The reactivity of aluminium compounds is dominated by their electron deficiency and consequent electrophilicity; these compounds are archetypal Lewis acids (electron-pair acceptors). The main industrial roles of aluminium, and classical methods of synthesizing aluminium-element bonds (for example, hydroalumination and metathesis), draw on the electron deficiency of species of the type AlR and AlCl. Whereas aluminates, [AlR], are well known, the idea of reversing polarity and using an aluminium reagent as the nucleophilic partner in bond-forming substitution reactions is unprecedented, owing to the fact that low-valent aluminium anions analogous to nitrogen-, carbon- and boron-centred reagents of the types [NX], [CX] and [BX] are unknown. Aluminium compounds in the +1 oxidation state are known, but are thermodynamically unstable with respect to disproportionation. Compounds of this type are typically oligomeric, although monomeric systems that possess a metal-centred lone pair, such as Al(Nacnac) (where (Nacnac) = (NDippCR)CH and R = Bu, Me; Dipp = 2,6- PrCH), have also been reported. Coordination of these species, and also of (η-CMe)Al, to a range of Lewis acids has been observed, but their primary mode of reactivity involves facile oxidative addition to generate Al(III) species. Here we report the synthesis, structure and reaction chemistry of an anionic aluminium(I) nucleophile, the dimethylxanthene-stabilized potassium aluminyl [K{Al(NON)}] (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene). This species displays unprecedented reactivity in the formation of aluminium-element covalent bonds and in the C-H oxidative addition of benzene, suggesting that it could find further use in both metal-carbon and metal-metal bond-forming reactions.

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Solid-state auride salts featuring the negatively charged Auion are known to be stable in the presence of alkali metal counter-ions. While such electron-rich species might be expected to be nucleophilic (cf. I -), their instability in solution means that this has not been verified experimentally. Here we report the two-coordinate gold complex (NON)AlAuP t Bu3 (3, NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) synthesised by the reaction of the potassium aluminyl complex [K{Al(NON)}]2 (1) with t Bu3PAuI, and which features a strongly polarized bond, Au(d-)-Al(d+). 3 has been studied computationally, with QTAIM charge analysis implying a charge at gold (-0.82) which is in line with the relative electronegativities of the two metals (Au: 2.54; Al: 1.61 on the Pauling scale). Consistently, 3 is found to act as an unprecedented nucleophilic source of gold, reacting with diisopropylcarbodiimide and CO2 to give the Au-C bonded insertion products (NON)Al(X2C)AuP t Bu3 (X = N i Pr, 4; X = O, 5).Transition elements are known to be able to access multiple oxidation states 1 , a property which underpins widespread application in fields such as small molecule activation and catalysis 2,3 . The vast majority of transition metal complexes however, feature cationic metals in positive oxidation states, ligated by neutral or anionic donors 1,4 . Systems featuring formal negative oxidation states, such as the tetracarbonylferrate 5 or bis(benzene)vanadium 6 anions are much less common, and usually require strong p-acceptor ligands, most frequently CO 7 . In this regard, gold is unique, being the only transition metal to give rise to a stable "naked" monoanion (Au -, auride) in the condensed phase 8 . In part, this is due to relativistic effects which contract the 6s orbital significantly, resulting in an electron affinity of 2.30 eV, the highest of any transition metal 9,10 .This value is more comparable to those of the chalcogens (e.g. S: 2.08 eV; Se: 2.02 eV) than to the lighter group 11 congeners (Cu: 1.23 eV; Ag 1.30 eV) 10 . The 12-electron auride anion is typically generated by the reduction of metallic gold with alkali metals, to give salts such as CsAu and RbAu 11,12 ; the solution chemistry of these salts, however, is restricted to liquid ammonia 13,14 .Reduction of organometallic gold compounds to give systems in low oxidation states (i.e. zero or below) has been attempted, but with limited success [15][16][17][18][19][20] . Thermodynamics typically drive the aggregation of molecular Au(0) systems to clusters of colloidal gold [15][16][17][18] . Recently however, electron-rich gold complexes have been reported by Bertrand and co-workers, by making use of strongly p-accepting cyclic(alkyl)(amino)carbenes (CAAC) ligands (I and II, Figure 1) 19 . In addition, a four-coordinate molecular 'boroauride' was reported by Harman and co-workers last year in which the gold centre is stabilized by a diboraanthracene-based scaffold (III, Figure 1) 20 .Notwithstanding these examples, and even though Auions...

Trivalent aluminium compounds are well known for their reactivity as Lewis acids/electrophiles, a feature that is exploited in many pharmaceutical, industrial and laboratory‐based reactions. Recently, a series of isolable aluminium(I) anions (“aluminyls”) have been reported, which offer an alternative to this textbook description: these reagents behave as aluminium nucleophiles. This minireview covers the synthesis, structure and reactivity of aluminyl species reported to date, together with their associated metal complexes. The frontier orbitals of each of these species have been investigated using a common methodology to allow for a like‐for‐like comparison of their electronic structure and a means of rationalising (sometimes unprecedented) patterns of reactivity.

Anionic molecular imide complexes of aluminium are accessible via a rational synthetic approach involving the reactions of organo azides with a potassium aluminyl reagent. In the case of K2[(NON)Al(NDipp)]2 (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene; Dipp=2,6‐diisopropylphenyl) structural characterization by X‐ray crystallography reveals a short Al−N distance, which is thought primarily to be due to the low coordinate nature of the nitrogen centre. The Al−N unit is highly polar, and capable of the activation of relatively inert chemical bonds, such as those found in dihydrogen and carbon monoxide. In the case of CO, uptake of two molecules of the substrate leads to C−C coupling and C≡O bond cleavage. Thermodynamically, this is driven, at least in part, by Al−O bond formation. Mechanistically, a combination of quantum chemical and experimental observations suggests that the reaction proceeds via exchange of the NR and O substituents through intermediates featuring an aluminium‐bound isocyanate fragment.

The alkali metal halide supported alkali metal materials, ca. 5% w/w Na/NaCl and 5% w/w K/KI, are prepared without specialist equipment by rapidly stirring molten alkali metal with finely ground alkali metal halide powder. Scanning electron microscopy reveals the particles of 5% w/w Na/NaCl to lie largely in the 10–100 μM size range. The freely flowing powders are easily dispersible in organic solvents and are used as reducing agents for the facile syntheses of three magnesium­(I) compounds, [{HC­(MeCNAr)2}­Mg]2, Ar = mesityl (Mes), 2,6-diethylphenyl (Dep), or 2,6-diisopropylphenyl (Dip), which can be obtained in yields of up to 12 g. The potential advantages Na/NaCl and K/KI powders offer to synthetic inorganic/organometallic chemists, relative to currently available alkali metal reducing agents, are discussed.

Aluminium oxides constitute an important class of inorganic compound that are widely exploited in the chemical industry as catalysts and catalyst supports. Due to the tendency for such systems to aggregate via Al‐O‐Al bridges, the synthesis of well‐defined, soluble, molecular models for these materials is challenging. Here we show that reactions of the potassium aluminyl complex K2[(NON)Al]2 (NON=4,5‐bis(2,6‐diiso‐propylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) with CO2, PhNCO and N2O all proceed via a common aluminium oxide intermediate. This highly reactive species can be trapped by coordination of a THF molecule as the anionic oxide complex [(NON)AlO(THF)]−, which features discrete Al−O bonds and dimerizes in the solid state via weak O⋅⋅⋅K interactions. This species reacts with a range of small molecules including N2O (to give a hyponitrite ([N2O2]2−) complex) and H2, the latter offering an unequivocal example of heterolytic E−H bond cleavage across a main group M−O bond.

This study details the synthesis and characterization of an unprecedented two-coordinate, high-spin manganese(0) complex that incorporates an unsupported Mn-Mg bond, viz. L(†)MnMg((Mes)Nacnac) (L(†) = -N(Ar(†))(SiPr(i)3), Ar(†) = C6H2{C(H)Ph2}2Pr(i)-2,6,4; (Mes)Nacnac = [(MesNCMe)2CH](-); Mes = mesityl). This compound has been utilized as an "inorganic Grignard reagent" in the preparation of the first two-coordinate manganese(I) dimer, L(†)MnMnL* (L* = -N(Ar*)(SiMe3), Ar* = C6H2{C(H)Ph2}2Me-2,6,4), and the related mixed valence, bis(amido)-hetereobimetallic complex, Mn(II)(μ-L(†))(μ-L*)Cr(0). It is also shown to act as a two-electron reducing agent in reactions with unsaturated substrates.