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

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 Complex
?max, nm Assignment trans-Cl(py)4Ru(MeCN)PF6 2
44 dp to p (py) 355 dp to p
(L) trans-Cl(py)4Ru(ArCN)PF6 241 dp to p
(py) 351 dp to p (L) trans-Cl(py)4Ru
(NCArCHO)PF6 247 dp to p (py) 329
dp to p (L) trans-Cl(py)4Ru(NCArCOMe)PF6
249 dp to p (py) 316 dp to p
(L) trans-Cl(py)4Ru(NCArCOOH)PF6 285 dp to
p (py) 376 dp to p (L) trans-Cl(py)4Ru(
NCArCl)PF6 249 dp to p (py) 398 dp to
p (L) trans-Cl(py)4Ru(NCArNH2)PF6 249 dp
to p (py) 397 dp to p
(L) trans-Cl(py)4Ru(NCArCN)PF6 244 dp to p
(py) 347 dp to p (L) trans-Cl(py)4Ru(NCA
rOH)PF6 247 dp to p (py) 399 dp to p
(L) trans-Cl(py)4Ru(NCArCH3)PF6 242 dp to
p (py) 358 dp to p (L)
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
para-substituted 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.
Synthetic Scheme

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
Methods and Materials 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 acetonedichloromethane (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.
Electrochemical Infrared Properties of
Complexes Complex E1/2mV v Ag-AgCl
IR(cm-1) trans-Cl(py)4Ru(ArCN)PF6 995
2200 (moderate) trans-Cl(py)4Ru(NCArCHO)PF6
1021.5 2192 (strong) trans-Cl(py)4Ru(NCArCOMe)
PF6 1009.5 2204 (moderate) trans-Cl(py)4Ru(N
CArCOOH)PF6 783.8 2108 (weak) trans-Cl(py)4R
u(NCArBr)PF6 995 trans-Cl(py)4Ru(NCArCl
)PF6 275.5 2131.8 (weak) trans-Cl(py)4Ru(NCAr
NH2)PF6 283.5 trans-Cl(py)4Ru(NCArCN)PF6 10
21 2196 (moderate) trans-Cl(py)4Ru(NCArOH)PF6
282 2131 (strong) trans-Cl(py)4Ru(NCArCH3)PF6
944 2108 (strong) converted from v SCE
CN
CN
H
H
CHO
CHO
Br
COCH3
Br
COCH3
CH3
CH3
References 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.
COOH
COOH
NH2
OH
Cl
OH
NH2
Cl
Acknowledgments 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