Electronic, Steric, and Ligand Influence on the Solid‐State Structures of Substituted Sodium and Potassium Anilides

Heavy Alkali Metal Manganate Complexes: Synthesis, Structures and Solvent-Induced Dissociation Effects

Rare examples of heavier alkali metal manganates [{(AM)Mn(CH2 SiMe3 )(N'Ar )2 }∞ ] (AM=K, Rb, or Cs) [N'Ar =N(SiMe3 )(Dipp), where Dipp=2,6-iPr2 -C6 H3 ] have been synthesised with the Rb and Cs examples crystallographically characterised. These heaviest manganates crystallise as polymeric zig-zag chains propagated by AM⋅⋅⋅π-arene interactions. Key to their preparation is to avoid Lewis base donor solvents. In contrast, using multidentate nitrogen donors encourages ligand scrambling leading to redistribution of these bimetallic manganate compounds into their corresponding homometallic species as witnessed for the complete Li - Cs series. Adding to the few known crystallographically characterised unsolvated and solvated rubidium and caesium s-block metal amides, six new derivatives ([{AM(N'Ar )}∞ ], [{AM(N'Ar )⋅TMEDA}∞ ], and [{AM(N'Ar )⋅PMDETA}∞ ] where AM=Rb or Cs) have been structurally authenticated. Utilising monodentate diethyl ether as a donor, it was also possible to isolate and crystallographically characterise sodium manganate [(Et2 O)2 Na(n Bu)Mn[(N'Ar )2 ], a monomeric, dinuclear structure prevented from aggregating by two blocking ether ligands bound to sodium.

Sigma/pi Bonding Preferences of Solvated Alkali-Metal Cations to Ditopic Arylmethyl Anions

Arylmethyl anions allow alkali-metals to bind in a σ-fashion to the lateral carbanionic centre or a π-fashion to the aryl ring or in between these extremities, with the trend towards π bonding increasing on descending group 1. Here we review known alkali metal structures of diphenylmethane, fluorene, 2-benzylpyridine and 4-benzylpyridine. Next, we synthesise Li, Na, K monomers of these diarylmethyls using polydentate donors PMDETA or Me6 TREN to remove competing oligomerizing interactions, studying the effect that two aromatic rings has on negative charge (de)localisation via NMR, X-ray crystallographic and DFT studies. Diphenylmethyl and fluorenyl anions maintain C(H)-M interactions regardless of alkali-metal, although the adjacent arene carbons engage in interactions with larger alkali-metals. Introducing a nitrogen atom into the ring (at the 2- or 4-position) encourages relocalisation of negative charge away from the deprotonated carbon and onto nitrogen. Phenyl(2-pyridyl)methyl moves from an enamide formation at one extremity (lithium) to an aza-allyl formation at the other extremity (potassium), while C- or N-coordination modes become energetically viable for Na and K phenyl(4-pyridyl)methyl complexes.

Straightforward synthesis of rubidium bis(trimethylsilyl)amide and complexes of the alkali metal bis(trimethylsilyl)amides with weakly coordinating 2,2,5,5-tetramethyltetrahydrofuran

Rubidium bis(trimethylsilyl)amide (rubidium hexamethyldisilazanide, Rb(hmds)) is accessible on a large scale with excellent yields via a magnetite-catalyzed metalation of hexamethyldisilazane (H(hmds)) in liquid ammonia. Recrystallization of solvent-free alkali metal hexamethyldisilazanides [A(hmds)]n of sodium to cesium from solutions containing 2,2,5,5-tetramethyltetrahydrofuran (Me4THF, thf*) yields the dinuclear complexes [(thf*)A(hmds)]2, which show a rather asymmetric coordination behavior of the bulky ether ligand with strongly bent A-A-O moieties for the heavier K, Rb, and Cs congeners, whereas in the Na complex, the ether ligand is clamped between the trimethylsilyl groups. In hydrocarbon solutions, dissociation of these compounds is observed leading to the liberation of this bulky and weakly binding cyclic ether.

Synthesis and structural study of new metallasilsesquioxanes of potassium and uranium

The first metallasilsesquioxanes comprising potassium and uranium have been synthesized and structurally characterized by single-crystal X-ray diffraction.

Structural Diversity in Alkali Metal and Alkali Metal Magnesiate Chemistry of the Bulky 2,6-Diisopropyl-N-(trimethylsilyl)anilino Ligand

Bulky amido ligands are precious in s-block chemistry, since they can implant complementary strong basic and weak nucleophilic properties within compounds. Recent work has shown the pivotal importance of the base structure with enhancement of basicity and extraordinary regioselectivities possible for cyclic alkali metal magnesiates containing mixed n-butyl/amido ligand sets. This work advances alkali metal and alkali metal magnesiate chemistry of the bulky arylsilyl amido ligand [N(SiMe3 )(Dipp)]- (Dipp=2,6-iPr2 -C6 H3 ). Infinite chain structures of the parent sodium and potassium amides are disclosed, adding to the few known crystallographically characterised unsolvated s-block metal amides. Solvation by N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA) or N,N,N',N'-tetramethylethylenediamine (TMEDA) gives molecular variants of the lithium and sodium amides; whereas for potassium, PMDETA gives a molecular structure, TMEDA affords a novel, hemi-solvated infinite chain. Crystal structures of the first magnesiate examples of this amide in [MMg{N(SiMe3 )(Dipp)}2 (μ-nBu)]∞ (M=Na or K) are also revealed, though these breakdown to their homometallic components in donor solvents as revealed through NMR and DOSY studies.

Salt metathesis versus protonolysis routes for the synthesis of silylamide Hauser base (R2NMgX; X = halogen) and amido-Grignard (R2NMgR) complexes

The preparation of silylamide Hauser base (R2NMgX; X = halide) and amido-Grignard (R2NMgR) complexes from simple Grignard reagents using [K{N(SiMe2(t)Bu)2}]n, [K{N(SiMe2(t)Bu)(Si(i)Pr3)}]n and [K{N(Si(i)Pr3)2}]n, and their parent silylamines, was explored. Both salt metathesis and protonolysis routes proved ineffective with allylmagnesium chloride as a starting material due to complex Schlenk equilibria, with [Mg(N(RR'))(μ-Cl)(THF)]2 (N(RR') = {N(Si(t)BuMe2)2}(-), 1; {N(Si(t)BuMe2)(Si(i)Pr3)}(-), 2; {N(Si(i)Pr3)2}(-), 3) and [Mg{N(Si(i)Pr3)2}(μ-C3H5)]∞ (4) identified as minor products. In contrast, salt metathesis protocols using potassium silylamides and methylmagnesium iodide gave [Mg(N(RR'))(μ-CH3)]2 (N(RR') = {N(Si(t)BuMe2)2}(-), 7a; {N(Si(t)BuMe2)(Si(i)Pr3)}(-), 8; {N(Si(i)Pr3)2}(-), 9) and [Mg{N(Si(t)BuMe2)2}(CH3)(DME)] (7b), with [Mg{N(Si(t)BuMe2)2}(μ-I)(THF)]2 (10) isolated as a side-product during the preparation of 7a. Unusually, methylmagnesium iodide, di-n-butylmagnesium and 7-9 did not react with HN(RR') under the conditions we employed. The synthesis of [Na{N(Si(t)BuMe2)2}(THF)]2 (5a) and [Na{N(Si(t)BuMe2)2}(DME)2] (5b) from benzyl sodium and HN(Si(t)BuMe2)2, and a solvent-free structure of [K{N(Si(t)BuMe2)2}] (6), are also reported. Complexes 1, 5b, 7a, 7b, 8, 9 and 10 are fully characterised by single crystal XRD, multinuclear NMR and IR spectroscopy and elemental analysis, whereas complexes 2-4, 5a and 6 were identified by XRD only.

Synthetic and reactivity studies of hetero-tri-anionic sodium zincates

The blue, red and green spheres represent three different anions present within a series of novel hetero-trianionic sodium zincates. The syntheses and structures of the complexes are reported as well as their reactivities with important organic molecules.

Accessible heavier s-block dihydropyridines: structural elucidation and reactivity of isolable molecular hydride sources

Transmetallation of lithiodihydropyridines with Group 1 alkoxides provides facile access to reactive MH (M = Na, K) sources, which show significant structural diversity due in part to the distinct ways that Na/K engage with the σ (green) and π (red) donor systems of the DHP ligands.