ligands in coordination compounds and extended solids. This is ultimately due to the lack of a suitable synthesis of cyaphide salts. Herein we report the synthesis and isolation of several magnesium–cyaphido complexes by reduction of iPr₃SiOCP with a magnesium(I) reagent. By analogy with Grignard reagents, these compounds can be used for the incorporation of the cyaphide ion into the coordination sphere of metals using a simple salt-metathesis protocol.

https://doi.org/10.1021/jacs.1c04417

Template-directed synthesis has been used to prepare a fully π-conjugated cyclic porphyrin octamer, composed of both β,meso,β-edge-fused porphyrin tape units and butadiyne-linked porphyrins. The UV–vis–NIR spectra of this partially fused nanoring show that π-conjugation extends around the whole macrocycle, and that it has a smaller HOMO–LUMO gap than its all-butadiyne-linked analogue, as predicted by TD-DFT calculations. The ¹H NMR shifts of the bound templates confirm the disrupted aromaticity of the edge-fused porphyrins in the neutral nanoring. NMR oxidation titrations reveal the presence of a global paratropic ring current in its 4+ and 8+ oxidation states and of a global diatropic ring current in the 6+ state of the partially fused ring. The paratropic ring current in the 4+ oxidation state is about four times stronger than that in the all-butadiyne-linked cyclic octamer complex, whereas the diatropic current in the 6+ state is about 40% weaker. Two isomeric K-shaped tetrapyridyl templates with trifluoromethyl substituents at different positions were used to probe the distribution of the ring current in the 4+, 6+, and 8+ oxidation states by ¹⁹F NMR, demonstrating that the ring currents are global and homogeneous.

https://doi.org/10.1021/jacs.0c09973