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Reaction of CuCl 2 ·2H 2 O with p-tert -butylthiacalix[4]arene (H 4 TC[4]A) affords a [CuII24] cage whose metallic skeleton conforms to a truncated octahedron in which the metal ions are strongly antiferromagnetically coupled. A structurally related [CuII8] cluster can be made using CuBr 2 in an otherwise identical reaction.

Oxoboranes (R-BO) are transient species that rapidly trimerise to form boroxines. To date, the only method used to stabilise oxoboranes is to add a Lewis base, but this forms a three-coordinate at boron oxoborane that has a different bonding/reactivity profile. Herein we report a base-free, two-coordinate oxoborane that is isolated as a Lewis adduct with AlCl 3 . This species, Mes*BO-AlCl 3 (Mes*=2,4,6- t Bu-C 6 H 2 ), has a ν 11 ΒΟ stretching frequency of 1843 cm -1 , indicating a strong BO bond. Computational analysis indicates this is due to a highly polarised BO bonding interaction combined with modest BO multiple bond character. While the polarisation of the BO bond on AlCl 3 coordination enhances the Lewis acidity at boron it also reduces the basicity at oxygen and the latter is key to accessing a base-free oxoborane. Finally, this oxoborane reacts with PhN 3 in a unique way to form an unprecedented boron heterocycle., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Organofluorine compounds are vital across multiple sectors, hence highly selective methods to install fluorine are of considerable importance. The deoxyfluorination of alcohols is a key approach to prepare organofluorine compounds, however, a highly secondary (2°)-selective deoxyfluorination of alcohols has not been realized to date. Herein, we report that borane-mediated deoxyfluorination results in high 2°-selectivity in inter- and intra-molecular competition reactions versus primary (1°), tertiary (3°) and even benzylic (Bn) alcohols. This is an operationally simple method using only commercial reagents (e.g., Et 3 N ⋅ 3HF) that starts from the alcohol which is converted to the O-alkyl-N-H-isourea in situ. The origin of the high 2°-selectivity was elucidated to be due to the relative barriers to carbodiimide elimination from the O-alkyl-N-(BR 2 )-isoureas. As the selectivity controlling step does not involve fluoride, this borane-mediated approach can be applied to other nucleophiles, as demonstrated by 2°-selective deoxychlorination using HCl occurring in preference to substitution of 1° and Bn analogues. This borane-mediated nucleophilic substitution therefore provides a new approach to circumvent the selectivity limitations inherent in classical S N 2 and S N 1 type reactions., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Porphyrin-based porous materials are of growing interest as heterogeneous catalysts especially for reactions that are of importance to sustainability. Here we demonstrate that porous molecular crystals can be prepared by the simple co-crystallisation of tetraphenylporphyrin (TPP) with octa(2',6'-di-iso-propylphenoxy)phthalocyanine or some of its metal complexes [(dipPhO) 8 PcM; M=H 2 , Al-OH, Ti=O, Mn-Cl, Fe-Cl, Co, Ni, Cu, Zn, Ga-Cl, Ag, In-Cl or Au-Cl]. This process is facilitated by the efficient formation of the supramolecular heterodimer between TPP and (dipPhO) 8 PcM, which is driven by the complementary shape and symmetry of the two macrocycles. The (dipPhO) 8 PcM component directs the crystal structure of the heterodimers to form Phthalocyanine Nanoporous Crystals (PNCs) of similar structure to those formed by (dipPhO) 8 PcM alone. The incorporation of TPP appears to partially stabilise the PNCs towards the removal of included solvent and for cocrystals containing (dipPhO) 8 PcCo stability can be enhanced further by the insitu addition of 4,4-bipyridyl to act as a "molecular wall tie". These stabilised PNC/TPP cocrystals have a Brunauer-Emmett-Teller surface area (SA BET ) of 454 m 2  g -1 and a micropore volume (V mp ) of 0.22 mL g -1 . The reactivity of both macrocycles within the PNC/TPP co-crystals is demonstrated by insitu metal insertion., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The first chiral tetracarbene indium(III) complexes have been synthesized by employing a rigid dianionic macrocyclic tetra-NHC ligand. The macrocyclic indium tetra-NHC bromide and ethoxide complexes are structurally similar to analagous salen complexes. The indium ethoxide complex effectively promotes living ring-opening polymerization of ε-caprolactone at room temperature.

The reaction of MnCl 2 ·4H 2 O with HL ((1-methyl-1H-imidazol-2-yl)methanol) and pdH 2 (1, 3 propanediol) in a basic MeCN solution results in the formation of a mixed-valence [Mn 20 ] cationic cluster and two [Mn II Cl 4 ] counter anions. The metallic skeleton of the cluster describes two geometrically equivalent mixed-valent, linked [Mn III 6 Mn II 4 ] supertetrahedra in which nearest-neighbor metal ions have a different oxidation state. Magnetic susceptibility, magnetization data and heat capacity measurements support evidence of predominant ferromagnetic correlations, leading to a s = 22 spin ground state for the [Mn III 6 Mn II 4 ] supertetrahedra, which are pair-linked by a weak antiferromagnetic coupling. The properties are discussed in the context of the magnetocaloric effect and the potential application of this compound in cryogenic refrigeration., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Agapaki, Charkiolakis, Nichol, Gracia, Evangelisti and Brechin.)

The Ni/PPh 3 -catalyzed homocoupling of aryl chlorides in DMF using Zn as the stochiometric reducing agent is one of a general class of Ni-catalyzed processes, where the mechanism has been a matter of long-standing debate. This study re-evaluates prior conclusions and insights. NMR spectroscopy is used to identify [(PPh 3 ) 2 Ni II (Ar)Cl] as a key intermediate and to explore the indirect roles of using Zn as the reductant. The [ZnCl 2 ] coproduct is responsible for several features, including a sequential transmetalation pathway involving [ArZnCl]. [ZnCl 2 ] also abstracts halide from [(PPh 3 ) 2 NiCl 2 ] to generate [Ni II Cl(DMF) 5 ] + [ZnCl 3 (DMF)] - , and in doing so, affects the Ni II + Ni 0 ↔ 2 Ni I speciation. [ZnCl 2 ] thus acts as an accelerator and inhibitor, resulting in mildly sigmoidal reaction profiles. When the [ZnCl 2 ] concentration becomes too high or the phosphine ligand concentration too low, catalysis stalls. Turnover is restored by the addition of further phosphine ligand, or chloride ion. In the presence of an exogenous chloride ion, turnover is rapid, again proceeding via [(PPh 3 ) 2 Ni II (Ar)Cl] but via dinuclear metathesis. The generation of [ZnCl 3 (DMF)] - results in mutually antagonistic effects between [ZnCl 2 ] and [Cl] - such that turnover proceeds via one mechanism or the other, depending on which species is in excess. The intermediacy of [ArZnCl] suggests a solution to the long-standing anomaly that many other reductants were found to be much less effective than Zn in inducing turnover of Ni/PPh 3 catalyzed aryl chloride homocoupling in DMF. The use of DMAc as a solvent in place of DMF inhibits stalling through the steric inhibition of mixed metalate generation.

The analysis of intervalence charge transfer (IVCT) in mixed-valence compounds can help understand electron transfer processes that are important in diverse applications such as molecular electronics and artificial photosynthesis. While mixed-valence complexes of the lanthanides are more difficult to access than their transition metal analogues, they have shown IVCT phenomena derived from Robin-Day Class II localized valency or even electronic transitions due to d - d metal-metal bonding. In contrast, we report here the synthesis, characterization, and computational analysis of a rare, Robin-Day Class III, singly reduced dinuclear Yb complex, which is best viewed as having delocalized oxidation states. In this case, no metal-metal bonding occurs and, for the first time, IVCT in a Robin-Day Class III complex resulting from f - f transitions is observed.

A flexible tripodal pyrrole-imine ligand (H 3 L) has been used to facilitate the controlled and sequential single-electron reductions of the uranyl dication from the U(VI) oxidation state to U(V) and further to U(IV), processes that are important to understanding the reduction of uranyl and its environmental remediation. The uranyl(VI) complexes UO 2 (HL)(sol) (sol = THF, py) were straightforwardly accessed by the transamination reaction of H 3 L with UO 2 {N(SiMe 3 ) 2 } 2 (THF) 2 and adopt 'hangman' structures in which one of the pyrrole-imine arms is pendant. While deprotonation of this arm by LiN(SiMe 3 ) 2 causes no change in uranyl oxidation state, single-electron reduction of uranyl(VI) to uranyl(V) occurred on addition of two equivalents of KN(SiMe 3 ) 2 to UO 2 (HL)(sol). The potassium cations of this new [U V O 2 (K 2 L)] 2 dimer were substituted by transmetalation with the appropriate metal chloride salt, forming the new uranyl(V) tetra-heterometallic complexes, [U V O 2 Zn(L)(py) 2 ] 2 and [U V O 2 Ln(Cl)(L)(py) 2 ] 2 (Ln = Y, Sm, Dy). The dimeric uranyl(V)-yttrium complex underwent further reduction and chloride abstraction to form the tetrametallic U(IV) complex [U IV O 2 Y III (py)] 2 , so highlighting the adaptability of this ligand to stabilise a variety of different uranium oxidation states.

Indolines are common motifs within pharamceuticals and natural products. Boron catalysis enables the chemoselective allylation of indoles to give allylic indolines in excellent diastereoselectivity. Mechanistic studies revealed in situ formation of the allylic borane, allylation of the imine tautomer of the indole and B-N/B-H transborylation for catalytic turnover.

The incorporation of phosphorus and boron into [3]dendralenes provides access to heavy heterodendralenes, a new class of main-group precursor to "doped" polycyclic hydrocarbons. [ n ]Dendralenes are a core class of unsaturated hydrocarbons built from geminally connected polyenes; the resulting arrangement of conjugated C═C bonds enables [ n ]dendralenes to undergo reactions that allow rapid access to complex polycyclic compounds. The increasing technological and synthetic importance of main-group-containing polycyclic hydrocarbons and their analogues makes new routes to access such systems highly attractive. Here we report the preparation of the first heavy heterodendralenes in the form of phosphorus- and boron-containing [3]dendralenes, prepared by a ring-opening reaction of a 1,2-phosphaborete. We reveal the electronic effect of P/B incorporation and demonstrate that, like their hydrocarbon analogues, phosphabora[3]dendralenes undergo diene-transmissive cycloaddition chemistry.

Triptycene derivatives are used extensively in supramolecular and materials chemistry, however, most are prepared using a multi-step synthesis involving the generation of a benzyne intermediate, which hinders production on a large scale. Inspired by the ease of the synthesis of resorcinarenes, we report the rapid and efficient preparation of triptycene-like 1,6,2',7'-tetrahydroxynaphthopleiadene directly from 2,7-dihydroxynaphthalene and phthalaldehyde. Structural characterisation confirms the novel bridged bicyclic framework, within which the planes of the single benzene ring and two naphthalene units are fixed at an angle of ∼120° relative to each other. Other combinations of aromatic 1,2-dialdehydes and 2,7-disubstituted naphthalenes also provided similar triptycene-like products. The low cost of the precursors and undemanding reaction conditions allow for rapid multigram synthesis of 1,6,2',7'-tetrahydroxynaphthopleiadene, which is shown to be a useful precursor for making the parent naphthopleiadene hydrocarbon. The great potential for the use of the naphthopleiadene scaffold in supramolecular and polymer chemistry is demonstrated by the preparation of a rigid novel cavitand, a microporous network polymer, and a solution-processable polymer of intrinsic microporosity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

C-H metalation is the most efficient method to prepare aryl-zinc and -aluminium complexes that are ubiquitous nucleophiles. Virtually all C-H metalation routes to form Al/Zn organometallics require stoichiometric, strong Brønsted bases with no base-catalyzed reactions reported. Herein we present a catalytic in amine/ammonium salt (Et 3 N/[(Et 3 N)H] + ) C-H metalation process to form aryl-zinc and aryl-aluminium complexes. Key to this approach is coupling an endergonic C-H metalation step with a sufficiently exergonic dehydrocoupling step between the ammonium salt by-product of C-H metalation ([(Et 3 N)H] + ) and a Zn-H or Al-Me containing complex. This step, forming H 2 /MeH, makes the overall cycle exergonic while generating more of the reactive metal electrophile. Mechanistic studies supported by DFT calculations revealed metal-specific dehydrocoupling pathways, with the divergent reactivity due to the different metal valency (which impacts the accessibility of amine-free cationic metal complexes) and steric environment. Notably, dehydrocoupling in the zinc system proceeds through a ligand-mediated pathway involving protonation of the β-diketiminate C γ position. Given this process is applicable to two disparate metals (Zn and Al), other main group metals and ligand sets are expected to be amenable to this transition metal-free, catalytic C-H metalation., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Silyl-heterocycles offer a unique handle to expand and explore chemical space, reactivity, and functionality. The shortage of catalytic methods for the preparation of diverse and functionalized silyl-heterocycles however limits widespread exploration and exploitation. Herein the borane-catalyzed intramolecular 1,1-carboboration of silyl-alkynes has been developed for the synthesis of 2,3-dihydrosilolyl and silylcyclobut-2-enyl boronic esters. Successful, catalytic carboboration has been achieved on a variety of functionally diverse silyl-alkynes, using a borane catalyst and transborylation-enabled turnover. Mechanistic studies, including 13 C-labelling, computational studies, and single-turnover experiments, suggest a reaction pathway proceeding by 1,2-hydroboration, 1,1-carboboration, and transborylation to release the alkenyl boronic ester product and regenerate the borane catalyst., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The synthesis and properties of a series of 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) inspired electron acceptors based on thiophene-fused quinone and triptycene motifs is presented. This has yielded insights into structure-property relationships for establishing and modulating simultaneous two-electron reduction processes in TCAQ analogues. These new compounds were synthesised using a Friedel-Crafts acylation between triptycene and thiophene-3,4-dicarbonyl chloride. Isomeric para-quinones featuring a [c]-fused thiophene on one side and a β,β- or α,β-fused triptycene on the other were isolated alongside a thiophene-3,4-diketone which bears two triptycene fragments. Knoevenagel condensation of these products with malononitrile produced a quinoidal bis(dicyanomethylene), an oxo-dicyanomethylene and an acyclic bis(dicyanomethylene). This series of new electron accepting molecules has been studied using X-ray crystallography and the implications of their 3D structures on NMR and UV/vis absorbance spectroscopy and cyclic voltammetry results have been ascertained with conclusions underpinned by computational methods., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A systematic study has been conducted on barbiturate complexes of all five alkali metals, Li-Cs, prepared from metal carbonates or hydroxides in an aqueous solution without other potential ligands present, varying the stoichiometric ratio of metal ion to barbituric acid (BAH). Eight polymeric coordination compounds (two each for Na, K, and Rb and one each for Li and Cs) have been characterised by single-crystal X-ray diffraction. All contain some combination of barbiturate anion BA - (necessarily in a 1:1 ratio with the metal cation M + ), barbituric acid, and water. All organic species and water molecules are coordinated to the metal centres via oxygen atoms as either terminal or bridging ligands. Coordination numbers range from 4 (for the Li complex) to 8 (for the Cs complex). Extensive hydrogen bonding plays a significant role in all the crystal structures, almost all of which include pairs of N-H···O hydrogen bonds linking BA - and/or BAH components into ribbons extending in one dimension. Factors influencing the structure adopted by each compound include cation size and reaction stoichiometry as well as hydrogen bonding., Competing Interests: The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Improving actinide separations is key to reducing barriers to medical and industrial actinide isotope production and to addressing the challenges associated with the reprocessing of spent nuclear fuel. Here, we report the first example of a supramolecular anion recognition process that can achieve this goal. We have designed a preorganized triamidoarene receptor that induces quantitative precipitation of the early actinides Th(IV), Np(IV), and Pu(IV) from industrially relevant conditions through the formation of self-assembled hydrogen-bonded capsules. Selectivity over the later An(III) elements is shown through modulation of the nitric acid concentration, and no precipitation of actinyl or transition-metal ions occurs. The Np, Pu, and Am precipitates were characterized structurally by single-crystal X-ray diffraction and reveal shape specificity of the internal hydrogen-bonding array for the encapsulated hexanitratometalates. This work complements ion-exchange resins for 5f-element separations and illustrates the significant potential of supramolecular separation methods that target anionic actinide species., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Herein we report the synthesis, isolation and polymerisation activity of two new zinc compounds based on a 2,6-diisopropylphenyl (Dipp) β-diiminate (NacNac) ligand framework with zinc also ligated by an amidate (2-pyridonate or 6-methyl-2-pyridonate) unit. The compounds crystallised as either monomeric (6-Me-2-pyridonate derivative) or dimeric (2-pyridonate) species, although both were found to be monomeric in solution via 1 H DOSY NMR spectroscopy, which was supported by DFT calculations. These observations suggest that both complexes initiate ring-opening polymerisation (ROP) through a single-site monometallic mechanism. High molecular weight poly ε-caprolactone (PCL) was achieved via exogenous initiator-free ROP conditions with both catalysts. An increase in the 2-pyridonate initiator steric bulk (6-Me- vs. 6-H-) resulted in an improved catalytic activity, facilitating complete monomer conversion within 1 h at 60 °C. Pyridonate end-groups were observed by MALDI-ToF mass spectrometry, contrasting with previous observations for Dipp NacNac-Zn acetate complexes (where no acetate end groups are observed), instead this more closely resembles the reactivity of Dipp NacNac-Zn alkoxide complexes in ROP (where RO end groups are observed). Additional major signals in the MALDI-ToF spectra were consistent with cyclic PCL species, which are attributed to back-biting ring-closing termination steps occuring in a process facilitated by the pyridonate unit being an effective leaving group. To the best of our knowledge, these complexes represent the first examples of pyridonate, and indeed amidate, initated ROP.

The structurally related odd and even numbered wheels [Fe III 11 Zn II 4 (tea) 10 (teaH) 1 (OMe)Cl 8 ] (1) and [Fe III 12 Zn II 4 (tea) 12 Cl 8 ] (2) can be synthesized under ambient conditions by reacting Fe III and Zn II salts with triethanolamine (teaH 3 ), the change in nuclearity being dictated by the solvents employed. An antiferromagnetic exchange between nearest neighbors, J = -10.0 cm -1 for 1 and J = -12.0 cm -1 for 2, leads to a frustrated S = 1/2 ground state in the former and an S = 0 ground state in the latter., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Doubly electrophilic pyrazabole derivatives (pyrazabole = [H 2 B(μ-C 3 N 2 H 3 )] 2 ) combined with one equiv. of base effect the ortho -borylation of N -alkyl anilines. Initial studies found that the bis(trifluoromethane)sulfonimide ([NTf 2 ] - ) pyrazabole derivative, [H(NTf 2 )B(μ-C 3 N 2 H 3 )] 2 , is highly effective for ortho -borylation, with this process proceeding through N-H borylation and then ortho C-H borylation. The activation of pyrazabole by I 2 was developed as a cheaper and simpler alternative to using HNTf 2 as the activator. The addition of I 2 forms mono or ditopic pyrazabole electrophiles dependent on stoichiometry. The ditopic electrophile [H(I)B(μ-C 3 N 2 H 3 )] 2 was also effective for the ortho -borylation of N -alkyl-anilines, with the primary C-H borylation products readily transformed into pinacol boronate esters (BPin) derivatives. Comparison of borylation reactions using the di-NTf 2 -and the diiodo-pyrazabole congeners revealed that more forcing conditions are required with the latter. Furthermore, the presence of iodide leads to competitive formation of side products, including [HB(μ-C 3 N 2 H 3 ) 3 BH] + , which are not active for C-H borylation. Using [H(I)B(μ-C 3 N 2 H 3 )] 2 and 0.2 equiv. of [Et 3 NH][NTf 2 ] combines the higher yields of the NTf 2 system with the ease of handling and lower cost of the iodide system generating an attractive process applicable to a range of N -alkyl-anilines. This methodology represents a metal free and transiently directed C-H borylation approach to form N -alkyl-2-BPin-aniline derivatives., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Crystallographic and computational studies suggest the occurrence of favourable interactions between polarizable arenes and halogen atoms. However, the systematic experimental quantification of halogen⋅⋅⋅arene interactions in solution has been hindered by the large variance in the steric demands of the halogens. Here we have synthesized molecular balances to quantify halogen⋅⋅⋅arene contacts in 17 solvents and solvent mixtures using 1 H NMR spectroscopy. Calculations indicate that favourable halogen⋅⋅⋅arene interactions arise from London dispersion in the gas phase. In contrast, comparison of our experimental measurements with partitioned SAPT0 energies indicate that dispersion is sufficiently attenuated by the solvent that the halogen⋅⋅⋅arene interaction trend was instead aligned with increasing exchange repulsion as the halogen increased in size (ΔG X ⋅⋅⋅ Ph =0 to +1.5 kJ mol -1 ). Halogen⋅⋅⋅arene contacts were slightly less disfavoured in solvents with higher solvophobicities and lower polarizabilities, but strikingly, were always less favoured than CH 3 ⋅⋅⋅arene contacts (ΔG Me ⋅⋅⋅ Ph =0 to -1.4 kJ mol -1 )., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Reaction of equimolar amounts of MnBr 2 ·4H 2 O and HL 1 ((3,5-dimethyl-1 H -pyrazol-1-yl)methanol) in a basic MeCN solution leads to the formation of [MnII4(L 1 ) 4 Br 4 (H 2 O) 4 ] (1), whose metallic skeleton is a [MnII4] tetrahedron and cluster core a [MnII4(μ 3 -O) 4 ] cubane. Replacing MnBr 2 ·4H 2 O with Mn(O 2 CMe) 2 ·4H 2 O affords [MnIII2MnII12O 2 (L 1 ) 4 (OAc) 22 ] (2) which is best described as a series of edge-sharing [Mn 4 ] tetrahedra that have self-assembled into a linear array in which each [Mn 2 ] pair is 'twisted' with respect to its neighbours in a corkscrew-like manner. Employment of the triangle [MnIII3O(OAc) 6 (py) 3 ](ClO 4 ) as a reactant instead of a Mn II salt results in the formation of [MnIII14MnII4O 14 (L 1 ) 4 (HL 1 ) 2 (OAc) 18 (H 2 O) 2 ] (3) whose core is comprised of three vertex-sharing [MnIII4] butterflies flanked on either side by one [MnIII4] cubane and one [MnIII2MnII2] tetrahedron. Dc magnetic susceptibility and magnetisation measurements of polycrystalline samples of 1-3 reveal the predominance of antiferromagnetic exchange interactions. For [Mn 4 ] (1) this leads to a diamagnetic ground state, while for [Mn 18 ] (3) competing exchange interactions result in Single-Molecule Magnet (SMM) behaviour with U eff = 22 K.

Amide directed C-H borylation using ≥two equiv. of BBr 3 forms borenium cations containing a R 2 N(R')C[double bond, length as m-dash]O→B(Ar)Br unit which has significant Lewis acidity at the carbonyl carbon. This enables reduction of the amide unit to an amine using hydrosilanes. This approach can be applied sequentially in a one-pot electrophilic borylation-reduction process, which for phenyl-acetylamides generates ortho borylated compounds that can be directly oxidised to the 2-(2-aminoethyl)-phenol. Other substrates amenable to the C-H borylation-reduction sequence include mono and diamino-arenes and carbazoles. This represents a simple method to make borylated molecules that would be convoluted to access otherwise ( e.g. N -octyl-1-BPin-carbazole). Substituent variation is tolerated at boron as well as in the amide unit, with diarylborenium cations also amenable to reduction. This enables a double C-H borylation-reduction-hydrolysis sequence to access B,N-polycyclic aromatic hydrocarbons (PAHs), including an example where both the boron and nitrogen centres contain functionalisable handles (N-H and B-OH). This method is therefore a useful addition to the metal-free borylation toolbox for accessing useful intermediates (ArylBPin) and novel B,N-PAHs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The host-guest chemistry of coordination cages continues to promote significant interest, not least because confinement effects can be exploited for a range of applications, such as drug delivery, sensing, and catalysis. Often a fundamental analysis of noncovalent encapsulation is required to provide the necessary insight into the design of better functional systems. In this paper, we demonstrate the use of various techniques to probe the host-guest chemistry of a novel Pd 2 L 4 cage, which we show is preorganized to selectively bind dicyanoarene guests with high affinity through hydrogen-bonding and other weak interactions. In addition, we exemplify the use of Raman spectroscopy as a tool for analyzing coordination cages, exploiting alkyne and nitrile reporter functional groups that are contained within the host and guest, respectively.

Heterobimetallic tert -butoxides of alkali metal cations with tetravalent actinide centers exhibit two distinctive structural motifs, [AnM 2 (O t Bu) 6 ] and [AnM 3 (O t Bu) 7 ] (An IV = Th, U and M I = Li, Na, K, Rb, Cs), evidently governed by the size of the alkali metal ions. Both [AnM 3 (O t Bu) 7 ] AnM3 (An IV = U, M I = Li; An IV = Th, M I = Li, Na) and [AnM 2 (O t Bu) 6 ] AnM2 (An IV = U, M I = Na-Cs; An IV = Th, M I = K-Cs) compounds are obtained in nearly quantitative yields by reacting actinide and alkali metal silyl amides with an excess of tert -butyl alcohol. The AnM3 complexes form a cubane-type coordination motif, whereas the AnM2 complexes display a geometry resembling two face-shared bipyramids. The sodium derivatives of thorium and uranium (ThNa3 and UNa2) allow the determination of the structural transition threshold as a function of the ratio of the ionic radii r i (An IV )/ r i (M I ). The AnM3 complexes are formed for ratios above 0.92 and the AnM2 type is formed for ratios below 0.87. All compounds are unambiguously characterized in both solution and solid states by NMR and IR spectroscopic studies and single crystal X-ray diffraction analyses, respectively.

Dimeric aminoboranes, [H 2 BNR 2 ] 2 (R = Me or CH 2 CH 2 ) containing B 2 N 2 cores, can be activated by I 2 , HNTf 2 (NTf 2 = [N(SO 2 CF 3 ) 2 ]), or [Ph 3 C][B(C 6 F 5 ) 4 ] to form isolable H 2 B(μ-NR 2 ) 2 BHX (for X = I or NTf 2 ). For X = [B(C 6 F 5 ) 4 ] - further reactivity, presumably between [H 2 B(μ-NMe 2 ) 2 BH][B(C 6 F 5 ) 4 ] and aminoborane, forms a B 3 N 3 -based monocation containing a three-center two electron B-(μ-H)-B moiety. The structures of H 2 B(μ-NMe 2 ) 2 BH(I) and [(μ-NMe 2 )BH(NTf 2 )] 2 indicated a sterically crowded environment around boron, and this leads to the less common O-bound mode of NTf 2 binding. While the iodide congener reacted very slowly with alkynes, the NTf 2 analogues were more reactive, with hydroboration of internal alkynes forming (vinyl) 2 BNR 2 species and R 2 NBH(NTf 2 ) as the major products. Further studies indicated that the B 2 N 2 core is maintained during the first hydroboration, and that it is during subsequent steps that B 2 N 2 dissociation occurs. In the mono-boron systems, for example, i Pr 2 NBH(NTf 2 ), NTf 2 is N-bound; thus, they have less steric crowding around boron relative to the B 2 N 2 systems. Notably, the monoboron systems are much less reactive in alkyne hydroboration than the B 2 N 2 -based bis-boranes, despite the former being three coordinate at boron while the latter are four coordinate at boron. Finally, these B 2 N 2 electrophiles are much more prone to dissociate into mono-borane species than pyrazabole [H 2 B(μ-N 2 C 3 H 3 )] 2 analogues, making them less useful for the directed diborylation of a single substrate., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

High oxidation-state carbonyl coupling partners including esters and lactones were reacted with enones to give aldol-type products directly using two-fold organoborane catalysis. This new retrosynthetic disconnection to aldol-type products is compatible with enolisable coupling partners, without self-condensation, and couples the high reactivity of secondary dialkylboranes with the stability of pinacolboronic esters. Excellent chemoselectivity, substrate scope (including those containing reducible functionalities and free alcohols) and diastereocontrol were achieved to access both the syn- and anti-aldol-type products. Mechanistic studies confirmed the two-fold catalytic role of the single secondary borane catalyst for boron enolate formation and formation of an aldehyde surrogate from the ester or lactone coupling partner., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The diastereo- and enantioselective allylation of ketones remains a synthetic challenge, with transition metal catalysis offering the most applied methods. Here, a boron-catalyzed allylation of ketones with allenes is presented. Excellent yield, regioselectivity, and diastereoselectivity were found across functionalized substrates. The reaction was further developed to accommodate an enantioenriched boron catalyst and thus gave asymmetric ketone allylation in good yield, diastereoselectivity, and enantioselectivity. Mechanistic studies supported a hydroboration-allylation-transborylation pathway., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The complex [NiII14(HL 2 ) 12 (HCOO) 14 Cl 14 (MeOH)(H 2 O)] describes an aesthetically pleasing wheel displaying ferromagnetic nearest neighbour exchange.

C-H functionalisation reactions offer a sustainable method for molecular construction and diversification. These reactions however remain dominated by precious metal catalysis. While significant interest in iron-catalysed C-H activation reactions has emerged, the isolation, characterisation and mechanistic understanding of these processes remain lacking. Herein the iron-catalysed C(sp 2 )-H bond hydrogen/deuterium exchange reaction using CD 3 OD is reported for both heterocycles and, for the first time, alkenes (38 examples). Isolation and characterisation, including by single-crystal X-ray diffraction, of the key iron-aryl and iron-alkenyl C-H metallation intermediates provided evidence for a reversible protonation of the active iron hydride catalyst. Good chemoselectivity was observed for both substrate classes. The developed procedure is orthogonal to previous iron-catalysed H/D exchange methods which used C 6 D 6 , D 2 , or D 2 O as the deuterium source, and uses only bench-stable reagents, including the iron(ii) pre-catalyst. Further, a new mechanism of iron-hydride formation is reported in which β-hydride elimination from an alcohol generates the iron hydride. The ability to produce, isolate and characterise the organometallic products arising from C-H activation presents a basis for future discovery and development., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The experimental isolation of H-bond energetics from the typically dominant influence of the solvent remains challenging. Here we use synthetic molecular balances to quantify amine/amide H-bonds in competitive solvents. Over 200 conformational free energy differences were determined using 24 H-bonding balances in 9 solvents spanning a wide polarity range. The correlations between experimental interaction energies and gas-phase computed energies exhibited wild solvent-dependent variation. However, excellent correlations were found between the same computed energies and the experimental data following empirical dissection of solvent effects using Hunter's α/β solvation model. In addition to facilitating the direct comparison of experimental and computational data, changes in the fitted donor and acceptor constants reveal the energetics of secondary local interactions such as competing H-bonds., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Paramagnetic complexes that possess magnetically switchable properties show promise in a number of applications. A significantly underdeveloped approach is the use of metallocages, whose magnetic properties can be modulated through host-guest chemistry. Here we show such an example that utilises a simple [Cu II 2 L 4 ] 4+ lantern complex. Magnetic susceptibility and magnetisation data shows an absence of exchange in the presence of the diamagnetic guest triflate. However, replacement of the bound triflate by ReBr 6 2- switches on antiferomagnetic exchange between the Cu and Re ions, leading to an S = 1/2 ground state for the non-covalent complex [ReBr 6 2- ⊂Cu II 2 L 4 ] 2+ . Comparison of this complex to a "control" palladium-cage host-guest complex, [ReBr 6 2- ⊂Pd II 2 L 4 ] 2+ , shows that the encapsulated ReBr 6 2- anions retain the same magnetic anisotropy as in the free salt. Theoretically calculated spin-Hamiltonian parameters are in close agreement with experiment. Spin density analysis shows the mode of interaction between the Cu II and Re IV centres is through the Re-Br⋯Cu pathway, primarily mediated through the Cu(d x 2 - y 2 )|Br sp |Re(d yz ) interaction. This is further supported by overlap integral calculations between singly occupied molecular orbitals (SOMOs) of the paramagnetic ions and natural bonding orbitals analysis where considerable donor-to-acceptor interactions are observed between hybrid 4s4p orbitals of the Br ions and the empty 4s and 4p orbitals of the Cu ions.

The kinetics of quinuclidine displacement of BH 3 from a wide range of Lewis base borane adducts have been measured. Parameterization of these rates has enabled the development of a nucleofugality scale ( N F B ), shown to quantify and predict the leaving group ability of a range of other Lewis bases. Additivity observed across a number of series R' 3- n R n X (X = P, N; R' = aryl, alkyl) has allowed the formulation of related substituent parameters ( n f PB , n f AB ), providing a means of calculating N F B values for a range of Lewis bases that extends far beyond those experimentally derived. The utility of the nucleofugality parameter is explored by the correlation of the substituent parameter n f PB with the hydrolyses rates of a series of alkyl and aryl MIDA boronates under neutral conditions. This has allowed the identification of MIDA boronates with heteroatoms proximal to the reacting center, showing unusual kinetic lability or stability to hydrolysis.

Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest, e.g. in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C-H borylation methodology has been developed that provides access to azaborine containing helicenes (BN-helicenes). This borylation process proceeds via protonation of an aminoborane with bistriflimidic acid. DFT calculations reveal the borenium cation formed by protonation to be more electrophilic than the product derived from aminoborane activation with BBr 3 . The synthesised helicenes include BN-analogues of archetypal all carbon [5]- and [6]helicenes. The replacement of a CC with a BN unit (that has a longer bond) on the outer helix increases the strain in the BN congeners and the racemization half-life for a BN-[5]helicene relative to the all carbon [5]helicene. BN incorporation also increases the fluorescence efficiency of the helicenes, a direct effect of BN incorporation altering the distribution of the key frontier orbitals across the helical backbone relative to carbo-helicenes., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Dissolution of FeBr 3 in a mixture of acetonitrile and 3,4-lutidine in the presence of an amine results in the formation of an [Fe 30 ] molecular metal oxide containing alternating layers of tetrahedral and octahedral Fe III ions. Mass spectrometry suggests the cluster is formed quickly and remains stable in solution, while magnetic measurements and DFT calculations reveal competing antiferromagnetic exchange interactions.

Dialumenes are neutral Al I compounds with Al=Al multiple bonds. We report the isolation of an amidophosphine-supported dialumene. Our X-ray crystallographic, spectroscopic, and computational DFT analyses reveal a long and extreme trans-bent Al=Al bond with a low dissociation energy and bond order. In solution, the dialumene can dissociate into monomeric Al I species. Reactivity studies reveal two modes of reaction: as dialumene or as aluminyl monomers., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Amido-zincates containing hydrides are underexplored yet potentially useful complexes. Attempts to access this type of zincate through combining amido-organo zincates and pinacolborane (HBPin) via Zn-C/H-BPin exchange led instead to preferential formation of amide-BPin and/or [amide-BPin(Y)] - (Y = Ph, amide, H), when the amide is hexamethyldisilazide or 2,2,6,6-tetramethylpiperidide and the hydrocarbyl group was phenyl or ethyl. In contrast, the use of a dipyridylamide (dpa) based arylzinc complex led to Zn-C/H-BPin metathesis being the major outcome. Independent synthesis and full characterisation of two L n Li[(dpa)ZnPh 2 ] (L = THF, n = 3; L = PMDETA, n = 1) complexes, 1 and 3, respectively, enabled reactivity studies that demonstrated that these species display zincate type reactivity (by comparison to the lower reactivity of the neutral complex (Me-dpa)ZnPh 2 , 4, Me-dpa = 2,2'-dipyridyl- N -methylamine). This included 1 performing the rapid deprotonation of 4-ethynyltoluene and also phenyl transfer to α,α,α-trifluoroacetophenone in contrast to neutral complex 4. Complex 1 reacted with one equivalent of HBPin to give predominantly PhBPin ( ca. 90%) and a lithium amidophenylzincate containing a hydride unit, complex 7-A, as the major zinc containing product. Complex 7-A transfers hydride to an electrophile preferentially over phenyl, indicating it reacts as a hydridozincate. Attempts to react 1 with >1 equivalent of HBPin or with catecholborane led to more complex outcomes, which included significant borane and dpaZn substituent scrambling, two examples of which were crystallographically characterised. While this work provides proof of principle for Zn-C/H-BPin exchange as a route to form an amido-zincate containing a hydride, amido-organozincates that undergo more selective Zn-C/H-BPin exchange still are required.

Heterometallic Anderson wheels of formula [(V IV O) 2 MII5(hmp) 10 Cl 2 ](ClO 4 ) 2 ·2MeOH (M = Ni, 1; Co, 2) have been synthesised from the solvothermal reaction of M(ClO 4 ) 2 ·6H 2 O and VCl 3 with hmpH (2-(hydroxymethyl)pyridine). The metallic skeleton describes a centred hexagon, with the two vanadyl ions sitting on opposing sides of the outer ring. Magnetic susceptibility and magnetisation measurements indicate the presence of both ferromagnetic and antiferromagnetic exchange interactions. Theoretical calculations based on density functional methods reproduce both the sign and strength of the exchange interactions found experimentally, and rationalise the parameters extracted.

Historically used in stoichiometric hydroalumination chemistry, recent advances have transformed aluminium hydrides into versatile catalysts for the hydroboration of unsaturated multiple bonds. This catalytic ability is founded on the defining reactivity of aluminium hydrides with alkynes and alkenes: 1,2-hydroalumination of the unsaturated π-system. This manuscript reports the aluminium hydride catalyzed dehydroborylation of terminal alkynes. A tethered intramolecular amine ligand controls reactivity at the aluminium hydride centre, switching off hydroalumination and instead enabling selective reactions at the alkyne C-H σ-bond. Chemoselective C-H borylation was observed across a series of aryl- and alkyl-substituted alkynes (21 examples). On the basis of kinetic and density functional theory studies, a mechanism in which C-H borylation proceeds by σ-bond metathesis between pinacolborane (HBpin) and alkynyl aluminium intermediates is proposed., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

We report the phospha-bora-Wittig reaction for the direct preparation of phosphaalkenes from aldehydes, ketones, esters, or amides. The transient phosphaborene Mes*P═B-NR 2 reacts with carbonyl compounds to form 1,2,3-phosphaboraoxetanes, analogues of oxaphosphetane intermediates in the classical Wittig reaction. 1,2,3-Phosphaboraoxetanes undergo thermal or Lewis acid-promoted cycloreversion, yielding phosphaalkenes. Experimental and density functional theory studies reveal far-reaching similarities between classical and phospha-bora-Wittig reactions.

The combination of two different Fe III salts in a solvothermal reaction with triethanolamine results in the formation of a high symmetry [FeIII15] cluster whose structure conforms to a centred, tetrakis hexahedron.

The separation and isolation of many of the platinum group metals (PGMs) is currently achieved commercially using solvent extraction processes. The extraction of rhodium is problematic however, as a variety of complexes of the form [RhCl n (H 2 O) 6-n ] (n-3)- are found in hydrochloric acid, making it difficult to design a reagent that can extract all the rhodium. In this work, the synergistic combination of a primary amine (2-ethylhexylamine, L A ) with a primary amide (3,5,5-trimethylhexanamide, L 1 ) is shown to extract over 85 % of rhodium from 4 M hydrochloric acid. Two rhodium complexes are shown to reside in the organic phase, the ion-pair [HL A ] 3 [RhCl 6 ] and the amide complex [HL A ] 2 [RhCl 5 (L 1 )]; in the latter complex, the amide is tautomerized to its enol form and coordinated to the rhodium centre through the nitrogen atom. This insight highlights the need for ligands that target specific metal complexes in the aqueous phase and provides an efficient synergistic solution for the solvent extraction of rhodium., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Cationic zinc Lewis acids catalyse the C-H borylation of heteroarenes using pinacol borane (HBPin) or catechol borane (HBCat). An electrophile derived from [IDippZnEt][B(C 6 F 5 ) 4 ] (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) combined with N , N -dimethyl- p -toluidine (DMT) proved the most active in terms of C-H borylation scope and yield. Using this combination weakly activated heteroarenes, such as thiophene, were amenable to catalytic C-H borylation using HBCat. Competition reactions show these IDipp-zinc cations are highly oxophilic but less hydridophilic (relative to B(C 6 F 5 ) 3 ), and that borylation proceeds via activation of the hydroborane (and not the heteroarene) by a zinc electrophile. Based on DFT calculations this activation is proposed to proceed by coordination of a hydroborane oxygen to the zinc centre to generate a boron electrophile that effects C-H borylation. Thus, Lewis acid binding to oxygen sites of hydroboranes represents an under-developed route to access reactive borenium-type electrophiles for C-H borylation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A [Mn18] wheel of wheels is obtained from the reaction of MnBr2·4H2O and LH3 in MeOH. The metallic skeleton reveals two asymmetric [MnIII6MnII2] square wheels connected into a larger wheel via two MnII ions. Magnetic susceptibility and magnetisation data reveal competing exchange interactions, supported by computational studies.

Heterolanthanide complexes are difficult to synthesize owing to the similar chemistry of the lanthanide ions. Consequently, very few purely heterolanthanide complexes have been synthesized. This is despite the fact that such complexes hold interesting optical and magnetic properties. To fine-tune these properties, it is important that one can choose complexes with any given combination of lanthanides. Herein we report a synthetic procedure which yields pure heterodinuclear lanthanide cryptates LnLn*LX 3 (X = NO 3 - or OTf - ) based on the cryptand H 3 L = N[(CH 2 ) 2 N[double bond, length as m-dash]CH-R-CH[double bond, length as m-dash]N-(CH 2 ) 2 ] 3 N (R = m -C 6 H 2 OH-2-Me-5). In the synthesis the choice of counter ion and solvent proves crucial in controlling the Ln-Ln* composition. Choosing the optimal solvent and counter ion afford pure heterodinuclear complexes with any given combination of Gd(iii)-Lu(iii) including Y(iii). To demonstrate the versatility of the synthesis all dinuclear combinations of Y(iii), Gd(iii), Yb(iii) and Lu(iii) were synthesized resulting in 10 novel complexes of the form LnLn*L(OTf) 3 with LnLn* = YbGd 1 , YbY 2 , YbLu 3 , YbYb 4 , LuGd 5 , LuY 6 , LuLu 7 , YGd 8 , YY 9 and GdGd 10 . Through the use of 1 H, 13 C NMR and mass spectrometry the heterodinuclear nature of YbGd, YbY, YbLu, LuGd, LuY and YGd was confirmed. Crystal structures of LnLn*L(NO 3 ) 3 reveal short Ln-Ln distances of ∼3.5 Å. Using SQUID magnetometry the exchange coupling between the lanthanide ions was found to be anti-ferromagnetic for GdGd and YbYb while ferromagnetic for YbGd., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Neutral arenes such as benzene have never been considered suitable ligands for electropositive actinide cations, yet we find that even simple U III UX 3 aryloxide complexes such as U(ODipp) 3 bind and reduce arenes spontaneously at room temperature, forming inverse arene sandwich (IAS) complexes X n U(μ-C 6 D 6 )UX m (X = ODipp, n =2, m =3; X = OBMes 2 n=m=2 or 3) (ODipp = OC 6 H 3 i Pr 2 -2,6; Mes = 2,4,6-Me 3 -C 6 H 2 ). In some of these cases, further arene reduction has occured as a result of X ligand redistribution. These unexpected spontaneous reactions explain the anomalous spectra and reported lack of further reactivity of strongly reducing U III centers of U(ODipp) 3 . Phosphines that are not considered suitable ligands for actinides can catalyze the formation of the IAS complexes. This enables otherwise inaccessible asymmetric and less congested IAS complexes to be isolated and the bonding in this series compared.

Reaction of Ni(OTf) 2 with the bisbidentate quaterpyridine ligand L results in the self-assembly of a tetrahedral, paramagnetic cage [Ni II 4 L 6 ] 8+ . By selectively exchanging the bound triflate from [OTf⊂Ni II 4 L 6 ](OTf) 7 ( 1 ), we have been able to prepare a series of host-guest complexes that feature an encapsulated paramagnetic tetrahalometallate ion inside this paramagnetic host giving [M II X 4 ⊂Ni II 4 L 6 ](OTf) 6 , where M II X 4 2- = MnCl 4 2- ( 2 ), CoCl 4 2- ( 5 ), CoBr 4 2- ( 6 ), NiCl 4 2- ( 7 ), and CuBr 4 2- ( 8 ) or [M III X 4 ⊂Ni II 4 L 6 ](OTf) 7 , where M III X 4 - = FeCl 4 - ( 3 ) and FeBr 4 - ( 4 ). Triflate-to-tetrahalometallate exchange occurs in solution and can also be accomplished through single-crystal-to-single-crystal transformations. Host-guest complexes 1-8 all crystallise as homochiral racemates in monoclinic space groups, wherein the four {NiN 6 } vertexes within a single Ni 4 L 6 unit possess the same Δ or Λ stereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [Ni II 4 ] complex, and between the host and the MX 4 n - guest, are of comparable magnitude and antiferromagnetic in nature. Theoretically derived values for the magnetic exchange are in close agreement with experiment, revealing that large spin densities on the electronegative X-atoms of particular MX 4 n - guest molecules lead to stronger host-guest magnetic exchange interactions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Oxidative addition and reductive elimination are defining reactions of transition-metal organometallic chemistry. In main-group chemistry, oxidative addition is now well-established but reductive elimination reactions are not yet general in the same way. Herein, we report dihydrodialanes supported by amidophosphine ligands. The ligand serves as a stereochemical reporter for reversible reductive elimination/oxidative addition chemistry involving Al I and Al III intermediates., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Acetate ligand metathesis results in the first hybrid [MIII(Pc)(PW11O39)]6- (M = Y, Dy, Tb) double-decker scaffolds, where a phthalocyanate (Pc2-) and one of the conceptually most simple polyoxotungstates, a monolacunary Keggin cluster, are interlinked via a single rare earth ion. Characterisation includes high-resolution mass spectrometry, synchrotron-based single-crystal X-ray diffraction, various spectroscopic and electrochemical methods, and magnetic studies revealing slow relaxation of the magnetisation for the Dy derivate.

Heterometallic cooperativity is an emerging strategy to elevate polymerisation catalyst performance. Here, we report the first heterotrimetallic Na/Zn 2 and K/Zn 2 complexes supported by a ProPhenol ligand, which deliver "best of both" in cyclic ester ring-opening polymerisation, combining the outstanding activity (Na/K) and good control (Zn 2 ) of homometallic analogues. Detailed NMR studies and density-functional theory calculations suggest that the Na/Zn 2 and K/Zn 2 complexes retain their heterometallic structures in the solution-state. To the best of our knowledge, the K/Zn 2 analogue is the most active heterometallic catalyst reported for rac -lactide polymerisation ( k obs = 1.7 × 10 -2 s -1 ), giving activities five times faster than the Na/Zn 2 complex. These versatile catalysts also display outstanding performance in ε-caprolatone and δ-valerolactone ring-opening polymerisation. These studies provide underpinning methodologies for future heterometallic polymerisation catalyst design, both in cyclic ester polymerisation and other ring-opening (co)polymerisation reactions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)