Comparison of inverse and regular 2-Pyridyl-1,2,3-triazole "click" Complexes: Structures, Stability, Electrochemical, and Photophysical Properties

Article abstract of DOI:10.1021/ic502557w

Two inverse 2-pyridyl-1,2,3-triazole "click" ligands, 2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyridine and 2-(4-benzyl-1H-1,2,3-triazol-1-yl)pyridine, and their palladium(II), platinum(II), rhenium(I), and ruthenium(II) complexes have been synthesized in good t

Full text of DOI:10.1021/ic502557w

Article
pubs.acs.org/IC
Comparison of Inverse and Regular 2‑Pyridyl-1,2,3-triazole “Click”
Complexes: Structures, Stability, Electrochemical, and Photophysical
Properties
Warrick K. C. Lo,† Gregory S. Huff,†,§ John R. Cubanski,† Aaron D. W. Kennedy,† C. John McAdam,†
David A. McMorran,† Keith C. Gordon,†,§ and James D. Crowley*,†
†Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
§MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand
S
* Supporting Information
ABSTRACT: Two inverse 2-pyridyl-1,2,3-triazole “click” ligands, 2-(4-phenyl-1H-
1,2,3-triazol-1-yl)pyridine and 2-(4-benzyl-1H-1,2,3-triazol-1-yl)pyridine, and their
palladium(II), platinum(II), rhenium(I), and ruthenium(II) complexes have been
synthesized in good to excellent yields. The properties of these inverse “click”
complexes have been compared to the isomeric regular compounds using a variety of
techniques. X-ray crystallographic analysis shows that the regular and inverse complexes
are structurally very similar. However, the chemical and physical properties of the isomers are quite different. Ligand exchange
studies and density functional theory (DFT) calculations indicate that metal complexes of the regular 2-(1-R-1H-1,2,3-triazol-4-
yl)pyridine (R = phenyl, benzyl) ligands are more stable than those formed with the inverse 2-(4-R-1H-1,2,3-triazol-1-yl)pyridine
(R = phenyl, benzyl) “click” chelators. Additionally, the bis-2,2′-bipyridine (bpy) ruthenium(II) complexes of the “click”
chelators have been shown to have short excited state lifetimes, which in the inverse triazole case, resulted in ejection of the 2-
pyridyl-1,2,3-triazole ligand from the complex. Under identical conditions, the isomeric regular 2-pyridyl-1,2,3-triazole
ruthenium(II) bpy complexes are photochemically inert. The absorption spectra of the inverse rhenium(I) and platinum(II)
complexes are red-shifted compared to the regular compounds. It is shown that conjugation between the substituent group R and
triazolyl unit has a negligible effect on the photophysical properties of the complexes. The inverse rhenium(I) complexes have
large Stokes shifts, long metal-to-ligand charge transfer (MLCT) excited state lifetimes, and respectable quantum yields which are
relatively solvent insensitive.
As they are viewed as readily functionalized analogs of the
ubiquitous 2,2′-bipyridine (bpy) moiety (1, Figure 2), the 2-(1-
R-1H-1,2,3-triazol-4-yl)pyridine family of ligands (2, Figure 2)
have become an important class of click chelator. These 2-
pyridyl-1,2,3-triazole containing ligands have been widely used
for the development of coordination complexes2b−d and
metallosupramolecular systems3 with interesting catalytic,4
INTRODUCTION
■
The copper catalyzed condensation of a substituted azide and a
terminal alkyne to form a 1,4-disubstituted 1,2,3-triazole,
known as the copper-catalyzed azide−alkyne cycloaddition
(CuAAC, Figure 1),1 has become a widely used tool for
creating functionalized ligands for coordination complexes.2
While some of these ligands include the 1,2,3-triazole moiety
solely as a linking unit, the heterocycle is capable of
coordinating to metal centers in a variety of modes (Figure 1).
Figure 2. N−N bidentate chelators, 2,2′-bipyridine (1), 2-(1-R-1H-
1,2,3-triazol-4-yl)pyridine (2, reg-pytri), [2-(4-R-1H-1,2,3-triazol-1-
yl)methyl]pyridine (3), and 2-(4-R-1H-1,2,3-triazol-1-yl)pyridine (4,
inv-pytri).
Figure 1. Copper-catalyzed azide−alkyne cycloaddition (CuAAC)
reaction (top) and the coordination modes displayed by 1,4-
disubstituted 1,2,3-triazole ligands (bottom).
Received: October 24, 2014
© XXXX American Chemical Society
A
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electrochemical,5 magnetic,6 biological,7 and photophysica-
l5a,7a,b,8 properties. The 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine
(reg-pytri, 2) ligands have been termed regular (reg) click
chelators as they coordinate through the more electron rich N3
nitrogen atom of the 1,2,3-triazole unit. Inverse (inv) 2-pyridyl-
1,2,3-triazole click chelators such as 3, which coordinate
through the N2 nitrogen atom, have also been studied.6b,9
However, inverse isomers of 2, the 2-(4-R-1H-1,2,3-triazol-1-
yl)pyridine (inv-pytri, 4) family of chelators, are much less
common.10 This is presumably due to the complications of
synthesizing such ligands arising from the ring−chain
tautomerism between 2-azidopyridine and pyridotetrazole in
solution.10b,11 The open chain form is necessary for the CuAAC
to proceed, and the conditions required to generate this species
from all but the most electron-poor pyridotetrazole units are
generally harsh. However, two recent reports have shown that
this transformation can now be reliably accomplished under
relatively mild conditions.11b,12
a
Scheme 1. Synthesis of Inverse Metal Complexes 5−8
Due to our interest in the development of click ligands and
complexes we set out to examine the coordination chemistry of
the inv-pytri family click chelators (4). We and others have
previously studied the chemistry of reg-pytri ligands (2) with a
range of metal ions, including palladium(II),9i platinum(II),9j,13
ruthenium(II),5a,8f,g,i,m,n,p,14 and rhenium(I).7b,g−j,8c,d,10a,15 In
this report we detail the synthesis and properties of the
isomeric palladium(II), platinum(II), rhenium(I), and
ruthenium(II) inv-pytri complexes. The structural, electro-
chemical, and photophysical properties of these complexes are
compared with the known reg-pytri analogues. Furthermore, it
is shown using competition experiments with the complexes
that the reg-pytri ligands form more stable complexes than the
inv-pytri family click chelators. Additionally, it is demonstrated
that ruthenium(II) bpy complexes of the inverse click chelators
are photochemically active. Irradiation of these complexes with
UV light leads to the ejection of the inv-pytri ligand from the
complex. The isomeric regular reg-pytri ruthenium(II) bpy
complexes are photochemically inert.
a
Conditions: (i) [Pd(CH3CN)4](BF4)2, CH3CN, (ii) cis-[Pt-
(DMSO)2Cl2], methanol, reflux, (iii) [Re(CO)5Cl], methanol, reflux,
(iv) (a) cis-[Ru(bpy)2Cl2], ethanol, microwave (125 °C, 200 W, 1 h),
and (iv) (b) NH4PF6(aq).
divalent charge of the palladium ions is balanced by two
noncoordinating BF4 anions. The ligands adopted a head-to-
−
tail arrangement around the Pd(II) ions, placing the peripheral
substituents as far apart as possible thereby avoiding any
unfavorable steric interactions. Additionally, this orientation of
the ligands appears to be further stabilized by a hydrogen
bonding interaction between the acidic C−H in the 6-position
of the pyridyl ring and the N3 nitrogen atom of the 1,2,3-
triazole unit on the adjacent ligand, a motif which was also
observed for the related regular complexes.9i The molecular
structures of platinum(II) complexes (6a−b) showed a Pt(II)
ion coordinated to an inv-pytri ligand and two chloride anions
(Figure 3b and Supporting Information Figure S46b).
RESULTS AND DISCUSSION
■
Synthesis and Structures. The inv-pytri ligands, 2-(4-
phenyl-1H-1,2,3-triazol-1-yl)pyridine (4a) and 2-(4-benzyl-1H-
1,2,3-triazol-1-yl)pyridine (4b), were synthesized in good yields
(63−72%) using modified literature procedures (Supporting
Information Scheme S1 and Figures S1−S8).11b,12 The
palladium(II),9i platinum(II),9j,13 ruthenium(II),5a,8f,i,m,n,p,14
and rhenium(I)7b,g−j,8c,d,10a,15 complexes of the inv-pytri ligands
(4a−b) were synthesized using the methods previously
exploited to generate the isomeric reg-pytri complexes (Scheme
1). Complexes 5−8 were characterized using elemental analysis,
high resolution electrospray ionization mass spectrometry
The molecular structures of the d6 rhenium(I) (7a−b) and
ruthenium(II) (8a−b) complexes displayed the expected
distorted octahedral coordination environment about the
metal ions. The rhenium(I) ions of 7a−b (Figure 3c and
Supporting Information Figure S46c) are coordinated to the
bidentate inv-pytri ligand, three carbonyl ligands, and a
chloride. The carbonyl ligands adopted the expected facial
arrangement about the Re(I) cation with a coordinated chloride
occupying the other apical position. The ruthenium(II) ions of
the inverse 8a−b complexes are coordinated to two bidentate
bpy ligands and one bidentate 2-pyridyl-1,2,3-triazole ligand
with divalent charge of the metal ion balanced by two
1
(HRESI-MS), IR, H and 13C NMR spectroscopies, and X-
ray crystallography (Supporting Information, Figures S9−S47).
The molecular structures of the palladium(II), platinum(II),
rhenium(I), and ruthenium(II) complexes of the inv-pytri
ligands (4a−b) were unambiguously confirmed by X-ray
crystallography (Figure 3, Tables 1 and 2, and Supporting
Information Figures S46−47).
The structures of the palladium(II) and platinum(II)
complexes revealed the expected square planar geometry at
the d8 metal ions. The palladium(II) ions in the complexes
(5a−b) were coordinated to two inv-pytri ligands via the 2-
pyridyl nitrogen and the N2 nitrogen atom of the triazole ring
(Figure 3a and Supporting Information Figure S46a). The
−
noncoordinating PF6 anions (Figure 3d and Supporting
Information Figure S46d). These tris-bidentate cations are
chiral and a racemic mixture of the Λ and Δ enantiomers are
present in the crystals.
The M−Ntriazolyl bond distances and N−M−N angles of the
inv-pytri chelators (5−8a-b) are almost identical to those found
in the structures of the analogous reg-pytri complexes
(Supporting Information Figure S48), and only very subtle
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Figure 3. Molecular structures of 5b·2CH3CN (a), 6b (b), 7b·CH2Cl2 (c), and 8b·2CH3CN, polymorph 1 (d) are shown as ORTEP16 diagrams.
Counter-anions and solvent molecules were omitted for clarity. The thermal ellipsoids were displayed at the 50% probability level. A figure showing
the analogous phenyl complexes (5−8a) can be found in the Supporting Information (Figure S46).
Table 1. Bond Lengths (Å) for Metal−Pytri Complexes Crystallized in This Work, Compared to Selected Examples from
Literature Reports
inv-pytri
reg-pytri
complex
M−Npyridyl
M−Ntriazolyl
complex
M−Npyridyl
M−Ntriazolyl
5a
5b
6a
6b
7a
2.026(2)
2.026(2)
2.027(3)
2.01(1)
2.24(1)
1.989(2)
1.983(2)
1.980(3)
2.00(1)
2.12(1)
9a9i
9b9i
2.045(2)
2.045(1)
2.044(7)
b
2.006(1)
1.995(1)
1.986(7)
b
10a13
10b
11a (NO2)8c
11a (Cl)8c
11b15e
2.214(2)
2.205(3)
2.197(5)
2.087(9)
2.077(2)
2.151(2)
2.155(3)
2.127(6)
2.02(1)
2.063(3)
2.038(3)
7b
8a
2.194(3)
2.062(4)
2.076(1)
2.084(2)
2.148(3)
2.050(3)
2.037(1)
2.022(3)
12a
a
8b (polymorph 1)
12b (this work)
1214c
8b (polymorph 2)
2.085(3)
a
b
Bond lengths from only one of the two [Ru(bpy)2(reg-benzyl)]2+ cations in the asymmetric unit were reported. The molecular structure has not
been determined.
differences are observed despite coordination through the
potentially more weakly binding N2 nitrogen atom (Tables 1
and 2).
stirred at room temperature for 30 min. The 1H NMR
spectrum (d6-DMSO, 298 K) of the resulting reaction mixture
indicated the exclusive formation of the regular palladium
complex [Pd(2b)2]2+ (9b) with inv-pytri ligand 4b uncom-
plexed in solution (Scheme 2i and Figure 5). In a second series
of competition experiments ligand 2b (2.1 equiv) and inverse
palladium complex 5b (1 equiv) were dissolved in d6-DMSO
and stirred at room temperature for 30 min (Scheme 2ii). Once
again, the 1H NMR spectrum (d6-DMSO, 298 K) of the
resulting reaction mixture indicated the exclusive formation of
the palladium complex 9b (Supporting Information Figure
S49). These data indicate, as expected, that the reg-pytri ligands
(2) form more stable coordination complexes than the
corresponding inv-pytri systems (4). The results from a recent
The molecular structures of the complexes show that the inv-
pytri (4a−b) ligands coordinate to metal ions via the more
electron deficient N2 nitrogen atom whereas the reg-pytri (2a−
b) ligands coordinate via the more electron rich N3 nitrogen
atom. It was postulated that the inv-pytri (4a−b) ligands would
form less stable metal complexes than those of the isomeric reg-
pytri (2a−b) ligands (Figure 4). Ligand exchange experiments
and DFT calculations were carried out to examine this (vide
infra).
Stability Studies on d8 Square Planar Triazole
Complexes. A mixture of [Pd(CH3CN)4](BF4)2 (1 equiv),
4b (2 equiv), and 2b (2 equiv) were dissolved in d6-DMSO and
C
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a
Table 2. N−M−N Angles (deg) for Metal−Pytri Complexes
Crystallized in This Work, Compared to Selected Examples
from Literature Reports
Scheme 2. Ligand Exchange Experiments
inv-pytri
reg-pytri
complex
Npyridyl−M−Ntriazolyl
complex
Npyridyl−M−Ntriazolyl
5a
5b
6a
6b
7a
79.11(8)
78.99(8)
79.8(1)
79.5(4)
74.6(6)
9a9i
79.56(6)
79.59(5)
79.9(3)
b
9b9i
10a13
10b
11a (NO2)8c
11a (Cl)8c
11b15e
12a
74.46(8)
74.6(1)
74.4(2)
78.8(4)
78.3(1)
7b
8a
73.8(1)
77.9(1)
77.96(6)
8b (polymorph
1)
12b (this
a
work)
12b14c
8b (polymorph
2)
77.6(1)
78.5(1)
a
Angles from only one of the two [Ru(bpy)2(reg-benzyl)]2+ cations in
b
the asymmetric unit were reported. The molecular structure has not
been determined.
a
Conditions: (i) [Pd(CH3CN)4](BF4)2, d6-DMSO, 298 K and (ii) 2b,
d6-DMSO, 298 K.
Stability Studies on d6 Octahedral Triazole Com-
plexes. The octahedral rhenium(I) (7b and 11b) and
ruthenium(II) (8b and 12b) complexes displayed different
behavior, compared to the square planar systems, in d6-DMSO
(Supporting Information Figures S53−S56). The rhenium(I)
inverse complex [Re(4b)(CO)3Cl] (7b) slowly loses the
inverse ligand in d6-DMSO (in the dark). After 4 days
approximately 15% of the complex has decomposed.10a
Conversely, the regular rhenium(I) complex [Re(2b)(CO)3Cl]
(11b) shows no sign of decomplexation after the same time
period. Neither the inverse (8b) nor regular (12b) ruthenium-
(II) complexes decomposed in d6-DMSO (in the dark) after a
week. These data indicate, as expected,6b,9f,i,17 that the reg-pytri
ligands (2) form more stable coordination complexes than the
corresponding inv-pytri ligands (4), consistent with data
obtained from ligand exchange experiments involving the
palladium(II) complexes.
Figure 4. Palladium(II) (9a−b),9i platinum(II) (10a),13 rhenium(I)
(11a−b),8c,15e and ruthenium(II) 12b14c complexes of reg-pytri ligands
that have previously been crystallographically characterized. The
structures of the ruthenium(II) complexes (12a−b) have been
determined as part of this work (Supporting Information Figure S48).
intramolecular competition experiment reported by Sangtrir-
utnugul and co-workers are also consistent with our findings.10b
The stability of the palladium complexes was also examined
using DFT calculations (B3LYP, Supporting Information
Figure S50). Consistent with the experimental results, the
DFT calculations indicate that formation of the regular
palladium complex 9b by displacement of 4b from 5b is
exothermic by 25.7 kcal mol−1. Similarly, formation of 9a by
displacement of 4a from 5a is downhill by 23.9 kcal mol−1.
The platinum(II) complexes display similar behavior to the
palladium(II) complexes. 1H NMR spectra of 6b and 10b in d6-
DMSO indicate that the [Pt(triazole)Cl2] complexes decom-
pose to free ligand and [Pt(DMSO)2Cl2]. The decomposition
of the inverse complex 6b was complete in 2 h whereas the
ligand of the corresponding regular complex 10b is not
completely decomplexed after 4 days (Supporting Information
Figures S51−S52).
Presumably the difference in stability between the inverse
and regular ligands is due to the weaker donor ability of the N2
nitrogen atom compared to the N3 nitrogen atom. To examine
this further the palladium(II) carbene probe system of Huynh
and co-workers18 was used to obtain an estimate of the ligand
donor strength (Supporting Information Scheme S2, Figures
S57−S74, and Tables S1−S2). Consistent with the results of
the competition experiments the probe system indicated that
the reg-pytri are stronger donors than the analogous inv-pytri
compounds (order of donor strength: bpy > phen > reg-benzyl
2b > reg-phenyl 2a > inv-benzyl 4b > inv-phenyl 4a).
The different behavior displayed by the d8 square planar and
d6 octahedral complexes is presumably in part due to the
different kinetic stability of the metal ions. However, the
octahedral Re(I) and Ru(II) complexes, which likely undergo
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1
Figure 5. Stacked partial H NMR (400 MHz, d6-DMSO, 298 K) spectra of [Pd(CH3CN)4](BF4)2 with 2 equiv each of ligands 2b and 4b added
(a), complex 9b (b), ligand 4b (c), and ligand 2b (d). The NMR experiment shows that the Pd(II) ion preferentially binds to the regular ligand 2b
over the inverse ligand 4b to give complex 9b.
Figure 6. Stacked partial 1H NMR (400 MHz, CD3CN, 298 K) spectra of the nonirradiated complex 8b (a), 8b after 6 h of irradiation (b), 8b after
24 h of irradiation (c), 8b after 30 h of irradiation (d) and the free inv-pytri ligand 4b (e). Expansion shows the benzylic proton signals used for
determining the degree of ligand ejection.
the dissociative ligand exchange mechanism, are more long-
lived/kinetically stable in d6-DMSO, whereas the square planar
Pd(II) and Pt(II) complexes, which favor the associative ligand
exchange mechanism,19 decompose far more rapidly in the
same solvent.
Photochemical Ligand Exchange. During the course of
the stability studies it became apparent that the ligand
decomplexation process could be accelerated by light. In the
dark, the inverse rhenium(I) complex 7b lost 4% of its ligand in
d6-DMSO after 1 day (Supporting Information Figure S75).
When the same complex was irradiated by UV light (λ = 254
nm), 25% of the ligand was ejected from the complex over the
24 h time period. Interestingly, the regular rhenium(I) complex
11b shows no sign of ligand ejection after 24 h of irradiation
(Supporting Information Figure S76).
E
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a
Scheme 3. Photochemical Ligand Loss Experiments
a
Conditions: UV irradiation (254 nm), 35 °C, 24−30 h.
a b
,
Table 3. Electrochemical Data for Triazole Ligands 2 and 4 and Their Ru(II) bpy Complexes
compound
Er°ed3 (triazole)/V
Er°ed2 (bpy)/V
Er°ed1 (bpy)/V
Eo°x (RuIII/II)/V
Eo°x − Er°ed1/mV
c
2a
−2.31
−2.42
−2.19
c
2b
4a
c
c
4b
8a
−2.28
−1.79 (98)
−1.85 (86)
−1.96 (90)
−2.05 (130)
−1.43 (70)
−1.44 (74)
−1.49 (80)
−1.49 (70)
−1.42 (58)
−1.24 (70)
−1.24 (68)
−1.28 (78)
−1.27 (70)
+1.40 (122)
+1.40 (127)
+1.32 (94)
+1.31 (90)
+1.29 (86)
2640
2640
2600
2580
2530
8b
12a
12b
d
[Ru(bpy)3](PF6)2
−1.68 (66)
−1.24 (56)
c
a
b
E° from DPV. Peak-to-peak (mV) separations for the 100 mV s−1 CV experiments. Irreversible reduction, Epc, from 100 mV s−1 CV experiment.
Third bpy reduction.
d
The inverse 8a−b and regular 12a−b ruthenium(II) bpy
ligand 4b. After the same time period in d7-DMF and CD3NO2
solvents, only 23% and <5% of the ligand 4b, respectively, had
been liberated from 8b.
complexes also displayed different photochemical stabilities.
Acetonitrile solutions (5 mM) of the inverse complexes 8a−b
were irradiated (λ = 254 nm) and the reactions monitored
using 1H NMR spectroscopy (Figure 6 and Supporting
Information Figure S77). During the course of the irradiation,
a series of new peaks, consistent with the free ligand (4a or 4b)
and [Ru(bpy)2(CH3CN)2]2+, appear in the 1H NMR spectra of
8a−b. At the same time the peaks due to the inverse complexes
8a−b slowly decrease in intensity and then eventually
disappear. These data are consistent with the photoactivated
ejection of the inverse ligands (4a or 4b) from their
corresponding complexes 8a−b. Similar behavior has recently
been documented for related [Ru(diimine)2(dimethylbpy)]2+
and [Ru(diimine)2(bi-1,2,3-triazole)]2+complexes.20 The rate of
ligand ejection in the two complexes is similar. After 24 h the
phenyl substituted complex 8a has ejected 96% of the inv-pytri
ligand 4a, whereas the benzyl substituted complex 8b has
liberated 90% of ligand 4b. This subtle difference in the rate of
decomplexation is consistent with the electronic properties of
the inv-pytri ligands. Acetonitrile solutions of 8a−b heated, in
the absence of light, at 323 K for 15 h show no signs of ligand
decomplexation confirming that the process is photochemically
but not thermally activated (Supporting Information, Figure
S78). Ligand ejection from the complexes 8a−b is more facile
in coordinating solvents. For example, after 24 h of UV
irradiation in CD3CN, 90% of 8b has ejected the inv-pytri
Interestingly, under analogous conditions, the isomeric
regular ruthenium(II) bpy complexes 12a−b are photochemi-
1
cally inert. After 24 h of photoirradiation the H NMR spectra
(CD3CN, 298 K) of 12a−b are essentially unchanged
(Supporting Information Figures S79−S80). Only a very
small amount (<5%) of the free ligands (2a−b) was detected
in the reaction mixture.
It is presumed that the decomplexation of the inv-pytri ligand
from the Ru(II) center proceeds via a two-step process
(Scheme 3).20a−c The first step involves the bond dissociation
of one of the two Ru−N bonds between the Ru(II) center and
the inv-pytri ligand and the coordination of an acetonitrile
molecule to give a [Ru(bpy)2(4a- or 4b-κN)(CH3CN)]2+
intermediate. The second step involves the complete
dissociation of the inv-pytri from the Ru(II) center and the
coordination of a second acetonitrile molecule to give a cis-
[Ru(bpy)2(CH3CN)2]2+ and “free” triazole ligand as the final
products.
DFT calculations (PBE0,21 Supporting Information, Table
S3) indicate the intermediate with the triazolyl nitrogen
remaining bound (intermediate a) has a lower energy than
the intermediate with the pyridyl nitrogen bound (inter-
mediate b) (ΔE = 4.9 kcal mol−1 for 8b, 4.5 kcal mol−1 for 8a).
Intermediate a then reacts with a second solvent CD3CN
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molecule to form [Ru(bpy)2(CD3CN)2]2+, and the appropriate
free inv-pytri ligand (4a or 4b). The H NMR spectrum of an
potential required): reg-benzyl 2b > reg-phenyl 2a > inv-benzyl
4b > inv-phenyl 4a.
1
irradiated sample of 8b displays an AB quartet signal at 4.21
ppm which we propose is due to the presence of an
intermediate complex as the signal decreases in intensity
upon further irradiation (Figure 6). Previous studies20 have
suggested that population of metal-centered triplet (3MC)
states are responsible for the photodissocation behavior
observed in these types of complexes. DFT calculation (vide
infra) suggest that this is also the case for 8a−b.
Electrochemistry. An electrochemical study of reg-pytri
(2a−b) and inv-pytri (4a−b) ligands and their Pt(II), Re(I),
and Ru(II) complexes (6−8 and 10−12) was undertaken using
cyclic voltammetry (CV) and differential pulse voltammetry
(DPV) in dimethylformamide (DMF) solution. Numerical data
are presented in Tables 3 and 4, and representative voltammo-
The electrochemistry of regular ruthenium(II) complex 12b
and the archetypal [Ru(bpy)3]2+ in acetonitrile has been
reported.5a,14c Their behavior in DMF follows the same pattern
and is similarly exhibited by the new ruthenium(II) complexes
8a−b and 12a (Figure 7). Thus, sweeping to cathodic potential
gives rise to two reversible reductions associated with the bpy
ligands, and a quasi-reversible reduction of the 2-pyridyl-1,2,3-
triazole ligand. Anodic scans show the expected RuIII/II
oxidation couple. Substitution of one of the bpy ligands on
[Ru(bpy)3]2+ with an inverse triazole ligand has no effect
(within the experimental error,
20 mV) on the reduction
potential of the remaining two bpy ligands (Table 3). The
effect of a regular triazole ligand is a small cathodic shift of 40
mV and 70 mV for E°red1 and Er°ed2, respectively. The effect on
the ruthenium oxidation potential is the reverse, with a small
anodic shift (20−30 mV) for the reg-pytri complexes; for inv-
pytri complexes 8a−b the shift is 110 mV. Both effects are
consistent with the inverse triazole ligands having poorer
electron donating ability than the regular counterparts. For 8a−
b and 12a−b, scanning to an increasingly cathodic potential
results in the observation of a third reduction which is
associated with the 2-pyridyl-1,2,3-triazole group. Compared to
the uncoordinated ligands, bidentate coordination to ruthenium
imparts stability; the reductions are observed as a quasi-
reversible couple, and are shifted ca. 400 mV in the positive
direction consistent with the lowering of electron density on
the triazole group. The order of reduction potentials (Er°ed3)
with respect to regular/inverse and phenyl/benzyl substitution
is as per Epc of the uncoordinated ligands.
Table 4. Reduction Potentials of Pt(II) and Re(I)
a
Complexes of Triazole Ligands 2 and 4
compound Epc (triazole)/V compound Epc (triazole)/V Epa (ReII/I)/V
b
b
b
b
b
b
b
b
b
b
b
b
6a
−1.19
−1.25
−1.45
−1.48
7a
−1.36
−1.41
−1.64
+1.55
+1.54
+1.48
+1.50
6b
7b
10a
11a
10b
11b
−1.69
a
b
Scan rate is 100 mV s−1 for CV experiments. Irreversible process;
Epc or Epa is given instead of E°.
The electrochemistry of rhenium(I) complexes 11a−b of reg-
pytri ligands in dichloromethane (CH2Cl2) solution has
previously been described.8d Similar redox behavior is observed
for these compounds in DMF solution. The results and those
for the inv-pytri complexes 7a−b are given in Table 4, and a
representative voltammogram, that of 7b, is given in the
Supporting Information (Figure S81). An irreversible oxidation
associated with the ReII/I couple occurs near the solvent limit.
For complexes 7a−b there is a small anodic shift (ca. 50 mV) of
Epa (ReII/I) with respect to the reg-pytri analogues 11a−b, the
same effect has been seen for the ruthenium(II) systems, and
again is consistent with the poorer electron donating ability of
the inv-pytri ligands. An irreversible ligand reduction is
observed in the range from −1.3 to −1.7 V. The order of
reduction potentials (Epc) with respect to regular/inverse and
phenyl/benzyl substitution pattern follows that of the
uncoordinated ligands and ruthenium(II) compounds as
described above.
Figure 7. Cyclic voltammograms of 8b (1 mM) in DMF. The blue
trace shows all four electrochemical processes (potential window =
−2.0 to +1.6 V) while the red trace shows only the two bpy-based
reductions (potential window = −1.7 to −0.3 V): supporting
electrolyte 0.10 M Bu4NPF6, scan rate 100 mV s−1, potential vs
decamethylferrocene reference [Fc*]+/0 = 0.00 V.
The electrochemical behavior of reg-pytri platinum(II)
complexes 10a−b in DMF (Table 4) resembles that described
in CH2Cl2 solutions.13 Coordination to the metal shifts the
irreversible ligand-based reduction (Supporting Information
Figure S82) in the predicted anodic direction, as described
above for the ruthenium(II) and rhenium(I) systems. Again
there is a small variation in shifting between phenyl and benzyl
triazole substituents, and for the complexes (6a−b) of the inv-
pytri ligands reduction is shifted ca. 250 mV anodically of the
regular variant.
grams illustrated in Figure 7 and the Supporting Information
(Figures S81−S82). For the ruthenium(II) complexes (8a−b
and 12a−b) the electrochemical cell was wrapped to exclude
light and minimize the possibility of photocatalyzed ligand
substitution reactions.
The electrochemistry in DMF of the uncoordinated reg-pytri
(2a−b) and inv-pytri (4a−b) ligands features an irreversible
reduction below −2 V (vs [Fc*]+/0, Table 3). The effect of
phenyl and benzyl substituents on the observed reduction is, as
predicted, the electron-withdrawing phenyl appended ligands
being ca. 100 mV easier to reduce than their benzyl analogues.
Additionally, the inv-pytri ligands are >100 mV easier to reduce
than their reg-pytri counterparts. The combination of these
effects gives a series in the order of Epc (increasingly negative
Photophysical Characterization. The electronic absorp-
tion and photophysical properties of the complexes were
examined to further understand the differences between the
regular and inverse pytri ligands. The absorption spectra of the
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inverse and regular complexes showed marked differences
(Figure 8 and Supporting Information Figures S83−84). The
origin of these differences was examined in more detail for the
Pt(II), Re(I), and Ru(II) triazole complexes (vide infra).
Figure 9. Electronic absorption and emission spectra for the
rhenium(I) complexes 7a and 7b in CH2Cl2 at 298 K.
corresponding benzyl substituted complex 7b and the
appearance of a shoulder at 307 nm. The red-shifted absorption
is consistent with the electrochemical results discussed above.
Time dependent density functional theory (TD-DFT)
calculations were used to model the electronic absorption
spectra. The results are summarized in Table 5 along with
electron transition densities calculated with GaussSum.26
Relevant frontier orbitals are shown in the Supporting
Information (Figure S87). The lowest energy band of both
compounds is composed of two MLCT transitions. The lower
of the two (MLCT − 1) is found in the tail of the band and is
mostly due to the highest occupied molecular orbital (HOMO)
to lowest unoccupied molecular orbital (LUMO) transition.
The second lowest transition (MLCT − 2) is predominantly
the HOMO − 1 to LUMO transition and has a much stronger
oscillator strength. The donor orbitals are mostly localized on
the metal center for 7b, however, for 7a the MLCT transitions
have a very small contribution from the phenyl ring. Although
the phenyl substituent in 7a has an insignificant effect on the
energy of the MLCT transitions, conjugation between the
triazolyl and phenyl rings appears to be responsible for the 307
nm shoulder which 7b lacks. This transition is essentially an
intraligand charge transfer (ILCT) from the phenyl and
triazolyl rings to the pyridyl ring. Further ILCT and MLCT
transitions are expected at higher energy.
Raman spectroscopy was used to better understand the
electronic structure of rhenium(I) complexes 7a and 7b (Figure
10 and Supporting Information Figure S88). Nonresonant
spectra at 830 nm excitation were compared to spectra
simulated by DFT calculations with B3LYP. The most
significant difference between 7a and 7b is the very strong
band at 1613 cm−1 in the spectrum of 7a. The 1613 cm−1 band
is composed of pyridyl and phenyl breathing modes, predicted
to be within 0.6 cm−1 of each other by the DFT calculations.
The intensity of these modes is known to be sensitive to the
degree of conjugation and the twist angle between aromatic
rings.27 The pyridine band shifts to 1616 cm−1 for the benzyl
complex and the aryl mode appears as a shoulder at 1604 cm−1.
These bands are much weaker than those in 7a due to the lack
of conjugation between the triazole and benzyl rings.
Figure 8. Electronic absorption spectra of the dichloroplatinum(II)
complexes (6a−b and 10a−b) in DMF.
Photophysical Properties of the Platinum Complexes.
The electronic absorption spectra of the inv-pytri (6a−b) and
reg-pytri (10a−b) platinum(II) complexes are shown in Figure
8. The lowest energy absorption for all complexes has an
extinction coefficient consistent with a metal-to-ligand charge
transfer (MLCT) band. This band is significantly red-shifted for
the inverse complexes compared with the regular complexes
and the substituent group has very little effect. The MLCT
band appears to be split into two partially resolved bands. This
is a feature commonly seen in Pt(II) complexes that has been
attributed to vibronic coupling in some cases22 and the
presence of two separate electronic transitions in others.23
Resonance Raman spectroscopy was used to study the
absorption properties further (Supporting Information Figures
S85−S86).
Resonance Raman experiments at 351, 356, and 364 nm
probed the split MLCT band of the Pt(II) complexes 6a−b.
The enhancement pattern is similar to that seen in the rhenium
complexes (vide infra). The same bands are enhanced at all
three wavelengths, implying that this is a single MLCT band
split by vibronic coupling. No enhancement of the phenyl
breathing mode is seen in 6a showing that the substituents have
little involvement in the MLCT transitions (vide infra).
Resonance Raman experiments at 407 and 413 nm were used
to probe the tail of the MLCT band. Here an unusual
enhancement pattern is found where only four of the 11 bands
enhanced at 351−364 nm for 6a appear. This could be
explained by resonant de-enhancement of some vibrational
modes due to forbidden d−d transitions.24
The platinum complexes were not found to be emissive in
DMF solution at room temperature. It is rare for
dichloroplatinum(II) complexes to be emissive25 due to low-
lying d−d transitions.22
Photophysical Properties of the Rhenium Complexes.
Electronic absorption and emission spectra for rhenium(I)
complexes 7a and 7b in CH2Cl2 solution are shown in Figure 9.
The absorption maxima of 7a−b are red-shifted compared to
the regular “click” complexes reported previously.8d The phenyl
substituent causes a slight red-shift when compared to the
Resonance Raman spectroscopy was used to probe the
MLCT transitions of the Re(I) complexes 7a−b. The
enhancement pattern is nearly identical at all wavelengths and
the same pattern is seen for both complexes. Several triazole
and pyridine based modes are enhanced. It was not possible to
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Table 5. Summary of the Relevant Experimental and Simulated Electronic Transitions for the Inverse Rhenium Complexes
(7a−b)
electron transition density difference (%)
λexp
ε (M−1 cm−1
)
λcalc
f
orbital contributions (%)
Re(CO)3Cl pyridine
triazole
R
7a
7b
MLCT − 1
MLCT − 2
ILCT
379
379
4140
4140
6580
16000
3840
3840
9380
405
381
321
312
402
379
311
0.0040
0.0880
0.0589
0.0178
0.0062
0.0886
0.0161
H → L (68), H − 1 → L (18)
H−1 → L (68), H → L (17)
H−3 → L (69)
86 → 9
91 → 9
20 → 9
85 → 2
94 → 9
94 → 9
94 → 2
1 → 51
3 → 51
3 → 51
1 → 87
1 → 52
3 → 52
1 → 88
8 → 39
3 → 39
22 → 39
8 → 9
4 → 39
3 → 39
4 → 10
6 → 1
2 → 1
56 → 1
6 → 2
1 → 0
0 → 0
1 → 0
305 (sh)
276 (sh)
374
MLCT − 3
MLCT − 1
MLCT − 2
MLCT − 3
H−2 → L (70)
H → L (97), H − 1 → L (2)
H − 1 → L (96), H → L (2)
H → L + 1 (98)
374
281
quantum yields for the inverse complexes in both solvents are
comparable to alkyl-substituted inverse 2-pyridyl-1,2,3-triazole
rhenium(I) complexes measured in DMSO/water mixtures
recently reported by Policar and co-workers.10a The regular
Re(I) complexes (11a−b) appear to be more sensitive to
coordinating solvents as shown by significantly longer lifetimes
and quantum yields in CH2Cl2 compared to CH3CN. The
radiative (kr) and nonradiative (knr) decay rate constants were
calculated from the quantum yields and lifetimes. Nonradiative
decay is faster for the higher energy emitting regular complexes
which is counter to what is expected from the energy gap law.29
Photophysical Properties of the Ruthenium Com-
plexes. The electronic absorption spectra of the ruthenium(II)
2-pyridyl-1,2,3-triazole complexes (8a−b and 12a−b) are
shown in Figure 11 with that of [Ru(bpy)3]2+ for comparison.
Figure 10. Raman spectra of the rhenium complex 7a (3 mM, in
DMF) at 298 K. Solvent bands are indicated by an asterisk (*).
differentiate between the two MLCT bands predicted by TD-
DFT because each involves the same acceptor orbital, and
therefore, produce the same enhancement pattern. The signal
corresponding to the phenyl/pyridyl breathing mode discussed
above is only slightly enhanced in the resonance Raman spectra
for 7a, further showing that the substituent is not involved in
the MLCT transitions.
The photophysical properties of the inverse (7a−b) and
regular (11a−b) rhenium(I) complexes were studied and
compared. A broad structureless emission band typical for this
class of complex is seen with 351 nm excitation (Figure 9). The
emission spectra of the inverse complexes are red-shifted
compared to that of the regular complexes. Emission quantum
yields and lifetimes were measured in both CH2Cl2 and
CH3CN (Table 6). All of the triazole complexes have improved
lifetimes and quantum yields compared to the prototypical
1,10-phenanthroline28 and bpy29 complexes in CH2Cl2. The
Figure 11. Electronic absorption spectra for the ruthenium(II)
complexes (8a−b, 12a−b, and [Ru(bpy)3]2+) in CH2Cl2 at 298 K.
The MLCT band for the Ru(II) 2-pyridyl-1,2,3-triazole
complexes is blue-shifted compared to [Ru(bpy)3]2+, and the
Table 6. Photophysical Properties of the Rhenium(I) Complexes (7a−b and 11a−b) in Argon Saturated Solutions at 298 K
a
a
solvent
CH2Cl2
complex
λAbs (nm)
λEm (nm)
τ (μs)
Φ
kr × 104 (s−1
)
knr × 105 (s−1
)
7a
379
374
337
346
359
356
336
330
596
591
550
547
593
589
532
532
1.3
0.053
0.053
0.087
0.049
0.057
0.049
0.036
0.012
4.1
4.1
10
7.7
7.7
11
12
12
9
7b
1.3
11a
11b
7a
0.88
0.80
0.83
1.1
6.1
6.9
4.5
23
CH3CN
7b
11a
11b
0.16
0.10
62
100
12
a
10%.
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Article
3
extinction coefficients are reduced by about one-third. This
implies that the acceptor orbitals for the MLCT transitions
remain bpy π* based. Therefore, the blue-shift is likely a result
of a decrease in the dπ donor orbital energy level. Presumably
this is because the triazole is a better π-acceptor than the
pyridine which it replaces.5a,8n,30 This is consistent with the
electrochemical data which show that the triazole complexes
have a higher oxidation potential compared to [Ru(bpy)3]2+
but a mostly unchanged first reduction potential. A plot of the
MLCT excitation energy vs the Eox shows a linear relationship
as has been seen in other Ru(II) complexes (Supporting
Information Figure S89).31
geometries of the ground state and MLCT states are very
similar to all Ru−N bonds calculated to be about 2.1 Å. Two
3MC states were optimized for each triazole complex with
elongation of the Ru−N bonds along the a or b axes as defined
in Figure 13. These correspond to the Ru−Ntriazolyl or Ru−
Further evidence for a bpy-based acceptor orbital was
obtained from resonance Raman spectra (Figure 12). The
Figure 13. 3MLCT state of 8a and axes used for comparing the triplet
state geometries.
Npyridyl bonds and the Ru−N bond of the bpy ligand trans to it.
These are referred to as the 3MCtri and 3MCpyr states,
3
respectively. In the MCtri state the Ru−Ntriazolyl bond length
Figure 12. Resonance Raman spectra (458 nm excitation) of the
ruthenium(II) complexes (8a−b, 12a−b, and [Ru(bpy)3]2+) at 1 mM
in CH2Cl2. Solvent bands are indicated by an asterisk (*).
is increased to about 2.5 Å while the trans-Ru−Nbpy bond
increases to about 2.3 Å. Elongation along the b axis in the
3MCpyr state is more pronounced with a Ru−Npyridyl bond
length of about 2.6 Å and a trans-Ru−Nbpy bond of about 2.4 Å.
458 nm excitation wavelength was used to probe the lowest
energy band of all ruthenium complexes. The Ru(II) 2-pyridyl-
1,2,3-triazole complexes show enhancement of bands at 1028,
1039, 1273, 1317, 1489, 1562, and 1605 cm−1 which is
indicative of an Ru → bpy MLCT transition.32 These are the
same modes enhanced for [Ru(bpy)3]2+, showing that the
triazolyl moiety is not involved in the lowest energy MLCT
transition.
3
One MC state with elongation of a pair of trans-Ru−N bonds
in [Ru(bpy)3]2+ was optimized for comparison. The bond
3
lengths increase from about 2.1 Å in the ground and MLCT
3
state to 2.45 Å in the MC state.
The relative energies of the triplet states play a factor in
controlling the rate of decay of the excited state. All relaxed
3MC states were calculated to be more stable than their
corresponding 3MLCT states. The driving force for decay from
The regular Ru(II) triazole complexes (12a−b) were found
to be very weakly emissive in CH2Cl2 at 298 K (quantum yield
= 0.001)8n while no emission was observed for the inverse
Ru(II) complexes (8a−b) (Supporting Information Figure
S90). Excited state lifetimes for all the ruthenium(II) complexes
were shorter than the time resolution of our instrument (<10
3
3
the MLCT to MC state (ΔE33= EMC − EMLCT) was found to
3
be larger for most MCtri and MCpyr states compared to the
3MC state of [Ru(bpy)3]2+ (Figure 14 and Supporting
Information Table S4). This is likely to be responsible for
the lack of phosphorescence from the 3MLCT states.35 All 3MC
3
ns). Despite the fact that these complexes possess an MLCT
3
states are lower in energy than their corresponding MLCT
state with the excited electron localized on one of the bpy
ligands this state is very short-lived in fluid solution due to rapid
relaxation to the ground state. This is likely mediated by a low-
lying nonemissive 3MC state as has been seen in similar
complexes.33 DFT calculations were used to further understand
this behavior.
states. The energy gap between these states (ΔE3 = EMC
−
EMLCT) is comparable for all complexes. This agrees with
previous reports that the shape of the triplet potential energy
surface plays more of a role in determining the stability of the
emissive state than ΔE3 does.35
The 3MC states are characterized by population of
antibonding d orbitals. The result is elongation of the metal−
ligand bonds along the orbital axis, rapid relaxation to the
singlet ground state, and potentially ligand loss. Using a method
developed by Persson and co-workers,34 ground state, 3MLCT,
and 3MC states were optimized for all the ruthenium
complexes. The structural parameters and relative energies
are given in the Supporting Information (Table S4). The
In three out of four Ru(II) triazole complexes, elongation of
the Ru−Npyridyl bond was more favorable than elongation of the
Ru−Ntriazolyl bond suggesting that the Ru−Npyridyl bond is more
labile, and therefore, more likely to break in photochemical
substitution when the 3MC state is populated. This is consistent
with the results from DFT calculations discussed earlier that
reaction intermediate a (triazolyl N bound) has a lower energy
than intermediate b (pyridyl N bound) in Scheme 3.
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EXPERIMENTAL SECTION
■
General Methods. All regents were laboratory reagent grade or
better and used as received. The ligands 2a and 2b9l and complexes
[Pd(2a)2](BF4)2 (9a),9i [Pd(2b)2](BF4)2 (9b),9i fac-[Re(2a)-
(CO)3Cl] (11a),8d and fac-[Re(2b)(CO)3Cl] (11b)8d were prepared
using our previously reported methods. Platinum(II) precursor cis-
[Pt(DMSO)2Cl2] was prepared by a literature method.37 A CEM S-
class microwave reactor was used to carry out microwave enhanced
reactions. All NMR spectra were recorded at 298 K. One-dimensional
(1H and 13C) and two-dimensional (gCOSY, TOCSY, HSQCAD, and
gHMBCAD) NMR spectra were recorded either on a Varian/Agilent
400-MR or Varian/Agilent 500 MHz AR spectrometer. All chemical
1
shifts (δ) are reported in parts per million (ppm). H NMR chemical
shifts are referenced to residual solvent peaks (CHCl3: 1H δ 7.26 ppm;
CD2HCN: 1H δ 1.94 ppm; d5-DMSO: 1H δ 2.50 ppm; d6-DMF: 1H δ
2.92 ppm). 13C NMR chemical shifts are referenced to solvent peak
(CDCl3: 13C δ 77.16 ppm; CD3CN: 13C δ 1.32 ppm; d7-DMF: 13C δ
29.76 ppm). Abbreviation ABq indicates an AB quartet NMR signal.
Coupling constants (J) are reported in Hertz (Hz). High resolution
electrospray ionization mass spectra (HRESI-MS) were recorded on a
Bruker micrOTOF-Q spectrometer. The mass spectrometer was
calibrated using an external calibrant of sodium formate clusters. UV−
visible absorption spectra were recorded at ambient temperature on a
PerkinElmer Lambda 950 UV−vis−near-IR spectrophotometer. Infra-
red spectra were recorded on a Bruker Optics ALPHA FT-IR
spectrometer equipped with a diamond ATR accessory. Elemental
analyses were performed at the Campbell Microanalytical Laboratory,
University of Otago. Photochemical reactions were carried out in a
custom built “merry-go-round” UV photochemical reactor (University
of Otago, Dunedin, New Zealand), containing six UV−C lamps
located symmetrically around the perimeter of the photoreactor that
emitted monochromatic 254 nm radiation (Rayonet RPR-2537A,
Southern New England Ultraviolet Co., Branford, CT).38 A fan was
used to maintain the temperature of the photoreactor at 35 °C during
irradiation.
Figure 14. Energy level diagram of the ruthenium(II) complexes
3
triplet state energies. ΔE3 is the energy difference between the MC
3
and MLCT states.
CONCLUSION
■
Using the “click” method developed by Wang, Hu, and co-
workers12 we have been able to readily synthesize two inv-pytri
click ligands, 2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyridine and 2-
(4-benzyl-1H-1,2,3-triazol-1-yl)pyridine) in good yield. The
palladium(II), platinum(II), rhenium(I), and ruthenium(II)
complexes of these inv-pytri ligands were synthesized and
1
characterized by elemental analysis, HRESI-MS, IR, H, and
13C NMR spectroscopies, and in each case the molecular
structures confirmed by X-ray crystallography. The properties
of these inv-pytri complexes have been compared to the
isomeric regular compounds. Structurally the regular and
inverse complexes are very similar, only very subtle differences
in the bond lengths and angles of the complexes were observed.
However, the chemical and physical properties of the isomers
are quite different. Ligand exchange studies and DFT
calculations indicate that metal complexes of the reg-pytri
ligands are more stable than those formed with the inv-pytri
click chelators. Additionally, it is shown that ruthenium(II) bpy
complexes of the inverse click chelators are photochemically
active, photoirradiation of these compounds leads to the
ejection of the inv-pytri ligand from the complex. Under
identical conditions the isomeric reg-pytri ruthenium(II) bpy
complexes are photochemically inert. DFT calculations show
that ligand ejection from the inv-pytri complexes is likely the
result of populating the low-lying metal-centered triplet states.
The electronic properties of the complexes of these inv-pytri
ligands have been examined using UV−vis, Raman and
emission spectroscopies, cyclic voltammetry, and DFT
calculations and were shown to be markedly different from
the corresponding reg-pytri complexes. The absorption spectra
of the inverse rhenium(I) and platinum(II) are red-shifted
relative to the regular analogues, and this suggests that new
derivatives of these inverse compound could be used to
developed new optically interesting materials.36 In particular
the rhenium(I) tricarbonyl complexes of the inverse ligands
have long excited state lifetimes and high quantum yields which
is promising for their use as phosphorescent bioprobes.10a
Additionally, the photoactivated ligand ejection behavior of the
inv-pytri ruthenium(II) bpy complexes could be exploited to
develop new photoactivated anticancer agents.20d−g Efforts to
use these inv-pytri ligands in these and other areas are
underway.
[Pd(4a)2](BF4)2 (5a). A solution of ligand 4a (96 mg, 0.43 mmol) in
acetone (5 mL) was added to a solution of [Pd(CH3CN)4](BF4)2 (95
mg, 0.21 mmol) in acetonitrile (2 mL). The resulting pale yellow
solution was stirred for 1 h, and an off-white solid precipitated after
this time. The reaction mixture was cooled to −4 °C and the
precipitate (complex 5a) was collected by filtration, washed with cold
acetonitrile and then diethyl ether, and dried under vacuum. Yield: 131
mg (85%). Pale yellow crystals of 5a suitable for X-ray crystallographic
analysis were obtained by vapor diffusion of methanol into a DMSO
solution of 5a. Anal. Calcd (%) for C26H20B2F8N8Pd: C 43.10, H 2.78,
1
N 15.47; found: C 42.74, H 2.92, N 15.03. H NMR (400 MHz, d7-
3
4
DMF) δ: 10.71 (s, 1H, He), 10.01 (dd, J = 5.7 Hz, J = 1.1 Hz, 1H,
3
4
3
Ha), 9.05 (td, J = 8.1 Hz, J = 1.4 Hz, 1H, Hc), 8.93 (d, J = 8.0 Hz,
1H, Hd), 8.46 (ddd, 3J = 7.3, 5.9 Hz, 4J = 1.2 Hz, 1H, Hb), 8.31 (dd, 3J
= 7.9 Hz, 4J = 1.5 Hz, 2H, Hf), 7.67−7.75 (m, 3H, Hg, Hh). 1H NMR
(400 MHz, CD3NO2) δ: 10.02 (dd, 3J = 5.8 Hz, 4J = 1.1 Hz, 1H, Ha),
9.56 (s, 1H, He), 8.79 (td, 3J = 8.1 Hz, 4J = 1.4 Hz, 1H, Hc), 8.50−8.54
(m, 1H, Hd), 8.23 (ddd, 3J = 7.5, 5.9 Hz, 4J = 1.2 Hz, 1H, Hb), 8.16−
8.21 (m, 2H, Hf), 7.62−7.74 (m, 3H, Hg, Hh). 13C NMR (100 MHz,
d7-DMF) δ: 150.3, 149.6, 146.7, 131.2, 130.0, 128.1, 127.5, 126.7,
124.7, 115.8, 110.1. HRESI-MS (DMF): m/z calcd for C26H21N8Pd+:
551.0928 [Pd(4a)2 + H]+; found: 551.0940 (95%), m/z calcd for
C26H20N8Pd2+: 275.0422 [Pd(4a)2]2+; found: 275.0435 (32%). UV−
vis (DMF) λmax (ε/M−1 cm−1) = 289 (34200) nm. IR (ATR): ν =
−
3127, 3092, 1038 (s, BF4 ) cm−1.
[Pd(4b)2](BF4)2·1.5CH3CN (5b·1.5CH3CN). A solution of ligand 4b
(96 mg, 0.43 mmol) in acetonitrile (3 mL) was added to a solution of
[Pd(CH3CN)4](BF4)2 (90 mg, 0.20 mmol) in acetonitrile (2 mL).
The resulting pale yellow solution was stirred for 1 h, and an off-white
solid precipitated after this time. The reaction mixture was cooled to
−4 °C and the precipitate (complex 5b·1.5CH3CN) was collected by
filtration, washed with diethyl ether, and dried under vacuum. Yield:
126 mg (76%). Pale yellow crystals of 5b·2CH3CN suitable for X-ray
crystallographic analysis were obtained by vapor diffusion of diethyl
K
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Article
ether into a DMF solution of 5b·2CH3CN. Anal. Calcd (%) for
C31H28.5B2F8N9.5Pd: C 45.73, H 3.53, N 16.34; found: C 45.80, H
3.56, N 16.52. 1H NMR (400 MHz, d7-DMF) δ: 9.95 (s, 1H, He), 9.78
(d, 3J = 5.8 Hz, 1H, Ha), 8.89−8.98 (m, 2H, Hc, Hd), 8.29 (td, 3J = 5.5
[Re(4b)(CO)3Cl]·0.5CH3OH (7b·0.5CH3OH). Ligand 4b (92 mg, 0.39
mmol) and [Re(CO)5Cl] (138 mg, 0.38 mmol) were suspended in
methanol (20 mL). The mixture was refluxed overnight. The reaction
mixture was concentrated to approximately 1 mL and then cooled to 4
°C. The resulting yellow precipitate was collected by filtration, washed
with ice-cold methanol, ice-cold diethyl ether and petroleum ether
(40−60 °C), and dried under vacuum. Yield: 176 mg (83%). Yellow
crystals of 7b·CH2Cl2 suitable for X-ray crystallographic analysis were
obtained by vapor diffusion of diethyl ether into a CH2Cl2 solution of
7b·0.5CH3OH. Anal. Calcd (%) for C17.5H14ClN4O3.5Re: C 37.67, H
2.53, N 10.04; found: C 37.87, H 2.64, N 10.02. 1H NMR (400 MHz,
d7-DMF) δ: 9.52 (s, 1H, He), 9.12 (ddd, 3J = 5.5 Hz, 4J = 1.5 Hz, 5J =
0.6 Hz, 1H, Ha), 8.69 (d, 3J = 8.3 Hz, 1H, Hd), 8.58 (ddd, 3J = 8.4, 7.6
Hz, 4J = 1.6 Hz, 1H, Hc), 7.86 (ddd, 3J = 7.5, 5.6 Hz, 4J = 1.2 Hz, 1H,
Hb), 7.36−7.45 (m, 4H, Hg, Hh), 7.28−7.34 (m, 1H, Hi), 4.31 (s, 2H,
Hf). 13C NMR (100 MHz, d7-DMF) δ: 153.0, 151.4, 148.2, 143.5,
138.1, 129.2, 129.1, 127.2, 126.8, 124.1, 115.3, 31.6. HRESI-MS
(CH3CN): m/z calcd for C17H12ClN4NaO3Re+: 565.0031 [7b + Na]+;
found: 565.0039 (100%). UV−vis (DMF): λmax (ε/M−1 cm−1) = 358
(4200) nm. IR (ATR): ν = 3125, 2026 (w, CO), 1941 (w, CO), 1884
(w, CO) cm−1.
4
3
3
Hz, J = 3.9 Hz, 1H, Hb), 7.51 (d, J = 7.1 Hz, 2H, Hg), 7.45 (t, J =
3
7.5, 2H, Hh), 7.37 (t, J = 7.2, 1H, Hi), 4.51 (s, 2H, Hf). 13C NMR
(100 MHz, d7-DMF) δ: 150.6, 149.7, 146.5, 137.5, 129.3, 129.2, 127.5,
127.4, 126.8, 115.9, 110.1, 31.8. HRESI-MS (CH3CN): m/z calcd for
C28H24FN8Pd+: 597.1148 [Pd(4b)2 + F]+; found: 597.1153 (76%), m/
z calcd for C28H24N8Pd2+: 289.0579 [Pd(4b)2]2+; found: 289.0583
(100%). UV−vis (DMF): λmax (ε/M−1 cm−1) = 273 (31300) nm. IR
−
(ATR): ν = 3142, 3048, 1048 (s, BF4 ) cm−1.
[Pt(4a)Cl2] (6a). To a mixture of cis-[Pt(DMSO)2Cl2] (145 mg,
0.343 mmol) and ligand 4a (85 mg, 0.38 mmol) was added methanol
(15 mL). The resulting mixture was refluxed for 45 min. Complex 6a
precipitated as a yellow solid, which was collected by filtration, washed
with methanol, then diethyl ether, and dried under vacuum. Yield: 141
mg (84%). Yellow crystals of 6a suitable for X-ray crystallographic
analysis were obtained by vapor diffusion of diethyl ether into a DMF
solution of 6a. Anal. Calcd (%) for C13H10Cl2N4Pt: C 31.98, H 2.06, N
1
11.48; found: C 32.08, H 1.97, N 11.47. H NMR (400 MHz, d7-
3
4
[Ru(bpy)2(4a)](PF6)2 (8a). Ethanol (10 mL) was added to a mixture
of cis-[Ru(bpy)2Cl2] (137 mg, 0.28 mmol) and ligand 4a (67 mg, 0.30
mmol). The mixture was stirred at room temperature for 5 min and
the resulting solution was degassed with argon. The solution was
heated at 125 °C in a microwave (200 W) for 1 h. During irradiation
the solution became orange-yellow. After cooling the solution to room
temperature, a saturated aqueous solution of NH4PF6 (15 mL) was
added dropwise. The crude product precipitated as an orange-yellow
solid immediately. The mixture was stirred for 10 min, and the orange-
yellow precipitate was collected by filtration. The crude product was
dissolved in acetone and the resulting solution was added dropwise to
a stirred diisopropyl ether solution. Complex 8a precipitated as an
orange-yellow solid and was collected by filtration, washed with ice-
cold water, then ice-cold ethanol, and finally with diethyl ether, and
dried under vacuum. Yield: 193 mg (74%). Orange-yellow crystals of
8a·2CH2Cl2 suitable for X-ray crystallographic analysis were obtained
by vapor diffusion of diisopropyl ether into a dichloromethane solution
of 8a. Anal. Calcd (%) for C33H26F12N8P2Ru: C 42.82, H 2.83, N
12.11; found: C 42.96, H 2.87, N 11.82. 1H NMR (500 MHz,
CD3CN) δ: 9.36 (s, 1H, He), 8.46−8.55 (m, 4H, bpyH), 8.21−8.26
(m, 1H, Hc), 8.18 (d, 3J = 8.0 Hz, 1H, Hd), 8.06−8.14 (m, 4H, bpyH),
7.89 (ddd, 3J = 5.6 Hz, 4J = 1.4 Hz, 5J = 0.7 Hz, 1H, bpyH), 7.86 (ddd,
DMF) δ: 10.33 (s, 1H, He4), 9.49 (dd, J = 5.9 Hz, J = 1.4 Hz, 1H,
3
3
Ha), 8.72 (td, J = 8.0 Hz, J = 1.5 Hz, 1H, Hc), 8.56 (d, J = 8.3 Hz,
1H, Hd), 7.92−8.09 (m, 3H, Hb, Hf), 7.58−7.65 (m, 2H, Hg), 7.51−
7.58 (m, 1H, Hh). 13C NMR (100 MHz, d7-DMF) δ: 148.8, 148.4,
148.0, 143.6, 130.6, 130.1, 129.1, 126.7, 126.5, 122.4, 114.8. HRESI-
MS (DMF): m/z calcd for C13H10Cl2N4NaPt+: 509.9823 [6a + Na]+;
found: 509.9800 (100%). UV−vis (DMF): λmax (ε/M−1 cm−1) = 366
(4170) nm. IR (ATR): ν = 3086, 1614, 1502, 1478, 1454, 1086, 761
cm−1.
[Pt(4b)Cl2] (6b). To a mixture of cis-[Pt(DMSO)2Cl2] (654 mg,
1.55 mmol) and ligand 4b (401 mg, 1.70 mmol) was added methanol
(45 mL). The resulting mixture was refluxed for 45 min. Complex 6b
precipitated as a yellow solid, which was collected by filtration, washed
with methanol, then diethyl ether, and dried under vacuum. Yield: 595
mg (76%). Yellow crystals of 6b suitable for X-ray crystallographic
analysis were obtained by vapor diffusion of diisopropyl ether into a
DMF solution of 6b. Anal. Calcd (%) for C14H12Cl2N4Pt: C 33.48, H
2.41, N 11.16; found: C 33.63, H 2.33, N 11.07. 1H NMR (400 MHz,
d7-DMF) δ: 9.57 (s, 1H, He), 9.45 (ddd, 3J = 5.9 Hz, 4J = 1.5 Hz, 5J =
0.6 Hz, 1H, Ha), 8.63 (ddd, 3J = 8.9, 7.5 Hz, 4J = 1.5 Hz, 1H, Hc), 8.57
(ddd, 3J = 8.3 Hz, 4J = 1.4 Hz, 5J = 0.6 Hz, 1H, Hd),7.93 (ddd, 3J = 7.4,
4
3J = 5.6 Hz, J = 1.3 Hz, J = 0.6 Hz, 1H, bpyH), 7.81 (ddd, J = 5.6
5.9 Hz, J = 1.4 Hz, 1H, Hb), 7.34−7.43 (m, 4H, Hg, Hh), 7.26−7.33
4
5
3
(m, 1H, Hi), 4.29 (s, 2H, Hf). 13C NMR (100 MHz, d7-DMF) δ:
149.8, 148.5, 147.9, 143.4, 138.4, 129.5, 129.4, 127.5, 126.5, 124.3,
114.8, 32.3. HRESI-MS (DMF): m/z calcd for C28H24ClN8Pt+:
702.1456 [Pt(4b)2 + Cl]+; found: 702.1425 (100%), m/z calcd for
C14H12Cl2N4NaPt+: 523.9980 [6b + Na]+; found: 523.9997 (34%).
UV−vis (DMF): λmax (ε/M−1 cm−1) = 363 (4530) nm. IR (ATR): ν =
3100, 3050, 1617, 1496, 1456, 1069, 760, 737, 709 cm−1.
4
5
3
4
Hz, J = 1.3 Hz, J = 0.6 Hz, 1H, bpyH), 7.76 (ddd, J = 5.6 Hz, J =
1.4 Hz, 5J = 0.7 Hz, 1H, bpyH), 7.71−7.75 (m, 3H, Ha, Hf), 7.38−7.51
1
(m, 8H, Hb, Hg, Hh, bpyH). H NMR (400 MHz, d7-DMF) δ: 10.39
(s, 1H, He), 8.92−9.04 (m, 4H), 8.75 (d, 3J = 8.1 Hz, 1H), 8.50 (t, 3J =
7.4 Hz, 1H), 8.23−8.37 (m, 6H), 8.12 (d, 3J = 5.6 Hz, 2H), 8.07−8.10
(m, 1H), 7.80 (d, 3J = 6.9 Hz, 2H), 7.69−7.76 (m, 2H), 7.62−7.69 (m,
3H), 7.43−7.56 (m, 3H). 13C NMR (125 MHz, CD3CN) δ: 158.4,
158.2, 158.1, 157.7, 153.5, 153.5, 153.1, 153.0, 152.4, 151.6, 149.6,
141.7, 139.5, 139.4, 139.4, 139.2, 130.8, 130.3, 129.1, 129.0, 128.7,
128.6, 128.0, 127.3, 126.7, 125.5, 125.4, 125.1, 124.8, 122.7, 115.6.
HRESI-MS (CH2Cl2): m/z calcd for C33H26F6N8PRu+: 781.0968
[Ru(bpy)2(4a) + (PF6)]+; found: 781.0909 (23%), m/z calcd for
C33H26N8Ru2+: 318.0661 [Ru(bpy)2(4a)]2+; found: 318.0652 (100%),
m/z calcd for C33H26N6Ru2+: 304.0630 [Ru(bpy)2(4a) − N2]2+;
found: 304.0621 (74%). UV−vis (CH2Cl2): λmax (ε/M−1 cm−1) = 424
(17400) nm. IR (ATR): ν = 3181, 3087, 1709, 1605, 1491, 1467,
[Re(4a)(CO)3Cl]·0.5CH3OH (7a·0.5CH3OH). Ligand 4a (77 mg, 0.35
mmol) and [Re(CO)5Cl] (123 mg, 0.34 mmol) were suspended in
methanol (20 mL). The mixture was refluxed overnight, and a yellow
solid precipitated after this time. The reaction mixture was reduced to
approximately 1 mL and then cooled to 4 °C. The resulting yellow
precipitate was collected by filtration, washed with ice-cold methanol,
then diethyl ether, and dried under vacuum. Yield: 164 mg, (89%).
Yellow crystals of 7a suitable for X-ray crystallographic analysis were
obtained by vapor diffusion of diethyl ether into a DMF solution of 7a·
0.5CH3OH. Anal. Calcd (%) for C16.5H12ClN4O3.5Re: C 36.43, H 2.22,
−
−
1446, 1222, 1062, 833 (s, PF6 ), 763, 731, 699, 556 (m, PF6 ) cm−1.
[Ru(bpy)2(4b)](PF6)2 (8b). Ethanol (10 mL) was added to a mixture
of cis-[Ru(bpy)2Cl2] (129 mg, 0.27 mmol) and ligand 4b (68 mg, 0.28
mmol). The mixture was stirred at room temperature for 5 min and
the resulting solution was degassed with argon. The solution was
heated at 125 °C in a microwave (200 W) for 1 h. During this time the
solution became orange-yellow. After cooling the solution to room
temperature, a saturated aqueous solution of NH4PF6 (15 mL) was
added dropwise. Complex 8b precipitated as an orange-yellow solid
immediately. The mixture was stirred for 10 min, and the orange-
1
N 10.30; found: C 36.89, H 2.36, N 10.44. H NMR (400 MHz, d7-
DMF) δ: 10.27 (s, 1H, He), 9.16−9.20 (m, 1H, Ha), 8.64−8.71 (m,
3
4
2H, Hc, Hd), 8.05−8.10 (m, 2H, Hf), 7.92 (ddd, J = 6.6, 5.6 Hz, J =
2.2 Hz, 1H, Hb), 7.60−7.66 (m, 2H, Hg), 7.52−7.59 (m, 1H, Hh). 13
C
NMR (100 MHz, d7-DMF) δ: 153.1, 150.4, 148.2, 143.7, 130.2, 129.8,
128.4, 127.1, 126.1, 122.2, 115.3. HRESI-MS (CH3CN): m/z calcd for
C16H10ClN4NaO3Re+: 550.9878 [7a + Na]+; found: 550.9882 (100%).
UV−vis (DMF): λmax (ε/M−1 cm−1) = 359 (4300) nm. IR (ATR): ν =
3136, 2026 (w, CO), 1906 (w, CO), 1889 (w, CO) cm−1.
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yellow precipitate was collected by filtration; washed with ice-cold
water, then ice-cold ethanol, and finally with diethyl ether; and dried
under vacuum. Yield: 197 mg (78%). Vapor diffusion of diisopropyl
ether and diethyl ether into a acetonitrile solutions of 8b gave orange
crystals of 8b·2CH3CN and 8b·CH3CN, respectively, suitable for X-
ray crystallographic analysis. Anal. Calcd (%) for C34H28F12N8P2Ru: C
command was used to model the C−Cl (1.77 Å) and Cl−Cl (2.92 Å)
distances while the ISOR command was used to model atoms C34,
C35, Cl1, Cl3, and Cl4 in the disordered dichloromethane molecules.
Data Refinement Details for 8b·CH3CN (Polymorph 2). All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
placed in calculated positions and refined using a riding model. The
PF6− anion consists of P2 and F7 through F12 was slightly disordered.
The fluorine atoms F9 through F12 were modeled with the ISOR
command.
Both solvent acetonitrile molecules were disordered. The ISOR
command was employed to model atoms N99 and C98 in one of the
acetonitrile molecules. The other acetonitrile molecule is highly
disordered and could not be appropriately modeled. The SQUEEZE
routine within PLATON was employed to resolve this problem,
resulting in a void electrons count of 40 that were assigned to two
disordered acetonitrile molecules (44 electrons in total).
Data Refinement Details for 12a·CH3CN. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were placed in
calculated positions and refined using a riding model. The solvent
acetonitrile molecule was slightly disordered. The ISOR command was
employed to model atoms N99, C99, and C98, and the DFIX
command was used to model the N99−C99 (1.14 Å) and C99−C98
(1.46 Å) distances. The PF6− anion consists of P2 and F7 through F12
is slightly disordered. The ISOR command was employed to model
atoms P2 and F8 through F12. The ellipsoids of atoms C11 through
C15, C17 through C20 and C29 through C33 were slightly elongated
when refined anisotropically. The ISOR command was used to model
these atoms.
1
43.46, H 3.00, N 11.93; found: C 43.29, H 2.91, N 11.87. H NMR
(500 MHz, CD3CN) δ: 8.69 (s, 1H, He), 8.42−8.54 (m,4H, bpyH),
3
4
8.15 (ddd, J = 8.3, 7.6 Hz, J = 1.5 Hz, 1H, Hc), 8.03−8.13 (m, 5H,
3
4
5
Hd, bpyH), 7.83 (ddd, J = 5.6 Hz, J = 1.5 Hz, J = 0.7 Hz, 1H,
3
4
5
bpyH), 7.79 (ddd, J = 5.7 Hz, J = 1.5 Hz, J = 0.7 Hz, 1H, bpyH),
7.77 (ddd, 3J = 5.6 Hz, 4J = 1.5 Hz, 5J = 0.7 Hz, 1H, bpyH), 7.71 (ddd,
3J = 5.7 Hz, J = 1.4 Hz, J = 0.7 Hz, 1H, bpyH), 7.68 (ddd, J = 5.7
Hz, 4J = 1.5 Hz, 5J = 0.7 Hz, 1H, Ha), 7.40−7.48 (m, 4H, Hb, bpyH),
7.37 (ddd, 3J = 7.6, 5.7 Hz, 4J = 1.3 Hz, 1H, bpyH), 7.29−7.34 (m, 2H,
Hh), 7.25−7.29 (m, 1H, Hi), 7.14−7.19 (m, 2H, Hg), 4.07 and 4.03
(ABq, 2J = 16.2 Hz, 2H, Hf). 1H NMR (400 MHz, d7-DMF) δ: 9.59 (s,
4
5
3
3
3
1H, He), 8.88−9.04 (m, 4H), 8.76 (d, J = 8.1 Hz, 1H), 8.42 (t, J =
4
3
8.2 Hz, J = 1.2 Hz, 1H), 8.23−8.36 (m, 4H), 8.21 (d, J = 4.7 Hz,
1H), 8.10−8.15 (m, 2H), 8.04−8.09 (m, 2H), 7.57−7.71 (m, 5H),
7.24−7.38 (m, 3H), 7.15−7.23 (m, 2H), 4.13 and 4.09 (ABq, 2J = 16.4
0.2 Hz, 2H, Hf). 13C NMR (125 MHz, CD3CN) δ: 158.4, 158.1,
158.1, 157.7, 153.4, 153.4, 153.1, 153.0, 152.3, 152.2, 149.7, 141.5,
139.4, 139.4, 139.3, 139.2, 138.4, 129.8, 129.6, 128.9, 128.6, 128.5,
128.0, 127.9, 127.1, 125.4, 125.4, 125.1, 124.9, 124.7, 115.7, 32.4.
HRESI-MS (CH2Cl2): m/z calcd for C34H28F6N8PRu+: 795.1125
[Ru(bpy)2(4b) + (PF6)]+; found: 795.1087 (18%), m/z calcd for
C34H28N8Ru2+: 325.0739 [Ru(bpy)2(4b)]2+; found: 325.0714 (100%),
m/z calcd for C34H28N6Ru2+: 311.0708 [Ru(bpy)2(4b) − N2]2+;
found: 311.0687 (24%), m/z calcd for C26H20N6Ru2+: 259.0394
[Ru(bpy)2(NC5H4−NC)]2+; found: 259.0360 (20%). UV−vis
(CH2Cl2): λmax (ε/M−1 cm−1) = 421 (16000) nm. IR (ATR): ν =
Data Refinement Details for 12b·0.5(C4H10O). All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were placed in
−
calculated positions and refined using a riding model. One of the PF6
anions was disordered over two sites. It was modeled with the PART
command with occupancies of 65% (P4 and F19 to F24) and 35% (P5
and F25 to F30) over two sites. The DFIX commands were used to fix
the P−F (1.60 Å) and F−F (2.26 Å) distances within the disordered
−
3153, 3087, 1604, 1547, 1494, 1467, 1447, 1063, 830 (s, PF6 ), 763,
−
731, 713, 556 (m, PF6 ) cm−1.
X-ray Crystallography. X-ray data for 5a, 5b·2CH3CN, 6a, 6b, 7a,
7b·CH2Cl2, 8a·2CH2Cl2, 8b·2CH3CN (polymorph 1), 8b·CH3CN
(polymorph 2), 12a·CH3CN, and 12b·0.5(C4H10O) were collected at
100 K on an Agilent Technologies Supernova system using Cu Kα
radiation with exposures over 1.0°. X-ray data were treated using
CrysAlisPro39 software. X-ray crystal structures were solved using SIR-
9740 and weighted full-matrix refinement on F2 was carried out using
SHELXL-9741 running within the WinGX42 package. The CCDC
reference numbers for these compounds are 1013165-1013174 and
1014293.
−
PF6 . The ISOR command was used to model fluorine atoms F23,
F25, F26, F27, F29, and F30.
Electrochemistry. Cyclic and differential pulse voltammetric
experiments in DMF were performed at 20 °C on solutions degassed
with argon. A three-electrode cell was used with a Cypress Systems
glassy carbon working electrode (1.4 mm diameter), a Ag/AgCl
reference electrode, and a platinum wire auxiliary electrode. The
solutions were approximately 1 mM of electroactive material and 0.10
M of tetrabutylammonium hexafluorophosphate (Bu4NPF6) as the
supporting electrolyte. Voltammograms were recorded with a
Powerlab/4sp computer-controlled potentiostat. Potentials are refer-
enced to the reversible formal potential (taken as E° = 0.00 V) for the
decamethylferrocenium/decamethylferrocene ([Fc*]+/0) couple,15
where E° was calculated from the average of the oxidation and
reduction peak potentials. Under the same conditions, E° calculated
Data Refinement Details for 5a, 5b·2CH3CN, 6a, 6b, 7b·CH2Cl2,
and 8b·2CH3CN (Polymorph 1). All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were placed in calculated positions
and refined using a riding model.
Data Refinement Details for 7a. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were placed in calculated
positions and refined using a riding model. Atoms Cl1, C1, C16, N2,
O2, and O3 became nonpositive definites when refined anisotropically
and were modeled with the ISOR command. The ellipsoids of atoms
C2, C7, C8, C12, C14, and O1 became slightly elongated or flattened
when refined anisotropically. These atoms were modeled with the
ISOR command. The triazolyl ring was modeled with the SIMU
command. The pyridyl and phenyl rings were modeled with a
combination of the SIMU and AFIX 66 commands.
The crystal lattice contained a smaller amount of diffuse electron
density that could not be appropriately modeled. The SQUEEZE
routine within PLATON was employed to resolve this problem,
resulting in a void electrons count of 128 that were assigned to two
disordered solvent dimethylformamide and four water molecules (120
electrons in total).
for ferrocenium/ferrocene couple ([FcH]+/0) was 0.48 V versus
16
[Fc*]+/0
.
Physical Measurements. Fourier-transform Raman (FT-Raman)
spectra were obtained from solid samples using a Bruker Equinox-55
FT-interferometer with an FRA106/5 Raman accessory and D418T
liquid-nitrogen-cooled Germanium detector with 1064 nm excitation
provided by a Nd:YAG laser. Raman spectra with 830 nm excitation
were recorded on an i-Raman spectrometer (B&W Tek Inc.) using
solid samples.
Electronic absorption spectra were recorded on an Ocean Optics
USB2000. Steady-state emission spectra were recorded on a Princeton
Instruments SP2150i spectrograph with 300 groove mm−1 grating and
Pixis 110 B CCD. A krypton-ion laser (Innova I-302, Coherent, Inc.)
provided excitation at 350.7 nm of 12 mW. [Ru(bpy)3]Cl2 was used as
a quantum yield standard.43 Quantum yield errors are 10%. Excited-
state lifetimes were obtained from transient emission and absorption
spectra acquired with an Edinburgh Instruments LP920 flash
photolysis system using the 354.7 nm pulsed output of a Brilliant
(Quantel) Nd:YAG laser for excitation.
Data Refinement Details for 8a·2CH2Cl2. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were placed in
calculated positions and refined using a riding model. There are two
solvent dichloromethane molecules one of which was disordered. The
disordered dichloromethane molecule was modeled with the PART
command and refined over two sites with 50% occupancy. The DFIX
M
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Inorganic Chemistry
Article
Resonance Raman spectra were recorded using a previously
described setup.44 Solutions were 1−5 mM in spectroscopic grade
solvents. Excitation wavelengths of 350.7, 356.4, 406.7, and 413.1 nm
were obtained from a krypton-ion laser (Innova I-302, Coherent Inc.),
457.9 nm from a diode-pumped solid-state laser (Cobolt Inc.), and
363.7 nm from an argon-ion laser (Innova Sabre 20, Coherent Inc.).
Laser power at the sample was about 30 mW. The incident beam and
collection lens were arranged in a 135° backscattering geometry to
reduce loss of Raman intensity by self-absorption.
(2) (a) Schulze, B.; Schubert, U. S. Chem. Soc. Rev. 2014, 43, 2522−
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Computational Methods. All density functional theory (DFT)
calculations were performed using Gaussian 09.45 The LANL2DZ46
effective core potential basis set was used for all metals and the 6-
31G(d) basis set for all other atoms. The B3LYP47 functional was used
to optimize the rhenium and platinum structures and to simulate
Raman spectra with the polarizable continuum model (PCM)48 in
DMF. Time-dependent DFT calculations for the rhenium complexes
used the Perdew−Burke−Ernzerhof exchange-correlation (PBE0)21
functional with PCM in CH2Cl2. Ligand competition calculations for
the Pd complexes were performed with the B3LYP functional in the
gas phase. The PBE0 functional was used for modeling all Ru
complexes. PCM solvation in dichloromethane was used for Ru
complexes except in modeling solvolysis where CH3CN was used. The
triplet state calculations for Ru complexes were based on a procedure
from Persson and co-workers.34 The singlet ground state was initially
optimized. This structure was used to optimize the 3MLCT state using
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3
unrestricted DFT. The MC states were optimized with unrestricted
DFT by initially elongating two Ru−N bonds of the 3MLCT structure
to about 2.4 Å.
ASSOCIATED CONTENT
■
S
* Supporting Information
McDaniel, N. D.; Muller-Bunz, H.; Bernhard, S.; Albrecht, M.
̈
Reaction scheme, supplementary experimental section, selected
NMR spectra, mass spectra, crystal structures, cyclic voltammo-
grams, UV−vis spectra, Raman spectra, emission spectra, DFT
calculations, .xyz files, and CIFs giving crystallographic data for
5a, 5b·2CH3CN, 6a, 6b, 7a, 7b·CH2Cl2, 8a·2CH2Cl2, 8b·
2CH3CN (polymorph 1), 8b·CH3CN (polymorph 2), 12a·
CH3CN, 12b·0.5(C4H10O), 14, 16a·0.5CH2Cl2, 16b, and 17b.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Angew. Chem., Int. Ed. 2010, 49, 9765−9768.
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: jcrowley@chemistry.otago.ac.nz. Fax: +64 3 479 7906.
Phone: +64 3 479 7731.
(7) (a) Baschieri, A.; Muzzioli, S.; Fiorini, V.; Matteucci, E.; Massi,
M.; Sambri, L.; Stagni, S. Organometallics 2014, 33, 6154−6164.
(b) Clede, S.; Lambert, F.; Saint-Fort, R.; Plamont, M.-A.; Bertrand,
H.; Vessieres, A.; Policar, C. Chem.−Eur. J. 2014, 20, 8714−8722.
(c) Deepthi, S. B.; Trivedi, R.; Giribabu, L.; Sujitha, P.; Kumar, C. G.
Inorg. Chim. Acta 2014, 416, 164−170. (d) Garcia, L.; Franzoni, S.;
Mussi, F.; Aumont-Nicaise, M.; Bertrand, H.; Desmadril, M.; Pelosi,
G.; Buschini, A.; Policar, C. J. Inorg. Biochem. 2014, 135, 40−44.
(e) Yano, S.; Ohi, H.; Ashizaki, M.; Obata, M.; Mikata, Y.; Tanaka, R.;
Nishioka, T.; Kinoshita, I.; Sugai, Y.; Okura, I.; Ogura, S.-i.;
Czaplewska, J. A.; Gottschaldt, M.; Schubert, U. S.; Funabiki, T.;
Morimoto, K.; Nakai, M. Chem. Biodiversity 2012, 9, 1903−1915.
(f) Deepthi, S. B.; Trivedi, R.; Sujitha, P.; Kumar, C. G.; Sridhar, B.;
Bhargava, S. K. J. Chem. Sci. 2012, 124, 1405−1413. (g) Francois, A.;
Auzanneau, C.; Le Morvan, V.; Galaup, C.; Godfrey, H. S.; Marty, L.;
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Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Department of Chemistry,
University of Otago. W.K.C.L., J.R.C., and G.S.H. thank the
University of Otago for doctoral scholarships. C.J.M. thanks the
NZ Ministry of Business, Innovation and Employment Science
Investment Fund (Grant no. UOOX1206), for financial
support.
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DOI: 10.1021/ic502557w
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