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Synthesis of monometallic and bimetallic 2,2′-bipyrimidine and 2,3-bis(2-pyridyl)pyrazine complexes of ruthenium, platinum and palladium
Po(vhedronVol. 7. No. 9. pp. 731-735. 1988 Printed in Great Britain
0277-5387/88 $3.00+.00 ~ 1988 Pergamon Press pie
SYNTHESIS OF MONOMETALLIC AND BIMETALLIC 2,2'-BIPYRIMIDINE AND 2,3-BIS(2-PYRIDYL)PYRAZINE COMPLEXES OF RUTHENIUM, PLATINUM AND PALLADIUM NICHOLAS C. THOMAS* and JERRY COX Chemistry Department, Auburn University at Montgomery, Montgomery, AL 36193, U.S.A.
(Received 11 December 1987 ; accepted 5 January 1988) Abstract--The reaction of 2,2'-bipyrimidine (bpym) or 2,3-bis(2-pyridyl)pyrazine (dpp) with [Ru(CO)2CI2], gives the monometallic Ru(CO)2Cl2(bidentate) (bidentate = bpym or dpp) complexes. The Ru(CO)2Cl2(bidentate) complexes react further with [Ru(CO)zC12], or with MCl2(dmso)2 (M = Pt, Pd) to yield the homobimetallic C12(CO)2Ru(bidentate) Ru(CO)2CI2 or heterobimetallic C12M(bidentate)Ru(CO)2C12 complexes, respectively. The complexes have been characterized by microanalysis and electronic absorption and IR spectroscopy.
The chemistry of homo- and heterobimetallic com- cm- i) were recorded as Nujol mulls between NaCi plexes containing bridging ligands has significantly plates with a Perkin-Elmer 167 instrument. Farexpanded in recent years. Of particular interest are IR spectra (500-200 cm- t) were recorded as Nujol bimetallic transition metal complexes linked via a mulls between polyethylene plates with a Perkincommon binucleating ligand, such as 2,2'-bi- "Elmer 457 instrument. Electronic absorption pyrimidine (bpym) or 2,3-bis(2-pyridyl)pyrazine spectra were obtained in DMF solutions with a (dpp), and the electronic interaction that exists Perkin-Elmer lambda 3A spectrophotometer. All reactions were shielded from light and carried between the two metal centres, i Recently, several examples of heterobimetallic out under an inert atmosphere of nitrogen. complexes of bipyrimidine have been described, 2-9 Methanol was HPLC grade (Aldrich) and debut no analogous bis(pyridyl)pyrazine complexes gassed for 15 min prior to use. The compounds appear to have been reported, and only a few homo- [Ru(CO)2CI2]. 12 and MCl2(dmso)2 (M = Pt, bimetallic complexes of this ligand are known. 10.i t Pd) ~3 were prepared by literature methods. These bimetallic complexes have a variety of potential applications, including use as models for biologically related systems4'9 and as multi-electron Preparation of complexes transfer catalysts. 1'6 In the present study, the (2,2' Bipyrimidine)dicarbonyldichlororuthensynthesis and spectroscopic properties of some new homo- and heterobimetallic ruthenium(II), ium(II). A solution of [Ru(CO)2C12], (0.64 g) in platinum(II) and palladium(II) complexes of both methanol (60 cm 3) was boiled for 5 min and filtered into a solution of 2,2"-bipyrimidine (0.70 g) bpym and dpp are described. in methanol (50 cm3). The mixture was heated under reflux for 10 min, cooled and the yellow prodEXPERIMENTAL uct collected by filtration. The solid was washed with methanol (2 x 10 cm3), ether (2 x 10 cm 3) and General dried in vacuo. Yield 0.72 g (67%). [2,3 - Bis(2 - pyridyl)pyrazine]dicarbonyldichloroMicroanalyses were performed by Galbraith Laboratories, Tennessee. IR spectra (4000-600 ruthenium(II). The complex was prepared by the above procedure from 2,3-bis(2-pyridyl)pyrazine * Author to whom correspondence should be addressed. (0.54 g) and [Ru(CO)2Cl2]. (0.41 g), and recrys731
N. C. THOMAS and J. COX
732
tallized from methanol to yield the yellow crystalline product. Yield 0.62 g (75%). It - (2,2' - Bipyrimidine)tetracarbonyltetrachlorodiruthenium(II). A filtered solution of [Ru(CO)2 C12], (0.25 g) in methanol (25 cm 3) and Ru(CO)2 Cl2(bpym) (0.10 g) were heated together under reflux for 1.5 h. The hot solution was filtered and the product washed with methanol, ether and dried in vacuo. Yield 0.12 g (75%). It - [2,3 - B/s(2 -pyridyl)pyrazine]tetracarbonyltetrachlorodiruthenium(II). The complex was prepared by the above procedure from [Ru(CO)2CI2], (0.16 g) and Ru(CO)2C12(dpp) (0.19 g). Yield 0.21 g (84%). Dichloroplatinum(II) - It - (2,2' - bipyrimidine) dicarbonyldiehlororuthenium(II). A mixture of Ru(CO)2Cl2(bpym) (0.073 g) and PtCl2(dmso)2 (0.083 g) in methanol (35 cm 3) was heated at reflux temperature for 3 h. The hot solution was filtered and the brown precipitate washed with methanol, ether and dried in vacuo. Yield 0.11 g (89%). Using the above procedure, the following compounds were also obtained : Dichloropalladium(II) - # - (2,2' - bipyrhnidine)dicarbonyldichlororuthenium(II): from Ru(CO)2
C12(bpym) (0.074 g) and PdC12(dmso)2 (0.073 g), yield 0.089 g (82%) ; Dichloroplatinum(II) - It - [2,3 - bis(2 - pyridyl)pyrazine]dicarbonyldichlororuthenium(II) : from Ru(CO)2Cl2(dpp) (0.065 g) and PtCl2(dmso)2 (0.067 g), yield 0.090 g (88%) ; Dichloropalladium(II) - It - [2,3 - bis(2 - pyridyl) pyrazine]dicarbonyldichlororuthenium(II) : from Ru(CO)zCl2(dpp) (0.021 g) and PdCl2(dmso)2 (0.025 g), yield 0.024 g (83%).
RESULTS AND DISCUSSION Syntheses
When an equimolar mixture of [Ru(CO)2C12], and either 2,2'-bipyrimidine (bpym) or 2,3-bis(2pyridyl)pyrazine (dpp) are refluxed together in methanol, the neutral monometallic Ru(CO)2CI2 (bidentate) complexes (bidentate = bpym or dpp) precipitate from solution as yellow solids. By this procedure, pure Ru(CO)2Cl2(bpym) is obtained, whereas recrystallization from methanol yields pure Ru(CO)2Cl2(dpp). Treatment of the Ru(CO)2Clz(bidentate) complexes with an excess of [Ru(CO)2CI2], in methanol yields the diruthenium complexes CI2(CO)_,Ru (bidentate)Ru(CO)2Cl2 as insoluble solids. A similar reaction between Ru(CO)2Cl2(bidentate) and MCl2(dmso)2 (M = Pt or Pd) gives the neutral
Table 1. Analytical data for complexes Complex Ru(CO)2Cl2(bpym) Ru(CO)2Cl2(dpp) CIz(CO)2Ru(bpym)Ru(CO)2CI: C12(CO)2Ru(dpp)Ru(CO)2CI2
CI2Pt(bpym)Ru(CO),Cl, CI2Pt(dpp)Ru(CO)zC12 Cl2Pd(bpym)Ru(CO)2Cl2
CI2Pd(dpp)Ru(CO) 2C1_,
% Found (calc.) C H N 31.3 (31.3) 41.6 (41.6) 23.4 (24.2) 31.3 (31.3) 18.2 (18.4) 26.9 (26.4) 20.9 (21.3) 30.1 (30.0)
1.6 (1.6) 2.1 (2.2) 1.0 (1.2) 1.5 (1.5) 0.9 (0.9) 2.0 (1.4) 1.2 (1.1) 2.1 (1.6)
14.5 (14.5) 12.1 (12.1) 9.1 (9.3) 8.3 (8.1) 8.5 (8.6) 7.3 (7.7) 9.8 (9.9) 8.2 (8.8)
heterobimetallic derivatives Cl2M(bidentate)Ru (CO)2C12 as brown solids in good yields (80-89%). Elemental analyses (Table 1) for the mono- and bimetallic complexes are consistent with the above formulations. Infrared spectra
The structures of all complexes may be determined from the IR data (Table 2). Spectra for the monometallic complexes show two strong bands in the v(CO) region, consistent with cis CO groups and a single v(Ru--Cl) band at ca 355 cm- ~indicating trans CI ligands [Fig. l(a)]. This stereochemistry is generally observed for Ru(CO)2C12(bidentate) complexes prepared from [Ru(CO)2CI2],. 14-16 Similar IR data for the bimetallic complexes also indicate cis CO and trans CI groups for the Ru(CO)2CI2 fragment in C l 2 ( C O ) 2 R u ( b i d e n t a t e ) R u ( C O ) 2 C l 2 and C I 2 M ( b i d e n t a t e ) R u ( C O ) 2 C l 2 (M = Pt or Pd) complexes [Fig. l(b) and (c)]. Spectra of the Cl2M(bidentate)Ru(CO)2Cl2 compounds contain two additional bands between 300-350 cm- ~which may be assigned to v(Pt--C1) or v(Pd--Cl) as expected for square-planar MC12(bidentate) complexes. 17 Several characteristic vibrational bands are also observed for the aromatic diimine bridging ligands (Table 2) and provide further evidence to distinguish between monometallic and bimetallic coordination of bpym and dpp. A single absorption in the 1570-1580 cm- ~region, due to C - - N and C - - C ring stretching, is observed for the bimetallic com-
Complexes of ruthenium, platinum and palladium
733
Table 2. IR absorptions for complexes
v(C--C) Complex Ru(CO)2Cl,(bpym) Ru(CO)2Cl2(dpp) CI 2(CO) 2Ru(bpym)Ru(CO) 2C12 CI_,(CO)_,Ru(dpp)Ru(CO) 2C12 Cl2Pt(bpym)Ru(CO)2CI2
v(CO)"
v(M~CI)
v(C--N)
2050 1991 2058 1998 2060 2007 2046 1991 2065 2016
358m 355m
1575m 1551m 1551w
353m
1574fia
779m 751m 738m 729m
340m
1591 w
772m
360m 340m 336sh 352m 346m 335sh 353m 347m 335sh 345m 337m 334sh
1580m
719m
1598w
775m
1578m
722m
1597w
779m
Cl2Pt(dpp)Ru(CO)2C1,
2068 2010
Cl_,Pd(bpym)Ru(CO)2CI2
2082 2031
CI2Pd(dpp)Ru(CO)2C12
2065 2008
n(C--H) 748m
All bands are strong. plexes and is characteristic for b p y m complexing to two metals.~8 By contrast, monometallic bpym complexes generally contain two bands in this region and accordingly two bands are observed for Ru(CO)2Cl2(bpym). The C - - H out-of-plane bending mode of b p y m is also sensitive to mono- and
bimetallic coordination t8 and we observe a corresponding 20-30 c m - t reduction in the C - - H vibration for the bimetallic complexes. The IR spectrum of Ru(CO)zC12(dpp) contains a weak ring stretching band at 1551 c m - t which in the bimetallic dpp complexes shifts to about 45
CI
Ru / j
(a)
CO----'-~N Cl
Cl ~
Cl I 1 co
Ru
Ru.
co.. |
CO
CO I C|
"'
"
I.
II
I Cl ~
Cl CI
(b)
(c)
Fig. 1. Representative structures of (a) Ru(CO)_,Cl2(bidentate); (b) CIz(CO)2Ru(bidentate) Ru(CO)2CI2 (bidentate = bpym) and (c) C1,M(bidentate)Ru(CO),C12 (M = Pt, bidentate = dpp) complexes.
N. C. THOMAS and J. COX
734
Table 3. Electronic absorption spectra for complexes
Complex Ru(CO) 2Cl2(bpym) CI,(CO)2Ru(bpym)Ru(CO)2CI2 Cl2Pt(bpym)Ru(CO).,Cl, CI2Pd(bpym)Ru(CO),CI2 Ru(CO).,Cl.,(dpp) Cl _,(CO)2Ru(dpp) Ru(CO) 2Cl., Cl.,Pt(dpp)Ru(CO).,Cl: C12Pd(dpp)Ru(CO),Cl,
2m.x (nm) [~ ( M - ' cm-~)]" 365 634 424 666 429 627 478 538
[15001 [1150] [3330] [350] [2750] [680] [1535] [1185]
596 448 598 432 603 443
[3590] [3220] [231O] [2860] [3650] [19001
"Recorded in DMF at 298 K.
c m - J higher. In addition, three bands observed in the 700-800 cm - I region for Ru(CO)_,Cl_,(dpp) become a single band when a second metal is added. Absorption spectra
Due to the low solubility of the bimetallic complexes in most common solvents, D M F was used to obtain absorption spectra (Table 3). Some complexes are very slightly soluble in dichloromethane and give similar, albeit weaker, spectra to those in D M F and therefore indicate the chemical stability of the complexes in D M F . The spectrum of Ru(CO)2Cl_,(bpym) contains the longest wavelength band at 2m~x= 365 nm (e = 1.5 x 103 M - t c m - ~), similar to that observed for Ru(CO)_,Cl2(bipyridyl) ( 2 m a x = 354 nm, e = 1.2x 103 M -~ cm z)~9 and can therefore be assigned to the metal-to-ligand charge-transfer transition (MLCT) from Ru(II) to bpym(g*). Upon coordination to a second metal, the absorption maxima for the M L C T band shifts to longer wavelengths ( > ca 420 nm) as previously observed for other related bpym complexes. L6.8A second weaker absorption occurs in the spectra of the bimetallic complexes at > 620 nm and may also be attributed to M L C T transitions. ~The absorption coefficient of the main band for the diruthenium bpym complex is about twice the value for Ru(CO)zClz(bpym), with one ruthenium centre. The M L C T band for the monometallic dpp complex also shifts to higher wavelength in the bimetallic compounds. The
additional band at higher energy for some of the bimetallic complexes may be assigned to the tA ~,~Ei ~ IA t LF transition. 5'2° By contrast to other bimetallic b p y m and dpp complexes, which absorb strongly in the visible region and therefore have potential for photon absorption and energy transfer reactions, the bimetallic ruthenium complexes prepared in this work absorb light to a lesser extent. However, in view of the numerous substitution reactions known for the monometallic MClz(bidentate) (M = Pt, Pd; bidentate = phenanthroline, bipyridyl) 21 and Ru(CO).,Cl2(bidentate)16 complexes, we are currently investigating the substitution reactions of C12M(bpym)Ru(CO)2Cl_, and Cl2M(dpp) Ru(CO),_CI2. Acknowledgements--The authors are grateful to the AUM Grant-in-Aid program for supporting this work and to the Chemistry Department, Tusgekee University for the far-IR spectra.
REFERENCES 1. J. D. Petersen, W. R. Murphy, R. Sahai, K. J. Brewer and R. R. Ruminski, Coord. Chem. Rev. 1985, 64, 261. 2. K. A. Goldsby and T. K. Meyer, Inory. Chem. 1984, 23, 3002. 3. M. P. Garcia, J. L. Millan, M. A. Esteruelas and L. A. Oro, Polyhedron 1987, 6, 1427. 4. R. H. Petty, B. R. Welch, L. J. Wilson, L. A. Bottomley and K. M. Kadish, J. Am. Chem. Soc. 1980, 102, 611. 5. C. Overton and J. A. Connor, Polyhedron 1982, 1, 53. 6. R. Sahai and D. P. Rillema, Inor9. Chim. Acta 1986, 118, L35. 7. S. Lanza, lnor9. Chim. Acta 1983, 75, 131. 8. A. Vogler and J. Kisslinger, Inor9. Chim. Acta 1986, 115, 193. 9. G. A. Brewer and E. Sinn, lnory. Chem. 1984, 23, 2532. 10. R. R. Ruminski and J. O. Johnson, Inor9. Chem. 1987, 26, 210. 11. C. H. Braustein, A. D. Baker, T. C. Streaks and H. D. Gafney, Inorg. Chem. 1984, 23, 857. 12. M. J. Cleare and W. P. Griffith, J. Chem. Soc. (A) 1969, 372. 13. J. H. Price, A. N. Williamson, R. F. Schramm and B. B. Wayland, Inor9. Chem. 1972, 11, 1280. 14. N. C. Thomas and G. B. Deacon, Synth. React. Inorg. Met.-Org. Chem. 1986, 16, 85. 15. D. St. C. Black, G. B. Deacon and N. C. Thomas, Aust. J. Chem. 1982, 35, 2445. 16. N. C. Thomas, Coord. Chem. Rev. 1986, 70, 121 and refs therein.
Complexes of ruthenium, platinum and palladium 17. A. H. Norbury and A. I. P. Sinha, J. lnory. Nucl. Chem. 1973, 35, 1211. 18. V. F. Sutcliffe and G. B. Young, Polyhedron 1984, 3, 87. 19. J. M. Kelly, C. M. O'Connell and J. G. Vos, J. Chem. Soc., Dalton Trans. 1986, 253.
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20. K.J. Moore and J. D. Petersen, Polyhedron 1983, 2, 279. 21. J. V. Marzik, A. D. Sabatelli, P. J. Fitzgerald and J. E. Sarneski, J. Chem. Ed. 1981, 58, 589 and refs therein.
0277-5387/88 $3.00+.00 ~ 1988 Pergamon Press pie
SYNTHESIS OF MONOMETALLIC AND BIMETALLIC 2,2'-BIPYRIMIDINE AND 2,3-BIS(2-PYRIDYL)PYRAZINE COMPLEXES OF RUTHENIUM, PLATINUM AND PALLADIUM NICHOLAS C. THOMAS* and JERRY COX Chemistry Department, Auburn University at Montgomery, Montgomery, AL 36193, U.S.A.
(Received 11 December 1987 ; accepted 5 January 1988) Abstract--The reaction of 2,2'-bipyrimidine (bpym) or 2,3-bis(2-pyridyl)pyrazine (dpp) with [Ru(CO)2CI2], gives the monometallic Ru(CO)2Cl2(bidentate) (bidentate = bpym or dpp) complexes. The Ru(CO)2Cl2(bidentate) complexes react further with [Ru(CO)zC12], or with MCl2(dmso)2 (M = Pt, Pd) to yield the homobimetallic C12(CO)2Ru(bidentate) Ru(CO)2CI2 or heterobimetallic C12M(bidentate)Ru(CO)2C12 complexes, respectively. The complexes have been characterized by microanalysis and electronic absorption and IR spectroscopy.
The chemistry of homo- and heterobimetallic com- cm- i) were recorded as Nujol mulls between NaCi plexes containing bridging ligands has significantly plates with a Perkin-Elmer 167 instrument. Farexpanded in recent years. Of particular interest are IR spectra (500-200 cm- t) were recorded as Nujol bimetallic transition metal complexes linked via a mulls between polyethylene plates with a Perkincommon binucleating ligand, such as 2,2'-bi- "Elmer 457 instrument. Electronic absorption pyrimidine (bpym) or 2,3-bis(2-pyridyl)pyrazine spectra were obtained in DMF solutions with a (dpp), and the electronic interaction that exists Perkin-Elmer lambda 3A spectrophotometer. All reactions were shielded from light and carried between the two metal centres, i Recently, several examples of heterobimetallic out under an inert atmosphere of nitrogen. complexes of bipyrimidine have been described, 2-9 Methanol was HPLC grade (Aldrich) and debut no analogous bis(pyridyl)pyrazine complexes gassed for 15 min prior to use. The compounds appear to have been reported, and only a few homo- [Ru(CO)2CI2]. 12 and MCl2(dmso)2 (M = Pt, bimetallic complexes of this ligand are known. 10.i t Pd) ~3 were prepared by literature methods. These bimetallic complexes have a variety of potential applications, including use as models for biologically related systems4'9 and as multi-electron Preparation of complexes transfer catalysts. 1'6 In the present study, the (2,2' Bipyrimidine)dicarbonyldichlororuthensynthesis and spectroscopic properties of some new homo- and heterobimetallic ruthenium(II), ium(II). A solution of [Ru(CO)2C12], (0.64 g) in platinum(II) and palladium(II) complexes of both methanol (60 cm 3) was boiled for 5 min and filtered into a solution of 2,2"-bipyrimidine (0.70 g) bpym and dpp are described. in methanol (50 cm3). The mixture was heated under reflux for 10 min, cooled and the yellow prodEXPERIMENTAL uct collected by filtration. The solid was washed with methanol (2 x 10 cm3), ether (2 x 10 cm 3) and General dried in vacuo. Yield 0.72 g (67%). [2,3 - Bis(2 - pyridyl)pyrazine]dicarbonyldichloroMicroanalyses were performed by Galbraith Laboratories, Tennessee. IR spectra (4000-600 ruthenium(II). The complex was prepared by the above procedure from 2,3-bis(2-pyridyl)pyrazine * Author to whom correspondence should be addressed. (0.54 g) and [Ru(CO)2Cl2]. (0.41 g), and recrys731
N. C. THOMAS and J. COX
732
tallized from methanol to yield the yellow crystalline product. Yield 0.62 g (75%). It - (2,2' - Bipyrimidine)tetracarbonyltetrachlorodiruthenium(II). A filtered solution of [Ru(CO)2 C12], (0.25 g) in methanol (25 cm 3) and Ru(CO)2 Cl2(bpym) (0.10 g) were heated together under reflux for 1.5 h. The hot solution was filtered and the product washed with methanol, ether and dried in vacuo. Yield 0.12 g (75%). It - [2,3 - B/s(2 -pyridyl)pyrazine]tetracarbonyltetrachlorodiruthenium(II). The complex was prepared by the above procedure from [Ru(CO)2CI2], (0.16 g) and Ru(CO)2C12(dpp) (0.19 g). Yield 0.21 g (84%). Dichloroplatinum(II) - It - (2,2' - bipyrimidine) dicarbonyldiehlororuthenium(II). A mixture of Ru(CO)2Cl2(bpym) (0.073 g) and PtCl2(dmso)2 (0.083 g) in methanol (35 cm 3) was heated at reflux temperature for 3 h. The hot solution was filtered and the brown precipitate washed with methanol, ether and dried in vacuo. Yield 0.11 g (89%). Using the above procedure, the following compounds were also obtained : Dichloropalladium(II) - # - (2,2' - bipyrhnidine)dicarbonyldichlororuthenium(II): from Ru(CO)2
C12(bpym) (0.074 g) and PdC12(dmso)2 (0.073 g), yield 0.089 g (82%) ; Dichloroplatinum(II) - It - [2,3 - bis(2 - pyridyl)pyrazine]dicarbonyldichlororuthenium(II) : from Ru(CO)2Cl2(dpp) (0.065 g) and PtCl2(dmso)2 (0.067 g), yield 0.090 g (88%) ; Dichloropalladium(II) - It - [2,3 - bis(2 - pyridyl) pyrazine]dicarbonyldichlororuthenium(II) : from Ru(CO)zCl2(dpp) (0.021 g) and PdCl2(dmso)2 (0.025 g), yield 0.024 g (83%).
RESULTS AND DISCUSSION Syntheses
When an equimolar mixture of [Ru(CO)2C12], and either 2,2'-bipyrimidine (bpym) or 2,3-bis(2pyridyl)pyrazine (dpp) are refluxed together in methanol, the neutral monometallic Ru(CO)2CI2 (bidentate) complexes (bidentate = bpym or dpp) precipitate from solution as yellow solids. By this procedure, pure Ru(CO)2Cl2(bpym) is obtained, whereas recrystallization from methanol yields pure Ru(CO)2Cl2(dpp). Treatment of the Ru(CO)2Clz(bidentate) complexes with an excess of [Ru(CO)2CI2], in methanol yields the diruthenium complexes CI2(CO)_,Ru (bidentate)Ru(CO)2Cl2 as insoluble solids. A similar reaction between Ru(CO)2Cl2(bidentate) and MCl2(dmso)2 (M = Pt or Pd) gives the neutral
Table 1. Analytical data for complexes Complex Ru(CO)2Cl2(bpym) Ru(CO)2Cl2(dpp) CIz(CO)2Ru(bpym)Ru(CO)2CI: C12(CO)2Ru(dpp)Ru(CO)2CI2
CI2Pt(bpym)Ru(CO),Cl, CI2Pt(dpp)Ru(CO)zC12 Cl2Pd(bpym)Ru(CO)2Cl2
CI2Pd(dpp)Ru(CO) 2C1_,
% Found (calc.) C H N 31.3 (31.3) 41.6 (41.6) 23.4 (24.2) 31.3 (31.3) 18.2 (18.4) 26.9 (26.4) 20.9 (21.3) 30.1 (30.0)
1.6 (1.6) 2.1 (2.2) 1.0 (1.2) 1.5 (1.5) 0.9 (0.9) 2.0 (1.4) 1.2 (1.1) 2.1 (1.6)
14.5 (14.5) 12.1 (12.1) 9.1 (9.3) 8.3 (8.1) 8.5 (8.6) 7.3 (7.7) 9.8 (9.9) 8.2 (8.8)
heterobimetallic derivatives Cl2M(bidentate)Ru (CO)2C12 as brown solids in good yields (80-89%). Elemental analyses (Table 1) for the mono- and bimetallic complexes are consistent with the above formulations. Infrared spectra
The structures of all complexes may be determined from the IR data (Table 2). Spectra for the monometallic complexes show two strong bands in the v(CO) region, consistent with cis CO groups and a single v(Ru--Cl) band at ca 355 cm- ~indicating trans CI ligands [Fig. l(a)]. This stereochemistry is generally observed for Ru(CO)2C12(bidentate) complexes prepared from [Ru(CO)2CI2],. 14-16 Similar IR data for the bimetallic complexes also indicate cis CO and trans CI groups for the Ru(CO)2CI2 fragment in C l 2 ( C O ) 2 R u ( b i d e n t a t e ) R u ( C O ) 2 C l 2 and C I 2 M ( b i d e n t a t e ) R u ( C O ) 2 C l 2 (M = Pt or Pd) complexes [Fig. l(b) and (c)]. Spectra of the Cl2M(bidentate)Ru(CO)2Cl2 compounds contain two additional bands between 300-350 cm- ~which may be assigned to v(Pt--C1) or v(Pd--Cl) as expected for square-planar MC12(bidentate) complexes. 17 Several characteristic vibrational bands are also observed for the aromatic diimine bridging ligands (Table 2) and provide further evidence to distinguish between monometallic and bimetallic coordination of bpym and dpp. A single absorption in the 1570-1580 cm- ~region, due to C - - N and C - - C ring stretching, is observed for the bimetallic com-
Complexes of ruthenium, platinum and palladium
733
Table 2. IR absorptions for complexes
v(C--C) Complex Ru(CO)2Cl,(bpym) Ru(CO)2Cl2(dpp) CI 2(CO) 2Ru(bpym)Ru(CO) 2C12 CI_,(CO)_,Ru(dpp)Ru(CO) 2C12 Cl2Pt(bpym)Ru(CO)2CI2
v(CO)"
v(M~CI)
v(C--N)
2050 1991 2058 1998 2060 2007 2046 1991 2065 2016
358m 355m
1575m 1551m 1551w
353m
1574fia
779m 751m 738m 729m
340m
1591 w
772m
360m 340m 336sh 352m 346m 335sh 353m 347m 335sh 345m 337m 334sh
1580m
719m
1598w
775m
1578m
722m
1597w
779m
Cl2Pt(dpp)Ru(CO)2C1,
2068 2010
Cl_,Pd(bpym)Ru(CO)2CI2
2082 2031
CI2Pd(dpp)Ru(CO)2C12
2065 2008
n(C--H) 748m
All bands are strong. plexes and is characteristic for b p y m complexing to two metals.~8 By contrast, monometallic bpym complexes generally contain two bands in this region and accordingly two bands are observed for Ru(CO)2Cl2(bpym). The C - - H out-of-plane bending mode of b p y m is also sensitive to mono- and
bimetallic coordination t8 and we observe a corresponding 20-30 c m - t reduction in the C - - H vibration for the bimetallic complexes. The IR spectrum of Ru(CO)zC12(dpp) contains a weak ring stretching band at 1551 c m - t which in the bimetallic dpp complexes shifts to about 45
CI
Ru / j
(a)
CO----'-~N Cl
Cl ~
Cl I 1 co
Ru
Ru.
co.. |
CO
CO I C|
"'
"
I.
II
I Cl ~
Cl CI
(b)
(c)
Fig. 1. Representative structures of (a) Ru(CO)_,Cl2(bidentate); (b) CIz(CO)2Ru(bidentate) Ru(CO)2CI2 (bidentate = bpym) and (c) C1,M(bidentate)Ru(CO),C12 (M = Pt, bidentate = dpp) complexes.
N. C. THOMAS and J. COX
734
Table 3. Electronic absorption spectra for complexes
Complex Ru(CO) 2Cl2(bpym) CI,(CO)2Ru(bpym)Ru(CO)2CI2 Cl2Pt(bpym)Ru(CO).,Cl, CI2Pd(bpym)Ru(CO),CI2 Ru(CO).,Cl.,(dpp) Cl _,(CO)2Ru(dpp) Ru(CO) 2Cl., Cl.,Pt(dpp)Ru(CO).,Cl: C12Pd(dpp)Ru(CO),Cl,
2m.x (nm) [~ ( M - ' cm-~)]" 365 634 424 666 429 627 478 538
[15001 [1150] [3330] [350] [2750] [680] [1535] [1185]
596 448 598 432 603 443
[3590] [3220] [231O] [2860] [3650] [19001
"Recorded in DMF at 298 K.
c m - J higher. In addition, three bands observed in the 700-800 cm - I region for Ru(CO)_,Cl_,(dpp) become a single band when a second metal is added. Absorption spectra
Due to the low solubility of the bimetallic complexes in most common solvents, D M F was used to obtain absorption spectra (Table 3). Some complexes are very slightly soluble in dichloromethane and give similar, albeit weaker, spectra to those in D M F and therefore indicate the chemical stability of the complexes in D M F . The spectrum of Ru(CO)2Cl_,(bpym) contains the longest wavelength band at 2m~x= 365 nm (e = 1.5 x 103 M - t c m - ~), similar to that observed for Ru(CO)_,Cl2(bipyridyl) ( 2 m a x = 354 nm, e = 1.2x 103 M -~ cm z)~9 and can therefore be assigned to the metal-to-ligand charge-transfer transition (MLCT) from Ru(II) to bpym(g*). Upon coordination to a second metal, the absorption maxima for the M L C T band shifts to longer wavelengths ( > ca 420 nm) as previously observed for other related bpym complexes. L6.8A second weaker absorption occurs in the spectra of the bimetallic complexes at > 620 nm and may also be attributed to M L C T transitions. ~The absorption coefficient of the main band for the diruthenium bpym complex is about twice the value for Ru(CO)zClz(bpym), with one ruthenium centre. The M L C T band for the monometallic dpp complex also shifts to higher wavelength in the bimetallic compounds. The
additional band at higher energy for some of the bimetallic complexes may be assigned to the tA ~,~Ei ~ IA t LF transition. 5'2° By contrast to other bimetallic b p y m and dpp complexes, which absorb strongly in the visible region and therefore have potential for photon absorption and energy transfer reactions, the bimetallic ruthenium complexes prepared in this work absorb light to a lesser extent. However, in view of the numerous substitution reactions known for the monometallic MClz(bidentate) (M = Pt, Pd; bidentate = phenanthroline, bipyridyl) 21 and Ru(CO).,Cl2(bidentate)16 complexes, we are currently investigating the substitution reactions of C12M(bpym)Ru(CO)2Cl_, and Cl2M(dpp) Ru(CO),_CI2. Acknowledgements--The authors are grateful to the AUM Grant-in-Aid program for supporting this work and to the Chemistry Department, Tusgekee University for the far-IR spectra.
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