Mixed-Substituent Cyclophosphazenes with Calamitic and

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Mixed-Substituent Cyclophosphazenes with Calamitic and Polycatenar Mesogens J. Jiménez,*,† L. Callizo,† J. L. Serrano,‡ J. Barberá,§ and L. Oriol§ †

Departamento de Química Inorgánica, Facultad de Ciencias - Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-C.S.I.C., Pedro Cerbuna 12, 50009 Zaragoza, Spain ‡ Departamento de Química Orgánica, Facultad de Ciencias - Instituto Universitario de Nanociencia de Aragón, Universidad de Zaragoza, Mariano Esquillor Edif. I+D, 50018 Zaragoza, Spain § Departamento de Química Orgánica, Facultad de Ciencias - Instituto de Ciencia de Materiales de Aragón (ICMA), Universidad de Zaragoza-C.S.I.C., Pedro Cerbuna 12, 50009 Zaragoza, Spain ABSTRACT: A synthetic strategy has been developed to prepare liquid crystalline cyclotriphosphazenes that have two different types of mesogenic units linked to the same phosphorus atom. Hexachlorocyclotriphosphazene, N3P3Cl6, was reacted with 3 mol of the calamitic unit 4-cyano-4′-hydroxybiphenyl to give a mixture of compounds in which the nongem-trans-trisubstituted derivative N3P3Cl3(OC6H4C6H4{CN}-p)3 was the major product. The substitution of all three chlorine atoms in this nongeminal compound gave rise to the hydroxyl-functional phosphazenes, nongem-trans-N3P3(OC6H4C6H4{CN}-p)3(OC6H4{OH}-p)3 or nongem-trans-N3P3(OC6H4C6H4{CH3}-p)3(OC6H4{OH}-p)3, from which the second mesogenic unit, a polycatenar one, was introduced. The chemical structure of the resulting materials, deduced from spectroscopic and MALDI-TOF techniques, was in accordance with monodisperse, fully functionalized cyclotriphosphazenes. Mesomorphism is highly dependent on the terminal group of the calamitic units, and liquid crystal phases were only detected on the cyano-derivatives. The calamitic or columnar nature of the mesophase depends on the number of alkyl chains of the polycatenar moieties.

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INTRODUCTION Phosphazenes, [NPR2], are an important type of inorganic compounds, whose properties can be tailored by the choice of appropriate side groups on phosphorus, R.1 They are usually prepared by nucleophilic substitution reactions that involve the use of halophosphazene cyclic trimers or high polymers as substrates for reactions with alkoxides, aryloxides or amines.1,2 In addition, with few restrictions, organic side groups incorporated into a phosphazene can themselves be modified by exposure to reagents that introduce additional functionality,3,4·as has been recently reviewed.5 Thus, single-substituent trimers or polymers with all the chloro atoms replaced by promesogenic units have been prepared in an effort to obtain liquid crystalline materials. In the case of polymers, only a few exploratory examples have been described so far and these incorporate calamitic promesogenic units (mainly azobenzene or biphenyl groups) with only a terminal group, which are separated from the skeleton by a flexible spacer.6 Cyclotriphosphazenes have also proved to be useful as a multi-armed central core upon which mesogenic units are linked to give supermolecular liquid crystals.7 In this regard, we have reported several series of these nonconventional liquid crystals having the promesogenic units directly attached to the inorganic ring.8 All of them are single-substituent trimers, which were synthesized from a six-armed cyclotriphosphazene core, N3P3(OC6H4OH-4)6 or N3P3(OC6H4{NH2}-4)6, by condensation of the peripheral hydroxyl or amine groups with mono- or © 2017 American Chemical Society

polycatenar benzoic acid derivatives. Their mesomorphic properties strongly depend on a suitable volume balance between the rigid core and the alkyl chains in the promesogenic group, which ranges from calamitic, discotic, to cubic mesomorphism when the number of terminal alkyl chains increases. Calamitic mesomorphism is promoted by monosubstituted units (e.g., having one terminal alkyl chain or monocatenar), and this behavior was explained in terms of the model shown in Figure 1a.8a,b,9 Columnar or cubic phases resulted from the incorporation of polycatenar units, which promote from a hexagonal columnar mesophase to a cubic mesophase upon increasing the number of chains in the periphery of the system. The columnar mesomorphism was explained in terms of the model shown in Figure 1b.8 Inherent in the nucleophilic substitution method to achieve functional cyclotriphosphazenes is the possibility that two or more different organic groups can be introduced in the same phosphazene ring or chain to give mixed-substituent trimers or polymers.1,2,3e,10 To the best of our knowledge, there are only three reports of liquid crystalline (LC) copolyphosphazenes, in which the second nucleophile is usually introduced to increase the solubility of the material,6b,11 and only one of them describes polyphosphazenes with two different calamitic units.11a However, no LC mixed-substituent cyclophosphazenes Received: March 14, 2017 Published: June 30, 2017 7907

DOI: 10.1021/acs.inorgchem.7b00612 Inorg. Chem. 2017, 56, 7907−7921

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Inorganic Chemistry

(nongeminal-cis-2,4,6) or with two toward one side and the third toward the other (nongeminal-trans-2,4,6). In this paper, we report the study of the reaction of N3P3Cl6 with 4-cyano-4′-hydroxybiphenyl, in a molar ratio of 1:3, in order to obtain the nongeminal trisubstituted derivatives purely (nongeminal-cis-2,4,6 and nongeminal-trans-2,4,6) to synthesize the first cyclophosphazenes with two different types of mesogenic units, one of them a typical calamitic 4cyanobiphenyl moiety and the other one a polycatenar moiety (Scheme 1). The thermal and mesomorphic properties of this new series of cyclophosphazenes are also reported here in an effort to continue the exploration of these nonconventional structures. Our aim was to study how the incorporation of columnar-promoting polycatenar moieties competes with the tendency of the calamitic ones, as 4-cyano-4′-hydroxybiphenyl, to favor a rodlike structure in cyclotriphosphazenes.

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Figure 1. Schematic models for: (a) the calamitic structure of cyclophosphazenes with monocatenar moieties, which point upward and downward with respect to the cyclotriphosphazene ring; (b) the star-shaped structure of cyclophosphazenes with polycatenar moieties, which arrange themselves parallel to the cyclotriphosphazene ring (represented as a black circle) in two levels (mesogens in the upper level indicated with a darker color and in lower level with a lighter color).

RESULTS AND DISCUSSION Reaction of N3P3Cl6 with 3 mol of 4-{NC}C6H4C6H4{OH}-4′. Synthesis and Spectroscopic Characterization of nongem-cis-N3P3Cl3(OC6H4C6H4{CN}-4)3 (1) and nongem-trans-N3P3Cl3(OC6H4C6H4{CN}-4)3 (2). The reaction of N3P3Cl6 with 4-cyano-4′-hydroxybiphenyl, in a molar ratio of 1:3, in the presence of K2CO3 at room temperature in acetone led to a mixture of compounds, in which the nongeminal-transtrisubstituted derivative 2 was the major product as was deduced by NMR (see Chart 1, collecting the three trisubstituted isomers). In fact, the NMR spectroscopy is one of the most powerful tools for the structural characterization of cyclophosphazenes, since the most critical structural information is available from the chemical shifts and spin−spin coupling data of their 31P{1H} NMR spectra.2d,13 Figure 2 shows the 31P{1H} NMR spectrum of the reaction mixture (after removing the ionic solids). Thus, compounds observed in this reaction mixture were identified due to the position and multiplicity of the signals, which are similar to other phenoxycyclotriphosphazenes,13 and are collected in Table 1. Compounds 1 and 2 could be isolated and then clearly characterized, as indicated below, which was also helpful to identify the products observed in the reaction mixture. The percentage of compounds in the mixture was calculated by integration of the signals in the 31P{1H} NMR spectrum.

are known so far. This prompted us to try obtaining cyclophosphazenes with two different types of mesogens and the study of their mesomorphic properties. In this regard, the substitution reaction of hexachlorocyclotriphosphazene has been extensively studied with primary interest in the regioand stereochemical pathways.2d,12 In particular, the partial substitution of hexachlorocyclotriphosphazene usually results not only in stoichiometrically different products but also in various geometrical and positional isomers that are not easy to separate from the isomeric mixture. Thus, reactions leading to the trisubstituted material, N3P3Cl3X3, usually result not only in the formation of trisubstituted regioisomers, i.e., 2,2,4- and 2,4,6- (numbering starts at the nitrogen atom), which are also referred to as geminal and nongeminal isomers, respectively, but also in di- and tetrasubstituted derivatives as minor products. Besides, the nongeminal materials can exist in two stereoisomeric forms with the three substituents toward the same side about the average plane of the phosphazene ring Scheme 1

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Figure 2. 31P{ 1H} NMR spectrum of the reaction mixture of N3P3Cl6 with 3 mol of 4-{CN}C6H4C6H4{OH}-4′ in the presence of K2CO3. (As in the case of tris-nongeminal derivatives, the bis- and tetra-nongeminal ones can also exist in two stereoisomeric forms with side groups being disposed in a cis or trans fashion about the average plane of the phosphazene ring).

Table 1. Compounds Detected by 31P{1H} NMR Spectroscopy in the Reaction Mixture of N3P3Cl6 with 3 mol of 4{CN}C6H4C6H4{OH}-4′ in the Presence of K2CO3b compound 2,4-N3P3Cl4(OR)2 (nongeminal) 2,4,6-cis-N3P3Cl3(OR)3 (nongeminal) (1) 2,4,6-trans-N3P3Cl3(OR)3 (nongeminal) (2) 2,2,4-N3P3Cl3(OR)3 (geminal) 2,4-N3P3Cl2(OR)4 (nongeminal)

%a

δ[PCl2]

spin system

δ[PCl(OR)]

δ[P(OR)2]

2

5 15 42

AB2 (cis or trans) A3 AB2

24.84 (“t”) (A), JAB = 64.6 Hz 15.21 (“d”) (B) 17.72 (s) δA: 18.23, δB: 17.98, 2JAB = 72.9 Hz

25 13

ABC AB2 (cis or trans)

26.18 (“t”) (A)

17.03 (“dd”) (B) 19.90 (“d”) (B), 2JAB = 80.6 Hz

2.05 (“dd”) (C) 4.66 (“t”) (A)

a

Calculated by integration of the signals in the 31P{1H} NMR spectrum of the reaction mixture. The yields for isolated compounds 1 and 2 were 0.4% and 15%, respectively. bData in CDCl3, values in ppm.

chromatography techniques, despite having similar rate factors (see the Experimental Section), and were characterized by elemental analysis, IR, 1H and 31P NMR spectroscopy, and MALDI-TOF mass spectrometry. All these data are given in the Experimental Section and are consistent with the formulas and structure indicated. MALDI-TOF mass spectrometry of both compounds 1 and 2, in dithranol as matrix, showed the peak at the expected molecular mass plus one proton (see Figure 3 for compound 2). No peaks corresponding to other derivatives were detected. The 1H and 31P NMR spectra have a particular relevance because they allow distinguishing both stereoisomers clearly. The 31P{1H} NMR spectra consisted of a singlet for 1 and an AB2 pattern for 2 with signals at similar positions to those observed for other nongeminal-trisphenoxy-derivatives

In accordance with the detected products, the regioselectivity in N3P3Cl6 for the reaction under study is strongly nongeminal due to the steric demands of the reagent, which has also been observed for other bulky alkoxy or aryloxy substituents.2d,13a,b,14· Steric effects also lead to a predominance of trans-isomer formation, although the stereoselectivity in the substitution reaction of N3P3Cl6 with alkoxy flexible derivatives such as 2-(2-methoxyethoxy)ethanol (MEE) has been observed by Sohn et al. to be strongly dependent on the reaction temperature.15 By dissolving this mixture of the reaction (Figure 2) in dichloromethane at room temperature and cooling below 5 °C, compound 2 containing ca. 1% of 1 precipitated as a white solid. Then, both compounds 1 and 2 were carefully isolated by 7909


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Figure 3. MALDI-TOF mass spectrum of 2 (matrix: dithranol). See inset: experimental isotopic pattern (up) and theoretical isotopic pattern (down).

Figure 4. (a) 31P{1H} and (b) 1H NMR spectra of compound 1 in CDCl3.

Figure 5. (a) 31P{1H} and (b) 1H NMR spectra of compound 2 in CDCl3.

(see Figures 4 and 5, respectively).13 For 1, the 1H NMR spectrum showed that all cyanobiphenyl groups are equivalent (two AA′BB′ spin systems), in accordance with their cisdisposition. However, for 2, two types of cyanobiphenyl groups with a relative integration of 2:1 are observed (two pairs of AA′BB′ spin systems, relative integration 2:1, in the proton

spectrum), according to their trans- arrangement. See Figures 4 and 5. Synthesis and Structural Characterization of MixedSubstituent Cyclotriphosphazenes with Two Different Types of Mesogenic Units. Once isolated, nongem-transN3P3Cl3(OC6H4C6H4{CN}-4)3 (2) was used for the synthesis of the phosphazene trimers 6−11 as it is shown in Scheme 2. 7910


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Figure 6. (a) 31P{1H} and (b) 1H NMR spectra of compound 4 in (CD3)2CO.

Compound nongem-trans-N3P3Cl3(OC6H4C6H4{CN}-p)3 (2) was reacted with excess 4-benzyloxyphenol in the presence of Cs2CO3 in acetone to yield 3. The 4-benzyloxyphenoxy units of 3 were converted to 4-hydroxyphenoxy groups with cyclohexene in a mixture of THF/ethanol, in the presence of Pd(OH)2 as a catalyst, to give 4 after heating under reflux for 2 h. Nevertheless, the repetition of the latter reaction under

similar conditions but using a different batch of the same catalyst, Pd(OH)2, produced the removal of the benzyl protecting groups and, the transformation of the cyano into methyl groups, yielding compound 5. In the first case, in which 4 was obtained, the complete deprotection of all groups benzylether required approximately 2 h at reflux, whereas, in the second case, in which 5 was obtained, complete 7911


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Inorganic Chemistry Table 2. 1H NMR Spectroscopic Data for Cyanobiphenyl Series 6−8a δ (Ar-H)

compound R= OC12H25 (6)

R= OC10H21 (7)

R = OCH2C6H2[3,4,5-(OC10H21)3] (8)

a

δ (OCH2)[3JH‑H(Hz)]

7.66−7.54 (m, 12H; C6H4CN) 7.52 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4)

4.13 (“t”, 2H) [6.4] 4.06 (“t”, 4H) [6.4]

7.44 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4) 7.36 (s, 2H; C6H2) 7.33 (s, 4H; C6H2) 7.13−7.01 (m, 18H; 6H OC6H4 + 12H OC6H4O) 7.66−7.55 (m, 12H; C6H4CN) 7.52 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4)

4.04 (“t”, 4H) [6.4] 3.99 (“t”, 8H) [6.4]

δ (CH2CH3) 1.81 (m, 18H) 1.48−1.26 (m, 162H) 0.88 (m, 27H)

4.10 (“t”, 2H) [6.4] 4.06 (“t”, 4H) [6.4]

1.81 (m, 18H) 1.48−1.27 (m, 126H) 0.87 (m, 27H)

7.44 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4) 7.36 (s, 2H; C6H2) 7.33 (s, 4H; C6H2) 7.13−7.01 (m, 18H; 6H OC6H4 + 12H OC6H4O) 7.60−7.40 (m, 24H; 12H C6H4CN + 6H OC6H4 + 6H C(O)C6H2) 7.21−6.89 (m, 18H; 6H OC6H4 + 12H OC6H4O)

5.14 (s, 2H; OCH2C6H2) 5.07 (s, 8H; OCH2C6H2)

6.67 (s, 4H; OCH2C6H2) 6.64 (s, 10H; OCH2C6H2) 6.61 (s, 4H; OCH2C6H2)

5.03 (s, 8H; OCH2C6H2) 3.94−3.83 (m, 36H; OCH2C) 3.79−3.73 (m, 18H; OCH2C)

4.04 (“t”, 4H) [6.4] 3.99 (“t”, 8H) [6.4]

1.71 (m, 54H) 1.46−1.26 (m, 372H) 0.87 (m, 81H)

Data using CDCl3 as solvent. All data in ppm.

Table 3. 1H NMR Spectroscopic Data for Methylbiphenyl Series 9−11a δ (Ar-H)

compound R = OC12H25 (9)

R = OC10H21 (10)

R = OCH2C6H2[3,4,5-(OC10H21)3] (11)

3

7.49 (“d”, 2H, JH‑H = 8.8 Hz; C6H4CH3) 7.43 (“d”, 2H, 3JH‑H = 8.1 Hz; OC6H4)

δ (OCH2)

δ (CH2CH3)

2.33 (s, 6H)

4.10−3.97 (m, 18H)

1.80 (m, 18H) 1.49−1.27 (m, 162H) 0.88 (m, 27H)

7.39 (“d”, 4H, 3JH‑H = 8.8 Hz; C6H4CH3) 7.36 (s, 2H; C6H2) 7.35 (s, 4H; C6H2) 7.35 (“d”, 4H, 3JH‑H = 8.1 Hz; OC6H4) 7.12−7.06 (m, 18H; 6H C6H4CH3 + 12H OC6H4O) 7.00−6.96 (m, 6H; OC6H4) 7.48 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CH3) 7.43 (“d”, 2H, 3JH‑H = 8.0 Hz; OC6H4)

2.33 (s, 6H) 2.29 (s, 3H)

4.09−3.95 (m, 18H)

7.38 (“d”, 4H; 3JH‑H = 8.4 Hz; C6H4CH3) 7.36 (s, 2H; C6H2) 7.35 (s, 4H; C6H2) 7.34 (“d”, 4H, 3JH‑H = 8.0 Hz; OC6H4) 7.13−7.05 (m, 18H; 6H C6H4CH3 + 12H OC6H4O) 7.00−6.96 (m, 6H; OC6H4) 7.53 (s, 4H; C6H2) 7.52 (s, 2H; C6H2)

1.80 (m, 18H) 1.48−1.27 (m, 126H) 0.88 (m, 27H)

2.28 (s, 6H) 2.25 (s, 3H)

5.09 (s, 2H) 5.05 (s, 4H)

1.72 (m, 54H) 1.46−1.26 (m, 378H) 0.88 (m, 81H)

7.51 (“d”, 2H, 3JH‑H = 8.6 Hz; C6H4CH3) 7.44 (“d”, 2H, 3JH‑H = 8.0 Hz; OC6H4) 7.37 (“d”, 4H, 3JH‑H = 8.6 Hz; C6H4CH3) 7.33 (“d”, 4H, 3JH‑H = 8.0 Hz; OC6H4) 7.22−6.93 (m, 18H; 6H C6H4CH3 + 6H OC6H4 + 12H OC6H4O) 6.63 (s, 12H; OCH2C6H2) 6.60 (s, 6H; OCH2C6H2) a

δ (CH3)

2.29 (s, 3H)

5.03 (s, 8H) 5.01 (s, 4H) 3.93−3.84 (m, 36H) 3.78−3.73 (m, 18H)

Data using CDCl3 as solvent. All data in ppm.

needed to monitor the complete removal of the benzyl protective groups in the reaction leading to compound 4, and also the complete transformation of the cyano into methyl groups in the reaction leading to compound 5. After purification, 4 and 5 were obtained in high yields, 79% and 93%, respectively, and characterized by IR, 1H and 31P{1H} NMR spectroscopy, mass spectrometry (MALDI-TOF techni-

deprotection and conversion of some cyano groups was already detected after refluxing for 1 h. The complete transformation of the cyano groups to give 5 required, however, between 3 and 6 h under reflux. The synthesis of 4 and 5 strongly depends on the activity of the catalyst and the experimental conditions of the reaction. Both reactions were easily monitored by using 1H NMR spectroscopy with (CD3)2CO as the solvent, which was 7912


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methyl protons of the biphenyl groups, are also observed, which clearly confirms the nongeminal-trans nature of all of these compounds. The 1H NMR spectrum of 9 is shown in Figure 7, as an example to make the data in Tables 2 and 3 clearer.

ques), and elemental analysis (see the Experimental Section). The 31P{1H} and 1H NMR spectra of all three compounds 3−5 provided evidence that all of them are nongeminal-trans, like the starting product 2. Thus, the expanded part of the 31P{1H} NMR spectra showed a multiplet due to a spin system AB2. Besides, the 1H spectra showed the signals corresponding to two types of biphenyl and two types of phenyl with a relative integration of 2:1. All of these data are summarized in the Experimental Section. 31P{1H} and 1H NMR spectra for compound 4 are shown in Figure 6, as an example. For 3 and 5, these spectra are very similar to those of 4. The proton spectrum in CDCl3 for 5 also shows resonances for methyl protons at 2.38 (s, 3H; CH3) and 2.39 ppm (s, 6H; CH3), and for 3, it contains resonances corresponding to benzyloxy protons at 4.95 (s, 2H; OCH2), 5.01 (s, 4H; OCH2), and 7.4− 7.3 (m, 15H; C6H5), which were replaced by signals due to OH protons after conversion to 4 (at 8.45 (s, 2H) and 8.39 (s, 1H) ppm) or 5 (at 8.41 (br, 3H) ppm). The cyano stretching peak in the IR spectra of 3 and 4 was observed at around 2225 cm−1, which was not detected in the spectrum of 5. The hydroxyl stretching peak for 4 and 5 appeared at ca. 3300 cm−1 in their IR spectra. MALDI-TOF mass spectrometry was carried out with dithranol as matrix and showed the peak for the expected molecular mass in all compounds 3−5. Treatment of 4 or 5 with an excess of the corresponding carboxylic acid (1.3 mol per mol of OH), in the presence of N,N′-dicyclohexylcarbodiimide (DCC, 1.1 mol per mol of acid) and 4-(dimethylamino)pyridinium 4-toluenesulfonate (DPTS) in dichloromethane, led to compounds 6−8 or 9−11, respectively (Scheme 2), by following a similar method to the one used previously to prepare liquid crystals by direct esterification of the N3P3(OC6H4OH-4)6 with promesogenic acids.8c These reactions were also monitored by 1H, 31P{1H} NMR spectroscopy to check that complete esterification of the hydroxyl groups of the starting cyclophosphazene took place. Thus, after approximately 2 days at room temperature, the appearance of a pseudosinglet in the 31P{1H} NMR spectrum indicated complete esterification. After purification, all cyclophosphazenes (6−11) were characterized by elemental analysis, IR, 1H, and 31P{1H} NMR spectroscopy, and MALDI-TOF mass spectrometry. All of these data are also provided in the Experimental Section and confirm the expected structure, all of them having the nongeminal-trans disposition, like in the starting products. The IR spectra of all of these compounds feature peaks at around 1162−1194 cm−1 (br) (PN) 16 (due to the phosphazene ring). Characteristic absorptions of methylene groups and aryl rings, and carbonyl stretching peak (at around 1722−1733 cm−1) were also observed. For compounds 6−8, the cyano stretching peak was also detected at ca. 2225 cm−1. 31 1 P{ H} NMR spectra consist of a multiplet (practically a pseudosinglet) for all phosphazenes 6−11 at around 9 ppm (in CDCl3), and the 1H NMR spectra also show the expected resonances for the formulas indicated and the nongeminal-trans stereochemistry. Accordingly, these spectra are complex, especially in the area of the aromatic protons. The signals were assigned by comparison with those of the starting cyclophosphazenes, the corresponding carboxylic acids,17 and with those observed for other similar compounds.6e,8 They are collected in Table 2 for the 4-cyanobiphenyl series and Table 3 for the 4-methylbiphenyl one and in the Experimental Section. In the case of 9−11 (4-methylbiphenyl series), two singlets at around 2.30 ppm of relative intensity 2:1, corresponding to the

Figure 7. 1H NMR spectrum of compound 9 in CDCl3.

MALDI-TOF mass spectrometry of all compounds 6−11, in dithranol as matrix, showed the peak at the expected molecular mass (see Figure 8 as an example). No peaks corresponding to the derivatives having incomplete condensation were detected, which was in accordance with the spectroscopic results. Thermal and Mesomorphic Properties. The thermal properties of the synthesized cyclotriphosphazenes were first studied by polarized optical microscopy and DSC to detect the presence of mesomorphism in these materials and characterize the phase transition temperatures. In fact, the structure of these cyclotriphosphazenes is unusual as it combines in the same molecule calamitic moieties with polycatenar ones. It has been widely reported that calamitic moieties, as 4-cyanobiphenyl, as single substituent directly linked to the cyclotriphosphazene ring compel the multi-armed molecules to adopt a rodlike structure and consequently tend to exibit calamitic (i.e., nematic or smectic) mesomorphism. However, polycatenar units favor to adopt a star-shaped conformation and stacking into columns or, if the number of terminal chains is quite high, cubic phases. Table 4 collects transition temperatures and enthalpies of the synthesized, mixed-substituent cyclotriphosphazenes as were detected by DSC on cooling from the isotropic liquid phase. Once the thermal history of the samples was homogeneous by heating them until isotropic liquid phase, the DSC curves of these samples were reproducible (Table 4 also gathers the transitions detected on second heating). The thermal behavior of these samples strongly depends on the terminal group (cyano or methyl) located at the biphenyl calamitic unit, and also on the number of alkyl chains of the polycatenar moieties. In fact, all the compounds are crystalline (or semicrystalline) as prepared, but once heated above isotropization and cooled, crystallization is hindered by the presence of the polycatenar moieties and all of them give rise to glassy materials upon cooling from the isotropic state. As mentioned above, the presence of the polar cyano group seems to play a key role in the stabilization of the anisotropic interactions of the cyclotriphosphazenes that favor a liquid crystalline state. Thus, on cooling from the isotropic state, both compounds 6 and 7, which have a very similar structure and 7913


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Figure 8. MALDI-TOF mass spectrum of 6 (matrix: dithranol). See inset: experimental isotopic pattern (up) and theoretical isotopic pattern (down).

Table 4. Phase Transitions Detected by DSC (10°C/min) on First Cooling from the Isotropic Liquid and Second Heatinga,c compound 6 7 8 9 10 11

1st cooling I I I I I I

45 (3.2) SmA 8 g 59 (3.5) SmA 16 g 39 (2.9) Colh 7 g 6g 7g 11 g

2nd heating g g g g g g

b

19 27 14 13 16 21

SmA 49 (1.3) I SmA 63 (3.8) I Colh 51 (3.8) I I I I

a

g: mesomorphic glass for 6, 7, and 8, or amorphous glass for 9, 10, and 11; SmA: smectic A mesophase; Colh: hexagonal columnar mesophase; I: isotropic liquid phase (nature of mesophases was confirmed by X-ray diffraction). bA small endothermic peak overlaps glass transition due to melting. cTemperature: °C; ΔH (in brackets): kJ/mol. Figure 9. DSC curves (10 °C/min) corresponding to first cooling (bottom) and second heating (top) of 7.

only differ in the length of alkyl chains, exhibit an endothermic peak corresponding to the appearance of a mesophase, which finally vitrifies at temperatures just below RT, as can be seen in Figure 9, which displays the curves corresponding to 7 as an example. When these compounds are observed under the optical microscope, a grainy and ill-defined texture is observed. Figure 10 shows a typical texture exhibited by these compounds on cooling at a temperature close to the isotropic−mesophase transition. This texture did not meet the common features exhibited by smectic or columnar compounds, and therefore, the mesophase could not be assigned on the basis of the microscope observations only. However, the mesophase of 6 and 7 was identified as smectic A by X-ray diffraction (see below). When the number of terminal alkyl chains is increased, as it occurs for cyclotriphosphazene 8 compared to 6 and 7, the thermal behavior is clearly different. This compound combines the 4-cyanobiphenyl moieties with polycatenar benzyl ethers,

Figure 10. Texture exhibited by 7 as appeared when cooled from the isotropic state (taken at 55 °C).

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Inorganic Chemistry typically described as promoting columnar or cubic phases.18 In fact, when this compound is observed under the microscope, birefringence was not clearly detected and only a dark texture was observed. However, the DSC curves of this compound display the existence of a peak at around 40 °C with a broad character typical of compounds of high molecular weight, and a subsequent vitrification at around 7 °C; see Figure 11. This

account and the reports by other authors,7−9 when 6 peripheral chains are present in cyclotriphosphazenes similar to those described in this work, nematic or smectic mesophases are produced. However, compounds having a number of chains ≥ 12 tend to generate columnar mesomorphism.8 An intermediate number of peripheral chains was not previously studied, but it seems that 9 chains are not enough to completely surround the central core and, instead, they orient themselves in a preferred direction, thus generating a calamitic (elongated cylinder) shape. In addition to the above-described features, the X-ray patterns of 6 contain some diffuse scattering at middle angles (Figure 12a) related to the width of this kind of molecule, whose cross section is very large compared to classical calamitics (vide inf ra). The same phenomenon was described by Levelut in another series of cyclophosphazenes.9a The oriented pattern recorded for 6 indicates a good degree of alignment as shown by the concentration of the scattered intensity in two directions: the meridian and the equator (Figure 12b). The low-angle maximum appears as a pair of symmetrical spots in the equatorial region (plane perpendicular to the capillary axis), and the high-angle halo appears as a pair of diffuse crescents concentrated in the meridian (direction of the capillary axis). The fact that the intensity of these crescents is highly concentrated in the meridian is typical of well-oriented smectic mesophases, as opposed to a columnar mesophase, in which the liquid-like chains conformationally disordered around the core usually produce a more isotropic diffuse ring. When the powder sample of 6 was studied several hours after thermal treatment, the patterns became more complex and several weak maxima appeared at middle angles, probably related to partial crystallization. These middle-angle maxima are visible in the oriented pattern shown in Figure 12b. The description of the X-ray diffraction patterns of 7 and the conclusions about the nature of the mesophase are very similar to the description and conclusions for 6, except for the oriented samples because we were unable to obtain patterns with a sufficient degree of alignment for 7. A powder sample of this compound studied immediately after thermal treatment yielded an X-ray pattern containing a single sharp maximum at low angles and a diffuse halo at high angles (Figure 12c). This kind of pattern is consistent with a smectic mesophase with a layer thickness of 40 Å. When comparing this spacing (40 Å) to the experimentally measured value for 6, 45 Å, the difference is consistent with the evolution expected of the different chain length assuming that it extends in a preferential direction. The difference we found of 5 Å is consistent with the different chain length, and it confirms that the hydrocarbon chains extend in a preferential direction to both sides. Concerning the nature of the smectic mesophase of 6 and 7, the diffuse character of the high-angle scattering and the absence of sharp reflections in this angular region point to a smectic A or C mesophase. In general, it is difficult to distinguish these two phases by X-ray diffraction only, and in this case, the optical textures do not give any useful information. However, there is some indirect information that suggests that the mesophase is smectic A. The fact that the layer spacing increases by 5 Å on passing from decyloxy (compound 7) to dodecyloxy chains (compound 6) is consistent with a fully extended conformation of the hydrocarbon chains oriented in the direction of the layer normal. Indeed, each C(sp3)−C(sp3) bond is known to contribute with

Figure 11. DSC curve (10 °C/min) corresponding to first cooling of 8.

behavior points to the existence of a mesophase that vitrifies upon cooling below RT in this cyclotriphosphazene. A similar behavior was previously described for the cyclotriphosphazene having six polycatenar benzyl moieties instead of three calamitic and three polycatenar moieties, which was characterized as cubic by X-ray measurements. In contrast to the tendency to mesomorphic arrangements exhibited by the cyclotriphosphazenes with a cyano group (compounds 6−8), the compounds with a methyl group (9− 11) did not exhibit mesomorphic behavior. In fact, these compounds only yield an isotropic phase when they are studied by optical microscopy and only show a glass transition when studied by DSC. Structural Study by XRD. Compounds exhibiting mesomorphism or evidence of mesomorphic states, as it was first inferred from the optical microscopy and DSC studies, were analyzed by X-ray diffraction in order to elucidate the nature and structural parameters of their mesophases. Powder samples of compounds 6, 7, and 8 were submitted to a diffraction study at room temperature after thermal treatment consisting of heating them up to the isotropic liquid state and then cooling down to room temperature. In the case of 6 and 7, mechanically aligned samples were also obtained by scratching with a metal rod the inner wall of the capillaries in which the samples are contained for the X-ray study. In the case of 6, a powder sample of this compound was studied immediately after the thermal treatment and yielded an X-ray pattern containing a single sharp maximum at low angles and a diffuse halo at high angles (Figure 12a). This kind of pattern is consistent with a smectic mesophase with a layer thickness of 45 Å, deduced by applying Bragg’s law to the X-ray maximum. The occurrence of calamitic mesomorphism for compound 6 can be understood if the presence of a total number of 9 peripheral chains is considered. Taking our own experience into 7915


Article

Inorganic Chemistry

Figure 12. X-ray diffractograms of the mesophases recorded at room temperature after thermal treatment. (a) Powder pattern of compound 6; (b) oriented pattern of compound 6; (c) powder pattern of compound 7, and (d) small-angle pattern of compound 8.

1.25 Å to the length of an all-anti chain.19 Since these molecules possess a statistical arrangement of chains to both sides (upward and downward), the observed difference of 5 Å matches this kind of arrangement well with an orientation of the chains on average orthogonal to the layers. Furthermore, the density ρ of a smectic mesophase is related to the molecular mass M and the layer spacing d by the following equation

orthogonal orientation and is within the range found in smectic liquid crystals for disordered aliphatic chains oriented, on average, normal to the layers, whereas considerably larger values are obtained for tilted smectic phases.20,21 A powder sample of compound 8 studied in any set of conditions yielded similar X-ray patterns, either in its virgin state, immediately after thermal treatment, or several hours or even several days after thermal treatment. The diffractograms contain two or three maxima at low angles and a diffuse halo at high angles (Figure 12d). The third low-angle maximum is only observed for the pristine sample and disappears after thermal treatment. The low-angle maxima correspond to spacings 40.3, 23, and 15.5 Å, respectively, and are in the reciprocal relationship 1:√3:√7. This kind of pattern is characteristic of a hexagonal columnar mesophase, and the three maxima can be indexed as the (1 0), (1 1), and (2 1) reflections from the 2D lattice of columns with a hexagonal lattice constant a = 46.6 Å. The hexagonal columnar nature of the mesophase is additionally supported by estimations based on the relationship between density, molecular mass, and mesophase parameters. Indeed, the density ρ of a hexagonal columnar mesophase is related to the molecular mass M and the lattice dimensions by the formula

ρ = (M × 1024)/(d × S × NA )

where S is the molecule cross-sectional area and NA is Avogadro’s number. Assuming that the density is 1 g cm−3, the estimated cross-sectional area is 110 Å2 for 6 and 115 Å2 for 7, values much larger than those for classical calamitics. Considering that there are on average 4.5 chains filling this cross section (the nine chains of each molecule are statistically oriented to both sides), the cross-sectional area per chain is 24.5 and 25.5 Å2, respectively (alternatively, it can be considered that two molecules fill a cross section which is twice as large as the one estimated for a single molecule and this doubled cross section contains nine chains to each side). A cross section of about 25 Å2 for a hydrocarbon chain is consistent with a rather elongated conformation in an 7916


Article

Inorganic Chemistry ρ = (M × Z × 1024)/(d10 × a × h × NA )

of mixed-substituent cyclotriphosphazenes with two different types of mesogenic units linked to the same phosphorus atom, calamitic and polycatenar ones, has been successfully achieved. The mesomorphic properties of these compounds, nongemtrans-N3P3(OC6H4C6H4{X}-p)3(OC6H4{OC(O)C6H2[3,4,5(R)3]}-p)3, strongly depend on the terminal group of the calamitic units, X (X = CN or CH3). Liquid crystal phases are only detected on the cyano-derivatives. Furthermore, the number of aliphatic terminal chains influences the type of mesomorphism, and polycatenar units with a high number of terminal chains are needed to force a starlike conformation Thus, an evolution from a smectic to a columnar organization of the cyclotriphosphazenes takes place when a larger hydrocarbon region is present.

where Z is the number of molecules per unit cell (per column “slice”), d10 is the observed spacing for the first reflection, a is the lattice constant, h is the “slice” thickness, and NA is Avogadro’s number. By assuming a mesophase density close to 1 g cm−3 and considering that Z is usually equal to 1 for disclike molecules (a single molecule fills the column cross section), it is deduced that each molecule is contained in a column “slice” of 5.8 Å thickness in the columnar mesophase, which is a reasonable value that compares well to the interdisc spacing found for other columnar mesophases. In fact, 5.8 Å is a distance slightly larger than those found for classical disc-like molecules. However, this is not unexpected considering the complex structure of the molecules of 8, which precludes the adoption of a completely flat shape. 8 has a total number of 27 peripheral chains. According to our experience in other series of cyclotriphosphazenes, columnar mesophases were observed for compounds with a total number of chains of 12 or 18, whereas a cubic mesophase was detected for a cyclotriphosphazenes with 54 terminal chains.8 Columnar mesophases were even observed in a series of cyclotriphosphazenes decorated with a dendritic periphery with 36 or 72 chains.22 Despite the unusual and mixed structure of compound 8, and according to these antecedents, it is not surprising that 8 yields columnar mesomorphim. The apparent isotropic character observed by optical microscopy can be due to a high tendency to homeotropic alignment. Our results are different from those obtained by Percec’s group in other systems based on the same units A1, A2, and A6 used for our work. Indeed, Percec found a tendency of A1 and A2 to promote columnar mesomorphism and a tendency of A6 to promote cubic mesomorphism.23 However, these different results are not surprising considering that, in Percec’s work, the central core is relatively small or does not exist at all, whereas the cyclotriphosphazene ring surrounded by a number of benzene rings used in our work generates an entity able to accommodate the mesogenic units in the appropriate conformation to produce smectic or columnar mesomorphism. Indeed, the nongem-trans structure of the compounds favors the arrangement of the tricatenar units A1 and A2 upward and downward needed for calamitic mesomorphism rather than a radial arrangement that furthermore would be rendered difficult by the scarce number of hydrocarbon chains to efficiently surround the central core. In the case of the nonacatenar unit A6, the cyclotriphosphazene does not provide enough space to accommodate all the chains in an elongated arrangement. Moreover, the nongem-trans structure can account for the absence of cubic mesomorphism even with a high number of hydrocarbon chains. Indeed, the nongem-trans structure and the large size of the central core produce a balance between the rigid region and the hydrocarbon periphery that favors a nearly radial arrangement of the mesogenic units required for columnar mesomorphism.

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EXPERIMENTAL SECTION

General Data. Instrumentation and general experimental techniques (elemental analysis, IR, thermogravimetry, and optical microscopy) were as described earlier.22,24 NMR spectra were recorded on a Bruker AV 400 spectrometer. Chemical shifts are quoted relative to SiMe4 (TMS, 1H and 13C, external) and H3PO4 (85%) (31P, external). MALDI-TOF mass spectrometry was carried out on a REFLEX III Bruker instrument using dithranol as matrix. DSC was performed using a DSC Q2000 from TA Instruments with samples (2−5 mg) sealed in aluminum pans and a scanning rate of 10 °C/min under a nitrogen atmosphere. In general, the peaks obtained were broad and the transition temperatures were therefore read at the maximum of the peaks. Glass transitions were read at the midpoint of the baseline jump. The X-ray diffraction patterns were obtained with a pinhole camera (Anton−Paar) operating with a point-focused Ni-filtered Cu− Kα beam. The samples were held in Lindemann glass capillary tubes (0.9 mm diameter) and heated, when necessary, with a variabletemperature oven. The patterns were collected on flat photographic films. The capillary axis and the film were perpendicular to the X-ray beam. Spacings were obtained using Bragg’s law. N3P3Cl6 (Stream Chemicals) was purified by recrystallization from hot hexane and dried in vacuo. Carboxylic acids17 and DPTS (4(dimethylamino)pyridinium 4-toluenesulfonate)25 were prepared by literature methods. Reaction of N3P3Cl6 with 3 mol of 4-{NC}C6H4C6H4{OH}-4′. Synthesis of nongem-cis-N3P3Cl3(OC6H4C6H4{CN}-4)3 (1) and nongem-trans-N3P3Cl3(OC6H4C6H4{CN}-4)3 (2). A mixture of N3P3Cl6 (3.13 g, 9 mmol), 4-{NC}C6H4C6H4{OH}-4′ (5.43 g, 27 mmol), and K2CO3 (7.46 g, 54 mmol) in acetone (400 mL) was stirred for 1 day. The solvent was removed under reduced pressure, and the residue was extracted with dichloromethane (3 × 20 mL). Evaporation of the solvent in vacuo gave a colorless oil (6.68 g, 96%), which is a mixture of ca. 15% of nongem-cis-N3P3Cl3(OC6H4C6H4{CN}-4)3 (1), 42% of nongem-trans-N3P3Cl3(OC6H4C6H4{CN}-4)3 (2), 25% of gem-N3P3Cl3(OC6H4C6H4{CN}-4)3, 5% of nongemN3P3Cl4(OC6H4C6H4{CN}-4)2 (cis- and/or trans-), and 13% of nongem-N3P3Cl2(OC6H4C6H4{CN}-4)4 (cis- and/or trans-). By solving of this mixture in dichloromethane at room temperature and cooling, a mixture of ca. 1% of 1 and 99% of 2 was obtained as a white solid. Compounds 1 and 2 were isolated by chromatography using a silica gel column and dichloromethane:hexane (2:1) as eluent. All compounds were dried in vacuum at 40 °C for 48 h. 1. Yield: 0.030 g, 0.4%. Anal. Calcd (%) for C39H24O3Cl3N6P3 (823.93): C, 56.85; H, 2.94; N, 10.20. Found: C, 56.73; H, 2.81; N, 9.50. IR (ATR): 2225 (w) cm−1 (CN); 1223 (s), 1175 (s), 1152 (vs, br) cm−1 (PN); 966 (s) cm−1 (P-O); 581 (s), 527 (vs) cm−1 (P-Cl). 31 1 P{ H} NMR (CDCl3) δ = 17.72 (s, 3P; N3P3 ring). 1H NMR (CDCl3) δ = 7.72 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CN), 7.6 (“d”, 2H, 3 JH‑H = 8.4 Hz; C6H4CN), 7.55 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 7.33 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4). MALDI-TOF (dithranol): m/z = 825.1 [M + H]+. 2. Yield: 1,11 g, 15%. Anal. Calcd (%) for C39H24O3Cl3N6P3 (823.93): C, 56.85; H, 2.94; N, 10.20. Found: C, 56.98; H, 2.88; N,

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CONCLUSION The regioselectivity in N3P3Cl6 for the reaction with the calamitic nucleophile 4-cyano-4′-hydroxybiphenyl is strongly nongeminal due to the steric demands of the reagent, which also lead to a predominance of trans-isomer formation. Once isolated, the major product of this reaction, nongem-transN3P3Cl3(OC6H4C6H4{CN}-p)3, was used to introduce the second mesogenic unit, a polycatenar one. Thus, the synthesis 7917


Article

Inorganic Chemistry 9.50. IR (ATR): 2225 (w) cm−1 (CN); 1228 (s, br), 1179 (s), 1154 (vs, br) cm−1 (PN); 957 (s, br) cm−1 (P-O); 598 (s), 585 (s), 533 (s) cm−1 (P-Cl). 31P{1H} NMR (CDCl3) δ = 18.23 (1P), 17.98 (2P) (AB2 system, 2JAB = 72.9 Hz). 1H NMR (CDCl3) δ = 7.74 (“d”, 2H, 3 JH‑H = 8.4 Hz; C6H4CN), 7.72 (“d”, 4H, 3JH‑H = 8.4 Hz; C6H4CN), 7.66 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CN), 7.62 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 7.61 (“d”, 4H, 3JH‑H = 8.4 Hz; C6H4CN), 7.57 (“d”, 4H, 3JH‑H = 8.4 Hz; OC6H4), 7.43 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 7.36 (“d”, 4H, 3JH‑H = 8.4 Hz; OC6H4). 13C{1H} NMR (CDCl3) δ = 150.23, 137.63, 127.80, 122.33 (6C; OC6H4); 150.17, 137.50, 127.74, 122.09 (12C; OC6H4); 144.41, 132.83, 128.86, 111.48 (6C; C6H4CN); 144.28, 132.80, 128.81, 111.55 (12C; C6H4CN); 118.82 (1C; CN); 118.74 (2C; CN). MALDI-TOF (dithranol): m/z = 825.1 [M + H]+. Synthesis of nongem-trans-N3P3(OC6H4C6H4{CN}-p)3(OC6H4{OCH2Ph}-p) 3 (3). A mixture of 2 (0.824 g, 1 mmol), p{PhCH2O}C6H4OH (0.741 g, 3.7 mmol), and Cs2CO3 (2.61 g, 8 mmol) in acetone (80 mL) was refluxed for 36 h. After completion, according to 31P{1H} spectroscopy, the volatiles were evaporated and the residue was extracted with dichloromethane (3 × 10 mL). The solution was evaporated to dryness, and addition of ethanol led to the precipitation of 3 as a white solid. 3. Yield: 1.01 g, 77%.Anal. Calcd (%) for C78H57O9N6P3 (1315.24): C, 71.23; H, 4.37; N, 6.39. Found: C, 71.06; H, 4.05; N, 6.23. IR (ATR): 2225 (w) cm−1 (CN); 1195 (s, br), 1164 (s, br) cm−1 (P N); 951 (s, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 9.51 (m, 3P; N3P3 ring). 31P{1H} NMR ((CD3)3CO) δ = 10.56 (m, 3P; N3P3 ring). 1 H NMR (CDCl3) δ = 7.62 (“d”, 4H, 3JH‑H = 8.4 Hz; C6H4CN), 7.56 (m, AA′BB′ system, 4H, 3JH‑H = 8.4 Hz; C6H4CN), 7.53 (“d”, 4H, 3 JH‑H = 8.4 Hz; C6H4CN), 7.4−7.3 (m, 21H; C6H5 + OC6H4), 7.09 (“d”, 4H, 3JH‑H = 8.4 Hz; OC6H4), 6.97 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 6.96 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4O), 6.88 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4O), 6.74 (“d”, 6H, 3JH‑H = 8.8 Hz; OC6H4O), 4.90 (s, 4H; OCH2), 4.87 (s, 2H; OCH2). 1H NMR ((CD3)3CO) δ = 7.84 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CN), 7.75 (m, 8H; C6H4CN), 7.73 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CN), 7.63 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4), 7.58 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4), 7.37 (m, 15H; C6H5), 7.10 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4), 7.09 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4), 6.99 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4O), 6.96 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4O), 6.89 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4O), 6.87 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4O), 5.01 (s, 4H; OCH2), 4.95 (s, 2H; OCH2). 13C{1H} NMR (CDCl3) δ = 151.16, 144.59, 136.68, 132.84, 128.84, 127.56, 122.09, 111.26 (24C; aromatic carbons from OC6H4C6H4CN); 151.16, 144.59, 136.65, 132.86, 128.86, 127.58, 122.14, 111.16 (12C; aromatic carbons from OC6H4C6H4CN); 156.16, 144.32, 135.94, 128.40, 128.37, 127.50, 121.80, 115.57 (24C; aromatic carbons from OC6H4OCH2Ph); 156.16, 144.32, 135.88, 128.45, 128.37, 127.42, 121.70, 115.57 (12C; aromatic carbons from OC6H4OCH2Ph); 118.9 (1C, CN), 118.8 (2C, CN); 70.54 (2C, OCH2), 70.52 (1C, OCH2). MALDI-TOF (dithranol): m/z = 1315.5 [M + H]+ Synthesis of nongem-trans-N3P3(OC6H4C6H4{CN}-p)3(OC6H4{OH}-p)3 (4). Cyclohexene (5 mL), palladium hydroxide (20 wt % on carbon, 0.5 g), and ethanol (5 mL) were added to a solution of 3 (0.658 g, 0.5 mmol) in dry THF (10 mL). The mixture was heated under reflux for 2 h. After completion, according to 31P{1H} and 1H NMR spectroscopy, the mixture was filtered. The solvent was evaporated, and subsequent addition of dichloromethane (20 mL) led to the precipitation of 4 as a white solid. 4. Yield: 0.413 g, 79%. Anal. Calcd (%) for C57H39O9N6P3 (1044.88): C, 65.52; H, 3.76; N, 8.04. Found: C, 63.28; H, 3.63; N, 8.14. IR (ATR): 3353 (w, br) cm−1 (OH); 2232 (w) cm−1 (CN); 1188 (m, sh), 1164 (s, br) cm−1 (PN); 952 (s, br); 940 (s, sh) cm−1 (P-O). 31P{1H} NMR ((CD3)2CO) δ = 10.58 (m, 3P; N3P3 ring). 1H NMR ((CD3)2CO) δ = 8.45 (s, 2H; OH), 8.39 (s, 1H; OH), 7.86 (m, AA′BB′ system, 4H, 3JH‑H = 8.4 Hz; C6H4CN), 7.74 (m, AA′BB′ system, 8H, 3JH‑H = 8.8 Hz; C6H4CN), 7.63 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 7.53 (“d”, 4H, 3JH‑H = 8.4 Hz; OC6H4), 7.02 (“d”, 6H, 3JH‑H = 8.4 Hz; OC6H4), 6.89 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.79 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.70 (“d”, 6H, 3JH‑H = 8.8 Hz; OC6H4OH). MALDI-TOF (dithranol): m/z = 1045.3 [M + H]+.

Synthesis of nongem-trans-N3P3(OC6H4C6H4{CH3}-p)3(OC6H4{OH}-p)3 (5). Cyclohexene (5 mL), palladium hydroxide (20 wt % on carbon, 0.5 g), and ethanol (5 mL) were added to a solution of 3 (0.658 g, 0.5 mmol) in dry THF (10 mL). The mixture was heated under reflux for 6 h. After completion, according to 31P{1H} and 1H NMR spectroscopy, the mixture was filtered and the solvent was evaporated to give 5 as a white solid. 5. Yield: 0.472 g, 93.2%. Anal. Calcd (%) for C57H48O9N3P3 (1011.93): C, 67.65; H, 4.78; N, 4.15. Found: C, 65.75; H, 5.27; N, 3.94. IR (ATR): 3233 (w, br) cm−1 (OH); 1186 (s, sh), 1161 (s, br) cm−1 (PN); 951 (s, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 9.80 (m, 3P; N3P3 ring). 31P{1H} NMR ((CD3)2CO) δ = 10.70 (m, 3P; N3P3 ring). 1H NMR (CDCl3) δ = 7.46 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CH3), 7.41(“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 7.36 (“d”, 4H, 3JH‑H = 8.4 Hz; C6H4CH3), 7.35 (“d”, 4H, 3JH‑H = 8.4 Hz; OC6H4), 7.24 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CH3), 7.19 (“d”, 4H, 3JH‑H = 8.4 Hz; C6H4CH3), 7.01 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 6.99 (“d”, 4H, 3 JH‑H = 8.4 Hz; OC6H4), 6.79 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.78 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.57 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.52 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4OH), 2.39 (s, 6H; CH3), 2.38 (s, 3H; CH3). 1H NMR ((CD3)2CO) δ = 8.41 (br, 3H; OH), 7.55 (m, 4H, 3JH‑H = 8.4 Hz; C6H4CH3), 7.45 (m, 8H; 2H from C6H4CH3 + 6H from OC6H4), 7.28 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CH3), 7.22 (“d”, 4H, 3JH‑H = 8.4 Hz; C6H4CH3), 7.02 (“d”, 2H, 3 JH‑H = 8.4 Hz; OC6H4), 7.0 (“d”, 4H, 3JH‑H = 8.4 Hz; OC6H4), 6.83 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.82 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.73 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4OH), 6.70 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4OH, 2.37 (br, 9H; CH3). MALDI-TOF (dithranol): m/z = 1012.3 [M + H]+. Synthesis of nongem-trans-N3P3(OC6H4C6H4{CN}-p)3(OC6H4{OC(O)C6H2[3,4,5-(R)3]}-p)3; R = OC12H25 (6); OC10H21 (7); OCH2C6H2{3,4,5-(OC10H21)3} (8). A mixture of 4 (0.105 g, 0.1 mmol), the corresponding carboxylic acid (0.39 mmol, 0.264 g of A1 for 6, 0.231 g of A2 for 7), and DPTS (24 mg, 0.078 mmol), in dry dichloromethane (10 mL), was cooled to 0 °C, and N,N′dicyclohexylcarbodiimide (DCC) (88 mg, 0.43 mmol) was added. The reaction mixture was vigorously stirred under an argon atmosphere for 2 days. After completion, according to 31P{1H} and 1 H NMR spectroscopy, the precipitated of DCU was filtered off and washed with dichloromethane (3 × 3 mL). The filtrate was evaporated to dryness, and subsequent addition of 20 mL of acetone (in the case of 6) or ethanol (in the case of 7) gave 6 or 7 as white solids, which were washed with acetone or ethanol, respectively. For the synthesis of 8, a similar method was used, using 0.05 mmol of 4 (0.053 g), 5 mL of dry dichloromethane, 0.20 mmol of carboxylic acid A3 (0.369 g), 0.039 mmol of DPTS (12 mg), and 0.22 mmol of DCC (44 mg). After filtering the precipitated of DCU, the solution was evaporated to dryness and the white solid of 8 was washed with ethanol. Compound 8 was purified by chromatography using a silica gel column and hexane:ethyl acetate (20:1) as eluent. All compounds were dried in vacuum at 40 °C for 48 h. 6. Yield: 0.205 g, 68%. Anal. Calcd (%) for C186H267O21N6P3 (3016,06): C, 74.07; H, 8.92; N, 2.79. Found: C, 73.99; H, 8.87; N, 2.59. IR (ATR): 2954 (m), 2917 (s), 2849 (m) cm−1 (CH); 2226 (w) cm−1 (CN); 1722 (m) cm−1 (CO); 1191 (s, br), 1166 (vs, br) cm−1(PN); 966 (s, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 8.92 (m, 3P; N3P3 ring). 1H NMR (CDCl3) δ = 7.66−7.54 (m, 12H; C6H4CN), 7.52 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4), 7.44 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4), 7.36 (s, 2H; C6H2), 7.33 (s, 4H; C6H2), 7.13−7,01 (m, 18H; 6H from OC6H4 + 12 H from OC6H4O), 4.13 (“t”, 2H, 3JH‑H = 6.4 Hz; OCH2), 4.06 (“t”, 4H, 3JH‑H = 6.4 Hz; OCH2), 4.04 (“t”, 4H, 3 JH‑H = 6.4 Hz; OCH2), 3.99 (“t”, 8H, 3JH‑H = 6.4 Hz; OCH2), 1.81 (m, 18H; CH2), 1.48−1.26 (m, 162H; CH2), 0.88 (m, 27H; CH3). MALDI-TOF (dithranol): m/z = 3017.4 [M + H]+. 7. Yield: 0.199 g, 72%. Anal. Calcd (%) for C168H231O21N6P3 (2763.58): C, 73.01; H, 8.43; N, 3.04. Found: C, 73.11; H, 8.81; N, 3.03. IR (ATR): 2953 (m), 2920 (s), 2851 (m) cm−1 (CH); 2226 (w) cm−1(CN); 1726 (m) cm−1 (CO); 1188 (s, br), 1162 (vs, br) cm−1 (PN); 955 (s, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 8.95 (m, 3P; N3P3 ring). 31P{1H} NMR ((CD3)2CO) δ = 10.28 (m, 3P; 7918


Article

Inorganic Chemistry N3P3 ring). 1H NMR (CDCl3) δ = 7.66−7.55 (m, 12H; C6H4CN), 7.52 (“d”, 2H, 3JH‑H = 8.8 Hz; OC6H4), 7.44 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4), 7.36 (s, 2H; C6H2), 7.33 (s, 4H; C6H2), 7.13−7.01 (m, 18H; 6H from OC6H4 + 12H from OC6H4O), 4.10 (“t”, 2H, 3JH‑H = 6.4 Hz; OCH2), 4.06 (“t”, 4H, 3JH‑H = 6.4 Hz; OCH2), 4.04 (“t”, 4H, 3JH‑H = 6.4 Hz; OCH2), 3.99 (“t”, 8H, 3JH‑H = 6.4 Hz; OCH2), 1.81 (m, 18H; CH2), 1.48−1.27 (m, 126H; CH2), 0.87 (m, 27H; CH3). 1H NMR ((CD3)2CO) δ = 7.88 (“d”, 2H, 3JH‑H = 8.4 Hz; OC6H4), 7.77−7.70 (m, 12H; C6H4CN), 7.64 (“d”, 4H, 3JH‑H = 8.4 Hz; OC6H4), 7.43 (s, 2H; C6H2), 7.30 (s, 4H; C6H2), 7.24−7.17 (m, 14H; 12H from OC6H4O + 2H from OC6H4), 7.04 (“d”, 4H, 3JH‑H = 8.8 Hz; OC6H4), 4.12 (“t”, 2H, 3JH‑H = 6.4 Hz; OCH2), 4.09 (“t”, 4H, 3JH‑H = 6.4 Hz; OCH2), 4.06 (“t”, 4H, 3JH‑H = 6.4 Hz; OCH2), 3.96 (“t”, 8H, 3JH‑H = 6.4 Hz; OCH2), 1.79 (m, 18H; CH2), 1.53−1.30 (m, 126H; CH2), 0.89 (m, 27H; CH3). MALDI-TOF (dithranol): m/z = 2764.7 [M + H]+ 8. Yield: 0.147 g, 45%. Anal. Calcd (%) for C411H645O48N6P3 (6531.45): C, 75.58; H, 9.95; N, 1.29. Found: C, 75.60; H, 10.04; N, 1.24. IR (ATR): 2948 (m), 2920 (s), 2850 (m) cm−1 (CH); 2225 (w) cm−1 (CN); 1730 (m) cm−1 (CO); 1191 (m), 1165 (s, br) cm−1 (PN); 954 (s, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 8.78 (m, 3P; N3P3 ring). 1H NMR (CDCl3) δ = 7.60−7.40 (m, 24H; 12H from C6H4CN + 6H from OC6H4 + 6H from C(O)C6H2), 7.21− 6.89 (m, 18H; 6H from OC6H4 + 12H from OC6H4O), 6.67(s, 4H; OCH2C6H2), 6.64 (s, 10H; OCH2C6H2), 6.61 (s, 4H; OCH2C6H2), 5.14 (s, 2H; OCH2C6H2), 5.07 (s, 8H; OCH2C6H2), 5.03 (s, 8H; OCH2C6H2), 3.94−3.83 (m, 36H; OCH2C), 3.79−3.73 (m, 18H; OCH2C), 1.71 (m, 54H; CH2), 1.46−1.26 (m, 372H; CH2), 0.87 (m, 81H; CH3). MALDI-TOF (dithranol): m/z = 6535.2 [M + H]+. Synthesis of nongem-trans-N3P3(OC6H4C6H4{CH3}-p)3(OC6H4{OC(O)C6H2[3,4,5-(R)3]}-p)3; R = OC12H25 (9); OC10H21 (10); OCH2C6H2{3,4,5-(OC10H21)3} (11). A mixture of 5 (0.051 g, 0.05 mmol), the corresponding carboxylic acid (0.21 mmol, 0.142 g of A1 for 9, 0.124 g of A2 for 10, and 0.387 g of A3 for 11), and DPTS (13 mg, 0.042 mmol), in dry dichloromethane (8 mL), was cooled to 0 °C, and N,N′-dicyclohexylcarbodiimide (DCC) (48 mg, 0.23 mmol) was added. The reaction mixture was vigorously stirred under an argon atmosphere for 3 days. After completion, according to 31P{1H} and 1H NMR spectroscopy, the precipitated of DCU was filtered off and washed with dichloromethane (3 × 3 mL). The filtrate was evaporated to dryness, and subsequent addition of 20 mL of ethanol gave 9−11 as white solids, which were thoroughly washed with ethanol to separate the excess of acid. Compounds 9 and 11 required additional purification by chromatography using a silica gel column and hexane:ethyl acetate (20:1) as eluent. All compounds were dried in vacuum at 40 °C for 48 h. 9. Yield: 0.094 g, 63%. Anal. Calcd (%) for C186H276O21N3P3 (2983.11): C, 74.89; H, 9.33; N, 1.41. Found: C, 74.99; H, 9.53; N, 1.33. IR (ATR): 2953 (m, sh), 2919 (s), 2850 (m) cm−1 (C-H); 1732 (m) cm−1 (CO); 1185 (s, sh), 1164 (vs, br) cm−1 (PN); 957 (vs, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 9.34 (m, 3P; N3P3 ring). 1 H NMR (CDCl3) δ = 7.49 (“d”, 2H, 3JH‑H = 8.8 Hz; C6H4CH3); 7.43 (“d”, 2H, 3JH‑H = 8.1 Hz; OC6H4); 7.39 (“d”, 4H, 3JH‑H = 8.8 Hz; C6H4CH3); 7.36 (s, 2H; C6H2); 7.35 (s, 4H; C6H2); 7.35 (“d”, 4H, 3 JH‑H = 8.1 Hz; OC6H4); 7.12−7.06 (m, 18H; 6H from C6H4CH3 + 12H from OC6H4O); 7.00−6.96 (m, 6H; OC6H4); 4.10−3.97 (m, 18H; OCH2); 2.33 (s, 6H; C6H4CH3), 2.29 (s, 3H; C6H4CH3), 1.80 (m, 18H; CH2), 1.49−1.27 (m, 162H; CH2), 0.88 (m, 27H; CH3). MALDI-TOF (dithranol + NaTFA): m/z (%) = 3005.8 (30) [M + Na]+, 2983.7 (100) [M + H]+. 10. Yield: 0.058 g, 42%. Anal. Calcd (%) for C168H240O21N3P3 (2730.63): C, 73.89; H, 8.86; N, 1.54. Found: C, 73.31; H, 8.74; N, 1.49. IR (ATR): 2948 (m, sh), 2919 (s), 2850 (m) cm−1 (C-H); 1733 (m) cm−1 (CO); 1185 (s), 1164 (vs, br) cm−1 (PN); 959 (vs, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 9.34 (br, 3P; N3P3 ring). 1H NMR (CDCl3) δ = 7.48 (“d”, 2H, 3JH‑H = 8.4 Hz; C6H4CH3); 7.43 (“d”, 2H, 3JH‑H = 8.0 Hz; OC6H4); 7.38 (“d”, 4H; 3JH‑H = 8.4 Hz; C6H4CH3); 7.36 (s, 2H; C6H2), 7.35 (s, 4H; C6H2), 7.34 (“d”, 4H, 3 JH‑H = 8.0 Hz; OC6H4); 7.13−7.05 (m, 18H; 6H from C6H4CH3 + 12H from OC6H4O); 7.00- 6.96 (m, 6H; OC6H4); 4.09−3.95 (m,

18H; OCH2); 2.33 (s, 6H; C6H4CH3), 2.29 (s, 3H; C6H4CH3), 1.80 (m, 18H; CH2), 1.48−1.27 (m, 126H; CH2), 0.88 (m, 27H; CH3). MALDI-TOF (dithranol + NaTFA): m/z (%) = 2752.5 (40) [M + Na]+, 2730.7 (33) [M + H]+. 11. Yield: 0.153 g, 47%. Anal. Calcd (%) for C411H654O48N3P3 (6498.50): C, 75.96; H, 10.14; N, 0.65. Found: C, 75.76; H, 10.40; N, 0.56. IR (ATR): 2948 (m, sh), 2920 (s), 2851 (m) cm−1 (C-H); 1732 (m) cm−1 (CO); 1194 (m), 1164 (vs, br) cm−1 (PN); 954 (vs, br) cm−1 (P-O). 31P{1H} NMR (CDCl3) δ = 9.19 (m, 3P; N3P3 ring). 1 H NMR (CDCl3) δ = 7.53 (s, 4H; C6H2), 7.52 (s, 2H; C6H2), 7.51 (“d”, 2H, 3JH‑H = 8.6 Hz; C6H4CH3), 7.44 (“d”, 2H, 3JH‑H = 8.0 Hz; OC6H4), 7.37 (“d”, 4H, 3JH‑H = 8.6 Hz; C6H4CH3), 7.33 (“d”, 4H, 3 JH‑H = 8.0 Hz; OC6H4), 7.22−6.93 (m, 18H; 6H from C6H4CH3 + 6H from OC6H4 + 12H from OC6H4O), 6.63 (s, 12H; OCH2C6H2), 6.60 (s, 6H; OCH2C6H2), 5.09 (s, 2H; OCH2C6H2), 5.05 (s, 4H; OCH2C6H2), 5.03 (s, 8H; OCH2C6H2), 5.01 (s, 4H; OCH2C6H2), 3.93−3.84 (m, 36H; OCH2C), 3.78−3.73 (m, 18H; OCH2C), 2.28 (s, 6H; C6H4CH3), 2.25 (s, 3H; C6H4CH3), 1.72 (m, 54H; CH2), 1.46− 1.26 (m, 378H; CH2), 0.88 (m, 81H; CH3). MALDI-TOF (dithranol + NaTFA): m/z (%) = 6507.9 (100) [M + H]+, 6530 (20) [M + Na]+.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: (+)34 976761187. ORCID

J. Jiménez: 0000-0002-3444-0851 L. Callizo: 0000-0002-3999-5258 J. L. Serrano: 0000-0001-9866-6633 J. Barberá: 0000-0001-5816-7960 L. Oriol: 0000-0002-0922-5615 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the MICINN, Spain, under the projects CTQ2015-70174-P, MAT2014-55205-P, and CTQ2011-22589, FEDER, Gobierno de Aragón-Fondo Social Europeo (Spain, Dpto. de Innovación, Investigación y Universidad, groups E-97 and E-09).

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DEDICATION Dedicated to the memory of Prof. Rafael Usón. REFERENCES

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Mixed-Substituent Cyclophosphazenes with Calamitic and

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