Reactions with Electrophiles and Nucleophiles

The interaction of PCSs with nucleophilic reagents was studied by us we took the reactions of hydrazine and phenylhydrazine with polyazines, poly(schiff base)s, and other polymers containing conjupted C=N bonds as an example40,41, U7,258.  

The addition of hydrazine (and phenylhydrazine) to these polymers proceeds with the opening of the C=N bonds. If the main chain consists of appropriate fragments, this reaction is followed by the degradation of this chain. 

Destructive hydrazinolysis is of importance for the establishment of the structure of the PCS main chain, since the reaction products can easily be identified. The importance of this reaction also results from the fact that C=C bonds do not undergo hydrazinolysis. A general scheme of the process of destructive hydrazinolysis may be given as follows  

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The other class of reactions includes those which are common to alicyclic analogues reactions with electrophiles and nucleophiles and through cyclic transition states. 

Radical ions are created in solution by chemically or electrochemically induced electron transfer to or from a conjugated ir-system. Even if these ions are thermodynamically stable they are only of limited persistence since they are susceptible to reactions with electrophiles and nucleophiles or undergo other processes like dimerization or electron-transfer induced bond cleavage [9, 10]. Pairs of radical anions and radical cations can also be formed by electron transfer between neutral donors and acceptors either in the ground state or upon photochemical excitation [11, 12]. 

Alkylidenecycloproparenes (benzotriafulvenes) are more strained than triafulvenes and readily undergo ring opening or rearrangement upon reaction with electrophiles and nucleophiles. For cycloadditions, different reactivity has been observed between diarylmethylenecyclopropa-benzenes 12 and -naphthalenes 13. While the former compounds give Diels-Aldcr adducts at the endocyclic double bond with diphenylisobenzofuran, the latter compounds produce rearrangement products via Diels-Alder adducts from reaction at the exocyclic C —C double bond. A [2-1-2] cycloaddition has also been observed for a naphtbo compound. 

Benzoxazolinones, reactions with electrophilic and nucleophilic agents ... 

Purine undergoes reactions with electrophiles and nucleophiles [147]. Protonation of purine occurs at N-1, but alkylation at N-7 and/or N-9. This is shown by its reactions with dimethyl... 

Halide, nitrosyl and phosphite derivatives of [Os oCss C)(00)24] " are obtained by reactions with electrophilic and nucleophilic reagents products characterised by X-ray diffraction are... 

MesSiCl gives substitution product 3.638 and with fluorenyl-lithium, the adduct 3.640 is produced. The successive introduction of substituents can be achieved by a sequence of reactions with electrophiles and nucleophiles. Thus electrophile Ei gives fulvene 3.642, followed by attack by nucleophile Nu to afford adduct 3.643, and again by electrophile Ei to give product 3.644. These reactions can lead to the preparation of a unique series of homogeneous catalysts for olefin polymerization for it is known that the indenyl complexes are often better catalysts for olefin polymerization than cyclopentadienyl analogs (Scheme 3.58) [308,315]. 

Nonetheless, and in sharp contrast to the polymerization of heterocycles, such achievements-as measured by the number of new stractures added to the pool of available monomers-have been somewhat hmited. This success rate is not surprising in itself if one considers the difficulty of the reaction involved, namely a C—C bond cleavage. Carbon—carbon single bonds are notoriously difficult to break as a rule, they do not react with free-radicals and rarely participate in reactions with electrophiles and nucleophiles [20]. In addition, as the two atoms making the bond are identical, no polarization is introduced into the system. 

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