Syntheses, structural studies and spectroscopic characterisation of pyridyl-phthalimide complexes of fac-(CO)3ReI-diimines

Article abstract of DOI:10.1016/j.jorganchem.2008.12.048

The mono-dentate ligands, 3-aminomethyl-N-phthalimido-pyridine (L¹) and 3-amino-N-phthalimido-pyridine (L²), were synthesised using a solvent-free melt method. These ligands were then used to access three pairs of functionalised lumi

Full text of DOI:10.1016/j.jorganchem.2008.12.048

Journal of Organometallic Chemistry 694 (2009) 1400–1406
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses, structural studies and spectroscopic characterisation
of pyridyl–phthalimide complexes of fac-(CO)3ReI-diimines
Flora L. Thorp-Greenwood a, Michael P. Coogan a, Andrew J. Hallett a, Rebecca H. Laye b, Simon J.A. Pope a,
*
a School of Chemistry, Main Building, Cardiff University, Park Place, Cardiff, Wales CF10 3AT, UK
b Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
a r t i c l e i n f o
a b s t r a c t
The mono-dentate ligands, 3-aminomethyl-N-phthalimido-pyridine (L1) and 3-amino-N-phthalimido-
pyridine (L2), were synthesised using a solvent-free melt method. These ligands were then used to access
three pairs of functionalised luminescent ReI complexes of the generic type fac-{Re(CO)3(diimine)(Ln)}(BF4)
[where diimine = 4,40-dimethyl-2,20-bipyridine (dmb); 2,20-bipyridine (bpy); 1,10-phenanthroline
(phen)]. X-ray crystallography has been used to structurally characterise five of the complexes showing
that in the cases of the L1 species the phthalimide unit is adjacent to and co-planar with the coordinated
diimine ligand. Solution state UV–Vis absorption, electrochemistry and IR studies confirm that the
proposed formulations and coordination modes exist in solution. The photophysical studies show that
the visible emission from each of the six complexes is 3MLCT at room temperature. Within each pair of
complexes the precise energy of the emission was subtly dependent upon the axial ligand, Ln with lumines-
cence lifetimes in the range 121–288 ns.
Article history:
Received 13 November 2008
Received in revised form 12 December 2008
Accepted 19 December 2008
Available online 16 January 2009
Keywords:
Rhenium
Diimine
Phthalimide
Luminescence
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Recent reports suggest utilising phthalimide derivatives to allow
development of the ‘TcI(CO)3’ core with amino acid-based chelat-
Diimine complexes of the ‘fac-{Re(CO)3}’ core can be exploited
as photoactive components within luminescent arrays allowing
the design of multimetallic species [1] and responsive chemosen-
sors [2]. More recently they have also been developed and utilised
in biological fluorescence imaging applications where stepwise
derivitisation allows tuning of the physical properties, exploitation
of triplet metal(rhenium)-to-ligand(diimine) charge transfer
(3MLCT) emission [3] and elucidation of organelle targeting behav-
iour including mitochondrial localisation [4]. Such species are
photophysically bio-compatible, allowing sensitisation in the visi-
ble region thus eradicating problematic endogenous autofluores-
cent backgrounds. Additional considerations are solubility and
charge, to give lipophilic, cationic species allowing cell uptake,
intracellular mobility and organelle localisation. In this study we
report the syntheses of a series of cationic fac-{Re(CO)3(diimine)-
Ln}+ complexes functionalised with a lipophilic, planar phthalimide
unit tethered via a coordinated pyridine, which we hope will pro-
vide a useful basis for biologically applied studies in the future.
Phthalimides are known to have potent biological activity [5] and
the free ligands L1 and L2 utilised in this study have also demon-
strated moderate promise in this regard [6] together with other
N-pyridinyl and N-quinolinyl substituted phthalimides which have
shown potent cytotoxicity towards several cultured cell lines [7].
ing ligands [8] for applications in positron emission tomography.
2. Synthesis
In contrast to the solvent-based reaction conditions previously
employed for accessing these ligand systems, L1 and L2 were syn-
thesised using a solvent-free melt method. Following recrystallisa-
tion from alcohol, yields were typically in excess of 90%. 1H NMR
spectra of the products were consistent with the proposed formu-
lations and in agreement with the literature [6].
The neutral diimine precursors were synthesised according to
the literature by reacting stoichiometric equivalents of pentacar-
bonlybromorhenium with either 2,20-bipyridine, 4,40-dimethyl-
2,20-bipyridine or 1,10-phenanthroline in toluene at 110 °C for
3 h [9]. Conversion to the cationic complexes was achieved by
abstracting the axial bromide ligand with AgBF4 in acetonitrile to
yield the intermediate species fac-{Re(CO)3(MeCN)(bisimine)}(BF4)
[10]. These were subsequently reacted with the pyridyl–phthali-
mide ligand (Ln) in chloroform at reflux. Typically the reaction
was followed by thin layer chromatography (silica, 9:1 dichloro-
methane:methanol) and complete within 24 h. Column chroma-
tography was not necessary to purify these complexes since the
desired complex often precipitated directly from the cooled reac-
tion mixture. Additional recrystallisation from acetonitrile/diethyl
ether provided crystalline samples.
* Corresponding author. Tel.: +44 029 20879316; fax: +44 029 20874030.
E-mail address: popesj@cardiff.ac.uk (S.J.A. Pope).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.12.048

F.L. Thorp-Greenwood et al. / Journal of Organometallic Chemistry 694 (2009) 1400–1406
1401
3.2. Single crystal X-ray diffraction studies of the complexes
3. Results and discussion
Crystals representing each of the diimine types (fac-{Re(CO)3
(bpy)L1}(BF4), fac-{Re(CO)3(bpy)L2}(BF4), fac-{Re(CO)3(phen)L1}(BF4),
fac-{Re(CO)3(phen)L2}(BF4) and fac-{Re(CO)3(dmb)L2}(BF4)) were
isolated and deemed to be suitable for diffraction studies. In each
case this was achieved by vapour diffusion of diethyl ether into a
concentrated acetonitrile solution of the complex and crystals were
grown over a period of 24 h. The parameters associated with each
data collection are shown in Table 1, with associated bond lengths
and bond angles in Supplementary material. In each case the struc-
tural analyses (Fig. 1) confirmed the proposed coordination geome-
try for rhenium with a fac-tricarbonyl arrangement supplemented
with the chelating bisimine and axial N-coordinated pyridyl–phthal-
imide. The two examples incorporating the methyl-linked ligand L1
show that the phthalimide unit is positioned adjacent to and
co-planar with the diimine unit. In contrast, for the L2 complexes
the more rigid architecture positions the phthalimide unit away
from the diimine. The bond lengths associated with the coordination
sphere are typical of related ReI complexes of this type [11]. Each of
the Re–CO distances lies within the range 1.914–1.933 Å whilst the
Re–N distances are typically longer at 2.159–2.225 Å. Generally,
the Re–N bond lengths with the axial mono-dentate pyridine are
longer (ca. 2.22 Å) than those associated with the chelating diimines
(ca. 2.17 Å). The bpy complex with L1 is more distorted (possibly due
to the flexible tethered phthalimide unit and packing forces) from
ideal octahedral symmetry (hCax–Re–Nax 175.95(13) vs. 178.89(13)
for L2 complex), which may account for a marginally weakened
Re–Nax interaction. In comparison, analysis of the fac-{Re(CO)3-
(phen)Ln}(BF4) structures shows that both are similarly distorted.
fac-{Re(CO)3(bpy)L1}(BF4) and fac-{Re(CO)3(phen)L1}(BF4) show that
when the diimine–Re bonding interaction is comparable, the axial
Re–N is similarly bonded. Comparison of fac-{Re(CO)3(bpy)L2}(BF4)
and fac-{Re-(CO)3(dmb)L2}(BF4) revealed that the stronger dii-
mine–Re interaction of the latter results in a weakened Re–Nax bond.
Therefore the factors determining the strength of the axial Re–
Nax(pyridyl) bond appear to be the donating ability of the diimine
co-ligand and the inherent level of distortion within the coordination
sphere.
3.1. Characterisation of the complexes
Solution state IR studies (Fig. 3) were conducted in chloroform.
For the fac-tricarbonyl core the local symmetry can be approxi-
mated to Cs and as a consequence three absorptions (2A0 + A00)
are expected although overlapping bands are common. Within
each pair of diimine complexes the highest frequency
m(CO)
band (CO trans to Ln) does not vary significantly with axial ligand
type.
Electrospray mass spectrometry (positive mode) was utilised
and for each complex revealed a cluster of peaks corresponding
to the cationic unit, i.e. {Re(CO)3(bisimine)(Ln)}+, the isotopic distri-
bution of which confirmed the presence of rhenium (185Re, 37.1%;
187Re 62.9%).
1H NMR spectra were also obtained for each of the six com-
plexes confirming the presence of the bisimine and pyridyl–
phthalimide ligands within the ReI coordination sphere.
L
+
N
N
N
N
N
N
N
N
OC
OC
Re
CO
bpy
phen
dmb
O
O
O
N
N
O
N
N
L1
L2
Scheme 1. Ligands and general cation of the rhenium complexes used in this study.
Table 1
Crystal data collection and refinement details for the complexesa.
{Re(CO)3(bpy)L2}(BF4)
{Re(CO)3(bpy)L1}(BF4)
{Re(CO)3(phen)L1}(BF4)
{Re(CO)3(phen)L2}(BF4)
{Re(CO)3(dmb)L2}(BF4)
Empirical formula
Formula weight
T (K)
C28H19BF4N5O5Re
778.49
120(2)
C29H21BF4N5O5Re
792.52
120(2)
C30H20BCl2F4N4O5Re
860.41
100(2)
C30H19BF4N5O5Re
802.51
100(2)
C29H24BF4N4O6Re
797.53
150(2)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
Monoclinic
P2(1)/c
0.71073
Orthorhombic
Pbca
0.71073
Monoclinic
P2(1)/c
0.71073
Monoclinic
P2(1)/c
0.71073
Monoclinic
I2/a
12.1221(4)
16.0830(8)
13.184(3)
11.965(3)
21.428(2)
b (Å)
19.0972(5)
13.3736(7)
18.508(5)
18.992(4)
12.3526(13)
c (Å)
12.5934(4)
26.8120(14)
13.851(3)
13.153(3)
22.346(18)
a
(°)
90.00
90.00
90.00
90.00°
90.00
b (°)
107.1890(10)
90.00
113.235(5)
106.249(11)
104.637(9)
c
(°)
90.00
2785.13(15)
90.00
5766.9(5)
90.00
3105.7(13)
90.00
2869.7(11)
90.00
5722.8(11)
V (Å3)
Z
4
8
4
4
8
Dcalc
1.857
1.826
1.840
1.858
1.851
Absorption coefficient
F(000)
4.439
1512
4.289
3088
4.156
1672
4.311
1560
4.324
3120
Crystal size (mm)
Reflections collected
Independent reflections
Goodness-of-fit on F
0.53 ꢀ 0.16 ꢀ 0.09
0.34 ꢀ 0.09 ꢀ 0.02
0.35 ꢀ 0.15 ꢀ 0.08
0.37 ꢀ 0.12 ꢀ 0.07
0.32 ꢀ 0.07 ꢀ 0.03
6391
6641
7090
6639
6585
5793
1.029
4690
0.928
6271
1.063
6028
1.046
5712
1.034
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0417, wR2 = 0.1067
R1 = 0.0444, wR2 = 0.1083
R1 = 0.0257, wR2 = 0.0534
R1 = 0.0462, wR2 = 0.0576
R1 = 0.0339, wR2 = 0.0878
R1 = 0.0392, wR2 = 0.0909
R1 = 0.0192, wR2 = 0.0451
R1 = 0.0225, wR2 = 0.0466
R1 = 0.0252, wR2 = 0.0617
R1 = 0.0324, wR2 = 0.0656
a
2
The structure was refined on Fo using all data.

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F.L. Thorp-Greenwood et al. / Journal of Organometallic Chemistry 694 (2009) 1400–1406
Fig. 1. Structural representations of the four complexes (a–e) fac-{Re(CO)3(bpy)L1}(BF4), fac-{Re(CO)3(phen)L1}(BF4), fac-{Re(CO)3(phen)L2}(BF4), fac-{Re(CO)3(bpy)L2}(BF4)
and fac-{Re(CO)3(dmb)L2}(BF4). Counter ions and solvent of crystallisation omitted for clarity, probability ellipsoids at 50%.
Table 2
IR, cyclic voltammetry, UV–Vis absorption, steady state and time-resolved luminescence: spectroscopic data associated with the complexes.
d
Complex
m
(CO)a
Eox/Vb
ꢁEred/Vb
kabs/nm (
e
/Mꢁ1 cmꢁ1
)
3MLCT emission
maximum/nme
3MLCT /nsf
s
fac-{Re(CO)3(bpy)L1}(BF4)
fac-{Re(CO)3(bpy)L2}(BF4)
fac-{Re(CO)3(phen)L1}(BF4)
fac-{Re(CO)3(phen)L2}(BF4)
fac-{Re(CO)3(dmb)L1}(BF4)
fac-{Re(CO)3(dmb)L2}(BF4)
2037, 1929br
1.8
–
1.8
1.8
1.8
1.8
1.2°, 1.4
346 (4800), 319 (15300), 305 (16300), 266 (22800)
340 (4600), 317 (14800), 305 (16000), 270 sh (22600)
363 (4800), 324 sh (8300), 275 (34200)
362 (4000), 321 sh (7800), 273 (32300)
342 sh (5800), 315 (16700), 302 (18300), 266 (25800)
336 (4700), 315 (13100), 302 (14100), 270 sh (20900)
556
548
543
539
544
538
128
148
281
266
121
129
g
2036, 1937, 1929
2034, 1936, 1924
2034, 1935, 1924
2038, 1938br
1.2c, 1.4
1.2c, 1.4, 2.0c
1.2c, 1.4
1.3c, 1.5, 2.1c
1.2c, 1.4, 2.1c
2037, 1939, 1928
a
In CHCl3 solution.
b
Referenced to Fc/Fc+ in dry acetonitrile, scan rate of 200 mV/s.
Irreversible.
c
d
e
f
In acetonitrile solution.
In aerated acetonitrile solution, kex = 380 nm.
In aerated acetonitrile solution, kex = 372 nm.
Difficult to obtain due to signal weakness and solvent window.
g
3.3. Electrochemistry
reduction potentials which are usually assigned to diimine reduc-
tion and/or the ReI/0 reduction. The first at ca. ꢁ1.2 V (ꢁ1.3 V for
the less reducible dmb ligand) is assigned to the 0/ꢁ1 couple of
the diimine ligands and was found to be irreversible for each com-
plex. The second reduction at ca. ꢁ1.4 V was reversible in each case
and attributed to the ReI/0 couple. The complexes fac-{Re(CO)3-
(phen)L1}BF4, fac-{Re(CO)3(dmb)L1}BF4 and fac-{Re(CO)3(dmb)L2}
BF4 each showed a third irreversible reduction wave in the region
ꢁ2.0 to ꢁ2.1 V. Although it is possible that this reduction may be
due to a new species formed as a consequence of the first irrevers-
ible reduction process, the differing values may allow a tentative
assignment to the 0/ꢁ1 couple of the pyridyl–phthalimide ligand
An investigation into the electrochemical behaviour of the six
complexes was undertaken in de-aerated acetonitrile solution.
The data associated with the oxidation potential of the rhenium
centre (ReI/ReII) and the reduction potential of the diimine are
presented in Table 2. With the anomolous exception of fac-
{Re(CO)3(bpy)L2}(BF4) for which we were unable to reliably record
a value (due to the limitations of the solvent window at ca. +1.9 V)
each of the complexes showed a reversible oxidation potential at
around +1.8 V assigned to the ReI/II couple in line with previous
observations [10]. Each of the complexes showed two or three

F.L. Thorp-Greenwood et al. / Journal of Organometallic Chemistry 694 (2009) 1400–1406
1403
2.5
A
2
B
1.5
C
1
0.5
0
250
300
350
400
450
500
wavelength / nm
250
350
450
550
650
wavelength / nm
A
1
B
0
250
300
350
400
450
500
wavelength / nm
0
250
350
450
550
650
Fig. 2. Top: Electronic absorption spectra recorded with 2 ꢀ 10ꢁ4
M MeCN
solutions. A, fac-{Re(CO)3(dmb)L2}(BF4); B, fac-{Re(CO)3(phen)L2}(BF4); C, fac-
{Re(CO)3(bpy)L2}(BF4). Bottom: normalised absorption spectra of A, superimposed
fac-{Re(CO)3(bpy)Ln}(BF4); B, fac-{Re(CO)3(bpy)MeCN}(BF4).
wavelength / nm
Fig. 3. Steady state excitation (grey) and emission (black, kex = 285 nm) spectra for
fac-{Re(CO)3(dmb)Ln}(BF4): L2 (top), L1 (bottom).
moiety, since phthalimides are known to undergo cathodic electro-
chemical reactions. Overall, the results show that electrochemi-
cally the rhenium centre is fairly insensitive to the changes in
ligand type. The variation in reduction potentials of the bipyridine
ligands within the pairs of bpy and dmb complexes, suggests that
the variation in axial ligand Ln can subtly influence the electronic
environment of the diimine, as suggested by the absorption and
emission data.
tureless emission band centred at ca. 550 nm consistent with
3MLCT phosphorescence [9a,10a]. The precise kem positioning of
the transition appeared to be ligand dependent: within each dii-
mine class L2 induced a subtle high energy shift for kem which
was most pronounced for the bpy complexes. The degree of MLCT
excited state stabilisation depends on the electron donating ability
of the axial ligand [10a–e]: L1 should be better able to donate
electron density towards the virtual Re2+ centre of the excited
state. The emission wavelength of both phen complexes was inde-
pendent of excitation wavelength and thus assigned to conven-
tional 3MLCT [9a,10h,12]. Room temperature luminescence
lifetime measurements of the complexes each gave single compo-
nent decay consistent with a 3MLCT assignment. sMLCT for the bpy
and dmb derivatives was between 120 and 150 ns, whilst the phe-
nathroline species were significantly longer-lived (despite possess-
ing almost identical emission energies to the dmb species)
reflecting the additional rigidity and limited excited state distor-
tion inherent within the phenanthroline ligand, which conse-
quently limit the vibrational deactivation pathways [10e].
However, although the dmb complexes possess higher emission
energies than the bpy analogues, the resultant lifetimes are longer
for the latter pair. Given that excited state distortion often in-
creases with increasing excited state energy the vibrational deacti-
vation of the dmb species may be more effective resulting in the
shortened luminescence lifetimes [10e] (see Table 2).
3.4. Luminescence studies
Each of the target complexes possessed solution-state (MeCN)
absorption characteristics consistent with the presence of both li-
gands in the rhenium coordination sphere (Fig. 2). Typically the
lowest energy feature (>330 nm) appears as a broadened (often
shoulder-like) transition and was assigned to a metal-to-ligand
charge transfer (1MLCT) d(Re) ?
p*(diimine) in accordance with
previous studies [9a,10a]. The absorptions at shorter wavelengths
300–330 nm are attributed to the intraligand transitions of the
bisimine moieties. As an example Fig. 2 shows a comparison of
the absorption profiles of fac-{Re(CO)3(bpy)Ln}(BF4) with the pre-
cursor fac-{Re(CO)3(bpy)MeCN}(BF4). These spectra clearly demon-
strate the additive effect of the axial pyridyl–phthalimide units to
the absorption profile <300 nm which, as a consequence, are as-
signed to IL (singlet
n ? *) transitions.
p ? p* with the possibility of phthalimide
p
The luminescence properties of the complexes were obtained
on dilute (approximately 10ꢁ5 M) aerated acetonitrile solutions
at room temperature. Firstly, steady state emission spectra were
obtained by selective irradiation of the 1MLCT transition using
wavelengths >360 nm. In all six cases this resulted in a broad struc-
The excitation spectra (probing the 3MLCT emission band) ob-
tained on 10ꢁ5 M solutions show significant variations with dii-
mine type and axial ligand. Each of the spectra show bands
assigned to MLCT transitions between 450 and 320 nm and defined

1404
F.L. Thorp-Greenwood et al. / Journal of Organometallic Chemistry 694 (2009) 1400–1406
peaks at higher energies which can be attributed to intraligand
transitions within the coordinated diimine ligand. There are differ-
ences in the spectra below 320 nm and thus it is also reasonable
that, by comparison with the absorption spectra, some of these
features can be assigned to the axial pyridyl–phthalimide ligands.
These spectra demonstrate that subtle variations in the periphe-
ral nature of the axial ligand can have an influence on the usable
range of excitation wavelengths for the 3MLCT emission (see
Scheme 1).
3.6.1. Synthesis of L1
3-Picolylamine (1 g, 9.25 mmol) and phthalic anhydride (1.37 g,
9.25 mmol) were mixed in a test tube. The mixture was heated to a
melt with a hot air gun with occasional agitation via glass rod. Mod-
erate heating was continued until water vapour was produced and
condensing on the test tube wall [care must be taken not to over-
heat the mixture and decompose the reactants and product]. Once
water vapour was no longer evident, heating was stopped and the
reaction mixture cooled. The mixture was added to hot ethanol
(ca. 50 cm3), filtered, and the resultant solute allowed to cool to
room temperature. Upon cooling the product precipitated as a
white crystalline solid. Further crops of product were isolated fol-
lowing concentration of the alcoholic solution and storage at 0 °C.
Examples relating to chromophore-sensitised ReI-based 3MLCT
emission are rare [13,14] although phthalimide chromophores
have been utilised to sensitise the visibly luminescent lanthanide
ions Tb(III) and Eu(III) [15]. Kahwa et al. showed that the excited
triplet state energy of such chromophores was estimated as ca.
23000 cmꢁ1. In our ReI complexes photoinduced energy transfer
is feasible on energetic grounds from either the phthalimide singlet
or triplet states, given that the 3MLCT lies at ca. 22000 cmꢁ1 (esti-
mated from the ground and excited state 0–0 transition). Following
excitation at 285 nm (in fac-{Re(CO)3(dmb)Ln}(BF4) pyridyl–
phthalimide ligand contributes ca. 75% absorbance at 285 nm)
3MLCT luminescence dominates, but for fac-{Re(CO)3(dmb)L2}(BF4)
there is a weak feature at ca. 418 nm attributed to residual pyri-
dyl–phthalimide emission. Time-resolved analysis of this peak re-
vealed sflu ca. 1.4 ns, consistent with a singlet fluorescence, which
may be a consequence of trace contaminant of highly fluorescent
free ligand, undetectable by other spectroscopic means. However,
comparison to the photophysical properties of uncoordinated L2
(fluorescence lifetime in MeCN solution is ca. 2.0 ns at an emission
maximum of 404 nm) more likely suggests that energy transfer
from the singlet excited state of the chromophore may also con-
tribute in these systems. Given that the energy transfer efficiency
using either the Dexter or Förster mechanisms is strongly distance
dependent (decreasing exponentially and by rꢁ6, respectively) it
seems likely that the average intramolecular inter-chromophoric
distance (i.e. phthalimide to diimine) is shorter in the complexes
of L1.
3.6.2. Synthesis of L2
As for L1, but using 3-aminopyridine (1 g, 10.6 mmol) and
phthalic anhydride (1.57 g, 10.6 mmol).
3.6.3. Synthesis of fac-{Re(CO)3(bpy)L1}(BF4)
The title compound was prepared by heating {Re(CO)3
(bpy)(NCCH3)}(BF4) (50 mg, 9.02 ꢀ 10ꢁ5 mol) and excess L1 (25 mg,
1.05 ꢀ 10ꢁ4 mol) in chloroform (10 cm3) under reflux in a nitrogen
atmosphere for 48 h. The product was precipitated from an aceto-
nitrile/diethyl ether mixture to give a pale yellow solid (29 mg,
43%). IR m
max (CHCl3, cmꢁ1) 1929, 1937, 2036. UV–Vis (MeCN) kmax
(e
/Mꢁ1 cmꢁ1) 346 (4800), 319 (15300), 305 (16300), 266 (22800)
nm. 1H NMR (400 MHz, CDCl3) dH 4.61 (2H, s, –CH2), 7.28 (1H, m,
py), 7.70 (4H, overlapping m, phth and bpy), 7.76 (2H, m, phth),
3
3
7.84 (1H, d, JHH = 8.1 Hz, py), 8.08 (1H, d, JHH = 5.1 Hz py), 8.23
(1H, s, py), 8.25 (2H, d, 3JHH = 8.1 Hz, bpy), 8.64 (2H, d, 3JHH = 8.1 Hz,
bipy), 9.03 (2H, d, 3JHH = 4.5 Hz, bpy) ES+ MS found m/z 665; calcu-
lated m/z 665 for {M+HꢁBF4}+. HR ESI found m/z 663.0805;
C27H18O5N4185Re requires 663.0801.
3.6.4. Synthesis of fac-{Re(CO)3(bpy)L2}(BF4)
As above, but using {Re(CO)3(bpy)(NCCH3)}(BF4) (50 mg,
9.02 ꢀ 10ꢁ5 mol) and excess L2 (25 mg, 1.12 ꢀ 10ꢁ4 mol) and chlo-
roform (10 cm3). A sandy brown coloured solid was isolated
(28 mg, 44%). IR mmax (CHCl3, cmꢁ1) 1929, 2037. UV–Vis (MeCN)
3.5. Conclusion
This paper reports the ReI coordination chemistry of two pyri-
dyl–phthalimide ligands to form cationic species of the general
form fac-{Re(CO)3(diimine)Ln}(BF4). X-ray structural studies con-
firm both the coordination mode and geometry of the complexes.
The strength of the pyridyl-rhenium interaction appears to be
determined by the degree of distortion at the octahedral ion, which
is more pronounced for the L1 species. In each case the complexes
possess visible 3MLCT emission with luminescent lifetimes in ex-
cess of 120 ns. The electronic nature of the axial ligand produces
subtle changes in the precise energy of the 3MLCT emission,
depending on the degree of excited state MLCT stabilisation. The
quenching of phthalimide fluorescence suggests that photoinduced
energy transfer can operate in these species, but that the poten-
tially greater inter-chromophoric distance of the L1 complexes
may account for any observed residual fluorescence. Importantly
this investigation shows that these rhenium complexes incorporat-
ing phthalimide-functionalised ligands retain their useful emission
properties, exploiting a range of excitation wavelengths, and thus
renders them attractive candidates in our ongoing investigation
into the biological application of such complexes in confocal fluo-
rescence microscopy.
kmax (e
/Mꢁ1 cmꢁ1) 340 (4600), 317 (14800), 305 (16000), 270 sh
(22600) nm. 1H NMR (400 MHz, MeOD) dH 7.45 (1H, m, py),
7.79–7.85 (6H, overlapping m, phth and bpy), 8.08 (1H, d,
3JHH = 7.8 Hz, py), 8.22 (1H, m, py), 8.25 (2H, m, bpy), 8.48 (1H, s,
3
3
py), 8.52 (2H, d, JHH = 8.0 Hz, bpy), 9.22 (2H, d, JHH = 7.6 Hz,
bpy). ES+ MS found m/z 651; calculated m/z 651 for {M+HꢁBF4}+.
HR ESI found m/z 649.0641; C26H16O5N4185Re requires 649.0645.
3.6.5. Synthesis of fac-{Re(CO)3(phen)L1}(BF4)
The title compound was prepared by heating equimolar quanti-
ties of {Re(CO)3(phen)(NCCH3)}(BF4) (30 mg, 5.19 ꢀ 10ꢁ4 mol) and
L1 (12 mg, 5.19 ꢀ 10ꢁ4 mol) in chloroform (10 cm3) under N2 for
48 h. The product was precipitated from acetonitrile using diethyl
ether to give a pale yellow solid (75 mg, 77%). IR
m
max (CHCl3, cmꢁ1
1928, 1939, 2037. UV–Vis (MeCN) kmax (e
/Mꢁ1 cmꢁ1) 363 (4800),
)
324 sh (8300), 275 (34200) nm. 1H NMR (250 MHz, MeOD) dH
4.48 (2H, s, –CH2), 7.59 (1H, m, py), 7.65 (2H, m, phth), 7.74 (2H,
m, phth), 7.81 (2H, s, phen), 8.03 (1H m, py), 8.08 (2H, m, phen),
3
3
8.29 (1H, d, py, JHH = 5.02 Hz), 8.44 (1H, d, py, JHH = 4.7 Hz),
8.77 (2H, dd, JHH = 8.3, 1.3 Hz, phen), 9.59 (2H, dd, JHH = 5.2,
1.4 Hz, phen). ES+ MS found m/z 689, calculated m/z 689 for
{M+HꢁBF4}+. HR ESI found m/z 687.0808; C29H18O5N4185Re re-
quires 687.0801.
3.6. Experimental
Materials: The neutral rhenium complexes, including ReBr(CO)5
[16], and the cationic acetonitrile intermediates were prepared
according to or based upon literature reports [10].
3.6.6. Synthesis of fac-{Re(CO)3(phen)L2}(BF4)
The title compound was prepared by heating equimolar quanti-
ties of {Re(CO)3(phen)(NCCH3)}(BF4) (20 mg, 3.46 ꢀ 10ꢁ5 mol) and

F.L. Thorp-Greenwood et al. / Journal of Organometallic Chemistry 694 (2009) 1400–1406
1405
L2 (8 mg, 3.46 ꢀ 10ꢁ5 mol) in chloroform (10 cm3) under reflux in a
nitrogen atmosphere overnight to give a yellow solid (14 mg, 53%)
which precipitated from the reaction medium. IR mmax (CHCl3,
quoted vs. the [Fe(
in CH3CN) as the internal standard.
g
5-C5H5)2]+/[Fe(
g
5-C5H5)2] couple (E° = +0.39 V
cmꢁ1) 1938, 2038. UV–Vis (MeCN) kmax /Mꢁ1 cmꢁ1) 362 (4000),
(e
5. Data collection and processing
321 sh (7800), 273 (32300) nm. 1H NMR (400 MHz, MeOD) dH
7.18 (1H, m, Py), 7.3–7.8 (5H, overlapping multiplet, phth (4H)
and py (1H)), 8.10 (2H, m, phen), 8.15 (2H, s, phen), 8.26 (1H, d,
3JHH = 5.2 Hz, py), 8.85 (2H, dd, J = 8.3, 1.1 Hz, phen), 8.89 (1H, s,
py), 9.62 (2H, dd, J = 5.1, 1.1 Hz, phen). ES+ MS found m/z 675, cal-
culated m/z 675 for {M+HꢁBF4}+. HR ESI found m/z 673.0640;
C28H16O5N4185Re requires 673.0645.
Crystal data, data collection and refinement parameters for the
complexes are given in Table 1; selected bond lengths and angles
in Supplementary material. Diffraction data were collected on a
Bruker KAPPA APEX 2 using graphite-monochromated Mo K
a
radiation (k = 0.71073 Å) at 100, 120 or 150 K. Software package
APEX 2 (v2.1) was used for the data integration, scaling and absorp-
tion correction.
3.6.7. Synthesis of fac-{Re(CO)3(dmb)L1}(BF4)
The title compound was prepared by heating equimolar quanti-
ties of {Re(CO)3(dmb)(NCCH3)}(BF4) (20 mg, 3.46 ꢀ 10ꢁ5 mol) with
L1 (8 mg, 3.46 ꢀ 10ꢁ5 mol) in chloroform (10 cm3) under reflux in a
nitrogen atmosphere, overnight. The yellow solution was dried and
dissolved in methanol (1 cm3) the product precipitated using
diethyl ether (5 cm3) to give a pale yellow solid (28 mg, 53%). IR
6. Structure analysis and refinement
The structure was solved by direct methods using SHELXS-97 and
was completed by iterative cycles of
DF-syntheses and full-matrix
least squares refinement. All non-H atoms were refined anisotrop-
ically and difference Fourier syntheses were employed in position-
ing idealised hydrogen atoms and were allowed to ride on their
mmax (CHCl3, cmꢁ1) 1924, 1935, 2034. UV–Vis (MeCN) kmax
(e/
ꢁ1 cmꢁ1) 342 (5800), 315 (13100), 302 (18300), 266 (25800)
parent C-atoms. All refinements were against F2 and used SHELX
-
M
nm. 1H NMR (400 MHz, CDCl3) dH 2.56 (6H, s, 2 ꢀ –CH3), 4.62
97.[17]
3
(2H, s, –CH2), 7.27 (1H, m, py), 7.44 (2H, d, JHH = 5.5 Hz, bpy),
3
7.69 (2H, m, phth), 7.76 (2H, m, phth), 7.84 (1H, d, JHH = 8.0 Hz,
Acknowledgements
py), 8.00 (1H, d, 3JHH = 4.9 Hz, py), 8.27 (1H, s, py), 8.49 (2H, s, bipy),
8.82 (2H, d, JHH = 5.7 Hz, bpy). ES+ MS found m/z 693, calculated
3
We thank the Universities of Cardiff and Sheffield for support.
EPSRC are also thanked for financial support. Prof. Michael D. Ward
(University of Sheffield) is acknowledged for granting access to X-
ray crystallographic facilities. We also recognise the efforts of the
EPSRC Mass Spectrometry National Service at the University of
Swansea.
m/z 693 for {M+HꢁBF4}+. HR ESI found m/z 691.1113;
C29H22O5N4185Re requires 691.1114.
3.6.8. Synthesis of fac-{Re(CO)3(dmb)L2}(BF4)
The title compound was prepared by heating was prepared by
heating equimolar quantities of {Re(CO)3(dmb)(NCCH3)}(BF4)
(20 mg, 3.43 ꢀ 10ꢁ5 mol) and L2 (8 mg, 3.43 ꢀ 10ꢁ5 mol) in chloro-
form (10 cm3) under reflux in a nitrogen environment overnight.
The yellow solid was precipitated with diethyl ether. IR mmax
Appendix A. Supplementary material
(CHCl3, cmꢁ1) 1924, 1936, 2034. UV–Vis (MeCN) kmax /Mꢁ1 cmꢁ1
(e )
CCDC 703241, 703242, 703243, 703244 and 703245 contain the
supplementary crystallographic data for fac-{Re(CO)3(phen)(L1)}
(BF4), fac-{Re(CO)3(bpy)(L2)}(BF4), fac-{Re(CO)3(dmb)(L2)}(BF4),
fac-{Re(CO)3(bpy)(L1)}(BF4) and fac-{Re(CO)3(phen)(L2)}(BF4).
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2008.12.048.
336 (4700), 315 (13100), 302 (14100), 270 sh (20900) nm. 1H
NMR (400 MHz, MeOD) dH 2.51 (6H, s, 2 ꢀ –CH3), 7.24 (1H, m,
py), 7.3–7.7 (6H, overlapping multiplet, bpy (2H), phth (4H)),
3
3
7.88 (1H, d, JHH = 5.5 Hz, py), 8.19 (1H, d, JHH = 4.9 Hz, py), 8.40
(2H, s, bpy), 8.89 (1H, s, py), 9.02 (2H, d, JHH = 6.1 Hz, bpy). ES+
3
MS found m/z 679, calculated m/z 679 for {M+HꢁBF4}+. HR ESI
found m/z 677.0955; C28H20O5N4185Re requires 677.0958.
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