Electronic Communication in Luminescent Dicyanorhenate-Bridged Homotrinuclear Rhenium(I) Complexes

Article abstract of DOI:10.1021/acs.inorgchem.9b00072

A series of cyano-bridged homotrinuclear Re(I) complexes with the general formula of {[Re]′[Re][Re]′}⁺ {[Re]′ = -[Re^I(CO)₂(LL)(X)]; [Re] = -[(NC)Re^I(CO)₂(phen)(CN)]-; LL = diimine, diphosphine, or two carbonyl ligands; X = triphenylphosphine or carbonyl ligand} and the corresponding mononuclear complex analogues were synthesized. The structures of most of the trinuclear Re(I) complexes have been determined by X-ray crystallography. The relative orientations of peripheral to central Re(I) units in these structures vary considerably. The photophysical properties of these trinuclear Re(I) complexes have been examined. Except for the trinuclear Re(I) complex with Br₂phen ligand, all the other triads display orange to red photoluminescence derived from the ³MLCT [dπ(Re) → π?(phen)] origin of the central Re(I) unit, suggestive of efficient energy transfer between the peripheral chromophores and the central unit. In addition to the efficient energy transfer processes between the Re(I) chromophores in these trinuclear complexes, the ability of the [NC-Re-CN] bridging ligands for electronic coupling between the rhenium metal centers is evidenced by ca. 0.2-0.3 V separation of the two rhenium metal-based oxidation potentials of the chemically equivalent peripheral units.

Full text of DOI:10.1021/acs.inorgchem.9b00072

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Electronic Communication in Luminescent Dicyanorhenate-Bridged
Homotrinuclear Rhenium(I) Complexes
Yelan Xiao,#,† Apple Wai-Yi Cheung,#,† Sze-Wing Lai,† Shun-Cheung Cheng,† Shek-Man Yiu,†
Chi-Fai Leung,‡ and Chi-Chiu Ko*,†
†Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China
‡Department of Science and Environmental Studies, The Education University of Hong Kong, 10 Lo Ping Road, Tai Po, N. T.,
Hong Kong, China
S
* Supporting Information
ABSTRACT: A series of cyano-bridged homotrinuclear Re(I) complexes
with the general formula of {[Re]′[Re][Re]′}+ {[Re]′ = −[ReI(CO)2(LL)-
(X)]; [Re] = −[(NC)ReI(CO)2(phen)(CN)]−; LL = diimine, diphosphine,
or two carbonyl ligands; X = triphenylphosphine or carbonyl ligand} and the
corresponding mononuclear complex analogues were synthesized. The
structures of most of the trinuclear Re(I) complexes have been determined
by X-ray crystallography. The relative orientations of peripheral to central
Re(I) units in these structures vary considerably. The photophysical
properties of these trinuclear Re(I) complexes have been examined. Except
for the trinuclear Re(I) complex with Br2phen ligand, all the other triads
display orange to red photoluminescence derived from the 3MLCT [dπ(Re)
→ π*(phen)] origin of the central Re(I) unit, suggestive of efficient energy
transfer between the peripheral chromophores and the central unit. In addition to the efficient energy transfer processes
between the Re(I) chromophores in these trinuclear complexes, the ability of the [NC−Re−CN] bridging ligands for electronic
coupling between the rhenium metal centers is evidenced by ca. 0.2−0.3 V separation of the two rhenium metal-based oxidation
potentials of the chemically equivalent peripheral units.
luminophores are less common,15 although there are reports
INTRODUCTION
■
of the heterotrinuclear Re(I)−Ru(II) system, [(CO)3(bpy)-
Cyano-bridged polynuclear transition metal complexes have
attracted intensive research efforts in the past few decades. On
the basis of the rich coordination chemistry of the cyanide
Re(μ-NC)Ru(bpy)2(μ-CN)Re(bpy)(CO)3]2+,15a with an effi-
cient intramolecular energy transfer process and the cyano-
bridged pentanuclear Re(I)−Ru(II) complex, [(phen)-
ligand (−:CN:) and its ambidentate nature, which enable
(CO)3Re(CN)[Ru(bpy)2(CN)]3Ru(bpy)2(CN)]4+, capable
construction of polynuclear complexes of different polynu-
of functioning as antenna-sensitizer system.16 While cyano-
clearity,1 geometries,2 and/or dimensionality,3 a large number
bridged homotrinuclear Ru(II) complexes with effective
of cyano-bridged polynuclear transition metal complexes have
been exploited for diverse applications such as molecular
metal−metal electronic coupling have been recently reported
by Pieslinger et al.,17 the corresponding study of cyano-bridged
devices,4 molecular sieves,3d,e,5 nanoparticles,6 and ion
sensors.7 In contrast, cyano-bridged polynuclear species are
homonuclear Re(I) complexes has only been confined to the
dinuclear one15a owing to the lack of synthetic methodology
also ideal candidates for the study of photoinduced intra-
molecular electron and energy-transfer processes.8 Through
for dicyano Re(I) diimine complexes.
spectroscopic, electrochemical,9 and time-resolved spectro-
On the basis of our recent work on dicarbonyl
scopic studies10 of these complexes, we gain a fundamental
understanding useful for the design of functional polynuclear
complexes with applications in many different areas such as
dicyanorhenate diimine complexes, cis,trans-[Re-
(CO)2(CN)2(N−N)],18 we herein describe the syntheses
and study of a new series of cyano-bridged triads with general
formula of {[Re]′[Re][Re]′}+ {[Re]′ = −[ReI(CO)2(LL)(X)];
[Re] = −[(NC)ReI(phen)(CO)2(CN)]−; LL = diimine,
diphosphine or two carbonyl ligands; X = triphenylphosphine
or carbonyl ligand}. Through photophysical and electro-
chemical properties, the electronic coupling and communica-
tion in these trinuclear complexes have been investigated.
photocatalysis,11 electrocatalysis,12 and antenna systems.13
Cyano Ru(II) polypyridine complexes represent the most
popular building blocks for the construction of photoactive
cyano-bridged polynuclear complexes.8e,9b,14 Selected examples
include the use of trinuclear Ru(II) complexes cis-[(CN)-
(bpy)2Ru−CN−Ru(LL)2−NC−Ru(bpy)2(CN)]n (bpy = 2,2′-
bipyridine, LL = 4,4′-dicarboxy-2,2′-bipyridine) as photo-
sensitizers in TiO2-based photovoltaic cells.13a,b In contrast,
photoactive cyano-bridged complexes comprising Re(I)
Received: January 9, 2019
© XXXX American Chemical Society
A
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RESULTS AND DISCUSSION
Scheme 2. Synthetic Routes for Trinuclear Re(I) Complexes
1−7
■
Synthesis and Characterization. cis,trans-[Re-
(CO)2(CN)2(phen)](nBu4N) (P1) was prepared by photo-
ligand substitution reaction of [Re(CO)3(phen)(CN)]19 with
a 1000-fold excess of cyanide according to the synthetic
procedures previously reported by us.18 When a smaller
amount of cyanide (100-fold excess) was used in the
photoreaction, a mixture of P1 and cis,cis-isomer (P2) was
formed (Scheme 1a). These isomers can be separated by
Scheme 1. Synthetic Routes for Synthetic Precursors for
Trinuclear Re(I) Complexes
P1 and P2. Although the two peripheral complex units in the
crystal structures of 2−6 are unsymmetrical (see below), the
bidentate ligands on these peripheral units only give rise to one
set of H NMR signals. This is due to the free rotation of the
peripheral units in the solution state, while for 5, since the
column chromatography on silica gel. To synthesize the
trinuclear Re(I) complexes bridged by these metalloligands,
[Re(CO)2(CN)2(N−N)]− (P1 and P2), precursor complexes
with labile acetonitrile (MeCN) or triflate (OTf−) ligand,
cis,trans-[Re(CO)2(PPh3)(N−N)(MeCN)](OTf)20 [N−N =
Me2bpy (M1), phen (M2), and Br2phen (M3)] (Scheme 1b),
1
peripheral complex moieties do not contain any proton, only
1
one set of H NMR signals for the phen ligand of the central
unit, which is downfield-shifted compared to P1, is observed.
The cis, trans- and cis, cis-isomerism of [Re-
(CO)2(CN)2(phen)]− of P1 and P2 or in the central bridging
metalloligand unit of the trinuclear complexes can be readily
distinguished by the symmetrical and unsymmetrical 1H NMR
signals of their phen ligand.
fac-[Re(CO)3 (dppe)(OTf)]2 1 [dppe
= 1,2-bis-
(diphenylphosphino)ethane] and [Re(CO)5(OTf)]22 were
prepared according to reported procedures for structurally
related complexes. The reactions of 2.3 mol equiv of these
complexes with P1 or P2 gave the target trinuclear Re(I)
complexes (Scheme 2): trans-[(PPh3)(N−N)(CO)2ReI(μ-
NC)ReI(CO)2(phen)(μ-CN)ReI(CO)2(N−N)(PPh3)]+ (N−
N = Me2bpy: 1; N−N = phen: 2; N−N = Br2phen: 3), trans-
[(dppe)(CO)3 ReI (μ-NC)ReI (CO)2 (phen)(μ-CN)-
ReI (CO)3 (dppe)]+ (4), trans-[(CO)5 ReI(μ-NC)-
ReI(CO)2(phen)(μ-CN)ReI(CO)5]+ (5), and trans- and cis-
[(phen)(CO)3 ReI (μ-NC)ReI (CO)2 (phen)(μ-CN)-
ReI(CO)3(phen)]+ (6 and 7, respectively). These ligand
substitution reactions were carried out at 50 °C for acetonitrile
complexes and 30 °C for triflate complexes. Purification of
these trinuclear complexes can be achieved by column
chromatography, and the excess tetra-n-butyl ammonium
salts from these reactions can be removed by washing the
dichloromethane solution of the complexes with copious
amounts of water.
All trinuclear Re(I) complexes (1−7) exhibit 2−3 CO
stretches and 1 or 2 active CN stretches in their IR spectra.
For the monomeric complexes M1−M3 with the general
formula of [Re(PPh3)(CO)2(MeCN)(N−N)]+, they can be
characterized by two CO stretches. For complexes 1−7,
these complexes display CN stretches of bridging cyanide
ligands in the range of 2083−2130 cm−1, which are ca. 22−34
cm−1 higher than those of the terminal cyanides of P1 and P2.
This is due to the kinematic coupling, where the CN motion is
constrained by the presence of the second metal center,23 that
leads to higher stretching frequency of the bridging cyanide
ligands.24 Concerning the CO stretches in the trinuclear
complexes, the carbonyl ligands in each Re(I) complex moiety
should exhibit 2 or 3 IR active stretches; therefore, the
trinuclear complexes are expected to show a number of CO
stretches. However, only two to three board IR stretches at
1844−2039 cm−1 were observed in their IR spectra. This is
probably due to the significant overlapping of the IR active
CO stretches as the stretching frequencies of these carbonyl
ligands are expected to be similar. In addition, the
The identities of all of the complexes were confirmed by the
1H NMR spectroscopy, IR spectroscopy, ESI mass spectrom-
etry, and elemental analyses. The structures of trinuclear
complexes 2−6 have also been determined by X-ray
crystallography.
NMR and IR Spectroscopy. Except for 5, all trinuclear
complexes show an integral proton ratio of bidentate ligands of
peripheral units to that of phen ligand of central unit of 2:1,
confirming the coordination of two peripheral Re(I) complexes
with both cyano ligands of the central bridging metalloligands,
−
hexafluorophosphate (PF6 ) anions in 1−5 are characterized
by ν(P−F) at 841−843 cm−1.
X-ray Crystal Structure Determination. The crystal
structures of trinuclear complexes 2−6 were determined by X-
ray crystallography. The perspective drawings of the complex
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cations with atomic numbering are displayed in Figure 1. The
crystal and structure determination data are tabulated in Table
S1, while the selected bond angles and distances are collected
in Table S2. As revealed from the crystal structures, trinuclear
complexes 2−6 show considerable variation in the relative
orientation of the peripheral units to the central Re(I) moiety.
With reference to the plane of the bidentate ligand and two
carbonyl ligands of central unit, the orientation of the central
unit of 2 is rotated 90 and 180° relative to the two peripheral
moieties, and the orientations of the two symmetrical
peripheral moieties are related by a 90° rotation. For 3, the
orientation of central unit is 90° relative to both peripheral
moieties, and the two symmetrical peripheral moieties are in
the same ligand orientation. For 4, the orientation of central
unit is rotated 90 and 0° relative to the two peripheral
moieties, and the orientations of the two symmetrical
peripheral moieties are related by a 90° rotation. For 5, the
orientation of the two symmetrical peripheral moieties is
related by a ca. 20° rotation. For 6, the orientation of central
unit is ca. 90° relative to both peripheral moieties, and the
orientations of the two symmetrical peripheral moieties are
related by a 180° rotation.
Except for 5, the rhenium metal centers of all these
structures adopted a distorted octahedral geometry as a result
of steric requirements of the bidentate ligands. The values of
the bite angles of the bidentate diimine and diphosphine
ligands are in the ranges of 74.8−76.3° and 80.6−81.7°,
respectively, which are common in other related rhenium
complexes bearing diimine and diphosphine ligands.25 Owing
to the lower rigidity of the diphosphine ligand relative to that
of other diimine ligands, the bite angle of diphosphine ligand
in 4 is larger compared to those of the diimine ligands in other
structures. The bending of cyanides in Re−CN−Re (averaged
bond angles of CN−Re and Re−CN) are in the range of
171.9−175.3°. This slight bending can be attributed to the π-
back-bonding interactions of cyanide ligands with both the
peripheral and central rhenium centers. The bond lengths of
CN, Re−CN, and Re−CO, in the ranges of 1.12−1.16 Å,
2.07−2.10 Å, and 1.88−2.05 Å, respectively, are in the typical
ranges reported in tricarbonyl rhenium and cyano rhenium
complexes.18,19,25b,c
UV−Vis Spectroscopy. The electronic absorption proper-
ties of complexes 1−7 and M1−M3 in CH2Cl2 solution have
been investigated. Their UV−vis absorption spectra are shown
in Figure 2, and the absorption data are summarized in Table
1. All of these complexes exhibit intense absorption,
corresponding to the spin allowed intraligand (IL) π → π*
transitions of the PPh3 and/or diimine moieties, in the UV
region of 248−381 nm with molar extinction coefficients on
the order of 104 dm3 mol−1 cm−1. Apart from the ligand-
centered transitions, an additional moderately intense
absorption band (ε > 103 dm3 mol−1 cm−1) was found in
the lower energy visible region in the absorption spectra. With
reference to the spectroscopic studies of related Re(I)
complexes,26 this lowest-energy absorption band, with
absorption maxima ranging from 405 to 475 nm, is assigned
to the 3MLCT [dπ(Re) → π*(N−N)] transitions. For
trinuclear complexes 1−3, 6, and 7, owing to the similar
transition energy of MLCT [dπ(Re) → π*(N−N)]
chromophores in both peripheral and central units, the
lowest-energy absorption band is assigned as a mixture of
two different MLCT [dπ(Re) → π*(N−N)] transitions.
Consequently, the absorption maxima of each type of MLCT
transitions are difficult to determine accurately. Furthermore,
the broader absorption bands, together with the almost
doubled extinction coefficient of 1−3 in comparison with
those of corresponding mononuclear complexes (M1−M3;
Figure 2a), are supportive of the assignment of admixture of
the MLCT transitions from peripheral and central Re(I)
Figure 1. Perspective drawing of the complex cation of (a) 2, (b) 3,
(c) 4, (d) 5, and (e) 6 with the atomic numbering. Hydrogen atoms
have been omitted for clarity. Thermal ellipsoids are shown at the
30% probability level.
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the electronic absorption properties of complexes 6 and 7
(Figure 2c).
For mononuclear complexes M1−M3, the lowest MLCT
[dπ(Re) → π*(N−N)] absorption energy decreases on
passing from a weaker π-accepting diimine ligand to a stronger
one, as reflected by the absorption maxima trend: M1 (405
nm) < M2 (407 nm) < M3 (431 nm). This can be rationalized
by the lower-lying π* orbital in the better π-accepting diimine
ligand, which therefore gives rise to a smaller MLCT energy
gap.
Emission Spectroscopy. With the exception of trinuclear
complex 3, all Re(I) complexes 1−7 and M1−M3 display
orange to red luminescence in CH2Cl2 solution at room
temperature upon photoexcitation (λ ≥ 350 nm). The
emission maxima of mononuclear complexes M1−M3 are in
the region of 618−660 nm, whereas those of trinuclear
complexes 1, 2, and 4−7 (Figure 3) are in the range of 650−
752 nm (Table 2).
Figure 2. Overlaid UV−vis absorption spectra of (a) M1−M3 and 1−
3, (b) 4 and 5, and (c) 6 and 7 in dichloromethane solution at 298 K.
Table 1. UV−Vis Absorption Data for 1−7 and M1−M3
complex
absorption, λabs/nm (ε/dm3 mol−1 cm−1
)
1
2
3
4
5
6
269 (54790), 292 (42470), 340 (18300), 469 (6820)
267 (69760), 295 sh (33045), 336 (15500), 470 (7575)
271(74610), 320 sh (22235), 344 sh (15025), 475 (8380)
268 (46170), 294 sh (19615), 333 sh (7250), 459 (3785)
268 (48650), 292 sh (19240), 319 sh (10230), 427 (4825)
267 (84200), 284 sh (44555), 313 sh (16085), 446 (5380)
267 (76385), 284 sh (42085), 312 sh (14885), 381 sh (7130),
471 (3610)
259 sh (16985), 275 (16560), 297 (20000), 405 (3590)
267 (31015), 296 sh (14170), 321 sh (4360), 407 (4930)
248 sh (31410), 281 (29160),305 sh (13760), 322 sh (7785),
431 (5160)
7
Figure 3. Overlaid normalized emission spectra of (a) mononuclear
complexes and (b) trinuclear Re(I) complexes in CH2Cl2 solution at
298 K.
M1
M2
M3
For the mononuclear complexes, the emission energy [M1
(618 nm) > M2 (625 nm) > M3 (660 nm)] (Figure 3a) is
inversely related to the π-accepting ability of the diimine
ligands: Br2phen > phen > Me2bpy. On the basis of the
sensitivity of emission energy to the electronic properties of
the diimine ligands as well as previous spectroscopic studies,
moieties. As the peripheral units in trinuclear complexes 4 and
5 do not possess any π-accepting diimine ligands, the
extinction coefficient of their lowest energy MLCT [dπ(Re)
→ π*(phen)] absorption bands resembles that of cis,trans-
[Re(CO)2(CN)2(phen)]−.18 The MLCT absorption energy of
5 (427 nm) is higher than that of 4 (459 nm) (Figure 2b).
This can be explained by the stronger electron-withdrawing
peripheral rhenium moieties [Re(CO)5]+ in 5, which render
the dπ(Re) orbital of central Re(I) unit more stabilized and
thus lead to a higher MLCT energy. The MLCT assignment is
consistent with the DFT calculations on selected complexes (2,
5, and 6), in which their HOMOs are mainly dπ(Re) orbital in
character and LUMOs are π* orbital of the phenanthroline
ligands (Table S3). Concerning the effect of the trans and cis
configurations of the two cyanide bridging ligands of the
central metalloligand, no obvious difference is noted between
3
these emissions are assigned to be derived from the MLCT
[dπ(Re) → π*(N−N)] excited state. The lower MLCT
emission energy in complexes with better π-accepting diimine
ligands can be attributed to the smaller MLCT energy gap as a
result of the lower-lying π*(N−N) orbital.
With reference to previous spectroscopic studies on related
Re(I) phenanthroline complexes,18,27 the emissions of
trinuclear complexes 4 and 5 (Figure 3b) are assigned as
MLCT [dπ(Re) → π*(phen)] phosphorescence. Due to the
nonemissive behavior of the peripheral rhenium moieties in 4
and 5, these emissions are ascribed to that of the central Re(I)
luminophore. The emission of 5 (650 nm) is blue-shifted as
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one Re(I) luminophore, only the MLCT phosphorescence of
the central unit with the lowest MLCT energy is observed in
the solution state at room temperature as well as in the glassy
state at low temperature. This suggests that the intramolecular
energy transfer processes between different Re(I) lumino-
phores are very efficient (Figure 4). The lower MLCT energy
Table 2. Emission Data for 1−7 and M1−M3
medium
(T/K)
emission, λem/nm
(τo/μs)
quantum yield,
a
complex
Φem × 102
CH2Cl2 (298)
glass (77)
752 (0.066)
625 (0.67)
752 (0.056)
635 (0.757)
c
0.30
1
b
CH2Cl2 (298)
0.71
c
2
b
glass (77)
CH2Cl2 (298)
3
b
glass (77)
CH2Cl2 (298)
glass (77)
679 (0.044)
600 (1.29)
650 (0.101)
590 (1.65)
696 (0.024)
612 (1.09)
681 (0.053)
615 (2.26)
618 (0.043)
553 (2.71)
625 (0.105)
556 (6.31)
660 (0.075)
580 (3.29)
1.32
7.32
0.78
0.91
3.04
5.40
4.11
4
b
CH2Cl2 (298)
5
b
glass (77)
CH2Cl2 (298)
6
b
glass (77)
CH2Cl2 (298)
7
b
glass (77)
CH2Cl2 (298)
M1
M2
M3
b
Figure 4. Schematic diagram showing the energy transfer process
between different MLCT luminophores.
glass (77)
CH2Cl2 (298)
b
glass (77)
of the central luminophore compared to those of peripheral
luminophores has also been confirmed by DFT calculations
(Figures 5 and S2, Table S3). Likewise, the emissions of the
CH2Cl2 (298)
b
glass (77)
a
Measured with 436 nm excitation using [Ru(bpy)3]Cl2 as the
b
c
reference. EtOH/MeOH = 4:1 (v/v). Nonemissive or not
detectable.
compared to that of 4 (679 nm). The higher emission energy
in 5 with the stronger electron-withdrawing peripheral
rhenium moieties [Re(CO)5]+ is consistent with the MLCT
[dπ(Re) → π*(phen)] excited state assignment, while for
trinuclear complexes 1, 2, 6, and 7, which consist of two
different MLCT luminophores, the emissions are also assigned
to be derived from the 3MLCT [dπ(Re) → π*(phen)] excited
state of the central luminophore. The assignment was done
based on the following considerations: (1) significant red-
shifted emission energies relative to that of corresponding
mononuclear analogues [1 (∼752 nm) vs M1 (∼618 nm); 2
(∼752 nm) vs M2 (∼625 nm); 6 (∼696 nm) and 7 (∼681
nm) vs [Re(CO)3(phen)(MeCN)]+ (532 nm)];28 (2)
insensitivity of emission maxima to the change in diimine
ligands [1 (∼752 nm) ≈ 2 (∼752 nm)] on the peripheral
units; (3) sensitivity of the geometrical isomerism of 6 and 7;
and (4) lower emission energies than that of 5 (Figure 3),
which is in line with the weaker electron-withdrawing
peripheral Re(I) complex units. In contrast to other trinuclear
complexes, the solution of 3 at room temperature is
nonemissive or very weakly emissive, which is not detectable.
Compared to 1 and 2, which show weak and low-energy
emission in the NIR region (peaking at 752 nm), the presence
of the electron-withdrawing bromo substituents in 3 would
Figure 5. Computed MO energies and the contour surfaces of
HOMO−4 to LUMO+3 of 6.
mononuclear components are also assigned as derived from the
3MLCT [dπ(Re) → π*(N−N)] excited state origin. The
observed emission lifetimes in the microsecond range further
support the phosphorescence assignment.
Electrochemistry. The electrochemical properties of
trinuclear Re(I) complexes 1−7 were studied by cyclic
3
n
render the MLCT state lower in energy, resulting in more
voltammetry in acetonitrile (0.1 mol dm−3 in Bu4NPF6).
efficient nonradiative thermal deactivation.
Except for 5, all trinuclear Re(I) complexes 1−7 display three
quasi-reversible oxidation couples (Table 3). The representa-
tive cyclic voltammograms of 6 are shown in Figure 6. To gain
insight into these oxidation processes, controlled-potential
coulometry of 6 by electrolysis at potentials (+0.1 V above
each oxidative wave) was performed, which showed that each
oxidation is a one-electron process. With reference to previous
electrochemical study,26a,30 all the Re(I) complex analogues
would undergo irreversible or quasi-reversible metal-centered
Re(I/II) oxidation at similar potentials. Therefore, these
These complexes also emit in EtOH/MeOH (4:1 v/v)
glassy medium at 77 K. These emissions are blue-shifted
relative to those of the solution state due to the “luminescence
rigidochromism”, which is typically found in other related
systems (Table 2, Figure S1).29 On the basis of the similar
emission energy trend, the emissions of trinuclear complexes 1,
2, and 4−7 at 77 K are also assigned as MLCT [dπ(Re) →
π*(phen)] phosphorescence of the central unit. Although
some of these trinuclear Re(I) complexes contain more than
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oxidations of the two peripheral rhenium units. These
assignments are further supported by the higher sensitivity of
the second and third oxidation potentials to the change in
bidentate and the ancillary ligands on peripheral units. The
splitting of the peripheral metal-centered oxidation potentials
of ca. 0.2−0.3 V was observed, suggesting significant metal−
metal electronic communication through the NC−Re−C
N bridge. The 200−300 mV difference between the two
oxidation potentials is comparable to that of many related
trimetallic cyano-bridged complexes with effective electronic
mixing.14c,17
In the reductive scan, due to the significant mixing and
overlapping of reductions from different moieties in trinuclear
complexes 1−7, only the first reduction potential was
determined. This reduction is ascribed to the diimine ligand-
based reduction (the peripheral complex moiety for 1−3, 6,
and 7 and the central complex unit for 4 and 5), as commonly
found in other Re(I) diimine complexes.26,27
Table 3. Electrochemical Data for 1−7 and M1−M3 in
a
n
CH3CN Solution (0.1 M Bu4NPF6) at 298 K
oxidation [E1/2/V vs SCE (Epa/ reduction [E1/2/V vs SCE (Epc/
b
b
complex
V vs SCE)]
V vs SCE)]
cd
,
1
2
3
4
5
6
7
0.71, 0.97, 1.19
0.68, 0.92, 1.17
0.73, 1.01, 1.25
0.87, 1.54, (2.09)
0.92, (1.75)
0.90, 1.39, 1.75
(−1.68)
−1.52
(−1.21)
−1.54
d
cd
,
c
c
cd
,
(−1.42)
d
−1.30
d
0.83, 1.41, 1.74
−1.33
P1
M1
M2
M3
0.43
1.17
1.20
1.23
−1.64
c
c
c
c
(−1.60), (−1.80), (−2.20)
(−1.42), (−1.61), (−1.97)
(−1.29)
c
c
e
a
b
Working electrode, glassy carbon; scan rate, 100 mVs−1. E1/2 is (Epa
+ Epc)/2; Epa and Epc are peak anodic and peak cathodic potentials,
respectively. Irreversible wave. Reduction potentials at more
cathodic region were not determined due to the significant mixing
and overlapping of reductions of various moieties, including the
ligand-based reductions and metal-centered reductions of the
c
d
CONCLUSION
■
The first series of cyano-bridged homotrinuclear Re(I)
complexes and their corresponding mononuclear analogues
have been synthesized. The structures of most of the trinuclear
complexes have been characterized by X-ray crystallography
and show different relative orientations of the peripheral to the
central Re(I) units. With the exception of 3, which is
nonemissive, all trinuclear Re(I) complexes exhibit orange to
red MLCT [dπ(Re) → π*(N−N)] phosphorescence in
dichloromethane solution at room temperature and in 77 K
e
peripheral and central rhenium moieties. Only one irreversible
reduction wave was determined, as it shows significant decomposition
on scanning to more negative potential.
3
glassy medium. This is ascribed to the MLCT [dπ(Re) →
π*(phen)] excited state origin of the central Re(I) unit. The
observation of the phosphorescence from the central Re(I)
luminophore is suggestive of efficient energy transfer process
between the peripheral and central Re(I) units. Detailed
electrochemical studies on these complexes revealed that all
trinuclear complexes generally exhibit three oxidation couples
and/or waves. The first oxidation couple is ascribed to the
oxidation of Re(I) to Re(II) of the central unit, whereas the
remaining two oxidation peaks are corresponding to the Re(I/
II) oxidation of the two peripheral units. The splitting of the
two oxidation waves of the chemically equivalent peripheral
rhenium metal centers with ΔE1/2 ≈ 0.2−0.3 V clearly
demonstrated the significant intermetallic electronic commu-
nication across the [NC−Re−CN] bridge in these complexes.
In short, the present study should also offer insights into the
electronic and luminescent properties of the dicyanorhenate
metalloligands and their trinuclear Re(I) complexes. It also
enables the development of Re(I)-based molecular wires and
networks with designed properties.
Figure 6. Cyclic voltammograms of (a) oxidative scan and (b)
reductive scan of 6 in MeCN (0.1 mol dm−3 nBu4NPF6). Scan rate:
100 mVs−1.
EXPERIMENTAL SECTION
■
Materials and Reagents. 1,10-Phenanthroline monohydrate
(phen), 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), triphenylphosphine
(PPh3), silver trifluoromethanesulfonate (AgOTf), and [Re2(CO)10]
were purchased from Strem Chemicals Company and used without
further purification. Trimethyl amine N-oxide dihydrate (Me3NO·
2H2O) and 1,2-bis(diphenylphosphino)ethane (dppe) were obtained
from Aldrich Chemical Co. [Re(CO)5Br] was synthesized from the
reaction between [Re2(CO)10] and bromine according to a literature
procedure.22 5,6-Dibromo-1,10-phenanthroline (Br2phen) was pre-
pared according to previously published procedure.31 cis,trans-
(nBu4N)[Re(CO)2(CN)2(phen)] (P1),22 fac-[Re(CO)3(Me2bpy)-
Br],30a fac-[Re(CO)3(phen)Br],30a fac-[Re(CO)3(dppe)Br],21 and
fac-[Re(CO)3(phen)(PPh3)](CF3SO3)32 were prepared according
oxidations were assigned as metal-centered Re(I/II) oxida-
tions. As the Re(I) metal center of the central moiety is more
electron-rich than those of the peripheral one, the first
oxidation couple is assigned to the Re(I/II) metal-centered
oxidation of the central moiety. Compared to Re(I/II) metal-
centered oxidation of P1, the oxidation potentials of the central
unit in these trinuclear complexes show an anodic shift,
consistent with the decrease of electron richness upon
coordination to two cationic peripheral coordination unit.
The two oxidation couples at more anodic potentials are
attributable to the successive Re(I/II) metal-centered
F
DOI: 10.1021/acs.inorgchem.9b00072
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
to literature procedures with slight modifications. All solvents were of
analytical reagent grade and were used without further purification.
The synthetic routes for the target trinuclear complexes are
summarized in Scheme 1. Unless specified in the procedure, all the
reactions were performed under anhydrous conditions and strictly
inert argon atmosphere using standard Schlenk techniques.
H’s), 7.17−7.23 (m, 13H, phenyl H of PPh3), 7.26−7.29 (m, 2H,
phenyl H of PPh3), 8.12 (d, J = 5.7 Hz, 6,6′-bpy H’s), 8.52 (s, 2H,
3,3′-bpy H’s). ESI-MS: m/z 728 [M]+. IR (KBr disc, ν/cm−1) 1867,
1939 ν(CO). Elemental analyses: Calcd for M1·CH3OH (found)
%: C 47.47 (47.77), H 3.76 (3.93), N 4.61 (4.74).
cis,trans-[Re(CO)2(phen)(PPh3)(MeCN)]CF3SO3 (M2). The title
compound was synthesized according to a previously published
procedure.23
cis,cis-K[Re(CO)2(CN)2(phen)] (P2). The title complex was
prepared from the reaction of fac-[Re(CO)3(phen)(CN)] (50 mg,
0.10 mmol) with KCN (650 mg, 10 mmol) in degassed MeOH/H2O
solution (6:1 v/v) (20 mL). After UV irradiation (λ = 254 nm) for 7
h at room temperature, the solvent was removed under reduced
pressure. The crude product was purified by column chromatography
on silica gel using dichloromethane/acetone/methanol (5:5:1 v/v/v)
as eluent. Yield: 14 mg, 0.03 mmol; 26%. 1H NMR (400 MHz,
CD3OD, 298 K): δ 7.78 (dd, 1H, J = 5.2, 8.2 Hz, 3-phen H’s), 7.96
(dd, 1H, J = 5.2, 8.2 Hz, 8-phen H’s), 8.11 (d, 2H, J = 0.9 Hz, 5,6-
phen H’s), 8.55 (dd, 1H, J = 1.4, 8.2 Hz, 4-phen H’s), 8.68 (dd, 1H, J
= 1.4, 8.2 Hz, 7-phen H’s), 9.64 (dd, 1H, J = 1.4, 5.2 Hz, 2-phen H’s),
9.81 (dd, 1H, J = 1.4, 5.1 Hz, 9-phen’s). ESI-MS: m/z 475 [M]−. IR
(KBr disc, ν/cm−1) 1827, 1905 ν(CO), 2061, 2096 ν(CN).
Elemental analyses: Calcd for P2 (found) %: C 37.42 (37.35), H 1.57
(1.76), N 10.91 (10.89).
cis,trans-[Re(CO)2(Br2phen)(PPh3)(MeCN)](CF3SO3) (M3). The
complex was synthesized according to a procedure similar to that for
M1 except that fac-[Re(CO)3(Br2phen)(PPh3)](CF3SO3) (183 mg,
0.18 mmol) was used in place of fac-[Re(CO)3(Me2bpy)(PPh3)]-
1
(CF3SO3). Yield: 111 mg, 0.11 mmol; 60%. H NMR (400 MHz,
CDCl3, 298 K): δ 2.13 (s, 3H, MeCN), 6.95−7.00 (m, 6H, phenyl H
of PPh3), 7.03−7.07 (m, 6H, phenyl H of PPh3), 7.13−7.15 (m, 3H,
phenyl H of PPh3), 7.54 (dd, 2H, J = 8.6, 5.2 Hz, 3,8-phenyl H’s),
8.77 (dd, 2H, J = 8.6, 1.2 Hz, 4,7-phenyl H’s), 8.80 (d, 2H, J = 5.1 Hz,
2,9-phenyl H’s). ESI-MS: m/z 882 [M]+. IR (KBr disc, ν/cm−1) 1869,
1941 ν(CO). Elemental analyses: Calcd for M3·CHCl3 (found) %:
C 37.53 (37.73), H 2.19 (2.33), N 3.65 (3.81).
[(PPh3)(Me2bpy)(CO)2Re(μ-CN)Re(CO)2(phen)(μ-CN)Re-
(CO)2(Me2bpy)(PPh3)](PF6) (1). A solution of M1 (50 mg, 0.057
mmol) and P1 (17 mg, 0.025 mmol, 0.43 mol equiv) in THF/
methanol (20:1 v/v, 60 mL) was warmed overnight at 50 °C. After
removal of the solvent under reduced pressure, the crude product was
purified by column chromatography on silica gel using dichloro-
methane/methanol (20:1 v/v) as eluent. Subsequent metathesis
reaction with a saturated methanolic ammonium hexafluorophosphate
fac-[Re(CO)3(Br2phen)Br]. Re(CO)5Br (500 mg, 1.23 mmol) was
mixed with Br2phen (500 mg, 1.48 mmol, 1.2 mol equiv) in benzene/
THF solution (1:1 v/v, 30 mL) and heated to reflux for 1 night. After
removal of the solvent under reduced pressure, the residue was
1
washed with petroleum ether. Yield: 331 mg, 0.98 mmol; 80%. H
NMR (400 MHz, CDCl3, 298 K): δ 7.97 (dd, 2H, J = 5.1, 8.6 Hz, 3,8-
phen H’s), 9.02 (dd, 2H, J = 8.5, 1.3 Hz, 4,7-phen H’s), 9.47 (dd, 2H,
J = 5.2, 1.2 Hz, 2,9-phen H’s). IR (KBr disc, ν/cm−1) 1900, 1938,
2024 ν(CO). Elemental analyses: Calcd for fac-[Re-
(CO)3(Br2phen)Br] (found) %: C 26.18 (25.90), H 0.88 (1.01), N
4.07 (4.28).
−
solution gave the target complex as a PF6 salt. The complex was
further purified by slowly diffusing diethyl ether vapor into a
concentrated dichloromethane/chloroform (20:1 v/v) solution of 1
1
to yield red crystalline solid. Yield: 33 mg, 0.017 mmol; 68%. H
NMR (400 MHz, CD3CN, 298 K): δ 2.36 (s, 12H, methyl H’s), 6.61
(d, 4H, J = 5.7 Hz, 5,5′-bpy H’s), 6.99−7.03 (m, 12H, phenyl H of
PPh3), 7.12−7.08 (m, 12H, phenyl H of PPh3), 7.16−7.20 (m, 10H,
3,3′-bpy H’s and phenyl H of PPh3), 7.46 (dd, 2H, J = 5.1, 8.2 Hz,
3,8-phen H’s), 7.78 (d, 4H, J = 5.7 Hz, 6,6′-bpy H’s), 8.04 (s, 2H, 5,6-
phen H’s), 8.40 (d, 2H, J = 8.2 Hz, 4,7-phen H’s), 8.56 (d, 2H, J = 5.1
Hz, 2,9-phenH’s). ESI-MS: m/z 1852 [M]+. IR (KBr disc, ν/cm−1)
842 ν(P−F), 1844, 1923 ν(CO), 2093 ν(CN). Elemental
analyses: Calcd for 1·0.5 CHCl3 (found) %: C 46.87 (46.81), H 3.35
(3.13), N 5.43 (5.20).
fac-[Re(CO)3(Me2bpy)(PPh3)](CF3SO3). A mixture of fac-[Re-
(CO)3(Me2bpy)Br] (250 mg, 0.47 mmol) and AgOTf (144 mg, 0.56
mmol, 1.2 mol equiv) was refluxed in THF solution for 2 h. The
resulting suspension was filtered to remove the precipitated AgBr.
Excess triphenylphosphine ligand (981 mg, 3.76 mmol, 8 mol equiv)
was added, and the reaction was heated to reflux overnight.
Subsequent removal of solvent under reduced pressure and
purification by column chromatography on silica gel using dichloro-
methane/acetone (3:1 v/v) as eluent gave analytically pure product.
1
Yield: 333 mg, 0.39 mmol; 82%. H NMR (400 MHz, CDCl3, 298
[(PPh3)(phen)(CO)2Re(μ-CN)Re(CO)2(phen)(μ-CN)Re-
(CO)2(phen)(PPh3)](PF6) (2). The title complex was synthesized
according to a procedure similar to that for 1 except that M2 (50 mg,
0.057 mmol) was used in place of M1 in the substitution reaction.
Red crystals of 2 were obtained by slow diffusion of diethyl ether
vapor into a concentrated dichloromethane/chloroform (5:1 v/v)
K): δ 2.63 (s, 6H, methyl H’s), 6.95 (d, 2H, J = 5.8 Hz, 5,5′-bpy H’s),
7.13−7.18 (m, 6H, phenyl H of PPh3), 7.28−7.33 (m, 6H, phenyl H
of PPh3), 7.37−7.41 (m, 3H, phenyl H of PPh3), 8.14 (d, 2H, J = 5.8
Hz, 6,6′-bpy H’s), 8.79 (s, 2H, 3,3′-bpy H’s). ESI-MS: m/z 718 [M]+.
IR (KBr disc, ν/cm−1) 1920, 1960, 2039 ν(CO). Elemental
analyses: Calcd for fac-[Re(CO)3(Me2bpy)(PPh3)]CF3SO3·CH2Cl2
(found) %: C 44.21 (44.01), H 3.07 (3.23), N 2.95 (2.73).
1
solution of 2. Yield: 32 mg, 0.016 mmol; 62%. H NMR (400 MHz,
CD3CN, 298 K): δ 6.84−6.88 (m, 12H, phenyl H of PPh3), 6.97−
7.02 (m, 12H, phenyl H of PPh3), 7.08−7.13 (m, 10H, 3,8-
phenperipheral H’s and phenyl H of PPh3), 7.20 (dd, 2H, J = 5.1, 8.1 Hz,
3,8-phencentral H’s), 7.67 (s, 4H, 5,6-phenperipheral H’s), 7.82 (s, 2H, 5,6-
phencentral H’s), 8.07 (d, 4H, J = 8.2 Hz, 4,7-phenperipheral H’s), 8.12 (d,
2H, J = 5.0 Hz, 4,7-phencentral H’s), 8.17 (d, 2H, J = 5.0 Hz, 2,9-
phencentral H’s), 8.30 (d, 4H, J = 5.3 Hz, 2,9-phenperipheral H’s). ESI-
MS: m/z 1844 [M]+. IR (KBr disc, ν/cm−1) 842 ν(P−F), 1846, 1925
ν(CO), 2087 ν(CN). Elemental analyses: Calcd for 2·0.5CHCl3
(found) %: C 47.06 (47.35), H 2.97 (2.48), N 5.45 (5.64).
[(PPh3)(Br2phen)(CO)2Re(μ-CN)Re(CO)2(phen)(μ-CN)Re-
(CO)2(Br2phen)(PPh3)](PF6) (3). The title complex was synthesized
according to a procedure similar to that for 1 except that M3 (59 mg,
0.057 mmol) was used in place of M1 in the substitution reaction.
Column chromatography on silica gel using dichloromethane/acetone
(3:1 v/v) as eluent gave 3 as red crystalline solid. Yield: 40 mg, 0.018
mmol; 70%. 1H NMR (400 MHz, CD3CN, 298 K): δ 6.85−6.90 (m,
12H, phenyl H of PPh3), 6.98−7.02 (m,12H, phenyl H of PPh3),
7.10−7.14 (m, 6H, phenyl H of PPh3), 7.17−7.20 (m, 6H, 3,8-phen
H’s and 3,8-Br2phen H’s), 7.78 (s, 2H, 5,6-phen H’s), 8.15 (d, 2H, J =
8.4 Hz, 4,7-phenH’s), 8.23 (d, 2H, J = 5.4 Hz 2,9-phen H’s), 8.37 (d,
fac-[Re(CO)3(Br2phen)(PPh3)](CF3SO3). The complex was syn-
thesized according to a procedure similar to that for fac-[Re-
(CO)3(Me2bpy)(PPh3)](CF3SO3) except that fac-[Re-
(CO)3(Br2phen)Br] (323 mg, 0.47 mmol) was used in place of fac-
1
[Re(CO)3(Me2bpy)Br]. Yield: 407 mg, 0.40 mmol; 85%. H NMR
(400 MHz, CDCl3, 298 K): δ 6.98−7.02 (m, 6H, phenyl H of PPh3),
7.22−7.26 (m, 6H, phenyl H of PPh3), 7.35−7.38 (m, 3H, phenyl H
of PPh3), 8.04 (dd, J = 5.2, 8.6 Hz,2H, 3,8-Br2phen H’s), 9.01 (d, 2H,
J = 8.5 Hz, 4,7-phenH’s), 9.17 (d, 2H, J = 5.4 Hz, 2,9-phen H’s). ESI-
MS: m/z 1013 [M]+. IR (KBr disc, ν/cm−1) 1919, 1961, 2040 ν(C
O). Elemental analyses: Calcd for fac-[Re(CO)3(Br2phen)(PPh3)]-
CF3SO3 (found) %: C 40.05 (40.26), H 2.08 (2.28), N 2.75 (2.51).
cis,trans-[Re(CO)2(PPh3)(Me2bpy)(MeCN)](CF3SO3) (M1). A
solution of fac-[Re(CO)3(Me2bpy)(PPh3)]CF3SO3 (150 mg, 0.18
mmol) and Me3NO·2H2O (24 mg, 0.21 mmol, 1.2 mol equiv) in
acetonitrile solution was warmed at ca. 80 °C overnight. The residue
was purified by column chromatography on silica gel using
dichloromethane/methanol (20:1 v/v) as eluent. Yield: 110 mg,
0.10 m.mol; 70%. 1H NMR (400 MHz, CDCl3, 298 K): δ 2.24 (s, 3H,
MeCN), 2.67 (s, 6H, methyl H’s), 6.87 (d, 2H, J = 5.8 Hz, 5,5′-bpy
G
DOI: 10.1021/acs.inorgchem.9b00072
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
4H, J = 8.4 Hz, 4,7-Br2phen H’s), 8.42 (d, 4H, J = 4.5 Hz, 2,9-Br2phen
H’s). ESI-MS: m/z 2158 [M]+. IR (KBr disc, ν/cm−1) 843 ν(P−F),
1854, 1930 ν(CO), 2093 ν(CN). Elemental analyses: Calcd for
3·CH3CN (found) %: C 41.88 (41.53), H 2.53 (2.82), N 5.36 (4.98).
[(dppe)(CO)3Re(μ-CN)Re(CO)2(phen)(μ-CN)Re(CO)3(dppe)]-
(PF6) (4). A mixture of [Re(CO)3(dppe)Br] (60 mg, 0.08 mmol) and
AgOTf (25 mg, 0.10 mmol, 1.2 mol equiv) in dichloromethane (30
mL) was stirred under argon at room temperature for 6 h. After
filtration of the resulting suspension to remove the precipitated AgBr,
P1 (25 mg, 0.034 mmol, 0.43 mol equiv) dissolved in methanol was
added. The reaction mixture was then warmed to 30 °C and stirred
overnight. Subsequent metathesis reaction in methanol with a
saturated methanolic solution of ammonium hexafluorophosphate
H’s), 8.56 (dd, 1H, J = 1.4, 8.2 Hz, phen H’s), 8.68 (dd, 1H, 1.4, 8.3
Hz, phen H’s), 8.77 (dt, 2H, 1.4, 6.8 Hz, phen H’s), 8.82 (dd, 1H, J =
1.4, 8.3 Hz, phen H’s), 9.01 (dd, 1H, J = 1.3, 5.1 Hz, phen H’s),
9.06−9.10 Hz, (m, 3H, phen H’s), 9.67 (dd, 1H, 1.4, 5.1 Hz, phen
H’s), 9.71 (dd, 1H, J = 1.4, 5.1 Hz, phen H’s). ESI-MS: m/z 1375
[M]+. IR (KBr disc, ν/cm−1) 1855, 1918, 2026 ν(CO), 2083, 2130
ν(CN). Elemental analyses: Calcd for 7·CHCl3 (found) %: C 35.71
(35.76), H 2.34 (2.02), N 6.66 (6.90).
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b00072.
−
afforded the target complex as a PF6 salt. Analytically pure red
crystals were obtained from slow diffusion of diethyl ether vapor into
a concentrated dichloromethane/ethanol solution of the complexes.
Yield: 40 mg, 0.02 mmol; 60%. 1H NMR (400 MHz, CDCl3, 298 K):
δ 1.79−1.89 (m, 4H, CH2CH2 H’s), 2.33−2.53 (m, 4H, CH2CH2
H’s), 7.08−7.14 (m, 10H, phenyl H of dppe), 7.29−7.82 (m, 32H,
3,8-phen H’s and phenyl H of dppe), 7.95 (s, 2H, 5,6-phen H’s), 8.14
(d, 2H, J = 5.0 Hz, 2,9-phen H’s), 8.27 (d, 2H, J = 8.0 Hz, 4,7-phen
H’s). ESI-MS: m/z 1811 [M]+. IR (KBr disc, ν/cm−1) 841 ν(P−F),
1856, 1923, 2030 ν(CO), 2085 ν(CN). Elemental analyses:
Calcd for 4·C2H5OH (found) %: C 45.39 (45.64), H 3.51 (3.42), N
2.79 (3.07).
Experimental details for physical measurements and
instrumentation, emission spectra of the complexes at 77
K EtOH/MeOH (4:1) glassy medium, calculated
energies and the compositions of the frontier orbitals
of 2, 5, and 6, crystal and structure determination data,
and selected bond lengths and bond angles (PDF)
Accession Codes
CCDC 1868105−1868109 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
[(CO)5Re(μ-CN)Re(CO)2(phen)(μ-CN)Re(CO)5](PF6) (5). The
title complex was synthesized according to a procedure similar to
that for 4 except that [Re(CO)5Br] (32 mg, 0.08 mmol) was used in
place of [Re(CO)3(dppe)Br] in the substitution reaction. Slow
diffusion of diethyl ether vapor into a concentrated dichloromethane
solution gave 5 isolated as orange crystals. Yield: 25 mg, 0.02 mmol;
1
60%. H NMR (400 MHz, CDCl3, 298 K): δ 7.96 (dd, 2H, J = 5.1,
AUTHOR INFORMATION
Corresponding Author
*E-mail: vinccko@cityu.edu.hk. Phone: (+852)-3442-6958.
Fax: (+852)-3442-0522.
■
8.2 Hz, 3,8-phen H’s), 8.18 (s, 2H, 5,6-phen H’s), 8.73 (dd, 2H, J =
1.4, 8.3 Hz, 4,7-phen H’s), 9.41 (dd, 2H, J = 1.3, 5.1 Hz, 2,9-phen
H’s). ESI-MS: m/z 1128 [M]+. IR (KBr disc, ν/cm−1) 843 ν(P−F),
1854, 1929, 2039 ν(CO), 2098 ν(CN). Elemental analyses:
Calcd for 5 (found) %: C 24.32 (24.63), H 1.57 (1.27), N 4.36
(4.66).
ORCID
Shun-Cheung Cheng: 0000-0002-7199-452X
Chi-Fai Leung: 0000-0003-2830-0737
Chi-Chiu Ko: 0000-0002-2426-3206
trans-[(phen)(CO)3Re(μ-CN)Re(CO)2(phen)(μ-CN)Re-
(CO)3(phen)](CF3SO3) (6). P1 (50 mg, 0.09 mmol) and fac-
[Re(CO)3(phen)(OTf)], prepared from the reaction of [Re-
(CO)3(phen)Br] (112 mg, 0.21 mmol) and AgOTf (58 mg, 0.21
mmol), in 30 mL of methanol was vigorously stirred overnight at
room temperature. After removal the solvent under reduced pressure,
crystals of 6 were obtained from slow diffusion of diethyl ether into a
concentrated chloroform/acetonitrile solution of 6. Yield: 55 mg, 0.04
mmol; 37%. 1H NMR (400 MHz, acetone-d, 298 K): δ 7.58 (dd, 2H,
J = 5.0, 8.2 Hz, 3,8-phencentral H’s), 7.81 (dd, 4H, J = 5.1, 8.2 Hz, 3,8-
phenperipheral H’s), 8.12 (s, 4H, 5,6-phenperipheral H’s), 8.26 (s, 2H, 5,6-
phencentral H’s), 8.29 (dd, 2H, J = 1.3, 5.0 Hz, 4,7-phencentral H’s), 8.65
(dd, 2H, J = 1.3, 8.2 Hz, 2,9-phencentral H’s), 8.72 (dd, 4H, J = 1.3, 8.2
Hz, 4,7-phenperipheral H’s), 8.99 (dd, 4H, J = 1.3, 5.1 Hz, 2,9-
phenperipheral H’s). ESI-MS: m/z 1375 [M]+. IR (KBr disc, ν/cm−1)
1850, 1918, 2024 ν(CO), 2092 ν(CN). Elemental analyses,
Elemental analyses: Calcd for 6·0.5CHCl3 (found) %: C 36.65
(36.48), H 2.39 (2.18), N 6.91 (7.18).
Author Contributions
#Y.X. and A.W.-Y.C. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work has been supported by the Hong Kong University
Grants Committee Area of Excellence Scheme (AoE/P-03-08)
and General Research Fund (Project No. CityU 11303515)
from the Research Grants Council of the Hong Kong SAR,
China. Yelan Xiao acknowledges receipt of a University
Postgraduate Studentship administrated by City University of
Hong Kong.
cis-[(phen)(CO)3 Re(μ-CN)Re(CO)2 (phen)(μ-CN)Re-
(CO)3(phen)](CF3SO3) (7). The title complex was synthesized
according to a procedure similar to that for 6 except that P2 was
used in place of P1. The crude product was purified by column
chromatography on silica gel with CHCl3/MeOH (9:1 v/v). Further
purification by recrystallization from slowing diffusion of n-pentane
into a concentrated chloroform solution of 7 gave pure complex as
crystalline solid. Yield: 53 mg, 0.03 mmol; 36%. 1H NMR (400 MHz,
acetone-d, 298 K): δ 7.60 (dd, 1H, J = 2.9, 5.2 Hz, phen H’s), 7.62
(dd, 1H, J = 2.9, 5.2 Hz, phen H’s), 7.89 (dd, 1H, J = 5.1, 8.2 Hz,
phen H’s), 7.94 (dd, 1H, J = 5.1, 8.3 Hz, phen H’s), 8.13 (dd, 1H, J =
1.4, 5.0 Hz, phen H’s), 8.17 (d, 2H, J = 0.5 Hz, phen H’s), 8.19 (d,
2H, J = 1.1 Hz, phen H’s), 8.30 (dd, 1H, J = 4.3, 7.5 Hz, phen H’s),
8.33 (dd, 1H, J = 4.2, 7.5 Hz, phen H’s), 8.37 (d, 2H, J = 1.2 Hz, phen
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