Rhenium(I) tricarbonyl complexes with multidentate nitrogen-donor derivatives

Article abstract of DOI:10.1016/j.poly.2012.08.078

The reaction of [Re(CO)₅X] (X = Cl, Br) with a series of six potentially multidentate nitrogen donor ligands (L1-L6) was studied. The ligands L1-L5 are coordinated bidentately in the neutral complexes of the type fac-[Re(CO)₃X(L)] (1-5). The complex salt [Re(CO)₃(L6)]Br (6) was formed by the reaction of [Re(CO)₅Br] with 2-aminobenzaldehyde (aba), in which the tridentate ligand L6 was formed by the Schiff base condensation of three aba molecules. The crystal structures for complexes 1-6 were determined by X-ray single crystal diffraction. UV-Vis absorption spectra of the complexes show the intraligand and MLCT transitions. Electrochemical behaviour of the complexes was studied with cyclic voltammetry.

Full text of DOI:10.1016/j.poly.2012.08.078

Polyhedron 49 (2013) 67–73
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Rhenium(I) tricarbonyl complexes with multidentate nitrogen-donor derivatives
a
a
c
Kim Potgieter a, Peter Mayer b, Thomas Gerber a, , Nonzaliseko Yumata , Eric Hosten , Irvin Booysen ,
⇑
Richard Betz a, Muhammed Ismail c, Bernardus van Brecht a
a Department of Chemistry, Nelson Mandela Metropolitan University, 6031 Port Elizabeth, South Africa
b Department of Chemistry, Ludwig-Maximilians University, D-81377 München, Germany
c School of Chemistry, University of Kwazulu-Natal, Pietermaritzburg, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2012
Accepted 28 August 2012
Available online 12 September 2012
The reaction of [Re(CO)5X] (X = Cl, Br) with a series of six potentially multidentate nitrogen donor ligands
(L1–L6) was studied. The ligands L1–L5 are coordinated bidentately in the neutral complexes of the type
fac-[Re(CO)3X(L)] (1–5). The complex salt [Re(CO)3(L6)]Br (6) was formed by the reaction of [Re(CO)5Br]
with 2-aminobenzaldehyde (aba), in which the tridentate ligand L6 was formed by the Schiff base con-
densation of three aba molecules. The crystal structures for complexes 1–6 were determined by X-ray
single crystal diffraction. UV–Vis absorption spectra of the complexes show the intraligand and MLCT
transitions. Electrochemical behaviour of the complexes was studied with cyclic voltammetry.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Multidentate ligands
Rhenium(I) tricarbonyl
Nitrogen-donors
X-ray structures
1. Introduction
2. Experimental
The coordination chemistry of the metals rhenium and techne-
tium has been well studied over the last half century, mainly be-
cause of the potential applications of their 186/188Re and 99mTc
isotopes in therapeutic and diagnostic agents in nuclear medicine
[1]. Initially the focus was mainly on the [MO]3+ core (M = Re,
Tc), but the discovery of the cardiac imaging agent [99mTc(MIBI)6]+
(MIBI = 2-methoxy-2-methylpropylisocyanide) has shifted the
attention to the +I oxidation state [2]. The commercial availability
of the compounds [Re(CO)5X] (X = Cl, Br) and the easy syntheses of
the synthons [M(CO)3(H2O)3]+ and [M(CO)3X3]2ꢀ have led to exten-
sive studies exploring the robust fac-[M(CO)3]+ core with a large
variety of multidentate ligands containing a combination of nitro-
gen, sulfur and oxygen donor atoms [1,3].
Complexes of the type [M(CO)3(NN)X] (NN = bidentate nitro-
gen-donor chelates) have been shown to possess interesting
photophysical, photochemical and excited-state redox properties
[4]. These properties have presented the possibility of using this
class of complexes as fluorescent probes, in addition to their poten-
tial application as radioimaging and therapeutical agents.
In this study a range of functionalized bidentate nitrogen-donor
ligands (L1–L6) are synthesized, and their coordination chemistry
with the fac-[Re(CO)3]+ core is investigated, together with their
structural and spectroscopic properties.
2.1. Materials and instrumentation
All materials were commercially available and were used as re-
ceived. [Re(CO)5X] and all the starting materials for the syntheses
of the ligands L1–L6 were obtained from Aldrich.
Infrared (IR) spectra were recorded on a Digilab FTS3100 Excal-
ibur HE spectrophotometer and were run as KBr pellets. 1H NMR
spectra were recorded on a Bruker Avance 300 MHz spectrometer
as solutions in DMSO-d6 at 25° C, using TMS as internal standard.
Electronic spectra were obtained with a Shimadzu UV-3100 spec-
trophotometer, and emission spectra at room temperature on a
Perkin Elmer LS45 fluorescence spectrometer. Microanalyses were
obtained on a Carlo Erba EA1108 elemental analyser, and melting
points were determined on an Electrothermal IA-900 apparatus.
Conductivity measurements (in the unit
X
ꢀ1 cm2 molꢀ1) were car-
ried out with 10ꢀ3 M solutions at 298 K with a Phillips PW9509
conductometer. The cyclic voltammetry (CV) studies were carried
out with a Bas Epsilon Version 1.30.64 system which consists of
a platinum working electrode, a platinum wire auxiliary electrode
and a pseudo silver/silver chloride Re-5 reference electrode. The
supporting electrolyte, tetrabutylammonium toluene-4-sulfonate,
had a concentration of 0.1 M and the respective complex concen-
trations were 2 mM. Dichloromethane was used as solvent for
the complexes. All the CV runs were done at a scan rate of
200 mV/s between 1500 and ꢀ1500 mV. Before runs the sample
solutions were deoxygenated by nitrogen.
⇑
Corresponding author. Fax: +27 41 5044236.
E-mail address: thomas.gerber@nmmu.ac.za (T. Gerber).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.078

68
K. Potgieter et al. / Polyhedron 49 (2013) 67–73
2.2. Syntheses of the complexes
7.4. Found: C, 46.2; H, 2.1; N, 7.1%. IR (cmꢀ1):
1927vs, 1885vs;
(C@N) 1579s. 1H NMR (ppm): 9.22 (d, 2H,
m(CO)fac 2011vs,
m
2.2.1. General method for complexes 1–5
H32), 8.58 (d, 2H, H33), 8.52 (s, 2H, H36), 8.39 (d, 2H, H13), 8.26
Two equivalents of ligands L1–L5 and 100 mg of [Re(CO)5X] in
20 cm3 of toluene were heated under reflux for 2 h under nitrogen.
The solutions were allowed to cool to room temperature, and the
precipitates were removed by filtration and were washed with
diethyl ether. Recrystallization from dichloromethane/n-hexane
(for complexes 1, 3–5) or methanol (for 2) produced crystals suit-
able for X-ray crystallography.
(d, 2H, H16), 7.73 (t, 2H, H14), 7.65 (t, 2H, H15). UV–Vis (DMF, kmax
(e
, Mꢀ1cmꢀ1)): 307 (19400), 331 (19300), 392 (4480). CV: 1.31 V
(versus Fc/Fc+). Conductivity (DMF): 26.
2.2.1.5. [Re(CO)3Br(L5)]ꢁH2O (5). Orange. Yield: 88 mg (57%), m.p.
235° C. IR (cmꢀ1):
m
m(CO)fac 2021vs, 1905vs br; m(C@O) 1688s,
(C@N) 1584s. 1H NMR (ppm): 9.70 (s, 1H, H4), 8.56 (d, 1H, H13),
8.41(d, 1H, H16), 7.79(t, 1H, H15), 7.46 (br s, 2H, NH2), 7.31 (t,
2.2.1.1. [Re(CO)3Br(L1)] (1). Colourless. Yield: 112 mg (68%), m.p.
289° C. Anal. Calc. for C25H28BrN2O3Re: C, 44.8; H, 4.2; N, 4.2.
1H, H14), 3.42(s, 3H, C(6)H3), 3.18(s, 3H, C(5)H3). UV–Vis (DMF,
kmax (e
, Mꢀ1 cmꢀ1)): 359 (6800), 440 (2200). CV: 0.81 V (versus
Found: C, 44.6; H, 4.1; N, 4.0%. IR (cmꢀ1):
m
CO)fac 2020vs, 1928vs,
(C@N) 1631s. 1H NMR (ppm): 9.21 (s, 2H, H5, H15),
6.94 (s, 2H), 6.88 (s, 2H), 4.46 (dd, 2H, CH2), 4.10 (dd, 2H, CH2),
Fc/Fc+). Conductivity (DMF): 21.
1869vs;
m
2.2.1.6. [Re(CO)3(L6)]Br (6). 2-Aminobenzaldehyde (82 mg, 1.0 m
2.51 (s, 6H), 2.32 (s, 6H), 2.25 (s, 6H). UV–Vis (CH2Cl2, kmax (e -
, Mꢀ1
mol) was added to a solution of 100 mg of [Re(CO)5Br] (246 lmol)
cmꢀ1)): 309 (196000), 351 (79600). CV: 0.99 V (versus Fc/Fc+).
Conductivity (CH3CN): 19.
in 20 cm3 of toluene, and the mixture was heated under reflux in a
nitrogen atmosphere for 3 h. After cooling to room temperature, an
orange precipitate was collected by filtration. It was washed with
diethyl ether and dried under vacuum. The mother liquor was
refrigerated for 2 days to produce needles, suitable for X-ray crys-
tallography. Total yield: 112 mg (73%), m.p. 285° C. IR (cmꢀ1):
2.2.1.2. [Re(CO)3Cl(L2)] (2). Red. Yield: 144 mg (69%), m.p. 231° C.
Anal. Calc. for C27H24ClN6O5Re.H2O: C, 43.1; H, 3.5; N, 11.2. Found:
C, 43.0; H, 3.7; N, 10.9%. IR (cmꢀ1):
m
(CO)fac 2017vs, 1905vs br;
(C@N) 1562s. 1H NMR (ppm): 8.88 (s, 2H, H1,
H2), 7.32–7.64 (m, 10H). UV–Vis (CH3CN, kmax
, Mꢀ1 cmꢀ1)):
(CO)fac 2020vs, 1946s, 1886vs; m
(C@N) 1610s. 1H NMR (ppm):
m(C@O) 1654s; m
m
10.49 (d, 3H, CH@N). UV–Vis (DMF, kmax (e
, Mꢀ1cmꢀ1)): 308
(e
(13700), 400 (2300). CV: 0.99 V (versus Fc/Fc+). Conductivity
(DMF): 42.
385 (50200), 402sh (47700), 510 (31400). CV: 1.00 V (versus Fc/
Fc+). Conductivity (CH3CN): 21.
2.2.1.3. [Re(CO)3Br(L3)] (3). Orange. Yield: 132 mg (63%), m.p.
278° C. Anal. Calc. for C32H27BrN7O5Re: C, 44.9; H, 3.2; H, 11.5.
2.3. X-ray crystallography
Found: C, 44.6; H, 3.3; N, 11.3%. IR (cmꢀ1):
m
(CO)fac 2020vs,
X-ray diffraction studies on the crystals of compound 1 were
done at 200(2) K on a Nonius Kappa CCD detector system, and all
the other complexes were studied with a Bruker Kappa Apex II dif-
fractometer. In crystals of 1 the coordinated bromide and CO share
the same coordination sites and are disordered, and a split model
was applied with a sof ratio of 0.63:0.37, and the C and O of the less
occupied part were refined isotropically.
1920vs, 1902vs;
m(C@O) 1658s br: m
(C@N) 1586 m br. 1H NMR
(ppm): 10.14 (s, 1H, H7), 9.33 (s, 1H, H6), 8.32 (m, 2H), 7.50–7.54
(m, 4H), 7.34–7.45 (m, 7H), 3.24 (s, 3H), 3.22 (s, 3H), 2.58 (s, 3H),
2.54 (s, 3H). UV–Vis (CH3CN, kmax (e
, Mꢀ1 cmꢀ1)): 371 (28200),
446 (16400). CV: 1.07 V (versus Fc/Fc+). Conductivity (CH3CN): 5.
2.2.1.4. [Re(CO)3Cl(L4)] (4). Orange. Yield: 54 mg (66%),
m.p. > 300° C. Anal. Calc. for C29H14ClN4O3ReS2: C, 46.3; H, 1.9; N,
The structures were solved by direct methods applying SIR97
[6] and refined by full-matrix least-squares procedures using the
Table 1
Crystal and refinement data for the complexes.
1
2
3
4
5
6
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
670.6
monoclinic
P21/c
19.4694(5)
8.6247(2)
15.7929(3)
109.965(1)
752.2
monoclinic
P21/c
15.3940(3)
10.5480(2)
20.9820(4)
122.544(1)
855.72
monoclinic
P21/c
14.284(2)
14.580(2)
17.233(3)
109.020(6)
752.24
monoclinic
C2/m
17.8280(3)
16.2170(3)
10.7570(3)
100.471(1)
627.43
monoclinic
P21/c
13.8880(3)
10.8576(2)
13.8173(3)
104.312(1)
677.52
triclinic
ꢀ
P1
9.1029(2)
9.3235(2)
14.9266(4)
b (°)
a
78.044(1)
b 82.103(1)
66.219(1)
c
V (Å3)
Z
2492.5(1)
4
1.787
2872.0(1)
4
1.740
3393.0(9)
4
1.675
3058.2(1)
4
1.634
2018.9(1)
4
2.064
1132.1(1)
2
1.988
7.168
Dcalc (g cmꢀ1
)
l
(mmꢀ1
)
6.506
4.376
4.808
4.233
8.039
Absorption correction
method
Multi-scan
numerical
numerical
multi-scan
numerical
numerical
F (000)
1304
1480
1672
1456
1192
648
h range (°)
Index ranges
3.2–27.6
ꢀ25/25,ꢀ11/
11,ꢀ20/20
37067
5740/4569
5740/313
1.06
2.3–28.3
ꢀ20/20,ꢀ11/
14,ꢀ27/27
26124
7050/6474
7050/381
1.27
2.5–27.4
ꢀ18/13,ꢀ18/
18,ꢀ22/22
30416
7707/6494
7707/415
1.05
1.7–28.4
ꢀ21/23,ꢀ21/
21,ꢀ14/14
24549
3939/3185
3939/187
0.96
2.4–46.1
ꢀ28/28,ꢀ21/
21,ꢀ27/27
124500
17589/12865
17589/255
1.04
2.6–28.3
ꢀ11/12,ꢀ12/
12,ꢀ19/19
19854
5621/5439
5621/298
1.10
Reflections measured
Independent/observed
Data/parameters
Goodness-of-fit (GoF) on
F2
Final R indices (I > 2
r
(I))
)
0.0264, 0.0555
1.52/ꢀ0.54
0.0199, 0.0475
1.36/ꢀ1.02
0.0421, 0.1262
2.15/ꢀ2.58
0.0336, 0.0680
1.42/ꢀ1.08
0.0304, 0.0889
3.02/ꢀ1.60
0.0136, 0.0338
0.57/ꢀ0.83
Largest peak/hole (e Åꢀ3

K. Potgieter et al. / Polyhedron 49 (2013) 67–73
69
Table 2
3.2. Synthesis and characterization of the complexes
Selected bond lengths (Å) and angles (°) for complexes 1–6.
The potentially bidentate nitrogen-donor ligands L1 and L2, the
tridentate chelators L3 and L5 and the potentially tetradentate L4
were reacted with [Re(CO)5X] (X = Cl, Br) under nitrogen in tolu-
ene. All these ligands produced the neutral complexes fac-
[Re(CO)3X(L)], in which the ligands L are coordinated bidentately
via two nitrogen-donor atoms. The use of a twofold molar excess
of ligands produced all these complexes in high yields. The ligand
L6 was formed by the metal-induced self-assembly condensation
reaction of three 2-aminobenzaldehyde molecules, and the com-
plex salt fac-[Re(CO)3(L6)]Br (6) is the result of the substitution
of two carbonyls and the bromide from [Re(CO)5Br] by L6 (see
Scheme 2). Metal-directed self-assembly as a technique has been
used extensively for the syntheses of macromolecular rectangular
[8], triangular [9] and square [10] compounds containing the fac-
[Re(CO)3]+ core.
1
Re–N(1)
Re–Br(1)
Re–Br(2)
N(1)–C(3)
N(1)–C(5)
N(2)–C(15)
C(1)–Re–N(2)
N(1)–Re–N(2)
C(1)–Re–C(2)
2.199(3)
2.616(1)
2.612(3)
l.474(7)
1.270(6)
1.266(6)
176.0(1)
77.5(1)
Re–N(2)
Re–C(1)
Re–C(2)
Re–C(31)
Re–C(41)
C(1)–O(1)
C(2)–Re–N(1)
C(5)–N(1)–C(3)
C(4)–N(2)–C(15)
2.209(3)
1.931(4)
1.912(4)
1.89(1)
1.88(1)
1.137(5)
175.9(2)
116.7(4)
117.1(4)
85.5(2)
2
Re–N(1)
Re–Cl(1)
N(1)–C(1)
N(1)–C(12)
C(1)–N(1)–C(12)
N(1)–Re–N(2)
Cl(1)–Re–N(1)
Cl(1)–Re–N(2)
2.173(2)
2.4741(8)
1.292(4)
1.401(3)
120.0(2)
74.08(8)
81.98(6)
84.63(7)
Re–N(2)
Re–C(90)
Re–C(91)
N(2)–C(2)
C(2)–N(2)–C(32)
N(1)–Re–C(92)
N(2)–Re–C(90)
Cl(1)–Re–C(90)
2.182(2)
1.918(3)
1.906(3)
1.303(3)
116.7(2)
174.7(1)
169.4(1)
92.7(1)
All the complexes 1–6 are stable in air. They are soluble in a
wide variety of solvents like dichloromethane, DMF, DMSO, aceto-
nitrile and acetone, and are non-electrolytes (except 6) in DMF and
acetonitrile. Their IR spectra are characterized by a sharp strong
band around 2020 cmꢀ1, and either a broad, intense absorption
around 1905 cmꢀ1 or two intense bands in the range 1885–
3
Re–N(1)
Re–Br(1)
N(2)–C(6)
N(1)–Re–N(2)
N(1)–Re–C(50)
C(6)–N(2)–C(12)
C(7)–N(3)–C(22)
2.223(6)
2.612(1)
1.289(8)
75.1(2)
170.3(3)
115.8(6)
120.6(6)
Re–N(2)
Re–C(50)
N(3)–C(7)
Br(1)–Re–N(1)
Br(1)–Re–N(2)
Br(1)–Re–C(50)
Br(1)–Re–C(52)
2.205(5)
1.905(8)
1.301(9)
83.5(2)
84.2(1)
91.3(2)
174.6(2)
1946 cmꢀ1, attributed to (CO) of the fac-[Re(CO)3]+ unit [11].
m
Additional evidence for the proposed compositions and formu-
lations of the ligands and complexes is provided by elemental anal-
ysis and 1H NMR data. In all the complexes the proton signals of
the ligands L display significant downfield shifts when compared
with the corresponding proton shifts of the free ligands. In the
spectra of complexes 1–3, 5 and 6 the signal of the methine proton
CH@N occurs the furthest downfield as a singlet in the range d
8.88–10.49 ppm. Because of the symmetrical nature of the ligands
L1–L4, the corresponding protons on their substituents are mag-
netically equivalent and consequently give signals at the same fre-
quency. For example, one signal (at 9.57 ppm) for the two methine
protons and only two singlets (at 2.48 and 3.25 ppm) for the four
methyl groups are observed in the spectrum of L3. However, in
complex 3 the magnetic equivalence of the corresponding protons
is removed, and two signals for the methine protons (at 10.14 and
9.33 ppm) and four singlets for the four methyl groups on the anti-
pyrine rings are observed. This observation intimates the bidentate
coordination of L3 in the complex 3. On the other hand, the mag-
netic equivalence of the corresponding protons on the benzthiazole
and pyridinic rings of L4 is retained in the complex 4, albeit shifted
downfield in the latter, implying that coordination occurs through
the two phenanthroline nitrogen atoms only, with free benzthiaz-
ole groups. In complex 6 only a single singlet is observed for the
three methine protons, and a single pattern of a doublet–triplet–
doublet–triplet for the four protons of the three phenyl rings.
The reaction of [Re(CO)5X] with bidentate nitrogen-donor li-
gands (L) has been well studied. Octahedral complexes of the type
fac-[Re(CO)3X(L)] have been isolated in all the cases with 2,2-
dipyridine [12], 1,10-phenanthroline [13] and piperazine [14]
and their derivatives as ligands. However, with tridentate benz-
imidazole and quinoline derivatives, complex salts of the type
[Re(CO)3(L)]X were obtained [15].
4
Re–N(2)
Re–Cl(1)
C(1)–N(1)
N(2)–Re–N(2i)
N(2)–Re–C(90)
2.210(3)
2.479(1)
1.292(5)
75.0(1)
Re–C(90)
Re–C(91)
C(1)–S(1)
Cl(1)–Re–C(91)
C(1)–N(1)–C(12)
1.905(4)
1.916(6)
1.743(4)
179.3(2)
109.3(3)
170.0(1)
5
Re–N(1)
Re–Br(1)
N(2)–C(4)
N(5)–C(24)
N(1)–Re–N(2)
C(4)–N(2)–C(21)
2.166(2)
2.6189(2)
1.295(3)
1.337(2)
74.85(6)
116.8(2)
Re–N(2)
Re–C(1)
Re–C(2)
Re–C(3)
Br(1)–Re–C(3)
N(1)–Re–C(1)
2.200(2)
1.922(2)
1.910(2)
1.904(2)
177.01(7)
175.10(8)
6
Re–N(1)
Re–N(2)
Re–N(3)
N(1)–C(17)
N(3)–C(19)
N(1)–Re–N(2)
N(2)–Re–N(3)
N(1)–Re–C(112)
N(1)–Re–C(111)
2.159(2)
2.145(2)
2.150(2)
1.284(3)
1.281(2)
79.14(6)
79.53(6)
170.31(7)
94.41(7)
N(1)–C(17)
N(2)–C(18)
N(3)–C(19)
N(2)–C(18)
1.284(3)
1.281(2)
1.281(2)
1.281(2)
1.436(2)
79.46(6)
117.7(2)
171.86(7)
97.06(8)
N(1)–C(31)
N(1)–Re–N(3)
C(17)–N(1)–C(31)
N(2)–Re–C(113)
N(3)–Re–C(112)
SHELXL-97 package [7]. All non-hydrogen atoms were refined aniso-
tropically, and the hydrogen atoms were calculated in idealized
geometrical positions. Crystal and structure refinement data are gi-
ven in Table 1, with selected bond distances and angles in Table 2.
3. Results and discussion
3.1. Ligand syntheses
The preparation of the ligands L1–L5 are summarized in Scheme
1. The ligand L1 was synthesized by the Schiff base formation con-
densation reaction between 1,2-diaminoethane and 2,4,6-trimeth-
ylbenzaldehyde in toluene. The Schiff base L2 was obtained from
glyoxal and 4-aminoantipyrine (aap), and L3 was prepared simi-
larly from 2,6-pyridinedicarbaldehyde and aap. The benzthiazole
derivative L4 was synthesized from 2-aminothiophenol and 1,10-
phenantroline-2,9-dicarbaldehyde [5] in polyphosphoric acid, and
L5 from the condensation of 4,5-diamino-1,3-dimethyl uracil and
pyridine-2-aldehyde.
3.3. Crystallographic studies
The X-ray crystallographic data confirms that all the complexes
contain the inert fac-[Re(CO)3]+ core in a distorted octahedral envi-
ronment around the rhenium(I) centre. The structures of the com-
plexes 1–6 are given in Figs. 1–6, respectively.
In complex 1 the rhenium(I) is coordinated to three carbonyl
donors in a facial orientation, to the two imino nitrogen atoms
N(1) and N(2), and to a bromide (Fig. 1). The Re–C bond distances

70
K. Potgieter et al. / Polyhedron 49 (2013) 67–73
Me
Me
HC
N
N
CH
Me
Me
2
+
Me Me
L1
H2N
NH2
OHC
Me
O
Me
O
H2N
O
Me
Me
N
N
N
N
N
N
+
2
N
O
O
N
C6H5
C6H5
C6H5
L2
N
H2N
O
O
O
N
2
N
N
+
N
N
N
C6H5
C6H5
C6H5
N
N
O
O
N
Me
Me
Me
Me
L3
NH2
SH
N
N
2
+
N
N
S
S
N
N
O
O
L4
Me
N
Me
N
H2N
N
O
H2N
H2N
O
N
N
+
N
N
Me
C
Me
CHO
H
O
O
L5
Scheme 1. Schematic representation of ligand synthesis.
are close to orthogonality. The N(1)–C(5) [1.270(6) Å] and N(2)–
C(15) [1.266(6) Å] are double bonds.
NH2
The different substituents on the imino nitrogen atoms in com-
plex 2 have an impact on the physical parameters of the compound
(Fig. 2). The bite angle [N(1)–Re–N(2) = 74.08(8)°] is considerable
smaller than in 1 [77.5(1)°], with the result that the distortion from
the ideal octahedron around the rhenium(I) is more severe. For
example, the trans angles N(1)–Re–C(92) = 174.7(1)° and N(2)–
Re–C(90) = 169.4(1)° are both smaller than the corresponding an-
gles in 1. The N(1)–C(1) [1.292(4) Å] and N(2)–C(2) [1.303(3) Å]
bonds are double and are considerably longer than in complex 1,
with a concomitant shorter C(1)–C(2) bond length [1.443(4) Å]
than the corresponding bond in 1 [C(3)–C(4) = 1.513(6) Å]. The
N(1)C(1)C(2)N(2) torsion angle is 5.0(4)°, compared with the corre-
sponding angle in 1 [N(1)C(3)C(4)N(2) = 54.8(5)°]. The average Re–
N bond length [2.178(2) Å] is shorter than in 1. The bond lengths
and angles in the antipyrine rings are normal and do not deserve
any comment.
Toluene
[Re(CO)5Br]
+
3
6
CHO
Scheme 2. Schematic representation of the synthesis of complex 6.
[average 1.90(1) Å] fall in the range observed [1.900(2)–1.928(2) Å]
for similar complexes [12–16]. The two Re–N bond lengths are
similar [average of 2.204(3) Å] and are typical for Re(I)–N(imine)
bonds [17]. The distortion from octahedral ideality is mainly the
result of the trans angles N(1)–Re(2)–C(2) = 175.9(2)°, N(2)–Re–
C(1) = 176.0(1)°, Br(1)–Re–C(31) = 178.9(3)° and Br(2)–Re–C(41)
= 176.6(4)°. These distortions are the result of the constraints im-
posed by the bidentate ligand, which forms a five-membered
[N(1)–Re–N(2) = 77.5(1)°] metalloring. The C(1)–Re–C(31) [89.9
(3)°], C(2)–Re–C(3) [89.6(3)°] and C(2)–Re–C(41) [89.4(4)°] angles

K. Potgieter et al. / Polyhedron 49 (2013) 67–73
71
O2
O31
O1
C24
C21
C13
C23
C20
C1
C8
C31
C2
C12
C7
C19
C9
C16
C15
Re1
C10
C18
N2
C6
N1
C17
Br1
C11
C5
C4
C3
C14
C22
Fig. 1. ORTEP diagram of the molecular structure of 1. Thermal ellipsoids are drawn at 40% probability, and hydrogen atoms have been omitted for clarity.
N1
N2
Re1
Cl1
C91
C90
C92
Fig. 2. Molecular diagram and atom numbering scheme for 2.
C3
C2
C1
Br1
C4
C5
O1
N3
C6
N2
N1
C51
C11
C22
C7
N5
C12
C21
O2
Re1
N4
C52
C13
C50
O51
O52
O50
Fig. 3. Structure of complex 3.
In complex 3 the ligand L3 is coordinated bidentately through
the pyridyl nitrogen N(1) [Re–N(1) = 2.223(6) Å] and the imine
nitrogen N(2) [Re–N(2) = 2.205(5) Å], with N(3) uncoordinated.
The small bite angle of L3 [N(1)–Re–N(2) = 75.1(2) Å] contributes
considerably to the distortion from the octahedral geometry,
with the average trans angle being 171.4(3)°. The N(1)
C(1)C(6)N(2) torsion angle is small [ꢀ1.4(9)°], and the N(2)–C
(6) bond [1.289(8) Å] is surprisingly shorter than the N(3)–C(7)
one [1.301(9) Å]. The rest of the bond lengths and angles are
unexceptional.

72
K. Potgieter et al. / Polyhedron 49 (2013) 67–73
C36
i
C34
C36
C34
C33
i
Cl1
i
C32
C1
C33
C35
i
C35
N2
S1
C31
i
C32
i
N2
Re1
i
C31
C11
C16
i
C90
C90
i
i
O90
C1
O90
i
S1
N1
C91
C12
C13
i
N1
i
C11
O91
i
C12
C15
C14
i
C16
i
C13
i
C15
i
C14
Fig. 4. ORTEP drawing of complex 4 with numbering scheme.
Br
N5
C4
N2
C21
C24
N1
C2
Re
C1
C3
O2
O1
O3
Fig. 5. Molecular diagram for 5.
In complex 4 the Cl(1)–Re–CO(91) axis [Cl(1)–Re–C(91) = 179.3
in 3 [2.205(5) Å], the Re–N(1) bond length is surprisingly and
considerably shorter [2.166(2) Å] than in 3 [2.223(6) Å]. This
difference can only be ascribed to steric and electronic effects of
the uncoordinated antipyrine substituent in 3. The difference in
the Re–Br bond lengths is insignificant [2.6189(2) Å in 5,
2.612(1) Å in 3]. The N(1)–Re–N(2) bite angle of 74.85(6)° is prac-
tically the same as in 3 [75.1(2)°].
The molecular structure of complex 6 is shown in Fig. 6. It
shows that the complex cation contains the fac-[Re(CO)3]+ core
which is coordinated to the three imino nitrogen atoms N(1),
N(2) and N(3) in a distorted octahedral geometry. The average
Re–N bond length is 2.151(2) Å, and the average N–Re–N bite angle
is 79.38(6)°, which is larger than in the previous complexes due to
the formation of six-membered metallorings, and contributes con-
siderably to the distortion. For example, the average N–Re–C trans
(2)°] lies in a rv mirror plane. The two Re–N bonds are identical
[2.210(3) Å], as are the two Re–C(90) bond lengths [1.905(4) Å].
The N(2)–Re–N(2i) bite angle equals 75.0(1)°, identical to that in
3, with the trans angle N(2)–Re–C(90) = 170.0(1)°. It is noticeable
that the repulsion between Cl(1) and the two nitrogen atoms are
more severe [Cl(1)–Re–N = 81.06(9)°] than with the carbon atoms
C(90) [Cl(1)–Re–C(90) = 90.5(1)°]. In the thiazole rings the N(1)–C
(1) bond is a distinct double bond [1.292(5) Å].
The potentially tridentate ligand L5 is coordinated in a biden-
tate manner in complex 5, with coordination via the pyridinic
nitrogen N(1) and imino nitrogen N(2), with a free amino N(5)H2
group. Since the coordination sphere is the same as in complex 3,
very similar bond parameters are expected. While the Re–N(2)
bond length of 2.200(2) Å is very similar to the corresponding bond

K. Potgieter et al. / Polyhedron 49 (2013) 67–73
73
potentially bidentate to tetradentate). In the products fac-[Re(CO)3-
Br(L)] the ligands L1–L5 are coordinated in a bidentate manner, but
in [Re(CO)3(L6)]Br the ligand L6 acts as a tridentate chelate. The
structures of all the complexes are distorted octahedral with the
robust fac-[Re(CO)3]+ core.
O2
O1
C2
Re
O3
N2
C1
C3
Appendix A. Supplementary data
CCDC 870709, 871799–871801, 880485 and 878940 contain the
supplementary crystallographic data for 1, 3, 2, 4, 5 and 6. These
data can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
N3
C19
C18
C31
N1
C17
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atoms is 118.07(2)°.
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less common. As is also shown in this study, they are difficult to
synthesize. For example, the reaction of [Re(CO)5Cl] with
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conditions, and by the use of Ag(CF3SO3) for halide abstraction,
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3.4. Electronic absorption
The absorption spectra of the complexes 1–6 consist of several
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absorption bands in the 300–520 nm spectral region. The intense
bands of the complexes, related to intraligand (p ?
p⁄) transitions,
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are observed in the UV spectral region (<380 nm), and they are red-
shifted in comparison to the free ligands. At lower energy, all com-
plexes exhibit the absorptions of a metal-to-ligand charge transfer,
dp
(Re) ? p⁄(N–N) (MLCT). It is noted that the MLCT absorptions
are more intense for complexes 3 and 4, which is reasonable since
they have more conjugated
p systems [19–21].
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3.5. Electrochemistry
Oxidation–reduction processes were determined by cyclic vol-
tammetry, and the potentials are given in the Experimental sec-
tion. All the complexes exhibit a single irreversible wave in the
region 0.80–1.31 V (versus Fc/Fc+), which are all assigned to a
Re(I)-based oxidation process (Re(I)/Re(II)) [19–22].
4. Conclusion
This study was a systematic attempt to study the reaction of
[Re(CO)5X] with a series of multidentate nitrogen ligands (from