Deaggregation of Trimethylsilylmethyllithium

Abstract

Polyamine donor bases such as N,N,N′,N′‐tetramethylethylenediamine (TMEDA), (–)‐sparteine and N,N,N′,N″,N″‐pentamethyldiethylentriamine (PMDETA) have been employed to deaggregate parent trimethylsilylmethyllithium (1). The crystal structures of the dimers [(TMEDA)·LiCH2SiMe3]2 (2) and [{(–)‐sparteine}·LiCH2SiMe3]2 (3) were determined and reveal a four‐membered ring as the central structural motif. The two lithium atoms are each coordinated by the chelating ligands and the carbanions. The Li–C contacts show alternating bond lengths. The monomer [(PMDETA)·LiCH2SiMe3] (4) has the shortest Li–C contact of the aggregates discussed, and the Me3Si group points toward the central nitrogen atom of the PMDETA ligand, even if this alignment seems unfavourable for steric reasons. The bond lengths and angles of compounds 2–4 are discussed in relation to the orientation of the lone pair at the carbanion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Coordination Abilities of Di‐2‐picolylphenylphosphane Judged on the Basis of Charge Density Investigations

“…The N1–Li1 and the P1–Li1 bond lengths are elongated (by about 12 and 8 pm, respectively) in comparison to 3 , which can be explained by the crowding in the unusual fivefold coordination pattern of Li1 in 5 . This trend is also obvious for the three lithium–nitrogen bonds to PMDETA (N3–Li1 231.5(9), N4–Li1 220.6(6) and N5–Li1 216.5(5) pm, respectively) that are elongated approximately 12–20 pm compared to the PMDETA monomer of trimethylsilyllithiummethanide 13…”

200 Years of Lithium and 100 Years of Organolithium Chemistry

“…When the concentration of the ligand TMEDA or TMCDA is high enough, n ‐butyllithium can also form dimers instead of tetramers ([Li n Bu‐TMEDA] 2 , or [Li n Bu‐TMCDA] 2 ). Dimers are also found for tert ‐butyllithium/Et 2 O ([Li t Bu‐Et 2 O] 2 ), bis(trimethylsilyl)methyllithium/THF ([LiCH(SiMe 3 ) 2 ‐THF] 2 ), iso propyllithium/TMEDA ([Li i Pr‐TMEDA] 2 ), trimethylsilylmethyllithium/TMEDA ([LiCH 2 SiMe 3 ‐TMEDA] 2 ), methyllithium/TMCDA ([LiMe‐TMCDA] 2 ), iso propyllithium/TMCDA ([Li i Pr‐TMCDA] 2 ), and phenyllithium/TMCDA ([LiPh‐TMCDA] 2 ) . If the corresponding alkyl group and the coordinating bi‐ or tridentate ligand is bulky enough, the formation of monomers is observed: tert ‐butyllithium/TMCDA, trimethylsilylmethyllithium/PMDETA, bis(trimethylsilyl)methyllithium/TMEDA, bis(trimethylsilyl)methyllithium/PMDTA, and phenyllithium/PMDTA …”

Synthesis and Structures of [(Trimethylsilyl)methyl]sodium and ‐potassium with Bi‐ and Tridentate N‐Donor Ligands

“…Surprisingly, considerably less is known about the alkali metal compounds of the smallest and simplest member of this family of silyl‐substituted methyl groups, namely the (trimethylsilyl)methyl (CH 2 SiMe 3 ) or monosyl group 20. Again, the most examined (trimethylsilyl)methyl compound to date is the lithium congener, [(trimethylsilyl)methyl]lithium [Me 3 SiCH 2 Li] n , which is known to form a hexamer ( n = 6) in the solid state,21 whereas both N , N , N′ , N′ ‐tetramethylethylenediamine (TMEDA) and the (–)‐sparteine adducts form dimers ( n = 2), and the higher‐denticity ligand N , N , N′ , N″ , N″ ‐pentamethyldiethylenetriamine (PMDETA) forms a monomer ( n = 1) 22. [(Trimethylsilyl)methyl]potassium has been used in C ‐metallation reactions of cyclohexene,23 toluene,24 and tetrahydrofuran,25 and in an N ‐metallation reaction of a secondary amine to form potassium 2,2,6,6‐tetramethylpiperidide26 in situ,27 which has recently been employed as a convenient precursor in synergic mixed‐metal chemistry 28.…”

“…[20] Again, the most examined (trimethylsilyl)methyl compound to date is the lithium congener, [(trimethylsilyl)methyl]lithium [Me 3 SiCH 2 Li] n , which is known to form a hexamer (n = 6) in the solid state, [21] whereas both N,N,NЈ,NЈ-tetramethylethylenediamine (TMEDA) and the (-)-sparteine adducts form dimers (n = 2), and the higher-denticity ligand N,N,NЈ,NЈЈ,NЈЈ-pentamethyldiethylenetriamine (PMDETA) forms a monomer (n = 1). [22] [(Trimethylsilyl)methyl]potassium has been used in C-metallation reactions of cyclohexene, [23] toluene, [24] and tetrahydrofuran, [25] and in an N-metallation reaction of a secondary amine to form potassium 2,2,6,6-tetramethylpiperidide [26] in situ, [27] which has recently been employed as a convenient precursor in synergic mixed-metal chemistry. [28] The primary aim of the present work is to fully characterise the [(trimethylsilyl)methyl] compounds of sodium and potassium as a prelude to developing them further in synthetic applications.…”