Deprotonation-substitution

In addition to providing fully alkyl/aryl-substituted polyphosphasenes, the versatility of the process in Figure 2 has allowed the preparation of various functionalized polymers and copolymers. Thus the monomer (10) can be derivatized via deprotonation—substitution, when a P-methyl (or P—CH2—) group is present, to provide new phosphoranimines some of which, in turn, serve as precursors to new polymers (64). In the same vein, polymers containing a P—CH group, for example, poly(methylphenylphosphazene), can also be derivatized by deprotonation—substitution reactions without chain scission. This has produced a number of functionalized polymers (64,71—73), including water-soluble carboxylate salts (11), as well as graft copolymers with styrene (74) and with dimethylsiloxane (12) (75). 

In addition to providing many new precursors to functionalized poly(alkyl/arylphosphazenes), the deprotonation/substitution reactions of these N-silylphosphoranimines serve as useful models for similar chemistry that can be carried out on the preformed polymers. New reactions and experimentation with reaction conditions can first be tried with monomers before being applied to the more difficult to prepare polymeric substrates. A considerable amount of preliminary work [e.g., with the silylated monomers (z z) and polymers (2 o) has demonstrated the feasibility of this model system approach. 

The compounds described herein were prepared by three methods. The first route involves deprotonation/substitution at the N-H sites of 1, the second consists of a cleavage reaction of an Si-N derivative of 1 with PhBCI2, and the third route is a transamination reaction between a bis(dimethylamino)boryl derivative of 1 and an aliphatic diamine. In the first approach, compound 1 is deprotonated by treatment with one equivalent of n-BuLi. Quenching of the resulting anion with various electrophiles produces the monosubstituted products 2-4 (eq 3). 

One would expect that deprotonated substituted phenols interact with the positively charged choline group [172]. However, 31P-NMR studies on the... 

Once the carboxylic acid is deprotonated, substitutions are prevented because (almost) no nucleophile will attack the carboxylate anion. Under neutral conditions, alcohols are just not reactive enough to add to the carboxylic acid but, with add catalysis, esters can be formed from alcohols and carboxylic acids. 

Hammett (and related sigma) relationships have been applied to aquatic reactions of several classes of aromatic contaminants. For example, alkaline hydrolysis of triaryl phosphate esters fits a Hammett relationship (Table 3) is t he sum of the substituent constants for the aromatic groups and k0 is the hydrolysis rate constant for triphenyl phosphate (0.27 M 1 s-1 t1/2 = 30 days at pH 8). Triaryl esters thus hydrolyze much more rapidly than trialkyl or dialkyl-monoaryl esters under alkaline conditions. Rates of photooxidation of deprotonated substituted phenols by singlet oxygen have been found to be correlated with Hammett a constants (Scully and Hoigne, 1987). The electronic cllects of substituents on pKa values of substituted 2-nitrophenols also fit a I lammett relationship this, of course, is not a kinetic LFER. Two compounds (4-phenyl-2-NP and 3-methyl-2-NP) did not fit the relationship and were not included in the regression. Steric effects may account for the discrepancy for the latter compound. Nitrophenols are used as intermediates in synthesis of dyes and pesticides and also used directly as herbicides and insecticides. 

Synthesis and polymerization of multifunctional cyclotriphosphazenes have been described <04PS%1>. A series of new nongeminal cyclophosphazenes 52 has been prepared via deprotonation-substitution reactions at the methyl groups of both cis and trans isomers of cyclotriphosphazene 51 with different electrophilic reagents <04PS817>. 

When there is a heteroatom as a second substituent on the anionic carbon bearing nitrogen, asymmetric reactions provide an enantioenriched formyl anion synthetic equivalent. Gawley has used the chiral auxiliary approach in a deprotonation-substitution sequence to make highly diastereoenriched 13 and 14, and converted the separated diastereoisomers to the enantiomeric diols 18 and 19 (Scheme 5). A number of cases are reported. Structural, kinetic and computational studies were carried out and found to be consistent with reaction via a complex species [13]. 

Because of the difficulty of accessing (-h)-sparteine, an alternative route to the enantiomeric enecarbamate products has been developed [100]. Synthesis of stannanes 149 and 150 by traditional deprotonation-substitution, followed by transmetallation and substitution with electrophiles provided products of the opposite configuration ent-151 (Scheme 46). Accessing this stereoisomer is possible because of the substitution of lithiated 141 with Me3SnCl occms with inversion and the subsequent transmetallation with retention generates the epimer of hthiated 141. 

The enantioselective C-silylation of allylic substrates such as (V-(terf-butoxycarbonyl)-A(-(p-methoxyphenyl)allylamines or 1,3-diphenylpropene is accomplished with butyUithium in the presence of (—)-sparteine, followed by the addition of TMSOTf (eq 47). The same procedure allows the asymmetric deprotonation-substitution of arenetricarbonyl(O) complexes, while chiral bis(oxazolines) have been the ligands of choice to perform such transformation with aryl benzyl sulfides in these reactions, different yields and enantioselectivities are reached if trimethylsilyl chloride is used as sUylating reagent, although there is a substrate dependence and no definite rules can be established. 

The deprotonation-substItution approach has also been used to prepare polymers with carboxylic acid and ester and carboxylated salt moieties attached to the phosphazene. (25) THF solutions of the parent polymer were treated with sufficient n-BuLi to facilitate deprotonation of 10, 25, or 50% of the methyl substituents. The resulting polymer anions were then treated with anhydrous carbon dioxide to produce the carboxylate salts 11 (eq 10). These salts were Isolated by removal of the solvent or were used in further reactions with dilute aqueous acid solutions (eq 11) or with p-nitrobenzylbromide (eq 12) to give the carboxylic acids, 12, or esters, 13, respectively. 

Despite early successes in substitution of sulfolenes, initial attempts to develop methods for the deprotonation/substitution of 3-sulfolenes using stronger bases such as NaH, BuLi, LDA, and Grignard reagents were unsuccessful. This is caused by cycloreversion of the labile a-carbanion (69) to the more thermodynamically stable butadienyl sulfinate (70) (Scheme 6.18). 

The deprotonation-substitution reactions of methylphenyl substituted cyelotriphosphazenes can be considered to be an important synthetic tool for the expansion of the area of organo-substituted cyclophosphazenes possessing a direet P-C bond. The reaction of tru i-(NPMePh)3 (212) with 3 moles of Bu Li followed by treatment with 3 moles of MeLi affords trans-(NPEtPh)3 (213) in high yield. The same reaction with cw-(NPMePh)3 (212) gives a mixture of bis(ethyl) [cw-(214)] and tris(ethyl) [cw-(213)] derivatives. 

Scheme 5.1 First enantioselective deprotonation-substitution sequence in a di-methylphosphorus compound and two views of the structure of (-)-sparteine.

The polymerization is in fact a chain-growth reaction and allows access to high molecular weight polyphosphazenes such as poly(dimethylphosphazene) and poly(methylphenylphosphazene) (2). Methyl deprotonation/substitution of these polymers as well as electrophilic aromatic substitution of the phenyl substituents in poly(methylphenylphosphazene) have been developed as versatile strategies for the derivatization of both of these polymers (eq. 3) (3). 

Poly(methylphenylphosphazene) can be derivatized through either deprotonation/substitution reactions at the methyl group or electrophilic aromatic substitution of the phenyl group. These reactions have been used to prepare a variety of new polyphosphazenes with all functional groups attached to the polymer backbone by direct P-C bonds. The synthesis and characterization of several of these new... 

When used in THF, Li(TMP)Al(i-Bu)j (2 equiv) is capable of deprotonating substituted benzenes such as anisole and A,A-diisopropylbenzamide at room temperature and sensitive substrates such as benzo-nitrile and l-chloro-4-iodobenzene at -78°C. Iodine is the electrophile of choice, but others can also be... 

Aziridines can be formed by nitrene (-like) additions to double bonds, or by carbene (-like) additions to imines. Both processes especially the latter one can also occur by a stepwise addition-elimination process [172]. Similar to cyclopropa-nations, aziridinations of imines can foUow two protocols alkylation-deprotonation-substitution and sulfide reactions with metallocarbenes. 

Scheme 7.50 Proposed catalytic cycle for epoxide formation with chalcogen-ylides via alkylation / deprotonation /substitution mechanism in a phase transfer system...

N-Phosphoryl Substituted Phosphoranimines. In addition to being use l as condensation "monomers Scheme 2), the N-silylphosphoranimines have a rich and varied chemistry of their own. Three distinct modes of reactivity Scheme 5) are well documented. Cleavage of the Si-N bond is typified by a series of transsilylation reactions with substituted chlorosilanes (75) while the deprotonation-substitution chemistry has led to a wide variety of P-CH2-E derivatives containing silyl, 16) phosphinyl, (77) and organic 18) functional groups. Some of these latter reactions serve as useful model systems for similar derivative chemistry of the preformed phosphazene polymers such as [Me(Ph)P=N]n. 6)... 

Variations in the Deprotonation-Substitution Reactions. As discussed in the previous paper in this volume, the preparation of copolymers with combinations of alkyl and aryl groups attached to the backbone by P-C bonds is readily achieved by the condensation polymerization of appropriate mixtures of N-silyl hosphoranimines. The highly methylated copolymers 15 are of particuhiar interest in terms of deprotonation-substitution reactions for several reasons. First, with even a low proportion of phen d groups, these copolymers remain soluble in THF, a solvent suitable for deprotonation-substitution reactions. Second, the of the copolymers are significantly lower than... 

In most of the deprotonation-substitution reactions discussed thus far, the degree of substitution has usually not exceeded 50 %. Although this could be due to either electronic ctors associated with the formation of charged sites along the chain or to siiiq)le steric effects, a recent P NMR spectroscopic study of the anion indicates that steric size of the electrophile is the limiting frctor in substitution. When one-half equivalent of fi-BuLi was added to [Me(Ph)PN]]x and the mixture was stirred at room... 

Acetylene-substituted Si-N-P compounds, synthesis, 236-237 Activated aluminas, description, 165 Aerogels, definition, 127 Aggregation of fractals, 104,106 Alcohol-substituted polymers from aldehydes and ketones, deprotonation-substitution reactions, 249-250 Alkenylborazine copolymers, quantitative reactivity studies of copolymerization reactions, 394... 

Alkenylfluorophosphazene copolymers, quantitative reactivity studies of copolymerization reactions, 390-394 Alkoxyalkoxy side groups, synthesis of n-silylphosphoranimines, 311-322 Alkyl-group polymers, deprotonation-substitution reactions, 248-249 Allylboration polymerization, polycyclo-diborazane synthesis, 407-408,409, 410 Alucone polymers characterization ceramics, 177 polymers, 173-178 examples, 166,167/ solid-state NMR spectroscopy limitations, 177,179/ quadrupolar broadening, 177-180 status, 180-181 syntheses ceramics, 170-174 polymers, 166,168-170 synthetic route, 166... 

---