Carbosilanes Compounding

A planar arrangement (297) for a cluster of four Li atoms, consisting of two equilateral triangles, is found by XRD for the solid complex 298. Each Li atom is coordinated to methylene groups of both types (from n-BuLi and the metallated carbosilane) and to N and O atoms of the substituent in the carbosilane. Further characterization of the solid 298 can be made by Li and CP/MAS NMR spectroscopies, and in solution by H, Li, and Si NMR spectroscopies. The combination of both organolithium compounds in 298 is found to form a more effective reagent than each of them alone °. 

In the group of van Koten, dilithiated precursors for the peripheral functionalization of carbosilane dendrimers were generated by deprotonation of compounds 32, 34a and 34b using f-butyllithium. The reaction was effected in n-pentane at room temperature, using the appropriate amount of the alkyllithium base. Dilithiated compounds 33, 35a and 35b were almost quantitatively obtained, the para positions of the aromatic ring systems... 

By the same method, the authors were able to synthesize dendrimers of the generations zero and one, bearing the para lithiated pincer ligands in their periphery. Compounds containing four and twelve lithium centres could be obtained cleanly and in almost quantitative yield (as an example, dodecalithiated carbosilane dendrimer 36 is shown in Figure 12). 

Attaching two different and incompatible chains, one an Rp-chain and at the opposite side an alkyl chain or any other chain which is incompatible with the Rp-chain (such as the carbosilane chain Rsi in compounds 188—190, Figs. 62-64) offers the possibility of creating liquid crystalline honeycombs with cells of different composition. If projected on a Euclidian plane, such a structure can be described as tiling by two or even more different color tiles (multi-color tilings) [42],... 

Recently, polyphilic compounds have been reported, where an Rp-chain and a carbosilane chain were attached at opposite sides of a terphenyl or oligo (p-phenylene ethinylene) core [42], Compound 188 with the longest oligo (p-phenylene ethinylene) core shows two hexagonal columnar phases separated by a thermoreversible continuous (second order) phase transition with critical behavior upon approaching the transition temperature. Based on XRD data it was... 

ROP of cyclic carbosilanes is one of the most promising techniques for the synthesis of well-defined polycarbosilanes. ROP of four-membered ring compounds, 1,3-disilacyclobutanes, and monosilacyclobutanes, as well as copolymerizations of mixtures of monomers, have been widely investigated in the last decades <1996JOMl, B-1996MI7621, B-2000MI247>. 

Their advantage over other types of dendrimers is their straightforward synthesis and, most importantly, their chemical and thermal stabilities. Two distinct steps characterize their synthesis a) an alkenylation reaction of a chlorosilane compound with an alkenyl Grignard reagent, and b) a Pt-cata-lyzed hydrosilylation reaction of a peripheral alkenyl moiety with an appropriate hydrosilane species. Scheme 2 shows the synthesis of catalysts Go-1 and Gi-1 via this methodology. In this case, the carbosilane synthesis was followed by the introduction of diamino-bromo-aryl groupings as the precursor for the arylnickel catalysts at the dendrimer periphery. The nickel centers of the so-called NCN-pincer nickel complexes were introduced by multiple oxidative addition reactions with Ni(PPh3)4. 

Compounds such as C6Hs meSi-CH2Li (me = CH3) and (C6H5)2meSi-CH2U are of decisive importance for the synthesis of Si-functional carbosilanes. However, C6H5me2SiCH2Cl does not react with lithium metal to form the desired compound. 

The synthesis of linear compounds with SiBr and CH2Br groups, respectively, attached to the beginning and end of the chain and the succeeding cyclization forms a general route to monocyclic carbosilanes. 

Carbosilanes with Si- and C-functional groups that can be used for cyclization are obtained by the reaction of phenyl compounds with bromine ... 

Bicyclic carbosilanes are more difficult to synthesize than compounds of the (me2Si-CH2) type, partly owing to differences in the reactivity of the functional intermediates caused by effects of the substituents. So far synthesis of the l,3,5,7-tetrasila-bicyclo-[3.3.1]nonane system and of the 1,3,5,7,9-penta-siladecaline system has been reported (16). 

H, CgHs, CH2-Sime2C6Hs X = Cl, Br)28 Synthesis of suitable Si-functional carbosilanes precussors for bi- and tricyclic compounds was planned, utilizing experience with synthesis of linear carbosilanes2 with Si-functional groups. The following compounds were available for use in the cyclization reaction ... 

The syntheses of l,l,3,3-tetramethyl-l,3-trisilacyclopentene 87 and of 1,1,3,3-tetramethyl-l,3-disila-4-methylene-cyclobutane 88 are described in Section C. By adding Br2 or HBr, the ring system is cleaved as a first reaction step (35). For syntheses of carbosilanes, information on the corresponding six- or seven-membered ring systems was required. Therefore, the synthesis of the compounds 179 and 180 was investigated (54). 

The investigations carried out on the organometallic synthesis of carbosilanes and presented in this paper indicate the progress achieved in this field in the years between 1967 and 1971 in cooperation with Dr. P. Schober, Dr. M. Hahnke and Dr. G. Maas. The yields of these syntheses are not all satisfactory yet, in most cases with the cyclization reaction. There is no doubt that the procedures described can be extended and simplified. However, it is also apparent that only some of the compounds (and their derivatives) which arise from the pyrolysis of the methylchlorosilanes and of tetramethylsilane can be obtained by organometallic synthesis38. The development of this field of chemistry requires extensive advances in methods for synthesis. 

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