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Synthesis, 13C NMR and IR spectroscopic studies of gold(I) complexes of imidazolidine-2-thione and its derivatives
Po~yhedrm Vol. 4, No. 10, pp. 1683-1688, Printed in Great Britain
1985 0
0277-5387/M 1985 Per~OU
S3.M)+ .oO Pras Ltd
SYNTHESIS, 13C NMR AND IR SPECTROSCOPIC STUDIES OF GOLD(I) COMPLEXES OF IMIDAZOLIDINE-2-THIONE AND ITS DERIVATIVES ANVARHUSEIN A. ISAB* and M. SAKHAWAT HUSSAIN Department of Chemistry, University of Petroleum and Minerals, Dhahran, Saudi Arabia (Received 22 March 1984; accepted 9 May 1984)
Abstract-The gold(I) complexes of imidazolidine-2-thione and its derivatives were synthesized and their i3C NMR and IR spectroscopic studies were carried out. When gold(II1) was reacted with the ligands using a 1: 4 metal to ligand ratio, gold(II1) was reduced to gold(I), the bis complexes of the general formula AuL,,X (where n = 2) were formed. However, when gold(II1) was reduced to gold(I) by a reducing agent followed by an addition of the ligand to an aqueous or methanolic solution of gold(I), only mono complexes of the type AuLX were obtained. The structures of the reported complexes are proposed on the basis of their spectroscopic measurements.
Imidazolidine-2-thione, Imt (Ia), its six-membered analog, Eapt (II), and its derivatives MeImt (Ib) and PrImt (1~) are interesting ligands because of their potential binding sites such as -NH and -C=S. These ligands exist in -N=C-SH or -NH-C=S formexhibiting thiol + thione equilibrium. However, it has been established that the thione form dominates in the solid state.lB2 The coordination chemistry of these ligands with various transition metal ions such as Cu(I), Zn(II), Pd(II), Co(II), Ni(I1) and Hg(I1) has been studied.“*s
By reacting copper(I1) chloride or bromide with these ligands, an immediate reduction of copper(I1) to copper(I) takes place in MeOH or in aqueous solution4*6 and the mono as well as the bis complexes of the general formulas CuLX and CuL,X are formed. The mono complexes are polymeric in nature whereas the bis complexes are dimeric.4*6 The reduction of gold(II1) to gold(I) with Imt was studied by Morgan and Burstall Usually a gold(II1) to ligand ratio of 1: 4 resulted in a bis complex of the formula AuL,X (X = Cl-, Br-). However, we have
HzC4-CH, H-N
?I
- R
H C/‘“‘\,, 2l I 2 H-N \ c /N-H
Imt : R = H ; imidazolidine-2-thione MeImt : R = CH, ; ~-methyl-imidazolidine2-thione PrImt: R = -CH,CHsCH, ; N-propyl-imidazolidine-2-thione
II (II)
*Author to whom all correspondence should be addressed.
Eapt : 1,3-bis(ethylamino)propane-2-thione
recently demonstrated* that, if the reduction of gold(II1) is carried out in aqueous solution using SO, gas, gold(I) is stabilized by the ligand forming only monomeric AuLX species.
1683
A. A. ISAB and M. S. HUSSAIN
1684
We have extended our studies on gold(IkImt systems, as a part of our continuing research program on synthetic and structural studies of crystalline gold(Ikthio1 complexes as model compounds for anti-arthritic drugsgyro such as Myocrisin or Solganol which are polymericin nature as identified by NMR and CD spectroscopy.“*12 In the present paper we report the synthesis and spectroscopic studies of some mono and bis gold(I)--imidazolidine-2-thione complexes. Most of these complexes were obtained in pure crystalline forms and the single crystal X-ray studies on some of them are currently in progress.
EXPERIMENTAL All chemicals were obtained from Fluka Chemical which was obtained Co. except “CDsOD from BDH. The ligands were prepared by the procedures described in the literature.13*14 Preparation of complexes offormula L,AuX
The ligands were dissolved in MeOH and the gold(II1) halides were dissolved in double deionized distilled water. The L : M ratio was kept at 4 : 1. As soon as gold(II1) was added to the ligand, an orange coloured residue was immediately formed which dissolved on stirring to give a colourless precipitate. The precipitate was dissolved in boiling MeOH to obtain crystalline products. In some cases the complexes could only be obtained in the form of a powder. Preparation of mono complexes offormula LAuX
The gold(II1) halides were reduced to gold(I) by passing SO, gas as described earlier.” As soon as the solution became colourless, the ligand was added, keeping the gold(I) to ligand ratio close to 1: 1. Usually a white residue was obtained. The elemental analyses of the products were carried out on a Carlo Erba (Italy) elemental analyzer. Using the above general procedures the following complexes were prepared : Gold(I)-imidazolidine - 2 - thione bromide: (1mt)AuBr. Bis(imidazolidine - 2 - thione)gold(I) chloride hydrate : (Imt),AuCl - H,O. Gold(IkN - methyl - imidazolidine - 2 - thione chloride : (MeImt)AuCl. Gold(I)-N - methyl - imidazolidine - 2 - thione bromide : (MeImt)AuBr. Bis(N - methyl - imidazolidine - 2 - thione)gold(I) chloride : (MeImt),AuCl.
Bis(l,3 propyl - imidazolidine - 2 - thione)gold(I) chloride : (Eapt),AuCl. Bis(N - propyl - imidazolidine - 2 - thione)gold(I) chloride : (PrImt),AuCl. Spectroscopic measurements
IR spectra of the pure ligands and their gold(I) compounds were obtained on a Perkin-Elmer IR 180 or on a Beckman Microlab IR spectrophotometer using KBr pellets. 13C NMR spectra were obtained on a Varian XL-200 NMR spectrometer operating at a 50.3 MHz frequency. The ligands and gold(I) complexes were dissolved in a 50: 50 (v/v) D20/‘2CD30D solvent. The complexes were not very soluble but enough dissolved to yield spectra except (Eapt),AuCl and (MeImt)AuCl which are extremely insoluble in the above solvents. The chemical shifts were measured relative to 1,4dioxane as internal reference having resonance at +67.4 ppm relative to DSS. 13C NMR spectra of PrImt, (PrImt)AuCl and (PrImt),AuCl were measured in de-acetone.
RESULTS
AND DISCUSSION
Mono and bis gold(I) complexes were formed by Imt and its N-methyl derivative, all of which were in pure crystalline state. In the case of Eapt only the bis complex was formed as indicated by the analytical data given in Table 1.
13C NMR studies
A representative 13C NMR spectrum is shown in Fig. 1 and Table 2 lists the “C NMR chemical shifts of the ligands and their complexes. As reported earlier,* in the case of mono complexes, the C-2 resonance is shifted by about 8 ppm compared to the free ligand but a less dramatic shift (- 0.768 ppm) was observed for C-4 and C-5 resonances. In the bis Imt-complexes, the C-2 resonance is shifted by +6.764 ppm whereas the C-4,5 resonance shows a slight shift of only - 0.836 ppm. The most significant shift for the (MeImt),AuCl complex is also for the C-2 resonance (+7.644 ppm). The C-4, C-5 and CH, resonances are only shifted by - 1.43, -0.96 and -0.627 ppm, respectively. The shift in the C-2 resonance of the (PrImt),AuCl complex is only about 2 ppm, which is significantly less than 8.292 ppm observed for the mono complex (PrImt)AuCl or about 7 ppm observed for any of the bis complexes. This variation in the C-2 shift (Fig. 2) can be explained on
Gold(I) complexes of imidazolidine-2-thione
1685
and its derivatives
Table 1. Analytical data for the ligands and gold(I) complexes* Melting point (“C)
Complex (1mt)AuBr
198199
Pale yellow powder
(Imt)~AuCl* H,O
247-249
White crystalline
(MeImt)AuCl
186187
White powder
(MeImt)AuBr
!67-168
Yellow powder
(MeImt)zAuC1
246247
Light brown crystalline
(Eapt),AuCl
286288
White crystalline
92-93
White crystalline
(PrImt)~AuCl
H
C
N
1.53 (1.58) 2.98 (3.08) 2.33 (2.29) 1.98 (2.04) 3.24 (3.44) 3.39 (3.44) 4.75 (4.66)
9.22 (9.55) 15.70 (15.84) 14.36 (13.77) 12.29 (12.21) 20.12 (20.66) 20.64 (20.66) 28.08 (27.66)
7.86 (7.38) 12.80 (12.32) 13.92 (14.92) 7.21 (7.12) 11.77 (12.05) 11.94 (12.05) 11.03 (10.76)
Colour
* The corresponding calculated values are given in parentheses.
the basis of the shielding effects on C-2 which is least shielded in the bis complexes and is most shielded in the mono compounds. An appreciable shift of the C-2 resonance in the i3C NMR spectra clearly indicates that, in al1 of these complexes, gold(I) is bonded to the ligand through sulfur atom only and the -NH group is not involved in any kind of bonding. Any bonding through -NH would have resulted in a considerable shift of the C-4 resonance in the (MeImt)~AuCl complex. A significant shift in 13C NMR for C=S carbon atoms consistently observed
in these complexes can be used as a diagnostic NMR observation for the location of bonding sites in solution phase of these and similar gold(I) complexes. The sulfur coordination of gold(I) in chloro (N - ethyl - 1,3 - imi~zolidine - 2 - thione)gold(I) and chloro(N - propyl - 1,3 - imidazolidine - 2 - thione) gold(I) complexes* was confirmed by the single crystal X-ray analysis in the solid state and a similar i3C shift for the C=S carbon was observed in both complexes. The + 1 oxidation state for gold in the (PrImt),AuCl was assumed on the basis of its white
A=
CH3
B=
2C=S--c_Au4--SzC CH3
c-2 CH3
Ref. ~
I
180
I
/
/
!
I
I
70
50
30
rm
Fig. 1. Representative
13C NMR spectra of MeImt ligand and its bis-gold(I) complex.
A. A. ISAB and M. S. HUSSAIN
1686
Table 2. 13C NMR chemical shifts of gold(I) complexes of imidazolidine-2-thione derivatives*
and its
Complex
c-z
c-4
C-5
a-CH,
B-CH,
Y-CH,
Imt (Imt)AuBr
182.69 t
-
-
175.926 (6.764) 183.084 175.44 (7.644) 184.469 182.508 (1.961) 176.181 (8.282)
45.205 45.973 (-0.768) 46.041 (-0.836) 51.461 52.891 - 0.96) 48.851 49.175 - 0.324) 49.505 (-0.654)
-
(Imt),AuCl
45.205 45.973 (-0.768) 46.041 (-0.836) 41.661 42.641 ( - 1.43) 48.539 48.749 (-0.21) 50.616 (-2.077)
-
-
-
-
-
33.828 34.455 (-0.627) 11.306 11.173 (0.133) 11.067 (0.239)
MeImt (MeImt)~AuCl PrImt (PrImt),AuCl (PrImt)AuCl
41.763 42.012 ( - 0.249) 42.712 (-0.49)
20.801 20.857 ( - 0.056) 20.795 (0.006)
* 13CNMR resonances are assigned as given in Faure et al., Org. Magn. Reson. 1977,9,688. The numbers in parentheses indicate shifts with respect to the free ligands. A positive value indicates
a high-field shift whereas a negative value shows a low-fieldshift. The spectrum of (MeImt)AuBr could not be recorded due to its insolubility in the 50/50 (v/v) CD,OD/D,O solvent. t The resonance could not be detected in the spectrum. colour. Both mono and bis complexes are white in colour. In the case of the mono complexes the reduction of gold(II1) to gold(I) was carried out by SO,, whereas an excess of the ligand was used for the reduction of the bis complexes. The MBssbauer and
single crystal X-ray studies are planned to identify the oxidation state of gold and to elucidate the solid state structures of these complexes. The (Eapt),AuCl complex is very insoluble in water and its analytical data (Table 1) show that no
I
I
Ill
I
I
I
I
I
200
180
160”
80
60
40
20
0
mm
Fig. 2. 13C NMR spectra of PrImt ligand and its mono- and bis-coordinated species showing variations in the chemical shift of C-2 as a function of shielding.
Gold(I) complexes of imidazolidine-2-thione
and its derivatives
Table 3. Significant IR bands for the ligands and their complexes in the region -200 v(C-N) +&N--H)
A(N-H)
v(C=S)
3300 3300 sh
1500 1520 sh
680 sh 660 sh
510 w 530 sh
(Imt),AuCl MeImt (MeImt)AuCl (MeImt)AuBr (MeImt),AuCl Eapt (Eapt),AuCl
3260 sh 3200 sh 3200 sh 3300 sh 3100 sh 3300 sh 3200 sh
1525 sh 1520 sh 1555 sh 1555 sh 1550 sh 1560 sh 1565 vs
665 sh 670 sh 635 sh 635 sh 640 sh 640 sh 635 sh
490 sh 520 sh 495 sh 490 sh 490 sh 510 w 520 sh
PrImt (PrImt),AuCl
3300 sh 3200 sh
1510 vs 1530 sh
610 sh 670 sh
515 vs 515 sh
Compound
v(N-H)
Imt (1mt)AuBr
H,O molecule is present. In contrast membered (Imt),AuCl
to this, the 5-
analog of Eapt forms the complex - HZ0 which is water soluble16 and its X-
ray analysis revealed an ionic structure with linear gold(I) coordination through sulfur atoms. Due to the high insolubility of (Eapt),AuCl, its 13C NMR spectrum could not be recorded.
IR absorption spectral studies
The IR spectra of the free ligands and their gold(I) complexes (Table 3) do not show S-H absorption in the region of 2500 cm-’ nor a C=N band at 17001590 cm-’ but exhibit a strong absorption around 3300 cm-’ corresponding to N-H stretch.” The presence of the band at 3300 cm-’ in the free ligand as well as in the gold(I) complexes clearly indicates the existence of thione forms in the solid state. A band at 375 w cm-’ in the gold(I)-diisobutyl dithiocarbamate dimer ” and a band at 342 cm- 1for Au(SMe); anionI have been assigned to the Au--S vibration. On a correlative basis the band at 345 cn - 1 found in all complexes of the present study can be assigned to the Au--S vibration. A shift of about 40 cm - ’ in the C=S band in all complexes is consistent with our conclusion that the gold(I) is bonded through sulfur. The band at 210 cm-’ for (1mt)AuBr and at 225 cm-’ for (MeImt)AuBr can be assigned to the Au-Br stretching.” The Au-Cl absorption is usually found in the region of 310320 cm-l for various gold(I) complexes2’ with coordinated chloride ion. This band was observed in the (MeImt)AuCl complex but was absent for (Imt),AuCl, (MeImt),AuCl and (PrImt)2AuCl complexes. This is consistent with the ionic nature of the
cm- ’
Vibrations below 450 cm- 1
345 w, 320 w, 295 w, 275 sh, 240 w, 210 w 385 w, 345 w, 290 w 390 w 415 w, 350 w, 320 sh 415 w, 275 w, 225 w 420 w, 345 w, 275 sh 415 sh, 340 sh 415 sh, 385 sh, 345 w, 315 sh 375 VW 350 w
chloride in the last three complexes which, of course, will not exhibit any Au-Cl stretching vibrations.16 The presence of an Au-Cl vibration at 3 15 cm - 1 in (Eapt),AuCl complex indicates that the gold(I) is three coordinated. The fact that this complex is insoluble in water/methanol solvent further indicates that the complex is neutral or polymeric in nature. CONCLUSIONS On the basis of’ 3C NMR and IR spectral data, the following conclusions can be drawn for gold(I) geometries in its complexes with imidazolidine-2thiones and its derivatives : (1) Imt and its derivatives exist in the thione forms both in the solution as well as in the solid phase. (2) When these ligands react with gold(I), different complexes of types AuLX and AuL,X are formed, in all of which the ligands exist in the thione form. (3) The IR and 13C NMR spectral studies revealed three coordination of the following kinds for the gold(I) complexes with the above ligands : (a) C=S -, Au-X for all mono complexes. (b) [C=S j Au c S=C] + for all bis complexes which are soluble in water or methanol.
7’
@)c=s +Au\
‘s=c
1688
A. A. ISAB and M. S. HUSSAIN for L,AuX Au(Eapt),Cl.
neutral
complex
such
as
Acknowledgements-This research was supported by the UPM Research Committee Project No. CY/METALION/54. One of us (A.A.1) is thankful to the UPM for providing facilities under the above project.
REFERENCES 1. C. Preti and G. Tosi, Can. J. Chem. 1976,54, 1558. 2. L. M. Butler, J. R. Creighton, R. E. Oughtred, E. S. Raper and I. W. Nowell, Znorg. Chim. Acta 1983,75, 149. 3. M. E. O’Neil, E. S. Raper and J. A. Daniels, Znorg. Chim. Acta 1981,54, L3. 4. L. P. Battagalia, A. B. Corradi, F. A. Devillanova and G. Verani, Transition Met. Chem. 1979,4,264. 5. E. S. Raper and P. H. Crakett, Znorg. Chim. Acta 1981, 50, 159. 6. F. A. Devillanova and G. Verani, Transition Met. Chem. 1977,2,120.
7. G. T. Morgan and F. H. Burstal., J. Chem. Sot. 1928,
143. 8. M. S. Hussain and A. A. Isab, J. Coord. Chem. 1985,14, 17. 9. P. J. Sadler, Struct. Bonding (Berlin) 1976,29, 171. 10. C, F. Shaw, Znorg. Perspect. Biol. Med. 1978,2,287. 11. A. A. Isab and P. J. Sadler, J. Chem. Sot., Dalton Trans. 1981,1657. 12. D. H. Brown, G. McKinaly and W. E. Smith, J. Chem. Sot., Dalton Trans. 1977,1874. 13. G. D. Thorn, Can. J. Chem. 1955,33,1278. 14. L. Maier, Helv. Chim. Acta 1970,53, 1417. 15. A. A. Isab and P. J. Salder, Biochim. Biophys. Acta 1977,492,322. 16. P. G. Jones and G. M. Sheldrick, Acta Crystallogr. 1976, B32,3321. 17. L. H. Little and R. H. Ottewill, Can. J. Chem. 1962,40, 2110. 18. F. J. Farrell and T. G. Spiro, Znorg. Chem. 1971, 10, 1606. 19. G. A. Bowmaker and B. C. Dobson, J. Chem. Sot., Dalton Trans. 1981,267. 20. G. E. Coates and C. Parkin, J. Chem. Sot. 1963,421.
1985 0
0277-5387/M 1985 Per~OU
S3.M)+ .oO Pras Ltd
SYNTHESIS, 13C NMR AND IR SPECTROSCOPIC STUDIES OF GOLD(I) COMPLEXES OF IMIDAZOLIDINE-2-THIONE AND ITS DERIVATIVES ANVARHUSEIN A. ISAB* and M. SAKHAWAT HUSSAIN Department of Chemistry, University of Petroleum and Minerals, Dhahran, Saudi Arabia (Received 22 March 1984; accepted 9 May 1984)
Abstract-The gold(I) complexes of imidazolidine-2-thione and its derivatives were synthesized and their i3C NMR and IR spectroscopic studies were carried out. When gold(II1) was reacted with the ligands using a 1: 4 metal to ligand ratio, gold(II1) was reduced to gold(I), the bis complexes of the general formula AuL,,X (where n = 2) were formed. However, when gold(II1) was reduced to gold(I) by a reducing agent followed by an addition of the ligand to an aqueous or methanolic solution of gold(I), only mono complexes of the type AuLX were obtained. The structures of the reported complexes are proposed on the basis of their spectroscopic measurements.
Imidazolidine-2-thione, Imt (Ia), its six-membered analog, Eapt (II), and its derivatives MeImt (Ib) and PrImt (1~) are interesting ligands because of their potential binding sites such as -NH and -C=S. These ligands exist in -N=C-SH or -NH-C=S formexhibiting thiol + thione equilibrium. However, it has been established that the thione form dominates in the solid state.lB2 The coordination chemistry of these ligands with various transition metal ions such as Cu(I), Zn(II), Pd(II), Co(II), Ni(I1) and Hg(I1) has been studied.“*s
By reacting copper(I1) chloride or bromide with these ligands, an immediate reduction of copper(I1) to copper(I) takes place in MeOH or in aqueous solution4*6 and the mono as well as the bis complexes of the general formulas CuLX and CuL,X are formed. The mono complexes are polymeric in nature whereas the bis complexes are dimeric.4*6 The reduction of gold(II1) to gold(I) with Imt was studied by Morgan and Burstall Usually a gold(II1) to ligand ratio of 1: 4 resulted in a bis complex of the formula AuL,X (X = Cl-, Br-). However, we have
HzC4-CH, H-N
?I
- R
H C/‘“‘\,, 2l I 2 H-N \ c /N-H
Imt : R = H ; imidazolidine-2-thione MeImt : R = CH, ; ~-methyl-imidazolidine2-thione PrImt: R = -CH,CHsCH, ; N-propyl-imidazolidine-2-thione
II (II)
*Author to whom all correspondence should be addressed.
Eapt : 1,3-bis(ethylamino)propane-2-thione
recently demonstrated* that, if the reduction of gold(II1) is carried out in aqueous solution using SO, gas, gold(I) is stabilized by the ligand forming only monomeric AuLX species.
1683
A. A. ISAB and M. S. HUSSAIN
1684
We have extended our studies on gold(IkImt systems, as a part of our continuing research program on synthetic and structural studies of crystalline gold(Ikthio1 complexes as model compounds for anti-arthritic drugsgyro such as Myocrisin or Solganol which are polymericin nature as identified by NMR and CD spectroscopy.“*12 In the present paper we report the synthesis and spectroscopic studies of some mono and bis gold(I)--imidazolidine-2-thione complexes. Most of these complexes were obtained in pure crystalline forms and the single crystal X-ray studies on some of them are currently in progress.
EXPERIMENTAL All chemicals were obtained from Fluka Chemical which was obtained Co. except “CDsOD from BDH. The ligands were prepared by the procedures described in the literature.13*14 Preparation of complexes offormula L,AuX
The ligands were dissolved in MeOH and the gold(II1) halides were dissolved in double deionized distilled water. The L : M ratio was kept at 4 : 1. As soon as gold(II1) was added to the ligand, an orange coloured residue was immediately formed which dissolved on stirring to give a colourless precipitate. The precipitate was dissolved in boiling MeOH to obtain crystalline products. In some cases the complexes could only be obtained in the form of a powder. Preparation of mono complexes offormula LAuX
The gold(II1) halides were reduced to gold(I) by passing SO, gas as described earlier.” As soon as the solution became colourless, the ligand was added, keeping the gold(I) to ligand ratio close to 1: 1. Usually a white residue was obtained. The elemental analyses of the products were carried out on a Carlo Erba (Italy) elemental analyzer. Using the above general procedures the following complexes were prepared : Gold(I)-imidazolidine - 2 - thione bromide: (1mt)AuBr. Bis(imidazolidine - 2 - thione)gold(I) chloride hydrate : (Imt),AuCl - H,O. Gold(IkN - methyl - imidazolidine - 2 - thione chloride : (MeImt)AuCl. Gold(I)-N - methyl - imidazolidine - 2 - thione bromide : (MeImt)AuBr. Bis(N - methyl - imidazolidine - 2 - thione)gold(I) chloride : (MeImt),AuCl.
Bis(l,3 propyl - imidazolidine - 2 - thione)gold(I) chloride : (Eapt),AuCl. Bis(N - propyl - imidazolidine - 2 - thione)gold(I) chloride : (PrImt),AuCl. Spectroscopic measurements
IR spectra of the pure ligands and their gold(I) compounds were obtained on a Perkin-Elmer IR 180 or on a Beckman Microlab IR spectrophotometer using KBr pellets. 13C NMR spectra were obtained on a Varian XL-200 NMR spectrometer operating at a 50.3 MHz frequency. The ligands and gold(I) complexes were dissolved in a 50: 50 (v/v) D20/‘2CD30D solvent. The complexes were not very soluble but enough dissolved to yield spectra except (Eapt),AuCl and (MeImt)AuCl which are extremely insoluble in the above solvents. The chemical shifts were measured relative to 1,4dioxane as internal reference having resonance at +67.4 ppm relative to DSS. 13C NMR spectra of PrImt, (PrImt)AuCl and (PrImt),AuCl were measured in de-acetone.
RESULTS
AND DISCUSSION
Mono and bis gold(I) complexes were formed by Imt and its N-methyl derivative, all of which were in pure crystalline state. In the case of Eapt only the bis complex was formed as indicated by the analytical data given in Table 1.
13C NMR studies
A representative 13C NMR spectrum is shown in Fig. 1 and Table 2 lists the “C NMR chemical shifts of the ligands and their complexes. As reported earlier,* in the case of mono complexes, the C-2 resonance is shifted by about 8 ppm compared to the free ligand but a less dramatic shift (- 0.768 ppm) was observed for C-4 and C-5 resonances. In the bis Imt-complexes, the C-2 resonance is shifted by +6.764 ppm whereas the C-4,5 resonance shows a slight shift of only - 0.836 ppm. The most significant shift for the (MeImt),AuCl complex is also for the C-2 resonance (+7.644 ppm). The C-4, C-5 and CH, resonances are only shifted by - 1.43, -0.96 and -0.627 ppm, respectively. The shift in the C-2 resonance of the (PrImt),AuCl complex is only about 2 ppm, which is significantly less than 8.292 ppm observed for the mono complex (PrImt)AuCl or about 7 ppm observed for any of the bis complexes. This variation in the C-2 shift (Fig. 2) can be explained on
Gold(I) complexes of imidazolidine-2-thione
1685
and its derivatives
Table 1. Analytical data for the ligands and gold(I) complexes* Melting point (“C)
Complex (1mt)AuBr
198199
Pale yellow powder
(Imt)~AuCl* H,O
247-249
White crystalline
(MeImt)AuCl
186187
White powder
(MeImt)AuBr
!67-168
Yellow powder
(MeImt)zAuC1
246247
Light brown crystalline
(Eapt),AuCl
286288
White crystalline
92-93
White crystalline
(PrImt)~AuCl
H
C
N
1.53 (1.58) 2.98 (3.08) 2.33 (2.29) 1.98 (2.04) 3.24 (3.44) 3.39 (3.44) 4.75 (4.66)
9.22 (9.55) 15.70 (15.84) 14.36 (13.77) 12.29 (12.21) 20.12 (20.66) 20.64 (20.66) 28.08 (27.66)
7.86 (7.38) 12.80 (12.32) 13.92 (14.92) 7.21 (7.12) 11.77 (12.05) 11.94 (12.05) 11.03 (10.76)
Colour
* The corresponding calculated values are given in parentheses.
the basis of the shielding effects on C-2 which is least shielded in the bis complexes and is most shielded in the mono compounds. An appreciable shift of the C-2 resonance in the i3C NMR spectra clearly indicates that, in al1 of these complexes, gold(I) is bonded to the ligand through sulfur atom only and the -NH group is not involved in any kind of bonding. Any bonding through -NH would have resulted in a considerable shift of the C-4 resonance in the (MeImt)~AuCl complex. A significant shift in 13C NMR for C=S carbon atoms consistently observed
in these complexes can be used as a diagnostic NMR observation for the location of bonding sites in solution phase of these and similar gold(I) complexes. The sulfur coordination of gold(I) in chloro (N - ethyl - 1,3 - imi~zolidine - 2 - thione)gold(I) and chloro(N - propyl - 1,3 - imidazolidine - 2 - thione) gold(I) complexes* was confirmed by the single crystal X-ray analysis in the solid state and a similar i3C shift for the C=S carbon was observed in both complexes. The + 1 oxidation state for gold in the (PrImt),AuCl was assumed on the basis of its white
A=
CH3
B=
2C=S--c_Au4--SzC CH3
c-2 CH3
Ref. ~
I
180
I
/
/
!
I
I
70
50
30
rm
Fig. 1. Representative
13C NMR spectra of MeImt ligand and its bis-gold(I) complex.
A. A. ISAB and M. S. HUSSAIN
1686
Table 2. 13C NMR chemical shifts of gold(I) complexes of imidazolidine-2-thione derivatives*
and its
Complex
c-z
c-4
C-5
a-CH,
B-CH,
Y-CH,
Imt (Imt)AuBr
182.69 t
-
-
175.926 (6.764) 183.084 175.44 (7.644) 184.469 182.508 (1.961) 176.181 (8.282)
45.205 45.973 (-0.768) 46.041 (-0.836) 51.461 52.891 - 0.96) 48.851 49.175 - 0.324) 49.505 (-0.654)
-
(Imt),AuCl
45.205 45.973 (-0.768) 46.041 (-0.836) 41.661 42.641 ( - 1.43) 48.539 48.749 (-0.21) 50.616 (-2.077)
-
-
-
-
-
33.828 34.455 (-0.627) 11.306 11.173 (0.133) 11.067 (0.239)
MeImt (MeImt)~AuCl PrImt (PrImt),AuCl (PrImt)AuCl
41.763 42.012 ( - 0.249) 42.712 (-0.49)
20.801 20.857 ( - 0.056) 20.795 (0.006)
* 13CNMR resonances are assigned as given in Faure et al., Org. Magn. Reson. 1977,9,688. The numbers in parentheses indicate shifts with respect to the free ligands. A positive value indicates
a high-field shift whereas a negative value shows a low-fieldshift. The spectrum of (MeImt)AuBr could not be recorded due to its insolubility in the 50/50 (v/v) CD,OD/D,O solvent. t The resonance could not be detected in the spectrum. colour. Both mono and bis complexes are white in colour. In the case of the mono complexes the reduction of gold(II1) to gold(I) was carried out by SO,, whereas an excess of the ligand was used for the reduction of the bis complexes. The MBssbauer and
single crystal X-ray studies are planned to identify the oxidation state of gold and to elucidate the solid state structures of these complexes. The (Eapt),AuCl complex is very insoluble in water and its analytical data (Table 1) show that no
I
I
Ill
I
I
I
I
I
200
180
160”
80
60
40
20
0
mm
Fig. 2. 13C NMR spectra of PrImt ligand and its mono- and bis-coordinated species showing variations in the chemical shift of C-2 as a function of shielding.
Gold(I) complexes of imidazolidine-2-thione
and its derivatives
Table 3. Significant IR bands for the ligands and their complexes in the region -200 v(C-N) +&N--H)
A(N-H)
v(C=S)
3300 3300 sh
1500 1520 sh
680 sh 660 sh
510 w 530 sh
(Imt),AuCl MeImt (MeImt)AuCl (MeImt)AuBr (MeImt),AuCl Eapt (Eapt),AuCl
3260 sh 3200 sh 3200 sh 3300 sh 3100 sh 3300 sh 3200 sh
1525 sh 1520 sh 1555 sh 1555 sh 1550 sh 1560 sh 1565 vs
665 sh 670 sh 635 sh 635 sh 640 sh 640 sh 635 sh
490 sh 520 sh 495 sh 490 sh 490 sh 510 w 520 sh
PrImt (PrImt),AuCl
3300 sh 3200 sh
1510 vs 1530 sh
610 sh 670 sh
515 vs 515 sh
Compound
v(N-H)
Imt (1mt)AuBr
H,O molecule is present. In contrast membered (Imt),AuCl
to this, the 5-
analog of Eapt forms the complex - HZ0 which is water soluble16 and its X-
ray analysis revealed an ionic structure with linear gold(I) coordination through sulfur atoms. Due to the high insolubility of (Eapt),AuCl, its 13C NMR spectrum could not be recorded.
IR absorption spectral studies
The IR spectra of the free ligands and their gold(I) complexes (Table 3) do not show S-H absorption in the region of 2500 cm-’ nor a C=N band at 17001590 cm-’ but exhibit a strong absorption around 3300 cm-’ corresponding to N-H stretch.” The presence of the band at 3300 cm-’ in the free ligand as well as in the gold(I) complexes clearly indicates the existence of thione forms in the solid state. A band at 375 w cm-’ in the gold(I)-diisobutyl dithiocarbamate dimer ” and a band at 342 cm- 1for Au(SMe); anionI have been assigned to the Au--S vibration. On a correlative basis the band at 345 cn - 1 found in all complexes of the present study can be assigned to the Au--S vibration. A shift of about 40 cm - ’ in the C=S band in all complexes is consistent with our conclusion that the gold(I) is bonded through sulfur. The band at 210 cm-’ for (1mt)AuBr and at 225 cm-’ for (MeImt)AuBr can be assigned to the Au-Br stretching.” The Au-Cl absorption is usually found in the region of 310320 cm-l for various gold(I) complexes2’ with coordinated chloride ion. This band was observed in the (MeImt)AuCl complex but was absent for (Imt),AuCl, (MeImt),AuCl and (PrImt)2AuCl complexes. This is consistent with the ionic nature of the
cm- ’
Vibrations below 450 cm- 1
345 w, 320 w, 295 w, 275 sh, 240 w, 210 w 385 w, 345 w, 290 w 390 w 415 w, 350 w, 320 sh 415 w, 275 w, 225 w 420 w, 345 w, 275 sh 415 sh, 340 sh 415 sh, 385 sh, 345 w, 315 sh 375 VW 350 w
chloride in the last three complexes which, of course, will not exhibit any Au-Cl stretching vibrations.16 The presence of an Au-Cl vibration at 3 15 cm - 1 in (Eapt),AuCl complex indicates that the gold(I) is three coordinated. The fact that this complex is insoluble in water/methanol solvent further indicates that the complex is neutral or polymeric in nature. CONCLUSIONS On the basis of’ 3C NMR and IR spectral data, the following conclusions can be drawn for gold(I) geometries in its complexes with imidazolidine-2thiones and its derivatives : (1) Imt and its derivatives exist in the thione forms both in the solution as well as in the solid phase. (2) When these ligands react with gold(I), different complexes of types AuLX and AuL,X are formed, in all of which the ligands exist in the thione form. (3) The IR and 13C NMR spectral studies revealed three coordination of the following kinds for the gold(I) complexes with the above ligands : (a) C=S -, Au-X for all mono complexes. (b) [C=S j Au c S=C] + for all bis complexes which are soluble in water or methanol.
7’
@)c=s +Au\
‘s=c
1688
A. A. ISAB and M. S. HUSSAIN for L,AuX Au(Eapt),Cl.
neutral
complex
such
as
Acknowledgements-This research was supported by the UPM Research Committee Project No. CY/METALION/54. One of us (A.A.1) is thankful to the UPM for providing facilities under the above project.
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