Towards a Paradigm Shift in Polar Organometallic Chemistry

Core tools of synthetic chemistry, polar organometallic reagents (typified by organolithium and Grignard reagents) are used worldwide for constructing compounds, especially aromatic compounds, which are ubiquitous in organic chemistry and thus in numerous commodities essential to everyday life. By isolation and characterisation of key organometallic intermediates, research in our group has led to the design of polar mixed-metal reagents imbued with synergistic effects that display chemical properties and reactivity profiles far exceeding the limits of traditional single-metal reagents. These studies have improved existing, or established new fundamentally important, synthetic methodologies based on either stoichiometric or catalytic reactions. Bimetallic cooperative effects have been demonstrated in an impressive array of important bond forming reactions including deprotonative metallation, transition-metal free C-C bond formation and metal-halogen exchange to name just a few. Towards greener, more sustainable, safer chemical transformations, our group has also pioneered the use of polar organometallic reagents under air and/or with water present using biorenewable solvents such as Deep Eutectic Solvents (DES) and 2-methyl THF. Herein we summarize some of our recent efforts in this intriguing area, which we believe can make the inroads towards a step change in the practice and future scope of polar organometallic chemistry

Tuning NaCo(II) Bimetallic Cooperativity to Perform Co–H Exchange / C–F Bond Activation Processes in Polyfluoroarenes

Recent advances in cooperative chemistry have shown the potential of heterobimetallic complexes combining an alkali-metal with an earth abundant divalent transition metal for the functionalisation of synthetically relevant aromatic molecules via deprotonative metalation. Pairing sodium with cobalt (II), here we provide an overview of the reactivity of bimetallic [NaCo(HMDS)3] [HMDS = N(SiMe3)2] towards C-H and C-F functionalisation of a wide range of perfluorinated molecules. These studies also uncover the enormous potential of this heterobimetallic base to perform Co-H exchanges with excellent selectivity and exceptional stoichiometric control as well as shedding light on the key role played by the alkali-metal

Alkali Metal Metal(ates) Containing Divalent Earth Abundant Transition Metals

Recent advances in cooperative chemistry have shown the enormous potential of main group heterobimetallic complexes for the functionalisation of aromatic molecules. Going beyond main group metal chemistry, here we provide an overview on the synthesis, structure and reactivity of bimetallic complexes which combine an alkali-metal (AM= Li, Na) with a divalent earth-abundant transition metal (M= Mn, Fe, Co, Ni), containing the utility silyl amide HMDS (HMDS = N(SiMe3)2). Advancing the understanding on how cooperative effects operate in these bimetallic (ate) systems, selected examples of their applications in deprotonative metalation are also discussed with special emphasis on the constitution of the metalated intermediates

Trans-metal-trapping meets FLP chemistry : Ga(CH2SiMe3)3 induced C-H functionalizations

Merging two topical themes in Main Group chemistry, namely cooperative bimetallics and FLP activity, this Forum Article focuses on the cooperativity-induced outcomes observed when the tris(alkyl)gallium compound GaR3 (R= CH2SiMe3) is paired with lithium amide LiTMP (TMP=2,2,6,6-tetramethylpiperidide) or the sterically hindered NHC ItBu (ItBu = 1,3-bis(tert-butyl)imidazol-2-ylidene). Drawing together some previously published work with new results, unique tandem reactivities are presented which are driven by the steric mismatch between the individual reagents of these multicomponent reagents. Thus the LiTMP/GaR3 combination, which on its own fails to form a co-complex, functions as a highly regioselective base (LiTMP)-trap (GaR3) partnership for metalation of N-heterocycles such as diazines, 1,3 benzo-azoles and 2-picoline in a trans-metal-trapping (TMT) process that stabilizes the emerging sensitive carbanions. Taking advantage of related steric incompatibility, a novel monometallic FLP system pairing GaR3 with ItBu has been developed for activation of carbonyl compounds (via C=O insertion) and other molecules with acidic hydrogen atoms such as phenol and phenylacetylene. Shedding new light on how these non-cocomplexing partnerships operate and showcasing the potential of Ga reagents to engage in metalation reactions or FLP activations, areas where the use of this Group 13 metal is scant, this Forum Article aims to stimulate more interest and activity towards the advancement of organogallium chemistry

Enhancing Metalating Efficiency of the Sodium Amide NaTMP in Arene Borylation Applications

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

Assessing Alkali-Metal Effects in the Structures and Reactivity of Mixed-Ligand Alkyl/Alkoxide Alkali-Metal Magnesiates

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(2)SiMe(3))(2)(dmem)](2) [dmem=2‐{[2‐(dimethylamino)ethyl]methylamino} ethoxide; M=Li, 1; Na, 2; (THF)K, 3] has been prepared. Structural and spectroscopic studies have established the constitutions of these heteroleptic/heterometallic species, which are retained in arene solution. Evaluation of their reactivity towards 2‐bromoanisole has uncovered a marked alkali‐metal effect with potassium magnesiate 3 being the most efficient of the three ate reagents. Studies probing the constitution of the exchange product from this reaction suggest that the putative [KMgAr(2)(dmem)](2) (Ar=o‐OMe−C(6)H(4)) intermediate undergoes redistribution into its single metal components [KAr](n) and [MgAr(dmem)](2) (5). This process can be circumvented by using a different potassium alkoxide containing an aliphatic chain such as KOR’ (R’=2‐ethylhexyl) which undergoes co‐complexation with Mg(CH(2)SiMe(3)) to give [KMg(CH(2)SiMe(3))(2)(OR’)](2) (7). This ate, in turn, reacts quantitatively with 2‐bromoanisole furnishing [KMgAr(2)(OR’)](2) (9) which is stable in solution as a bimetallic compound. Collectively this work highlights the complexity of these alkali‐metal mediated Mg−Br exchange reactions, where each reaction component can have a profound effect not only on the success of the reaction; but also the stability of the final metalated intermediates prior to their electrophilic interception