Synthesis, crystal structure, and redox and photophysical properties of novel bisphosphinoaryl RuII-terpyridine complexes

Article abstract of DOI:10.1021/om049503u

Novel organometallic [Ru(PCP)(tpy)]Cl complexes, containing the terdentate coordinating monoanionic bisphosphinoaryl ligands [C₆H ₃(CH₂PR₂)₂-2,6]^- (PCP) (R = Ph (11); iPr (12)) and 2,2′:6′,2″-terpyridine, have been synthesized by two different synthetic pathways in good yields. The molecular structure in the solid state of [Ru{C₂H₂(CH ₂PPh₂)₂-2,6}(tpy)](OTf) (14) has been determined by X-ray crystallography. The spectroscopic and electrochemical properties of the [Ru(PCP)(tpy)]Cl complexes were compared with those obtained for [Ru{C₆H₃(CH₂NMe₂) ₂-2,6}(tpy)](Cl) (3) containing the monoanionic bisaminoaryl ligand [C₆H₃(CH₂NMe₂)₂-2,6]- (NCN). The obtained results revealed that substitution of the NCN-pincer ligand by PCP-pincer ligands offers a powerful tool to tune the redox and photophysical properties as well as the reactivity of the ruthenium(II) metal centers in the resulting photoactive monomeric species.

Full text of DOI:10.1021/om049503u

Organometallics 2004, 23, 5833-5840
5833
Synthesis, Crystal Structure, and Redox and
Photophysical Properties of Novel Bisphosphinoaryl
RuII-Terpyridine Complexes
Marcella Gagliardo,† Harm P. Dijkstra,† Paolo Coppo, Luisa De Cola,
Martin Lutz,‡ Anthony L. Spek,‡,§ Gerard P. M. van Klink,† and
Gerard van Koten*,†
Debye Institute, Department of Metal-Mediated Synthesis, and Bijvoet Center for
Biomolecular Research, Department of Crystal and Structural Chemistry, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands, and Institute of Molecular Chemistry,
Molecular Photonic Materials Group, University of Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands
Received July 5, 2004
Novel organometallic [Ru(PCP)(tpy)]Cl complexes, containing the terdentate coordinating
monoanionic bisphosphinoaryl ligands [C6H3(CH2PR2)2-2,6]- (PCP) (R ) Ph (11); iPr (12))
and 2,2′:6′,2′′-terpyridine, have been synthesized by two different synthetic pathways in good
yields. The molecular structure in the solid state of [Ru{C6H2(CH2PPh2)2-2,6}(tpy)](OTf) (14)
has been determined by X-ray crystallography. The spectroscopic and electrochemical
properties of the [Ru(PCP)(tpy)]Cl complexes were compared with those obtained for
[Ru{C6H3(CH2NMe2)2-2,6}(tpy)](Cl) (3) containing the monoanionic bisaminoaryl ligand
[C6H3(CH2NMe2)2-2,6]- (NCN). The obtained results revealed that substitution of the NCN-
pincer ligand by PCP-pincer ligands offers a powerful tool to tune the redox and photophysical
properties as well as the reactivity of the ruthenium(II) metal centers in the resulting
photoactive monomeric species.
Introduction
temperature emission3), the higher symmetry of the
resultant complexes is much more favorable. The tri-
dentate coordination mode of terpyridine ligands results
in high stereochemical control by avoiding the formation
of isomeric mixtures present in tris-bidentate systems.4
Most recent work on the possible modification of the
tridentate ligand has highlighted new strategies to
improve the photophysical properties of the ruthenium-
(II) complex. Thus, the replacement of a nitrogen atom
on a pyridine ring by a carbon atom considerably
modifies the electronic properties of terpyridine-type
ligands.5 The resulting anionic C,N,N or N,C,N chelat-
ing subunits, which lead to the formation of organome-
tallic complexes containing a strong covalent metal-
carbon bond, allow the MLCT state to be longer living
and lead to luminescent ruthenium complexes at room
temperature.5 In fact, these cyclometalating ligands
cause a decrease in energy of the luminescent triplet
For the past decade, monomeric ruthenium polypyr-
idine complexes have been widely used as efficient
photosensitizers in covalently linked multicomponent
systems due to their chemical stability, redox properties,
and excited state reactivity.1 The most common poly-
pyridyl ligands employed as terminal ligands in such
species are 2,2′-bipyridine (bpy) and 2,2′:6′,2′′-terpyri-
dine (tpy). Considerable attention was focused on the
[Ru(bpy)3]2+ and [Ru(tpy)2]2+ molecular systems.2 Al-
though [Ru(tpy)2]2+-type complexes exhibit less favor-
able photophysical behavior as compared to [Ru(bpy)3]2+
(shorter excited state lifetime and the absence of a room-
* Corresponding author. Phone: +31-30-2533120. Fax: +31-30-
2523615. E-mail: g.vankoten@chem.uu.nl.
† Debye Institute, Department of Metal-Mediated Synthesis.
Institute of Molecular Chemistry, Molecular Photonic Materials.
‡ Bijvoet Center for Biomolecular Research, Department of Crystal
and Structural Chemistry.
3
metal to ligand charge transfer, MLCT. As a conse-
quence, the energy gap between the emitting state and
the nonradiative metal-centered 3MC state, responsible
for the quenching at room temperature of the emission
in
§ Corresponding author for crystallographic data. Phone: +31-30-
2532538. Fax: +31-30-2523940. E-mail: a.l.spek@chem.uu.nl.
(1) (a) Sauvage, J.-P.; Collin, J.-P.; Chambron, J.-C.; Guillerez, S.;
Coudret, C.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L.
Chem. Rev. 1994, 94, 993. (b) Harriman, A.; Ziessel, R. Chem. Commun.
1996, 1707. (c) Constable, E. C. In Electronic Materials: The Oligomer
Approach; Wiley: VCH: Weinheim, 1998. (d) Schwab, P. F. H.; Levin,
M. D.; Michl, J. Chem. Rev. 1999, 99, 1863. (e) Barigelletti, F.;
Flamigni, L. Chem. Soc. Rev. 2000, 29, 1. (f) Padilla-Tosta, M. E.; Lloris,
J. M.; Mart´ınez-Ma´n˜ez, R.; Benito, A.; Soto, J.; Pardo, T.; Miranda,
M. A.; Markos, M. D. Eur. J. Inorg. Chem. 2000, 741. (g) Constable,
E. C.; Housecroft, C. E.; Johnston, L. A.; Armspach, D.; Neuburger,
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N.; Balzani, V.; Constable, E. C.; Cargill Thompson, A. M. W. Inorg.
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C.; Sutin, N. J. Am. Chem. Soc. 1987, 109, 2381.
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von Zelensky, A. Stereochemistry of Coordination Compounds, Wiley:
Chichester, 1996.
(5) (a) Padilla-Tosta, M. E.; Lloris, J. M.; Mart´ınez-Ma´n˜ez, Pardo,
T.; Soto, J.; Benito, A.; Markos, M. D. Inorg. Chem. Commun. 2000, 3,
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von Zelensky, A. Coord. Chem. Rev. 1998, 84, 85.
10.1021/om049503u CCC: $27.50 © 2004 American Chemical Society
Publication on Web 10/16/2004

5834 Organometallics, Vol. 23, No. 24, 2004
Gagliardo et al.
Scheme 1. Synthesis of [Ru(NCN)(tpy)]Cl
Complexes
Figure 1. Monoanionic bisaminoaryl [C6H2(CH2NMe2)2-
2,6-R′-4]- (1) and bisphosphinoaryl [C6H2(CH2PR2)2-2,6-
R′-4]- (2) pincer ligands.
Scheme 2. Synthesis of [Ru(PCP)(tpy)]Cl
Complexes via Direct Ruthenation of PCP-Pincer
Ligands by [RuCl2(PPh3)3]
[Ru(tpy)2]2+-type compounds, becomes so large that the
emitting state can no longer be thermally populated.
The structural and chemical properties of RuII com-
plexes containing the terdentate coordinating mono-
anionic bisaminoaryl pincer ligands [C6H2(CH2NMe2)2-
2,6-R′-4]- (NCN) (1, Figure 1) were widely investigated.6
The complexation of terpyridine ligands resulted in
excellent stability of the NCN-RuII moieties and the
concomitant use of [Ru(NCN)(tpy)]Cl complexes as
building blocks for dimeric architectures having poten-
tial optical and/or electronic applications.7 RuII com-
plexes containing the related monoanionic η3-P,C,P-
coordinating bisphosphinoaryl ligands [C6H2(CH2PR2)2-
2,6-R′-4]- (2, Figure 1) have also received considerable
attention.8 These complexes were used successfully as
homogeneous catalysts in various metal-mediated or-
ganic transformations.8h However, despite the increas-
ing interest in the influence of tertiary phosphines on
the spectroscopic and redox properties of low-valent RuII
complexes, the lack of a convenient synthetic route to
[Ru(PCP)(tpy)]Cl complexes has considerably hampered
their potential application as small devices specifically
reacting to external stimuli.
Results and Discussion
Synthesis of [RuII(PCP)(tpy)]X (X ) Cl, OTf)
Complexes. In the course of our investigations directed
toward the synthesis and reactivity of pincer-type
arylruthenium(II) complexes containing the monoan-
ionic terdentate coordinating bisaminoaryl [C6H2(CH2-
NMe2)2-2,6-R′-4]- (NCN) ligand, strategies for the prepa-
ration of new NCN-RuII species containing the 2,2′:6′,2′′-
terpyridine (tpy) ligand ([Ru(NCN)(tpy)]Cl) were de-
veloped (Scheme 1).6 The results obtained using [Ru-
(NCN)(tpy)]Cl complexes for the preparation of new
molecular systems that can be regarded as suitable
components for the fabrication of optical devices7
prompted us to attempt the synthesis of analogous RuII-
tpy compounds containing the monoanionic bisphos-
phinoaryl pincer ligand [C6H3(CH2PR2)2-2,6]- (PCP) (2,
Figure 1).9 The common synthetic pathway, which
involves reaction of [RuCl{C6H3(CH2PR2)2-2,6}(PPh3)]
(R ) Ph (9); iPr (10), vide infra Scheme 3) and tpy in
MeOH at room temperature, gave the desired com-
pounds unfortunately only in low yield.8a Although
[RuCl(NCN)(PPh3)] and [RuCl(PCP)(PPh3)] complexes
are structurally closely related,6a,8b the observed de-
crease in the overall yield for the reaction with tpy
reflects changes in the electronic and steric properties
operative at and around the metal center. Additionally,
the concomitant formation of [RuCl2(tpy)(PPh3)] (4)
(Scheme 2) proved to be a major inhibiting factor for
selective and quantitative synthesis of [Ru(PCP)(tpy)]-
Cl complexes. This limitation was ascribed to the nature
of [RuCl(PCP)(PPh3)] prepared via direct cyclometala-
tion of meta-bisphosphinoarene ligand (Figure 1) with
[RuCl2(PPh3)3] used as starting material (Scheme 2).8a,g
In this paper, a facile route to synthesize RuII-tpy
complexes containing PCP-pincer ligands is presented.
In addition, it is shown how pincer ligand systems allow
the tuning of the redox and photophysical properties of
the chromophores prepared. The presence of soft donors
(tertiary phosphines), together with hard donor nitrogen
centers in the same complex, is useful to modulate the
electronic properties of the metal centers and allows for
additional use of 31P NMR spectroscopy as an important
characterization tool.
(6) (a) Sutter, J.-P.; James, S. L.; Steenwinkel, P.; Karlen, T.; Grove,
D. M.; Veldman, N.; Smeets, W. J. J.; Spek, A. L.; van Koten, G.
Organometallics 1996, 15, 941. (b) Steenwinkel, P.; James, S. L.; Grove,
D. M.; Veldman, N.; Spek, A. L.; van Koten, G. Chem. Eur. J. 1996, 2,
1440.
(7) Steenwinkel, P.; Grove, D. M.; Veldman, N.; Spek, A. L.; van
Koten, G. Organometallics 1998, 17, 5647.
(8) (a) Karlen, T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten,
G. Organometallics 1996, 15, 5687. (b) Jia, G.; Lee, H. M.; Williams,
I. D. J. Organomet. Chem. 1997, 534, 173. (c) Rybtchinski, B.; Ben-
David, Y.; Milstein, D. Organometallics 1997, 16, 3786. (d) Jia, G.; Lau.,
C. P. J. Organomet. Chem. 1998, 565, 37. (e) Steenwinkel, P.;
Kolmschot, S.; Gossage, R. A.; Dani, P.; Veldman, N.; Spek, A. L.; van
Koten, G. Eur. J. Inorg. Chem. 1998, 477. (f) van der Boom, M. E.;
Kraatz, H.-B.; Hassner, L.; Ben-David, Y.; Milstein, D. Organometallics
1999, 18, 3873. (g) Dani, P.; Albrecht, M.; van Klink, G. P. M.; van
Koten, G. Organometallics 2000, 19, 4468. (h) Dani, P.; Karlen, T.;
Gossage, R. A.; Gladiali, S.; van Koten, G. Angew. Chem., Int. Ed. 2000,
39, 743. (i) Dani, P.; van Klink, G. P. M.; van Koten G. Eur. J. Inorg.
Chem. 2000, 1465. (j) Albrecht, M.; van Koten, G. Angew. Chem., Int.
Ed. 2001, 40, 3750. (k) Dijkstra, H. P.; Albrecht, M.; Medici, S.; van
Klink, G. P. M.; van Koten, G. Adv. Synth. Catal. 2002, 344, 1135. (l)
Medici, S.; Gagliardo, M.; Williams, B. S.; Lutz, M.; Spek, A. L.;
Gladiali, S.; van Klink, G. P. M.; van Koten, G. Submitted. (m)
Singleton, J. T. Tetrahedron 2003, 59, 1873.
(9) Karlen, T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten,
G. Organometallics 1996, 15, 5687.

Bisphosphinoaryl RuII-Terpyridine Complexes
Organometallics, Vol. 23, No. 24, 2004 5835
Table 1. Selected Bond Lengths (Å), Bond Angles (deg), and Torsion Angles (deg) for the First
Independent Molecule of Complex 4 (values for the second independent molecule are given in
square brackets)
Bond Lengths (Å)
Ru1-Cl1
Ru1-P1
Ru1-N2
2.4491(11) [2.4338(11)]
2.2895(12) [2.2919(11)]
1.943(3) [1.942(3)]
Ru1-Cl2
Ru1-N1
Ru1-N3
2.4545(11) [2.4679(11)]
2.073(3) [2.052(3)]
2.072(3) [2.070(3)]
Bond Angles (deg)
N1-Ru1-N3
P1-Ru1-Cl2
N2-Ru1-N3
Cl1-Ru1-N1
P1-Ru1-N2
P1-Ru1-Cl1
Cl2-Ru1-N2
Cl2-Ru1-Cl1
159.39(14) [159.54(14)]
178.87(4) [177.34(4)]
79.90(14) [79.63(14)]
100.72(10) [95.61(10)]
93.85(10) [93.16(10)]
94.84(4) [92.54(4)]
N2-Ru1-Cl1
N1-Ru1-N2
N3-Ru1-Cl1
P1-Ru1-N1
P1-Ru1-N3
Cl2-Ru1-N1
Cl2-Ru1-N3
171.27(10) [173.36(10)]
79.63(14) [80.59(14)]
99.16(10) [103.55(10)]
93.15(10) [94.12(9)]
90.59(10) [92.15(9)]
85.96(9) [88.23(9)]
85.32(10) [85.99(10)]
86.00(4) [88.47(4)]
90.01(10) [85.22(9)]
Torsion Angles (deg)
N2-C10-C11-N3
N1-C5-C6-N2
C16-P1-Ru1-N2
3.9(5) [5.5(5)]
6.4(2) [34.90(19)]
-6.7(5) [-3.9(5)]
Scheme 3. Synthesis of [RuCl(PCP)(PPh3)]
Complexes Using the Transcyclometalation
Procedure
Unidentified oligomeric PCPRuII species, present as
impurities in the prepared [RuCl(PCP)(PPh3)] com-
plexes,9 coordinate in refluxing MeOH with tpy, giving
the octahedral 18e RuII complex 4 in approximately 20%
yield. Unfortunately, attempts to purify the desired
[Ru(PCP)(tpy)]Cl complexes from 4 failed. The presence
of 4 can be easily confirmed by 1H and 31P NMR
spectroscopy. The 31P NMR spectrum is particularly
useful to identify complex 4 from a singlet at 21.5 ppm
in CD2Cl2, which is indicative of the PPh3 coordinated
to the ruthenium metal center. The molecular structure
of complex 4 (Figure 2; bond lengths, angles, and torsion
angles in Table 1) has been characterized by X-ray
diffraction analysis of single crystals grown by slow
diffusion of Et2O vapor in a CH2Cl2 solution containing
both complexes 4 and 11.
To overcome the above-mentioned limitations, a new
synthetic approach for the preparation of [RuCl(PCP)-
(PPh3)] compounds8g was developed. This alternative
synthetic route employs the transcyclometalation (TCM)
reaction (Scheme 3), which represents an elegant meth-
odology for the formation of a metal-carbon bond under
relatively mild conditions and proceeds selectively and
in quantitative yield. The reaction pathway (Scheme 3),
similar to an electrophilic aromatic substitution reac-
tion, involves the formal exchange of a terdentate
coordinated monoanionic bisaminoaryl ligand, [C6H3(CH2-
NMe2)2-2,6]-, in complex [RuCl{C6H3(CH2NMe2)2-2,6}-
(PPh3)] (7) by a corresponding terdentate coordinated
bisphosphinoaryl ligand [C6H3(CH2PR2)2-2,6]-, leading
to the formation of [RuCl(PCP)(PPh3)] complexes. The
only coproduct is the bisaminoarene 8, which is highly
Figure 2. Displacement ellipsoid plot (50% probability
level) of 4. Only the first of two independent molecules is
shown. Hydrogen atoms and solvent molecules have been
omitted for clarity.
soluble in apolar solvents and allows for simple separa-
tion from the desired product. Furthermore, the forma-
tion of secondary products is suppressed as chlorinated
solvents are not used, and thus HCl cannot be generated
during the reaction. Recent results demonstrated that
the TCM reaction is also superior over established
metalation procedures if several ruthenium metal cen-
ters are to be introduced in shape-persistent macromo-
lecular multi(pincer) ligands.10
The synthesis of complexes 9 and 10 (Scheme 3) was
performed using the TCM methodology by reaction of a
1:1 molar mixture of ligands 5 and 6, respectively, with
7 in refluxing C6H6 (Scheme 3).8g,k The resultant
complexes 9 and 10 were isolated pure as green, air-
sensitive solids in good yields. Spectroscopic character-
ization confirmed that both complexes 9 and 10 have
square pyramidal geometries with the PPh3 ligand
occupying the apical position.8b,f,i As shown in Scheme
(10) Dijkstra, H. P.; Albrecht, M.; van Koten, G. Chem. Commun.
2002, 126.

5836 Organometallics, Vol. 23, No. 24, 2004
Gagliardo et al.
Scheme 4. Synthesis of [Ru(PCP)(tpy)]Cl
Complexes
(CH2PPh2)2-2,6}(tpy)](OTf) (14) as a red solid in good
yield (90%).
In the second and even faster and more convenient
one-pot synthesis, the chloride was replaced in situ in
dry MeOH with a stoichiometric amount of AgOTf in
the presence of tpy. After stirring at room temperature
for 3 h the reaction was complete and the silver chloride
was removed by filtration. After workup of the metha-
nolic solution, [Ru{C6H3(CH2PPh2)2-2,6}(tpy)](OTf) (14)
was obtained pure in 86% yield as a red air-stable
powder. The same synthetic procedure applied under
reflux conditions did not accelerate the reaction but
showed, surprisingly, the concomitant formation (10%)
of an AgI(tpy) complex ([AgI(tpy)(PPh3)]OTf), which was
characterized by single-crystal X-ray diffraction.11
Crystal Structure of [RuCl2(tpy)(PPh3)] (4) and
[Ru{C6H3(CH2PPh2)2-2,6}(tpy)](OTf) (14). The crys-
tal structure of the Et2O/CH2Cl2 solvate of 4 contains
two crystallographically independent RuII complexes,
which mainly differ in the orientation of the PPh3
ligand. In the first molecule, the PPh3 group is eclipsed
with N2 of the tpy ligand (C16-P1-Ru1-N2 ) 6.4(2)°),
while in the second molecule the PPh3 ligand is stag-
gered (C16-P1-Ru1-N2 ) 34.90(19)°). A molecular
plot of the first independent molecule is depicted in
Figure 2. A selection of bond lengths, angles, and torsion
angles of 4 is summarized in Table 1.
Scheme 5. Synthesis of [Ru(PCP)(tpy)](OTf)
Complex 14 by Method (a) (top) and Method
(b) (bottom)
The RuII center is in a severely distorted octahedral
environment coordinated to a tridentate tpy ligand, one
PPh3 ligand, and two chloride anions in a mutual cis-
arrangement. The distortion is reflected in the octahe-
dral angle variance12 of 46.46° (44.87° for the second
molecule) compared to 0.0° for an ideal octahedron. The
reason for this distortion is the strain generated by the
chelating η3-tpy ligand. This strain can also be seen in
the Ru-N distances, which are significantly shorter for
the central N2 (1.943(3) and 1.942(3) Å for the PPh3
eclipsed and staggered, respectively) than for the ter-
minal N1 and N3 atoms (2.052(3)-2.073(3) Å). Similar
differences can also be found in the literature.13 The
Ru-Cl1 distances (2.4491(11) and 2.4338(11) Å), which
are trans to N2 of the tpy ligand, are slightly shorter
than the Ru-Cl2 distances (2.4545(11) and 2.4679(11)
Å), which are trans to the PPh3 ligand. As expected for
a RuII complex, the tpy ligand is essentially planar and
the metal is situated in this plane.
Single crystals of 14 suitable for X-ray crystallography
were grown from a CH2Cl2 solution into which diethyl
ether vapor was allowed to diffuse slowly. Figure 3
depicts the molecular structure of 14 (a selection of bond
lengths, angles, and torsion angles of 14 is summarized
in Table 2). In the molecular structure of 14, the
ruthenium center is in a distorted octahedral geometry
with both the tpy and the bis(ortho-)chelating PCP
ligands coordinated meridionally. The distortion of the
octahedron, with an angle variance of 102.71°, is even
larger than in the two independent molecules of com-
4, [Ru(PCP)(tpy)]Cl complexes 11 and 12 are readily
prepared in high yield (86 and 84%, respectively) by
reaction of [RuCl(PCP)(PPh3)] complexes 9 and 10,
respectively, with tpy in dry MeOH at reflux tempera-
ture.9 The red complexes 11 and 12 are soluble in apolar
solvents and alcohols, such as methanol and ethanol,
and were fully characterized by NMR spectroscopy in
CD2Cl2 and elemental analysis. Because of the long
reaction times (3 days at reflux), other preparative
procedures were examined in order to obtain the desired
complexes faster and with comparable selectivity. The
low reactivity of [RuCl(PCP)(PPh3)] complexes toward
tpy is partly due to their sparingly solubility nature in
methanol. In addition, the ability of the chloride anion
to act as leaving group in complex 9 proved to be a
fundamental and crucial step for the rapid and selective
formation of desired [Ru(PCP)(tpy)]Cl complexes. Two
halide-abstracting strategies were investigated for re-
placing the chloride for a better leaving group such as
the trifluoromethanesulfonate anion (triflate, OTf,
F3CSO3-). The first method involved the reaction of a
solution of complex 9 in benzene with an excess of
Me3SiOTf at room temperature for 1 h, to afford the
corresponding triflate complex 13 (Scheme 5). After
removal of the solvent and Me3SiCl (a volatile liquid)
and washing out of the residual Me3SiOTf (highly
soluble in apolar solvents), an equimolar solution of tpy
in methanol was added to the resultant green solid
residue. The reaction mixture was stirred at room
temperature for 3 h, yielding after workup [Ru{C6H3-
(11) Lutz, M.; Spek, A. L.; Gagliardo, M.; van Klink, G. P. M.; van
Koten, G. To be submitted.
(12) Robinson, K.; Gibbs, G. V.; Ribbe P. H. Science 1971, 172, 567.
(13) (a) Beley, M.; Collin, J.-P.; Louis, R.; Metz, B.; Sauvage, J.-P.
J. Am. Chem. Soc. 1991, 113, 8521. (b) Constable, E. C.; Cargill
Thompson, A. M. W. New J. Chem. 1992, 16, 855. (c) Encinas, S.;
Flamigni, L.; Barigelletti, F.; Constable, E. C.; Housecroft, C. E.;
Schofield, E. R.; Figgemeier, E.; Fenske, D.; Neuburger, M.; Vos, J.
G.; Zehnder, M. Chem. Eur. J. 2002, 8, 137.

Bisphosphinoaryl RuII-Terpyridine Complexes
Organometallics, Vol. 23, No. 24, 2004 5837
Figure 4. Cyclic voltammograms of complexes 3 (NCN),
11 (PCP-Ph), and 12 (PCP-iPr) measured in butyronitrile
at 298 K (0.1 M TBAH; scan rate ) 100 mV s-1).
Table 3. Absorption and Electrochemical Data of
3, 11, and 12
complex
(ligand)
λmax (nm)a
E1/2(ox) (V)b
E1/2(red) (V)b
ꢀmax (M-1 cm-1
)
RuII/RuIII
tpy/tpy-
3 (NCN)
11 (PCP-Ph)
12 (PCP-iPr)
524 (65 800)
479 (43 850)
513 (41 350)
-0.178
0.167
0.056
-2.031
-1.946
-1.978
Figure 3. Displacement ellipsoid plot (50% probability
level) of the cationic portion of 14. Hydrogen atoms, the
triflate anion, and solvent molecules have been omitted for
clarity.
a Absorption maxima relative to 1MLCT transitions. Measured
at 298 K in CH3CN. b Measured at 298 K in butyronitrile solutions
containing 0.1 M TBAH. Potentials in V reported vs Fc/Fc+.
Table 2. Selected Bond Lengths (Å), Bond Angles
(deg), and Torsion Angles (deg) for 14
proximately planar, with torsion angles between the
terminal rings and the directly bonded rings being
4.0(3)° and -3.5(3)°.
Bond Lengths (Å)
Ru1-N1
Ru1-N3
Ru1-P1
2.083(2)
2.078(2)
2.3241(7)
Ru1-N2
Ru1-C1
Ru1-P2
2.0090(19)
2.108(2)
2.3094(7)
The ligand arrangement of [Ru(PCP)(tpy)]Cl com-
plexes observed in the molecular structure of complex
1
14 is preserved in solution. The H NMR spectrum of
Bond Angles (deg)
14, recorded at room temperature in CD2Cl2, shows a
single resonance for the benzylic hydrogens, indicative
of a molecular mirror plane containing the benzylic
carbon atoms. In the 31P NMR spectra only one singlet
resonance for the phosphorus nuclei is observed. Since
the NMR data of complexes 11 and 12 show similar
patterns, it can be deduced that their molecular struc-
tures are analogous to the structure of complex 14.
Electrochemical and Photophysical Properties
of Complexes 3, 11, and 12. The presence of hard and
soft donor centers in the NCN- and PCP-pincer ligand
systems, respectively, results in tunable and interesting
electrochemical and spectroscopic behavior of the pre-
pared complexes [Ru(NCN)(tpy)]Cl (3) and [Ru(PCP)-
(tpy)]Cl (11 and 12).
The anodic region of the cyclic voltammogram of
complexes 3, 11, and 12 (Figure 4) is dominated by a
reversible wave corresponding to one-electron oxidation
of the RuII state, while the cathodic regions exhibit
defined reversible waves related to the reduction of the
coordinated tpy ligand. The measured E1/2 values versus
the couple Fc/Fc+ for all three compounds are reported
in Table 3. The oxidation potentials of [Ru(NCN)(tpy)]-
Cl and [Ru(PCP)(tpy)]Cl complexes are significantly
lower than that of [Ru(tpy)2](PF6)2 (0.92 V vs Fc/Fc+)1a.
This indicates that the σ-donor capability of the mon-
omeric NCN- and PCP-pincer ligands is much stronger
than that of tpy.13b,14 The electron donation ability of
the coordinated ligands, which results in an easier
oxidation of the ruthenium ion, is reflected in the
N1-Ru1-N3
P1-Ru1-P2
N2-Ru1-N3
C1-Ru1-N1
P1-Ru1-N2
P1-Ru1-C1
P2-Ru1-N2
P2-Ru1-C1
157.29(8)
156.09(2)
78.74(8)
104.27(9)
101.28(5)
78.41(7)
102.63(6)
77.73(7)
N2-Ru1-C1
N1-Ru1-N2
N3-Ru1-C1
P1-Ru1-N1
P1-Ru1-N3
P2-Ru1-N1
P2-Ru1-N3
177.15(9)
78.55(8)
98.44(9)
91.20(6)
93.24(6)
93.30(6)
91.61(6)
Torsion Angles (deg)
4.0(3) N2-C42-C43-N3
-26.3(3) C1-C6-C20-P2
N1-C37-C38-N2
C1-C2-C7-P1
-3.5(3)
-23.4(3)
pound 4. In addition to the steric strain of the tpy ligand,
which is also present in 4, there is the steric strain
imposed by the PCP-pincer ligand, leading to a consid-
erable distortion of the complex. The P1-Ru1-P2 bond
angle is 156.09(2)°, which is significantly less than
linear. The resulting Caryl-Ru-P bite angles of the
bis(ortho-)chelating PCP ligand, C1-Ru1-P1 and C1-
Ru1-P2, are 78.41(7)° and 77.73(7)°, respectively. The
strain of the PCP-pincer ligand can also be seen in the
Ru-P distances, which are significantly different (2.3094-
(7) and 2.3241(7) Å). The terdentate coordination of the
PCP-pincer ligand affords a Ru1-C1 bond of 2.108(2)
Å, significantly longer than the Ru1-C1 bond in the
analogous complex [Ru(NCN)(tpy)]Cl (3) (Ru1-C1 )
1.982(7) Å).6a However, this value falls in the range of
reported values for other PCP-RuII complexes.8b,f
The Ru-N bonds lengths (Ru1-N1 ) 2.083(2) Å;
Ru1-N2 ) 2.0090(19) Å; Ru1-N3 ) 2.078(2) Å) are
similar to those found for other RuII complexes contain-
ing terdentate tpy ligands.1g,13 As observed for other RuII
complexes containing tpy ligands, the Ru-N contacts
to the central ring of the tpy ligand are shorter than
those to the terminal rings. The tpy ligand is ap-
(14) (a) Beley, M.; Collin, J.-P.; Sauvage, J.-P. Inorg. Chem. 1993,
32, 4539. (b) Bardwell, D.; Cargill Thompson, A. M. W.; Jeffery, J. C.;
McCleverty, J. A.; Ward, M. D. J. Chem. Soc., Dalton Trans 1996, 873.
(c) Koizumi, T.; Tomon, T.; Tanaka, K. Organometallics 2003, 22, 970.

5838 Organometallics, Vol. 23, No. 24, 2004
Gagliardo et al.
in ipsochromic shifts of the MLCT bands for complexes
11 and 12. Also the MLCT transitions for 11 and 12
are slightly different since the substituents on the
coordinating phosphorus atoms, iPr and Ph, have dif-
ferent electronic properties, which influence the electron
density on the metal ion. These results are in good
agreement with the more positive RuII/RuIII redox
potential values observed in the cyclic voltammetry
studies, and a relationship between electrochemical
redox potentials and the energy of the absorption
maxima may be found. Assuming that the π(t2g) metal
orbital and the π* orbital, involved in the first oxidation
and in the first reduction processes, respectively, are
also the orbitals involved in the MLCT absorption
process, a linear correlation between the absorption
maximum energy with increasing ∆E1/2 () e[E1/2(ox) -
E1/2(red)]) is expected.1h The observed trend for com-
plexes 3, 11, and 12, which shows an increase in the
Figure 5. UV-vis absorption spectra of complexes 3
(NCN), 11 (PCP-Ph), and 12 (PCP-iPr) measured in CH3-
CN at 298 K.
oxidation potentials for complexes 3, 11, and 12.14 The
RuII/RuIII redox potentials of complexes 11 and 12
(E1/2 ) 0.167 and 0.056 V vs Fc/Fc+, respectively) are
more positive than that of complex 3 (E1/2 ) -0.178 V
vs Fc/Fc+) by approximately 0.3 V. The observed in-
crease in the oxidation potential is a sign of the softer
σ-donor properties combined with the back-donation of
the PCP-pincer ligands compared to NCN-pincer ligands.
However, the σ electron-donating and π withdrawing
properties of PCP-pincer ligands can be easily modu-
lated by varying the substituents on the phosphorus
atoms. The presence of more donating groups, such as
iPr, increases the stability of the RuIII species, resulting
in a lower redox potential of complex 12 compared to
11. The influence of the NCN- and PCP-pincer ligands
is reflected in different reactivity of [Ru(NCN)(tpy)]Cl
complexes toward oxidants as compared to [Ru(PCP)-
(tpy)]Cl complexes.15
absorption maximum energy with increasing ∆E1/2, is
in accordance with the data previously reported for
other RuII-polypyridine complexes.1h
Complexes 3, 11, and 12 do not show light emission
in solution at room temperature and at 77 K, as
expected for terpyridine-based RuII complexes, due to
3
3
the low energy gap between the MLCT and the MC,
which can then be thermally activated, leading to a
nonradiative decay path.1,16 The lack of radiative decay
in these complexes is consistent to some extent with the
observation that σ-donors stronger than terpyridine (as
PCP and NCN pincer ligands are) contribute to increase
dramatically the nonradiative rate constant.1h Investi-
gations on the photophysical processes occurring in a
wider range of NCN and PCPRuII complexes are ongo-
ing.
The absorption spectra of 3, 11, and 12, measured in
CH3CN at room temperature (Figure 5), show features
that can be easily interpreted by comparison with
literature data.1,6a Table 3 shows the absorption maxima,
λmax, and the molar extinction coefficient, ꢀmax, values
for all the complexes in their +2 oxidation state. The
spectra exhibit intense spin-allowed ligand-centered
(LC) π f π* transitions in the UV region and broad
spin-allowed d(π) f π* metal-to-ligand charge transfer
(MLCT) absorption bands in the visible region. The
terpyridine π f π* absorptions are the same for all the
complexes and are centered at about 310 nm. The PCP
and NCN ligands are electronically quite different, and
their transitions occur at 270 and 280 nm, respectively.
It is interesting to note that due to the heteroleptic
nature of the complexes, the lowest MLCT excited state
could involve either the terpyridine or the cyclometa-
lated ligand. It is clear that in our systems the lowest
excited state involves the terpyridine ligand since the
strong electron-donating character for the NCN and to
a lesser extent for the PCP ligand shifts the Ru f tpy
transition to lower energy. In fact a more accurate
analysis of the absorption spectra reveals more than one
absorption band between 450 and 600 nm, particularly
evident in the NCN complex 3, with the lowest transi-
tion involving the tpy ligand. Furthermore substitution
of the NCN-pincer ligand by PCP-pincer ligands results
Conclusions
The influence of the auxiliary ligands on the reactivity
of [RuCl(NCN)(PPh3)] and [RuCl(PCP)(PPh3)] com-
plexes toward 2,2′:6′,2′′-terpyridine has been demon-
strated. New versatile synthetic strategies have been
developed for the preparation of [Ru(PCP)(tpy)]Cl com-
plexes which show high stability to moisture and air.
Substitution of the monoanionic bisaminoaryl ligand
[C6H3(CH2NMe2)2-2,6]- (NCN) by the monoanionic bis-
phosphinoaryl pincer ligand [C6H3(CH2PR2)2-2,6]- (PCP)
results in tunable and interesting electrochemical and
spectroscopic behavior. The enhanced accepting char-
acter of the phosphorus atoms of the PCP ligands, which
can be finely modulated by changing the substituents,
accounts for the stabilization of Ru(dπ) orbitals, result-
ing in a more positive RuIII/II redox couples and higher
energy of the MLCT transitions.
Experimental Section
General Procedures. All experiments were carried out
under a dry nitrogen atmosphere using standard Schlenk
(16) Excitation of the three complexes (λexc ) 480 nm) in a buty-
ronitrile glass at 77 K resulted in a weak emission centered at 600
nm. If this emission arose from a 3MLCT decay in complexes 3, 11,
and 12, one would expect the maximum to be shifted according to the
different electronic properties of the PCP- and NCN-type ligands.
However, by the shape and features of the emission, combined with
the lifetime at 77 K, it is likely that this emission was due to small
impurities of highly emitting [Ru(tpy)2](PF6)2.1a,h
(15) Gagliardo, M.; Amijs, C. H.; Lutz, M.; Spek, A. L.; van Klink,
G. P. M.; van Koten, G. To be submitted.

Bisphosphinoaryl RuII-Terpyridine Complexes
Organometallics, Vol. 23, No. 24, 2004 5839
techniques. Benzene, toluene, pentane, hexane, diethyl ether,
and tetrahydrofuran were distilled over sodium/benzophenone.
Dichloromethane was dried over CaH2. Methanol was dried
over magnesium and used freshly distilled. Compounds 3,6
5,8b,c and 68b,c and [RuCl(NCN)(PPh3)] (7) and [RuCl(PCP)-
(PPh3)] (9) complexes8g were prepared according to literature
procedures. All other reagents were used as purchased. 1H
(200.1 or 300.1 MHz), 13C (75 MHz), and 31P (81 MHz) NMR
spectra were recorded at 298 K on a Varian AC200 or Varian
INOVA 300 spectrometer. Chemical shifts are in ppm relative
to the residual solvent signal (1H and 13C NMR spectra) or
are externally referenced to 85% H3PO4 solution in water (31P
NMR spectra). Elemental analyses were performed by Dornis
und Kolbe, Mikroanalytisches Laboratorium, Mu¨llheim a. d.
Ruhr, Germany.
Refined parameters: 768. Restraints: 3. R (obsd reflns):
R1 ) 0.0465, wR2 ) 0.1444. R (all data): R1 ) 0.0715,
wR2 ) 0.1541. Weighting scheme w ) 1/[σ2(Fo ) + (0.0912P)2],
2
2
where P ) (Fo + 2Fc2)/3. GoF ) 1.139. Residual electron
density between -0.51 and 1.64 e/Å3.
Compound 14: [C47H38N3P2Ru][CF3O3S] + disordered sol-
vent, fw ) 956.88, red plate, 0.15 × 0.15 × 0.03 mm3, triclinic,
space group P1h (no. 2), a ) 10.1323(1) Å, b ) 11.2911(2) Å, c
) 20.5214(3) Å, R ) 83.4955(6)°, â ) 84.9604(6)°, γ ) 88.7150-
(5)°, V ) 2323.43(6) Å3, Z ) 2, F ) 1.368 g/cm3. An absorption
correction based on multiple measured reflections was applied
(µ ) 0.51 mm-1, correction range 0.94-1.00). A total of 38 869
reflections were measured up to a resolution of sin θ/λ ) 0.65
Å-1, of which 10 415 were unique (Rint ) 0.064). The triflate
anion was disordered over two positions with a population of
0.67:0.33. The crystal structure contains large voids (304.3 Å3/
unit cell) filled with disordered solvent molecules. Their
contribution to the structure factors was secured by back-
Fourier transformation (program PLATON,19 CALC SQUEEZE,
68 e-/unit cell). Refined parameters: 614. Restraints: 175. R
(obsd reflns): R1 ) 0.0393, wR2 ) 0.0840. R (all data): R1 )
Cyclic Voltammetry Experiments. The electrochemical
experiments were performed with an EG&G potentiostat/
galvanostat model 263A controlled by model 270/250 Research
Electrochemistry Software (version 4.23). A three-electrode
system was used, consisting of a platinum (Pt) working
electrode, a platinum (Pt) auxiliary electrode, and a Ag/AgCl
reference electrode separated from the test solution by a glass
frit. The experiments were carried out in butyronitrile at room
temperature in a nitrogen atmosphere with tetrabutylammo-
nium hexafluorophosphate (TBAH) as electrolyte (0.1 M). All
potentials are reported relative to SCE. Linear voltammo-
0.0646, wR2 ) 0.0932. Weighting scheme w ) 1/[σ2(Fo ) +
2
(0.0421P)2], where P ) (Fo + 2Fc2)/3. GoF ) 1.047. Residual
2
electron density between -0.59 and 0.60 e/Å3.
Synthesis of [Ru{C6H3(CH2PPh2)2-2,6}(tpy)](Cl) (11). To
a solution of complex [RuCl{C6H3(CH2PPh2)2-2,6}(PPh3)] (9)
(90 mg, 0.1 mmol) in MeOH (15 mL) was added a solution of
tpy (25 mg, 0.1 mmol) in MeOH (5 mL). The reaction mixture
was stirred at reflux temperature for 3 days. The solvent was
then evaporated in vacuo to give a red solid residue, stable in
air and water, which was dissolved in 5 mL of CH2Cl2. Addition
of pentane/Et2O (1:5) resulted in precipitation of an air-stable
red powder, which was collected by filtration, washed with
grams were obtained at a scan rate of 100 mV s-1
.
Electronic Spectroscopic Measurements. UV-vis ab-
sorption spectra were obtained on a Varian Cary 1 spectro-
photometer using matched 1 cm cells and operating with 0.5
nm spectral resolution. Peak positions are given with a 0.5
nm accuracy. Steady state luminescence was measured in
butyronitrile glasses at 77 K using a SPEX fluorimeter. For
nanosecond time-resolved emission measurements, a continu-
ously tunable Coherent Infinity XPO laser (tuned at 450 nm),
with a pulse of 2 ns fwhm, was used as excitation source. Full
spectra and decays were recorded using a Hamamatsu C5680-
21 streak camera, equipped with a M 5677 sweep unit.
Crystal Structure Determinations. X-ray intensities
were measured on a Nonius KappaCCD diffractometer with
rotating anode and Mo KR radiation (graphite monochromator,
λ ) 0.71073 Å) at a temperature of 150(2) K. The structures
were solved with automated Patterson methods17 (compound
4) or direct methods18 (compound 14) and refined with
SHELXL-9719 against F2 of all reflections. Non-hydrogen atoms
were refined freely with anisotropic displacement parameters,
and hydrogen atoms were refined as rigid groups. The draw-
ings, structure calculations, and checking for higher symmetry
were performed with the program PLATON.20
Compound 4: C33H26Cl2N3PRu‚0.5CH2Cl2‚0.3C4H10O +
disordered solvent, fw ) 732.21, dark red block, 0.39 ×
0.24 × 0.12 mm3, monoclinic, space group C2/c (no. 15), a )
34.885(3) Å, b ) 13.6771(15) Å, c ) 35.108(3) Å, â ) 117.326-
(9)°, V ) 14882(3) Å3, Z ) 16, F ) 1.307 g/cm3. An absorption
correction based on multiple measured reflections was applied
(µ ) 0.71 mm-1, correction range 0.76-0.92). A total of 51 763
reflections were measured up to a resolution of sin θ/λ ) 0.61
Å-1, of which 13 711 were unique (Rint ) 0.048). Some of the
solvent molecules were refined as discrete molecules; others
were heavily disordered and included using the SQUEEZE
routine of PLATON20 (back-Fourier transformation of 503
e-/unit cell distributed over voids of 2363.2 Å3/unit cell).
1
hexane, and dried in vacuo (72 mg, 86% yield). H NMR (200
3
MHz, CD2Cl2): δ 8.73 (d, 2H, JH-H ) 8.0 Hz, PyrH(3′, 5′)),
3
3
8.39 (t, 1H, JH-H ) 8.3 Hz, PyrH(4′)), 8.24 (d, 2H, JH-H
)
8.4 Hz, PyrH(6)), 7.54-7.05 (m, 9H, PyrH(3, 4, 5), ArH), 6.92
(t, 10H, 3JH-H ) 7.0 Hz, ArH), 6.57-6.40 (m, 10H, ArH), 4.00
(t, 4H, 3JH-H ) 4.1 Hz, CH2). 13C NMR (75.4 MHz, CD2Cl2): δ
2
182.1 (t, JC-P ) 5.9 Hz, Cipso), 157.9, 155.0, 153.0, 147.4 (t,
2JC-P ) 9.1 Hz), 135.1, 134.1, 132.9 (t, 3JC-P ) 17.0 Hz), 130.5
(t, 3JC-P ) 4.8 Hz), 129.8, 128.8 (t, 3JC-P ) 4.2 Hz), 126.7, 123.8,
3
3
123.5, 122.9, 122.8 (t, JC-P ) 7.9 Hz), 41.98 (t, JC-P ) 17.0
Hz). 31P NMR (81 MHz, CD2Cl2): δ 42.9. Anal. Calcd for C47H38-
ClN3P2Ru: C, 66.94; H, 4.54; N, 4.98. Found: C, 67.12; H, 4.68;
N, 5.11.
Synthesis of [Ru{C6H3(CH2PiPr2)2-2,6}(tpy)](Cl) (12).
The air-stable complex 12 was prepared by applying the
synthetic procedure described for complex 11 employing 95 mg
(0.26 mmol) of 10 in MeOH (15 mL) and 60 mg of tpy (0.26
mmol) in MeOH (5 mL) (155 mg, 84% yield). 1H NMR (200
MHz, CD2Cl2): δ 8.72 (d, 2H, 3JH-H ) 8.0 Hz, PyrH(3′,5′)), 8.63
3
3
(d, 2H, JH-H ) 7.7 Hz, PyrH(6)), 8.26 (d, 2H, JH-H ) 4.75
3
Hz, PyrH(5)), 8.16 (t, 1H, JH-H ) 8.0 Hz, PyrH(4′)), 7.99 (t,
2H, 3JH-H ) 7.8 Hz, PyrH(4)), 7.31 (t, 2H, 3JH-H ) 6.7 Hz, Pyr
3
3
H(3)), 7.23 (d, 2H, JH-H ) 7.0 Hz, ArH), 6.96 (t, 1H, JH-H
)
7.1 Hz, ArH), 3.28 (m, 4H, CH2), 1.48 (m, 4H, CH), 0.59 (dd,
12H, 3JH-H ) 6.23 Hz, 3JH-P ) 20.16 Hz, CH3), 0.11 (dd, 12H,
3JH-H ) 6.60 Hz, 3JH-P ) 20.26 Hz, CH3). 13C NMR (75.4 MHz,
CD2Cl2): δ 182.7 (m, Cipso), 159.51, 154.54, 153.54, 146.65 (t,
3JC-P ) 8.5 Hz), 135.1, 135.55, 132.0, 126.68, 124.01, 122.82,
3
122.31, 122.21, 122.16, 37.68 (t, JC-P ) 14.6 Hz, CH2), 23.48
(t, 3JC-P ) 8.5 Hz, P-CH), 18.40 (d, 3JC-P ) 11.6 Hz, P-CH3).
31P NMR (81 MHz, CD2Cl2): δ 51.63. Anal. Calcd for C35H46-
ClN3P2Ru: C, 59.44; H, 6.56; N, 5.94. Found: C, 59.59; H, 6.51;
N, 6.09.
(17) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The
DIRDIF99 program system, Technical Report of the Crystallography
Laboratory; University of Nijmegen: The Netherlands, 1999.
(18) Sheldrick, G. M. SHELXS-97, Program for crystal structure
solution; University of Go¨ttingen: Germany, 1997.
(19) Sheldrick, G. M. SHELXL-97, Program for crystal structure
refinement; University of Go¨ttingen: Germany 1997.
(20) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
Synthesis of [Ru{C6H3(CH2PPh2)2-2,6}(tpy)](OTf) (14).
Method a. Me3SiOTf (136 mg, 0.6 mmol) was added to a
solution of complex [RuCl{C6H3(CH2PPh2)2-2,6}(PPh3)] (9) (179
mg, 0.2 mmol) in C6H6 (15 mL). The reaction mixture was
stirred at room temperature for 3 h. All the volatiles were

5840 Organometallics, Vol. 23, No. 24, 2004
Gagliardo et al.
evaporated in vacuo, and the obtained green residue washed
with hexane. A solution of tpy (46 mg, 0.2 mmol) in MeOH
(15 mL) was added to the dried green solid residue, and the
obtained mixture was subsequently stirred at room temper-
ature for 3 h. The color of the reaction mixture turned
instantaneously from green to deep red. The solvent was
removed in vacuo and the red solid residue dissolved in 5 mL
of CH2Cl2. The air- and water-stable red powder which
precipitated by addition of a pentane/Et2O (1:5) solution was
collected by filtration, washed with hexane, and dried in vacuo
(163 mg, 90% yield).
Method b. AgOTf (130 mg, 0.4 mmol) was added to a stirred
solution of [RuCl{C6H3(CH2PPh2)2-2,6}(PPh3)] (8) (352 mg, 0.4
mmol) and tpy (105 mg, 0.45 mmol) in MeOH (20 mL). An
instantaneous color change of the reaction mixture from green
to red was observed. After stirring at room temperature for 3
h, the red solution was separated from the AgCl formed by
filtration over Celite. MeOH was removed in vacuo and the
residue dissolved in 5 mL of CH2Cl2. Addition of pentane/Et2O
(1:5) resulted in precipitation of an air-stable red powder (321
mg, 86% yield), which was collected by filtration, washed with
hexane, and dried in vacuo. NMR data of the obtained complex
14 prepared by applying both synthetic procedures were
consistent with values earlier reported.9 Crystals suitable for
X-ray diffraction determination were obtained by slow diffusion
of diethyl ether vapor into a solution of 14 in CH2Cl2. A
selection of bond lengths, angles, and torsion angles is sum-
marized in Table 2.
Acknowledgment. The authors kindly acknowledge
Dr. F. Hartl and Dr. C. A. van Walree for their
assistance during CV measurements. This work was
supported by the Council for Chemical Sciences from
the Dutch Organization for Scientific Research (CW-
NWO).
Supporting Information Available: Cif files of crystal
data collection and refinement parameters, atomic coordinates,
bond lengths and angles, and anisotropic displacement pa-
rameters for complexes 4 and 14. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM049503U