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Using diphenylacetylene as a π-accepting ligand allows access to a new family of alkali-metal nickelates, which can effectively promote the [2 + 2 + 2] cyclotrimerisation of diphenylacetylene.

Using a bimetallic base combining Na and Co(ii) enables the regioselective sodium-mediated di-cobaltation of fluoroarenes as well as transforming the three C–F bonds of trifluorobenzene into C–N bonds via a cascade activation process.

Hydrogen isotope exchange (HIE) has become one of the most studied methods to prepare deuterated molecules, with the primary focus recently on metal-catalyzed C-H activation with transition metals. Here we report the use of a simple sodium amide, NaTMP (TMP = 2,2,6,6-tetramethylpiperidide), combined with tridentate Lewis donor PMDETA (

The Ni-catalysed hydrogenolysis and cross-coupling of aryl ethers has emerged as a powerful synthetic tool to transform inert phenol-derived electrophiles into functionalised aromatic molecules. This has attracted significant interest due to its potential to convert the lignin fraction of biomass into chemical feedstocks, or to enable orthogonal reactivity and late-stage synthetic modification. Although the scope of nucleophiles employed, and hence the C–C and C–heteroatom bonds that can be forged, has expanded significantly since Wenkert’s seminal work in 1979, mechanistic understanding on how these reactions operate is still uncertain since the comparatively inert Caryl–O bond of aryl ethers challenge the involvement of classical mechanisms involving direct oxidative addition to Ni(0). In this review, we document the different mechanisms that have been proposed in the Ni-catalysed hydrogenolysis and cross-coupling of aryl ethers. These include: (i) direct oxidative addition; (ii) Lewis acid assisted C–O bond cleavage; (iii) anionic nickelates, and; (iv) Ni(I) intermediates. Experimental and theoretical investigations by numerous research groups have generated a pool of knowledge that will undoubtedly facilitate future discoveries in the development of novel Ni-catalysed transformations of aryl ethers.1 Introduction2 Direct Oxidative Addition3 Hydrogenolysis of Aryl Ethers4 Lewis Acid Assisted C–O Bond Cleavage5 Anionic Nickelates6 Ni(I) Intermediates7 The ‘Naphthalene Problem’8 Conclusions and Outlook

Summary While 1,4-disubstituted 1,2,3-triazoles can be readily prepared by copper(I) alkyne/azide cycloaddition, the methods available to access the alternative 1,5-disubstituted isomers have been significantly less well developed. Exploiting chemical cooperativity, here we report the first examples of s-block bimetallic catalysis using a sodium magnesiate precatalyst as an efficient and versatile new method to synthesize 1,5-disubstituted triazoles via azide/alkyne ligation. Showing an excellent substrate scope and selectivity under mild reaction conditions, this bimetallic approach has also been successfully applied to access symmetrical and non-symmetrical di-triazoles. Mechanistic insights on how the Na/Mg cooperative partnership is established are also provided, supporting a stepwise process where initial deprotonation of the alkyne renders a highly nucleophilic tetra-alkynyl sodium magnesiate to which the azide can coordinate, facilitating its insertion into an Mg-C bond and subsequent cyclization, which is favored by π-coordination of Na to the alkyne C≡C triple bond.

Operating via a special type of Zn/Zn′ cooperation, an atom-efficient method for the arylation of N-tosylimines has been developed combining nucleophilic ZnAr2 with Lewis acidic Zn(C6F5)2.

Exploiting the high aggregation of organolithium complexes, a new structurally diverse family of lithium nickelate clusters has been uncovered, which can be accessed by treating Ni(COD)2 with a large excess of aliphatic lithium acetylides.

While cobalt complexes have already shown their potential for C-H and C-F bond activation of fluoroarenes, their reactivity as metalating agents via Co-H exchange towards these substrates has not been explored. Herein, we report a Co(HMDS)

By switching on cooperative effects, main-group heterobimetallic reagents find widespread applications in cornerstone stoichiometric transformations, offering special reactivities and selectivities inaccessible by conventional monometallic reagents. Recent advances have successfully upgraded these stoichiometric successes to catalytic regimes that are underpinned by the unique cooperative partnership between the two distinct metals.

Advancing the understanding of lithum nickelate complexes, here we report a family of homoleptic organonickelate complexes obtained by reacting Ni(COD)

Exploiting the steric incompatibility of the tris-(alkyl)gallium GaR3 (R = CH2SiMe3) and the bulky N-heterocyclic carbene (NHC) 1,3-bis(tert-butyl)imidazol-2-ylidene (ItBu), here we report the B−H bond activation of pinacolborane (HBPin), which has led to the isolation and structural authentication of a novel ion pair, [{ItBu-BPin}+{GaR3(μ-H)-GaR3}−] (2). Contrastingly, neither ItBu or GaR3 was able to react with HBPin under the conditions of this study. Combining an NHC-stabilized borenium cation, [{ItBu-BPin}+], with an anionic dinuclear gallate, [{GaR3(μ-H)GaR3}−], 2 proved to be unstable in solution at room temperature, evolving to the abnormal NHC-Ga complex [BPinC{{N(tBu)]2CHCGa(R)3}] (3). Interestingly, the structural isomer of 2, with the borenium cation residing at the C4 position of the carbene, [{aItBu-BPin}+{GaR3(μ-H)GaR3}−] (4), was obtained when the abnormal NHC complex [aItBu·GaR3] (1) was heated to 70 °C with HBPin, demonstrating that, under these forced conditions, it is possible to induce thermal frustration of the Lewis base/Lewis acid components of 1, enabling the activation of HBPin. Building on these stoichiometric studies, the frustrated Lewis pair (FLP) reactivity observed for the GaR3/ItBu combination with HBPin could then be upgraded to catalytic regimes, allowing the efficient hydroboration of a range of aldehydes and ketones under mild reaction conditions. Mechanistic insights into the possible reaction pathway involved in this process have been gained by combining kinetic investigations with a comparative study of the catalytic capabilities of several gallium and borenium species related to 2. Disclosing a new cooperative partnership, reactions are proposed to occur via the formation of a highly reactive monomeric hydride gallate, [{ItBu- BPin}+{GaR3(H)}−] (I). Each anionic and cationic component of I plays a key role for success of the hydroboration, with the nucleophilic monomeric gallate anion favoring the transfer of its hydride to the C=O bond of the organic substate, which in turn is activated by coordination to the borenium cation.

While it is known that the addition of Group 1 alkoxides to s-block organometallics can have an activating effect on reactivity, the exact nature of this effect is not that well understood. Here we describe the activation of sBu2 Mg towards substituted bromoarenes by adding one equivalent of LiOR (R=2-ethylhexyl), where unusually both sBu groups can undergo efficient Br/Mg exchange. Depending on the substitution pattern on the bromoarene two different types of organometallic intermediates have been isolated, either a mixed aryl/alkoxide [{LiMg(2-FG-C6 H4 )2 (OR)}2 ] (FG=OMe; NMe2 ) or a homoaryl [(THF)4 Li2 Mg(4-FG-C6 H4 )4 ] (FG=OMe, F). Detailed NMR spectroscopic studies have revealed that these exchange reactions and the formation of their intermediates are controlled by a new type of bimetallic Schlenk-type equilibrium between heteroleptic [LiMgsBu2 (OR)], alkyl rich [Li2 MgsBu4 ] and Mg(OR)2 , with [Li2 MgsBu4 ] being the active species performing the Br/Mg exchange process.

A new method for regioselective zincations of challenging N-heterocyclic substrates such as pyrimidines and pyridazine was reported using bimetallic bases TMPZnX⋅LiX (TMP=2,2,6,6-tetramethylpiperidyl; X=Cl, Br). Reactions occurred under mild conditions (25-70 °C, using 1.75 equivalents of base without additives), furnishing 2-zincated pyrimidines and 3-zincated pyridazine, which were then trapped with a variety of electrophiles. Contrasting with other s-block metalating systems, which lack selectivity in their reactions even when operating at low temperatures, these mixed Li/Zn bases enabled unprecedented regioselectivities that cannot be replicated by either LiTMP nor Zn(TMP)2 on their own. Spectroscopic and structural interrogations of organometallic intermediates involved in these reactions have shed light on the complex constitution of reaction mixtures and the origins of their special reactivities.

Though LiTMP (TMP=2,2',6,6'-tetramethylpiperidide) is a commonly used amide, surprisingly the heavier NaTMP has hardly been utilised. Here, by mixing NaTMP with tridentate donor PMDETA (N,N,N',N'',N''-pentamethyldiethylenetriamine), we provide structural, and mechanistic insights into the sodiation of non-activated arenes (e.g. anisole and benzene). While these reactions are low yielding, adding B(OiPr)3 has a profound effect, not only by intercepting the CAr -Na bond, but also by driving the metalation reaction towards quantitative formation of more stabilized sodium aryl boronates. Demonstrating its metalating power, regioselective C2-metalation/borylation of naphthalene has been accomplished contrasting with single-metal based protocols which are unselective and low yielding. Extension to other arenes allows for in situ generation of aryl boronates which can then directly engage in Suzuki-Miyaura couplings, furnishing a range of biaryls in a selective and efficient manner.

While Ni{N(SiMe3)2}2 is unstable, the thermally stable and chemically robust tris-amido sodium nickelate [Ni{N(SiMe3)2}3][Na(PMDETA)2] can be prepared directly from NiBr2 and 3 equiv of Na{N(SiMe3)...

Exploiting the cooperative action of Lewis acid Zn(C6F5)2 with diarylzinc reagents, the efficient arylation of N,O-acetals to access diarylmethylamines is reported. Reactions take place under mild reaction conditions without the need for transtion-metal catalysis. Mechanistic investigations have revealed that Zn(C6F5)2 not only acts as a Lewis acid activator, but also enables the regeneration of nucleophilic ZnAr2 species, allowing a limiting 50 mol% to be employed., Operating via a special type of Zn/Zn′ cooperation, a new transition-metal free and atom efficient method of arylating N,O-acetals has been developed combining nucleophilic ZnPh2 with Lewis acidic Zn(C6F5)2.

Using the bimetallic combination sBu2Mg⋅2 LiOR (R=2‐ethylhexyl) in toluene enables efficient and regioselective Br/Mg exchanges with various dibromo‐arenes and ‐heteroarenes under mild reaction conditions and provides bromo‐substituted magnesium reagents. Assessing the role of Lewis donor additives in these reactions revealed that N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDTA) finely tunes the regioselectivity of the Br/Mg exchange on dibromo‐pyridines and quinolines. Combining spectroscopic with X‐ray crystallographic studies, light has been shed on the mixed Li/Mg constitution of the organometallic intermediates accomplishing these transformations. These systems reacted effectively with a broad range of electrophiles, including allyl bromides, ketones, aldehydes, and Weinreb amides in good yields., Using the bimetallic combination sBu2Mg⋅2 LiOR (R=2‐ethylhexyl) in toluene enables a very fast regioselective Br/Mg exchange of dibromo(hetero)arenes in toluene. The regioselectivity of the exchange can be finely tuned by the coordination preference of lithium, which can be switched, in some cases, by the addition of Lewis donors such as PMDTA.

More than four decades ago, a complex identified as the planar homoleptic lithium nickelate "Li

Alkali-metal amides have become key reagents in synthetic chemistry, with special focus in deprotonation reactions. Despite the higher reactivity found in the heavier sodium and potassium amides, their insolubility and low stability has favoured the use of the more soluble lithium analogues, converting them into the most used non-nucleophilic bases. Studying the coordination effects of Lewis donor molecules such as tridentate amine PMDETA (N,N,N’,N’’,N’’-pentamethyldiethylenetriamine) in combination with the sodium amide NaTMP (TMP = 2,2’,6,6’-tetramethylpiperidide), we have been able to unlock the use of these reagents for the functionalisation of arenes, i.e. the deuterium incorporation by hydrogen isotope exchange and the deprotonative borylation of unactivated arenes. These findings show how sodium amides are not just a simple more sustainable replacement of their lithium counterparts, but also that they can display significantly enhanced reactivities allowing for the development of new transformations.

Recent advances in heterobimetallic chemistry have revealed the potential for mixed-metal systems to facilitate reactions that are unattainable with their single-metal components. This perspective explores the pairing of nickel(0) complexes with organo-alkali-metal reagents, which yield highly reactive alkali-metal nickelates. These previously underexplored systems have re-emerged as a promising area of research, with recent studies uncovering their unique bonding and structural motifs. Furthermore, the discovery of nickelates as potential intermediates in cross-coupling reactions has provided the foundation for the development and mechanistic understanding of stoichiometric and catalytictransformations.

Advancing the applications of s-block heterobimetallic complexes in catalysis, we report the use of potassium magnesiate (PMDETA)2K2Mg(CH2SiMe3)4 [PMDETA=N,N,N’,N’,N’’-pentamethyldiethylenetriamine] for the catalytic hydrophosphinylation of styrenes under mild conditions. Exploiting chemical cooperation, this bimetallic approach offers greater catalytic activity and chemoselectivity than the single-metal components KCH2SiMe3 and Mg(CH2SiMe3)2. Stoichiometric studies between (PMDETA)2K2Mg(CH2SiMe3)4 and Ph2P(O)H help to elucidate the constitution of the active catalytic species, and illustrate the influence of donors on the potassium cation coordination, and how this may impact catalytic activity. Mechanistic investigations support that the rate determining step is the insertion of the olefinic substrate.

More than four decades ago, a complex identified as the planar homoleptic lithium nickelate “Li3NiPh3(solv)3” was reported by Taube and co-workers. This and subsequent reports involving this complex have lain dormant since; however, the absence of an X-ray diffraction structure leaves questions as to the nature of the Ni–PhLi bonding and the coordination geometry at Ni. By systematically evaluating the reactivity of Ni(COD)2 with PhLi under different conditions, we have found that this classical molecule is instead a unique octanuclear complex, [{Li3(solv)2Ph3Ni}2(μ-η2:η2-C6H4)] (5). This is supported by X-ray crystallography and solution-state NMR studies. A theoretical bonding analysis from NBO, QTAIM, and ELI perspectives reveals extreme back-bonding to the bridging C6H4 ligand resulting in dimetallabicyclobutane character, the lack of a Ni–Ni bond, and pronounced σ-bonding between the phenyl carbanions and nickel, including a weak σC–Li → sNi interaction with the C–Li bond acting as a σ-donor. Employing PhNa led to the isolation of [Na2(solv)3Ph2NiCOD]2 (7) and [Na2(solv)3Ph2(NaC8H11)Ni(COD)]2 (8), which lack the benzyne-derived ligand. These findings provide new insights into the synthesis, structure, bonding and reactivity of heterobimetallic nickelates, whose prevalence in organonickel chemistry and catalysis is likely greater than previously believed., This work has been supported by the European Research Council (ERC Starting Grant, CoopCat, 756575), the Spanish Ministry of Science and Innovation (Project PID2019-110856GA-I00) and Junta de Andalucía (P18-FR-4688). The authors gratefully acknowledge the financial support provided by the Swiss National Science Foundation (SNSF) (Award 188573 to EH). A. N. and D. B. acknowledge the support from the Norwegian Research Council through the Hylleraas Centre for Quantum Molecular Sciences (Project 262695) and the Norwegian Metacenter for Computational Science (NOTUR; Grant nn4654k). The Rigaku Synergy-S instrument used for X-ray diffraction studies was purchased through the SNSF R'Equip grant 206021_177033.

Advancing the understanding of using alkali-metal alkoxides as additives to organomagnesium reagents in Mg-Br exchange reactions, a homologous series of mixed-ligand alkyl/alkoxide alkali-metal magnesiates [MMg(CH

A tandem protocol to access tertiary alcohols has been developed which combines the organocatalytic oxidation of secondary alcohols to ketones followed by their chemoselective addition by several RLi reagents. Reactions take place at room temperature, under air and in aqueous solutions, a trio of conditions that are typically forbidden in polar organometallic chemistry.

Exploiting cooperative effects between Na and FeII centres present in tris(amide) ferrate complexes has led to the chemoselective ferration of pentafluorobenzene, benzene, toluene, anisole, and pyridine being realised at room temperature. The importance of this bimetallic partnership is demonstrated by neither the relevant sodium amide (NaHMDS or NaTMP) nor the FeII amide Fe(HMDS)2 efficiently metallating these substrates under the conditions of this study. By combining NMR studies with the isolation of key intermediates and DFT calculations, we offer a possible mechanism for how these reactions take place, uncovering a surprising reaction pathway in which the metals cooperate in a synchronised manner. Although the isolated products are formally the result of Fe‐H exchange, theoretical calculations indicate that the aromatic substrates undergo Na‐H exchange followed by fast intramolecular transmetallation to Fe, thus stabilizing the newly generated aryl fragment., Combining iron with sodium in tris(amido) complexes has led to the selective ferration of non‐activated arenes being accomplished. A new cooperative mechanism is disclosed, whereby the sodium performs the metal‐H exchange and this is followed by a fast intramolecular trans‐metal trapping of the aryl anion by the iron centre.

Over the past decade s-block metal catalysis has undergone a transformation from being an esoteric curiosity to a well-established and consolidated field towards sustainable synthesis. Earth-abundant metals such as Ca, Mg, and Al have shown eye-opening catalytic performances in key catalytic processes such as hydrosilylation, hydroamination or alkene polymerization. In parallel to these studies, s-block mixed-metal reagents have also been attracting widespread interest from scientists. These bimetallic reagents effect many cornerstone organic transformations, often providing enhanced reactivities and better chemo- and regioselectivities than conventional monometallic reagents. Despite a significant number of synthetic advances to date, most efforts have focused primarily on stoichiometric transformations. Merging these two exciting areas of research, this Perspective Article provides an overview on the emerging concept of s/p-block cooperative catalysis. Showcasing recent contributions from several research groups across the world, the untapped potential that these systems can offer in catalytic transformations is discussed with special emphasis placed on how synergistic effects can operate and the special roles played by each metal in these transformations. Advancing the understanding of the ground rules of s-block cooperative catalysis, the application of these bimetalic systems in a critical selection of catalytic transformations encompassing hydroamination, cyclisation, hydroboration to C–C bond forming processes are presented as well as their uses in important polymerization reactions., Exporting cooperative effects in main group heterobimetallic reagents to catalytic regimes, this Perspective showcases key advances in their applications for hydroelementation, cyclisation, C–C bond formation and polymerization processes.

Mixed s-block metal organometallic reagents have been successfully utilised in the catalytic intramolecular hydroalkoxylation of alkynols. This success has been attributed to the unique manner in which these reagents can overcome the challenges of the reaction: namely OH activation and coordination to and then addition across a C≡C bond. In order to optimise the reaction conditions and to garner vital catalytic system requirements, a series of alkali metal magnesiates were enlisted for the catalytic intramolecular hydroalkoxylation of 4-pentynol. In a prelude to the main investigation, the homometallic magnesium dialkyl reagent MgR2 (where R = CH2SiMe3) was utilised. This reagent was unsuccessful in cyclising the alcohol into 2-methylenetetrahydrofuran 2a or 5-methyl-2,3-dihydrofuran 2b, even in the presence of multidentate Lewis donor molecules such as N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA). Alkali metal magnesiates MIMgR3 (when MI = Li, Na or K) performed the cyclisation unsatisfactorily both in the absence/presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) or PMDETA. When higher-order magnesiates (i.e., MI2MgR4) were employed, in general a marked increase in yield was observed for MI = Na or K; however, the reactions were still sluggish with long reaction times (22–36 h). A major improvement in the catalytic activity of the magnesiates was observed when the crown ether molecule 15-crown-5 was combined with sodium magnesiate Na2MgR4(TMEDA)2 furnishing yields of 87% with 2a : 2b ratios of 95 : 5 after 5 h. Similar high yields of 88% with 2a : 2b ratios of 90 : 10 after 3 h were obtained combining 18-crown-6 with potassium magnesiate K2MgR4(PMDETA)2. Having optimised these systems, substrate scope was examined to probe the range and robustness of 18-crown-6/K2MgR4(PMDETA)2 as a catalyst. A wide series of alkynols, including terminal and internal alkynes which contain a variety of potentially reactive functional groups, were cyclised. In comparison to previously reported monometallic systems, bimetallic 18-crown-6/K2MgR4(PMDETA)2 displays enhanced reactivity towards internal alkynol-cyclisation. Kinetic studies revealed an inhibition effect of substrate on the catalysts via adduct formation and requiring dissociation prior to the rate limiting cyclisation step.

A series of new Mg(ii) amides featuring a bulky β-diketiminate backstop ligand, has been synthesised. These complexes are demonstrated to be excellent sources of nucleophilic amides that can participate in rapid C-F activation of several fluoroarenes at room temperature or using microwave assistance, leading to the installment of synthetically important C-N bonds via nucleophilic substitution.

Expanding the scope and applications of anionic N-heterocyclic carbenes (NHCs), a novel series of magnesium NHC complexes is reported using a mixed sodium-magnesium approach. Sequential reactivity of classical imidazol- 2-ylidene carbene IPr with NaR and MgR2 (R=CH2 SiMe3 ) affords [(THF)3 Na(μ-IPr- )MgR2 (THF)] (2) [IPr- =:C{[N(2,6-iPr2 C6 H3 )]2 CHC] containing an anionic NHC ligand, whereas surprisingly sodium magnesiate [NaMgR3 ] fails to deprotonate IPr affording instead the redistribution coordination adduct [IPr2 Na2 MgR4 ] (1). Compound 2 undergoes selective C2-methylation when treated with MeOTf furnishing novel abnormal NHC complex [{aIPrMe MgR2 }2 ] (3). Dissolving 3 in THF led to the dissociation of this complex into MgR2 and aIPrMe with the latter isomerizing to the olefinic NHC IPr=CH2 . The ability of 2 and 3 to transfer their anionic and abnormal NHC ligands, respectively to AuI metal fragments has been investigated allowing the isolation and structural characterization of [RAu(μ-IPr- )MgR(THF)2 ] (4) and [aIPrMe AuR] (5) respectively. In both cases transfer of an alkyl R group is observed. However while 3 can also transfer its abnormal NHC ligand to give 5, in 4 the anionic NHC still remains coordinated to Mg via its C4 position, whereas the {AuR} fragment occupies the C2 position previously filled by a donor-solvated {Na(THF)3 }+ cation.

A series of heteroleptic monoamido‐monohydrido‐dialkylaluminate complexes of general formula [iBu2AlTMPHLi⋅donor] were synthesized and characterised in solution and in the solid state. Applying these complexes in catalytic hydroboration reactions with representative aldehydes and ketones reveals that all are competent, however a definite donor substituent effect is discernible. The bifunctional nature of the complexes is also probed by assessing their performance in metallation of a triazole and phenylacetylene and addition across pyrazine. These results lead to an example of phenylacetylene hydroboration, which likely proceeds via deprotonation, rather than insertion as observed with the aldehydes and ketones. Collectively, the results emphasise that reactivity is strongly influenced by both the mixed‐metal constitution and mixed‐ligand constitution of the new aluminates.

N-heterocyclic carbenes (NHCs) have become indispensable ligands across a broad swathe of the synthetic and catalytic landscape, not in small part due to their ease of electronic and steric tuneability. One of the latest additions to this important family of ligands are anionic NHCs, which have become valuable precursors to access abnormal NHC complexes as well as shown great potential for further NHC functionalisation. Deprotonative metallation has emerged as one of the most versatile methodologies to access anionic NHCs, where judicious choice of reaction conditions and metallating agent can finely tune the regioselectivity of the reaction. This Feature Article focuses on the recent emergence of s-block metal-mediated NHC metallations and the new opportunities this methodology offers.

While Fe(II) complexes have shown little promise in deprotonative metallation chemistry, pairing iron bis(amide) Fe(HMDS)2 with Na(HMDS) to form new sodium ferrate base [(dioxane)0.5·NaFe(HMDS)3] (1) enables regioselective mono and di-ferration (via direct Fe-H exchange) of a wide range of fluoroaromatic substrates under mild reaction conditions. Trapping of several ferrated intermediates has provided key insight into how synchronised Na/Fe cooperation operates in these transformations. Furthermore using excess 1 at 80oC switches on a remarkable cascade process inducing the collective 2-fold C-H/3-fold C-F bond activation, where each C-H bond is transformed to C-Fe bonds whereas each C-F bond is transformed into a C-N bond.

Combining alkali-metal-mediated metalation (AMMM) and N-heterocyclic carbene (NHC) chemistry, a novel C-N bond activation and ring-opening process is described for these increasingly important NHC molecules, which are generally considered robust ancillary ligands. Here, mechanistic investigations on reactions of saturated NHC SIMes (SIMes=[:C{N(2,4,6-Me3 C6 H2 )CH2 }2 ]) with Group 1 alkyl bases suggest this destructive process is triggered by lateral metalation of the carbene. Exploiting co-complexation and trans-metal-trapping strategies with lower polarity organometallic reagents (Mg(CH2 SiMe3 )2 and Al(TMP)iBu2 ), key intermediates in this process have been isolated and structurally defined.

Regioselective 1,1′,3,3′-tetrazincation [C–H to C–Zn(tBu)] of ferrocene has been achieved by reaction of a fourfold excess of di-t-butylzinc (tBu2Zn) with sodium 2,2,6,6-tetramethylpiperidide (NaTMP) in hexane solution manifested in the trimetallic iron–sodium–zinc complex [Na4(TMP)4Zn4(tBu)4{(C5H3)2Fe}], 1. X-ray crystallographic studies supported by DFT modelling reveal the structure to be an open inverse crown in which two [Na(TMP)Zn(tBu)Na(TMP)Zn(tBu)]2+ cationic units surround a {(C5H3)2Fe}4− tetraanion. Detailed C6D6 NMR studies have assigned the plethora of 1H and 13C chemical shifts of this complex. It exists in a major form in which capping and bridging TMP groups interchange, as well as a minor form that appears to be an intermediate in this complicated exchange phenomenon. Investigation of 1 has uncovered two distinct reactivities. Two of its peripheral t-butyl carbanions formally deprotonate toluene at the lateral methyl group to generate benzyl ligands that replace these carbanions in [Na4(TMP)4Zn4(tBu)2(CH2Ph)2{(C5H3)2Fe}], 2, which retains its tetrazincated ferrocenyl core. Benzyl-Na π-arene interactions are a notable feature of 2. In contrast, reaction with pyridine affords the crystalline product {[Na·4py][Zn(py*)2(tBu)·py]}∞, 3, where py is neutral pyridine (C5H5N) and py* is the anion (4-C5H4N), a rare example of pyridine deprotonated/metallated at the 4-position. This ferrocene-free complex appears to be a product of core reactivity in that the core-positioned ferrocenyl anions of 1, in company with TMP anions, have formally deprotonated the heterocycle., A tetrazincated ferrocene complex displays divergent basicity towards aromatic substrates through either its core or peripheral ligands.

Pairing lithium and manganese(II) to form lithium manganate [Li2 Mn(CH2 SiMe3 )4 ] enables the efficient direct Mn-I exchange of aryliodides, affording transient (aryl)lithium manganate intermediates which in turn undergo spontaneous C-C homocoupling at room temperature to furnish symmetrical (bis)aryls in good yields under mild reaction conditions. The combination of EPR with X-ray crystallographic studies has revealed the mixed Li/Mn constitution of the organometallic intermediates involved in these reactions, including the homocoupling step which had previously been thought to occur via a single-metal Mn aryl species. These studies show Li and Mn working together in a synergistic manner to facilitate both the Mn-I exchange and the C-C bond-forming steps. Both steps are carefully synchronized, with the concomitant generation of the alkyliodide ICH2 SiMe3 during the Mn-I exchange being essential to the aryl homocoupling process, wherein it serves as an in situ generated oxidant.

A wide range of polyfunctional diaryl-and diheteroarylzinc species were prepared in toluene within 10 min to 5 h through an I/Zn or Br/Zn exchange reaction using bimetallic reagents of the general formula R’2Zn·2LiOR (R’=sBu, tBu, pTol). Highly sensitive functional groups, such as a triazine, a ketone, an aldehyde, or a nitro group, were tolerated in these exchange reactions, enabling the synthesis of a plethora of functionalized (hetero)arenes after quenching with various electrophiles. Insight into the constitution and reactivity of these bimetallic mixtures revealed the formation of highly active lithium diorganodialkoxyzincates of type[R’2Zn-(OR)2Li2].

Main group bimetallic complexes, while being increasingly used in stoichiometric deprotonation and metal–halogen exchange reactions, have not yet made a significant impact in catalytic applications. This paper explores the ability of alkali metal magnesiates to catalyse the intermolecular hydroamination of alkynes and alkenes using sytrene and diphenylacetylene as principle setting model substrates. By systematically studying the role of the alkali–metal and the formulation of the heterobimetallic precatalyst, this study establishes higher order potassium magnesiate [(PMDETA)2K2Mg(CH2SiMe3)4] (7) as a highly effective system capable of catalysing hydroamination of styrene and diphenylacetylene with several amines while operating at room temperature. This high reactivity contrasts with the complete lack of catalytic ability of neutral Mg(CH2SiMe3)2, even when harsher reaction conditions are employed (24 h, 80 °C). A pronounced alkali metal effect is also uncovered proving that the alkali metal (Li, Na, or K) is not a mere spectating counterion. Through stoichiometric reactions, and structural and spectroscopic (DOSY NMR) investigations we shed some light on the potential reaction pathway as well as the constitution of key intermediates. This work suggests that the enhanced catalytic activity of 7 can be rationalised in terms of the superior nucleophilic power of the formally dianionic magnesiate {Mg(NR2)4}2− generated in situ during the hydroamination process, along with the ability of potassium to engage in π-interactions with the unsaturated organic substrate, enhancing its susceptibility towards a nucleophilic attack by the amide anion.

Despite their ubiquitous presence in synthesis, the use of polar organolithium reagents under environmentally benign conditions constitutes one of the greatest challenges in sustainable chemistry. Their high reactivity imposes the use of severely restrictive protocols (e.g., moisture- and oxygen-free, toxic organic solvents, inert atmospheres, low temperatures, etc.). Making inroads towards meeting this challenge, a new air- and moisture-compatible organolithium-mediated methodology for the anionic polymerization of different olefins (e.g., styrenes and vinylpyridines) was established by pioneering the use of deep eutectic solvents (DESs) as an eco-friendly reaction medium in this type of transformation. Fine-tuning of the conditions (sonication of the reaction mixture at 40 °C in the absence of protecting atmosphere) along with careful choice of components of the DES [choline chloride (ChCl) and glycerol (Gly) in a 1:2 ratio] furnished the desired organic polymers (homopolymers and random copolymers) in excellent yields (up to 90 %) and low polydispersities (IPD 1.1-1.3). Remarkably, the in situ-formed polystyril lithium intermediates exhibited a great resistance to hydrolysis in the eutectic mixture 1ChCl/2Gly (up to 1.5 h), hinting at an unexpected high stability of these otherwise highly reactive organolithium species in these unconventional reaction media. This unique stability can be exploited to create well defined block-copolymers.