Transcript Slide 1

Impact of substituents on the metal-based redox potential for a series of
+
complexes based on trans-[Cl(pyridine)4Ru-L] where L is a para-substituted
derivative of cyanobenzene
Laura M. Fischetti, Meghan M. Gordon,
Michael R. Reardon, and Cliff J. Timpson
Roger Williams University, One Old Ferry Road, Bristol, Rhode Island 02809
Spectroscopic Properties of
Complexes
Synthetic Scheme
Abstract
Over the past four 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 continued synthesis, characterization, and
study of a series of monomeric complexes of the type trans-[Cl(pyridine)4Ru-L]+ where L is a parasubstituted cyanobenzene derivative, NCArCOOH, NCArCOMe, NCArCHO, NCArBr, NCArCl,
NCArNH2, NCArOH, NCArCH3, and NCArCN. The work presented here will detail our efforts to
prepare and to purify each of the complexes. Correlations between the metal-based E1/2 values and
the electron donating or withdrawing effects of the substituents will be discussed.
DMSO
Heat~30 min
DMSO
Argon gas
Excess acetone DMSO
Freeze 24 hrs.
RuCl3
Cl
DMSO
Ru
DMSO
Cl
Complex
trans-[Cl(py)4Ru(MeCN)]PF6
λmax, nm
244
355
Assignment
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(ArCN)]PF6
241
351
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(NCArCHO)]PF6
247
329
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(NCArCOMe)]PF6
249
316
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(NCArCOOH)]PF6
py
Reflux w/ py and
NaNO2 15 min
285
376
dπ to π* (py)
dπ to π* (L)
py
Rotary evaporate
wash w/ cold water
trans-[Cl(py)4Ru(NCArCl)]PF6
249
398
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(NCArNH2)]PF6
249
397
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(NCArCN)]PF6
244
347
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(NCArOH)]PF6
247
399
dπ to π* (py)
dπ to π* (L)
trans-[Cl(py)4Ru(NCArCH3)]PF6
242
358
dπ to π* (py)
dπ to π* (L)
Cl
Reflux w/ py
2.5 hrs.
py
py
Ru
Rotary evaporate py
wash w/ acetone
py
Cl
Introduction
Over the past four years, a number of studies have been aimed at exploring the photochemical and
electrochemical properties of monomeric and dimeric complexes based on trans-[Cl(pyridine)4Ru-L]+.
The reason for this attention is the ability of the ruthenium polypyridyl to function as an efficient
photosensitizer 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. This research
will explore the chemistry of trans-[Cl(pyridine)4Ru-L]+ as potential building blocks for larger oligomeric
complexes which could possibly exhibit interesting photochemical and/or redox active properties.5 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.3
Cl
py
Reflux w/ conc. HCl py
~30 min
Add NH3PF6
py
wash w/ ether
py
Ru
py
NO2
py
NO
Ru
NO2
L= Ligands
NC
Excess Sodium Azide
w/ acetone under Argon py
Add Ligand
py
monitor rxtn w/
UV/Visible Spectroscopy
Methods and Materials
Br
NC
CN
H
NC
NH2
NC
OH
Cl
py
NC
Ru
py
NC
L
CH3
O
NC
Cl
NC
py=pyridine
Spectroscopic grade solvents (Aldrich) 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.2,3 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 Bio-Analytical Systems (BAS) CV-50W.
H
N
NC
O
O
NC
OH
CH3
Electrochemical & Infrared Properties of
Complexes
Electron Withdrawing Effect of Cyanobenzene
Substituents
Complex
trans-[Cl(py)4Ru(ArCN)]PF6
trans-[Cl(py)4Ru(NCArCHO)]PF6
trans-[Cl(py)4Ru(NCArCOMe)]PF6
trans-[Cl(py)4Ru(NCArCOOH)]PF6
trans-[Cl(py)4Ru(NCArBr)]PF6
trans-[Cl(py)4Ru(NCArCl)]PF6
trans-[Cl(py)4Ru(NCArNH2)]PF6
trans-[Cl(py)4Ru(NCArCN)]PF6
trans-[Cl(py)4Ru(NCArOH)]PF6
trans-[Cl(py)4Ru(NCArCH3)]PF6
*converted from v SCE
Cyclic Voltammogram of 4-Acetylbenzonitrile Complex
1200
scan rate = 250mV/s
2.00 mm dia. Pt0 v. Ag-AgCl
in 0.1M TBAH/CH3CN
E1/2 v Ag-AgCl
1000
H
CH
CH3 3
CN
CN
H
Br
Br
800
CHO
CHO
COCH3
COCH3
400
200
NH2
Cl
OH
Cl
1200
1000
800
600
400
mVolts v. Ag-AgCl
200
0
2196 (moderate)
2131 (strong)
2108 (strong)
Acknowledgments
0
-1.5
2131.8 (weak)
1. Zakeeruddin, S.M.; Nazeeruddin, M.K.; Pechy, P.; Rotzinger, F.P.; Humphry-Baker,
R.; Kalyanasundaram, K.; Gratzel, M. Inorg. Chem., 1997, 36, 5937.
2. Coe, B.J.; Meyer, T.J.; White, P.S. Inorg. Chem., 1993, 32, 4012.
3. Coe, B.J.; Meyer, T.J.; White, P.S. Inorg. Chem., 1995, 34, 593.
4. Juris, A.; Campanga, S.; Balzani, V.; Belser, P.; von Zelewsky, A. Coord. Chem.
Rev., 1988, 84, 85.
5. Balzani, V.; Scandola, F. Supermolecular Photochemistry; Wiley, Chinchester, UK,
1991
6. Carol, F.A. Perspectives on Structure and Mechanism in Organic Chemistry. First ed.
Brooks Cole: 1997; 384.
600
OH
IR(cm-1)
2200 (moderate)
2192 (strong)
2204 (moderate)
2108 (weak)
References
COOH
COOH
NH2
E1/2mV v Ag-AgCl
995*
1021.5
1009.5
783.8
995
275.5
283.5
1021
282
944
-1
-0.5
0
+
Sigma Values
0.5
6
1
LMF, MMG and MRR gratefully acknowledge:
Kate Dedeian, Hannah Nandor and Steve Hira for the synthesis of trans-[Ru(py)4Cl(NO)](PF6)2
Financial support from the RWU Undergraduate Student Research Grant
CJT gratefully acknowledges:
Financial support from a grant from the RWU Faculty Research Foundation
www.rwu.edu