Organophosphazenes. 15. Reactions of hexafluorocyclotriphosphazene with tert- and n-butyllithium reagents

Regio- and stereochemical control in substitution reactions of cyclophosphazenes

“…137 While the reactions of N3P3F6 with methyl-138 and n-butyllithium139 lead to low yields of the disubstituted geminal derivatives, reactions with fert-butyllithium give good yields of the frarcs-N3P3F6_n(t-C4H9),l (n = 2,3) derivatives. 139 The later reaction is the only known regio-and stereospecific cyclophosphazene reaction.…”

“…190 In the vinyloxy derivatives (section 4), the associative interaction leads to the 2,4-disubstituted isomers as the major product.128 Thus, the stereoselectivity in the lithiometallocene reactions is controlled by steric effects and in that regard resembles the behavior observed in reactions of tert-butyllithium. 139 The dilithiometallocenes and bis(dilithiobenzene)chromium reagents also give rise to nongeminal products but the transanular bridge necessitates a cis configuration. The steric effect of the metallocene is again noted in the fact that the nongeminal (4,6) positions undergo substitution in the reaction N3P3F5Ph while the electronically more favorable geminal site undergoes substitution in the reaction of N3P3F4[(C5H4)2Fe] with the less sterically demanding methyllithium.…”

Organophosphazenes. 26. Factors Controlling the Pathways Observed in the Reactions of Ethynyl Lithium Reagents with Hexafluorocyclotriphosphazene

“…Allcock has shown that the reactions of Grignard reagents with hexachlorocyclotriphosphazene, N 3 P 3 Cl 6 , proceed by a halogen abstraction pathway, leading to metalated phosphazene intermediates . A similar pathway is followed in the reactions of organolithium reagents. , The corresponding reactions with hexafluorocyclotriphosphazene, N 3 P 3 F 6 , are more typical of the nucleophilic substitutions referred to above. ,, A geminal pathway is preferred for certain alkyl, ,, alkenyl, , phenylethynyl, , and trimethylsilylethynyl lithium reagents, while nongeminal products are obtained for a variety of aryllithium reagents , and t -butyl lithium . With the exception of the region and stereospecific t -butyl lithium case, the observed pathways are all regioselective with nongeminal products accompanying geminal products. , The resulting organofunctional phosphazenes have proved to be useful synthetic intermediates.…”

“…A similar pathway is followed in the reactions of organolithium reagents. , The corresponding reactions with hexafluorocyclotriphosphazene, N 3 P 3 F 6 , are more typical of the nucleophilic substitutions referred to above. ,, A geminal pathway is preferred for certain alkyl, ,, alkenyl, , phenylethynyl, , and trimethylsilylethynyl lithium reagents, while nongeminal products are obtained for a variety of aryllithium reagents , and t -butyl lithium . With the exception of the region and stereospecific t -butyl lithium case, the observed pathways are all regioselective with nongeminal products accompanying geminal products. , The resulting organofunctional phosphazenes have proved to be useful synthetic intermediates. The alkenylphosphazenes undergo addition polymerization at the exocyclic olefin site. − The ethynyl center in phenylethynyl phosphazenes can react with metal carbonyls to give the appropriate organometallic derivatives ,,− or undergo cyclooligomerization reactions. − Recent detailed work by Elias and co-workers has shown how these processes may be used to create phosphazenes with structurally complex organic substituents. − In order to understand better the role of the carbanionic species in the observed reaction pathways of N 3 P 3 F 6 and to provide additional ethynylphosphazenes for reactions with organometallic reagents, we have examined the reactions of alkylethynyl lithium reagents and mixed substituent ethynyl lithium reagents and aryl lithium reagents.…”

“…All of the bis derivatives showed three peaks in the GC-MS with the same parent ion peaks, indicating that all of the isomers were present. Previous work has shown that the 31 P and 19 F NMR spectra can be used for definitive structural assignment for fluorophosphazene derivatives. ,,,, However, in the case of the ethynylphosphazenes, the spectra were complicated by second order effects and resonance overlap due to the small difference in chemical shifts between the various phosphorus centers to such a degree that it is difficult to make more than a rough estimate of the major NMR parameters and impossible to assign the various isomers in the disubstituted derivatives. This problem was overcome by hydrogenation of the ethynyl center (and also the olefin in 6A and 6B ) in the ethynyl phosphazenes (Scheme ).…”