Indolyl-3-spiro(N/N)cyclotriphosphazenes: syntheses, spectral, crystallographic and thermal analyses

In this study, tetrakis(secondaryamino)-N¹-[(1H-indol-3-yl)methyl]-N²-methylspiro(N/N)cyclotri-phosphazenes were obtained and their syntheses, crystal structures, spectral and thermal properties were investigated. Primarily, N¹-[(1H-indol-3-yl)methyl]-N²-methyl-1,2-diaminoethane (L1) was synthesized from the reaction of indole-3-carboxaldehyde and N-methyl-1,2-diaminoethane in the equimolar ratio 1:1. Reactions of hexachlorocyclotriphosphazene (HCCP), N₃P₃Cl₆ (1), with equimolar amounts of L1 gave tetrachloro-N¹-[(1H-indol-3-yl)methyl]-N²-methylspiro(N/N)cyclotriphosphazene (2). Tetrakis(secondaryamino)-N¹-[(1H-indol-3-yl)methyl]-N²-methylspiro(N/N)cyclotriphosphazenes (2a-2d) were prepared from the condensation reactions of spiro 2 with an excess of pyrrolidine, piperidine, morpholine and 1,4-dioxa-8-azaspiro[4,5]decane (DASD), respectively, The structures of the new products L1, 2 and 2a–2d were proven by microanalysis, HRMS, FTIR, HSQC, ¹H, ¹³C and ³¹P data. The molecular and crystal structures of 2a and 2d were evaluated by single crystal X-ray crystallography. The six-membered N₃P₃ rings of 2a and 2d were in nearly planar and flattened boat conformations with total puckering amplitudes Q_T of 0.0419 (14) Å (2a) and 0.1192 (23) Å (2d). In addition, the thermal characterizations of the new phosphazenes are evaluated by TG and DTA techniques. The limited oxygen index (LOI) parameters of the compounds were determined from the TGA data to determine their oxidation resistance values. The values found are in the range of 28.4–31.6, indicating that these compounds are in the group of self-extinguishing materials.