The smaller, the better? How the aggregate size affects the reactivity of (trimethylsilyl)methyllithium

Abstract

An unexpected influence of the nature of stabilizing additives to alkyllithium compounds on an aggregate's reactivity was examined experimentally and theoretically.

Structural Motifs of Alkali Metal Superbases in Non‐coordinating Solvents

“…Accordingly,e ven higher Np contents did not lead to the formation of the "ideal" neopentyl LSB, but to the formation of mixed aggregates enriched with lithium and alkyl/alkoxy ratios close to 1/1. The two compounds Li 4 K 3 Np 3 (OtBu) 4 , 2 (% 2 3 )( Figure 5) and Li 4 KNp 2 (OtBu) 3 , 3 (% 3 2 )( Figure6)w ere isolated from such mixtures and characterized by X-ray crystallography and NMR spectroscopy.A gain, both compounds exhibit partial group disorderb etween OtBu and Np as seen before in compound 1, suggesting the existence of neopentyl-rich compounds such as Li 4 K 3 Np 4 (OtBu) 3 , 2 4 and Li 4 KNp 3 (OtBu) 2 , 3 3 .…”

“…The negative charge on the carbon atom renders it a very strong reducing agent on one side, as well as a reactive Lewis base, leading to nucleophilic behavior or high Brønsted basicity on the other. The degree of aggregation of organometallic alkali metal compounds has a large influence on the solubility of such compounds; quantitative effects on the reactivity are also discussed [4] . However, the influence of different grades of aggregation on reaction rates is far from being simple [5]…”

“…The degree of aggregation of organometallic alkali metal compoundsh as al arge influence on the solubility of such compounds; quantitative effects on the reactivity are also discussed. [4] However,t he influence of different grades of aggregation on reactionr ates is far from being simple. [5] At this point, it is very important to mention the necessary distinction between different classes of organic groups in organometallic compounds.…”

A monomeric (trimethylsilyl)methyl lithium complex: synthesis, structure, decomposition and preliminary reactivity studies

“…For these reasons, synthetic organometallic chemists have devoted decades of effort to synthesising the LiR monomers and studying their structures and reactivity. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] The most successful strategy to break the LiR aggregates and isolate LiR monomers is to employ neutral multidentate amines, 4 which coordinate to the Li and kinetically stabilise the LiR monomers. Since the 1980s, this multidentate amine strategy has been successfully implemented by several groups to isolate a series of [Li(R)(L)] monomers (L = multi-amine ligands; R = CH 2 SiMe 3 , 5,6 CH(SiMe 3 ) 2 , 7,8 t Bu, 9,10 s Bu, 8 i Pr, 11 benzyl [12][13][14][15][16][17] ).…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18] The most successful strategy to break the LiR aggregates and isolate LiR monomers is to employ neutral multidentate amines, 4 which coordinate to the Li and kinetically stabilise the LiR monomers. Since the 1980s, this multidentate amine strategy has been successfully implemented by several groups to isolate a series of [Li(R)(L)] monomers (L = multi-amine ligands; R = CH 2 SiMe 3 , 5,6 CH(SiMe 3 ) 2 , 7,8 t Bu, 9,10 s Bu, 8 i Pr, 11 benzyl [12][13][14][15][16][17] ). Recently, we reported the first methyllithium monomer [Li(CH 3 )(DETAN)], enabled by a bespoke hexadentate ligand [{Et 2 NCH 2 CH 2 N(CH 2 CH 2 )} 3 ], namely N,N′,N″tris-(2-N-diethylaminoEthyl)-1,4,7-triAza-cycloNonane (DETAN).…”