Chlorination, Iodination, and Silylation of Poly(2,2′-dioxy-1,1′-biphenylphosphazene). New Halogenated Polyphosphazenes with Sterically Hindered Reactivity

Abstract

The polyphosphazene {[NP(O2C12H8)]} n (1) [(O2C12H8) = 2,2′-dioxy-1,1′-biphenyl] with [PO2C12H8] cycles in the repeating units reacts slowly with chlorine in concentrated sulfuric acid to give the 5,5′-chlorinated {[NP(O2C12H8)]1−x [NP(O2C12H7Cl)] x } n (2) (x = 0.2−1), with limiting oxygen index (LOI) in the interval 26−33 (estimated from the TGA residues), corresponding to potential self-extinguishing flame retardants. The reaction of 1 with [Ipy2]BF4 in CH2Cl2 in the presence of CF3SO3H gave the 5,5′-iodinated {[NP(O2C12H8)]1−x [NP(O2C12H7I)] x } n (3) (x = 0.2−1) which, in contrast, are thermally unstable, leaving almost no TGA residues. The potential of 2 and 3 as precursors for the chemical derivation of 1 was assessed by the silylation method (reaction with LiBu t at −78 °C followed by addition of ClSiMe3 and a complete characterization of the resulting trimethylsilyl derivatives). The isolation of polymers {[NP(O2C12H8)]0.65[NP(O2C12H7Cl)]0.15[NP(O2C12H7SiMe3)]0.2} n (4) and {[NP(O2C12H8)]0.8[NP(O2C12H7SiMe3)]0.2} n (5) demonstrated that the lithiation was 40−50% efficient with the chlorine derivatives and approached 100% with the iodine analogues. The silylation of the available Li sites was less effective with the higher lithiated polymers and always below the levels usually observed. The reactivity of polyphosphazenes with 2,2′-dioxy-1,1′-biphenylphosphorus repeating units is therefore limited by steric and conformational effects reinforced by the proximity of the reaction centers to the main chain.

Direct Functionalization of Poly(spirophosphazene)s via the Regioselective Lithiation of the Aromatic Rings Using a Cooperative Superbase

“…The 13 C‐NMR spectra of the deuterated polymer also confirmed the presence of [NP(O 2 C 12 H 7 D )] units in polymer 3 (see the Supporting Information). The regioselectivity of the reaction at the C 3 of the [NP(O 2 C 12 H 8 )] units is not surprising since other electrophilic reactions (i.e., nitration, chlorination, and iodination) performed over the same polyphosphazene 1 , resulted in mixtures of C 3 ‐ and C 5 ‐substitutions (i.e., ortho‐ and para‐position with respect to the carbon linked to the phosphazene chain) . However, in the case of the lithiation reaction, the C 3 position can be favored by the coordination of the lithium to the nitrogen of the phosphazene main chain, as observed in the lithiation of (triphenyl)iminophosphorane derivatives of general formula Ph 3 PNSiMe 3 .…”

“…Thus, TGA thermograms of polymers 4 and 5 containing PPh 2 and Bpin moieties, respectively, showed a final pyrolitic residue at 800 °C of 50% and 40% of their initial mass (see Table ). These ceramic residues are significantly larger than those of the precursor 1 (30%) and the silylated polymer 2h (32%), and can be compared with those of other polyphosphazenes containing chlorine or butylamino substituents, making them potential self‐extinguishing. The DSC traces showed that the attachment of functional groups on the C 3 of the [NP(O 2 C 12 H 8 )] units induced an increase in the T g values (Table ).…”

“…The regioselectivity of the reaction at the C 3 of the [NP(O 2 C 12 H 8 )] units is not surprising since other electrophilic reactions (i.e., nitration, chlorination, and iodination) performed over the same polyphosphazene 1, resulted in mixtures of C 3 -and C 5 -substitutions (i.e., ortho-and para-position with respect to the carbon linked to the phosphazene chain). [14,15] However, in the case of the lithiation reaction, the C 3 position can be favored by the coordination of the lithium to the nitrogen of the phosphazene main chain, as observed in the lithiation of (triphenyl)iminophosphorane derivatives of general formula Ph 3 PNSiMe 3 . [19] This hypothesis was confirmed by performing low temperature 31 P-NMR spectroscopy experiments with the lithiated polymeric intermediates (as prepared under the condition described in entry 8 of Table 1).…”

“…However, the direct functionalization of the cyclic dioxy‐biphenyl‐phosphorus units has been very little explored. Thus, we reported the nitration of [NP(O 2 C 12 H 8 )] n ( 1 ) by treatment with aqueous HNO 3 in concentrated sulfuric acid, and the chlorination and iodination with chlorine gas or [Ipy 2 ] 2 BF 4 , respectively . Herein, we wish to report the controlled and regioselective macromolecular lithiation of [NP(O 2 C 12 H 8 )] n ( 1 ) by using the Li t Bu/KO t Bu “superbase,” known as Schlosser's base.…”

“…Thus, we reported the nitration of [NP(O 2 C 12 H 8 )] n (1) by treatment with aqueous HNO 3 in concentrated sulfuric acid, [14] and the chlorination and iodination with chlorine gas or [Ipy 2 ] 2 BF 4 , respectively. [15] Herein, we wish to report the controlled and regioselective macromolecular lithiation of [NP(O 2 C 12 H 8 )] n (1) by using the Li t Bu/KO t Bu "superbase," known as Schlosser's base. The resulting lithiated polyphosphazenes were very efficiently derivatized with SiMe 3 , PPh 2 , and B(O 2 C 6 H 12 ) (Bpin) moieties, without degradation of the polymeric chains during the reactions.…”