Synthesis and Characterization of Phosphine and Arsine Complexes of Ruthenium (Ii & Iii) Ligated With 3-(4-Pyridyl)-4-Substituted-Triazoline-5-Thione

Introduction

Literature survey reveals that secondary thioamides have versatile coordinating ability and interesting insights into structure and bonding^1-3. Bowman-James’s group^4-5 and Kanbara and Co-worker^6-8 have reported that thioamide based Pincer complexes are photoluminescent and have catalytic activity. The group of Henderson^9-11 has reported the synthesis and structural characterization of various transition metal complexes containing chelating thioamide derivatives. The reactions, structures and anti-tumour activity of transition metal ions with thioamide ligands are reported by Mohr et al¹². The current interest in organometallic ruthenium complexes with anti-tumour activity^13-15 prompted us to investigate this class of complexes with 3-(4-Pyridyl)-4-substituted-Triazoline-5-thione which contains secondary thioamide group. Prior to this work low-valent Pd(0), Pt(0) and Rh(I) complexes of this ligand are reported in our previous communication¹⁶. The present study embodies synthesis and characterization of some novel organometallic derivatives of ruthenium (II & III) with 3-(4-Pyridyl)-4-substituted-triazoline-5-thione (I).

 

Scheme 1  Click here to View Scheme

 

Experimental

All chemicals used were either CP grade or AR grade. Solvents were distilled and dried before use. The ligands 3-(4-Pyridyl)-triazoline-5-thione (PytTH) and 3-(4’-Pyridyl)-4-phenyl-triazoline-5-thione (PPytTH) were prepared by the method of Dutta et al¹⁷. The ligands were recrystallized from ethanol before use. The precursor complexes, [RuX₃(Ef₃)₃] (X = Cl/Br; E = P/As), [RuH(CO)(Ef₃)₃Cl] (E = P/As) were prepared following the literature pathway^18-22.

Preparation of new ruthenium (II) complexes

All ruthenium (II) complexes were prepared by ligand substitution reactions using precursors [RuH(CO)(Ef₃)₃Cl] (E = P/As)^18-19 and ethanolic solution of ligands, PytTH or PPytTH in equimolar ratio using our previous method²³.

Analysis

Sl. No.1 : [RuCl(CO)(PΦ3)₂(PytT)] (deep brown) : Calculated (%) for RuC₄₄H₃₅N₄OSClP₂Ru (865.5) : C = 61.00; H = 5.08; N = 6.47; Ru = 11.66; Found (%) : C = 61.18; H = 5.18; N = 6.50; Ru = 11.72;

Sl. No.2 :    [RuCl(CO)(AsΦ3)₂(PytT)] (Brown) : Calculated (%) for RuC₄₄H₃₅N₄OSAs₂Cl (953.34) : C = 55.38; H = 3.67; N = 5.87; Ru = 10.59; Found (%) : C = 55.42; H = 3.77; N = 5.92;            Ru = 10.62;

Sl. No.3 : [RuCl(CO)(PΦ₃)₂(PPytT)]        (yellowish brown) : Calculated (%) for RuC₅₀H₃₉N₄SP₂Cl (941.50) : C = 63.72; H = 4.14;  N = 5.95; Ru = 10.72; Found (%) : C = 63.82; H = 4.21;  N = 6.02; Ru = 10.77;

Sl. No.4 : [RuCl(CO)(AsΦ₃)₂(PPytT)]  (yellowish brown) : Calculated (%) for RuC₅₀H₃₉N₄SAs₂Cl (1025.5) : C = 58.50; H = 3.80;  N = 5.46; Ru = 9.84; Found (%) : C = 58.62; H = 3.91; N = 5.38;  Ru = 9.92;

Preparation of ruthenium (III) complexes

All the reactions were carried out strictly anhydrous conditions and the complexes were prepared using a general method. Benzene solution of [RuX₃(Ef₃)₃] (X = Cl/Br; E = P/As) and ligand were mixed in equimolar ratios and stirred on magnetic stirrer for 15 mints and heated on reflux till the brown colour changed to yellowish green. The working mixture was concentrated and cooled. Addition of light petroleum ether produced solid products which was filtered and dried in vacuo over anhydrous CaCl₂. (yield = 76%)

Analysis

Sl. No.5 : [RuCl₂(PΦ₃)₂(PytT)] (yellowish green) : Calculated (%) for RuC₄₃H₃₅N₄P₂SCl₂ (873) : C = 59.10; H = 4.00; N = 6.41; Ru = 11.56; Found (%) : C = 59.01; H = 3.98; N = 6.38; Ru = 11.49;

Sl. No.6 : [RuCl₂(AsΦ₃)₂(PytT)]  (greenish yellow) : Calculated (%) for RuC₄₃H₃₅N₄As₂SCl₂ (960.84) : C = 53.70; H = 3.64; N = 5.82;   Ru = 10.51; Found (%) : C = 54.01; H = 3.70; N = 5.78;            Ru = 10.60;

Sl. No.7 : [RuBr₂(PΦ₃)₂(PytT)]       (brownish green) : Calculated (%) for RuC₄₃H₃₅N₄P₂SBr₂ (962) : C = 53.63; H = 3.63; N = 5.82; Ru = 10.49; Found (%) : C = 55.63; H = 3.68; N = 5.80; Ru = 10.52;

Sl. No.8 :    [RuBr₂(Asf₃)₂(PytT)]     (brownish green) : Calculated (%) for RuC₄₃H₃₅N₄As₂SBr₂ (1049.74) : C = 49.15; H = 3.33; N = 5.33; Ru = 9.62; Found (%) : C = 49.32; H = 3.40; N = 5.23; Ru = 9.68;

Sl. No.9 :    [RuCl₂(Pf₃)₂(PPytT)]     (yellowish green) : Calculated (%) for RuC₄₉H₃₉N₄SP₂Cl₂ (949) : C = 61.95; H = 4.10; N = 5.90; Ru = 10.64; Found (%) : C = 62.11; H = 4.20; N = 6.01; Ru = 10.68;

Sl. No.10 :  [RuCl₂(AsΦ₃)₂(PPytT)] (yellowish green) : Calculated (%) for RuC₄₉H₃₉N₄SAs₂Cl₂ (1033) : C = 56.92; H = 4.74; N = 6.42;  Ru = 9.77; Found (%) : C = 57.01; H = 4.80; N = 5.50; Ru = 9.89;

Sl. No.11 :  [RuBr₂(PΦ₃)₂(PPytT)]  (greenish brown) : Calculated (%) for RuC₄₉H₃₉N₄SP₂Br₂ (1037.8) : C = 56.65; H = 3.75; N = 5.39;    Ru = 9.73; Found (%) : C = 56.66; H = 3.88; N = 5.42; Ru = 9.80;

Sl. No.12 :  [RuBr₂(AsΦ₃)₂(PPytT)]   (greenish brown) : Calculated (%) for RuC₄₉H₃₉N₄SAs₂Br₂ (1125.64) : C = 52.23; H = 3.46; N = 4.97; Ru = 8.97; Found (%) : C = 52.40; H = 3.50; N = 5.01; Ru = 9.00;

The analysis of C, H and N were performed at CDRI, Lucknow, India. IR spectra of ligand and complexes were recorded on a Perkin Elmer 577 spectrophotometer in the range of 4000-200 cm^-1 as KBr pellet technique. Electronic spectra of ligand and complexes were recorded on a Backmann Du-6 spectrophotometer. The molar conductance of complexes (10^-3 M) were measured in DMF using Wiss-Werkstatter Weihem obb type LBR conductivity meter. The magnetic susceptibility was measured on a gouy balance using Hg[CO(SCN)₄] as calibrant.

Results And Discussion

The reactions of [RuHCl(CO)(Ef₃)₂] (E = P/As) (Scheme I) and [RuX₃(Ef₃)₃] (X = Cl/Br; E = P/As) with thioamide ligands (Scheme II) in 1:1 molar ratio in benzene afforded new hexa-coordinated complexes and ligands acts as mononegative bidentate anion.

Scheme 1,2 Click here to View scheme

 

The analytical data are in good agreement with general molecular formula proposed. The mononegative bidentate thioamide ligands replaces are triphenyl phosphine or triphenyl arsine molecule, one chlorido or bromido group from precursors [RuX₃(EΦ₃)₃] and hydrido group and one PΦ₃ or AsΦ₃ from precursors, [RuHCl(CO)(EΦ₃)₃]. All the isolated products were air-stable and non-hygroscopic nature and fair soluble in acetone, EMK, DMF & DMSO.

Magnetic moment and UV-Vis Spectra

The substitution products [RuCl(CO)(EΦ₃)₂(PytT)] and [RuCl(CO)(Ef₃)₂(PPytT)] were diamagnetic indicating Ru⁺⁺ (d⁶) and ¹A_1g ground state. The d – d transition bands (table 2) consistent with octahedral structure²⁴.

The magnetic moment value of [RuX₂(EΦ₃)₂(PytT)] or [RuX₂(Ef₃)₂(PPytT)] (X = Cl/Br; E = P/As) are in the range of 1.80-1.95 BM corresponding to a single unpaired electron in a low spin T_2g⁵_eg⁰ configuration and oxidation state of ruthenium is +3. So, the ground state of Ru (III) is ²T_2g and first excited doublet level in order of increasing energy are ²A_2g and ²A_1g which arises from t_2g⁴_eg¹ configuration²⁵. The electronic spectra of complexes exhibit bands around 18585 (²T_2g →²A_2g), 22935 (T_2g → π*, MLCT), 38760   (n→ π*) and 49020 cm-1 (p →π*) are consistent with octahedral structure of other ruthenium (III) complexes²⁶.

Infrared Spectra

The IR bands of interest of ligands and complexes are given in Table 1. A comparison of the infrared bands of the ligands and complexes indicate the simultaneous formation of Ru – N and Ru – S bonds.

1. Two bands having contribution from nNH and nCH are present at 3120 cm^-1 and 3080 cm^-1 in PytTH and at 3060 cm^-1 in PPytTH. But there is only one band centred at 3080 cm^-1 in the spectra of complexes of PytTH and found to be absent in the complexes PPytTH. This suggests that H-atom of N-H group of ligands has been replaced by the Ru(II) and Ru(III) ions leading to the formation of Ru^II-N and Ru^III-N bonds.
2. Thioamide band IV has main contribution from vC …– S observed at 850 cm^-1 (PytTH) and at 785 cm^-1 (PPytTH) in the spectra of the ligands shift to lower frequency by 30-50 cm^-1 indicating coordination of thioamide ligands through thione sulphur and formation of ruthenium – S bond following our previous observations²⁶.
3. The simultaneous Ru-N and Ru-S bonding results in a decrease in the frequency of thioamide band IV by 30-50 cm^-1, blue shift to higher frequency of 10-15 cm^-1 of band II and red shift to the extent of 35-55 cm^-1 in thioamide band I. These observations are in good agreement with previous literature²⁷. New bands at 435-465 cm^-1 (Ru-N) and 405-410 cm^-1 (Ru-S) due to stretching modes further supports these observations.
4. The presence of bands near 540, 680, 750 and 1550 cm^-1 are attributed to coordinated PΦ₃/AsΦ₃ in complexes^29-30. The presence of single Ru-P stretching modes at 510-500 cm^-1 confirms two bulkyu PΦ₃ groups are at mutual Trans-disposition in octahedral structure of complexes (Str. I & II). However, more than one Ru-X stretching mode in Ru (III) complexes indicates cis-disposition of two chlorine or two bromine atoms in octahedral structure (Str. III & IV).

 

Figure1: (X = Cl/Br; E = P/As)   Click here to View figure

 

Figure2: (X = Cl/Br; E = P/As)   Click here to View figure

 

Figure3: (X = Cl/Br; E = P/As)   Click here to View figure

 

Figure4: (X = Cl/Br; E = P/As)   Click here to View figure

 

5.  The non-ligand band at 1950-1960 cm-1 in carbonyl complexes of ruthenium (II) supports terminal C º O group slightly higher frequency than in precursor complex.

Thus, the ligands behaves as mononegative bidentate (N, S) donor.

Table-1 : Assignment of Major infrared bands of 3-(4-Pyridyl)-4-substituted-triiazoline-5-thioneand their Ru (II & III) complexes in (cm^-1).

Compounds	nN-H + nCH	Thioamide Bands				nRu-S	nRu-N	nRu-X
		Band I	Band II	Band III	Band IV
PytTH (ligand)	3120 m 3080 m	1570 (sb)	1205 (s)	960 (s)	850 (ms)	¾	¾	¾
[RuIICl(CO)(PΦ3)2(PytT)]	3080 m	1535 (s)	1210 (s) 1200 (m)	925 (m)	810 (m)	406 w	441 (m)	370 w 340 w
[RuIICl(CO)(AsΦ3)2(PytT)]	3085 m	1530 (s)	1220 m 1200w	935 (m)	820 (m)	410 w	445 (m)	370 w 350 w
[RuIIICl2(PΦ3)2(PytT)]	3060 m	1545 (s)	1215 m 1200 m	945 (m)	830 (m)	425 (m)	448 (m)	364 m 343 m
[RuIIICl2(AsΦ3)2(PytT)]	3070 m	1540 (s)	1215 (m) 1200 (m)	940 (m)	825 (m)	430 m	450 m	356 m 335 m
[RuIIIBr2(PΦ3)2(PytT)]	3065 m	1535 (s)	1200 w 1185 m	945 (m)	820 (m)	430 w	445 m	355 m 330 m
[RuIIIBr2(AsΦ3)2(PytT)]	3070 m	1545 (s)	1220 m 1190 m	950 (s)	825 (m)	430 w	430 m	360 m 330 m
PPytTH (ligand)	3060 m	1480 (s)	1290 (s) 1240 (m)	1090 (m)	785 m	¾	¾	¾
[RuIICl(CO)(PΦ3)2(PPytT)]		1435 (s)	1235 (s) 1210 (m)	1035 (m)	765 m	428 w	464	364 m
[RuIICl(CO)(AsΦ3)2(PPytT)]		1460 (s)	1240 (s) 1220 (m)	1040 w	765 m	436 (w)	458 m	356
[RuIIICl2(PΦ3)2(PPytT)]		1445 m	1250 (s) 1230 (m)	1065 (m)	770 (m)	440 w	476	365 m 345
[RuIIICl2(AsΦ3)2(PPytT)]		1440 (ms)	1245 (s) 1235 (m)	1070 (m)	772 (m)	436 w	458 m	356 m 335 m
[RuIIIBr2(PΦ3)2(PPytT)]		1465 (m)	1250 m 1235 m	1065 (m)	760 m	440 w	460 m	350 m 330 m
[RuIIIBr2(AsΦ3)2(PPytT)]		1460 (m)	1250 m 1220 (m)	1065 (m)	765 m	438 w	470 m	345 m 332 m

 

Table2 :  Magnetic, Conductometric and Electronic spectral data of ruthenium (II & III) complexes  Click here to View table

 

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