Intermetallic lithium-magnesium hexamethyldisilazide: Synthesis and structure, discovery of an oxygen-centered variant, and a reaction with benzonitrile that produces a novel amidinate cage compound with a trigonal bipyramidal Li4MgO core

Intermetallic lithium-magnesium hexamethyldisilazide [{(Me3Si)2N}3LiMg], 1, has been synthesized from a nonstoichiometric 2:1 ratio of LHMDS and Mg(HMDS)2 in hexane/toluene solution. Its crystal structure reveals a simple dinuclear arrangement based on a near-planar NMgNLi ring: the Mg center occupies a distorted trigonal planar environment of three N atoms, while the Li center occupies a distorted tetrahedral N2C2 environment due to two additional C-Li interactions with the -N(SiMe3)2 substituents. This structure appears to be retained in arene solution on the basis of the evidence of 1H NMR spectral data. In the presence of trace amounts of oxygen, the surprising peroxide-oxide variant [{(Me3Si)2N}4 Li2Mg2(O2)x(O)y] preferentially crystallizes from solution. X-ray crystallography has established that its structure contains peroxide predominantly [x = 0.715(7); y = 0.285(7)], the presence of which induces an aggregation state increase relative to 1: the four indistinguishable metal centers, held in a square-planar arrangement, side-on-coordinate to the peroxide molecule and bind to two N atoms. The oxygen-scavenging ability of this system has been exploited further in a reaction with benzonitrile. This has yielded a third intermetallic lithium-magnesium crystalline compound, having the composition [{PhC(NSiMe3)2}4Li4Mg(O)]. X-ray crystallography has revealed its remarkable cage structure built around an unprecedented distorted trigonal bipyramidal Li4MgO core, at the center of which lies a 5-O atom. Interestingly, all the metal centers lie out of the benzamidinate NCN ligand planes to indicate a significant degree of -bonding. One NCN ligand also adopts an unusual face-capping mode to a Li3 triangle, the like of which has previously only been observed in transition metal cluster compounds

Synthesis and structural characterisation of 'solvent-free' lithium-calcium hexamethyldisilazide, [Li{mu-N(SiMe3)(2)}(2)Ca{N(SiMe3)(2)}], exhibiting a double ration of agostic H3C center dot center dot center dot Li and H3C center dot center dot center dot Ca intramolecular interactions

Addition of lithium hexamethyldisilazide to an equimolar amount of calcium bis(hexamethyldisilazide) in toluene gave 'solvent-free'. [Li{mu-N(SiMc(3))(2)}(2)Ca{N(SiMe3)(2)] (1). An X-ray study reveals a dinuclear arrangement based on a planar LiNCaN four-membered ring: both metals engage in additional H3C...M (where M = Lt. Ca) interactions with the mu-N(SiMe3)(2) substituents resulting in a distorted tetrahedral geometry at lithium and a distorted trigonal-bipyramidal geometry at calcium. This contrasts with the previously reported mixed Li-Mg analogue, [Li{mu-N(SiMe3)(2)}(2)Mg{N(SiMe3)(2)}], where only the lithium centre engages in such intramolecular agostic H3C...Li interactions

Synthesis and crystal structure of the new heteroleptic magnesium bis(amide) [{Mg[mu-N(H)Ph][N(SiMe3)(2)]center dot THF}(2)], and density functional MO calculations on model systems

Reaction of Mg[N(SiMe3)(2)](2) with one molar equivalent of the primary amine PhNH2 in THF solution gave the transaminated THF-solvated heteroleptic bis(amide) [{Mg[mu -N(H)Ph][N(SiMe3)(2)]. THF}(2)]. In the crystalline state the new amide is dimeric with a central, planar azamagnesacyclic (NMg)(2) ring. The resonance stabilised anilido units prefer to bridge to the magnesium centres whereas the bulkier secondary hexamethyldisilazanzide groups occupy terminal sites. Terminal solvation by THF completes the distorted tetrahedral environment about magnesium. Comparisons of this structure with other crystallographically characterised heteroleptic magnesium bis(amides) are made. The interesting, almost square geometry of this (NMg)(2) ring has also prompted a density functional MO study on magnesium systems and related molecules of Groups 1, 2 and 13, the results of which are also reported

Mixed-metal sodium-magnesium macrocyclic amide chemistry: A template reaction for the site selective dideprotonation of arene molecules

A remarkable pair of macrocyclic amides has been synthesized and crystallographically characterized; these consist of a twelve-membered (N6Na4Mg2)2+ cationic ring host with [C6H3(CH3)]2- or (C6H4)2- dianionic guests (see picture) derived from toluene and benzene, respectively

Alkali metal cation-pi interactions stabilized solely by [M{N(SiMe3)(2)}(3)](-) anions (M = Mg or Zn): The competing influence of alkali metal center dot center dot center dot C(Me) agostic interactions

A series of [K(ar)(2)](+) and [Rb(toluene)(3)](+) cations (ar = benzene, toluene, o-xylene, or p-xylene) has been synthesized and crystallized in the presence of [M{N(SiMe3)(2)}(3)](-) anions (M = Mg or Zn). In the solid state all form either extended supermolecular, dimeric or supramolecular, polymeric structures. Only [K(toluene)(2)][Mg{N(SiMe3)(2)}(3)] was found to exist as both suprastructural isomers. Introducing cyclopentadienyl to the system gave a similar zincate with the unusual [K2CP](+) cation. The absence of any traditional Lewis bases facilitates' short metal-to-arene contact distances and makes these species excellent candidates for the study of alkali metal cation-pi interactions. It is shown that K-pi interactions and to a lesser extent Rb-pi interactions are heavily influenced by the number and nature of agostic methyl interactions, especially when the electron-donating ability of these is maximized by adoption of near-linear geometries. These features combine so that the weakest potassium-to-arene interaction observed is that with benzene

Solvent-free and TMEDA-solvated mixed alkali metal-magnesium tris-diisopropylamides

A trio of heterobimetallic tris-diisopropylamides, the solvent-free potassium-magnesium amide [{KMg(NiPr2)(3)}(infinity)], its TMEDA solvate [KMg(NiPr2)(3).TMEDA] and the sodium congener [NaMg(NjPr(2))(3).TMEDA] has been synthesised by mixing the appropriate metal alkyl reagents with three molar equivalents of diisopropylamine in a hydrocarbon medium, to which, in the last two cases, TMEDA is added. All three amides have been successfully crystallographically characterised by X-ray diffraction studies. Representing the first pure s-block mixed-metal diisopropylamide free of solvent molecules or other stabilising anionic co-ligands, the first compound adopts an infinite spiral chain of ...K-(mu-N)(2)-Mg-N... links, the metal-N framework of which is supported by agostic K...C intra-dinuclear and inter-dinuclear contacts. The dinuclear tris-amido motif is maintained in both TMEDA complexes, the metal-N cores of which are essentially isostructural, but the presence of the chelating diamine blocks the propagating terminal site on the alkali metal and so gives rise to discrete molecular structures

Trimagnesium-bridged trinuclear ferrocenophanes cocomplexed with solvated mononuclear alkali metal amide molecules

Three prototypes of the remarkable new class of compound referred to in the title have been synthesised by treating ferrocene with the same mixed lithium (or sodium)magnesium amide recipes as those used previously to make s-block metal inverse crowns

Structural chemistry of monodentate donor-solvated mixed lithium-magnesium secondary amide complexes

The monodentate donor-solvated intermetallic lithium-magnesium amide complexes [Mg(HMDS)(3)Li . (THF)] 1 [HMDS=N(SiMe3)(2)], [Mg(HMDS)(3)Li . (Pyr)] 2 and [Mg{N(Cy)(2)}(3)Li . (THF)] 3 [N(Cy)(2)=dicyclohexylamide] have been prepared and characterised by NMR spectroscopy and X-ray crystallography. Synthesis was achieved by the reaction of equimolar amounts of n-BuLi and n,sec-Bu2Mg with three equivalents of the appropriate amine in hexane/donor solution. The molecular structures of 1, 2 and 3 are essentially isostructural containing a central, planar LiNMgN four-membered ring: two amide units bridge to the metal centres whilst the third binds exclusively to magnesium in the terminal position to complete a three-coordinate distorted trigonal planar geometry. The lithium achieves a similar geometry with solvation from a single monodentate donor molecule. Three co-crystalline by-products were also isolated from solution and are included for completeness: [Mg(HMDS)(2)(Bu)Li . Pyr] 4, [(LiHMDS . Pyr)(2)] 5 and [Mg(HMDS)(2). (Pyr)(2)] 6. Complex 4 exhibits a similar structure to 1, 2 and 3 with an alkyl group (consisting of disordered n- and sec-butyl groups) replacing the terminal amido functionality. Complex 4 is produced by a similar method to 2 via incomplete amination in the presence of two equivalents of hexamethyldisilazane (HMDS(H)). In contrast, 5 and 6 are simple homometallic amides formed when an excess of pyridine is introduced into the reaction system. To conclude the study a series of reactions were undertaken in which the stoichiometry of both amine and donor was altered systematically. The results from this study imply that intermetallic aggregation is hindered by the presence of excess donor solvent

Inverse crown ether complexes: extension to potassium through the synthesis of [{[(Me3Si)(2)N](4)K2Mg2(O-2)}(infinity)], a peroxo- centred macrocycle linked into infinite chains by intermolecular K center dot center dot center dot CH3(SiMe2) interac

The title compound represents the first potassium example of a novel class of amide-supported heterobimetallic macrocycle having a dicationic (N4K2Mg2)2+ octagonal ring framework surrounding a dianionic (O2)2- core