Synthesis, structure, photophysical and electrochemical properties of Ru(TFA)(CO)(PPh3)2(L) (L=2-phenylpyridine, 2-p-tolylpyridine) and Ru(CO)(PPhMe2)2(L)(L′) (L= TFA, H) (L′= bipyridine, L′= 4,4′-dimethylbipyridine) relationships between ancillary ligand structure and luminescent properties

Article abstract of DOI:10.1016/j.jorganchem.2017.03.026

The synthesis, structure and photophysical properties of the complexes [Ru[(CO)(TFA) (PPh₃)₂(L)][(L = ppy = 2-phenylpyridine, (1a); L = 2–(p–tolyl)pyridine] (1b), are reported. The complexes were characterized by UV-VIS, IR and NMR and by single-crystal X-ray diffraction techniques. We also report the synthesis, structure and photophysical properties of [Ru(CO)(L)(PPhMe₂)₂(L′)]⁺[PF₆]^? [L′ = bipyridine, L = TFA, (3a); L = H, (3b) and L = H, L′ = 4,4′-dimethlyl bipyridine (3c)]. These compounds were characterized by UV-VIS, IR and NMR techniques and by a single crystal X-ray diffraction in the case of 3a. The solid state structure of [Ru(Me₂PhP)₂(CO)₂(TFA)₂ (2) which is the starting material for the synthesis 3a-3c is also reported to verify the trans relationship of the less bulky PPhMe₂ and for comparison with the previously reported PPh₃ analogs. The purpose of this study was to determine the impact, if any, of replacing bpy with ppy in the case of 1a and alkylation of the benzene ring in the case of 1b on the photophysical and electrochemical properties compared to related Ru(bpy) complexes. In contrast to the bpy analogs 1a and 1b showed reversible 1e^? oxidations and blue-shifted MLCT absorptions. In the case of 3a-3c we were interested in the effect on the photophysical properties of substituting PPh₃ with the less bulky but more electron donating PPhMe₂. There were only minor changes in the photophysical and electrochemical properties relative to the previously reported PPh₃ analogs.

Full text of DOI:10.1016/j.jorganchem.2017.03.026

Accepted Manuscript
Synthesis, structure, photophysical and electrochemical properties of Ru(TFA)(CO)
(PPh ) (L) (L=2-phenylpyridine, 2-p-tolylpyridine) and Ru(CO)(PPhMe ) (L)(L′) (L=
3 2
2 2
TFA, H) (L’= bipyridine, L’= 4,4’-dimethylbipyridine) relationships between ancillary
ligand structure and luminescent properties
Shyam Pohkrel, Dan Decato, Edward Rosenberg, J.B. Alexander Ross, Michelle
Terwilliger
PII:
S0022-328X(17)30174-2
10.1016/j.jorganchem.2017.03.026
JOM 19860
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 15 November 2016
Revised Date: 9 March 2017
Accepted Date: 11 March 2017
Please cite this article as: S. Pohkrel, D. Decato, E. Rosenberg, J.B.A. Ross, M. Terwilliger, Synthesis,
structure, photophysical and electrochemical properties of Ru(TFA)(CO)(PPh ) (L) (L=2-phenylpyridine,
3 2
2-p-tolylpyridine) and Ru(CO)(PPhMe ) (L)(L′) (L= TFA, H) (L’= bipyridine, L’= 4,4’-dimethylbipyridine)
2 2
relationships between ancillary ligand structure and luminescent properties, Journal of Organometallic
Chemistry (2017), doi: 10.1016/j.jorganchem.2017.03.026.
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ACCEPTED MANUSCRIPT
Table of Contents Graphic
Synthesis,
structure,
photophysical
and
electrochemical
properties
of
Ru(TFA)(CO)(PPh3)2(L)
(L=2-phenylpyridine,
2-p-tolylpyridine)
and
Ru(CO)(PPhMe2)2(L)(L’) (L= TFA, H) (L’= bipyridine, L’= 4,4’-dimethylbipyridine)
relationships between ancillary ligand structure and luminescent properties≠
Shyam Pohkrel, Dan Decato, Edward Rosenberg,* J. B. Alexander Ross and Michelle
Terwilliger
Department of Chemistry and Biochemistry, University of Montana, Missoula, MT
59812, USA

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis, structure, photophysical and electrochemical properties of
Ru(TFA)(CO)(PPh3)2(L) (L=2-phenylpyridine, 2-p-tolylpyridine) and
Ru(CO)(PPhMe2)2(L)(L’) (L= TFA, H) (L’= bipyridine, L’= 4,4’-dimethylbipyridine)
relationships between ancillary ligand structure and chemical properties≠
by
Shyam Pohkrel, Dan Decato, Edward Rosenberg,* J. B. Alexander Ross and Michelle
Terwilliger
Department of Chemistry and Biochemistry, University of Montana, Missoula, MT
59812, USA
Corresponding Author: Edward Rosenberg, email: edward.rosenberg@mso.umt.edu

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Abstract
The synthesis, structure and photophysical properties of the complexes
[Ru[(CO)(TFA)(PPh3)2(L)][(L= ppy=2-phenylpyridine, (1a); L= 2–(p–tolyl)pyridine]
(1b), are reported. The complexes were characterized by UV-VIS, IR and NMR and by
single-crystal X-ray diffraction techniques. We also report the synthesis, structure and
photophysical properties of [Ru(CO)(L)(PPhMe2)2(L’)]+[PF6]− [L’ = bipyridine, L =
TFA, (3a); L = H, (3b) and L= H, L’ = 4,4’-dimethlyl bipyridine (3c)]. These
compounds were characterized by UV-VIS, IR and NMR techniques and by a single
crystal X-ray diffraction in the case of 3a.
The solid state structure of
[Ru(Me2PhP)2(CO)2(TFA)2 (2) which is the starting material for the synthesis 3a-3c is
also reported to verify the trans relationship of the less bulky PPhMe2 and for comparison
with the previously reported PPh3 analogs. The purpose of this study was to determine
the impact, if any, of replacing bpy with ppy in the case of 1a and alkylation of the
benzene ring in the case of 1b on the photophysical and electrochemical properties
compared to related Ru(bpy) complexes. In contrast to the bpy analogs 1a and 1b showed
reversible 1e- oxidations and blue-shifted MLCT absorptions. In the case of 3a-3c we
were interested in the effect on the photophysical properties of substituting PPh3 with the
less bulky but more electron donating PPhMe2. There were only minor changes in the
photophysical and electrochemical properties relative to the previously reported PPh3
analogs.
________________________________________________________________________
Key words: Ru complexes, phosphine ligands, bipyridine, 2-phenyl pyridine,
photophysical properties, electrochemistry
1

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1.0 Introduction
We have been studying the photophysical properties of ruthenium diimine
complexes with a view towards developing probes for biomolecular dynamics with
longer-lived excited states and higher quantum yields relative to the well-known
Ru(tris-diimine)2+ complexes [1,2]. Later, we immobilized the same complexes on
solid surfaces and noted a large change in excited-state lifetime, an effect that could
be useful in photo-promoted electron transfer chemistry [3]. The complexes of
general formula [Ru(CO)(X)(L)(L’)2]PF6 (X =H, TFA)(L = bpy)(L’=PPh3) did exhibit
the sought-after photophysical properties, having excited-state lifetimes in the
neighborhood of 1 μs and quantum yields of 0.25 to 0.5. However, the complexes
were only moderately stable in solution [4]. Measurements of the excitation spectra
and time dependent density functional theory calculations indicates the phosphine
ligand has a significant contribution to the excited state in these complexes [5].
With these observations in mind we decided to synthesize the 2-phenylpyridine
(ppy) analogs of the bpy complexes and replaced the bulky PPh3 with the smaller
and more electron-donating PPhMe2. The ppy complexes of transition metals are
more thermally stable than their bpy analogs due to the presence of one formally
covalent bond and one coordinate covalent bond rather than the two coordinate
covalent bonds formed with bpy [6]. The greater thermal stability of the ppy
complexes has led to their extensive use in dye-sensitized solar cells [6e-6g].
Employing the less bulky PPhMe2 could provide more surface mobility for the
purported probe applications, however, the effect of a more electron-donating
phosphine on the luminescent properties is unknown. We report here the synthesis,
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structure,
photophysical,
and
electrochemical
properties
of
Ru[(TFA)(CO)(PPh3)2(L)] (L=2-phenylpyridine, 1a; 2-p-tolylpyridine, 1b) and
Ru(CO)(PPhMe2)2(L)(L’) (L=TFA, L’=bpy 3a; L=H, L’=bpy 3b; L=H, L’= 4,4’-
dimethylbipyridine, 3c) to understand the relationships between ancillary ligand
structure and luminescent properties.
2.0 Experimental
2.1 Materials
Reactions were carried out using standard Schlenk line techniques under
nitrogen unless otherwise noted. Column chromatography was performed using 60
Å pore size 230–400 mesh silica gel (Sorbent Technologies) and 58 Å pore size
activated neutral alumina (Sigma–Aldrich). All solvents used such as ethylene glycol,
dichloromethane and hexane used were reagent grade. Tetrahydrofuran (THF) was
distilled from sodium benzophenone ketyl. Acetone and ethylene glycol were
purchased from Fischer Scientific and VWR International, respectively. Ruthenium
dodecacarbonyl, triphenylphosphine and dimethylphenylphosphine (Strem
Chemicals) 2,2′–bipyridine, 4,4′–dimethyl–2,2′–bipyridine 2–phenylpyridine, 2–(p–
tolyl)pyridine (Sigma–Aldrich) were used without further purifications. N,N–
Diisopropylethylamine (DIPEA) was purchased from MP Biomedical LLC and
Rhodamine–B needed for measurement of quantum yield was purchased from
Sigma−Aldrich.
The
starting
complexes
K+[Ru(CO)3(TFA)3]−
and
Ru[(CO)2(TFA)2(PPh3)2] were synthesized according to literature procedures [1].
2.2 Methods
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2.2.1 Spectroscopic Measurements
Solution NMR measurements were performed on a Bruker NMR systems
spectrometer at 400 MHz, 376.55 MHz and 162 MHz for proton, fluorine and
phosphorus, respectively and chemical shifts are reported relative to TMS (1H),
CFCl3 (19F) and H3PO4 (31P). IR spectra were recorded on a Nicolet iS7 and Thermo–
Nicolet 633 FT–IR spectrometer as KBr pellets. Steady–state UV–Visible absorption
and emission spectra were collected on Molecular Devices Spectra Max M2.
2.2.2 Excited–State Lifetime Measurements
Time-resolved luminescence decay measurements were performed by time
correlated single-photon counting (TCSPC), using the Quantum Northwest FLASC
1000 sample Chamber (Spokane, WA). Pulsed excitation at 470 nm and a repetition
rate of 50 KHz (external trigger) from a LDH–P–C 470 laser diode (PicoQuant,
Berlin, Germany) were used to excite the complex for time-dependent studies. The
luminescence decays were collected in the FLASC 1000 orthogonal to the excitation
beam path at the magic angle polarization condition [7-8] using a 620/50 nm band
pass filter (Chroma, Rockingham, VT, USA) to isolate the emissions and excitation
scatter. All the measurements were taken at room temperature under normal
atmospheric pressure. The decay curves were collected using the NanoHarp 250 PCI
board (PicoQuant, Berlin) with a timing resolution of 560 ps/channel until 4×104
counts at the peak were reached (see Supplementary Materials and Figure 1s) [9].
2.2.3. Solid State Structure of complexes
X-ray diffraction data for 1a, 1b, 2, and 3a were collected at 100 K on a
Bruker D8 Venture using MoΚα-radiation (λ=0.71073 Å). Data for 1a, 1b and 3a
4

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have been corrected for absorption using SADABS [11] area detector absorption
correction program. Using Olex2 [12], the structures were solved with the
ShelXT[13a] structure solution program using Direct Methods and refined with the
ShelXL [13b] refinement package using least squares minimization. All non-
hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen
atoms in the investigated structures were located from difference Fourier maps but
finally their positions were determined geometrically, and refined with isotropic
thermal parameters. Calculations and refinement of structures were carried out
using APEX2 [14], SHELXTL [13c], and Olex2 software. Structure 2 was found to be a
non-merohedral twin. The twin law found by Cell_Now was -1.001 -0.001 0.000,
0.656 0.532 -0.471, -0.652 -1.524 -0.531 [13d]. Intensity data for 2 were integrated
as two domains using SAINT [14b], and scaled with TWINABS [13e]. Refinement of
HKLF5 data with ShelXL [13b] resulted in a BASF of 0.1129.
2.2.4. Electrochemical measurements
Half-wave potentials were measured on a BAS−100 electrochemical analyzer.
Redox behavior of complexes was studied using a three-electrode standard cell with
a glassy carbon electrode (diameter 0.1 cm sealed in epoxy resin) as the working
electrode, an Ag/AgCl electrode as the reference and a platinum wire as the
−3
auxiliary electrode. Complexes (1×10
M) were dissolved in dichloromethane
+
containing 0.1 M [NBu4 PF6 −] as the supporting electrolyte and the cell was
deoxygenated with argon prior to each scan.
3.0 Synthesis
5

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3.1 Synthesis of Ru[(PPh3)2(CO)(TFA)(ppy-R)(R=H, 1a; R=Me,1b)
Ru[(PPh3)2(CO)2(TFA)2], [1] (100 mg, 0.109 mmol), was treated with 2–
phenylpyridine (18.46 mg, 0.119 mmol) or 2–(p–tolyl)pyridine (20.19 mg, 0.119
mmol) in ethylene glycol (15 mL) and stirred for 72 h at 140 °C under nitrogen
atmosphere. When the color of the reaction mixture turned to greenish–yellow, the
reaction was cooled to room temperature and then filtered and washed three times
with DI water to remove ethylene glycol. The solid was collected by centrifugation at
3000 rpm, washed 2× in DI water, followed by centrifugation, and then washed 1×
with diethyl ether. Following the ether wash and rotary evaporation, the product
was dissolved in a small amount of dichloromethane and then purified by neutral
alumina column in a 1:1 mixture of hexane and dichlormethane as eluent. Two
bands were observed and the slower greenish–yellow band was collected and
solvent was removed by rotary evaporation followed by drying under high vacuum
overnight. Greenish–yellow powders of Ru[(PPh3)2(CO)(TFA)(ppy)] (1a) (30mg,
29.57%) and Ru[(PPh3)2(CO)(TFA)(ppy–Me)] (1b) (35mg, 34 %) respectively were
obtained. Elemental Analysis for 1a calcd: C50H38F3NO3P2Ru: 65.21%, C; 4.16%, H;
1.52%, N; 6.73%, P. Found: 67.38%, C; 4.49%, %H; 1.80%, %N, 7.32% P. IR data for
1a (as KBr pellets): 3047 (w) 1931(vs), 1684 (vs), 1433 (m), 695 (vs), 521 (vs) cm−1.
NMR data for 1a: (in CD2Cl2): 1H, δ 6.73–8.78 (m, 38H); 19F δ −75.39 (s), 31P δ 33.50
(s). IR data for 1b (as KBr pellets): 2900–3100, (w), 1931 (vs), 1685 (vs) 1433 (m),
695 (vs), 521 (vs) cm −1. NMR data for 1b (in CD2Cl2): δ 6.56–8.78 (m, 37H), 1.93 (s,
3H); 19F δ −75.27 (s); 31P δ 34.10 (s).
6

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3.2 Synthesis of Ru[(PPhMe2)2(CO)2(TFA)2] (2)
The ionic complex K+[Ru(CO)3(TFA)3]− (300 mg, 0.54 mmol) was refluxed
with dimethyl phenyl phosphine (150 mg 1.08 mmol) in acetone solution for 24 h
under a nitrogen atmosphere. Progress of the reaction was monitored by thin layer
chromatography (TLC). After reaction the solvent was removed by rotary
evaporation and the residue was dissolved in dichloromethane and
chromatographed on a silica gel column. Elution with dichloromethane/acetone
solution (98:2 v/v) gave two colorless bands. The faster moving band was collected
and the solvent was removed by rotary evaporation and then dried overnight under
high–vacuum. The product, 2, was obtained (80 mg; 27%) as a shiny milky powder
2. IR (as KBr pellets): 2800−2950 (w), 2062 (vs), 2000 (vs), 1685 (vs), 1200 (vs)
cm-1. 1H NMR (in CDCl3): δ 7.47−7.52 (m, 10H), 1.74 (t, 2JP-H=8 Hz, 12H); 19F NMR: δ
−74.16 (s); 31P{1H} NMR: δ 4.8 (s).
3.3 Synthesis of [Ru(PPhMe2)2(CO)(X)(bpy–R)]+[PF6]− (3a, X = TFA, R=H), (3b,
X = H R=H) and (3c, X = H, R=Me)).
Reaction of complex 2 (100 mg, 0.15 mmol) with 2,2′–bipyridyl (25 mg, 0.15
mmol) in ethylene glycol (20 mL) at 140 °C for 72 h produced an orange colored
solution of the cationic complexes of 3a while the same reaction heated under the
same conditions for 84 h with 2,2′–bipyridyl and 4,4′–dimethyl 2,2′–bipyridyl (28
mg, 0.15 mmol) gave a reddish–yellow solution of 3b and 3c respectively. Both
solutions were treated with an aqueous solution of NH4PF6 (concentration 1g/10
mL) dropwise until a precipitate was observed (6.5 mL). The resulting solution was
refrigerated overnight to promote the complete precipitation, filtered and the
7

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residue was washed several times with DI water to remove ethylene glycol, followed
by centrifugation and finally washed with diethyl ether. The resulting product was
dissolved in 5:2:2 hexanes/MeOH/CH2Cl2 and then chromatographed using neutral
alumina using the same solvent mixture as eluent which gave a single product band.
Complete removal of solvent followed by drying under high vacuum overnight gave
Ru[(PPhMe2)2(CO)(TFA)(2,2′–bpy)]+[PF6]−
[Ru(PPhMe2)2(CO)(2,2′–bpy)(H)]+[PF6]−
(40
mg,
34
28
%),
(3a),
(42mg,
%),
(3b)
and
[Ru(PPhMe2)2(CO)(4,4–dimethyl–2,2′–bipyridyl)(H)]+[PF6]− (38 mg, 29 %), 3c. IR
data for 3a: (as KBr pellets): 3055–2850 (w), 1970 (vs), 1680 (s) 840 cm-1 (vs) cm-1.
NMR data for 3a (CDCl3): 1H δ 6.66–8.51 (m, 18H), 1.56 (t, 2JP-H=8.0 Hz, 6H), 1.52(t,
2JP-H=8.0 Hz, 6H); 19F NMR δ −71.78(d), −73.80(s); 31P{1H} δ 3.37(s), −155 (sep). IR
Data for 3b: (as KBr pellets) 2850–2964 (w) 2028 (w), 1961 (vs), 838 (vs) cm −1.
NMR data for 3b (CDCl3): 1H δ 6.66–8.23 (m, 18H), 1.50 (t, 6H, 2J=8.0 Hz), 1.48(t, 2JP-
2
H=8.0 Hz, 6H), −12.36 (t, 1H, JP-H=20); 19F NMR ( −72.09, −73.98), 31P{1H} δ 7.72
(s), −155(sep). IR Data for 3c: (as KBr pellets): 2875 (w), 2077 (w), 1933 (vs), 908
(vs), 841 (vs), cm −1, NMR data for 3c (CDCl3): δ 6.72–8.75 (m, 16H), 2.44 (s, 3H),–
2.39 (s, 3H), 1.46 (t, 2JP-H=8.0 Hz, 6H), 1.43 (t, 2JP-H=8.0 Hz, 6H), −12.5 (t, 1H, 2JP-H
=20); 19F NMR δ −73.95 (s), −71.98(d); 31P{1H} NMR δ 8.23 (s), −155 (sep.).
Elemental Analysis for 3c: calcd. for C29H34N2F6OP3Ru: C, 47.35%; H, 4.80%; N,
3.81%; P, 12.63%; found: C, 46.58%; H, 4.82%; N, 3.65%; P, 13.5%.
4.0 Results and Discussion
4.1 Synthesis and characterization of the 2-ppy complexes 1a and 1b
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In our prior work on the synthesis of phosphine substituted diimine
complexes of ruthenium we found that the anionic complex K+[Ru(TFA)3(CO)3]- is
convenient starting material [1]. It is synthesized in high yield by refluxing
Ru3(CO)12 in trifluoroacetic acid followed by the addition of K2CO3. Although the
starting material is much more expensive the resulting complex (intermediate A,
Scheme 1) undergoes selective substitution with phosphines to give a trans-
diphosphine as the only product under mild conditions (intermediate B scheme 1).
Subsequent reaction with 2-ppy or 2-(p-tolylphenyl pyridine to give
[Ru(CO)(TFA)(PPh3)2(ppy-R)] (ppy=2-phenylpyridine (1a) and 2–(p–tolyl)pyridine (1b)
respectively, by refluxing in ethylene glycol:
-
CO
TFA
K+
CO
CO
Reflux
Ru
Ru3(CO)12
+ CF3COOH
+ K2CO3
TFA
TFA
(A)
Acetone
reflux
+2PPh3
R
PPh3
Ru
PPh3
OC
CO
TFA
CO
ppy-R, 140°C
Ru
Ethylene glycol, 72hr
TFA
TFA
N
PPh3
PPh3
(B)
R = H (1a), Me (1b)
Scheme 1. Synthesis of 1a and 1b
Although there are numerous examples of ppy complexes in the literature [6] 1a and 1b
are novel for Ru in containing two phosphines and a trifluoroacetate (TFA) ligand. They
represent more thermally stable analogs of the recently reported bis-phoshine-bpy
9

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analogs [6]. Thermal stability could be an important factor in the applications of these
complexes for photo-promoted electron transfer.
The spectroscopic data for 1a and 1b are consistent with the structure proposed in
Scheme 1. Both show a single νCO at 1931 cm-1 and carbonyl stretch at 1685 cm-1
assigned to the TFA ligand, in addition to the expected bands in hydrocarbon and
fingerprint region. The proton NMR of 1a shows the expected aromatic resonances as
does 1b which also shows the tolyl methyl group at δ 1.93. Both compounds show nearly
identical singlet resonances in the19F (δ -75.39 and -75.27 respectively) and 31P NMR
(δ 33.50 and 34.10 respectively). Curiously, the elemental analysis for 1a is in good
agreement with the calculated % for H, N and P but gives a %C that is 2% higher
than the calculated value. We attribute this to adsorbed solvent.
Single-crystal X-ray diffraction studies confirmed the structures of both 1a
and 1b. Figures 1 and 2 show their solid-state structures. Relevant bond lengths
and bond angles are given in the figure captions and crystal data is given in Table 1.
10

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Figure 1. Solid-state structure of 1a showing the 50% probability ellipsoids. All
hydrogen atoms have been omitted for clarity. Ru(1)-P(1)=2.3758(3), Ru(1)-
P(2)=2.4108(3), Ru(1)-O(2)=2.1957(9), Ru(1)-N(1)=2.1528(11), Ru(1)-C(1)=
2.0432(13), Ru(1)-C(14)=1.8457(13) Å; P(1)-Ru(1)-P(2)=178.807(12), O(2)-Ru(1)-
P(1)=87.24(3), O(2)-Ru(1)-P(2)=93.95(3), N(1)-Ru-P(1)=92.35(3), C(14)-Ru(1)-
C(1)=90.90(6), C(6)-C(1)-Ru(1)=114.93(9)0.
11

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Figure 2. Solid-state structure of 1b showing the 50% probability ellipsoids. All
hydrogen atoms have been omitted for clarity. Ru(1)-P(1)=2.375(6), Ru(1)-
P(2)=2.4200(6), Ru(1)-O(2)=2.2026(16), Ru(1)-N(1)=2.1541(18), Ru(1)-C(2)=
2.036(2), Ru(1)-C(1)=1.848(2) Å; P(1)-Ru(1)-P(2)=177.37(2), O(2)-Ru(1)-
P(1)=88.14(4), O(2)-Ru(1)-P(2)=94.50(4), N(1)-Ru-P(1)=93.04(5), C(1)-Ru(1)-
C(2)=90.67(9), C(7)-C(2)-Ru(1)=115.09(16)0.
12

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Table 1. Summary of crystal data and structure refinement for compound 1a, 1b, 2 and 3a
Identification code
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
1a
C50H38F3NO3P2Ru
920.82
1b
C51H40F3NO3P2Ru
934.85
2
C22H22F6O6P2Ru
659.40
3a
C29H30F9N2O3P3Ru
819.53
100
monoclinic
P21/c
11.5337(7)
17.7170(10)
20.5182(12)
90
97.265(2)
90
100
monoclinic
P21/c
11.6934(12)
17.5395(18)
20.976(2)
90
94.796(3)
90
100
triclinic
P-1
100
monoclinic
Pn
9.3528(6)
14.9723(10)
12.2752(8)
90
111.739(2)
90
9.3336(9)
10.5722(10)
15.2426(14)
97.768(4)
96.740(3)
115.384(3)
1320.3(2)
2
b/Å
c/Å
α/°
β/°
γ/°
Volume/Å3
Z
4159.1(4)
4
1.471
4287.1(8)
4
1.448
1596.68(18)
2
ρcalc g/cm3
1.659
0.792
1.705
0.729
μ/mm-1
0.513
0.499
F(000)
1880.0
1912.0
660.0
824.0
Crystal size/mm3
Radiation
2Θ range for data
collection/°
0.25 × 0.25 × 0.15
MoKα (λ = 0.71073)
0.2 × 0.15 × 0.1
MoKα (λ = 0.71073)
0.4 × 0.4 × 0.3
MoKα (λ = 0.71073)
0.2 × 0.15 × 0.15
MoKα (λ = 0.71073)
5.684 to 61.208
5.814 to 54.968
5.576 to 55.19
6.51 to 61.146
-16 ≤ h ≤ 16, -25 ≤ k
≤ 25, -29 ≤ l ≤ 29
243760
-15 ≤ h ≤ 15, -22 ≤ k
≤ 22, -27 ≤ l ≤ 27
119854
-12 ≤ h ≤ 11, -13 ≤ k
≤ 13, 0 ≤ l ≤ 19
6088
6088 [Rint =0.0557,
Rsigma = 0.0391]
-13 ≤ h ≤ 13, -21 ≤ k
≤ 21, -17 ≤ l ≤ 17
24363
9732 [Rint = 0.0345,
Rsigma = 0.0501]
Index ranges
Reflections collected
Independent
12796 [Rint = 0.0481, 9824 [Rint = 0.1071,
reflections
Rsigma = 0.0186]
Rsigma = 0.0395]
Data/restraints/par
ameters
12796/0/541
9824/0/551
6088/0/339
9732/2/428
Goodness-of-fit on F2
Final R indexes
[I>=2σ (I)]
1.056
R1 = 0.0270, wR2 =
0.0621
1.039
R1 = 0.0392, wR2 =
0.0954
1.060
R1 = 0.0359, wR2 =
0.0779
1.089
R1 = 0.0388, wR2 =
0.0775
Final R indexes [all
data]
R1 = 0.0354, wR2 =
0.0661
R1 = 0.0527, wR2 =
0.1043
R1 = 0.0479, wR2 =
0.0832
R1 = 0.0521, wR2 =
0.0831
Largest diff.
0.78/-0.50
2.01/-1.18
1.06/-0.56
1.18/-0.85
peak/hole / e Å-3
Crystals of 1a and 1b were grown by slow evaporation of a concentrated chloroform
solution under a layer of pentane at room temperature. Both complexes crystallize
in the monoclinic space group, P21/c with four molecules in the unit cell.
The complexes 1a and 1b display distorted octahedral geometry where ppy-H or
ppy-Me along with the carbonyl and TFA groups occupy a plane approximately
perpendicular to the two trans-triphenylphosphine ligands. The P(1)–Ru–P(2) bond
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angles for 1a and 1b are 178.8°(12) and 177.37°(2) (close to 180°) respectively. These
angles are very similar to those in the osmium analog of 1a, which exhibits a P–Ru–P
angle of 176.78(6)° [15]. The average Ru-P distances are 2.392 Å for 1a and 2.397 Å for
1b. These values are similar to those found in related octahedral iridium complexes
where the average bond distance between central metal and phosphorous atom is 2.390Å
[16]. As expected the Ru(1)–C(1) bond length in complex 1a and the Ru(1)–C(2) in 1b,
are relatively shorter than the corresponding Ru−N bond distances in these complexes as
well as in the related bpy complexes [1,17]. The formally anionic C(1) and C(2) are
expected to be stronger σ donors than the nitrogen atoms in the ppy or bpy complexes.
This results in an elongation of the Ru(1)–O(2) in 1a (2.195Å) and the Ru(1)–O(2) in 1b
(2.201Å) being significantly longer than the Ru-O bonds in closely related Ru-TFA
complexes (2.086 to 2.148 Å) [where the Ru-O bond is trans to N and P respectively
{1,17]. A shorter Ru-O bond is also seen in 3a relative to the same bonds in 1a and 1b
(vide infra). This differential bond distance can be explained in terms of trans–effect of
the coordinating groups. In both complexes the TFA and CO groups are cis- to each other
with C(14)–Ru(1)–O(2) and C(1)–Ru(1)–O(2) 102 (5)° and 112.12(8)° respectively. The
presence of methyl group in 1b increases the electron donating ability of the phenyl
carbon to the metal center that causes a shortening of Ru(1)–C(11) (2.036(2) Å) bond in
1b relative to Ru(1)–C(1) (2.043(12) Å) bond in 1a.
4.2 Synthesis and characterization of [Ru(PPhMe2)2(CO)2(TFA)2] (2) and
[Ru(PPhMe2)2(CO)X(bpy-R) (L’)]+[PF6]− (3a-3c)
In our prior work with the series of bis-phosphine ruthenium diimine complexes
we focused on the PPh3 and the 1,2-diphenylphosphinoehtene (dppene) ligands [1]. To
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understand the relationship between phosphine bulkiness, electron donor ability and
emission frequency we decided to synthesize PPhMe2 analogs of the previously reported
complexes. The first step involved the synthesis of the previously unknown precursor
Ru(PPhMe2)2(CO)2(TFA)2 (2). Refluxing the ionic complex K+[Ru(CO)3(TFA)3]− with
PPhMe2 in acetone solution for 24 h under a nitrogen atmosphere gave 2 in 27%
yield. The IR showed the expected two νCO at 2062 and 2000 cm-1 and a carbonyl
stretch for the TFA ligand at 1685 cm-1. The 19F NMR showed a singlet δ −74.16 and
the 31P{1H} NMR showed a singlet at δ 4.8. Interestingly, in addition to the expected
phenyl resonances at δ 7.5 the methyl protons appeared as a 1:2:1 triplet instead of
the expected doublet (Figure 3). We attribute this to the presence of a large 31P-31P
coupling that results in a virtual coupling as if the methyl groups were coupled to
two equivalent phosphine ligands. This phenomenon is well documented in the
literature and is common in complexes containing two trans-phosphine ligands [18]
and in some cases with cis-phosphine ligands as well [19]. The outer wings of the
triplet are taken as the value of the 2JP-H for the doublet expected in the absence of
virtual coupling, 8 Hz in the case of 2.
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ppm
1.59
1.54
Figure 3. Methyl region of complex 2 (left); methyl region of complex 3a (right)
To verify the proposed structure and the purported virtual coupling we
undertook a single-crystal X ray-diffraction study of 2. The solid-state structure of 2
is shown in Figure 4, with relevant bond length and angles are given in the figure
caption and crystal data is given in Table 1. Complex 2 exists as an octahedral
molecule with the two phosphine ligands in an almost perfect trans-position (P(1)-
Ru-P(2)=176.30(3)0). The almost linear relationship between the two phosphorous
atoms is consistent with strong 31P-31P coupling that gives rise to the observed
virtual coupling. The two carbonyl groups and the two TFA groups are cis- to each
other as one would expect based on the strong π-acceptor properties of CO. All of
the bond angles between the neighboring ligands are close to 900 except the O(3)-
Ru(1)-O(5) angle which is 79.64(8)0. The two carbonyl oxygen atoms of the TFA
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groups point away from each other and the contraction in the bond angle could be
the result of steric effect with the neighboring CO ligands. The Ru-P bonds are only
slightly different than the same bonds in complexes 1a and1b.
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Figure 4. Solid-state structure of 2 showing the 50% probability ellipsoids. All
hydrogen atoms have been omitted for clarity. Ru(1)-P(1)=2.3810(8), Ru(1)-
P(2)=2.3790(8), Ru(1)-O(3)=2.103(2), Ru(1)-O(5)=2.0968(19), Ru(1)-
C(1)=1.862(3), Ru(1)-C(2)=1.875(3) Å, P(1)-Ru(1)-P(2)=176.30(3), O(3)-Ru(1)-
P(1)=87.60(6), O(3)-Ru(1)-P(2)=92.17(6), O(3)-Ru(1)-O(5)=79.64(8)0.
Refluxing 2 and bpy in ethylene glycol followed by addition of NH4PF6 gave
[Ru(CO)(bpy)(PPhMe2)2(TFA)]+[PF6]− (3a) (Scheme 2) in 28.2% yield. The IR
spectroscopic data of 3a shows the expected νCO at 1970 cm-1 and a carbonyl stretch
from the TFA ligand at 1680 cm-1. The proton NMR shows the expected aromatic
resonances at δ 6.66 – 8.51. As for 2, virtual coupling is observed for the methyl
resonances of the PPhMe2 ligands where two triplets are observed at δ1.52 and 1.56 (2JP-
H =8Hz for both). The two triplets arise from the fact that in 3a the methyl groups are
diastereotopic due to the lack of symmetry in the plane perpendicular to the purported
two mutually trans-phosphine ligands. Although the spectroscopic data is consistent with
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the proposed structure a solid-state structural investigation was undertaken to verify our
interpretation of the NMR data.
R
R
PPhMe2
PPhMe2
TFA
Ru
TFA
PPhMe2
1. ethylene glycol
N
N
N
N
140°C
L
+
OC
OC
-
PF6
Ru
CO
PPhMe2
+
2. Aq. NH4PF6
R
R
3a. R = H, L = TFA
3b. R=H, L = H
3c. R =Me, L = H
Scheme 2. Synthesis of 3a-3c starting with 2.
The solid-state structure of 3a is shown in Figure 5, relevant bond distances and
angels are given the figure caption and crystal data is given in Table 1.
Figure 5. Solid-state structure of (3a) showing the 50% probability ellipsoids. All
hydrogen atoms and the PF6 anion have been omitted for clarity. Ru(1)-
P(1)=2.3755(12), Ru(1)-P(2)=2.3785(12), Ru(1)-O(2)=2.089(3), Ru(1)-N(1)=2.053(4),
Ru(2)-N(2)=2.102(4), Ru(1)-C(1)=1.868(5) Å. P(1)-Ru(1)-P(2)=175.49(6), O(2)-Ru(1)-
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N(2)=89.71(14), C(1)-Ru(1)-N(1)=95.22(18), N(1)-Ru(1)-N(2)=78.61(15), C(1)-Ru(1)-
O(2)=96.46(18)0.
The solid-state structure of 3a is that predicted from the NMR data. The two trans-
phosphine ligands are perpendicular to the plane of the bpy, CO and TFA ligands and the
bond lengths are similar to complexes 1a, 1b, 2 and related PPh3 complexess [1]. The
bond angles are close to the expected 900 with the exception of the N(1)-Ru(1)-N(2)
(78.61(15)0) where the constraints of the bpy ligand geometry result in this smaller angle.
Interestingly, the solid state structure of 3a shows the phenyl groups of the PPhMe2 lying
directly over the bpy ring with the two phosphine ligands are in an eclipsed conformation
with respect to each other. The distances between the centroids of the phenyl groups of
the PPhMe2 ligands and one of the aromatic rings of the bpy are 3.603(3) and 3.758(2) Å
suggesting π-stacking interactions (Figure 6). However, the distances to the other bpy
ring are significantly longer, being 4.471(3) and 4.284(3) Å. Although we cannot exclude
the possibility that the observed ligand conformations are the result of crystal packing
considerations the fact that the distances are shorter to one bpy ring supports the π-
stacking argument. [20] (Figure 6). In crystal structures π-stacking interactions between
aromatic or heteroaromatic rings range from 3.30 to 4.00 Å placing the observed values
in the middle of this range for one of the two bpy rings and the phosphine phenyl ring in
3a [20].
Heating complex 3a in ethylene glycol leads to its conversion to the
corresponding hydride, 3b, a phenomenon that we previously observed in related
Ru(bpy)(phosphine complexes) [1]. This is evident from the appearance of a triplet
2
resonance at δ −12.36 (t, 1H, JP-H=20) and a weak band in the IR spectrum at 2028
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cm-1. As for 3a the phosphine methyl groups in 3b appear as two triplets due to
strong virtual 31P-31P coupling and the diastereomeric environment of the trans-
phosphine ligands δ 1.50 (t, 6H, 2J=8.0 Hz), 1.48(t, 2JP-H=8.0 Hz, 6H).
Figure 6. Complex 3a showing the possible π-π stacking of the phosphine phenyl
and the bpy aromatic rings
A proposed target for the use of the Ru(bpy)(phosphine complexes is to
immobilize the complex on a surface to probe surface structure and its influence on
photophysical properties [3]. In our previous studies we used peptide-coupling chemistry
to bind the Ru complexes to the surface and poor loading was observed [2,3].
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Functionalizing the bpy ring with a benzylic halide seemed like a promising alternative to
a carboxylic acid and so we undertook the synthesis of a 4,4’dimethyl-bpy derivative and
thought it would be interesting to compare its photophysical and electrochemical
properties with the unsubstituted bpy analogs, 3a and 3b.
Prolonged heating of complex 2 in the presence of 4,4’-bipyridine in ethylene
glycol gave [Ru(PPhMe2)2(CO)(bpy-Me)(H)]+[PF6]− 3c in 29.47% yield. Elemental
analysis was in reasonable agreement with the formulation and the IR spectrum
showed the expected frequencies for the hydride and the CO at 2077(w) and
1933(vs) cm-1 respectively. The proton NMR of 3c shows two triplets at δ 1.46 (t,
2
2JP-H=8.0 Hz, 6H), 1.43 (t, JP-H=8.0 Hz, 6H), evidence for strong virtual 31P-31P
coupling as observed for 2, 3a and 3b. Two singlet resonances of each of relative
intensity three are observed at δ 2.44 and 2.39 and are assigned to the methyl
groups on the bpy ring which are magnetically nonequivalent by being trans- to
either the hydride or the carbonyl groups. The hydride appears as a triplet at δ
2
−12.5 (1H, JP-H =20). The aromatic region at δ 6.72–8.75 integrates for 16 protons
and resonances similar to 3a and 3b are observed in the 31P and 19F NMR. Based on
these data 3c is a direct structural analog of 3a and 3b.
4.3 Electrochemical behavior of 1a, 1b, 3b and 3c
The redox properties of 1a, 1b, 3b and 3c were evaluated by cyclic voltammetry
+
−
with Ag/AgCl as the reference electrode and 0.1M [NBu4 PF6 ] CH2Cl2 solution as the
electrolyte at a scan rate 50-100 mV/sec using a glassy carbon-working electrode. The
complexes 1a and 1b exhibited quasi-reversible and reversible 1e-, metal-centered
oxidation at +0.95 and +1.0 V respectively (Figure 7). The small shift to more positive
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oxidation potential for 1b cannot be attributed to the electron donating influence of
the methyl group in the trans-position of the phenyl ring of the 2-ppy ligand as
making the metal more electron rich would be expected to make the metal center
more electron rich and easier to oxidize. This small difference could arise from
changes in orbital energies at the metal center. The cathodic regions of 1a and 1b did
not show any well-defined reductive waves and so are not included here
4
2
0
-2
1b
1a
-4
-6
-8
0.7
0.9
1.1
1.3
1.5
E(V) vs. Ag/AgCl
Figure 7. CV of a 1.0 mM solution of 1a and 1b in CH2Cl2 containing 0.10
M[NBu4][PF6], at a glassy carbon working electrode
In the bipyridyl–based complexes, (3b and 3c), the cyclic voltammetry responses
are not well resolved and show a number of ill–defined peaks. Stabilization of a
particular oxidation state is determined by the σ–donor and π–acceptor tendencies of
surrounding ligands (Figure 8). The σ donor properties of ligands tend to stabilize Ru
(III) over Ru (II) while the π–acceptor ligands lead to the stabilization of Ru (II) state.
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For complex, 3b two irreversible potential are observed at E° = −1.3 and E° = −1.5 V
respectively versus Ag/AgCl. As expected the presence of the methyl groups trans- to the
nitrogen atoms of the bpy ring in 3c shifted the reduction potential to less negative values
due to increased electron density at the metal and showed only one irreversible wave at -
1.6V. No well-defined anodic waves were observed as for the previously reported bpy
complexes [1]
100
90
80
70
60
50
40
30
20
10
0
I(μA)
3c
3b
-2.3
-1.8
-1.3
-0.8
E(V) vs.Ag/AgCl
Figure 8. CV of a 1.0 mM solution of 3b and 3c in CH2Cl2 containing 0.10
M[NBu4][PF6], at a glassy carbon working electrode
This general trend of irreversible multiple reduction potentials was observed in
the previously reported hydrido-PPh3 analogs of 3b and 3c and the potentials observed
were similar to that reported here suggesting that increasing the electron-donating
24

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properties of the phosphine has only a minimal effect on reduction potentials at the metal
and the bpy ligand [1].
4.4. Photophysical properties of complexes
The photophysical properties of the complexes of 1a, 1b, 3b and 3c are
summarized in Table 2. All the complexes show the expected MLCT transitions with
the most significant difference being that between 1a and 1b compared with 3b and
3c. The MLCT is significantly blue-shifted 80-90 nm in 1a and 1b with respect to 3b
and 3c.
Table 2. UV–Vis absorption and emission data in CH2Cl2
Compound
λabs MLCT
λexc(nm)
λε(nm)
τ (ns)
(nm)
390
400
480
480
390
400
470
470
_
_
1a
1b
3b
3c
_
–
600
610
330
270
There is a small but significant red shift in the MLCT 1b and 3c relative to 1a
and 3b as a result of methyl substitution, again due to the better electron donation
that increases the HOMO-LUMO gap. All the complexes show intense absorptions in
the range of 300-350 nm due to the intraligand absorptions of the ppy and bpy
ligands. In the case of 3c tails of these absorptions obscured the MLCT band but
irradiation at 470 nm did give an emission at 610nm. Measurement of the excitation
spectrum, monitoring at 610 nm, clearly showed that the emission at 610 nm came
25

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from a hidden MLCT band at 470 nm that is obscured by the tail of the shorter
wavelength absorptions (Figure 9).
Compounds 1a and 1b showed no significant emissions when irradiated at
the MLCT. This is likely due to the increase in the HOMO-LUMO gap resulting from
the strong σ-donor properties of the carbon atom bound to Ru. This results in a blue
shifted MLCT band that brings this transition into close proximity with intraligand
transitions leading to high internal conversion and radiationless decay. We have
seen this phenomenon in related bpy complexes that exhibit blue-shifted MLCT
[2,17].
Complexes 3b and 3c on the other hand showed red shifted emissions of
sufficient intensity to allow measurement of their excited-state lifetimes. Here,
unlike the case of the absorption and emission spectra of the PPh3 analogs, 3a and
3b show a significant difference in lifetime. Complexes 3b and 3c showed much
shorter lifetimes being 330 and 270 ns respectively whereas the related hydrido-
triphenyl phosphine complexes showed lifetimes in the 500-700 ns range [1-3]. The
lifetime of the triplet state will depend upon spin-orbit coupling and environmental
factors that contribute to non-radiative decay [7], but we can tentatively point out
that the PPhMe2 ligand would be expected to have a lesser ability to delocalize
electron density in the excited-state relative to the PPh3 analogs.
26