Unexpected formation of ansa isomers enabled by phosphazene ring flexibility in the reactions of cyclotetraphosphazene with 1,2-ethanediol.

In this work, the nucleophilic substitution reactions of the cyclotetraphosphazene, tetramer, (1) (N4P4Cl8) with the disodium salt of 1,2-ethanediol in THF solution at different mole ratios were demonstrated. Surprisingly, one double bridged (2) and three ansa derivatives [bis (3), tris (4) and tetrakis (5)] were formed demonstrating two competing pathways in these reactions. The new type cyclotetraphosphazene compounds (2-5) consisting of multiple rings were characterized by elemental analysis, mass spectrometry, 1H and 31P NMR spectroscopy and X-Ray crystallography. Although 1,2-ethanediol, a short chain diol, can only produce spiro type products with cyclotriphosphazene, (N3P3Cl6), it was able to give ansa type products with cyclotetraphosphazene which suggests the role of the ring flexibility of 1. Crystallographic evidence shows the distortion of the cyclotetraphosphazene ring.

Synthesis of new cyclotriphosphazene derivatives bearing Schiff bases and their thermal and absorbance properties.

In this study, a series of cyclotriphosphazene derivatives containing a Schiff base (3a-3d) were synthesized by the reactions of hexachlorocyclotriphosphazene (1) with bis-aryl Schiff bases ( 2a - 2d ) having different terminal groups (H, F, Cl, and Br). The products ( 3a - 3d ) were characterized by elemental and mass analyses, FT-IR, and 1 H, 13 C, and 31 P NMR spectroscopies. Furthermore, the structure of compound 3a was also determined by X-ray crystallography. The thermal behaviors and the spectral properties of the new cyclotriphosphazene compounds ( 3a - 3d ) were investigated and the results were compared in the series.

Regiochemical Control in the Substitution Reactions of Cyclotriphosphazene Derivatives with Secondary Amines.

The substitution reactions of the monospiro and geminally disubstituted cyclotriphosphazene derivatives N3P3Cl4R2 (R2 = OCH2(CF2)2CH2O (1a), SPh (1b), OCH2CH2CH2O (1c), NHPh (1d), OCH2CH2CH2NH (1e), NHBut (1f)) with two secondary amines (pyrrolidine and dimethylamine) were carried out to investigate geminal or non-geminal directing effects in mixed substituent cyclophosphazenes. The relative amounts of isomeric products, geminal and non-geminal trans or cis, was established quantitatively from the 31P NMR spectra of the reaction mixtures. Although secondary amines generally follow a non-geminal pathway in the reactions with hexachlorocyclotriphosphazene, in this work, the reactions of two different secondary amines with some N3P3Cl4R2 (R2 = OCH2CH2CH2NH, NHPh, NHBut) derivatives lead to the formation of geminal products. We have shown that this observation depends on the electron-donating properties of the PR2 groups. Isolated compounds were analyzed by standard techniques such as elemental analysis, mass spectrometry, and 1H and 31P NMR spectroscopy. The structures of compounds for which suitable crystals could be obtained were characterized by X-ray crystallography.

New Synthetic Approach to Molecular Rods Using Cyclophosphazene-Based Oligospiranes.

A synthetic approach was developed to prepare a new type of highly functionalized inorganic-organic heterocyclic molecular rod (3a and 3b) consisting of cyclophosphazene and carbocyclic units. Single-crystal X-ray diffraction analysis of 3a revealed that the molecular length was ca. 2.5 nm. The products of this high-yield process have the potential for derivatization via known phosphazene reactions.

Unexpected Ring Expansion of a Four-Membered Cyclophosphazane.

Nucleophilic substitution reactions of the N(R),N(R)-spiro-bridged octachlorobis(cyclotriphosphazene), N3P3Cl4[N(CH2)5CH3]2N3P3Cl4 (1), with sodium salts of alcohols (1,3-propanediol, 2,2,3,3,4,4-hexafluoro-1,5-pentanediol, and phenol) give ansa products (2-4) via an unexpected rearrangement. These products were characterized by elemental analysis, mass spectrometry, and (1)H and (31)P NMR spectroscopy. The molecular structures of compounds 3 and 4 were also established by X-ray crystallography. This new class of phosphazene structures consists of three fused P3N3 rings that arise from expansion of the four-membered phosphazane ring in 1 to a six-membered N3P3 ring during alcoholysis reactions.

Silver(I) coordination polymers assembled from flexible cyclotriphosphazene ligand: structures, topologies and investigation of the counteranion effects.

The reactions of a flexible ligand hexakis(3-pyridyloxy)cyclotriphosphazene (HPCP) with a variety of silver(I) salts (AgX; X = NO3(-), PF6(-), ClO4(-), CH3PhSO3(-), BF4(-) and CF3SO3(-)) afforded six silver(I) coordination polymers, namely {[Ag2(HPCP)]·(NO3)2·H2O}n (1), {[Ag2(HPCP)(CH3CN)]·(PF6)2}n (2), {[Ag2(HPCP)(CH3CN)]·(ClO4)2}n (3), [Ag3(HPCP)(CH3PhSO3)3]n (4), [Ag2(HPCP)(CH3CN)(BF4)2]n (5) and {[Ag(HPCP)]·(CF3SO3)}n (6). All of the isolated crystalline compounds were structurally determined by X-ray crystallography. Changing the counteranions in the reactions, which were conducted under similar conditions of M/L ratio (1:1), temperature and solvent, resulted in structures with different types of topologies. In complexes (1)-(6), the ligand HPCP shows different coordination modes with Ag(I) ions giving two-dimensional layered structures and three-dimensional frameworks with different topologies. Complex (1) displays a new three-dimensional framework adopting a (3,3,6)-connected 3-nodal net with point symbol {4.6(2)}2{4(2).6(10).8(3)}. Complexes (2) and (3) are isomorphous and have a two-dimensional layered structure showing the same 3,6L60 topology with point symbol {4.2(6)}2{4(8).6(6).8}. Complex (4) is a two-dimensional structure incorporating short Ag...Ag argentophilic interactions and has a uninodal 4-connected sql/Shubnikov tetragonal plane net with {4(4).6(2)} topology. Complex (5) exhibits a novel three-dimensional framework and more suprisingly contains twofold interpenetrated honeycomb-like networks, in which the single net has a trinodal (2,3,5)-connected 3-nodal net with point symbol {6(3).8(6).12}{6(3)}{8}. Complex (6) crystallizes in a trigonal crystal system with the space group R\bar 3 and possesses a three-dimensional polymeric structure showing a binodal (4,6)-connected fsh net with the point symbol (4(3).6(3))2.(4(6).6(6).8(3)). The effect of the counteranions on the formation of coordination polymers is discussed in this study.

Synthesis of a new class of fused cyclotetraphosphazene ring systems.

Octachlorocyclotetraphosphazene (1) was reacted with butylamines [n-butyl, i-butyl, sec-butyl, and t-butyl] in a 1:0.8 mol ratio in THF to obtain cyclotetraphosphazenes bearing a P-NH group, N4P4Cl7(NHR) [R = n-butyl (2a), i-butyl (2b), sec-butyl (2c), t-butyl (2d)](2a-d). The cyclotetraphosphazene derivatives 2a, 2b, and 2c were treated with sodium hydride giving rise to a new type of cyclophosphazene compounds (P8N8 ring) consisting of three fused tetramer rings (3a-c). Whereas reaction of sodium hydride with the t-butylaminocyclophosphazene derivative (2d) gave a P-O-P bridged compound (4) presumably as a result of hydrolysis reaction associated with moisture in the solvent. It is likely that the 16-membered cyclooctaphosphazene derivatives (3a-c) are formed by a proton abstraction/chloride ion elimination, intramolecular nucleophilic attack, ring opening and intermolecular condensation processes, respectively.

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

The reactions of cyclophosphazenes with 10-membered ansa-{N3P3Cl4[OCH2(CF2)3CH2O] (1a)} and 11-membered ansa-{N3P3Cl4[OCH2(CF2)4CH2O] (1b)} rings with the sodium salts of methanol in a THF solution at different molar ratios were used to investigate the reaction pathways and mechanism of nucleophilic substitution at the PCl2 and PCl(OR) phosphorus atoms. The reactions afforded eleven products, whose structures have been characterized by elemental analysis, mass spectrometry, (1)H, (19)F and (31)P NMR spectroscopy and X-ray crystallography; mono-methoxy derivatives (2a, 3a, 3b), di-methoxy derivatives (5a-7a, 5b), tri-methoxy derivatives (8a, 8b) and the tetra-methoxy derivatives (9a, 9b). The X-ray crystallographic studies of four compounds (6a-8a and 8b) demonstrated unambiguously that nucleophilic substitution reactions at the ansa-ring PCl(OR) phosphorus atoms of the cyclotriphosphazene compounds N3P3Cl4[OCH2(CF2)nCH2O] n = 3 (1a) and 4 (1b) occurred with a retention of configuration for both the 10- and 11-membered fluorodioxy ansa rings, respectively. The results confirmed that the reactions with 1a containing the 10-membered ansa-ring occurred competitively at both the PCl2 and P(OR)Cl moieties with an approximate 8 : 1 preference at the PCl2 group, whereas reactions with 1b containing the 11-membered ansa-ring occurred exclusively at the PCl2 group before the P(OR)Cl moiety. The results were mainly rationalized in terms of the P-Cl bond lengths of the reactants and the cation-assisted mechanism of reaction.

Conversion of a cyclotriphosphazene to a cyclohexaphosphazene by ring expansion.

Deprotonation of a cyclotriphosphazene with a tert-butylamino group in the side chain results in ring expansion to a very stable, planar cyclohexaphosphazene derivative that still contains eight P-Cl bonds suitable for forming macromolecular structures.

Stereo-selectivity in a cyclotriphosphazene derivative bearing an exocyclic P-O moiety.

Nucleophilic substitution reactions of N(3)P(3)Cl(4)[O(CH(2))(2)NCH(3)], (1) with the sodium salts of mono- and di-functional alcohols [methanol (2), phenol (3), tetraethyleneglycol (4) and 1,3-propanediol (5)] were carried out in order to investigate a possible directing effect of the spiro O-moiety on the formation of mono-substituted (2a, 3a), non-geminal di-substituted (2c, 3c) and ansa (4a, 5a) derivatives. Compounds isolated from the reactions were characterized by elemental analysis, mass spectrometry, (1)H and (31)P NMR spectroscopy and X-ray crystallographic analysis showed that the substituent OR in compounds (2a, 3a and 2c, 3c) and the ansa-ring in compounds (4a, 5a) formed cis to the P-O moiety of the exocyclic [O(CH(2))(2)NCH(3)] spiro ring. The formation of products (2a-d, 3a-d, 4a, 5a and 5b) was quantified from the (31)P NMR spectra of the reaction mixtures, which showed an overwhelming preference for derivatives (2a, 3a, 2c, 3c, 4a, 5a) with the substituent cis to the P-O moiety of the exocyclic spiro ring (2a, 3a, 2c, 3c, 4a, 5a), except for reaction with 1,3-propanediol where the six-membered ring spiro derivative (5b) was about three times more abundant than the eight-membered ring ansa-derivative (5a). Overwhelming formation of products with the substituent cis to the exocyclic P-O moiety is proof that the cation-assisted mechanism is responsible for the stereo-selectivity in the reactions with alkoxides.

Bridged cyclophosphazenes resulting from deprotonation reactions of cyclotriphophazenes bearing a P-NH group.

Cyclotriphosphazene derivatives containing a P-NHR group in the side-chain react in the presence of a strong base to form stable intermolecular bridged products. Reaction of sodium hydride with mono-spiro cyclophosphazene derivatives having a P-NH group, N(3)P(3)Cl(4)[O(CH(2))(3)NH], (1a) or N(3)P(3)Cl(4)[CH(3)N(CH(2))(3)NH], (1b) leads to formation of bis-cyclophosphazenes bridged with an eight-membered cyclophosphazene ring in an ansa arrangement (2a, 2b) whereas reaction of sodium hydride with mono-amino cyclophosphazene derivatives [N(3)P(3)Cl(5)(NHR), R = n-hexyl, 3a; i-Pr, 3b; Ph, 3c] give bis-cyclophosphazenes bridged with a four-membered cyclophosphazane ring in a spiro arrangement (4a-c). In the latter reaction P-O-P bridged compounds (5a-c) were also obtained as a result of hydrolysis reactions associated with the amount of moisture in the solvent tetrahydrofuran. In addition, it was found that reaction of a mixture of cyclotriphosphazene with either mono spiro compound, (1a) or (1b), in the presence of sodium hydride lead to formation of the first examples of asymmetrically-bridged cyclophosphazenes (6a-b).

Competitive formation of cis and trans derivatives in the nucleophilic substitution reactions of cyclophosphazenes having a mono-spiro P-NHR group.

Nucleophilic substitution reactions of N(3)P(3)Cl(4)[NH(CH(2))(3)NMe] (1) and N(3)P(3)Cl(4)[NH(CH(2))(3)O] (2) with mono-functional alcohols (methanol, 2,2,2-trifluoroethanol, phenol) and a secondary amine (pyrrolidine) were used to investigate the relationship between the incoming nucleophile and the proportions of products with substituents that are cis or trans to the spiro NH moiety. The reaction products were characterized by elemental analysis, mass spectrometry, (1)H and (31)P NMR spectroscopy and the configurational isomers by X-ray crystallography. Six products have been characterised with the substituent cis to the spiro NH group for the alcohol (methanol, phenol) and pyrrolidine derivatives of both compounds 1 and 2, compared to just one derivative with the substituent trans to the spiro NH group, that for the pyrrolidine derivative of compound 2. For each reaction the relative proportions of cis and trans isomers were determined by (31)P NMR measurements of the reaction mixtures. It was found that the reactions of compound 1 with all three alcohols and of compound 2 with methanol lead to exclusive formation of isomers with the substituent cis to the NH moiety, whereas all other reactions lead to mixtures of cis and trans isomers in different ratios under standard reaction conditions. However, when crown ether is included in the reaction medium for the reactions of compound 2 with both 2,2,2-trifluoroethanol and phenol, it is found that only cis isomers are formed. All these results are rationalised in terms of the competition between at least two effects; the cis-directing effect by hydrogen bonding of the incoming nucleophile to the spiro N-H group already present on the cyclophophazene ring and the cis-directing effect of the sodium cation coordinating to the oxygen lone pairs of the P-O moiety of the spiro ring.

Stable P-N bridged cyclophosphazenes with a spiro or ansa arrangement.

Deprotonation reactions of cyclophosphazenes containing secondary amino groups in the side chain lead to a doubly bridged tricyclophosphazene structure or to a cyclophosphazene-cyclophosphazane-cyclophosphazene compound, which are very stable and could be used as building blocks for larger structures.

A spiro to ansa rearrangement in cyclotriphosphazene derivatives.

Nucleophilic substitution reactions of cyclotriphosphazene derivatives having five-membered spiro rings, N(3)P(3)Cl(4)[O(CH(2))(2)X] (X = NH or O) with alkoxides (of tetraethylene glycol and some mono-functional alcohols) give unexpected rearrangements to form stable seven-membered ring ansa compounds, even though crystallographic evidence shows ring distortion and compression of the cyclophosphazene ring. With weaker nucleophiles such as sodium phenoxide and pyrrolidine substitution at a PCl2 group is preferred and no rearrangement takes place. In contrast, reactions of the analogous phosphazenes containing six-membered spiro rings, N(3)P(3)Cl(4)[O(CH(2))(3)X], with all of the above reagents give only normal substitution reactions at the PCl2 moieties and no rearrangement products. The spiro to ansa rearrangements in cyclophosphazenes are remarkable as the reported primary reaction products with the same difunctional reagents HO(CH(2))(2)XH are predominantly spiro, with some dangling and bridging derivatives, but no ansa compounds.

Comparison of high-performance liquid chromatography of cyclotriphosphazene derivatives with one or two equivalent stereogenic centres.

High-performance liquid chromatographic (HPLC) methods have been developed for investigating the stereogenic properties of two analogous series of dibenzylamino derivatives of cyclotriphosphazene containing either one or two equivalent stereogenic centres. Separation of the enantiomers of all the racemic compounds has been investigated by chiral HPLC using Whelk-01 and Chiralcel OD columns. In all cases, conditions for separation of enantiomers have been found using a Whelk-01 column with different ratios of tetrahydrofuran in n-hexane as the mobile phase. It is found that both the separation factor (alpha) and resolution factor (R(S)) of molecules with two equivalent stereogenic centres are greater than those for analogues with only one centre.

Retention of configuration in the nucleophilic substitution reactions of some nine-membered ansa derivatives of cyclotriphosphazatriene.

X-ray crystallographic evidence shows that nucleophilic substitution reactions of two different types of cyclophosphazene derivatives with relatively rigid nine-membered ansa rings leads to the first demonstration of retention of configuration in these molecular systems.

Anomalous NMR behavior of meso compounds with remote stereogenic centers on addition of chiral shift reagent or chiral solvating agent.

A problem has arisen in using chiral shift reagents (CSR) and chiral solvating agents (CSA) to determine meso and racemic forms of diastereoisomers in which the stereogenic centers of the molecules are separated by achiral spacers. It is found that NMR signals of both meso and racemic forms of diastereoisomers may exhibit doubling on addition of CSR/CSA, which means that unequivocal assignments cannot be made without characterizing the effects for separate meso and racemic forms; this is particularly important for additions of CSR/CSA at relatively low concentrations, which always result in the splitting of some NMR signals of diastereoisomers. The phenomenon is demonstrated in the (31)P NMR spectra of meso and racemic forms of three spermine-bridged gem-disubstituted cyclotriphosphazatrienes, 1a-c, and compared with analogous achiral molecules, the per-substituted spermine-bridged cyclotriphosphazatrienes 2a-d. As expected, only one set of (31)P NMR signals was observed for the achiral compounds 2a-d, even on addition of CSA. Two sets of (31)P NMR ABX multiplets corresponding to meso and racemic diastereoisomers were observed for compounds 1a-c; on addition of CSA, the signals of at least one of the multiplets for each compound separated into more than the expected groups of three lines with an intensity distribution of 2:1:1. To understand this phenomenon, the meso and racemic forms of 1a and 1b and the meso form of 1c have been separated and characterized by X-ray crystallography. On addition of CSA to the racemic forms of 1a and 1b, the (31)P NMR spectrum shows the expected doubling of signals, but, unexpectedly, the same is observed for each of the meso forms of 1a-c. Analogous results using both CSA and CSR have been obtained for the meso and racemic forms of the diastereoisomeric piperazine-bridged macrocyclic-phosphazene compound, 3, whereas no effect was observed for the two meso forms of the doubly bridged macrocyclic-phosphazene compound 4. The phenomenon of doubling of the (31)P NMR signals of the meso form of singly bridged cyclotriphosphazatrienes, 1a-c and 3, is explained by consideration of the equilibrium in solution of independent complexation of a chiral ligand with molecules that have two chiral cyclophosphazene moieties separated by an achiral spacer group. The results show that the stereogenicity of such diastereoisomeric molecules in solution cannot be characterized unequivocally by NMR measurements on addition of either CSR or CSA.

Structural investigations of phosphorus-nitrogen compounds. 5. Relationships between molecular parameters of 2,2-diphenyl-4,6-cis-oxytetra(ethyleneoxy)-4,6-R2-cyclotriphosphazatrienes (R = Cl, OCH2CF3, OPh, OMe, NHPh, NHBut) and substituent basicity constants.

A systematic study of the products of nucleophilic substitution reactions of cis-ansa N(3)P(3)Ph(2)[O(CH(2)CH(2)O)(4)]Cl(2) (3) is reported. These reactions give a number of new structures with the general formula N(3)P(3)Ph(2)[O(CH(2)CH(2)O)(4)]R(2) [where R = OCH(2)CF(3) (4), OPh (5), OMe (6), NHPh (7 x H(2)O), NHBu(t) (8)]. A comparison has been made between the sum of the substituent basicity constants, Sigmaalpha(R), that are obtained in nitrobenzene solution and eight molecular parameters of the N(3)P(3) ring [the P-N bond lengths a, b, c; the internal bond angles alpha, beta, gamma, delta; and the difference between the bond lengths a and b, Delta(P-N)]. It is found that the systematic changes in the molecular parameters of (3)-(8) are in line with changes in alpha(R) values. This result implies the similarity in relative electron-releasing capacity of substituents R in the solid state and in solution.

Structural investigations of phosphorus-nitrogen compounds. 4. Steric and electronic effects in dibenzylamino derivatives of hexachlorocyclotriphosphazatriene and 4,4,6,6-tetrachloro-2,2-diphenylcyclotriphosphazatriene.

A systematic study is presented on the products of aminolysis of N(3)P(3)Cl(6) (1) and N(3)P(3)Ph(2)Cl(4) (4) with dibenzylamine. Two series of mono- and disubstituted derivatives of compounds (1) and (4), namely N(3)P(3)Cl(5)[N(CH(2)Ph)(2)] (2) and N(3)P(3)Cl(4)[N(CH(2)Ph)(2)](2) (3) and N(3)P(3)Ph(2)Cl(3)[N(CH(2)Ph)(2)] (5) and N(3)P(3)Ph(2)Cl(2)[N(CH(2)Ph)(2)](2) (6) [where (2), (3), (5) and (6) are new structures], are investigated in order to determine whether steric or electronic effects prevail in the formation of dibenzylamino-substituted cyclophosphazenes. The influence of an electron-releasing group (i.e. phenyl) on the stereochemistry and degree of substitution of the product is analysed by comparison of the above two series. The difference in unsymmetrically substituted endocyclic P-N bond lengths, Delta, is used as a measure of the degree of the electronic contribution, in combination with basicity constants, to quantify the degree of the electron-releasing capacity of the R group. In order to compare geminal versus non-geminal substitution, a difunctional secondary amine was used to form the compound N(3)P(3)Cl(4)[NMe(CH(2))(3)NMe] (7) (a reinvestigation) for inclusion in this study. It is shown that electron-releasing groups have a greater effect on the lengthening of P-Cl bonds as opposed to endocyclic P-N bonds and that this effect is greater in the non-geminal PRCl case than for geminal PCl(2). However, steric effects are shown to be dominant in the reactions of dibenzylamine with N(3)P(3) derivatives, with a disposition to a trans stereochemistry in bisdibenzylamino derivatives.