Synthesis of a new phenoxy-cyclophosphazene derivative Schiff base and its Ru(II),Co(III) complexes

Abstract

In this study, a new phenoxy cyclophosphazene derivative bis(2-formyl-phenyl)4,4,6,6-bis[spiro(2’,2”-dioxy-1’,1”biphenylyl)]cyclotriphosphazene (P2) was synthesis in by the reactions between 2,2-dichloro-4,4,6,6-bis[spiro(2’,2”-dioxy-1’,1”biphenylyl)]cyclotriphosphazene (P1) with salicyl aldehyde in presence of K₂CO₃ at room temperature in THF under argon atmosphere, and the new phenoxy cyclophosphazene derivative Schiff bases which are containing long-chain alkyl groups and salicyl aldehyde, bis[spiro(2’,2”-dioxy-1’,1”biphenylyl)2,3-diphenoxy-2-imidododesyl]cyclotriphosphazene (P3) synthesized by condensation reactions in suitable conditions with (P2) and dodecylamine. Synthesized ligands have been investigated with the methods of FTIR, ³¹P NMR, Uv-vis, MS spectroscopies, elemental and thermal analysis (TGA and DSC). Co(III), Ru(II) complexes were synthesized (L/M) 1:2 ratio and characterized FTIR, UV-vis and MS spectra, together with elemental and thermal analysis.

Keywords

Cyclotriphosphazene Schiff bases phenoxyphosphazane transition metal complexes

1 Introduction

Phosphazenes and their derivatives are a unique class of hybrid inorganic-organic compounds contained alternating phosphorus and nitrogen in their skeleton and organic groups in their branched chain. Phosphazenes are compounds that contain a framework of alternating phosphorus and nitrogen atoms, either in cyclic or linear form [1]. The phosphazene derivatives have various physical and biological properties [2 –8].

The synthesis and different reactions of phosphazenes containing 2,2’-dioxybiphenyl groups were reported [9, 10]. There are also a large number of literature reports on reactions of the functional groups on phosphazene substituents [11 –13].

Schiff bases derivatives of phosphazanes have a wide range of applications. It is mostly used in biological fields [14 –18].

In this study, a new phenoxy cyclophosphazene was synthesized. And then the phenoxy compound (P2) was reacted with dodecylamine in order to get a new linear alcyl phenoxy Schiff base phosphazane compound (P3) and its (Ru(II), Co(III) complexes were synthesized and characterized with spectroscopic and thermal analysis techniques. The new phosphazene compounds and synthesized complexes can be used as drug substances.

2 Experimental

2.1 Materials and physical measurements

All reactions were carried out under an argon inert atmosphere. K₂CO₃ was dried at 300°C prior to use. The 2,2-dichloro-4,4,6,6-bis[spiro(2’,2”-dioxy-1’,1”biphenylyl)]cyclotriphosphazene (P1) and [RuCl₂(bpy)₂]·2H₂O were prepared using reported procedures [10 , 20]. All the chemicals were of the highest grade available. Hexachlorocyclotriphosphazatriene (N₃P₃Cl₆) was purchased from Aldrich and recrystallized from dry hexane. Uv-vis spectra were recorded on Agilent 8453 spectrometer. Elemental analyses were determined on a Thermo Finnigan Flash EA 112 instrument. LC/MS Q-TOF B.05.01 was Agilent 6530, FTIR spectra were recorded on a Mattson 1000 FTIR spectrometer. ³¹P NMR spectra were recorded with the use of Varian UNITY INOVA 500 MHz (CDCl₃-d6) spectrometer. TGA-DSC curves were obtained with a TA SDT Q 600 thermal analyzer apparatus using flowing nitrogen 100 mL min^–1, temperature range 50-1200°C, at heating rate of 10°C min^–1, all the samples were heated in alumina crucibles. Magnetic properties of complexes were obtained with a Sherwood Scientific Magnetic Susceptibity Balance. Melting points were obtained with a Büchi Melting point B-540 apparatus in open capillaries.

2.2 Synthesis

The 2,2-dichloro-4,4,6,6-bis[spiro(2’,2”-dioxy-1’,1”biphenylyl)]cyclotriphosphazene (P1) was synthesized from hexachlorocyclotriphosphazene (HCCP) using reported procedures [10].

2.2.1 Synthesis of P2

2.822 g (4.56 mmol) of P1 substance, 1.18 mL (9.12 mmol) salicyl aldehyde and 1.876 g (13.68 mmol) K₂CO₃ were stirred in 20 mL THF at room temperature and argon atmosphere for 48 hours. After the solvent was removed, a white solid formed. The residue was washed with 4x20 mL of dichloromethane and filtered. The filtrate was evaporated. The obtained white solid was dissolved in acetone and crystallized in hexane. Yielded 1.528 g, 45 %. Anal. calc. for P2; C₃₈H₂₆N₃O₈P₃: C, 61.22; H, 3.52; N, 5.64%, M, 745.5. Found: C, 59.99; H, 3.54; N, 5.88%. MP: 210°C P2 is good soluble in acetone, THF, dichloromethane, methanol and chloroform. ATR-IR, ν(cm^- 1): 3068 (Ar), 2875, 2763 (ald.-CH), 1693 (C = O), 1273-1088, (PO), 882 (PNP) (Fig. 2). ESI-MS: m/z (m/1) at 746.098 (C₃₈H₂₆ N₃O₈P₃₊ H)⁺ and 768.096 (C₃₈H₂₆N₃O₈P₃₊ Na)⁺ (Fig. 3).

Fig. 1

The FT-IR spectra of P2.

Fig. 2

The FT-IR spectra of P3.

Fig. 3

Mass spectrum of compound of P2.

2.2.2 Synthesis of P3

1.0318 g (1.368 mmol) of P2 was dissolved in 15 mL of THF and 5.07 g (27.36 mmol) of dodecylamine dissolved in 25 mL of THF was added into P2 solution and refluxed for 4 hours in argon atmosphere. After the solvent was removed, a light yellow solid obtained and the substance dissolved in acetone and crystallized in hexane. Yielded 1.1962 g, 81%. MP: 84.5°C, Anal. calc. for P3; C₆₂H₇₆N₅O₆P₃: C, 68.94; H, 7.09; N, 6.48%, M, 1080.2. Found: C, 69.87; H, 7.54; N, 6.68%. ATR-IR, ν(cm^- 1): 3063 (Ar), 2917-2850 (Alip.-CH), 1644 (C = N), 1274-1092 (PO), 885 (PNP). ³¹P-NMR; (ppm, CDCl3-d): 25. 28 (d, 2P, J: 1.68), 10. (dd, 1P, J: 1) (Fig. 6). P2 is good soluable in acetone, THF, dichloromethane, methanol, ethanol, acetone and chloroform.

Fig. 4

Mass spectrum of compound of P3- Co(II) complex.

Fig. 5

Mass spectrum of compound of P3-Ru(II) complex.

Fig. 6

Proton decoupled ³¹P NMR spectrum of compound P3.

2.2.3 Synthesis of P3-Co(III) complex

5.52 g (5 mmol) of P3 was dissolved in 50 mL of methanol and was added to 2.38 g (10 mmol) of CoCl₂.6H₂O dissolved in 20 mL of methanol. NaOH solution in methanol was added until the pH value was approximately 7. The solvent was removed, a brown P3-Co(III) complex obtained. Yielded 1.519 g, 21% . MP > 350°C, P3-Co(II) is good soluable in ethanol. Anal. calc. for P3-Co(III) complex; C₆₂H₈₈Cl₄ Co₂N₅O₁₂P₃: C, 51.43; H, 6.13; N, 4.84% , M, 1447.9 Found: C, 51.84; H, 6.34; N, 4.88% . ATR-IR, ν(cm^- 1): 2920, 2808(-CH2), 1590(-CN), 1297, 1054(PO), 804(PNP). ESI-MS: m/z (m/3) at 477.4326 (C₆₂H₈₈C_l4Co₂N₅O₁₂P₃+ 3H-[3H₂O]), 483.4489 (C₆₂H₈₈C_l4Co₂N₅O₁₂P₃+ 3H+3), 505.4202; C₆₂H₈₈C_l4Co₂N₅O₁₂P₃+ 3Na+3) (Fig. 4).

2.2.4 Synthesis of P3-Ru(II) complex

8.325 g (5 mmol) of P3 was dissolved in 50 mL of methanol and 6.4053 g of Ru(II)bipyridine (10 mmol) complex dissolved in 20 mL of methanol was mixed, a solution of NaOH in methanol was added until the pH value was approximately 7, and the mixture was approximately 6. days left to crystallize. The P3-Ru(II) complex is red-brown in color. Yielded 1.498 g, 18%. MP > 350°C, P3-Ru(II) is good soluable in ethanol. Anal. calc. for P3-Ru(II) complex; C₈₂H₉₂Cl₂N₉O₆P₃ Ru₂: C, 59.13; H, 6.13; N, 5.57%, M, 1665.6 Found: C, 59.74; H, 6.22; N, 5.78%. ATR-IR, ν(cm^- 1): 3068 (Ar), 2953, 2850 (-CH₂), 1632(-CN), 1271, 1092(PO), 804(PNP). ESI-MS: m/z (m/3) at 537.4684 (C₈₂H₉₂N₅O₆P₃Ru₂ + 3H+3), 559.4435 (C₈₂H₉₂ N₅O₆P₃ Ru₂ + 3Na+3) (Fig. 5).

3 Results and discussion

3.1 Synthesis and characterization of compounds

In our study; as a starting material 4.4.6.6-bis[spiro(2’,2”-dioxy-1’,1”biphenyl)] cyclotriphosphazene (P1) was prepared as reported in the literature. After that a new phosphazene compound 4.4,6.6-bis(spiro(2,2’-dioxy-1,1’-biphenyl)2,3-diphenoxycyclotri phosphazene (P2) was obtained from the reaction of P1 and salicyl aldehyde. A new Schiff base ligand (P3) is named bis[spiro(2’,2”-dioxy-1’,1”biphenylyl)2,3-diphenoxy-2-imidododesyl]cyclotriphosphazene, which contains salicylaldehyde, phenoxy phosphazene and linear alkyl groups, was synthesized from the condensation reaction of salicylaldehyde phosphazene compound (P2) with dodecylamine.

The general synthesis route and the structures of compounds P1-P3 and P3 complexes are shown in Scheme 1. All compounds were characterized with spectroscopic and thermal analysis techniques.

Scheme 1

The synthesis pathway of Schiff base (P3) and molecular structure of P3-Co(III) and P3-Ru(II) complexes.

3.1.1 The FT-IR spectra of compounds

P1, P2 and P3 showed characteristic stretching bands at 3062, 3068 and 3063 cm^–1 (aromatic C–H groups), 1171, 882 and 885 cm^–1 (P = N-P), and 1095, 1088 and 1092 cm^–1 (P–O), as expected. The FT-IR spectra of compounds P2 and P3 are given Figs. 1, 2. When the IR spectrum of compound P2 was compared with that of compound P3, it was seen that the C = O vibration in the 1693 cm^–1 disappeared in the spectrum of compound P3 and a new band appeared in the 1644 cm^–1 region because of C = N absorption. The compound P3 showed characteristic C-H strong (alip.) stretching vibrations were observed between 2917-2850 cm^–1 as sharp bands.

The presence of complexation in the IR spectrum of the P3-Co(III) and P3-Ru (II) complex is evident from the broadening of peaks.

P3-Co(III) and Ru(II) complexes; The shifts in the C = N are from 1644 cm^- 1 to 1590 and 1632 cm^- 1, respectively). From here, we think that in the Co(III) and Ru(II) complex, the metals are coordinated from the C = N nitrogen.

3.1.2 The LC/MS spectra of compounds

P2, P3, P3-Co(III) and P3-Ru(II) provided definitive characterization and the results are given the mass spectrum of compounds Figs. 3 –5.

The molecular ion peak of the P2 substance was determined as m/z (m/1) at 746.098 (C₃₈H₂₆ N₃O₈P_3⁺ H)⁺ and 768.096 (C₃₈H₂₆N₃O₈P_3⁺ Na)⁺.

The molecular ion peak of the P3-Co(III) substance was determined as m/z (m/3) at 477.4326 (C₆₂H₈₈C_l4Co₂N₅O₁₂P_3⁺ 3H-[3H2O]), at 483.4489 (C₆₂H₈₈C_l4Co₂N₅O₁₂P_3⁺ 3H+3) and 505.4202 C₆₂H₈₈C_l4Co₂N₅O₁₂P_3⁺ 3Na+3) (Fig. 4).

The molecular ion peak of the P3-Ru(II) substance was determined as m/z (m/3) at 537.4684 C₈₂H₉₂N₅O₆P₃ Ru₂ + 3H+3 and 559.4435 ((C₈₂H₉₂ N₅O₆P₃ Ru₂ + 3Na+3) (Fig. 5).

3.1.3 The ³¹P NMR spectra of compounds

The proton decoupled 31P NMR spectra of compounds P3 exhibit an A2X type spin system. The ³¹P NMR spectrum of compound P3 (in CDCl3), shown as an example in Fig. 6, exhibited triplet at 8.6-10.4 ppm for 1P (Schiff base P) and duplet at 24.4-26.0 ppm for 2P (phenyl-P). The values found are in accordance with the phosphors in the molecular structure and the literature values [13].

3.1.4 The Uv-vis absorption properties of P3 and P3-Co(III) and P3-Ru(II) complexes

The optical properties of new cyclotriphosphazene derivative (P3) and P3-Co(III) and P3-Ru(II) complexes were evaluated with Uv-vis spectroscopy. All of the spectral measurements were carried out in a spectroscopic quartz cuvette at 25°C. The ligands and P3- Co(III) and Ru(II) complexes were dissolved in ethanol and their electronic spectra were obtained in the range of 200–800 nm (Fig. 7). The transitions observed around 300 nm in ligands and complexes in the Uv-vis spectrum are due to π-π* and n-π* transitions. The metal center atom accepts electrons from the ligand, causing the energy of these electrons to decrease and the wavelength to increase. This was observed in the Uv-vis spectrum of the Ru(II) complex as a wavelength shift from 294 nm to 500 nm. We could not observe the shift due to the very low solubility of the Co(III) complex.

Fig. 7

Uv-vis absorption spectra of 1×10^–5 M P3 and P3-Ru(II) and P3-Co(III) complexes in ethanol.

3.1.5 Thermal properties (TGA-DSC)

Thermal properties cyclotriphosphazene, exhibits unusual thermal properties such as flame retardancy and self-extinguishing ability [26]. Additionally, it can be substituted with thermally and chemical stable groups (For example Schiff base) increase its thermal stability. Synthesized compounds (P3, P3-Co and P3-Ru) were determined by DSC technique and are shown in Figs. 8 –10.

Fig. 8

TGA curves of P3 25°C to 1200°C at a heating rate of 10°C /min under N₂ flow of 100 mL/min.

Fig. 9

TGA curves of P3-Ru(II) 25°C to 1200°C at a heating rate of 10°C /min under N₂ flow of 100 mL/min.

Fig. 10

TGA curves of P3-Co(III) 25°C to 1200°C at a heating rate of 10°C /min under N₂ flow of 100 mL/min.

The thermal analysis of ligands and their complexes was investigated by TGA-DSC technique in the range of 25–1200° C. Some clues about the molecular structure of ligands and complexes have been studied.

The TGA-DSC spectrum of the P3 ligand is observed in Fig. 8. Two step degradation was observed in the thermal analysis of the ligand. The small endothermic peak around 80°C corresponds to humidity. Other reductions of 11.59%and 73.36%correspond to exothermic fragmentation. It is 3.77%residual carbon black at 1200°C.

When the TGA-DSC spectrum of the P3-Ru(II) complex is examined (Fig. 9), the decrease occurred in approximately 2 steps and a total exothermic decrease of 96.99%. We think that about 3%of the residue is made up of carbon black. It has been stated that ruthenium oxides show volatile properties as can be seen from the literature researches. We think that due to the volatile properties of ruthenium oxides, there are no residues [22 –25].

When the TGA-DSC spectrum of the P3-Co(III) complex was examined (Fig. 10), the reductions were 29%and 8.44%exothermically in 2 stages. In this complex, the %residue is higher due to the metal oxide. In the Co complex, 61.50%residual consists of Co₂O₃ and carbon black.

3.1.6 Magnetic properties of complexes

It is used in magnetic susceptibility coordination compounds, in structure elucidation, in the determination of the stereochemistry, bond type, and oxidation step of the metal atom.

The magnetic susceptibility of the complexes was measured by the Gouy method. As a result of the measurement was calculated how many unpaired electrons are in the coordination compound (Table 1). Since n: 0, the P3-Ru(II) complex is diamagnetic. This result approximately indicates that the P3-Co(III) complex has a high spin complex structure with n: 4 unpaired electrons in the central atom.

Table 1

Magnetic properties of complexes

Comp.	Wo (g)	W (g)	W-Wo	l(Cm)	Ro	R	C_bal	X_g	X_m	μ_{eff (B . M)}	n
P3-Ru(II)	0.8243	0.8309	0.0066	1	0	0.05	1.12	8.48x10^- 9	1.41x10^- 5	0.183	0
P3-Co(III)	0.8243	0.9221	0.0978	1	–39	483	1.12	6.42x10^- 6	9.30x10^- 3	4.70	4

Conflict of interest

The authors declare that there is no conflict of interests regarding the publication of this article.

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Synthesis of a new phenoxy-cyclophosphazene derivative Schiff base and its Ru(II),Co(III) complexes

Abstract

Keywords

1 Introduction

2 Experimental

2.1 Materials and physical measurements

2.2 Synthesis

2.2.1 Synthesis of P2

2.2.4 Synthesis of P3-Ru(II) complex

3 Results and discussion

3.1 Synthesis and characterization of compounds

3.1.2 The LC/MS spectra of compounds

3.1.3 The 31P NMR spectra of compounds

3.1.4 The Uv-vis absorption properties of P3 and P3-Co(III) and P3-Ru(II) complexes

Conflict of interest

References

3.1.3 The ³¹P NMR spectra of compounds