Synthesis and Characterization of Lithiated Dendrimers

Abstract

The synthesis of the precursor phenylthiomethyl-functionalized carbosilane dendrimers Si[(CH2)3SiMe2CH2SPh]4 (1) and Si{(CH2)3Si[(CH2)3SiMe2CH2SPh]3}4 (2) is described. Reacting 1 and 2 with lithium naphthalenide gives the first lithiomethyl-functionalized dendrimers Si[(CH2)3SiMe2CH2Li]4 (7) and Si{(CH2)3Si[(CH2)3SiMe2CH2Li]3}4 (11). Deutero, trimethylsilyl, trimethylstannyl, and tri-n-butylstannyl derivatives of these dendrimers, as well as a method to enable isolation of the lithiated dendrimers as solids, are described.

Selective lithiation and crystal structures of G1-carbosilane dendrimers with dimethoxybenzene functionalities

“…This is a general problem of dendrimers lithiated at the periphery [19][20][21] (only ''inner sphere'' lithiated dendrimers possess C-Li functionalities that are screened from intermolecular interaction and do not aggregate) [37]. The insolubility of the lithiated dendrimer precludes crystal growth and therefore single crystal structure determination, however, we predict a three-dimensional diamond-type structure.…”

“…One such application is in homogeneous catalysis using dendrimers containing transition metal chain-ends [10][11][12][13][14][15][16]. Dendrimers with selectively lithiated chain-ends can be used in the syntheses of metal-containing dendritic systems [19][20][21]. The high reactivity of organolithium reagents assures complete functionalization, a prerequisite in dendrimer syntheses.…”

“…Also, the versatility of lithium reagents in organic as well as organometallic syntheses contributes to the enormous potential of dendrimers in which the chain-ends can be lithiated selectively. In continuation of our recent work on lithiated dendrimers [21], we here describe the syntheses and crystal structure of two G1-dendrimers with methoxy-substituted aryl groups on its surface. The presence of these functionalities allows a selective and smooth lithiation of the dendrimer arms.…”

Chloromethylsilane functionalised dendrimers: synthesis and reactivity

“…We also previously reported on the synthesis of CpRe(CO) 3 functionalised benzylphenyl ether dendrimers [12] and decided to investigate the reaction of K[CpRe(CO) 3 ] with dendrimer 1 but unfortunately the reaction of dendrimer 1 with K[CpRe(CO) 3 ] was also proved unsuccessful. Reaction of dendrimer 1 with tetramethylcyclopentadienyllithium or -sodium in refluxing THF did not give the expected tetramethylcyclopentadiene terminated dendrimer, nor did reaction of 1 with eight equivalents of tert-BuLi in diethyl ether at )78°C result in the lithiated dendrimer [13]. We attributed these unsuccessful reactions to the relative inertness of the chlorine atom on the methylene functionality since apparently the chloro group was stabilised by the silicon atom, which removed sufficient electron density from the chloro group.…”

Lithiated dimethylaminomethyl ferrocenes and ruthenocenes

“…Previously, we have isolated polylithiated carbosilanes of the type Si[(CH 2 ) 3 SiMe 2 CH 2 Li] 4 by treating Si[(CH 2 ) 3 SiMe 2 CH 2 SnBu 3 ] 4 with n-BuLi in tetrahydrofuran (thf) at À78°C; the Bu 4 Sn byproduct was removed by successive washes with pentane [7]. We have now adopted this methodology to isolate 3a, 3b and 6a, 6b, since the ferrocenyl or ruthenocenyl stannanes are readily prepared and the C-Sn bond can be cleaved quantitatively to yield the appropriate lithiated metallocene.…”