Supramolecular assistance to regioselectivity in the reactions of chlorocyclophosphazenes with sodium oxyanions: macrocyclic effect and anion dependence

Doubly activated supramolecular reaction: transesterification of acyclic oligoether esters with metal alkoxides

Transesterification reactions of acyclic oligoether esters E3-E10 with metal alkoxides were accelerated upon noncovalent complexation of the esters with metal ions. In the reaction of monovalent alkaline metal alkoxides, CH(3)ONa and CH(3)OK, plots of the observed rate constants k(obs) with respect to the chain length of E3-E10 showed selective acceleration of the transesterification. Compared with the shortest E3, which can hardly bind metal ion, 4.3- and 6.6-fold accelerations in the maxima were achieved in the combinations of E5/CH(3)ONa and E6/CH(3)OK, respectively. Supramolecular intermediate complex could be spectrometrically visualized by ESI-FT-ICR-MS in the course of reaction. Kinetic experiments, together with structural analyses by means of NMR, mass spectrometry, and DFT calculations of the intermediate complexes, indicate that a size-fit complex of host substitute with alkali metal ion allows strong electron withdrawing due to the close contact of the carbonyl oxygen to the metal ion, resulting in the selective rate enhancement of the reaction, while in the reaction of E3-E10 with a divalent alkaline earth metal alkoxide, (CH(3)CH(2)O)(2)Ba, the k(obs) values increased stepwise with elongation of the side arm to attain an dramatic large acceleration. In comparison with the k(obs) of E3, 4610-fold acceleration was achieved in the reaction of E10. The double activation of the host substrate and guest counter nucleophile at once brings about this extraordinary rate acceleration. The strong wrapping complexation of long oligoether ester with barium ethoxide allows for the effective electron withdrawal from the ester carbonyl group (host activation) as well as separation of the accompanying guest alkoxide anions (guest activation).

Preparation of the First Examples of Ansa−Spiro Substituted Fluorophosphazenes and Their Structural Studies: Analysis of C−H···F−P Weak Interactions in Substituted Fluorophosphazenes

The reactions of fluorophosphazenes, endo ansa FcCH(2)P(S)(CH(2)O)(2)[P(F)N](2)(F(2)PN) (1) (Fc = ferrocenyl) and spiro [RCH(2)P(S)(CH(2)O)(2)PN](F(2)PN)(2) (R = Fc (2), C(6)H(5) (3)], with dilithiated diols have been explored. The study resulted in the formation of the first examples of ansa-spiro substituted fluorinated cyclophosphazenes as well as a bisansa substituted fluorophosphazene. The bisansa compound [1,3-[FcCH(2)P(S)(CH(2)O)(2)]][1,5-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (4) was found to be nongeminaly substituted with both the ansa rings in cis configuration, which is in stark contrast to the observations on cyclic chlorophosphazenes where geminal bisansa formation has been observed. The ansa-spiro compounds (5-7) underwent the ansa to spiro transformation leading to dispiro compounds in the presence of catalytic amounts of CsF at room temperature. Two of the ansa-spiro compounds, endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (5) and endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[FcCH(2)P(S)(CH(2)O)(2)]]N(3)P(3)F(2) (6), were structurally characterized, and the crystal structures indicate boat-chair conformation as well as crown conformation for the eight-membered ansa rings. Weak C-H.F-P interactions observed in the crystal structures of the ansa-spiro substituted fluorophosphazene derivatives have been analyzed and compared with C-H.F-P interactions of other fluorinated phosphazenes and thionyl phosphazenes.

Diastereoisomeric singly bridged cyclophosphazene-macrocyclic compounds

31P NMR spectroscopy and added chiral shift reagent (CSR) or chiral solvating agent (CSA) have been used to show that unsymmetrically substituted singly bridged macrocyclic phosphazene compounds exist as 1:1 diastereoisomers of two racemic mixtures, in contrast to previous work (ref 2) on symmetrically substituted diastereoisomeric analogues, which exist as meso and racemic forms. The cis-ansa cyclotriphosphazatriene-macrocycle, 1, is meso and monosubstitution of the >P(O-macrocycle)Cl group with 2-naphthol gives a racemic product (7), in which the macrocyclic ring exists in a trans-ansa configuration. Reaction of 7 with the di-secondary amine, piperazine, gives an unsymmetrically disubstituted racemic compound (8) having a cis-ansa configuration of the macrocyclic ring. Reaction of 8 with a further quantity of 1 forms a singly bridged derivative (9) with the macrocyclic rings in cis-trans configurations, and further reaction of 9 with pyrrolidine gives compound 10 with the macrocyclic rings in cis-cis configurations. Both 9 and 10 have four stereogenic centers giving rise to diastereoisomeric compounds existing as mixtures of two racemates. The results are consistent with inversion of configuration at phosphorus at each step of the reaction of >P(OR)Cl groups with nucleophile Z (i.e., Z = naphthoxy, piperazino, pyrrolidino) to form >P(OR)Z derivatives.