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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.

No MeSH data available.


a) Asymmetric unit of the structure of [NaMg{N(SiMe3)(Dipp)}2(μ‐nBu)]∞ (9). Note that Na1 and Na2 are at half occupancy. b) Section of extended framework structure showing atomic connectivity between the metals, n‐butyl and connecting N atom of the [N(SiMe3)(Dipp)] ligands. Thermal ellipsoids are displayed at 35 % probability and hydrogen atoms and iPr groups have been omitted for clarity. The dashed lines illustrate the Na⋅⋅⋅aryl contacts. Symmetry operation to generate equivalent atoms denoted ′: −x+1, y, −z+1/2. Selected bond lengths [Å] and angles [°]: Na1−C16 2.779(2); Na1−C4 2.793(2); Na1−C5 2.913(2); Na1−C3 3.2535(20); Na2−Centroid 2.5311(1); Mg1−N1 2.0263(16); Mg1−N2 2.0393(15); Mg1−C16 2.1533(19); Si1−N1 1.7030(16); Si2−N2 1.7042(16); N1−C1 1.414(2); N2−C20 1.405(2); centroid‐Na2‐centroid 180.0; Mg1‐C16‐Na1 126.94(8); C16′‐Na1‐C16 132.53(9); N1‐Mg1‐N2 129.36(7); N1‐Mg1‐C16 112.50(7); N2‐Mg1‐C16 117.83(7); C1‐N1‐Si1 120.85(12); C1‐N1‐Mg1 105.48(11); Si1‐N1‐Mg1 133.55(9); C20‐N2‐Si2 122.86(11); C20‐N2‐Mg1 109.11(11); Si2‐N2‐Mg1 127.99(8).
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chem201602683-fig-0010: a) Asymmetric unit of the structure of [NaMg{N(SiMe3)(Dipp)}2(μ‐nBu)]∞ (9). Note that Na1 and Na2 are at half occupancy. b) Section of extended framework structure showing atomic connectivity between the metals, n‐butyl and connecting N atom of the [N(SiMe3)(Dipp)] ligands. Thermal ellipsoids are displayed at 35 % probability and hydrogen atoms and iPr groups have been omitted for clarity. The dashed lines illustrate the Na⋅⋅⋅aryl contacts. Symmetry operation to generate equivalent atoms denoted ′: −x+1, y, −z+1/2. Selected bond lengths [Å] and angles [°]: Na1−C16 2.779(2); Na1−C4 2.793(2); Na1−C5 2.913(2); Na1−C3 3.2535(20); Na2−Centroid 2.5311(1); Mg1−N1 2.0263(16); Mg1−N2 2.0393(15); Mg1−C16 2.1533(19); Si1−N1 1.7030(16); Si2−N2 1.7042(16); N1−C1 1.414(2); N2−C20 1.405(2); centroid‐Na2‐centroid 180.0; Mg1‐C16‐Na1 126.94(8); C16′‐Na1‐C16 132.53(9); N1‐Mg1‐N2 129.36(7); N1‐Mg1‐C16 112.50(7); N2‐Mg1‐C16 117.83(7); C1‐N1‐Si1 120.85(12); C1‐N1‐Mg1 105.48(11); Si1‐N1‐Mg1 133.55(9); C20‐N2‐Si2 122.86(11); C20‐N2‐Mg1 109.11(11); Si2‐N2‐Mg1 127.99(8).

Mentions: Magnesiates 9 and 10, which both have a 2:1 amido/butyl stoichiometric ratio different to the 3:1 ratio in the aforementioned pre‐inverse‐crown template base [Na4Mg2(TMP)6(nBu)2], were expected to adopt different structural architectures from this TMP derivative. X‐ray crystallographic determinations duly confirmed this expectation. The salient difference is that both 9 and 10 have infinite helical chain structures (Figures 10–13) and not the ring architecture that appears to be the key feature behind the special templating metallation ability of [Na4Mg2(TMP)6(nBu)2].8, 10, 11


Structural Diversity in Alkali Metal and Alkali Metal Magnesiate Chemistry of the Bulky 2,6 ‐ Diisopropyl ‐ N ‐ (trimethylsilyl)anilino Ligand
a) Asymmetric unit of the structure of [NaMg{N(SiMe3)(Dipp)}2(μ‐nBu)]∞ (9). Note that Na1 and Na2 are at half occupancy. b) Section of extended framework structure showing atomic connectivity between the metals, n‐butyl and connecting N atom of the [N(SiMe3)(Dipp)] ligands. Thermal ellipsoids are displayed at 35 % probability and hydrogen atoms and iPr groups have been omitted for clarity. The dashed lines illustrate the Na⋅⋅⋅aryl contacts. Symmetry operation to generate equivalent atoms denoted ′: −x+1, y, −z+1/2. Selected bond lengths [Å] and angles [°]: Na1−C16 2.779(2); Na1−C4 2.793(2); Na1−C5 2.913(2); Na1−C3 3.2535(20); Na2−Centroid 2.5311(1); Mg1−N1 2.0263(16); Mg1−N2 2.0393(15); Mg1−C16 2.1533(19); Si1−N1 1.7030(16); Si2−N2 1.7042(16); N1−C1 1.414(2); N2−C20 1.405(2); centroid‐Na2‐centroid 180.0; Mg1‐C16‐Na1 126.94(8); C16′‐Na1‐C16 132.53(9); N1‐Mg1‐N2 129.36(7); N1‐Mg1‐C16 112.50(7); N2‐Mg1‐C16 117.83(7); C1‐N1‐Si1 120.85(12); C1‐N1‐Mg1 105.48(11); Si1‐N1‐Mg1 133.55(9); C20‐N2‐Si2 122.86(11); C20‐N2‐Mg1 109.11(11); Si2‐N2‐Mg1 127.99(8).
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chem201602683-fig-0010: a) Asymmetric unit of the structure of [NaMg{N(SiMe3)(Dipp)}2(μ‐nBu)]∞ (9). Note that Na1 and Na2 are at half occupancy. b) Section of extended framework structure showing atomic connectivity between the metals, n‐butyl and connecting N atom of the [N(SiMe3)(Dipp)] ligands. Thermal ellipsoids are displayed at 35 % probability and hydrogen atoms and iPr groups have been omitted for clarity. The dashed lines illustrate the Na⋅⋅⋅aryl contacts. Symmetry operation to generate equivalent atoms denoted ′: −x+1, y, −z+1/2. Selected bond lengths [Å] and angles [°]: Na1−C16 2.779(2); Na1−C4 2.793(2); Na1−C5 2.913(2); Na1−C3 3.2535(20); Na2−Centroid 2.5311(1); Mg1−N1 2.0263(16); Mg1−N2 2.0393(15); Mg1−C16 2.1533(19); Si1−N1 1.7030(16); Si2−N2 1.7042(16); N1−C1 1.414(2); N2−C20 1.405(2); centroid‐Na2‐centroid 180.0; Mg1‐C16‐Na1 126.94(8); C16′‐Na1‐C16 132.53(9); N1‐Mg1‐N2 129.36(7); N1‐Mg1‐C16 112.50(7); N2‐Mg1‐C16 117.83(7); C1‐N1‐Si1 120.85(12); C1‐N1‐Mg1 105.48(11); Si1‐N1‐Mg1 133.55(9); C20‐N2‐Si2 122.86(11); C20‐N2‐Mg1 109.11(11); Si2‐N2‐Mg1 127.99(8).
Mentions: Magnesiates 9 and 10, which both have a 2:1 amido/butyl stoichiometric ratio different to the 3:1 ratio in the aforementioned pre‐inverse‐crown template base [Na4Mg2(TMP)6(nBu)2], were expected to adopt different structural architectures from this TMP derivative. X‐ray crystallographic determinations duly confirmed this expectation. The salient difference is that both 9 and 10 have infinite helical chain structures (Figures 10–13) and not the ring architecture that appears to be the key feature behind the special templating metallation ability of [Na4Mg2(TMP)6(nBu)2].8, 10, 11

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.