Organoruthenium (II) Complexes with Thioamide Ligands

Introduction

Organometallic Chemistry of ruthenium (II) is currently receiving a lot of attention due to catalytic^1-3 medicinal^4-5, anti-bacterial⁶ and significant biological activities^7-8. The present communication comprises synthesis, spectral characterization structural investigations and nature of metal ligand bonding in some new organometallic compounds of ruthenium (II) with 1, 2, 3, 4 – tetrazoles having thiomide group (I). Moreover, the ligands selected for study are claimed to possess anti-convulsant⁹, radio protective¹⁰ and spermatostatic¹¹ propeties. The anti-bacterial activities against staphylococcus aureus and Escharichia Coli have been reported by copwer et al¹².

Experimental

All the reagent used were of anal R or chemically pure grade. Solvents were dried before use. 1-substituted tetrazoline-s-thione were prepared by the method described by Lieber et al.¹³ The precursor complexes ¹⁴ and ¹⁵ were prepared according to the literature procedures.

Procedure 

Preparation of Complexes 

To  a solution of  (950 mg, 1 m-mol) Or  (1 g, 1m.mol) in benzene (30 ml) the respective ligands (1m.mol) were added. The resulting solution was stirred on magnetic stirror and concentrated to Ca. 5 ml and the product was separated by the addition of ether. It was filtered and dried in vacuum (yield = 75.80%).

The C, H and N analyses were performed at the C.D.R.I, Lucknow, India. ¹H and ³¹P NMR spectra were recorded on Bruker 400 MHz or varian  instruments using TMS and orthophosphoric acid as references, respectively. Electronic spectra were recorded with Zeiss (Jena) model of automatic recording system. IR spectra of ligands and complexes were recorded by means of Perkin-Elmer 521 spectrophotometer in the range of 4000 – 200 cm^-1 using KBr pellets. Molar conductance of complexes were measured in DMF using Wiss-Werkstatter Weithem obb type conductivity meter. The magnetic moment of the complexes were measured at 300 K using gouy balance.

Table 1 : Analytical data of new Ru(II) complexes

Complex/(Colour)	Analysis (%) : Found (Calcd)				(Cm–1)	Assignment
	C	H	N	Ru
Molecular formula   (yellow)	59.38 (59.60)	4.60 (4.61)	6.61 (6.62)	11.95 (11.94)	19230 16660 28570 34480	(CT intra ligand)
(dull yellow)	53.90 (53.99)	4.10 (4.17)	6.11 (5.99)	10.90 (10.81)	19600 16950 28735 35715	( intra-ligand)
(yellow)	61.30 (61.32)	4.10 (4.20)	6.51 (6.36)	11.50 (11.48)	19230 16950 28575 35090	(CT intra-ligand)
(faint yellow)	55.92 (55.81)	3.79 (3.82)	5.79 (5.78)	10.40 (10.43)	19420 16950 33890 34245	(CT Intra-ligands)
(yellow)	61.68 (61.77)	4.40 (4.36)	6.28 (6.26)	11.35 (11.30)	19450 16720 28570 35090	(CT Band Intra-ligands)
(Dull yellow)	56.31 (56.24)	3.95 (3.97)	5.75 (5.70)	10.30 (10.29)	19270 16530 28400 35090	(CT Band)

Results and Discussion

All thioamide ligands interacts with precursor complexes in a 1 : 1 molar ratio in  giving solid derivatives  (; HL = ligands) and acts as mononegative bidentate ligands.

Complexes are thermally stable up to 150ºC, non-hygroscopic, air-stable and shiny crystalline solids. These are sparingly soluble in methanol, benzene, soluble in dichloromethane, acetone, acetonitrile, DMF, DMSO and insoluble in diethyl ether. Analytical data of the complexes are consistent with our formulations. The conductance behavior suggest their non-electrolytic nature.

Table 2 : IR, ¹H NMR and ³¹P NMR spectral data

Compd.	Thio amide Bands (cm–1)				1H NMR (PPM)			31P NMR (PPM)
	I	II	III	IV	Aromatic Protons	N-H Protons	Protons
HL (ligand)	1500s	1280m	1065m	805m	–	1.52	2.93	–
	1485s	1305m	1045m	770m	7.92	–	2.92	28.72
	1480s	1300m	1050m	775m	8.00	–	2.94	–
HL1 (ligand)	1510s	1290m	1050m	810m	7.85	1.54	–	–
	1490s	1310m	1030m	765m	7.86	–	2.93	28.82
	1500s	1315m	1035m	780m	7.92	–	2.95	–
HL2 (ligand)	1504s	1286m	1055m	790m	7.56	1.51	2.95	–
	1495s	1305m	1045m	765m	7.86	–	2.98	28.80
	1490m	1310m	1035m	770m	7.92	–	2.93	–

Electronic Spectra 

All complexes are diamagnetic indicating the presence divalent ruthenium () and  ground term in octa hedral crystal field. Two spin allowed transitions  and  may be expected¹⁶. The electronic spectral bands at 20400 – 19230 cm^–1 and 18660 – 16600 cm^–1 assigned to  and  transition respectively indicate octahedral structure of complexes¹⁷. The other high intensity bands in UV region at 28570 cm–1 () and at 34480 cm^–1 are probably due to charge transfer. The nature of the electronic spectra are similar to those observed for other octahedral ruthenium (II) complexes¹⁸.

IR Spectra 

A comparison of IR spectra of ligands and respective complexes indicate formation of  and  bonds. The  (2550 cm^–1) and  (3180 cm^–1) bands of ligand disappear from the spectra of complexes indicating deprotonation of imino proton on complexation and formation of Ru – N bond. The formation of simultaneous Ru – S and Ru – N bond blue shift thioamide band II (20-30 cm^–1) and red shift thioamide band I ( 15-20 cm^–1), band III (25-30 cm^–1) and band IV (30-40 cm^–1) of ligand due to increase in CN bond order and decrease in CS bond  order.^19-21 The terminal coordinated  group appeared at 1944 – 1980 cm^–1 in all complexes and the characteristic bands due to  or  are also present in the expected region²².

¹HNMR and ³¹P NMR sectra

All the complexes showed signals in the  range due to the aromatic protons of ²³. However, broad multiplet in the  region due to phenyl protons of ligands. The broadening of this peak probably due to presence of four nitrogen atoms which may cause large quadrupole resonance broadening effect. The signal for methyl protons appears in the region . The resonances due to imino proton in the ligands observed at  is absent in the spectra of complexes suggesting the formation of  bond and deprotonation of N-H group on complexation.

The ³¹P NMR spectra of three complexes were recorded in order to confirm the presence of  groups and to determine the stereochemistry of the complexes. The appearance of a signal around 28.82 PPM in the spectra of complexes confirmed the presence of magnetically equivalent phosphorous atoms and thus suggesting that two  groups are trans to each other in octahedral structure²⁴ (II).

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