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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

Exploiting bimetallic cooperation alkali-metal manganate (II) complexes can efficiently promote oxidative homocoupling of terminal alkynes furnishing an array of conjugated 1,3-diynes. The influence of the alkali-metal on these C−C bond forming processes has been studied by preparing and structurally characterizing the alkali-metal tetra(alkyl) manganates [(TMEDA)2Na2Mn(CH2SiMe3)4] and [(PMDETA)2K2Mn(CH2SiMe3)4]. Reactivity studies using phenylacetylene as a model substrate have revealed that for the homocoupling to take place initial metalation of the alkyne is required. In this regard, the lack of basicity of neutral Mn(CH2SiMe3)2 precludes the formation of the diyne. Contrastingly, the tetra(alkyl) alkali-metal manganates behave as polybasic reagents, being able to easily deprotonate phenylacetylene yielding [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4]. Controlled exposure of [{(THF)4Na2Mn(C≡CPh)4}∞] and [(THF)4Li2Mn(C≡CPh)4] to dry air confirmed their intermediary in formation of 1,4-diphenyl-1,3-butadiyne in excellent yields. While the Na/Mn(II) partnership proved to be the most efficient in stoichiometric transformations, under catalytic regimes, the combination of MC≡CAr (M= Li, Na) and MnCl2 (6 mol %) only works for lithium, most likely due to the degradation of alkynylsodiums under the aerobic reaction conditions.

The Ni‐catalysed cross‐coupling of aryl ethers is a powerful method to forge new C−C and C−heteroatom bonds. However, the inert C(sp2)−O bond means that a canonical mechanism that relies on the oxidative addition of the aryl ether to a Ni0 centre is thermodynamically and kinetically unfavourable, which suggests that alternative mechanisms may be involved. Here, we provide spectroscopic and structural insights into the anionic pathway, which relies on the formation of electron‐rich hetero‐bimetallic nickelates by adding organometallic nucleophiles to a Ni0 centre. Assessing the rich co‐complexation chemistry between Ni(COD)2 and PhLi has led to the structures and solution‐state chemistry of a diverse family of catalytically competent lithium nickelates being unveiled. In addition, we demonstrate dramatic solvent and donor effects, which suggest that the cooperative activation of the aryl ether substrate by Ni0‐ate complexes plays a key role in the catalytic cycle., Assessment of the rich co‐complexation chemistry of Ni(COD)2 and PhLi has led to a new family of structurally diverse lithium nickelates being uncovered. Combined stoichiometric, catalytic, and kinetic studies reveal that these hetero‐bimetallic complexes may be the key intermediates that facilitate the smooth C−O bond cleavage and cross‐coupling of aryl ethers under mild conditions.

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

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.

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.

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.

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

Exploiting chemical cooperation between Na and Fe(II) within the bimetallic base [dioxane ⋅ NaFe(HMDS) 3] (I), (dioxane=1,4-dioxane, HMDS=N(SiMe 3) 2) the selective ferration of fluorobenzene, 1-fluoronaphthalene, 1,4-difluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1-bromo-3,5-difluorobenzene, 3-fluoroanisole and 3,5-difluoroanisole has been realized, affording sodium ferrates [dioxane ⋅ Na(HMDS)(2-F-C 6H 4)Fe(HMDS)] ∞ (1), [dioxane ⋅ Na(HMDS)(2-F-C 10H 6)Fe(HMDS)] ∞ (2), [dioxane ⋅ {Na(HMDS)(2,5-F 2-C 6H 3)Fe(HMDS)} 2] ∞ (3), [dioxane ⋅ {Na(HMDS)(2,3,6-F 3-C 6H 2)Fe(HMDS)} 2] ∞ (4), [(dioxane) 1.5 ⋅ Na(HMDS)(2,4,6-F 3-C 6H 2)Fe(HMDS)] 2 (5), [(dioxane) 1.5 ⋅ {Na(HMDS)(4-Br-2,6-F 2-C 6H 2)Fe(HMDS) 2] (6), [{(dioxane) 2 ⋅ Na 2Fe(HMDS) 2(2-methoxy-6-F-C 6H 3)} +{Fe(HMDS) 3} −] ∞ (7) and [dioxane ⋅ {Na(HMDS)(4-methoxy-2,6-F 2-C 6H 2)Fe(HMDS)} 2] ∞ (8), respectively. Reactions take place under mild reaction conditions, with excellent control of the selectivity and no competing C−F bond activation is observed. Showcasing complex polymeric arrangements in some cases, the structures of compounds 1–8 have been determined by X-ray crystallographic studies. In all cases, the Fe(II) centers occupy the position in the relevant fluoroarene that was previously filled by a proton, confirming that these metallations are actually ferration processes whereas the Na atoms prefer to form Na⋅⋅⋅F dative interactions. Compounds 1–8 are thermally stable and do not undergo benzyne formation (through NaF elimination) and their formation contrasts with the inertness of Fe(HMDS) 2 which fails to act as a base to metallate fluoroarenes.

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.

Alkali‐metal ferrates containing amide groups have emerged as regioselective bases capable of promoting Fe−H exchanges of aromatic substrates. Advancing this area of heterobimetallic chemistry, a new series of sodium ferrates is introduced incorporating the bulky arylsilyl amido ligand N(SiMe3)(Dipp) (Dipp=2,6‐iPr2‐C6H3). Influenced by the large steric demands imposed by this amide, transamination of [NaFe(HMDS)3] (HMDS=N(SiMe3)2) with an excess of HN(SiMe3)(Dipp) led to the isolation of heteroleptic [Na(HMDS)2Fe{N(SiMe3)Dipp}]∞ (1) resulting from the exchange of just one HMDS group. An alternative co‐complexation approach, combining the homometallic metal amides [NaN(SiMe3)Dipp] and [Fe{N(SiMe3)Dipp}2] induces lateral metallation of one Me arm from the SiMe3 group in the iron amide furnishing tetrameric [NaFe{N(SiCH2Me2)Dipp}{N(SiMe3)Dipp}]4 (2). Reactivity studies support that this deprotonation is driven by the steric incompatibility of the single metal amides rather than the basic capability of the sodium reagent. Displaying synergistic reactivity, heteroleptic sodium ferrate 1 can selectively promote ferration of pentafluorobenzene using one of its HMDS arms to give heterotrileptic [Na{N(SiMe3)Dipp}(HMDS)Fe(C6F5)]∞ (4). Attempts to deprotonate less activated pyridine led to the isolation of NaHMDS and heteroleptic Fe(II) amide [(py)Fe{N(SiMe3)Dipp}(HMDS)] (5), resulting from an alternative redistribution process which is favoured by the Lewis donor ability of this substrate., Influenced by the large steric demands imposed by the 2,6‐diisopropyl‐N‐(trimethylsilyl)anilide ligand, N(SiMe3)Dipp, new examples of chemical cooperativity on sodium ferrates have been disclosed. This includes: (a) the chemoselective ferration of pentafluorobenzene by a heteroleptic tris(amido) sodium ferrate; and, (b) the lateral metallation of a N(SiMe3)Dipp group at one Me of its SiMe3 substituent when attempting the co‐complexation of the sodium and iron (II) single‐metal amides.

S.E.G.-G. and J.G.A thank the Spanish MINECO and MIC (Project PID2020-113473GB-I00). J.G.-A. thanks: i) the Fundación BBVA for the award of a “Beca Leonardo a Investigadores y Creadores Culturales 2017”; and ii) PhosAgro/UNESCO/IUPAC for the award of a “Green Chemistry for Life Grant”. A.P.S is indebted to Spanish MINECO (Project CTQ2014-56345-P, CTQ2017-88357-P, and RYC-2012-09800), and Gobierno del Principado de Asturias (FICYT, Project FC-15-GRUPIN14-106) for financial support. E.H. acknowledges the SNF (188573) and the EPSRC (EP/S020837/2) for their generous financial support

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.

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.

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.

This study establishes a new trans‐metal‐trapping (TMT) procedure based on a mixture of LiTMP (the base) and tris(trimethylsilylmethyl)gallium [Ga(CH2SiMe3)3, GaR3] (the trap) that, operating in a tandem manner, is effective for the regioselective deprotonation of sensitive diazines in hydrocarbon solution, as illustrated through reactions of pyrazine, pyridazine, and pyrimidine, as well as through the N‐S heterocycle benzothiazole. The metallo‐activated complexes of all of these compounds were isolated and structurally defined.

By sequentially treating the unsaturated carbene IPr (IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) with heavier alkali-metal alkyls NaR or KR (R = CH2SiMe3) and GaR3, novel heteroleptic gallates 1 and 2 have been prepared. Incorporating anionic NHC ligands, these bimetallic complexes react selectively with electrophilles to afford neutral abnormal NHC Ga complexes under mild conditions.

By exploring co-complexation reactions between the manganese alkyl Mn(CH2SiMe3)2 and the heavier alkali-metal alkyls M(CH2SiMe3) (M=Na, K) in a benzene/hexane solvent mixture and in some cases adding Lewis donors (bidentate TMEDA, 1,4-dioxane, and 1,4-diazabicyclo[2,2,2] octane (DABCO)) has produced a new family of alkali-metal tris(alkyl) manganates. The influences that the alkali metal and the donor solvent impose on the structures and magnetic properties of these ates have been assessed by a combination of X-ray, SQUID magnetization measurements, and EPR spectroscopy. These studies uncover a diverse structural chemistry ranging from discrete monomers [(TMEDA)2 MMn(CH2SiMe3)3] (M=Na, 3; M=K, 4) to dimers [{KMn(CH2SiMe3)3 ⋅C6 H6}2] (2) and [{NaMn(CH2SiMe3)3}2 (dioxane)7] (5); and to more complex supramolecular networks [{NaMn(CH2SiMe3)3}∞] (1) and [{Na2Mn2 (CH2SiMe3)6 (DABCO)2}∞] (7)). Interestingly, the identity of the alkali metal exerts a significant effect in the reactions of 1 and 2 with 1,4-dioxane, as 1 produces coordination adduct 5, while 2 forms heteroleptic [{(dioxane)6K2Mn2 (CH2SiMe3)4(O(CH2)2OCH=CH2)2}∞] (6) containing two alkoxide-vinyl anions resulting from α-metalation and ring opening of dioxane. Compounds 6 and 7, containing two spin carriers, exhibit antiferromagnetic coupling of their S=5/2 moments with varying intensity depending on the nature of the exchange pathways.

Developing new green solvents in designing chemical products and processes or successfully employing the already existing ones is one of the key subjects in green chemistry and is especially important in organometallic chemistry, which is an interdisciplinary field. Can we advantageously also use unconventional reaction media in place of current harsh organic solvents for polar organometallic compounds? This microreview critically analyses the state of the art with regard to this topic and showcases recent developments and breakthroughs that are becoming new research directions in this field. Because metals cover a vast swath of the Periodic Table the content is organised into three sections discussing the reactivity of organometallic compounds of s-, p- and d-block elements in unconventional solvents.

This study explores the synthetic utility of homo(aryl) lithum zincate reagents [LiZnPh3] (2) and [Li2ZnPh4] (3), made by cocomplexation of variable amounts of their monometallic components LiPh and ZnPh2 (1), as chemoselective nucleophilic arylating reagents. Lithium zincates 2 and 3 were both characterized by multinuclear (1H, 13C, and 7Li) NMR spectroscopy, and in the case of 2, a classical reagent in heterobimetallic chemistry, the molecular structure of its OnBu2 solvate [LiZnPh3(OnBu2)2] 2·2OBu2 has been established by X-ray crystallography. Using the synthetically relevant N-heterocyclic molecule acridine (acr, NC13H9), a new zincate-mediated arylating approach is demonstrated which allows the chemoselective arylation of acr at its C9 position, affording 9,10-dihydro-9-phenylacridine (4) in 95% yield using microwave irradiation (125 °C, 20 min). These conditions are in contrast with previous transition-metal-catalyzed methodologies using ZnPh2 as an arylating reagent, which require significantly longer reaction times (130 °C, 20 h). Oxidation of 4 with DDQ furnished 9-phenylacridine (5) in a 71% yield. New insights into the constitution of the intermediate organometallic species involved in these reactions prior to the hydrolysis step have been gained by trapping homometallic [(THF)3Li(NC13H9-Ph)] (6). Interestingly the reaction of acr with 3 equiv of PhLi/TMEDA led to the isolation of a different product, namely the novel paramagnetic [(THF)(TMEDA)Li{NC13H8-Ph}•−] (7), which contains a radical anion of 9-phenylacridine. The structure of the donor−acceptor complex [(acr)ZnPh2] (8) has also been included as a result of the reaction of 1 with acr.

Cooperativity between the Li and Al centres is implicated in catalytic hydroboration reactions of aldehydes and ketones with pinacolborane via heteroleptic lithium diamidodihydridoaluminates. In addition to implementing hydroalumination, these versatile heteroleptic ates can also perform as amido bases as illustrated with an acidic triazole.

Using bis(amide) Zn(HMDS)2 (HMDS = 1,1,1,3,3,3-hexamethyldisilazide) as a precursor, this study explores the synthesis of N-heterocyclic carbene stabilized mixed amido-hydride zinc complexes using two alternative hydride sources, namely dimethylamine borane (DMAB) and phenylsilane PhSiH3. Hydride-rich zinc cluster Zn4(HMDS)2H6·2IPr (1) (IPr = 1,3-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene), which can be envisaged as a co-complex of IPr·ZnH2 and (HMDS)ZnH, is obtained when DMAB is employed, with the concomitant formation of heteroleptic bis(amido)borane [HB(NMe2)(HMDS)] and H2 evolution. NMR studies in d8-THF show that although the bulky carbene IPr does not bind to the zinc bis(amide), its presence in the reaction media is required in order to stabilise 1. Reactions using the slightly less sterically demanding NHC IXy (IXy = 1,3-bis-(2,6-dimethylphenyl)imidazol-2-ylidene) led to the isolation and structural elucidation of the carbene adduct Zn(HMDS)2·IXy (2). Contrastingly, mixtures of equimolar amounts of PhSiH3 and the zinc bis(amide) (60 °C, 3 h, hexane) afforded monomeric heteroleptic hydride (HMDS)ZnH·IPr (3). NMR studies, including DOSY experiments, revealed that while the integrity of 3 is retained in polar d8-THF solutions, in lower polarity C6D6 it displays a much more complex solution behaviour, being in equilibrium with the homoleptic species ZnH2·IPr, Zn(HMDS)2 and IPr.