Strongly phosphorescent neutral rhenium(I) isocyanoborato complexes: Synthesis, characterization, and photophysical, electrochemical, and computational studies

Article abstract of DOI:10.1002/chem.201405291

A new series of neutral isocyanoborato rhenium(I) diimine complexes [Re(CO)₃(N∧N)(CNBR₃)], where N∧N=bpy, 4,4′-Me₂bpy, phen, 4,7-Me₂phen, 2,9-Me₂phen, 3,4,7,8-Me₄phen; R=C₆F₅, C₆H₅, Cl, 4-ClC₆H₄, 3,5-(CF₃)₂C₆H₃, with various isocyanoborate and diimine ligands of diverse electronic and steric nature have been synthesized and characterized. The X-ray crystal structures of six complexes have also been determined. These complexes displayed intense bluish green to yellow phosphorescence at room temperature in dichloromethane solution. The photophysical and electrochemical properties of these complexes had been investigated. To elucidate the electronic structures and transitions of these complexes, DFT and TD-DFT calculations have been performed, which revealed that the lowestenergy electronic transition associated with these complexes originates from a mixture of MLCT [dπ(Re)→π?(N∧N)] and LLCT [π(CNBR₃)→π?(N∧N)] transitions.

Full text of DOI:10.1002/chem.201405291

DOI: 10.1002/chem.201405291
Full Paper
&
Phosphorescent Materials
Strongly Phosphorescent Neutral Rhenium(I) Isocyanoborato
Complexes: Synthesis, Characterization, and Photophysical,
Electrochemical, and Computational Studies
Wing-Kin Chu, Xi-Guang Wei, Shek-Man Yiu, Chi-Chiu Ko,* and Kai-Chung Lau*[a]
Abstract: A new series of neutral isocyanoborato rhenium(I)
diimine complexes [Re(CO)3(N^N)(CNBR3)], where N^N=bpy,
4,4’-Me2bpy, phen, 4,7-Me2phen, 2,9-Me2phen, 3,4,7,8-
Me4phen; R=C6F5, C6H5, Cl, 4-ClC6H4, 3,5-(CF3)2C6H3, with
various isocyanoborate and diimine ligands of diverse
electronic and steric nature have been synthesized and
characterized. The X-ray crystal structures of six complexes
have also been determined. These complexes displayed
intense bluish green to yellow phosphorescence at room
temperature in dichloromethane solution. The photophysical
and electrochemical properties of these complexes had
been investigated. To elucidate the electronic structures and
transitions of these complexes, DFT and TD-DFT calculations
have been performed, which revealed that the lowest-
energy electronic transition associated with these complexes
originates from a mixture of MLCT [dp(Re)!p*(N^N)] and
LLCT [p(CNBR3)!p*(N^N)] transitions.
Introduction
a new series of neutral rhenium(I) diimine complexes with vari-
ous isocyanoborate and diimine ligands of diverse electronic
and steric nature.
Phosphorescent materials, and especially the most popular
luminescent PtII and IrIII transition-metal complexes, have been
widely used in the fabrication of organic light-emitting devices
(OLEDs) with outstanding efficiencies.[1] In contrast, despite the
well-known phosphorescence of the tricarbonyl rhenium(I)
diimine complexes[2] and their excellent applications in the
development of photocatalysts,[3] photosensitizers,[4] and lumi-
nescent sensors,[5] applications of these complexes in electro-
luminescent devices are relatively much less investigated.[6]
This is because many of the highly emissive rhenium(I) diimine
complexes are cationic and therefore unable to be processed
by vacuum deposition. Regarding our work on isocyano
rhenium(I) diimine luminophores,[7] we have demonstrated the
use of anionic isocyano tris(pentafluorophenyl)borate ligand in
the development of strongly sky-blue phosphorescent charge-
neutral rhenium(I) complexes, which are stable for vacuum
sublimation and suitable for electroluminescent device applica-
tion.[8] To design phosphorescent materials from these isocya-
noborato complexes, it is crucial to understand their electronic
properties as well as their photophysics. To provide insights
and elucidate these properties and their structural correlation,
herein we report the detailed syntheses, characterizations,
photophysics, electrochemistry, and computational study of
Results and Discussion
Synthesis and characterization
Two different synthetic routes, which started from the
cyano tricarbonyl rhenium(I) diimine precursor complexes,
[Re(CO)3(N^N)CN],[5g,8] were used to prepare the neutral isocya-
noborato rhenium(I) diimine complexes (Scheme 1). Complexes
{Re(CO)3(N^N)[CNB(C6F5)3]} (1a–6a, N^N=diimine ligand) and
[Re(CO)3(phen)(CNBCl3)] (3c) were prepared in moderate yields
from the Lewis acid–base reactions between the cyano precur-
sor complexes with B(C6F5)3 and BCl3, respectively, in dichloro-
[a] W.-K. Chu, X.-G. Wei, Dr. S.-M. Yiu, Dr. C.-C. Ko, Dr. K.-C. Lau
Department of Biology and Chemistry, City University of Hong Kong
Tat Chee Avenue, Kowloon, Hong Kong (P.R. China)
Fax: (+852)3442-0522
E-mail: vinccko@cityu.edu.hk
kaichung@cityu.edu.hk
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405291.
Scheme 1. Synthetic routes to [Re(CO)3(N^N)(CN)] and [Re(-
CO)3(N^N)(CNBR3)].
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methane.[8,9] When the stable tetraphenyl borate salt and its
substituted phenyl derivatives such as NaBPh4, KB(C6H4Cl)4 and
NaB[C6H3(CF3)2]4 are available, the corresponding isocyanobora-
to complexes can be obtained by the reactions of the cyano
precursor complexes with the respective borate salts in acidi-
fied methanolic solution.[10] These reactions are illustrated in
the preparation of [Re(CO)3(N^N)(CNBPh3)] (1b–4b) and
[Re(CO)3(phen)(CNBR3)] [3d: R=C6H4Cl; 3e: R=C6H3(CF3)2].
After recrystallization from the slow evaporation of the concen-
trated dichloromethane solution of the complexes or slow dif-
fusion of diethyl ether vapor into the concentrated dichloro-
methane or acetone solutions of these complexes, analytically
pure complexes were isolated as pale yellow to yellow crystal-
line solids. All of these newly synthesized neutral isocyanobor-
ato rhenium(I) diimine complexes were characterized by 1H
and 19F NMR spectroscopy, IR spectroscopy, and ESI mass spec-
trometry and gave satisfactory elemental analyses. Six of the
complexes were also structurally characterized by X-ray crystal-
lography.
are all slightly deviated from linearity, with CꢁNꢀB angles of
168.3–178.28. This is the result of p-back-bonding interaction
between the rhenium metal center and the isocyanoborate li-
gands.[14] The CꢁN and NꢀB distances are in the range of 1.14–
1.19 ꢁ and 1.54–1.59 ꢁ, respectively, which are in the typical
ranges (CꢁN: 1.132–1.174 ꢁ, NꢀB: 1.548–1.618 ꢁ) reported in
other isocyanoborato transition-metal complexes.[8–10]
UV/Vis absorption and emission properties
The electronic absorption properties of all of the complexes in
CH2Cl2 solution were investigated. The overlaid UV/Vis absorp-
tion spectra of selected complexes are shown in Figure 2a and
the Supporting Information, Figure S1, S2, and the UV/Vis ab-
sorption data are summarized in Table 1. All of the isocyano-
borato complexes exhibited intense ligand-centered (LC) p–p*
absorptions of the diimine and isocyanoborate ligands with
molar absorptivity on the order of 104 dm3 molꢀ1 cmꢀ1 in the
UV region (<320 nm).[2,7] At the lower energy region, these
complexes showed moderately intense transitions with molar
absorptivity on the order of 103 dm3 molꢀ1 cmꢀ1 in the region
of 310–380 nm. With reference to previous spectroscopic stud-
ies on the isocyano carbonyl rhenium(I) diimine complexes,
these absorptions were ascribed to the mixing of the metal-to-
ligand charge transfer (MLCT) transitions of [dp(Re)!p*(N^N)],
[dp(Re)!p*(CNBR3)] and the ligand-to-ligand charge transfer
(LLCT) [p(CNBR3)!p*(N^N)] transition. As the electronic prop-
erties and orbital energy level of isocyanoborate ligands are
not well-studied, computational studies on selected complexes
at the DFT level have been performed to provide in-depth in-
sight into these low-energy electronic transitions and orbitals
of these isocyanoborato rhenium(I) complexes.
IR and NMR spectroscopy
The facial configuration of the carbonyl ligands in these com-
plexes were confirmed by the observation of three carbonyl
stretches[11] in the range of 1900–2040 cmꢀ1 in the IR spectra
1
and one set of H signals for the two pyridyl moieties of the
diimine ligand, indicating the symmetrical chemical environ-
ments of the pyridyl moieties. In general, the CꢁO stretches in
the cyano complexes occurred at lower frequencies than those
in the isocyanoborato complexes. This is due to the competi-
tion of the stronger p-accepting isocyanoborate ligands. In ad-
dition to the carbonyl stretches, all isocyanoborato complexes
were also characterized by one CꢁN stretches ranging from
2176–2210 cmꢀ1, which are in the typical range of the iso-
cyanoborato complexes[8–10] and lower than that observed in
MeCNB(C6F5)3 (2367 cmꢀ1)[12] owing to the p-back-bonding
interaction.
Considering the absorption of the free ligands and as illus-
trated in the calculations, the LC, MLCT, and LLCT transitions
are similar in energy and therefore the peaks of these transi-
tions are not well-resolved and thus cannot be accurately de-
termined in their absorption spectra. Despite significant mixing
of different types of transitions, the assignment of the lowest-
energy absorption of these complexes to the predominant
MLCT [dp(Re)!p*(N^N)] admixed with LLCT [p(CNBR3)!
p*(N^N)] transitions is supported by the absorption energy
dependence on the electronic nature of the diimine ligands,
which is in line with the expected p*-orbital energy level of
the diimine ligands (bpy <4,4’-Me2bpy; phen <2,9-Me2phen
ꢂ4,7-Me2phen <3,4,7,8-Me4phen) for complexes with the
same isocyanoborate ligands (Supporting Information,
Figures S1 and S2). On the other hand, the lowest-energy ab-
sorption energy of all complexes were found to be significantly
blue-shifted compared to their corresponding cyano precursor
complexes [Re(CO)3(N^N)(CN)] and slightly varied with the
electronic properties of the borane moiety (Figure 2a). This is
due to the much lower-lying p*(CNBR3) orbitals, which
rendered better stabilization of dp(Re) orbital (see below in
the computation section and electrochemistry).
X-ray crystal structures
By slow evaporation of the concentrated dichloromethane
solutions of the complexes or slow diffusion of diethyl ether
vapor into the concentrated dichloromethane or acetone solu-
tions of the complexes, single crystals of six of the isocyano-
borato complexes of quality suitable for X-ray crystallographic
structure determination were obtained. Perspective drawings
of these complexes are shown in Figure 1. The structure deter-
mination data and selected bond lengths and angles are sum-
marized in the Supporting Information, Tables S1 and S2, re-
spectively. In all of these structures, the rhenium metal centers
adopted distorted octahedral geometry with the bite angles of
the diimine ligands in the range of 74.5–75.88, which is typical
for diimine transition-metal complexes.[7,13] The ReꢀCO and
ReꢀCNBR3 bond distances are in the range of 1.90–1.97 ꢁ and
2.07–2.12 ꢁ, respectively, which are comparable to those ob-
served in other carbonyl isocyano rhenium(I) complexes.[7b,c,e,14]
For the isocyanoborate ligands in these crystal structures, they
Upon excitation into the lowest-energy absorption (l<
400 nm), these isocyanoborato complexes exhibited long-lived
bluish green to yellow phosphorescence (lem =481–554 nm)
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Figure 1. ORTEP representations of a) 1a, b) 5a, c) 6a, d) 1b, e) 2b, and f) 3d with atom numbering. Hydrogen atoms have been omitted for clarity; ellipsoids
are set at 30% probability.
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Figure 2. Overlaid a) UV/Vis absorption and b) normalized corrected emis-
sion spectra for P3 and 3a–3e in CH2Cl2 solution at room temperature.
Figure 3. Overlaid normalized corrected emission spectra for a) 1a–6a and
b) 1b–4b in CH2Cl2 solution at room temperature.
with quantum yields up to 0.67 in CH2Cl2 solution at room
temperature (Figure 3, Table 1). Their emission bands were
independent of the excitation wavelength and all of the
complexes were photostable even upon prolonged photo-
excitation. With the exception of 4a and 6a, all other isocya-
noborato complexes show structureless emission bands with
similar lifetimes in a microsecond range. The emission energy
not only varied with the nature of diimine ligand (emission
Table 1. Photophysical data for P1–P6, 1a–6a, 1b–4b, and 3c–3e.
[b]
Complex
Medium (T [K])
Emission[a] lem [nm] (to [ms])
fem
Absorption[c] labs [nm] (e [Lmolꢀ1 cmꢀ1])
P1
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
CH2Cl2 (298)
solid (298)
589 (0.28)
548
579 (0.33)
536
577 (2.0)
534
559 (5.6)
557
564 (0.43)
552
544 (12.0)
588
549 (1.4)
507
544 (1.6)
487
538 (6.6)
463, 491, 520
488, 517 (34.5)
474, 508, 542
513 (4.2)
508
481, 510 (37.8)
479, 510, 543
554 (1.0)
520
544 (1.2)
518
549 (4.3)
535
528 (1.2)
524
518 (6.2)
539
0.02
0.55
0.04
0.42
0.12
0.04
0.20
0.07
0.03
0.08
0.21
0.04
0.30
0.84
0.34
0.68
0.54
0.85
0.52
0.23
0.67
0.68
0.50
0.20
0.10
0.20
0.13
0.34
0.32
0.19
0.36
0.06
0.28
0.20
0.34
0.33
0.08
0.75
247 (22770), 252 (22905), 286 (24145), 313 (11565), 373 (5560), 427 sh (1490)
P2
P3
P4
P5
P6
1a
2a
3a
4a
5a
6a
1b
2b
3b
4b
3c
3d
3e
255 (17090), 281 (16255), 310 (8340), 365 (3905), 402 sh (2075)
262 (28550), 289 (12960), 357 (4480), 397 sh (3130)
260 (29250), 281 (15980), 349 (5575), 383 sh (4005)
260 (25665), 274 (21600), 321 sh (6555), 376 sh (3120)
261 (32310), 278 (32255), 291 (20430), 316 sh (9030), 366 sh (5590)
249 (27950), 262 (25625), 306 (14515), 317 (14930), 351 (5330), 377 sh (3520)
253 (38220), 302 (18645), 313 (18680), 341 (7270), 372 sh (4455)
255 (35265), 269 (33920), 273 (33990), 325 (8410), 355 sh (5810)
260 (34675), 266 (32570), 273 (34165), 321 (10010), 350 sh (6660)
251 (22425), 284 (20740), 301 (13485), 319 sh (7460), 349 sh (2470)
249 (44750), 279 (44950), 312 sh (15430), 345 sh (7030)
251 (19400), 286 (16685), 317 (9110), 363 (4160), 393 sh (2755)
255 (22550), 286 (18165), 313 (9955), 357 (4395), 387 sh (2795)
258 (26585), 271 (23835), 286 (15750), 317 sh (4930), 361 sh (3915)
258 (26275), 271 (23525), 332 sh (5840), 357 sh (4530)
253 (24535), 273 (26500), 322 (6660), 351 sh (4200)
534 (4.6)
529
522 (1.6)
483, 503
257 (30255), 268 (28170), 327 sh (6130), 357 sh (5010)
256 (26125), 267 (25860), 273 (25570), 326 (5640), 353 sh (4160)
[a] Excitation at 380 nm. Emission maxima are corrected values. [b] For CH2Cl2 solutions, luminescence quantum yields were measured with excitation at
350 nm using quinine sulfate as a standard; for samples in solid state, absolute luminescence quantum yields were measured with excitation at 350 nm.
[c] In dichloromethane solution at 298 K.
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maxima of 1a–6a, Table 1, Figure 3a) but also showed strong
dependence on the electronic nature of the borane moiety as
reflected by the overlaid emission spectra of 3a–3e (Fig-
ure 2b). It is anticipated that the emission characteristics could
be further tuned through systematic variations of substituents
on the borane. The emissions of these complexes (except 4a
structured emission peak maxima were in the range of
1200–1300 cmꢀ1, which were typical of aromatic C=C and C=N
vibrational modes of bipyridine or phenanthroline ligand.
Electrochemistry
3
and 6a) were assigned to the MLCT [dp(Re)!p*(N^N)] mixed
The electrochemical behaviors of all of the complexes in aceto-
nitrile (0.1m nBu4NPF6) were investigated by cyclic voltam-
metry. The electrochemical data are summarized in Table 2 and
3
with LLCT [p(CNBR3)!p*(N^N)] excited state origin. Compared
with the phosphorescence of cyano complex precursors P1–P6
(Table 1) and [Re(CO)3(bpy)Cl] (lem =622 nm, fem =0.005),[15a]
these isocyanoborato complexes display substantially blue-
shifted emission with much higher quantum efficiency. Among
these complexes, the solution emission of 5a is of the highest
energy. In fact, this emission represents the bluest structureless
MLCT phosphorescence with the highest quantum efficiencies
compared to all other reported neutral tricarbonyl rhenium(I)
diimine complexes with various diimine and anionic ancillary
ligands including Brꢀ, Clꢀ, OTfꢀ, RCꢁCꢀ, RCOOꢀ, NCSꢀ, and
pyrazolide.[2c,k,3c,6b,15] This is even comparable to the highest-
energy MLCT phosphorescent cationic tricarbonyl rhenium(I)
diimine complexes.[16]
Table 2. Electrochemical data for P1–P6, 1a–6a, 1b–4b, and 3c–3e in
acetonitrile solution with 0.1m nBu4NPF6 at 298 K.[a]
Complex
Oxidation,[b] E1/2/V vs. SCE
[DEp/mV][d] (Epa/V vs. SCE)
Reduction,[b] E1/2/V vs. SCE
[DEp/mV][d]
P1
P2
P3
P4
P5
P6
1a
2a
3a
4a
5a
6a
1b
2b
3b
4b
3c
3d
3e
(1.49)[c]
ꢀ1.37 [81][d]
ꢀ1.46 [71][d]
ꢀ1.36 [91][d]
ꢀ1.50 [69][d]
ꢀ1.47 [70][d]
ꢀ1.59 [69][d]
ꢀ1.32 [100][d]
ꢀ1.42 [69][d]
ꢀ1.31 [85][d]
ꢀ1.45 [97][d]
ꢀ1.40 [85][d]
ꢀ1.55 [71][d]
ꢀ1.35 [101][d]
ꢀ1.43 [87][d]
ꢀ1.34 [86][d]
ꢀ1.45 [72][d]
ꢀ1.26 [101][d]
ꢀ1.30 [93][d]
ꢀ1.29 [80][d]
(1.45)[c]
(1.48)[c]
(1.44)[c]
(1.54)[c]
(1.44)[c]
1.75 [103][d]
1.73 [71][d]
1.75 [85][d]
1.72 [81][d]
1.77 [89][d]
1.69 [85][d]
(1.53)[c]
For complexes 4a and 6a, they displayed different emission
profiles with highly structured emission bands and much
longer lifetimes (t0 >34 ms), which suggested different emis-
sion excited state origins. Based on these emission characteris-
3
tics and the close resemblance of these emissions with the LC
(1.47)[c]
phosphorescence of related substituted phenanthroline com-
plexes,[17] their emissions were ascribed to predominant 3LC
phosphorescence. Compared to their cyano precursor com-
plexes, the emissions of the isocyanoborato complexes are
substantially blue-shifted and significant enhanced in terms of
the quantum efficiency (Figure 2b, Table 1). The blue-shift as
well as the improvement on the emission properties of these
complexes were attributed to the very strong p-accepting
properties of the isocyanoborate ligands, leading to effective
stabilization of the dp(Re) orbital as well as raising of the non-
radiative deactivating ligand-field state.
(1.59)[c]
(1.52)[c]
(1.85)[c]
(1.60)[c]
1.75 [87][d]
[a] Working electrode: glassy carbon; scan rate, 100 mVsꢀ1. [b] E1/2 is
(Epa +Epc)/2, where Epa and Epc are the anodic and cathodic peak poten-
tials, respectively. [c] Irreversible oxidation; anodic peak potential (Epa/V
vs. SCE). [d] DEp is jEpaꢀEpc j.
Owing to the rigidochormic effect,[18] the solid-state emis-
sions of most of these isocyanoborato complexes were blue-
shifted relative to their solution emissions. As a consequence,
some of the isocyanoborato complexes are blue-emitting solid
(Supporting Information, Figures S3–S5). Except complexes 3b,
4a, 4b, and 6a, all other isocyanoborato complexes show
higher luminescence quantum yields in the solid state than
those in the CH2Cl2 solution. Similarly, the emissions of these
complexes in 77 K 4:1 (v/v) EtOH/MeOH glassy medium were
also considerably blue-shifted compared to those in CH2Cl2
solution (Supporting Information, Table S3). This is typically ob-
served in MLCT phosphorescent emitters.[7,18] As a result of the
representative cyclic voltammograms of 3a and 3d are shown
in the Supporting Information, Figure S9 and in Figure 4,
respectively. All of the complexes showed the first reduction as
electrochemically quasi-reversible couple with potentials
ranging from ꢀ1.26 V to ꢀ1.59 V vs. SCE. The potentials of
these reductive couples are sensitive to the electron richness
of the diimine ligand (bpy <Me2bpy; phen <Me2phen
3
blue-shifted MLCT excited state in these media, the emissions
of some of these complexes (1a–6a, 3c, 3e, and 4b) changed
from the MLCT/3LLCT to predominant LC excited state. The
changes of their emissive excited state can be characterized by
the observation of highly structured emission bands (Support-
ing Information, Figures S6–S8) and much longer emission
lifetimes (Supporting Information, Table S3). The vibrational
progressional spacings calculated from the well-resolved
3
3
Figure 4. Cyclic voltammograms of the a) oxidative scan and b) reductive
scan of 3d in acetonitrile solution (0.1m nBu4NPF6). Scan rate: 100 mVsꢀ1
.
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<Me4phen) as reflected by the trends: P1> P2; P3> P4ꢂ
P5> P6 for the cyano complexes; 1a> 2a; 3a> 4aꢂ 5a>
6a for the isocyanoborato complexes. On the other hand, the
potentials were relatively insensitive to the electronic effect of
the isocyanoborate ligands as illustrated by the slight variation
of the potentials ranging from ꢀ1.26 V to ꢀ1.34 V vs. SCE for
the phenanthroline complexes (3a–3e) even though the elec-
tronic properties of the isocyanoborate ligands had been
changed drastically. On the basis of these trends, the reduc-
tions were assigned to the diimine-based ligand-centered
reduction.
As with other tricarbonyl rhenium(I) diimine complexes,[2,7]
these complexes also exhibited one irreversible wave or quasi-
reversible oxidative couple with Epa or E1/2 in the range of
+1.44 V to +1.85 V vs. SCE, attributable to ReI/II metal-cen-
tered oxidation. The oxidation potentials not only showed
strong dependence on the p-accepting ability of the ancillary
ligand (cyanide or isocyanoborate ligand) but also slightly
varied with the electronic properties of the diimine ligands.
The variations of the oxidation potentials across the cyano
precursor complexes (P1–P6) are similar to those across the
isocyanoborato complexes (1a–6a), suggesting a similar elect-
ronic effect of the diimine ligand on these oxidations. These
dependences are consistent with the metal-centered oxidation.
dp(Re) orbital, which is due to the much stronger p-accepting
ability of the isocyanoborate ligands (CNBR3) in the isocyano-
borato complexes and the higher-lying of p(CNBR3) orbital
compared with the p(CN) orbital. This explanation can be
illustrated with the calculated MO energy diagrams for these
complexes (Figure 5). The electronic effect of the substituents
on borane moiety on the dp(Re) orbital could be revealed by
orbital energy levels of 3a and P3 (Figure 5).
The singlet excited states in these complexes were also
computed (Supporting Information, Table S6). For the cyano
complex P3, the calculated lowest-energy singlet excited state
was entirely composed of HOMO!LUMO excitation. Based on
the composition of the HOMO and LUMO of P3, it can be as-
signed as predominant MLCT [dp(Re)!p*(phen)] transition.
Several higher-lying singlet excited states of P3 were also de-
rived from the predominant MLCT transitions. For P3, singlet
excited states from different types of transitions were of much
higher-lying in energy. For the isocyanoborato complexes (3a,
3d, 4a, and 6a), their lowest-lying singlet excited states were
of higher energy than that of the cyano complex precursors
(P3). This is consistent with trends in UV/Vis absorption proper-
ties. Unlike P3, two different types of singlet excited states
from MLCT [dp(Re)!p*(phen)], LLCT [p(CNBR3)!p*(phen)],
and also their admixture, can be found in the energetically
similar low-lying singlet excited states. This is supportive of the
assignment of the lowest-energy absorptions of these isocya-
noborato complexes to the mixture of the MLCT and LLCT
transitions.
Electronic structure calculations
To gain better insight into the nature of the rhenium-isocyano-
borate interaction and its effect on the electronic transitions,
DFT, and TD-DFT calculations on selected complexes (P3, 3a,
3d, 4a, and 6a) were performed at the B3LYP level with the 6-
31G* basis set for non-metals and LanL2DZ for Re. The calcu-
lated metal–ligand (M–L), CꢁO, and CꢁN bond distances in the
optimized structures are comparable (within 0.05 ꢁ) to those
found in the X-ray crystal structures (Supporting Information,
Table S4). The calculated frontier molecular orbitals (MOs) for
these complexes have also been examined. The composition
of frontier MOs in these complexes were collected in the Sup-
porting Information, Table S5. The frontier MOs for all of the
isocyanoborato complexes (3a, 3d, 4a, and 6a) were similar in
nature with the very closely lying HOMO to HOMOꢀ5 mainly
composed of the p(CNBR3) orbital with the combination of var-
ious contributions of dp(Re) orbital or predominantly dp(Re)
orbital and the LUMO being the p*(phen) orbital (Supporting
Information, Table S5). In contrast, the calculated frontier orbi-
tals for the cyano complex analogue P3 are less complicated
with the HOMO and HOMOꢀ1 mainly contributed from the
dp(Re) orbital with minor p*(CꢁO) component. These orbitals
were well-separated from other lower-lying orbitals (>0.3 eV
for HOMOꢀ2 and >0.7 eV for HOMOꢀ3). The LUMO and
LUMO+1 of P3 were also composed of the p*(phen) orbital.
These frontier MOs of P3 are similar to those found in previous
computational studies on most tricarbonyl ReI diimine sys-
tems.[11b,19] The spatial plots of selected frontier molecular orbi-
tals of P3 and 3a were shown in Figure 5. The difference be-
tween the frontier MOs of P3 and those of the isocyanoborato
complexes can be attributed to the much more stabilized
Conclusion
A new series of strongly emissive neutral isocyanoborato rhe-
nium(I) diimine complexes, [Re(CO)3(N^N)(CNBR3)], with various
diimine and isocyanoborate ligands have been synthesized
using simple and versatile routes. The detailed spectroscopic
and photophysical properties of these complexes have been
investigated. This work further corroborated our earlier
postulation that the incorporation of the strong p-accepting
isocyanoborate ligands to cationic luminophores is an effective
strategy to develop neutral phosphorescent materials with im-
proved quantum efficiency and blue-shifted emission energy.[8]
It also illustrated the capability of fine-tuning the emission
properties of these complexes through the modifications of
the substituents on isocyanoborate ligands. It is anticipated
that these complexes are also potentially useful for OLED
device applications, as illustrated in our earlier work.[8] Through
the computational studies on selected complexes, the elec-
tronic structures, rhenium-CNBR3 interaction and its effect on
the electronic transitions have been elucidated. This should
provide in-depth insights not only for fundamental under-
standing but also for the future design of isocyanoborato
complexes with desirable properties.
Experimental Section
Materials and reagents: 1,10-Phenanthroline (phen), 4,7-dimethyl-
1,10-phenanthroline (4,7-Me2phen), 2,2’-bipyridine (bpy), 4,4’-di-
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Figure 5. The orbital energy levels and contour maps of the selected molecular orbitals for 3a (left) and P3 (right).
methyl-2,2’-bipyridine (4,4’-Me2bpy), and tris(pentafluoro)phenyl-
borane [B(C6F5)3] were purchased from Acros Organic Chemical
Company. 2,9-Dimethyl-1,10-phenanthroline (2,9-Me2phen), 3,4,7,8-
tetramethyl-1,10-phenanthroline (3,4,7,8-Me4phen), and sodium tet-
raphenylborate (NaBPh4) were purchased from Meryer Chemical
Company. Potassium tetrakis(4-chlorophenyl)borate [KB(C6H4Cl)4]
mental analyses were performed on an Elementar Vario MICRO
Cube elemental analyzer. IR spectra of the solid samples as KBr
discs were recorded in the range of 400–4000 cmꢀ1 using an
AVATAR 360 FTIR spectrometer.
All of the electronic absorption spectra were recorded on a Hew-
lett–Packard 8453 or Hewlett–Packard 8452 A diode array spectro-
photometer. Steady-state emission and excitation spectra at room
temperature were recorded on a Horiba Jobin Yvon Fluorolog-3-
TCSPC spectrofluorometer. The solutions were rigorously degassed
on a high vacuum line in a two-component cell with not less than
four successive freeze–pump–thaw cycles. Measurements of the
EtOH/MeOH (4:1 v/v) glass samples at 77 K were carried out with
the dilute EtOH/MeOH sample solutions contained in a quartz tube
inside a liquid-nitrogen-filled quartz optical Dewar flask. Lumines-
cence quantum yields of samples in CH2Cl2 solutions were deter-
mined according to the method described by Crosby et al.[20] using
quinine sulfate in aqueous sulfuric acid (0.5m) as reference stan-
dard. Absolute luminescence quantum yields of solid samples were
measured on a Hamamatsu C9920–03 absolute PL quantum yield
measurement system. Luminescence lifetimes were measured
using time-correlated single photon counting (TCSPC) technique
on the TCSPC spectrofluorometer in a Fast MCS mode with
a NanoLED-375 LH excitation source, which has its excitation peak
and
sodium
tetrakis[3,5-
bis(trifluoromethyl)phenyl]borate
{NaB[C6H3(CF3)2]4} were purchased from TCI Chemical Company
and used without further purification. [Re(CO)3(N^N)(CN)] were
synthesized according to previously reported procedures.[5g,8]
[Re(CO)3(phen)(CN)]
(P3),
[Re(CO)3(4,7-Me2phen)(CN)]
(P4),
[Re(CO)3(phen){CNB(C6F5)3}] (3a), and
[Re(CO)3(4,7-Me2phen){CNB(C6F5)3}] (4a) were prepared by our
previously reported procedures.[8] All of the other reagents and
solvents were of analytic reagent grade, and commercial deuterat-
ed solvents were used without further purification.
Physical measurements and instrumentation: 1H and 19F NMR
spectra were recorded on a Bruker AV400 (400 MHz) FT-NMR spec-
trometer. Chemical shifts (d, ppm) were reported relative to tetra-
methylsilane (Me4Si). All positive-ion ESI mass spectra were record-
ed on PE-SCIEX API 150 EX single quadrupole mass spectrometer.
Mass spectra of target complexes were performed in acetonitrile
solution with small quantity of potassium iodide for ionization. Ele-
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wavelength at 375 nm and pulse width shorter than 750 ps. The
photon counting data were analyzed by Horiba Jobin Yvon Decay
Analysis Software.
[Re(CO)3(bpy){CNB(C6F5)3}] (1a): Yield: 64 mg, 0.07 mmol; 60%;
1H NMR (400 MHz, CDCl3, 298 K): d=7.63 (td, 2H, J=8.2, 1.5 Hz,
5,5’-bipyridyl H), 8.18 (td, 2H, J=8.2, 1.5 Hz, 4,4’-bipyridyl H), 8.25
(d, 2H, J=8.2 Hz, 3,3’-bipyridyl H), 9.02 ppm (d, 2H, J=4.8 Hz, 6,6’-
bipyridyl H); 19F NMR (376 MHz, CDCl3, 298 K): d=ꢀ134.29 (dd, 6F,
J=20.6, 8.2 Hz, o-phenyl F), ꢀ158.87 (t, 3F, J=20.6 Hz, p-phenyl F),
ꢀ164.83 ppm (td, 6F, J=20.6, 8.2 Hz, m-phenyl F); ESI-MS: m/z
1005 [M+K]+. IR (KBr disc): n˜ =1922, 1953, 2035 cmꢀ1 n(CꢁO);
2203 cmꢀ1 n(CꢁN); elemental analysis calcd (%) for 1a: C 39.85,
H 0.84, N 4.36; found: C 39.78, H 1.14, N 4.54.
Cyclic voltammetric measurements were performed by using a CH
Instruments, Inc. Model CHI 620 Electrochemical Analyzer. Electro-
chemical measurements were performed in acetonitrile solutions
with 0.1m nBu4NPF6 as the supporting electrolyte at room temper-
ature. The reference electrode was a Ag/AgNO3 (0.01m in acetoni-
trile) electrode, and the working electrode was a glassy carbon
electrode (CH Instruments, Inc.) with a platinum wire as the coun-
ter electrode. The working electrode surface was polished with
a 1 mm a-alumina slurry (Linde) and then a 0.3 mm a-alumina slurry
(Linde) on a microcloth (Buehler Co.). The ferrocenium/ferrocene
couple (FeCp2+/0) was used as the internal reference. All solutions
for electrochemical studies were deaerated with pre-purified argon
gas prior to measurements.
[Re(CO)3(4,4’-Me2bpy){CNB(C6F5)3}] (2a): Yield: 56 mg, 0.06 mmol;
54%; 1H NMR (400 MHz, CDCl3, 298 K): d=2.64 (s, 6H, methyl H),
7.40 (d, 2H, J=6.0 Hz, 5,5’-bipyridyl H), 8.00 (s, 2H, 3,3’-bipyridyl
H), 8.80 ppm (d, 2H, J=6.0 Hz, 6,6’-bipyridyl H); 19F NMR (376 MHz,
CDCl3, 298 K): d=ꢀ134.20 (dd, 6F, J=20.5, 8.3 Hz, o-phenyl F),
ꢀ159.06 (t, 3F, J=20.5 Hz, p-phenyl F), ꢀ165.04 ppm (td, 6F, J=
20.5, 8.3 Hz, m-phenyl F); ESI-MS: m/z 1033 [M+K]+. IR (KBr disc):
n˜ =1918, 1948, 2034 cmꢀ1 n(CꢁO); 2207 cmꢀ1 n(CꢁN); elemental
analysis calcd (%) for 2a: C 41.15, H 1.22, N 4.23; found: C 41.08,
H 1.27, N 4.13.
X-ray crystal structure determination: The crystal structures were
determined on an Oxford Diffraction Gemini S Ultra X-ray single
crystal diffractometer using graphite monochromatized CuKa (l=
1.54178 ꢁ) or MoKa (l=0.71073 ꢁ) radiation. The structure was
solved by direct methods employing SHELXL-97 program[21] on PC.
Re and many non-H atoms were located according to the direct
methods. The positions of other non-hydrogen atoms were found
after successful refinement by full-matrix least-squares using
SHELXL-97 program[21] on PC. In the final stage of least-squares re-
finement, all non-hydrogen atoms were refined anisotropically. H
atoms were generated by program SHELXL-97.[21] The positions of
H atoms were calculated based on riding mode with thermal pa-
rameters equal to 1.2 times that of the associated C atoms, and
participated in the calculation of final R-indices.
[Re(CO)3(phen){CNB(C6F5)3}] (3a): The complex has previously been
reported.[8] Yield: 58 mg, 0.58 mmol; 56%; 1H NMR (400 MHz,
CDCl3, 298 K): d=7.96 (dd, 2H, J=8.2, 5.2 Hz, 3,8-phen H), 8.11 (s,
2H, 5,6-phen H), 8.67 (dd, 2H, J=8.2, 1.4 Hz, 4,7-phen H),
9.37 ppm (dd, 2H, J=5.2, 1.4 Hz, 2,9-phen H); 19F NMR (376 MHz,
CDCl3, 298 K): d=ꢀ134.80 (dd, 6F, J=23.0, 8.2 Hz, o-phenyl F),
ꢀ158.95 (t, 3F, J=23.0 Hz, p-phenyl F), ꢀ164.80 ppm (td, 6F, J=
23.0, 8.2 Hz, m-phenyl F); ESI-MS: m/z 1029 [M+K]+. IR (KBr disc):
n˜ =1927, 1946, 2033 cmꢀ1 n(CꢁO); 2199 cmꢀ1 n(CꢁN); elemental
analysis calcd (%) for 3a: C 41.31, H 0.82, N 4.25; found: C 41.42,
H 1.06, N 4.47.
CCDC 1022479(1a), 1022480(1b), 1022483(2b), 1022482(3d),
1022483(5a), and 1022484(6a) contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[Re(CO)3(4,7-Me2phen){CNB(C6F5)3}] (4a): The complex has previous-
ly been reported.[8] Yield: 52 mg, 0.05 mmol; 52%; 1H NMR
(400 MHz, CDCl3, 298 K): d=2.92 (s, 6H, methyl H), 7.65 (dd, 2H,
J=5.3, 0.8 Hz, 3,8-phen H), 8.15 (s, 2H, 5,6-phen H), 9.08 ppm (d,
2H, J=5.3 Hz, 2,9-phen H); 19F NMR (376 MHz, CDCl3, 298 K): d=
ꢀ134.67 (dd, 6F, J=20.6, 8.2 Hz, o-phenyl F), ꢀ159.17 (t, 3F, J=
20.6 Hz, p-phenyl F), ꢀ165.06 ppm (td, 6F, J=20.6, 8.2 Hz, m-
phenyl F); ESI-MS: m/z 1057 [M+K]+; IR (KBr disc): 1921, 1951,
2036 cmꢀ1 n(CꢁO); 2208 cmꢀ1 n(CꢁN); elemental analysis calcd (%)
for 4a: C 42.54, H 1.19, N 4.13; found: C 42.30, H 1.51, N 4.32.
Computational details: The ground-state (S0) structures of select-
ed complexes (P3, 3a, 3d, 4a, and 6a) were optimized using den-
sity functional theory (DFT) with the B3LYP[22] hybrid functional.
The LanL2DZ basis sets[23a] were used for rhenium and 6–31G*
basis sets were used for non-metal atoms. The quasi-relativistic
pseudopotential with 15 valence electrons for Re atom is employ-
ed.[23b] Vibrational frequency calculations were performed to verify
that all optimized structures are minimal. Based on optimized
structures of S0 state, time-dependent (TD)-DFT[24] calculations
were carried out to obtain the vertical excitation transition ener-
gies for various singlet excited states. The solvent effect of di-
chloromethane (CH2Cl2) was taken account by the polarized contin-
uum model (PCM).[25] All calculations were done with the Gaussi-
an09 package of programs.[26]
[Re(CO)3(2,9-Me2phen){CNB(C6F5)3}] (5a): Yield: 38 mg, 0.04 mmol;
38%; 1H NMR (400 MHz, CDCl3, 298 K): d=3.28 (s, 6H, methyl H),
7.84 (d, 2H, J=8.2 Hz, 3,8-phen H), 7.90 (s, 2H, 5,6-phen H),
8.42 ppm (d, 2H, J=8.2 Hz, 4,7-phen H); 19F NMR (376 MHz, CDCl3,
298 K): d=ꢀ134.65 (dd, 6F, J=20.5, 8.2 Hz, o-phenyl F), ꢀ158.94 (t,
3F, J=20.5 Hz, p-phenyl F), ꢀ164.84 ppm (td, 6F, J=20.5, 8.2 Hz,
m-phenyl F); ESI-MS: m/z 1057 [M+K]+. IR (KBr disc): n˜ =1934,
1953, 2035 cmꢀ1 n(CꢁO); 2206 cmꢀ1 n(CꢁN); elemental analysis
calcd (%) for 5a·0.5CH2Cl2: C 41.34, H 1.38, N 3.96; found: C 41.68,
H 1.51, N 4.15.
Syntheses: Reactions for 1a–6a, 1c were carried out under strictly
anaerobic conditions in an inert argon atmosphere by using stan-
dard Schlenk techniques.
[Re(CO)3(3,4,7,8-Me4phen){CNB(C6F5)3}]
(6a):
Yield:
38 mg,
1
0.04 mmol; 39%. H NMR (400 MHz, CDCl3, 298 K): d=2.67 (s, 6H,
methyl H), 2.87 (s, 6H, methyl H), 8.19 (s, 2H, 5,6-phen H),
9.03 ppm (s, 2H, 2,9-phen H); 19F NMR (376 MHz, CDCl3, 298 K): d=
ꢀ134.68 (dd, 6F, J=20.1, 6.7 Hz, o-phenyl F), ꢀ159.17 (t, 3F, J=
20.1 Hz, p-phenyl F), ꢀ165.23 ppm (td, 6F, J=20.1, 6.7 Hz, m-
phenyl F); ESI-MS: m/z 1085 [M]+. IR (KBr disc): n˜ =1918, 1950,
2032 n(CꢁO); 2204 n(CꢁN); elemental analysis calcd (%) for 6a·H2O:
C 42.95, H 1.71, N 3.95; found: C 42.83, H 1.93, N 4.11.
General procedure for the syntheses of [Re(CO)3(N-
N){CNB(C6F5)3}]: A mixture of [Re(CO)3(N^N)(CN)] (1.0 mol equiv)
and B(C6F5)3 (1.2 mol equiv) was dissolved in dried and deoxygen-
ated dichloromethane (20 mL).[8,9] The resulting solution was re-
fluxed overnight, during which the solution changed from yellow
to pale yellow. After removing the solvent under reduced pressure,
the residue was purified by column chromatography on silica gel
with dichloromethane as eluent. Further purification was achieved
by the slow evaporation of the concentrated dichloromethane so-
lution of the complexes as pale yellow to yellow crystalline solid.
General procedure for the syntheses of [Re(CO)3(N-N)(CNBPh3)]:
Hydrochloric acid (2.0 mL, 3.0m) was added to a stirred solution of
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[Re(CO)3(N^N)(CN)] (1.0 mol equiv) in methanol (10 mL). After
30 min, NaBPh4 (1.2 mol equiv) was added. The resulting solution
was stirred overnight at room temperature, during which time
a pale yellow precipitate gradually appeared. The precipitate was
then collected by filtration and washed with water and methanol.
Further purification was achieved by slow diffusion of diethyl ether
vapor into a concentrated dichloromethane or acetone solution of
the complex as yellow crystalline solid.
(1.2 molequiv) was added. The resulting solution was refluxed
overnight. The solution mixture was then extracted with dichloro-
methane and washed with water. Analytical pure sample was ob-
tained by the slow evaporation of the concentrated dichlorome-
thane solution of the complexes. Yield: 40 mg, 0.04 mmol; 34%;
1H NMR (400 MHz, CDCl3, 298 K): d=7.02 (m, 6H, o-phenyl H), 7.55
(m, 3H, p-phenyl H), 7.95 (dd, 2H, J=8.4, 5.2 Hz, 3,8-phen H), 8.06
(s, 2H, 5,6-phen H), 8.63 (d, 2H, J=8.4 Hz, 4,7-phen H), 9.40 ppm
(d, 2H, J=5.2 Hz, 2,9-phen H); 19F NMR (376 MHz, CDCl3, 298 K):
d=ꢀ62.39 (s, 18F, methyl F); ESI-MS: m/z 1168 [M+K]+; IR (KBr
disc): n˜ =1937, 1956, 2039 cmꢀ1 n(CꢁO); 2197 cmꢀ1 n(CꢁN); ele-
mental analysis calcd (%) for 3e: C 42.65, H 1.52, N 3.73; found:
C 42.38, H 1.74, N 4.02.
[Re(CO)3(bpy)(CNBPh3)] (1b): Yield: 55 mg, 0.08 mmol; 72%;
1H NMR (400 MHz, CDCl3, 298 K): d=6.88 (m, 6H, o-phenyl H), 6.98
(m, 9H, m,p-phenyl H), 7.56 (m, 4H, J=4,4’,5,5’-bipyridyl H), 8.08
(d, 2H, J=4.96 Hz, 3,3’-bipyridyl H), 9.08 ppm (d, 2H, J=5.7 Hz,
6,6’-bipyridyl H); ESI-MS: m/z 735 [M+K]+. IR (KBr disc): n˜ =1934,
1916, 2027 cmꢀ1 n(CꢁO); 2186 cmꢀ1 n(CꢁN); elemental analysis
calcd (%) for 1b: C 55.34, H 3.34, N 6.05; found: C 55.16, H 3.68,
N 6.16.
Acknowledgements
[Re(CO)3(4,4’-Me2bpy)(CNBPh3)] (2b): Yield: 50 mg, 0.07 mmol;
67%; 1H NMR (400 MHz, CDCl3, 298 K): d=2.60 (s, 6H, methyl H),
6.88–7.01 (m, 15H, phenyl H), 7.34 (dd, 2H, J=5.6, 1.4 Hz, 5,5’-bi-
pyridyl H), 7.84 (s, 2H, 3,3’-bipyridyl H), 8.84 ppm (d, 2H, J=5.6 Hz,
6,6’-bipyridyl H); ESI-MS: m/z 763 [M+K]+; IR (KBr disc): n˜ =1922,
1946, 2031 cmꢀ1 n(CꢁO); 2198 cmꢀ1 n(CꢁN); elemental analysis
calcd (%) for 2b·H2O: C 55.14), H 3.95, N 5.67; found: C 55.21,
H 3.98, N 5.75.
This work has been supported by Hong Kong University Grants
Committee Area of Excellence Scheme (AoE/P-03–08) and
a RGC GRF grant from the Research Grants Council of the
Hong Kong SAR, China (Project No. CityU 101212). W.-K.C. ac-
knowledges receipt of a University Postgraduate Studentship
and a Research Tuition Scholarship administrated by City Uni-
versity of Hong Kong. We sincerely thank Professor V. W.-W.
Yam of The University of Hong Kong for access to the
equipment for luminescent quantum yield measurements of
our solid samples.
[Re(CO)3(phen)(CNBPh3)] (3b): Yield: 51 mg, 0.07 mmol; 68%.
1H NMR (400 MHz, CDCl3, 298 K): d=6.65 (d, 6H, J=6.2 Hz, o-
phenyl H), 6.85–6.93 (m, 9H, m,p-phenyl H), 7.87 (dd, 2H, J=8.2,
5.2 Hz, 3,8-phen H), 8.04 (s, 2H, 5,6-phen H), 8.58 (dd, 2H, J=8.2,
1.4 Hz, 4,7-phen H), 9.37 ppm (d, 2H, J=5.2 Hz, 2,9-phen H); ESI-
MS: m/z 759 [M+K]+; IR (KBr disc): n˜ =1902, 1945, 2029 cmꢀ1 n(Cꢁ
O); 2202 n(CꢁN); elemental analysis calcd (%) for 3b: C 56.83,
H 3.23, N 5.85; found: C 56.68, H 3.45, N 5.99.
Keywords: charge
transfer
·
emissive
materials
·
isocyanoborate · phosphorescence · rhenium
[Re(CO)3(4,7-Me2phen)(CNBPh3)] (4b): Yield: 44 mg, 0.06 mmol;
60%; 1H NMR (400 MHz, CDCl3, 298 K): d=2.97 (s, 6H, methyl H),
6.64 (d, 6H, J=6.9 Hz, o-phenyl H), 6.85–6.89 (m, 9H, m,p-phenyl
H), 7.65 (d, 2H, J=5.2 Hz, 3,8-phen H), 8.15 (s, 2H, 5,6-phen H),
9.18 ppm (d, 2H, J=5.2 Hz, 2,9-phen H); ESI-MS: m/z 787 [M+K]+;
IR (KBr disc): n˜ =1924, 1940, 2030 cmꢀ1 n(CꢁO); 2193 cmꢀ1 n(CꢁN);
elemental analysis calcd (%) for 4b: C 57.91, H 3.64, N 5.63; found:
C 57.81, H 3.78, N 5.79.
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[Re(CO)3(phen)(CNBCl3)] (3c): The complex was synthesized accord-
ing to a procedure similar to that used for 3a, except BCl3 was
used in place of B(C6F5)3. Yield: 18 mg, 0.03 mmol; 29%; 1H NMR
(400 MHz, CDCl3, 298 K): d=8.00 (dd, 2H, J=8.3, 5.1 Hz, 3,8-phen
H), 8.14 (s, 2H, 5,6-phen H), 8.70 (dd, 2H, J=8.3, 1.3 Hz, 4,7-phen
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[M+K]+. IR (KBr disc): n˜ =1932, 1961, 2030 cmꢀ1 n(CꢁO); 2176
n(CꢁN); elemental analysis calcd (%) for 3c: C 32.37, H 1.36, N 7.08;
found: C 32.32, H 1.62, N 7.16.
[Re(CO)3(phen){CNB(C6H4Cl)3}] (3d): The complex was synthesized
according to a procedure similar to that used for 3b, except
KB(C6H4Cl)4 was used in place of NaBPh4. Yield: 51 mg, 0.07 mmol;
1
56%; H NMR (400 MHz, CDCl3, 298 K): d=6.52 (dd, 6H, J=8.2 Hz,
m-phenyl H), 6.83 (dd, 6H, o-phenyl H), 7.90 (dd, 2H, J=8.2, 5.1 Hz,
3,8-phen H), 8.07 (s, 2H, 5,6-phen H), 8.63 (dd, 2H, J=8.2, 1.2 Hz,
4,7-phen H), 9.34 ppm (dd, 2H, J=5.1, 1.2 Hz, 2,9-phen H); ESI-MS:
m/z 862 [M+K]+. IR (KBr disc): n˜ =1915, 1943, 2030 cmꢀ1 n(CꢁO);
2188 cmꢀ1 n(CꢁN); elemental analysis calcd for 3d·0.5H2O: C 49.06,
H 2.72, N 5.05; found: C 49.21, H 2.74, N 5.22.
[Re(CO)3(phen)([CNB[C6H3(CF3)2]3})] (3e): Hydrochloric acid (2.0 mL,
3.0m) was added to a stirred solution of [Re(CO)3(phen)(CN)]
(1.0 molequiv) in methanol (10 mL). After 30 min, NaB[C6H3(CF3)2]4
ˇ
Towrie, A. Vlcek, Jr., J. Phys. Chem. A 2005, 109, 3000–3008; f) P. H.-M.
Chem. Eur. J. 2015, 21, 2603 – 2612
www.chemeurj.org
2611
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: September 16, 2014
Published online on December 11, 2014
Chem. Eur. J. 2015, 21, 2603 – 2612
www.chemeurj.org
2612
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim