Transcript Slide 1

Synthesis, characterization, and study of a series of metal complexes
+
based on trans-[Cl(pyridine)4Ru-L] (L= NCArX)
Meghan M Gordon, Michael R Reardon,
Cliff J. Timpson, and Daniel Von Riesen
Roger Williams University, One Old Ferry Road, Bristol, Rhode Island 02809
Abstract
Cyclic Voltammogram of 4-Acetylbenzonitrile Complex
Introduction
1025
Methods and Materials
Spectroscopic grade solvents (Burdick and Jackson, Aldrich, Fisher) and reagents (Aldrich) were obtained commercially and
used as supplied. All reactions were conducted under an argon atmosphere and were shielded from ambient light. The complex
trans-[ClRu(py)4(NO)](PF6)2 was prepared according to procedures previously reported by Coe.5,6 Column chromatography was
carried out using silica gel 60 (70-230 mesh) (Aldrich) with varying proportions of acetone:dichloromethane (5% to 50%
acetone) as the eluent. All products were dried at room temperature in a vacuum dessicator for a minimum of 24 h before
use. UV-Vis spectra and kinetic data were collected on a Hewlett-Packard HP-8453 Diode Array spectrophotometer. Infrared
data was collected on a Perkin-Elmer 1600 series FT-IR, and cyclic voltammetric measurements were obtained using a BioAnalytical Systems (BAS) CV-50W. Photolysis studies were accomplished by irradiating the complexes (ca. 10-5 M) in CH3CN
with a 50W halogen light source equipped with a 355 nm cutoff filter. The irradiating light was passed through 5 cm of water to
minimize heating of the photolysis solution.
1200
1010
1005
1000
R2 = 0.6872
py
1000
800
600
400
mVolts v. Ag-AgCl
200
0
0
0.2
Spectroscopic Properties of Complexes
λmax, nm(ε, M-1cm-1)
Assignment
Complex
trans-[Cl(py)4Ru(MeCN)]PF6
226 (22 650)
244 (23 250)
355 (29550)
π to π*
π to π*
dπ to π* (py)
trans-[Cl(py)4Ru(ArCN)]PF6
202 (33 200)
241 (32 000)
351 (27 400)
π to π*
π to π*
dπ to π* (py)
198 (25 754)
247 (18 493)
347 (9 647)
429 (5 660)
π to π*
π to π*
dπ to π* (py)
dπ to π* (L)
200 (27 245)
246 (25 553)
349 (13 759)
416 (7 842)
π to π*
π to π*
dπ to π* (py)
dπ to π* (L)
200 (~22 000)
246 (~20 000)
349* (~10 000)
π to π*
π to π*
dπ to π* (py)
trans-[Cl(py)4Ru(NCArCHO)]PF6
trans-[Cl(py)4Ru(NCArCOMe)]PF6
trans-[Cl(py)4Ru(NCArCOOH)]PF6
+
Ru
1015
990
L
0.4
0.6
0.8
Sigma Values7
Results and Conclusions
• A variety of N-bound aromatic nitrile complexes of the form trans-[Cl(py)4RuL]+ can be easily obtained from versatile
starting material complex trans-[Cl(py)4Ru(NO)](PF6)2.
• Efforts to obtain pure samples of the complex trans-[Cl(py)4Ru(NCArCOOH)]+ were complicated by the carboxylic acid
functionality makes the complex difficult to chromatograph on silica and alumina. Efforts in our labs are currently
underway to purify the trans-[Cl(py)4Ru(NCArCOOH)]+ complex.
• For the complexes trans-[Cl(py)4RuNCArCHO]+ and trans-[Cl(py)4RuNCArCOMe]+, the low energy absorption features
present in CH3CN solution at 429 and 416 respectively can be assigned as a MLCT type, dpp*(NCArX) transitions. A
similar absorption feature is clearly evident as a low energy shoulder (~400nm) on trans-[Cl(py)4RuNCArCOOH]+.
• Each of the complexes of trans-[Cl(py)4RuL]+ (L = NCArCHO, NCArCOMe, and NCArCOOH ) were shown to be
thermally stable in CH3CN solution at 298K.
Complexes Studied
Cl
1020
995
Ruthenium polypyridyl complexes have received considerable attention in the chemical literature due in part to their ability to
function as efficient photosensitizers in photovoltaic devices.1-4 In the course of these studies, researchers have come to
appreciate the critical role molecular geometry plays in the operation of these devices.3,4 The work presented here seeks to
explore the chemistry of trans-[Cl(pyridine)4Ru(L)]+ (L = 4-cyanobenzaldehyde, 4-acetlybenzonitrile, and 4-cyanobenzoic acid )
complexes as potential “building blocks” for larger oligomeric complexes which might exhibit interesting photochemical and/or
redox active properties. The trans- geometry of the tetrapyridine ruthenium monomer, combined with appropriate bridging
ligands, should ultimately allow fabrication of supramolecular complexes that exhibit linear or pseudo-linear geometries.
py
scan rate = 250mV/s
2.00 mm dia. Pt0 v. Ag-AgCl
in 0.1M TBAH/CH3CN
Electrochemical & Infrared Properties of Complexes
Complex
E1/2mV v Ag-AgCl (∆Ep, mV)
IR(cm-1)
trans-[Cl(py)4Ru(PhCN)]PF6
995* (95)
2200 (moderate)
trans-[Cl(py)4Ru(NCArCHO)]PF6
1021.5 (61)
2192 (strong)
trans-[Cl(py)4Ru(NCArCOMe)]PF6
1009.5 (61)
2204 (moderate)
trans-[Cl(py)4Ru(NCArCOOH)]PF6
1011.5 (63)
2194 (weak)
trans-[Cl(py)4Ru(NCArBr)]PF6
995
(70)
*converted from v SCE
E1/2 v Ag-AgCl
Over the past three years, a number of studies in our group have been aimed at exploring the photochemical and
electrochemical properties of monomeric and dimeric complexes based on trans-[Cl(pyridine)4Ru-L]+. Our current efforts
involve the synthesis, characterization, and study of a new series of monomeric complexes of the type trans-[Cl(pyridine)4RuL]+ where L is a cyanobenzene derivative, NCArCOOH, NCArCOMe and NCArCHO. The work presented here will detail
our efforts to prepare and to purify each of the complexes. Results of the spectroscopic and electrochemical characterization
will be presented as well as an assessment of the thermal and photochemical stabilities of each complex.
Electron Withdrawing Effect of Cyanobenzene Substituents
• Irradiation of the complexes trans-[Cl(py)4RuL]+ (L = NCArCHO, NCArCOMe, and NCArCOOH ) with visible light (l >
355nm) in CH3CN at 298K leads to changes in the UV-Visible spectra which can be ascribed to photochemically induced
cleavage of the Ru-NC-ArX bond.
N
py
• Based on our results of investigating related systems, we expect that extended (3 hr) irradiation of the complexes trans[Cl(py)4RuL]+ (L = NCArCHO, NCArCOMe, and NCArCOOH ) will lead quantitatively to formation of the solvent
substituted complex trans-[Cl(py)4Ru(CH3CN)]+ when irradiated in CH3CN.
py = pyridine
py
trans-[Ru(py)4Cl(L)]+
Photolysis of trans-[Cl(py)4Ru(NCArCHO)]PF6 in Acetonitrile
25000
L = Ligands =
Time (s)
H
NC
NC
O
NCPhH
O
H
NCPhCOH
NC
NC
OH
CH 3
NCPhCOOH
NCPhCOCH3
Synthetic Scheme
RuCl3
py
Ru
Cl
0.25 h
DMSO
py
NaN3
py
Cl
py
DMSO
py
conc. HCl
NO
0.50 h
Ru
O2N
NO2
py
20000
500
1000
Dark Light
On
1500
2000
2500
3000
3500
4000
py
15000
-8.8
-8.9
References
Kphoto decomp=-1.98 x 10-4 s-1
R2 = 0.999
-9
-9.1
10000
-9.2
Photolysis followed at 429nm
-9.3
5000
0
200
300
400
500
600
700
NaNO2
Wavelength (nm)
py/H2O
0.25 h
O
S=
1.00 h
py
Ru
Cl
py
2+
py
Photolysis trans -[Cl(py)4Ru(NCArCOMe)]PF6 in Acetonitrile
S
• Extended (3 hr) irradiation of the solvent complex trans-[Cl(py)4Ru(NCCH3)]+ at l > 355 nm does not lead to an
appreciable photochemical loss of pyridine, nor do we find any UV-Vis evidence for trans to cis isomerization.
-8.7
Cl
py
py
py
Ru
Cl
2.50 h
2+
py
Ru
Cl
py
py
DMSO
DMSO
DMSO
0
-8.6
ln [Concentration]
O
Extinction Coefficient
-8.5
py
1. Roundhill, D.M. Photochemistry and Photophysics of Coordination Compounds, Wiley, New York, 1994.
Juris, A; Campanga,S; Balzani, V.; Belser, P.;von Zelewsky, A. Coord. Chem. Rev., 1988, 84, 85.
2. Zakeeruddin, S.; Nazeeruddin, M.; Rotzinger, F.; Kalyanasundaram, K., Grätzel, M., Inorg. Chem., 1997, 36, 5937.
3. Frank, A; et al., Presentation at IEEE Photovoltaic Conference, Sept. 1997, available via
www.nrel.gov/ncpv/ndf/ieee.pdf. See also Solar Energy Materials and Solar Cells, Lampert, C.M. Ed., Vol. 32,
No. 3, March 1994.
4. Balzani, V.; Scandola, F. Supermolecular Photochemistry; Wiley, Chinchester, UK, 1991.
5. Coe, B.; Meyer, T. J.; White, P.S. Inorg. Chem., 1993, 32, 4012.
6. Coe, B.; Meyer, T. J.; White, P.S. Inorg. Chem., 1995, 34, 593.
7. Hansch, C; Leo, A. Exploring QSAR: Fundamentals and Applications in Chemistry and Biology. American
Chemical Society; Salem, MA: 1995. Page 17
in situ
10.0 eq.
12.0 hr
Time (s)
NC
Cl
py
py
-8.9
H
0
py
O
py
NCPhCOH
NC
Cl
10.0 eq.
12.0 hr
py
py
py
NC
Cl
py
py
py
CH3
O
py
NCPhCOOH
20000
15000
500
1000
1500
2000
2500
3000
3500
4000
Dark Light On
-9
-9.1
-9.15
Kphoto decomp=-9.00 x 10-5 s-1
R2 = 0.9998
-9.2
10000
py
py
OH
Photolysis Followed at 416nm
-9.25
CJT and DVR gratefully acknowledge:
Financial support from a grant from the RWU Faculty Research Foundation
5000
Syntheses of Complexes
0
200
Acknowledgments
MMG and MRR gratefully acknowledge:
Kate Dedeian and Hannah Nandor for the synthesis of trans-[Ru(py)4Cl(NO)](PF6)2
Steve Hira for collecting electrochemical data
Randy Petrichko for the synthesis of trans- [Ru(DMSO)4(Cl)2] complex
-9.05
NC
Cl
10.0 eq.
12.0 hr
O
py
NCPhCOCH3
10.0 eq.
12.0 hr
H
-8.95
ln [Concentration]
NCPhH
25000
py
Extinction Coefficient
py
300
400
500
Wavelength (nm)
600
700
www.rwu.edu