Polyimides from a Novel Monomer 3,6-Bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II) for a Catalytic Application

Journal of Inorganic and Organometallic Polymers, Vol. 14, No. 3, September 2004 (© 2004)

Polyimides from a Novel Monomer 3,6-Bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II) for a Catalytic Application 1 Nevin G¨ ¨ Turgay Seckin,1,3 S¨uleyman Koytepe,1 Ismail Ozdemir, urb¨uz,1 2 and Bekir C ¸ etinkaya

Received March 9, 2004; revised May 13, 2004 Tricyclic heteroaraomatic dye-based monomer containing NMe2 units, 6bis(dimethylamino)acridine(p-cymene)dichlororuthenium (II), was used to prepare novel polyimides via a one-stage solution polycondensation due to their stability under a variety of oxidative and reductive conditions. The Ru(II) complex monomer was synthesized starting from [RuCl2 (p-cymene)]2 and 3,6-bis(dimethylamino)acridine. A series of stable polyimides was synthesized from the Ru(II) complex of 3,6-bis(dimethylamino)acridine and various aromatic dianhyrides. The polymers had inherent viscosities ranging from 1.72 to 2.11 dL/g and were soluble in polar solvents. The glass transition temperatures were 192–278 ◦ C, and the 10% weight loss temperatures were above 503–635 ◦ C. Ruthenium-substituted polyimides were tested for catalytic activity in the furan formation reaction of (Z)-3-methylpent-2-en-4-yn-1-ol. The polymeric catalyst was added to (Z)-3-methylpent-2-en-4-yn-l-ol without a solvent and the pure furan was isolated by distillation under reduced pressure. The conversion of the starting, enynol, was determined by gas chromatography (GC). KEY WORDS: Polyimide; thermally stable polymers; catalyst; ruthenium(II) complex; furan formation reaction.

INTRODUCTION One of the main reasons for the use of polymers in catalyzed reactions is their easy processing and fabrication; e.g., the polymers may be solution 1

Department of Chemistry, Inonu University, Malatya, Turkey. Department of Chemistry, Ege University, Izmir, Turkey. 3 To whom correspondence should be addressed. E-mail: [email protected] 2

177 1053-0495/04/0900-0177/0 © 2004 Springer Science+Business Media, Inc.

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cast or melt stretched into thin film, extruded and molded into almost any desired shape, spun into fibers or formed into composite materials. Also, because of the variety of polymeric materials available, the requirement of each particular application may always be closely met by selecting a polymer with the proper combination of properties [1–3]. The catalytic properties of organometallic polymers are of the great concern due to the properties arise that cannot be met by the catalyst itself. For example, polyimides possess the required properties for catalytic applications because they exhibit excellent thermal and thermo-oxidative stability, chemical and solvent resistance, and light stability [4–11]. Polyimides can be prepared from a variety of starting materials and by a variety of synthetic procedures. Since polyimides are insoluble in common organic solvents and decompose before melting, variations in properties can be ultimately overcome the solubility problems by altering the starting monomers. A general approach to improve the process ability of aromatic polyimides is the introduction of pendant groups that reduce interchain interactions and produce effective chain separations, which lower the cohesive energy density [12–17]. Transition metal complexes with nitrogen-containing ligands have recently shown potential in performing selective catalytic transformations of molecules with atom economy [18]. Specifically, a variety of [RuX2 (arene)(L)] complexes have promoted catalytic reactions such as nuc1eophi1ic addition to trip1e bonds to form furans (where L = imidazoline, tetrahydropyrimidine [19], benzimidazole [20]), hydrogen transfer (where L = amino acid [21], amino alcohol [22]), cyclopropanation (where L = diamine [23]), or DielsAlder cycloaddition and Claisen rearrangement (where L = bisoxazoline [24, 25]). It is also well established that [RuCl2 (arene)(L)] complexes can easily be transformed via activation of propargylic alcohols into cationic ruthenium allenylidene complexes, which have shown catalytic properties in olefin metathesis [26] and cyclic isomerization [27]. The synthesis and characterization of imide oligomers from acridine yellow using pyromellitic dianhyride (PMDA), 3,3 ,4,4 -benzophenone tetracarboxylic acid dianhyride (BPDA) and 2,2 -bis(3,4-dicarboxyphenyl) hexafluoropropane dianhyride was reported earlier. However, the 2-stage technique at lower temperatures gave little or no oligomeric product due to the poor reactivity of the acridine yellow [28]. In this paper, we describe the synthesis, characterization, and catalytic properties of new polyimides that are obtained from a tricyclic heteroaromatic dye ruthenium(II) substituted acridine orange, 3,6-bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II). The poor reactivity of the acridine yellow was overcome by substituting the amine protons

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with methyl groups. The improved reactivity was evidenced by the formation of high molecular weight polyimides that are obtained via a one-pot process. Once the model compound (6-bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II)) was obtained, the monomer was reacted with various anhyrides. EXPERIMENTAL Manipulations were carried out using standard Schlenk techniques under an inert atmosphere (nitrogen) with previously dried solvents. Infrared spectra were recorded as KBr pellets in the range 400–4000 cm−1 on an ATI UNICAM 2000 spectrometer. 1 H-NMR (300 MHz) and 13 C NMR (75.5 MHz) spectra were recorded on a Bruker AM 300 WB FT spectrometer with chemical shifts referenced to residual solvent CDCl3 . ¨ Microanalyses were performed by the TUBITAK analyses center. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetry (TGA) were performed with Shimadzu DTA-50 and TGA-50 thermal analyzers at a heating rate of 10 ◦ C/min under nitrogen or air. All chemicals were purchased from Aldrich and used after purification. 1-methyl-2-pyrrolidinone (NMP) was distilled over CaH2 under reduced pressure and stored over 4 Å molecular sieves. Reagent grade aromatic dianhydrides such as PMDA, 3,3 ,4,4 -BPDA, 4,4 -oxydiphthalic anhydride (ODPA) that was sublimed at 250 ◦ C under reduced pressure, and 3,3 ,4,4 -biphenyltetracarboxylic dianhydride (BTDA) were used after crystallization from the proper solvents. All the dianhydrides were dried under vacuum at 120 ◦ C prior to use. Inherent viscosities (ηinh =Lnηr /c at polymer concentration of 0.5 g/dL) were measured with an Ubbelohde suspended-level viscometer at 30 ◦ C using NMP as the solvent. GPC analyses were performed at 30 ◦ C using NMP as eluant at a flow rate of 0.5 mL/min. A differential refractometer was used as a detector. The instrument (Agilent 1100 series GPC-SEC system) was calibrated with a mixture of polystyrene standards (Polysciences; molecular masses between 200 and 1,200,000 Da) using GPC software for the determination of the average molecular masses and polydispersity of the polymer samples. Synthesis of 3,6-bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II) The general conditions for the preparation of the 3,6-bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II) were as follows: 3,6-bis (dimethylamino)acridine (1.061 g, 4 mmol), the required [RuCl2 (p-cymene)] (1.224 g, 2 mmol) and toluene (40 mL) were heated under

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Scheme 1. Synthesis of 3,6-bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II).

reflux for 6 h. Upon cooling to room temperature, orange crystals were deposited. They were filtered, washed with Et2 O (3 × 15 mL) and recrystallized in CH2 Cl2 /Et2 O; Yield, 1.010 g (88%). Anal. calcd. for C27 H33 N3 Cl2 Ru: C, 56.70; H, 5.77; N, 7.35; found: C, 56.77; H, 5.83; N, 7.29. 1 H-NMR in CDC1 [∂(ppm), J(Hz), multiplicity, integration, assignment]: 3 8.26 [s, 1H, (CH3 )2 NC6 H3 CHNC6 H3 N(CH3 )2 ], 7.28 [m, 6H, (CH3 )2 NC6 H3 CHNC6 H3 N(CH3 )2 ], 5.44 and 5.28 [d, J = 5.9 Hz, 4 H, (CH3 )2 CHC6 H4 CH3 -p], 3.14 [s, 12 H, (CH3 )2 NC6 H3 CHNC6 H3 N(CH3 )2 ], 2.87[sept, J = 7.1 Hz, 1 H, (CH3 )2 CHC6 H4 CH3 -p], 2.13 [s, 3H, (CH3 )2 CHC6 H4 CH3 p], 1.20 [d, 6 H, (CH3 )2 CHC6 H4 CH3 -p]. I 3 C1H -NMR in CDC13 , ∂ (ppm) [assignment]: 154.2, 143.4, 142.5, 130.4, 116.8, 114.5, 107.3 [(CH3 )2 N C6 H3 CHN C6 H3 N(CH3 )2 ], 102.3, 98.4, 81.3, 80.5 [CH3 )2 CH C6 H4 CH3 p], 40.5 [(CH3 )2 NC6 H3 CHNC6 H3 N(CH3 )2 ], 31.9 [CH3 )2 CHC6 H4 CH3 -p], 22.2 [(CH3 )2 CHC6 H4 CH3 -p] and 19.3 [CH3 )2 CHC6 H4 CH3 -p]. Catalytic Reactions The cyclization experiments were carried out in a 10 mL Schlenk tube equipped with a magnetic stirring bar. The Schlenk tube was evacuated and flushed with argon before the reaction mixture was introduced. (Z)-3methylpent-2-en-4-yn-1-ol (10 mmol) and the proper amount of the matrix were mixed and the mixture was stirred in an oil bath at 80 ◦ C. The progress of the reaction was monitored by gas chromatography (GC). The product was characterized after purification and was found to be 2,3-dimethylfuran as evidenced by 1 H- and 13 C-NMR spectra. The analyses were performed quantitatively on a capillary GC equipped with a thermal conductivity detector and a 6-foot column of 10% = V-101 on chromosorb W-HP, 100–120 mesh.

Synthesis of Polyimides A typical polyimide (AO-PI-1 to AO-PI-5, Scheme 2) synthesis was performed as follows: The Ru(II) complex of 3,6-bis(dimethylamino)acri-

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dine (2) (2.54 g, 4.15 mmol) was dissolved in NMP (15 mL) in a 50 mL Schlenck tube equipped with a nitrogen line, overhead stirrer, a xylene filled Dean-Stark trap, and a condenser. PMDA (0.90 g, 4.15 mmol) was added to the amine solution and stirred overnight to give a viscous solution. The mixture was heated to 70 ◦ C, xylene (5 mL) was added, and the mixture was refluxed for 3 h. Following the removal of xylene by distillation, the reaction mixture was cooled to room temperature and the product was precipitated by addition of a large excess of methanol. A yellow product was isolated and dried at 100 ◦ C under vacuum and then at 200–250 ◦ C under nitrogen for 2 h; Yield, 86%.

Scheme 2. Polyimide synthesis and symbols.

Symbol AO-PI-1 AO-PI-2 AO-PI-3 AO-PI-4 AO-PI-5

Ar PMDA BPDA BPPDA ODPA 6FDA

Pyromellitic dianhydride 3,3 ,4,4 -Benzophenonetetracarboxylic dianhydride 2,2-Bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride 4,4 -Oxydiphthalic anhydride 4,4 -Hexafluoroisopropylidenediphthalic anhydride

RESULTS AND DISCUSSION 3,6-bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II) was synthesized from 3,6-bis(dimethylamino)acridine and the required amount of [ RuCl2 (p-cymene) ] and toluene under reflux. The NMR spectra of the monomer were diagnostic. Only a single set of signals was observed for two pendant groups of dimethylamine in both the 1 H- and 13 C-NMR spectra that indicate the two arms of the ligands are magnetically equivalent in solution. The polyimide reaction takes place at high temperature in an aprotic solvent such as NMP. The reaction mechanism involves a cyclic polyimide without going through polyamic acid formation as evidenced by

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Table I. Properties of the Polyimides Polymer

AO-PI-1

AO-PI-2

AO-PI-3

AO-PI-4

AO-PI-5

Anhydride Yield (%) d (g/cm3) a η (dL/g) b Solubility c NMP DMF DMAc Ethanol Ether THF Hexane DMSO

PMDA 79 1.44 1.87

BPDA 84 1.58 2.11

BPPDA 72 1.30 1.72

ODPA 74 1.32 1.77

6FDA 71 1.23 1.80

+ ± + − − − − −

+ + + − − ± − ±

+ + + − − − − ±

+ + + − − − − ±

+ ± + − − − − −

by suspension method at 30 ◦ C. at a concentration of 0.5g/dL in NMP at 30 ◦ C using an Ubbelohde viscometer. c Solubility tested at 2% solid concentration; + soluble at room temperature (25 ◦ C); ± soluble upon heating; − insoluble at room temperature. a Determined b Measured

the formation of dimethyl ether. Although the polyimide has a very rigid structure, the fully cyclized polyimide is mainly soluble in dipolar aprotic media. To determine the optimal conditions for polymerization, the polymerization of the 3,6-bis(dimethylamino)acridine Ru(II) complex with various aromatic dianhyrides was studied in detail. Table I summarizes some of the physico-chemical properties of the polymers. On the basis of these results, the polymerization of the monomer with the corresponding anhyrides was performed in NMP at high temperatures. Polymers with inherent viscosities ranging from 1.72 to 2.11 dL/g were obtained. The FT-IR spectra (Fig. 1) showed characteristic absorptions for aliphatic C–H stretching frequencies at 2850–2890 cm−1 , symmetric imide stretching vibration νC=O at 1720–1738 cm−1 , asymmetric imide stretching vibration νC=O at 1745–1790 cm−1 , and C–N imide ring stretching at 1368 cm−1 , whereas the imide ring deformation band appeared at 1050 cm−1 and the C–N bending band occurred at 727–730 cm−1 [ 29–34 ]. The formulas of the polyimides and the monomers are consistent with the FT–IR spectral data and the elemental analyses, which are in agreement with the calculated data (Table II). Table I summarizes the solubilities of the polyimides; that is, all of the polymers are soluble in polar aprotic solvents such as NMP, N, N-dimethylformamide (DMF),

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Fig. 1. FTIR spectra of the monomer (AO-M) and polyimides (AO-PI-1 to AO-PI-5).

and N, N -dimethylacetamide (DMAc) at room temperature, whereas AOPI-2, AO-PI-3 and AO-PI-4 are soluble in dimethylsulfoxide (DMSO) on heating. The solubility of polymers AO-PI-1 and AO-PI-5 are 1ess than polymers AO-PI-2, AO-PI-3 and AO-PI-4. The solubility of the polymers may be a result of differences in the structure of the polyimides; e.g., AOPI-1 having a rigid structure has low solubility. The molecular weight of polymers having inherent viscosities near 1.80 dL/g was determined with GPC. The chromatograms give Mn values in the range between 122,000 and 386,000, whereas Mw values are between 232,000 and 792,000 relative to polystyrene standards. The polydispersities (Mw /Mn ) are, therefore, from 1.90 to 2.89 (Table III).

C27 H33 N3 Cl2 Ru

(C33 H23 N3 O4 Cl2 Ru)n

(C40 H27 N3 O5 Cl2 Ru)n

(C54 H41 N3 O6 Cl2 Ru)n

(C39 H27 N3 O5 Cl2 Ru)n

(C42 H27 N3 O4 F6 Cl2 Ru)n

AO-PI-1

AO-PI-2

AO-PI-3

AO-PI-4

AO-PI-5

Formula

AO-M

Polymer

Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found Calcd Found

56.74 56.77 56.82 57.31 59.93 60.26 64.86 65.92 59.32 60.40 54.61 55.46

C 5.82 5.77 3.32 3.37 3.40 3.87 4.13 4.66 3.45 3.05 2.95 2.89

H

Elemental Analysis

7.35 7.29 6.02 6.59 5.24 6.46 4.20 4.39 5.32 5.38 4.55 4.65

N

1764

1770

1780

1778

1779

–

Asym C = O Stretch

1722

1720

1718

1722

1720

–

Sym C = O Stretch

IR (cm−1 )

Table II. Elemental Analysis and Spectroscopic Data of the Monomer and Polyimides

1392

1382

1384

1392

1390

–

C−N−C Stretch

727

726

727

729

724

–

C−N Bending

184 ¨ Seckin, Koytepe, Ozdemir, G¨urb¨uz, and C ¸ etinkaya

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Table III. Properties of Polyimides Obtained by the One-step Method Polyimide

Dianhydride

[η] (dL/g)a

Mn × 10−5

Mw × 10−5

Polydispersityb

AO-PI-1 AO-PI-2 AO-PI-3 AO-PI-4 AO-PI-5

PMDA BPDA IPPDA ODPA 6FDA

1.87 2.11 1.72 1.77 1.80

3.44 3.86 1.22 1.43 1.97

7.53 7.92 2.32 4.13 5.37

2.19 2.05 1.90 2.89 2.72

a Measured

at a concentration of 0.5 dL/g in NMP at 30 ◦ C using an Ubbelohde

viscometer. (10 mg/mL NMP solution; polystyrene standards).

b GPC

The thermal properties of the polymers were evaluated by DTA (Fig. 2), TGA (Fig. 3) and DSC. The data are summarized in Table IV. The DTA and TGA thermograms of the monomer are given in Fig. 4 for comparative purposes. The melting point exotherm and the degradation peaks are consistent with the tricyclic nature of the monomer. A 10% weight loss under nitrogen occurs at 503–635 ◦ C. Typical TGA curves for the polymers are shown in Fig. 3. TGA analysis of the polyimides under nitrogen indicated that polymer decomposition commences between 498 and 558 ◦ C. This result may be attributed to the flexibility, polarity and associations of the chains in the polymeric backbones. A more stable polymer is obtained for AO-PI-1 where BPDA is used as condensing agent in polymerization. Small variations in thermal decomposition temperature

Fig. 2. DTA thermograms of the polyimides (AO-PI-1 to AO-PI-5).

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Fig. 3. TGA thermograms of the polyimides (a; AO-PI-1, b; AO-PI-2, c; AO-PI-3, d; AO-PI-4, e; AO-PI-5).

Fig. 4. DTA and TGA curves of the monomer (AO-M).

are probably due to differences in molecular weight and chain stiffness. The glass transition temperatures (Tg ) as measured by DSC are given in Table IV. The polyimide prepared from PMDA has a relatively high Tg , again attributed to its rigid structure. The relative order of thermal stability is AO-PI-1 > AO-PI-2 > AO-PI-5 > AO-PI-3 > AO-PI-4. In a first test of catalytic activity of Ru(II)-substituted polyimides in furan formation, classical conditions for solvent and base were chosen. In all the experiments, where a recycling of the catalyst was attempted, a small decrease in activity was observed from one run to the next (Table V). The results clearly indicate that the Ru(II)-polyimides are effec-

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Table IV. Thermal Properties of the Polyimides Polymer TGA analysis Onset temp. (◦ C) End temp. (◦ C) % 10 temp. (◦ C) a Char yield (◦ C) b IDT (◦ C)c DTA analysis d TDP(◦ C) e Onset temp. (◦ C) End temp. (◦ C) H (kJ/g) DSC analysis Onset temp. (◦ C) End temp. (◦ C) Transition (mW) Tg(◦ C) f

AO-PI-1

AO-PI-2

AO-PI-3

AO-PI-4

AO-PI-5

581 701 635 36 577

552 712 598 30 524

449 733 512 15 433

477 602 503 24 406

506 627 545 35 419

530 478 594 22.78

558 470 629 8.33

535 486 592 3.98

498 445 536 6.39

530 484 608 6.62

262 281 −3.21 278

215 226 −2.14 225

197 208 −1.35 205

208 223 −2.75 220

187 194 −1.65 192

of 10% weight loss was assessed by TGA at a heating rate of 10 ◦ C/min under a N2 atmosphere. b Assessed by TGA at 800 ◦ C under a N atmosphere. 2 c IDT (initial decomposition temperature) is the temperature at which an initialloss of mass is observed. d DTA thermograms of polyimides with a heating rate of 10 ◦ C/min in air. e TDP (thermal decomposition peak). f Determined by DSC under a N atmosphere. 2 a Temperature

tive catalysts for furan formation of (Z)-3-methylpent-2-en-4-yn-1-ol without solvent. We also examined the ability of separating and recycling the polymeric catalyst by simple filtration. Thus the matrix, which was in contact with the substrate (enynol) under typical reaction conditions (Table V) for several hours and subsequently filtered, rinsed and dried under vacuum for reuse, continued to exhibit catalytic activity and cyclic furan formation when added to a fresh reaction mixture. This procedure was repeated three times with each subsequent use of the catalyst demonstrating catalytic activity, albeit at a diminished level from the initially prepared material. The recovery and recycling is noteworthy as the homogeneous catalyst deactivates in the process. The demonstration of recycling provides evidence for the site isolation of Ru(II) complex in the chain. The diminished activity of the catalyst after each cycle is partly due to the extended reaction times used to test the catalyst and establish higher per-

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Table V. Catalytic synthesis of 2,3-dimethylfuran at 80 ◦ C by the ruthenium substituted polyimides

Entry

Catalyst

Yielda,b , (%)

1 2 3 4 5 6

AO-M AO-PI-1 AO-PI-2 AO-PI-3 AO-PI-4 AO-PI-5

95c 93 87 86 91 88

a Reaction

conditions: To 0.1 g of catalyst was added 10 mmol of neat (Z)-3- methylpent2-en-4-yn-l-ol. The mixture was stirred in an oil bath at 80 ◦ C for 4 h. b Yields were determined by gas chromatography. c 80 ◦ C, 1.5 h.

formance. As with other heterogeneous systems, the level of the furan cyclization in our system is higher than those reported under similar conditions.

CONCLUSIONS The polyimides obtained from the tricyclic heteroatomic dye, acridine orange, with Ru(II) complex side groups were obtained from reaction of 3,6-bis(dimethylamino)acridine with Ru(II) in aprotic solvent. Most of the Ru(II) complexes were largely or completely soluble in dipolar aprotic solvents. The synthetic approach offers a 2-fold advantage over conventional polyimides; first, fusible polyimides can be utilized without lowering thermal and heat stability, and second, owing to the presence of the ruthenium side groups, the polymeric materials show catalytic activity for furan formation.

ACKNOWLEDGMENTS We gratefully acknowledge the support of this research by the TUBITAK, Turkish Research Council TBAG 2017 (101T029), and IU BAP 2003/69 for partial support.

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