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

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ABSTRACT

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‐C6H3). 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.

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Alternative methods to prepare complexes 4 and 5.
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chem201602683-fig-5001: Alternative methods to prepare complexes 4 and 5.

Mentions: Monometallic complexes 1–8 were all synthesised by deprotometallation of the starting amine N(H)(SiMe3)(Dipp) by a metal alkyl reagent. In the lithium and sodium cases this was the relevant metal n‐butyl reagent, whereas the lower stability of potassium alkyls necessitated switching to the more stable silylalkyl reagent KCH2SiMe3, which unlike the n‐butyl reagent does not possess any β‐hydrogen atoms, and so avoids possible decomposition by such an elimination reaction. Ruhlandt‐Senge16 previously made [K{N(SiMe3)(Dipp)}] (probably as a THF solvate) by deprotonation of the amine with potassium hydride in THF and used it in situ to generate Group 2 bis(amides) by salt metathesis with the relevant Group 2 metal iodide. Anwander13 used a similar salt metathesis approach to make a series of rare earth metal amide complexes, during which he isolated [K{N(SiMe3)(Dipp)}] in powder form and crystallised the tris(THF) solvate of [Li{N(SiMe3)(Dipp)}] and determined its monomeric structure. In our study we observed no benefit in making the PMDETA solvates 4 and 5 through the salt metathesis of the lithium amide [Li{N(SiMe3)(Dipp)}] with sodium tert‐butoxide and potassium tert‐butoxide, respectively, as crystalline yields of all the products were about 50 % from both deprotometallation and metathesis methods (Scheme 1). It is worth noting that irrespective of the method employed, 1H NMR monitoring of the filtrates from reaction solutions showed essentially quantitative conversions of the amine to amide in all cases. Both the starting metal reagent and, where relevant, the donor solvent employed in these reactions were added in slight excess compared to the parent amine.1


Structural Diversity in Alkali Metal and Alkali Metal Magnesiate Chemistry of the Bulky 2,6 ‐ Diisopropyl ‐ N ‐ (trimethylsilyl)anilino Ligand
Alternative methods to prepare complexes 4 and 5.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5096043&req=5

chem201602683-fig-5001: Alternative methods to prepare complexes 4 and 5.
Mentions: Monometallic complexes 1–8 were all synthesised by deprotometallation of the starting amine N(H)(SiMe3)(Dipp) by a metal alkyl reagent. In the lithium and sodium cases this was the relevant metal n‐butyl reagent, whereas the lower stability of potassium alkyls necessitated switching to the more stable silylalkyl reagent KCH2SiMe3, which unlike the n‐butyl reagent does not possess any β‐hydrogen atoms, and so avoids possible decomposition by such an elimination reaction. Ruhlandt‐Senge16 previously made [K{N(SiMe3)(Dipp)}] (probably as a THF solvate) by deprotonation of the amine with potassium hydride in THF and used it in situ to generate Group 2 bis(amides) by salt metathesis with the relevant Group 2 metal iodide. Anwander13 used a similar salt metathesis approach to make a series of rare earth metal amide complexes, during which he isolated [K{N(SiMe3)(Dipp)}] in powder form and crystallised the tris(THF) solvate of [Li{N(SiMe3)(Dipp)}] and determined its monomeric structure. In our study we observed no benefit in making the PMDETA solvates 4 and 5 through the salt metathesis of the lithium amide [Li{N(SiMe3)(Dipp)}] with sodium tert‐butoxide and potassium tert‐butoxide, respectively, as crystalline yields of all the products were about 50 % from both deprotometallation and metathesis methods (Scheme 1). It is worth noting that irrespective of the method employed, 1H NMR monitoring of the filtrates from reaction solutions showed essentially quantitative conversions of the amine to amide in all cases. Both the starting metal reagent and, where relevant, the donor solvent employed in these reactions were added in slight excess compared to the parent amine.1

View Article: PubMed Central - PubMed

ABSTRACT

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‐C6H3). 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.

No MeSH data available.