Cyclophosphazene Ring Research Articles

Recent advances in the supramolecular assembly of cyclophosphazene derivatives.

Cyclophosphazenes are a fascinating group of inorganic heterocyclic compounds whose rings are constituted by the repetition of phosphorus and nitrogen atoms. They have received particular attention due to their easy functionalization and thermal stability and as an excellent core for the preparation of advanced materials. Rigid trispirocyclic derivatives of cyclophosphazenes afford numerous supramolecular structures that are suitable for the formation of host-guest complexes with a variety of guest molecules such as gas molecules and molecular rotor compounds. Also, the donor nitrogen atoms of the cyclophosphazene ring can participate in non-covalent interactions such as hydrogen bonding and metal coordination. It can also be used in the construction of supramolecular dendrimeric or polymeric systems as either the starting compound or the carrier of supramolecular groups. Thus, cyclophosphazenes have been employed in the preparation of supramolecular systems for about past 30 years. This review focuses on the state of recent advances in the construction of cyclotriphosphazene-based supramolecular systems built by non-covalent interactions and their applications such as host-guest complexes, liquid crystals, coordination polymers and nanostructures. The future perspective of cyclophosphazene supramolecular assemblies is also discussed.

DFT study of structure, IR and Raman spectra of the first generation dendrimer built from cyclotriphosphazene core with terminal pyrazine groups

A phosphorus-containing dendrimer with pyrazine end groups that can be used for biological purposes has been synthesized. The vibrational spectra of the first generation dendrimer G1 constructed from the cyclotriphosphazene core, six repeating units OC6H4–CHNN(CH3)–P(S)< and twelve 4-oxyphenethylamidopyrazine end groups OC6H4–(CH2)2–NHCOC4N2H3 were registered. Analysis of the IR spectra of G1 shows that the amide groups form an intermolecular hydrogen bond. Optimization of the structure and analysis of normal vibrations were carried out for dendrimer G1 using the density functional theory (DFT). The six repeating units are arranged in a symmetric manner about the cyclophosphazene ring; each side of the ring contains three repeating units. It turned out that dendrimer G1 is a double bowl with almost flat repeating units which represent the concave surface and a core as a bottom of the bowl. The assignment of bands in the vibrational spectra was carried out by analyzing the distribution of the potential energy. Amide groups show bands at 3393, 1675cm−1 in the IR spectrum of G1. The line at 1577cm−1 in the Raman spectrum is characteristic of repeating units.

Reactions of alkyne- and butadiyne-derived fluorinated cyclophosphazenes with diiron and dimolybdenum carbonyls.

The reaction of (β-phenylethynyl)pentafluorocyclotriphosphazene, [(PhC≡C)(F)PN](PNF2)2, with Fe2(CO)9 in refluxing hexane resulted in five new compounds, namely, [Fe(CO)2{η(2):η(2)-2,4-(P3N3F5)2Ph2C4Fe(CO)3}-μ-CO] (1), [Fe(CO)2{η(2):η(2)-2,5-(P3N3F5)2Ph2C4Fe(CO)3}-μ-CO] (2), [Fe(CO)2{η(5)-2,5-(P3N3F5)2Ph2C4CO}C(Ph)═C(P3N3F5)](3), [Fe(CO)3{η(2):η(2)-2,4-(P3N3F5)2Ph2C4CO] (4), and [Fe(CO)3{η(2):η(2)-2,5-(P3N3F5)2Ph2C4CO] (5). While compounds 1, 2, 4, and 5 have five-membered ferracyclopentadiene or cyclopentadienone rings coordinated to the Fe(CO)3 unit in the η(2):η(2) mode, compound 3 has a 2,5-cyclopentadienone ring attached to an Fe(CO)2(P3N3F5)C═C(Ph) unit, where Fe is η(5)-bonded to the cyclopentadienone ring, and the carbon that is α to the phenyl unit of the Fe(CO)2(P3N3F5)C═C(Ph) group is σ-bonded to the oxygen atom of the cyclopentadienone ring. Formation of five-membered cyclic compounds having two fluorophosphazene units on the vicinal carbon atoms of C4R2R'2Y rings was not observed in this reaction. No examples of Fe(CO)3-bound cyclobutadiene complexes were also isolated from this reaction. A similar reaction in the presence of trimethylamine N-oxide, NMe3O, was found to proceed at -20 °C with the formation of compounds 4 and 5 only. In contrast to the Fe2(CO)9 reaction, a reaction of alkyne-derived pentafluorocyclotriphosphazenes, [(RC≡C)(F)PN](PNF2)2 [R = Ph, Fe(C5H5)2] with the molybdenum complex Cp(CO)3Mo-Mo(CO)3Cp (Cp = cyclopentadienyl) in refluxing toluene resulted in the simple tetrahedral clusters Cp(CO)2Mo(P3N3F5)C-C(Ph)Mo(CO)2Cp (6) and Cp(CO)2Mo(P3N3F5)C-C(Fc)Mo(CO)2Cp (7) (Fc = ferrocenyl). A similar reaction of Cp(CO)3Mo-Mo(CO)3Cp with butadiyne-derived fluorophosphazenes, [(RC≡C-C≡C)(F)PN](PNF2)2 [R = Ph, Fe(C5H5)2], yielded the tetrahedral clusters Cp(CO)2Mo(P3N3F5)C-C(C≡CPh)Mo(CO)2Cp (8) and Cp(CO)2Mo(P3N3F5)C-C(C≡CFc)Mo(CO)2Cp (9) with the tetrahedral Mo2C2 unit forming exclusively with the alkyne unit of the butadiyne group bound to the cyclophosphazene ring. The crystal structures and infrared spectral data of these molybdenum clusters showed the presence of a semibridging carbonyl on one of the molybdenum units. All new compounds were characterized by IR, NMR [(1)H, (13)C{(1)H}, (31)P{(1)H}, and (19)F{(1)H}] and high-resolution mass spectrometry studies. Compounds 2, 3, 5, and 7-9 were also structurally characterized using single-crystal X-ray diffraction studies.

Reduction reactions of alkyne and butadiyne derived fluorinated cyclophosphazenes

Alkyl derivatives of fluorinated cyclophosphazenes having phenyl or ferrocenyl units separated by two and four CH2 units from the cyclophosphazene ring are prepared by hydrogenation of the alkyne/butadiyne unit of the corresponding alkyne/dialkyne derived cyclic fluorophosphazenes. Hydrogenation of the ethynyl units in compounds [PhC≡C(F)PN](PNF2)2, [FcC≡C(F)PN](PNF2)2 and [(FcC≡C)2PN](PNF2)2 using Pd/C as catalyst resulted in compounds Ph(CH2)2P3N3F5 (1), Fc(CH2)2P3N3F5 (2) and [(FcCH2CH2)2PN](PNF2)2 (3) (Fc=ferrocenyl), respectively. Similar, hydrogenation reaction of the butadiynyl units in compounds [PhC≡C−C≡C(F)PN](PNF2)2, [FcC≡C−C≡C(F)PN](PNF2)2 and [(FcC≡C−C≡C)2PN](PNF2)2 using Pd/C as catalyst resulted in compounds Ph(CH2)4P3N3F5 (4), Fc(CH2)4P3N3F5 (5) and [{Fc(CH2)4}2PN](PNF2)2 (6), respectively. Hydrogenation of the butadiynyl and ethynyl units in the unsymmetrically substituted cyclophosphazene [(FcCC)(FcC≡C−C≡C)PN](F2PN)2 resulted in the alkyl derived cyclophosphazene [{Fc(CH2)4}{Fc(CH2)2}PN](F2PN)2 (7). Partial hydrogenation of [FcC≡C(F)PN](PNF2)2 using Lindlar catalyst resulted in the alkene derived cyclophosphazene [FcCHCH(F)PN](PNF2)2 (8) which was further reduced using Pd/C catalyst to give the alkyl derivative Fc(CH2)2P3N3F5 (2). An attempted hydrogenation of chlorinated phosphazene, [FcC≡C(Cl)PN](PNCl2)2 using Pd/C as catalyst resulted in compound [(FcCH2CH2)(OCH3)PN](PNCl2)2 (9) having methoxy substitution on the alkyl substituted phosphorus atom. All new compounds were characterized by IR, NMR [1H, 13C{1H}, 31P{1H}, and 19F{1H}] and HRMS studies. Compounds [FcC≡C(F)PN](PNF2)2 and 2 have also been structurally characterized.

Metalation studies of 3- and 4-pyridyloxycyclophosphazenes: metallamacrocycles to coordination polymers

Pyridyloxy cyclophosphazenes, spiro-N3P3(O2C12H8)(O-C5H4N-3)4 (L1), dispiro-N3P3(O2C12H8)2(O-C5H4N-3)2 (L2) and dispiro-N3P3(O2C12H8)2(O-C5H4N-4)2 (L3) were prepared and characterized. The crystal structure of L1 was determined which showed that the cyclophosphazene ring is planar. The reaction of L1 with anhydrous copper(II) chloride or silver nitrate afforded L2M4 metallamacrocycles [{L1}2{ClCu(μ-Cl)2CuCl}]2·8CHCl3 (3) and [{L1}2{(DMF)0.5(NO3)0.5Ag}2{Ag(μ2-(O)NO2)(H2O)}2]{μ-[NO3]}·CH3OH (4) respectively. The molecular structure of 3 reveals that two CuCl2 dimers are bridged to each other in a complex metallamacrocycle that involves four metal ions and two ligands. The molecular structure of 4 is similar to that of 3 except for the presence of weak argentophilic interactions between the two Ag(I) centers. Also, a nitrate anion, which is trapped in the centre of the tetrameric assembly, assists in holding two Ag(I) ions together and 4 serves as a single source precursor for silver nanoparticles. The reaction L1 with ZnCl2 and Cd(NO3)2·4H2O afforded the 1D-coordination polymers [{L1}{ZnCl2}2]n·2nCH3OH·2nH2O (5) and [{L1}2{Cd(CH3OH)2(NO3)2}2{Cd(NO3)2(H2O)}]n·3nCH3OH·3nH2O (6) respectively. While in 5 the 20-membered macrocycles are inter-connected directly, in 6 they are bridged by a Cd(II) connector. The reaction of L2 with CoCl2 afforded the 1D-coordination polymer [{L2}2{CoCl2}]n·2nCHCl3 (7) which also contains interconnected 20-membered metallamacrocycles. On the other hand, the reaction of L2 with CuCl2 afforded [{L2}2{ClCu(μ-Cl)}2]n·2nCHCl3·nH2O (8) which is a 1D-coordination polymer that contains {ClCu(μ-Cl)2CuCl} units. The reaction of L3 with CuCl2 and Cd(NO3)2·4H2O afforded [{L3}2{CuCl2}]n·nDMF (9) and [{L3}2{Cd(NO3)2}]n·nCHCl3·nCH2Cl2·nH2O (10) respectively. While 9 is a 2D-coordination polymer containing 48-membered metallamacrocycles, 10 is a 1D-coordination polymer containing interconnected 24-membered metallamacrocycles which possess spirocyclic cadmium ions as nodes.

Investigation of a spiro to ansa rearrangement with di-functional alcohols in cyclotriphosphazene derivatives

A spiro to ansa rearrangement has been investigated by the reactions of cyclotriphosphazene derivatives having five-membered spiro rings, N3P3Cl4[O(CH2)2NH], (1) and N3P3Cl4[O(CH2)2O], (2) with disodium salts of 1,3-propanediol and 2,2,3,3-tetrafluoro-1,4-butanediol. Compounds 1 and 2 with the strong nucleophile, 1,3-propapanediol, give rearrangement reactions to form stable ansa–ansa compounds, whereas reaction of compounds 1 and 2 with the fluorinated alkoxide results in normal nucleophilic substitution at the PCl2 groups and no rearrangement takes place with the weaker nucleophile. The synthesised compounds (3a, 3b, 4b, 5a–d, 6c and 6d), have been fully characterised by elemental and mass (MS) analysis, and by 1H and 31P NMR spectroscopy. Crystal structures of 3b, 4b, 5b–d and 6c have been characterised by X-ray crystallography. It is found that 1,3-propapanediol is a sufficiently strong nucleophile to cause a spiro to ansa rearrangement in the mono-spiro cyclotriphosphazenes compounds 1 and 2, even though crystallographic evidence shows that formation of the seven- and eight-membered ansa–ansa rings in compound 3b results in distortion and compression of the cyclophosphazene ring. A possible mechanism, which depends on attack of the anionic oxygen nucleophile at spiro-bearing phosphorus atom, was used to help understand the spiro-to-ansa rearrangement reaction.

Multiporphyrin Arrays on Cyclophosphazene Scaffolds: Synthesis and Studies

The stable and robust cyclotriphosphazene and cyclotetraphosphazene rings were used as scaffolds to prepare hexa- and octaporphyrin arrays by treating N(3)P(3)Cl(6) and N(4)P(4)Cl(8), respectively, with 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl)porphyrin (N(4) core) or with its thiaporphyrin analogues (N(3)S and N(2)S(2) cores) in THF in the presence of Cs(2)CO(3) under simple reaction conditions. Thiaporphyrins were examined in addition to the normal porphyrin to tune the electronic properties of the resultant arrays. Observation of the molecular ion peaks in the mass spectra confirmed the molecular structures of the arrays. 1D and 2D NMR techniques were employed to characterize the multiporphyrin arrays in detail. The (1)H NMR spectra of the multiporphyrin arrays each show a systematic set of signals, indicating that the porphyrin units are arranged in a symmetrical fashion around the cyclophosphazene rings. All signals in the (1)H NMR spectra were assigned with the aid of COSY and NOESY experiments. The protons of each porphyrin unit are subject to upfield and downfield shifts because of the ring-current effects of neighboring porphyrin units. Optical, electrochemical, and fluorescence studies of the arrays indicated that the porphyrin units retain their independent ground- and excited-state characteristics. Cu(II) and Ni(II) derivatives of hexaporphyrin and octaporphyrin arrays containing N(4) porphyrin units and N(3)S porphyrin units were synthesized, and complete metalation of the arrays was confirmed by their mass spectra and by detailed NMR characterization of the Ni(II) derivatives of hexa- and octaporphyrin arrays containing N(4) porphyrin units. Electrochemical studies indicated that Cu(II) and Ni(II) ions present in the thiaporphyrin units of the arrays can be stabilized in the +1 oxidation state, which is not possible with arrays containing normal porphyrin units.

Complexes of silver(i) ions with tetrapyrrolidinyl- and tetramorpholinyl-PNP-lariat ethers in acetonitrile and methanol solutions

This work concerns the investigation of stability constants of silver(I) ions with the tetrapyrrolidinyl-PNP-lariat ether L1 in acetonitrile solution and tetramorpholinyl-PNP-lariat ether L2 in acetonitrile and methanol solutions. The new tetramorpholinyl-PNP-lariat ether L2 was synthesized on the basis of the procedure described in a previous publication. Stability constants of complexes with silver ions were determined using a simple potentiometric titration. Furthermore, NMR spectra were obtained to investigate how the complexation of silver(I) ions by the investigated macrocyclic ligand occurs. Spectrometric data analyses and potentiometric measurements indicate that complexation of Ag+ involves participation of the endocyclic nitrogen atom of the cyclophosphazene ring and polyether oxygen donors. As regards L1 the stability of the obtained complex is influenced by pyrrolidinyl groups. On the other hand, L2 includes the morpholinyl subunits attached to the exocyclic P atom, having in their structure the oxygen atom, which pulls out the electrons of the cyclophosphazene ring and thereby destabilizes the formation of a coordination system.

ChemInform Abstract: Crystal and Molecular Structures of the First trans-Macro-Ansa Monocyclophosphazene Macrocycle, trans-N3P3Cl4 (HN-(CH2)3-O-(CH2)6-O-( CH2)3-NH)

Abstract The reaction of N3P3Cl6 with 4,11-dioxatetradecane-1,14-diamine (designated 3O6O3) in a heterogeneous medium (interface process) of toluene and saturated aqueous Na2CO3 leads stereoselectively to a trans monocyclophosphazene 19-crown-ether species (trans MACRO-ANSA 3O6O3) which crystallizes in the monoclinic system, P21/n a=8.539(2), b=8.997(3), c=30.123(4) A, β=91.65(2)°, V=2313(2) A3, Z=4, Dx=1.456 Mg m−3, R=0.054 for 2826 unique reflections and 236 variable parameters. The structure exhibits a spatial arrangement with one [HN-(CH2)3-O-(CH2)6-O-(CH2)3-NH] as an arch, grafted in a trans configuration onto two different phosphorus atoms (trans non-gem disubstitution) of one N3P3Cl4 moiety. This fortuitously discovered trans-19-crown-ether-shaped macrocyclic structure defies the well-established description of the electronic structure of six-membered cyclophosphazene rings.

X-ray crystal structures and DFT calculations of differently charged aminocyclophosphazenes

Molecular structures of hexakis(amino)cyclotriphosphazene, N 3P 3(NH 2) 6, neutral and cationic forms of hexakis(ethylamino)cyclotriphosphazene, N 3P 3(NHC 2H 5) 6, and dicationic form of octakis(ethylamino)cyclotetraphosphazene, N 4P 4(NHC 2H 5) 8, were established through the X-ray diffraction experiments at 120(2), 165(2) and 110(2) K, respectively. Geometry of the six- and eight-membered cyclophosphazene rings of the molecules are discussed with the help of B3LYP/6-311G ∗∗ method/basis DFT calculations of their methylamino analogs and topological analysis of the electron density distribution. In all cases P–N bonds show high polar nature with considerable P → N charge transfer. Change of the P–N bond lengths upon the cycle protonation well correlated with the net charge redistribution at the P and N centers but separately for the endocyclic and exocyclic bonds. Presence of the additional π-bonding covalent contribution, as it is evidenced from the analysis of the bonds ellipticity, has to be suggested to explain these separate correlations. In the cyclotriphosphazene cation the finer details of the endocyclic P–N bond lengths changes can be attributed to the interplay of the variable π-bonding contribution with the change in the bond ionicity. In the crystal all compounds demonstrate large variety of bridged hydrogen bond patterns though the N–H…N and N–H…Cl interactions.

New Approaches to Hybrid Polymers that Contain Phosphazene Rings

New methods are described for the incorporation of cyclophosphazene rings into macromolecules. These include polynorbornenes with cyclophosphazene side units produced by ROMP reactions, polystyrenes linked to phosphazene rings by azide coupling processes, and cyclolinear polymers by ADMET and Heck coupling reactions. These last species are wavelength-emission tailored electroluminescent materials.

Oxazoline-Containing Phosphazene Derivatives Part II Polymer Preparation and Modification Through the Reactivity of Oxazoline Moieties on Cyclophosphazenes

In this paper we report the synthesis, the characterization and the practical utilization of two cyclophosphazenes (CPs) substituted with two (C-2-OXA) and six (C-6-OXA) 2-(4-hydroxyphenyl)-2-oxazoline groups, respectively. The first chemical observation on these substrates is that the reactivity of the oxazoline groups is preserved even when these products are attached to the phosphorus atoms of a cyclophosphazene ring. By reaction of C-2-OXA with organic molecules, e.g. adipic acid, and macromolecules, e.g. poly(ethylene terephthalate) (PET), the oxazoline substituents open their heterocycles to form cyclolinear polymers or to act as chain extenders. Similarly, the ring-opening polymerization reaction of C-6-OXA in the presence of cationic initiators allows the production of a new class of cyclomatrix polymers. The characterization of the new materials is reported.

Conformational Flexibility in 2,2‘-Dioxybiphenyl-chloro-cyclotetraphosphazenes and its Relevance to Polyphosphazene Analogues

The reaction of the cyclotetraphosphazene, [N4P4Cl8], with the difunctional reagent, 2,2'-biphenol, in the presence of potassium carbonate in acetone produced the spiro-substituted derivatives, 2,2'-dioxybiphenylhexachlorocyclotetraphosphazene, bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene, and tris(2,2'-dioxybiphenyl)dichlorocyclotetraphosphazene. Both cis and trans geometrical isomers of the bis compound are observed. Although chromatographic separation of these was unsuccessful, a sample of the trans isomer was obtained by fractional crystallization. The compounds all show non-first-order 31P NMR spectra which were simulated to extract the spectral parameters. Single-crystal X-ray structures of both the trans bis and the tris compounds show that the cyclophosphazene rings exhibit conformational flexibility which gives rise to different crystalline forms being obtained from the same solvent systems. Crystals of trans-bis(2,2'-dioxybiphenyl)tetrachloro-cyclotetraphosphazene were obtained in two different space groups: Pnna (orthorhombic) and P21/n (monoclinic). In the orthorhombic structure, the dominant (72%) conformation of one phosphazene ring is a chair form, and the other (28%) resembles a boat. While for the monoclinic structure, the ring is virtually flat with an oval shape. In both cases the dioxybiphenyl groups are found in R and S configurations in the same molecule and are pi stacked in columns (Pnna) or involved in pi-pi or pi-H interactions (P21/n), thus anchoring the phosphorus atoms of the cyclotetraphosphazenes but still allowing flexibility in the ring conformations. Three crystalline modifications of tris(2,2'-dioxybiphenyl)dichloro-cyclotetraphosphazene were obtained: two in space group P (triclinic), which contained two molecules of dichloromethane in the unit cell, and one solvent-free form in space group P21/n (monoclinic). The cyclophosphazene rings exhibit puckered conformations with the trans-dioxybiphenyl moieties having opposing RS or SR conformations. DFT calculations were carried out on each of the phosphazene ring conformations in trans-bis(2,2'-dioxybiphenyl)tetrachlorocyclotetraphosphazene identified from the X-ray diffraction analysis. It is concluded that intermolecular interactions (i.e., pi-pi or pi-H) between the dioxybiphenyl groups is a factor that modifies the nature of the potential energy surface between the different conformers. The flexibility of the phosphazene ring is supported computationally through the calculated low-energy barriers and experimentally through the highly disordered phosphazene ring conformations observed in the solid state. The results on 2,2'-dioxybiphenyl-substituted cyclotetraphosphazenes provide evidence that microcrystalline domains in their 2,2'-dioxybiphenyl-substituted polyphosphazene analogues will be generated by similar pi-pi and pi-H interactions.

Surface functionalization with phosphazene substrates, Part IV: Silica and Si(100) surface functionalization using cyclophosphazenes partially substituted with trialkoxysilane derivatives and PEG-750 monomethylether, 2,2,3,3-tetrafluoropropanol and 4-hydroxyazobenzene

This paper deals with the possibility of functionalizing the surface of silicon-based materials by exploiting cyclophosphazenes containing suitable substituent groups. Thus, phosphazene trimers were prepared, containing about 50% of the reactive sites substituted by γ-aminopropyltriethoxy silane (APTES), while the residual positions in the cycle contain poly(ethylene glycol) monomethylether (MW approx. 750; PEG-750-ME), tetrafluoropropanol (TFP) and 4-hydroxyazobenzene (AzB). Using these novel materials we succeeded in surface functionalizing SiO2 beads in the coating of silicon wafers or sodalime slides and in the preparation of cyclophosphazene-based monoliths in the presence of hydrolyzed TEOS by sol–gel technique. The whole series of products has been characterized by standard spectroscopic (IR, UV-Vis, 1H-, 13C-, 29Si- and 31P-NMR, both in solution and in solid state) and thermal (DSC and DMTA) techniques. This approach to the surface functionalization of silicon-based materials containing carefully selected substituents is completely general and can be used to attach to the hydroxylated surfaces practically any type of nucleophile that can be supported on the cyclophosphazene ring.

Stereogenic properties of spiranes combined with four equivalent conventional centres of chirality

Derivatives of the tri-spirane pentaerythritoxy-cyclophosphazene compound, 1, have been used to investigate the stereogenic properties of spiranes combined with four equivalent conventional centres of chirality. In compound 1 the two inner rings are carbocyclic and symmetrical and the two outer rings are cyclotriphosphazenes substituted in different positions to provide the conventional centres of chirality. The case of combining spiranes with four equivalent centres of chirality has been investigated by the reaction of 1 with dimethylamine in a 1 : 8 molar ratio to give four diastereoisomeric products, in which the two cyclophosphazene rings are non-geminally di-substituted in either cis or trans configurations; viz. the cis-cis (2a), cis-trans (2b) and two trans-trans substituted dimethylamine derivatives 2c and 2d. The structure and stereogenic properties of compound 2a (C2 symmetry) have been characterized previously by both X-ray crystallography and 31P NMR spectroscopy on addition of a chiral solvating agent (CSA) and the structures and stereogenic properties of compounds 2b (C1) and 2d (C2) have been similarly characterized in this work. The structure of compound 2c has been characterised by X-ray crystallography and found to be meso with the relatively rare S4 symmetry. The four diastereoisomeric products 2a-2d represent all the possible stereochemical isomers of a spirane combined with four equivalent conventional centres of chirality.

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.

Di- and Trinuclear Complexes Derived from Hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P−O Bond Cleavage in the Formation of [{(L‘CuCl)2(Co(NO3)}Cl] (L‘ = N3P3(OC5H4N)5(O))

Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl3)], [L(CuCl)(ZnCl3)], [L(CoCl)(ZnCl3)], and [L(ZnCl2)2]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a eta5-gem-N5 mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an eta(1)-N(1) fashion. In the homobimetallic derivative, [L(ZnCl2)2], one of the zinc ions is five-coordinate (eta3-nongem-N3), while the other zinc ion is tetracoordinate(eta2-gem-N2). The reaction of L with CuCl2 followed by Co(NO3)2.6H2O yields a trinuclear heterobimetallic complex [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens).

Divalent cobalt, nickel and zinc halide complexes with multimodal ligands based on the cyclotriphosphazene platform: A structural study

The reaction of hexakis(2-pyridyloxy)cyclotriphosphazene (L) and hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene (MeL) with the dihalides of cobalt(II), nickel(II) and zinc(II) afford the complexes [CoLX 2], [Co(MeL)X 2], [(CoLX)CoX 3], [{Co(MeL)X}CoX 3], [CoLX]PF 6 (X = Cl or Br), [NiLCl]PF 6, [NiLCl 2] (a green and a red isomer) and [(ZnCl 2) 2L]. Single crystal X-ray structures on a selection of the complexes show that L and MeL are versatile multimodal ligands, which exhibit a variety of coordination modes. [Co(MeL)Br 2] and the red isomer of [NiLCl 2] have the metal atom in a distorted trigonal bipyramidal environment ( τ = 0.83 and 0.78, respectively) with the ligand acting as a κ 3 N donor coordinating via the nitrogen atoms from two non-geminal pyridyloxy pendant arms, a nitrogen atom in the phosphazene ring and two halide ions. For the cobalt complex the pyridyloxy groups are cisoid and for the nickel complex they are transoid. The dimetallic complexes, [{Co(MeL)X}CoX 3] (X = Cl or Br) are zwitterionic with one cobalt atom in a rhombic coordination sphere with the ligand acting as κ 5 N donor binding to the metal through the nitrogen atoms of four pyridyloxy pendant arms, phosphazene nitrogen atom and a halide ion. The second cobalt atom is in a distorted tetrahedral site with the ligand acting as a κ 1 N donor via one pyridyloxy nitrogen, the remaining ligands being three halide ions. The dimetallic zinc complex, [(ZnCl 2) 2L], contains two ZnCl 2 units in distorted trigonal bipyramidal ( τ = 0.82) and tetrahedral coordination environments. In the five-coordinate site, L acts in a κ 3 N non-geminal transoid fashion as observed for the red nickel complex [NiLCl 2]. In the other site, L acts as a κ 2 N geminal bidentate via two pyridyloxy arms, with two chloride ions completing the coordination sphere. The cationic cobalt complexes, [MLBr]PF 6 (M = Co or Ni) both contain the metal atom in a rhombic environment similar to that found in the dimetallic [{Co(MeL)X}CoX 3] species. The green isomer of [NiLCl 2] contains a six coordinate ‘NiN 4Cl 2’ distorted octahedral coordination sphere with L behaving as a κ 4 N donor via the nitrogen atoms from three pyridyloxy pendant arms and one nitrogen in the cyclophosphazene ring; two halide ions complete the coordination sphere. In all the complexes the phosphazene ring atoms remain virtually coplanar as a consequence of the flexibility of the phenoxy-hinge, which links the pyridine pendant donors to the cyclophosphazene platform. The formation of the resulting six-membered chelate rings enhances the binding of the phosphazene nitrogen to metal bond which, in each of the five- or six-coordinate metal binding sites, is always shorter than the pyridyloxy nitrogen to metal bonds [2.023(6)–2.1075(18) cf. 2.157(4)–2.397(3) Å].

Control of the conjugation length and solubility in electroluminescent polymers

AbstractA new type of cyclolinear polymer, poly(phenylene vinylene‐alt‐cyclotriphosphazene), was synthesized through Heck‐type coupling reactions to produce π‐conjugated macromolecules with excellent solubility and precise electronic control of the band‐gap energy. This synthesis method is capable of producing well‐defined alternating polymers. The method is highly adaptable and can be readily used for other chromophore systems. The resulting polymers were also capable of accommodating a wide variety of substituents on the cyclophosphazene rings with minimal effect on the electronic properties. The band gap and electron affinities of the polymer were varied through the manipulation of the π‐conjugated unit located between the insulating phosphazene rings. Each chromophore matched the intended conjugation length consistently throughout the macromolecules. The polymers were good film formers because of the chosen substituents on the phosphazene rings. The absorbance of the polymers indicated minimal spectral shift from the monomer absorbance. This suggested an effective insulation of each chromophore unit from its neighbors by the phosphazene rings. Solution photoluminescence efficiencies were found to be up to 44.1%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 69–76, 2006

Stereoisomerism in Pentaerythritol‐Bridged Cyclotriphosphazene Tri‐Spiranes: Spiro and Ansa 1,3‐Propanediyldioxy Disubstituted Derivatives

AbstractIn each spirane structure in Figure 1 on p. 1043 of the original article[1] the spiro atom of the left‐hand cyclophosphazene ring should be phosphorus rather than nitrogen; the correct Figure 1 is shown below.