Metallation of polystyrene

Metallated polystyrenes are versatile intermediates for the preparation of a number of polystyrene derivatives. Metallated polystyrene has been prepared from haloge-nated polystyrenes by halogen-metal exchange [41,42,65,66] and by direct metallation of polystyrene [67-69] (see Chapter 4). Electrophiles suitable for the derivatization of metallated polystyrene include carbon dioxide, carbonyl compounds, sulfur, trimethyl borate, isocyanates, chlorosilanes, alkyl bromides, chlorodiphenylphosphine, DMF, oxirane, selenium [70], dimethyldiselenide [71], organotin halides [69], oxygen [72], etc. [41,42,65-67],... 

Functional polystyrene derivatives are starting materials for further reactions in many multistep syntheses. An example is a metalation of polystyrenes for use as intermediates [227] ... 

Barium and strontium salts of polystyrene with two active end-groups per chain were prepared by Francois et al.82). Direct electron transfer from tiny metal particles deposited on a filter through which a THF solution of the monomer was percolated yields the required polymers 82). The A.max of the resulting solution depends on the DPn of the formed oligomers, being identical with that of the salt of polymers with one active end-group per chain for DPn > 10, but is red-shifted at lower DPn. Moreover, for low DPn, (<5), the absorption peak splits due to chromophor-chromophor interaction caused by the vicinity of the reactive benzyl type anions. 

Silane radical atom transfer (SRAA) was demonstrated as an efficient, metal-free method to generate polystyrene of controllable molecular weight and low polydispersity index values. (TMSlsSi radicals were generated in situ by reaction of (TMSlsSiH with thermally generated f-BuO radicals as depicted in Scheme 14. (TMSlsSi radicals in the presence of polystyrene bromide (PS -Br), effectively abstract the bromine from the chain terminus and generate macroradicals that undergo coupling reactions (Reaction 70). 

There has been considerable recent research interest in the activation of carbon monoxide en route to more complex organic molecules. Among the various reactions that have been investigated and/or newly discovered, the transition metal catalyzed reduction of CO to hydrocarbons (Fischer-Tropsch synthesis) has enjoyed particular attention (l- ). Whereas most of the successful efforts in this area have been directed toward the development of heterogeneous catalysts, there are relatively few homogeneous systems. Among these, two are based on clusters (10,11) and others are stoichiometric in metal (12-17). In this report we detail the synthesis and catalytic chemistry of polystyrene ( ) supported... 

There are several polymer supported transition metal hydrofomylation catalysts (42 ). Most are attached by phosphine ligation and suffer fron catalyst leaching. There are no n5-cyclo-pentadienyl half sandwich systems despite the potentially, clearly advantageous presence of the relatively strong Cp-metal bond (43,MO. Resin 5 was used in the following brief study in which the potential of polystyrene-supported CpCo(C0)2 to function as a hydrofomylation catalyst was tested. 

The development of polystyrene is by no means finished. On the contrary. The opinion is often put that the heyday of thermoplastics - and thus of polystyrene - is over and gone, because the raw material from which they are made, crude oil, continues to increase in price and is in short supply. However, this view is superficial, because what is overlooked is the fact that traditional materials (metals, glass, porcelain, ceramics, wood, paper, wool, cotton, etc.) cannot be produced without energy. If the total energy balances for different materials and their processing are compared, it will be seen that plastics, including polystyrene, come off better than their competitors. Plastics, compared with these other materials, require very little energy for fabrication (9J, 92, ... 

A study of methods for controlling the grafting sites of polystyrene polymers may serve as an example for the quantitative and structural analysis of the site of lithiation. Trimethylsilyl chloride serves as the quenching agent owing to the low incidence of side reactions besides metal replacement. Thus, on varying the conditions of metallation of low molecular weight polystyrene (409) and poly(4-methylstyrene) (410), aromatic and... 

A flexible means of access to functionalized supports for solid-phase synthesis is based on metallated, cross-linked polystyrene, which reacts smoothly with a wide range of electrophiles. Cross-linked polystyrene can be lithiated directly by treatment with n-butyllithium and TMEDA in cyclohexane at 60-70 °C [1-3] to yield a product containing mainly meta- and para-Iithiated phenyl groups [4], Metallation of noncross-linked polystyrene with potassium ferf-amylate/3-(lithiomethyl)heptane has also been reported [5], The latter type of base can, unlike butyllithium/TMEDA [6], also lead to benzylic metallation [7]. The C-Iithiation of more acidic arenes or heteroar-enes, such as imidazoles [8], thiophenes [9], and furans [9], has also been performed on insoluble supports (Figure 4.1). These reactions proceed, like those in solution, with high regioselectivity. 

More reactive carbon nucleophiles than enolates can also be prepared on insoluble supports (see Chapter 4) and are used to convert aldehydes or ketones into alcohols. Organolithium compounds have been generated on cross-linked polystyrene by deprotonation of formamidines and by metallation of aryl iodides (Table 7.5). Similarly, support-bound organomagnesium compounds can be prepared by metallation of aryl and vinyl iodides with Grignard reagents. The resulting organometallic compounds react with aldehydes or ketones to yield the expected alcohols (Table 7.5). 

Thioethers have also been prepared on cross-linked polystyrene by radical addition of thiols to support-bound alkenes and by reaction of support-bound carbon radicals (generated by addition of carbon radicals to resin-bound acrylates) with esters of l-hydroxy-l,2-dihydro-2-pyridinethione ( Barton esters Entry 6, Table 8.5). Additional methods include the reaction of metallated supports with symmetric disulfides (Entries 7-9, Table 8.5) and the alkylation of polystyrene-bound, a-lithiated thioani-sole [65],... 

One convenient means of access to carboxyl-functionalized, cross-linked polystyrene involves metallation of the support, followed by treatment with carbon dioxide [150,155-158], Alternatively, better control of the loading and homogeneity of car-boxylated polystyrene can be achieved by converting chloromethyl polystyrene into... 

Gebhard and Killmann69 reported an ellipsometric study of the adsorption of polystyrene onto various metal surfaces from theta solvents, M ranging from 76 x 103 to 340 x 103. A proportionality between t,ms and M1/2 was also observed, and the adsorb-ance was found to increase with rising M. 

Tin organohalogenides can be used as catalysts to produce ethers of phosphoric acid and to polymerise lactons forming colourless polyesters. Various halogen derivatives of dibutyltin have been put forward as catalysts for the solidification of silicone elastomers, as agents preventing the cracking of polystyrene, as inhibitors of metal corrosion in silicone polymers. 

Another application of the direct alkylation of metal-14 anions is the synthesis of polymer-supported organotin hydrides. These were prepared by the reaction of stannyl group was separated from the phenyl ring of polystyrene by two, three or even four carbon spacers. These polymers were found to contain 0.8-1.4 mmol of Sn-H per gram. The reducing ability of the polymer-supported organotin hydrides was monitored by reactions with haloalkanes (Scheme 22)142. 

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