Li vs Na: Divergent Reaction Patterns between Organolithium and Organosodium Complexes and Ligand-Catalyzed Ketone/Aldehyde Methylenation

Abstract

Organosodium chemistry is underdeveloped compared with organolithium chemistry, and all the reported organosodium complexes exhibit similar, if not identical, reactivity patterns to their lithium counterparts. Herein, we report a rare organosodium monomeric complex, namely, [Na(CH 2 SiMe 3 )(Me 6 Tren)] (1-Na) (Me 6 Tren: tris[2-(dimethylamino)ethyl]amine) stabilized by a tetra-dentate neutral amine ligand Me 6 Tren. Employing organo-carbonyl substrates (ketones, aldehydes, amides, ester), we demonstrated that 1-Na features distinct reactivity patterns compared with its lithium counterpart, [Li(CH 2 SiMe 3 )(Me 6 Tren)] (1-Li). Based on this knowledge, we further developed a ligand-catalysis strategy to conduct ketone/aldehyde methylenations, using [NaCH 2 SiMe 3 ] ∞ as the CH 2 feedstock, replacing the widely used but hazardous/expensive C�O methylenation methods, such as Wittig, Tebbe, Julia/Julia-Kocienśki, Peterson, and so on.

The quest for organo-alkali metal monomers: unscrambling the structure–reactivity relationship

“…We compared the reactivity of [NaCH 2 SiMe 3 ] ∞ , [Na(CH 2 SiMe 3 )(Me 6 Tren)] ( 10 ) and [Li(CH 2 SiMe 3 )(Me 6 Tren)] ( 9 ) towards benzophenone. 8 As expected, we found that both the [NaCH 2 SiMe 3 ] ∞ polymer and [Li(CH 2 SiMe 3 )(Me 6 Tren)] ( 9 ) resulted in the nucleophilic addiction product [MO{C(Ph) 2 (CH 2 SiMe 3 )}] 4 (M: Li, Na). In contrast, methylation resulted using [Na(CH 2 SiMe 3 )(Me 6 Tren)] ( 10 ), which produced 1,1-diphenyl ethylene, free Me 6 Tren and [Na 9 (OSiMe 3 ) 10 ] − [Na(C 6 H 6 )(Me 6 Tren)] + .…”

“…A NaCH 2 SiMe 3 monomer [Na(CH 2 SiMe 3 )(Me 6 Tren)] ( 10 ) conducted CO bond methylenation, while [NaCH 2 SiMe 3 ] ∞ polymer underwent nucleophilic addition towards the CO bond. 8…”

“…Exploring different metal identities would potentially unlock another totally unexplored chemical space. Very recent works from the Hevia group 84 and us, 8 started challenging the paradigm that all Group-1 metal alkyl complexes following the same reaction patterns. We proved that, by changing metal identity ( e.g.…”

“…However, we have to point out here that, the presumed low thermostability of these heavy alkali metal complexes is not necessarily true: recently, we proved that [NaCH 2 SiMe 3 ] ∞ is at least as stable as its Li congener in C 6 D 6 solution. 8…”

“…The first and so far the only NaCH 2 SiMe 3 monomer, [Na(CH 2 SiMe 3 )(Me 6 Tren)] ( 10 ) (Fig. 9), was reported simultaneously by the Hevia group 84 and us 8 in 2023, but from rather different perspectives especially regarding reactivity standing points. Hevia and co-workers employed Me 6 Tren, among other ligands ( e.g.…”