Polyfluoroalkoxy and aryloxy cyclic phosphazenes: an alternative synthetic route to substitution reactions using siloxanes in the presence of fluoride ion catalysts

Abstract

The first detailed investigations on the reactions of polyfluoromonoand dialkoxysilanes with cyclic fluorophosphazenes are carried out and compared with reactions of the nonfluorinated analogues. The method offers an easy and elegant route to the hitherto poorly studied bridged and dangling phosphazene compounds. For the first time a transformation of bridged phosphazene compounds to spiro compounds is observed and monitored by 19FNMR studies. An explanation is offered for the poor yields and inability to isolate bridged derivatives experienced by previous workers. The method offers a convenient way of using CF3CH20SiMe3, which is a byproduct of many polymerization reactions, as a reagent in substitution reactions on fluorophosphazene monomers and polymers with possible extension to chlorophosphazenes as well in the presence of a fluorinating agent. The present study contributes to the explanation of the mechanistic aspects of the possible modes of formation of the various products isolable from reactions of cyclophosphazenes with difunctional reagents. Reactions of NsP3F6 with [CF2CH20SiMe3]2, 1, and CF2[CF2CH2OSiMe3]2,2, in the presence of CsF as catalyst are found to proceed readily under mild conditions to yield the monospiro and the bridged fluorophosphazenederivatives (CF2CH20)2N3P3F4,3, C F Z ( C F ~ C H ~ O ) ~ N ~ P ~ F ~ 5, FsN3P3O C H ~ ( C F ~ ) ~ C H ~ O N ~ P ~ F S 4, and FsN~P~OCH~(CF~)~CH~~N~P~FS, 6, in good yields. ubsequent reactions of the bridged derivative 4 with 4-FC6H40SiMe3,3-FC6H40SiMe3, CF3CH20SiMe3, and 1 give the additional substitution products (~-FC~H~O)SP~N~OCH~CF~CF~CH~ON~P~(~-FC~H~O)S, 7, ( -FC~H~~)SP~N~OCH~CF~CF~CH~O N ~ P ~ ( ~ F C ~ H ~ ~ ) S , 8, and (CF~CH~O)SP~N~OCH~CF~CF~CH~ON~P~(CF~CH~O)S, 9, and an incompletely characterized dispiro bridged moiety with the facile elimination of Me3SiF. The reaction of Me3SiO(CH2)30SiMe3 with N3P3F6 in the presence of CsF gives the monospiro, dangling 11 and the bridged 12 derivatives in varying yields depending upon the reaction parameters. Reactions of N3P3F6 with excess CF3CH20SiMe3 in the presence of catalytic amounts of CsF or N3P3C16 with excess KF and CFsCH20SiMe3 in the absence of solvent proceed at 80 OC to yield [CF3CH20]6N3P3 and Me3SiF. The X-ray crystal structures of spiro [CF2CH20]2N3P3F4,3, and the bridged (~-FC~H~~)SP~N~OCH~CF~CF~CH~~N~P~(~-FC~H~O)S, 7, phosphazenes are determined. Compound 3 crystallizes in the monoclinic system, space group P21/c, with a = 14.695(5) A, b = 8.532(2) A, c = 9.600(3) A, 6 = 102.38(2)', V = 1175.6(6) AS, Dwlc 2.096 mg/m3, Z = 4, and R = 0.0656. Compound 7 crystallizes in the monoclinic system, space group P 2 , / n , with u = 7.738(2) A, b = 46.849(9) A, c = 9.516(2) A, fl = 108.65(3)', V = 3262.8(13) AS, Dwlc = 1.568 mg/m3, Z = 2, and R = 0.740. The bridged phosphazene derivatives 4 and 6 are found to undergo a facile transformation to the spiro phosphazenes 3 and 5, respectively, on heating at 82 OC in the presence of CsF in THF which is monitored by variable-temperature/-time 19F NMR.