Organometallic Derivatives of Ruthenium (II & III) Ligated by Quinazole-2-Thione-4-One

INTRODUCTION

Quinazole-2-thione-4-one (Str. I) contains amide and thioamide groups having interesting donor sites.¹ We have reported some complexes of low-valent² and high-valent³ metal ions with this ligand in our earlier communication. The present paper reports synthesis, spectral characterization and structural investigation of some ruthenium (II & III) chelates with this ligand.

Scheme :1 Click here to View Scheme

 

EXPERIMENTAL

All chemicals used in this work were either of Anal R grade or chemically pure grade. The Quinazoline-2-thione-4-one (QTH)⁴ precursor complexes, [RuCl₂(Pf₃)₄]⁵, [RuHCl(CO)(Pf₃)₃]⁶, [RuHCl(CO)(Asf₃)₃]⁷, [RuHCl(CO)(Pf₃)₂(Py)]⁸, [RuCl₃(Pf­)₃]⁹, [RuBr₃(Pf₃)₃]¹⁰ and [RuCl₃(Asf₃)₃]¹¹ were prepared by reported literature methods.

Preparation of new ruthenium (II) complexes

All new ruthenium (II) complexes of composition [RuCl(CO)(Ef₃)₂(QT)]    (E = As/P) were prepared by the ligand substitution in benzene using precursor complexes and ligand reported in our previous method.¹² The other ruthenium (II) complex of composition [Ru(Pf₃)₂(QT)₂] was prepared by direct reaction of [RuCl₂(Pf₃)₄] with ligand (QTH) following our previous method.¹³

Analysis

[RuCl(CO)(Pf₃)₂(QT)] (yellow) : Calculated (%) for RuC₄₅H₃₅N₂O₂P₂SCl (865.5) : C = 62.39; H = 4.04; N = 3.23; Cl = 4.10; Ru = 11.66; Found (%) : C = 62.42; H = 4.10; N = 3.33; Cl = 4.21; Ru = 11.55;

[RuCl(CO)(Asf₃)₂(QT)] (yellow) : Calculated (%) for RuC₄₅H₃₅N₂O₂As₂SCl (953.5) : C = 56.63; H = 3.74; N = 2.99; Cl = 3.72; Ru = 10.59; Found (%) : C = 56.11; H = 3.77; N = 3.01; Cl = 80; Ru = 10.32;

EXPERIMENTAL

All chemicals used in this work were either of Anal R grade or chemically pure grade. The Quinazoline-2-thione-4-one (QTH)⁴ precursor complexes, [RuCl₂(Pf₃)₄]⁵, [RuHCl(CO)(Pf₃)₃]⁶, [RuHCl(CO)(Asf₃)₃]⁷, [RuHCl(CO)(Pf₃)₂(Py)]⁸, [RuCl₃(Pf­)₃]⁹, [RuBr₃(Pf₃)₃]¹⁰ and [RuCl₃(Asf₃)₃]¹¹ were prepared by reported literature methods.

Preparation of new ruthenium (II) complexes

All new ruthenium (II) complexes of composition [RuCl(CO)(Ef₃)₂(QT)]    (E = As/P) were prepared by the ligand substitution in benzene using precursor complexes and ligand reported in our previous method.¹² The other ruthenium (II) complex of composition [Ru(Pf₃)₂(QT)₂] was prepared by direct reaction of [RuCl₂(Pf₃)₄] with ligand (QTH) following our previous method.¹³

Analysis

[RuCl(CO)(Pf₃)₂(QT)] (yellow) : Calculated (%) for RuC₄₅H₃₅N₂O₂P₂SCl (865.5) : C = 62.39; H = 4.04; N = 3.23; Cl = 4.10; Ru = 11.66; Found (%) : C = 62.42; H = 4.10; N = 3.33; Cl = 4.21; Ru = 11.55;

[RuCl(CO)(Asf₃)₂(QT)] (yellow) : Calculated (%) for RuC₄₅H₃₅N₂O₂As₂SCl (953.5) : C = 56.63; H = 3.74; N = 2.99; Cl = 3.72; Ru = 10.59; Found (%) : C = 56.11; H = 3.77; N = 3.01; Cl = 80; Ru = 10.32;

Preparation of new ruthenium (III) complexes

All ruthenium complexes were prepared by following our previous method reported in literature.¹⁴

 [RuCl2(Pf₃)₂(QT)] (Brown) : Calculated (%) for RuC₄₄H₃₅N₂OSP₂Cl₂ (873) :   C = 60.48; H = 4.00; N = 3.20; Ru = 11.56; Found (%) : C = 60.47; H = 4.11;    N = 3.21; Ru = 11.66;

[RuCl₂(Asf₃)₂(QT) (Brown) : Calculated (%) for RuC₄₄H₃₅N₂OAs₂Cl₂ (961) :   C = 54.94; H = 3.64; N = 2.91; Cl = 7.38;    Ru = 10.50; Found (%) : C = 55.01; H = 3.66; N = 3.01; Cl = 7.48; Ru = 10.55;

[RuBr₂(Pf₃)₂(QT)] (Brown) : Calculated (%) for RuC₄₄H₃₅N₂OP₂Br₂ (962) :     C = 54.88; H = 3.62; N = 2.91; Ru = 10.49; Found (%) : C = 54.98; H = 3.71;  N = 3.01; Ru = 10.50 The analysis of C, H and N were performed at CDRI, Lucknow, India. The IR spectra of ligand and complexes were recorded on a Perkin-Elmer Model-577 Spectrophotometer in the range of 4000-200 cm^-1 as KBr pillets. The magnetic measurements were made on a Gouy balance and diamagnetic corrections for the ligand molecule were applied. Electronic spectra were recorded with Beckmann DU-6 spectrophotometer. The molar conductance of complexes (10^-3 M) were measured in DMF using Wiss-Wekstatter Weighein obb type LBR conductivity meter. The ¹H NMR spectra were recorded on Bruker 400 MHz using TMS as reference.

Formula 1,2,3

 

The analytical data is consistent with the proposed stoichiometeries of the complexes. In all the above reactions, the thioamide ligand behaves as mononegative bidentate ligand. All isolated solid products are air stable in the solid state at room temperature and are non-hygroscopic in nature. All synthesized complexes are soluble in DMF, DMSO and acetonitrile producing intense coloured solution. The molar conductance in DMF (10^-3 M) are found in the range of 10.16 – 15.5 Ù^-1cm²mol^-1 indicating their non-electrolytic nature.¹⁵ The chloride or bromide ion in corresponding complexes are present in the inner sphere and coordinated nature.

Magnetic Moment and Electronic Spectra

All ruthenium (II) chelates are diamagnetic indicating the ground state ¹A_1g arising from T_2g⁶eg⁰ configuration in octahedral structure.¹⁶ The excited state corresponding to the T_2g⁵eg¹ configuration are ³T_1g, ³T_2g, ¹T_1g and ¹T_2g. Hence, four bands corresponding to the transition, ¹A_1g ® ³T_1g, ¹A_1g ® ³T_2g, ¹A_1g ® ¹T_1g and ¹A_1g ® ¹T_2g are possible in order of increasing energy. The electronic  spectra [RuCl(CO)(Ef₃)₂(QT)] (E = P/As) exhibits bands at 21740 cm^-1 (¹A_1g ® ¹T_1g), 23255 cm^-1 (T_2g ® p*, LMCT), 29850 cm^-1 (n ® p*, LC) and 33890 cm^-1 (p ® p*, LC) and 33890 cm^-1 (p ® p*, LC) similar to those observed for the low-spin (Ru⁺⁺, d⁶) complexes containing N,S-chelating thioamide, Pf₃ or Asf₃ and chloride  ligands.^17-19 The magnetic moment of [RuCl₂(EΦ₃)₂(QT)] (E = P/As) chelates are found between 1.85 – 1.95 BM corresponding to one unpaired electron in T_2g⁵ (Ru⁺⁺⁺) in octahedral environment.²⁰ The  ground state of Ru (III) in octahedral environment is ²T_2g arising from T_2g⁵eg⁰ configuration. Hence, two bands corresponding to ²T_2g ® ²A_2g and ²T_2g ® ²T_1g are possible. The complexes display bands at 15870 cm^-1 (²T_2g ® ²A_2g), 21970 cm^-1 (LMCT) and 33115 (p ® p*) which indicates octahedral environment around ruthenium (III) ion and consistent with the other ruthenium (III) octahedral complexes.²¹

IR Spectra

A comparison of the IR spectra (table 1) of the ligand (QTH) and ruthenium (II & III) complexes brings out the following facts to light The medium broad nN-H bands of the ligand at 3446 and 3350 cm^-1 are severely affected on coordination. The 3446 cm^-1 band almost disappears indicating displacement of N-H hydrogen by means of Ru(II)/Ru(III) ion and formation of Ru(II)-N/Ru(III)-N bond. While the 3350 cm^-1 band shift to lower frequency and gets split. (ii) The nC=O band of the ligand at 1710 cm^-1 is found to be almost at the same place in the spectra of complexes indicating absence of bonding through carbony oxygen atom.²² (iii) All carbonyl complexes of ruthenium (II) display a new strong band in the region 1955-1960 cm^-1 which is attributed due to terminally coordinated carbonyl group and is observed at higher frequency than in the precursor complexes.²³ (iv) Thioamide bands^24-26 I, II, III and IV are observed at 1530 (s), 1295 (m), 960 (m) and 790 (m) cm^-1 in the spectrum of ligand (QTH). Band I splits, Band II blue shift to higher frequency, while band III and band IV red shift with reduction in intensity. (table 1) on complexation indicating simultaneous bonding with N and S atoms of QTH considering our previous observations.^27-29 (v) New bands around 535, 685, 740 and 1560 cm^-1 due to coordinated Asf₃ and around 540, 690, 740 and 1535 cm^-1 due to coordinated Pf₃ molecule are in agreement with previous literature.^30-32 (vi) The single Ru(III)-Cl stretching mode in [RuCl₂(Ef₃)₂(QT)] indicates two mutual chlorine atoms are at Trans-position in octahedral structure (Str. III). Thus, the thioamide ligand acts as N, S-chelating mononegative bidentate nature in octahedral structure.

Table – 1 : Major IR Spectral bands (cm^-1) of ligand (QTH) and complexes

Compounds	nCºO	Thioamide Bands				nRu-N/
						nRu-S
		Band I	Band II	Band III	Band IV
QTH (ligand)	–	1530 (s)	1295 (m)	960 (m)	790 (m)	– (-)
[RuCl(CO)(Pf3)2(QT)]	1565 (m)	1535 m	1310 m	955 w	780 w	455 m
		1510 m				(420 w)
[RuCl(CO)(Asf3)2(QT)]	1566 (s)	1535 m	1315 m	950 w	780 w	465 m
		1515 m				(425 w)
[RuCl(CO)(Pf3)(Py)(QT)]	1570 ms	1530 m	1315 m	950 w	780 w	470 m
		1515 m				(420 w)
[RuCl2(Pf3)2(QT)]	–	1530 m	1310 ms	945 vw	780 w	465 m
		1510 m				(425 w)
[RuCl2(Asf3)2(QT)]	–	1535 m	1310 m	945 vw	785 w	460 m
		1515 m				(410 m)
[RuBr2(Pf3)2(QT)]	–	1535 m	1315 m	950 w	780 w	455 m
		1510 m				(415 w)
[Ru(Pf3)2(QT)2]	–	1530 m	1316 m	950 w	775 w	465 m
		1515 m				(420 w)

 

¹H NMR Spectra

¹H NMR spectra of ligand and some complexes (Sl. No. 1, 2 & 3) were recorded in CDCl₃/TMS to substantiate further metal-ligand bonding. The aromatic protons signals are observed at d7.8 – 8.6 PPM and the aromatic proton at position -5 is deshielded by carbonyl oxygen so the extreme signal at d8.3 PPM is considered to be due to this proton. The imino protons of the ligand observed at d3.2 – 3.6 PPM found to be absent in complexes indicate deprotonation of imino group. The ¹H NMR spectra of complexes show a multiplet around d6.2-7.7 PPM which is assigned to aromatic protons of Pf₃/Asf₃.³³ The resonances in the region d7.68 PPM, d8.2 PPM and d8.8 PPM assignable to the protons of Pyridine ligand along with the resonances due to aromatic protons in complexes.³⁴ Thus, on the basis of physico-chemical, conductometric, magnetic,     UV-vis, IR and ¹H NMR data octahedral structure of both Ru(II) and Ru(III) complexes may be reasonably assigned.

 

Scheme :2 Click here to View Scheme

 

ACKNOWLEDGEMENT

One of the authors (KVG) gratefully acknowledge UGC (New Delhi) to award Junior Research Fellowship (JRF, NET) and thanks to Principal, Dr. R.K. Verma, College of Commerce (M.U.), Patna-800020 for necessary facilities.

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