Crystallographic Proof of Double Walden Inversion in Nucleophilic Substitution Reactions of Macrocyclic Cyclotriphosphazene Derivatives

Abstract

Using X-ray crystallography it is demonstrated unambiguously that a double Walden inversion reaction occurs for successive nucleophilic substitution of the mono-spiropropanoxyamino derivative of the cis-ansa-macrocyclic cyclophosphaz-The spiropropanoxyamino moiety enables groups above and below the plane of the N 3 P 3 ring to be distinguished. The first nucleophilic substitution of compound 3 with X -(e.g., X = 2-naphthoxy) gives N 3 P 3 [O(CH 2 ) 3 4 ]X 2 (5a), in which the macrocyclic ring is cis-ansa again, but it is now on the opposite side of the N 3 P 3 ring from that of the starting material 3 as a result of the second inversion re-

Nucleophilic substitution reactions of 10- and 11-membered fluorodioxy ansa cyclotriphosphazene derivatives

“…The configuration mechanism (inversion or retention) in the cis-ansa derivatives of cyclotriphosphazene was investigated using X-ray crystallographic evidence previously. 42,43 The inversion of configuration occurs in the nucleophilic substitution reactions on the two phosphorus atoms adjacent to the cisansa groups consist of macrocyclic ring with sixteen atoms, 42 whereas nucleophilic substitution of cyclophosphazene derivatives with nine-membered cis-ansa rings leads to retention of configuration. 43 In order to investigate how general the retention/inversion of configuration mechanism might be, we selected as starting compounds the fluorodioxy-ansa derivatives N 3 P 3 Cl 4 [OCH 2 (CF 2 ) n CH 2 O] n = 3 (1a) and n = 4 (1b), which have ten and eleven membered mono-cis-ansa rings.…”

“…Some bond and conformational parameters of compounds 2a, 3a, 5a-9a (10-membered) and 3b, 5b, 8b, and 9b (11-membered ansa-dioxy rings) are summarized (ESI table †) and are found to be similar to those observed for the starting compounds 1a 45 and 1b 46 and in the normal range found for ansa substituted cyclotriphosphazene derivatives. 42,43,[45][46][47] In particular, the size of the ansa ring has an effect on the P2-N2-P3 bond angle encompassing the nitrogen atom belonging to both the phosphazene and the ansa rings, i.e. it is slightly smaller (117.6-120.9°) in compounds 2a, 3a, 5a-9a containing the 10-membered ansa-ring compared to those observed (121.2-122.5°) in compounds containing the 11-membered ansa-ring (3b, 5b, 8b, and 9b).…”

“…Therefore, investigating the mechanism of the nucleophilic substitution reaction at phosphorus(V) atoms is important for the prediction of the regio-and stereo-chemical isomer distribution. S N 1 (racemization) and S N 2 (inversion) mechanisms [39][40][41][42] are seen predominantly whereas the S N i (retention of configuration) mechanism is only rarely observed at the reaction centre. 43,44 However, the effects of the substituent already present on the phosphazene ring must not be forgotten.…”

“…43,44 However, the effects of the substituent already present on the phosphazene ring must not be forgotten. For example an inversion of configuration occurred in the nucleophilic substitution reactions on the two phosphorus atoms adjacent to the cis-ansa groups consisting of a macrocyclic ring with sixteen atoms, 42 whilst the nucleophilic substitution of cyclophosphazene derivatives with nine-membered cis-ansa rings led to the retention of configuration. 43 Hence, in order to investigate in more detail the size of the ansa ring on the reaction mechanism and determine the reaction pathway for ansa fluorodiol derivatives, we selected the fluorodioxy cis-ansa derivatives of cyclotriphosphazene; the hexafluoropentanedioxy derivative, N 3 P 3 Cl 4 [OCH 2 (CF 2 ) 3 CH 2 O] (1a), 45 which has a cis-ansa ring with ten atoms and the octafluorohexanedioxy derivative, N 3 P 3 Cl 4 [OCH 2 (CF 2 ) 4 CH 2 O] (1b), 46 which has an eleven membered cis-ansa ring.…”

Reactions of cyclochlorotriphosphazatriene with 1-amino-2-propanol. Calorimetric and spectroscopic investigations of the derived products

“…The selectivity of the substitution reactions of trimer (1) with difunctional regeants is strongly depended on the temperature [25], solvent and the type of nucleophilic regeants [24][25]. Solvent effect plays an important role in determining the stereo and regio sellective control on the cyclophosphazene rings [22][23][24][25].…”