Coordination of bidentate aniline derivatives to the fac-[Re(CO) 3]+ core

Article abstract of DOI:10.1016/j.poly.2011.04.019

A series of rhenium(I) tricarbonyl complexes, containing bidentate derivatives of aniline, was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the '2+1' complex salt fac-[Re(CO)₃(Hpda) ₂]Br was isolated. The neutral complex [Re(CO)₃(Hapa)Br] was formed with 2-aminodiphenylamine (Hapa) as ligand. 2-Aminophenol (Hopa) also produced the neutral '2+1' complex [Re(CO)₃(opa)₂(Hopa)], but with 2-mercaptophenol (Hspo) the bridged dimer [Re₂(CO) ₇(spo)₂] was found. In the complex [Re(CO) ₃(Htpn)Br] (Htpn = N′-{(2-methylthio)benzylidene}benzene-1,2- diamine) the potentially tridentate ligand Htpn is coordinated via the methylthio sulfur and imino nitrogen atoms only, with a free amino group.

Full text of DOI:10.1016/j.poly.2011.04.019

Polyhedron 30 (2011) 1739–1745
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Coordination of bidentate aniline derivatives to the fac-[Re(CO)3]+ core
a
a
a
b
T.I.A. Gerber a, , R. Betz , I.N. Booysen , K.C. Potgieter , P. Mayer
⇑
a Department of Chemistry, Nelson Mandela Metropolitan University, 6031 Port Elizabeth, South Africa
Department of Chemistry, Ludwig-Maximilians University, D-81377 Munchen, Germany
b
}
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of rhenium(I) tricarbonyl complexes, containing bidentate derivatives of aniline, was synthesized
and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)3
(Hpda)2]Br was isolated. The neutral complex [Re(CO)3(Hapa)Br] was formed with 2-aminodiphenyl-
amine (Hapa) as ligand. 2-Aminophenol (Hopa) also produced the neutral ‘2+1’ complex [Re(CO)3(opa)2
(Hopa)], but with 2-mercaptophenol (Hspo) the bridged dimer [Re2(CO)7(spo)2] was found. In the com-
plex [Re(CO)3(Htpn)Br] (Htpn = N0-{(2-methylthio)benzylidene}benzene-1,2-diamine) the potentially tri-
dentate ligand Htpn is coordinated via the methylthio sulfur and imino nitrogen atoms only, with a free
amino group.
Received 15 March 2011
Accepted 11 April 2011
Available online 23 April 2011
Keywords:
Bidentate ligands
Aniline derivatives
Rhenium(I) tricarbonyl
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
(Hapa), 2-aminophenol (Hopa) and 2-mercaptophenol (Hspo) were
obtained from Aldrich. The ligand Htpn was synthesized by the
The nuclear properties of the 99mTc and 186/188Re isotopes have
made them ideal for application as diagnostic and therapeutic
radiopharmaceuticals respectively [1]. Initially most research ef-
forts were focussed on the [MVO]3+ core (M = Tc, Re), since it could
easily be obtained from the permetalate, but since the discovery of
the cardiac imaging agent [99mTc(MIBI)6]+ (MIBI = 2-methoxy-2-
methylpropylisocyanide) [2] and the easy preparation of the syn-
thons [M(CO)3(H2O)3]+ and [M(CO)3X3]2ꢀ (X = Cl, Br), the research
efforts have shifted to the +I oxidation state [3]. Studies on these
synthons have illustrated a high substitution lability of the three
halides and water molecules, with a concomitant stability of the
three carbonyl ligands [4]. It was therefore not surprising that tri-
dentate chelates with a combination of oxygen, sulfur, nitrogen
and phosphorus donor atoms were initially investigated as possi-
ble ligands for the [M(CO)3]+ core [5].
simple condensation of equimolar amounts of (2-methylthio)
benzaldehyde with 1,2-diaminobenzene in ethanol/toluene [6].
Infrared (IR) spectra were recorded on a Digilab FTS 3100 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.
Microanalyses were obtained on a Carlo Erba EA1108 elemental
analyzer, and melting points were determined on an Electrother-
mal IA-900 apparatus. Conductivity measurements (in the unit
ohmꢀ1 cmꢀ2 molꢀ1) were carried out with 10ꢀ3 M solutions in
methanol at 293 K with a Phillips PW 9509 conductometer.
2.2. Synthesis of the complexes
2.2.1. General method
In this paper we report on the synthesis and structural charac-
terization of the rhenium(I) complexes formed by the reaction of
[Re(CO)5Br] and the potentially bi- and tridentate ligands depicted
in Scheme 1.
The ligands Hpda, Hapa, Hopa, Hspo and Htpn (490
lmol) were
added to a solution of [Re(CO)5Br] (100 mg, 246 mol) in 20 mL of
l
toluene, and the mixtures were heated at reflux for an hour under
nitrogen. After cooling to room temperature, the solutions were fil-
tered and left to evaporate slowly at room temperature. After
3 days light yellow crystals, suitable for X-ray diffraction studies,
were collected from the mother liquor. They were washed with
diethyl ether and dried under vacuum.
2. Experimental
2.1. Materials and instrumentation
2.2.1.1. [Re(CO)3(Hpda)2]Br (1). Yield 0.079 g (57%), m.p. 252 °C.
Anal. Calc. for C15H16N4O3BrRe: C, 31.8; H, 2.8; N, 9.9. Found: C,
All materials were commercially available and used as received.
[Re(CO)5Br], 1,2-diaminobenzene (Hpda), 2-aminodiphenylamine
31.8; H, 3.0; N, 9.7%. IR (cmꢀ1):
m(NH2) 3104m, 3169m, 3194m,
3245m;
m(C„O) 2031s, 1925s, 1880s; m(ReAN) 528m, 513m,
⇑
484m. 1H NMR (ppm): 7.14–7.34 (m, 4H), 6.48 (d, 1H, H12), 6.17
Corresponding author. Fax: +27 41 5044236.
E-mail address: thomas.gerber@nmmu.ac.za (T.I.A. Gerber).
(m, 3H). Conductivity: 126.
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.04.019

1740
T.I.A. Gerber et al. / Polyhedron 30 (2011) 1739–1745
X
Y
7.89–7.33 (m, 5H), 7.11 (t, 1H), 6.72 (t, 1H), 6.55 (t, 1H), 3.08 (s,
3H, SCH3). Conductivity: 75.
2.3. X-ray crystallography
CH=N
X-ray diffraction studies on the crystals of compounds 1, 2, 3
and 5 were performed at 200(2) K on a Nonius Kappa CCD detector
system using the
x scan technique with Mo Ka radiation. Crystals
of 4 were studied with a Bruker Kappa Apex II diffractometer. In
complex 1 the monodentate Hpda ligand is disordered, and a split
model was applied with a sof ratio of 0.7:0.3. The non-hydrogen
atoms of the main part were refined anisotropically, and those of
the minor part isotropically. The structures were solved by direct
methods applying SIR97 [7] and refined by full-matrix least-squares
procedures using the SHELXL-97 package [8]. All non-hydrogen
atoms were refined anisotropically, and the hydrogen atoms were
calculated in idealized geometrical positions. Crystal and structure
refinement data are given in Table 1, with selected bond distances
and angles in Table 2.
SMe
X
Scheme 1. Structures of the ligands used in the study.
2.2.1.2. [Re(CO)3(Hapa)Br] (2). Yield 0.083 g (62%), m.p. 131 °C.
Anal. Calc. for C15H12N2O3BrReꢁ0.125C7H8: C, 34.9; H, 2.4; N, 5.1.
Found: C, 34.7; H, 2.6; N, 5.0%. IR (cmꢀ1):
m
(NH, NH2) 3170m,
3192m, 3267m; m(CO) 2032s, 1926s, 1882s; m(ReN) 533m, 513m.
1H NMR (ppm): 7.10–7.35 (m, 5H, H6, H7, H12, H13, H14), 6.55
(d, 2H, H5, H8), 6.20 (d, 2H, H11, H15), 3.47 (br s, 3H, N(1)H2,
N(2)H). Conductivity: 37.
3. Results and discussion
2.2.1.3. [Re(CO)3(opa)(Hopa)] (3). Yield 0.078 g (65%), m.p. >300 °C.
Anal. Calc. for C15H13N2O5Re: C, 37.0; H, 2.7; N, 5.7. Found: C, 36.8;
3.1. Synthesis and characterization
H, 2.7; N, 2.6%. IR (cmꢀ1):
m
(NH2) 3273m, 3207m;
m(CO) 2029s,
1925s, 1882s;
m
(ReN) 416m. 1H NMR (ppm): 7.76–7.83 (m, 4H,
The compounds 1–5 were synthesized by the reactions of
[Re(CO)5Br] with the corresponding ligands in toluene.
H6, H7, H8, H9), 7.27–7.34 (m, 4H, H12, H13, H14, H15), 6.50 (s,
4H, 2 ꢂ NH2), 3.23 (s, 1H, OH). Conductivity: 32.
The complex salt [Re(CO)3(Hpda)2]Br (1) was formed by the
substitution of two carbonyls and the bromide from [Re(CO)5Br].
The substitution of two carbonyls only from [Re(CO)5Br] by
2-aminodiphenylamine (Hapa) produced the neutral complex
[Re(CO)3(Hapa)Br] (2), with bidentate coordination of Hapa.
Although reasonably good yields of [Re(CO)3(opa)(Hopa)] (3) were
obtained from a 2:1 molar ratio of 2-aminophenol (Hopa) and [Re(-
CO)5Br], the best yield (81%) was achieved with a 5:1 molar ratio.
The reaction of 2-mercaptophenol (Hspo) with [Re(CO)5Br] formed
the neutral dimeric complex [Re2(CO)7(spo)2] (4), with a deproto-
nated sulfur atom of each spo ligand forming a double bridge.
The potentially tridentate ligand Htpn is coordinated as a neutral
bidentate chelate in the complex [Re(CO)3(Htpn)Br] (5).
2.2.1.4. [Re2(CO)7(spo)2] (4). Yield 0.062 g (62%), m.p. 155 °C. Anal.
Calc. for C19H10O9S2Re2: C, 27.9; H, 1.2. Found: C, 27.8; H, 1.5%.
IR (cmꢀ1):
m
m
(CO) 2016s, 1932s, 1914s, 1887s;
m(ReAO) 472m;
(ReAS) 357m. 1H NMR (ppm): 7.12 (d, 1H, H6), 7.04 (d, 1H,
H12), 6.84–6.91 (m, 2H, H4, H10), 6.61–6.66 (m, 2H, H5, H11),
6.44 (d, 2H, H3, H9). Conductivity: 33.
2.2.1.5. [Re(CO)3(Htpn)Br] (5). Yield 0.096 g (66%), m.p. 195–197 °C.
Anal. Calc. for C17H14N2O3SBrRe: C, 34.5; H, 2.4; N, 4.7. Found: C,
34.6; H, 2.6; N, 4.9%. IR (cmꢀ1):
m
(NH2) 3064m;
m(CO) 2033s,
1923s, 1896s;
m
(ReS) 354m. 1H NMR (ppm): 9.36 (s, 1H, H11),
Table 1
Crystal and structure refinement data for the complexes.
1
2
3
4
5
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
C
15H16N4O3BrRe
C15H12N2O3BrRe
545.96
C15H13N2O5Re
487.48
monoclinic
P21/n
13.2298(2)
13.0295(4)
19.1889(5)
C19H10S2O9Re2
818.83
monoclinic
P21/n
12.5117(5)
9.1612(3)
18.9629(8)
C17H14N2O3SBrRe
592.48
monoclinic
P21/c
7.0339(1)
19.7023(3)
12.8887(2)
566.42
triclinic
P1
triclinic
ꢀ
ꢀ
P1
8.3815(2)
10.5477(2)
10.8571(3)
108.126(2)
92.235(2)
105.478(2)
871.28(4)
2
12.3607(4)
14.4372(5)
19.8623(7)
92.841(3)
97.270(3)
99.281(3)
3461.1(2)
8
b (Å)
c (Å)
a
(°)
b (°)
104.588(1)
94.910(1)
94.362(1)
c
(°)
V (Å3)
3201.1(1)
8
2.023
7.618
1856
2165.6(1)
4
2.511
11.411
1512
1781.0(1)
4
2.210
9.202
1120
Z
Dcalc (g cmꢀ1
)
2.151
9.287
532
2.091
9.344
2042
l
(mmꢀ1
)
F(0 0 0)
h Range (°)
3.2–27.5
4.1–25.3
3.3–27.5
2.9–28.3
3.2–27.5
Index ranges
ꢀ10/10, ꢀ13/13, ꢀ14/14 ꢀ15/15, ꢀ11/18, ꢀ24/24 ꢀ17/17, ꢀ16/15, ꢀ24/22 ꢀ16/16, ꢀ7/12, ꢀ25/25 ꢀ9/9, ꢀ25/25, ꢀ16/16
Reflections measured
Independent/observed
reflections
18 983
24 861
50 739
20 003
46 334
3971/3587
12 476/7612
7306/5054
5316/5012
4076/3769
Data/parameters
3971/222
1.06
12 476/809
0.73
7306/415
1.03
5316/289
1.13
4076/227
1.06
Goodness-of-fit on F2
Final R indices (I > 2
r
(I))
)
0.0213, 0.0452
0.92/ꢀ0.71
0.0309, 0.0441
0.80/ꢀ0.77
0.0303, 0.0640
1.53/ꢀ1.25
0.0432, 0.1112
3.20, ꢀ4.19
0.0193, 0.0458
0.87/ꢀ1.04
Largest peak/hole (e Åꢀ3

T.I.A. Gerber et al. / Polyhedron 30 (2011) 1739–1745
1741
Table 2
and presence of the chelates in the complexes, but due to the over-
lapping of peaks in the aromatic region the assignment of signals
could not be made with confidence. However, the methine proton
C(11)H in 5 occurs the furthest downfield at d 9.36 ppm. All of
them (except 1, which is a 1:1 electrolyte) are non-electrolytes in
methanol.
Selected bond lengths (Å) and angles (°) for the complexes.
1
Re–C(13)
Re–C(14)
Re–C(15)
N(1)–C(1)
1.906(4)
1.906(4)
1.904(4)
1.456(5)
1.41(2)
76.8(1)
115.8(2)
87.9(2)
Re–N(1)
Re–N(2)
Re–N(3)
N(3)–C(7)
O(1)–C(13)
N(1)–Re–C(13)
N(2)–Re–C(14)
N(3)–Re–C(15)
2.211(3)
2.224(3)
2.256(3)
1.501(9)
1.162(5)
176.3(1)
171.6(1)
178.1(2)
N(4)–C(8)
N(1)–Re–N(2)
Re–N(3)–C(7)
C(13)–Re–C(15)
3.2. Description of the structure of complex 1
2
A perspective view of the asymmetric unit of 1 is shown in
Fig. 1. The X-ray results show that the rhenium(I) complex cation
contains the chemically robust fac-[Re(CO)3]+ core in a distorted
octahedral geometry. The rhenium(I) is coordinated to three car-
bonyl donors in a facial orientation, to the two amino nitrogen
atoms N(1) and N(2) of one Hpda ligand, and to one nitrogen atom
N(3) of a second Hpda. The amino group N(4)H2 is uncoordinated.
The ReAC bond distances [average of 1.905(4) Å] fall in the range
observed [1.900(2)–1.928(2) Å] for similar complexes [10]. The
two ReAN bond lengths of the bidentate ligand is similar [average
of 2.218(3) Å, and noticeably shorter than the ReAN(3) length
[2.256(3) Å] (see Table 2). However, all three lengths are typical
for ReAN(amino) bonds [11].
Re–Br(1)
Re–C(1)
N(1)–Re–N(2)
C(9)–N(2)–C(10)
2.6429(8)
1.873(9)
76.1(2)
Re–N(1)
Re–N(2)
N(1)–Re–C(3)
N(2)–Re–C(1)
2.202(4)
2.217(5)
171.7(2)
172.9(3)
114.2(5)
3
Re(1)–N(1)
Re(1)–O(1)
O(2)–C(11)
O(1)–Re(1)–N(1)
O(1)–Re(1)–C(2)
N(2)–Re(1)–C(3)
2.213(4)
2.133(3)
1.363(6)
77.2(1)
172.6(2)
174.9(2)
Re(1)–N(2)
Re(1)–C(2)
Re(2)–N(4)
Re(1)–N(2)–C(10)
O(1)–Re(1)–C(1)
N(2)–Re(1)–C(2)
2.259(4)
1.908(6)
2.270(4)
119.2(3)
96.4(2)
94.6(2)
4
Re(1)–S(11)
Re(2)–S(11)
Re(1)–O(12)
O(12)–C(12)
Re(1)–C(1)
2.488(1)
2.527(1)
2.220(5)
1.397(8)
1.912(6)
2.003(7)
98.65(5)
98.06(5)
168.9(2)
172.7(2)
Re(1)–S(21)
Re(2)–S(21)
Re(1)–C(2)
O(22)–C(22)
Re(2)–C(4)
Re(2)–C(6)
S(11)–Re(1)–S(21)
S(11)–Re(2)–S(21)
C(5)–Re(2)–C(6)
S(11)–Re(2)–C(4)
2.522(1)
2.516(1)
1.895(6)
1.377(8)
1.931(6)
2.007(7)
81.63(4)
80.98(4)
178.0(3)
175.4(2)
Table 3
Re(2)–C(5)
Hydrogen bond data (Å) for complexes 1, 3 and 5.
Re(1)–S(11)–Re(2)
Re(1)–S(21)–Re(2)
S(21)–Re(1)–C(1)
S(11)–Re(1)–C(3)
DAHꢁ ꢁ ꢁA
d(DAH)
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
\(DHA)
1
N(1)H(1A)ꢁ ꢁ ꢁBr(1)
N(1)H(1B)ꢁ ꢁ ꢁBr(1)
N(2)H(2A)ꢁ ꢁ ꢁBr(1)
N(2)H(2A)ꢁ ꢁ ꢁO(1)
N(2)H(2B)ꢁ ꢁ ꢁO(1)
N(3)H(3A)ꢁ ꢁ ꢁBr(1)
N(3)H(3A)ꢁ ꢁ ꢁN(4)
N(3)H(3B)ꢁ ꢁ ꢁBr(1)
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
2.64
2.53
2.66
2.58
2.39
2.60
2.48
2.52
3.529(3)
3.422(3)
3.495(3)
2.893(4)
2.893(4)
3.506(3
2.827(6)
3.428(3)
163
164
151
100
115
167
103
168
5
Re–Br(1)
Re–N(1)
Re–S(1)
N(1)–C(11)
N(1)–Re–C(2)
S(1)–Re–C(1)
Br(1)–Re–C(3)
C(1)–N(1)–C(12)
C(4)–S(1)–C(5)
2.6263(3)
2.202(2)
2.4684(8)
1.287(4)
177.0(1)
175.7(1)
175.2(1)
114.3(2)
99.7(2)
Re–C(1)
Re–C(2)
Re–C(3)
N(2)–C(13)
Br(1)–Re–S(1)
Br(1)–Re–N(1)
Br(1)–Re–C(1)
Br(1)–Re–C(2)
C(2)–Re–C(3)
1.934(3)
1.924(3)
1.911(3)
1.361(4)
85.31(2)
83.35(6)
93.0(1)
93.8(1)
90.9(1)
3
N(1)H(1A)ꢁ ꢁ ꢁO(2)
O(2)H(2)ꢁ ꢁ ꢁO(3)
N(2)H(2A)ꢁ ꢁ ꢁO(2)
N(3)H(3B)ꢁ ꢁ ꢁO(4)
O(4)H(4)ꢁ ꢁ ꢁO(1)
N(4)H(4B)ꢁ ꢁ ꢁO(4)
0.92
0.84
0.92
0.92
0.84
0.92
2.06
1.73
2.31
2.00
1.73
2.36
2.867(5)
2.566(4)
2.683(5)
2.821(5)
2.533(4)
2.703(4)
146
169
104
148
160
102
All the complexes 1–5 are stable in air. They are soluble in a
wide variety of solvents like methanol, DMF, DMSO, acetonitrile
and acetone, but insoluble in dichloromethane and chloroform.
Their IR spectra are characterized by three intense bands around
5
N(2)H(2B)ꢁ ꢁ ꢁBr(1)
0.88
0.88
2.59
2.56
3.457(2)
2.868(3)
167
101
2030, 1925 and 1880 cmꢀ1, typical of (C„O) of the fac-[Re(CO)3]+
m
N(2)H(2B)ꢁ ꢁ ꢁN(1)
unit [9]. The 1H NMR spectra clearly establish the diamagnetism
C11
C12
C10
C7
N3
Br1
C6
N1
C5
O2
C1
C8
C9
C14
Re1
N4
O1
C4
C2
C3
N2
C13
C15
O3
Fig. 1. ORTEP view of complex 1, showing 40% probability displacement ellipsoids and the atom-labeling.

1742
T.I.A. Gerber et al. / Polyhedron 30 (2011) 1739–1745
mild conditions by the simple ligand substitution of [Re(CO)5X]
(X = Cl, Br) is unusual. For example, the reaction of 2,20:6;200-terpyr-
idine (terpy) with [Re(CO)5Cl] led to the formation of [Re(CO)3
C5
C6
(r
2-terpy)Cl]. Only by drastic action (by refluxing with silver per-
C4
N1
chlorate in acetonitrile overnight) could the cationic complex [Re
Br1
C7
(CO)3(r
2-terpy)(CH3CN)]+ be formed [14]. Complex 1 is a unusual
example of a ‘2+1’ compound with the [Re(CO)3]+ core prepared
in an one-pot procedure. A similar example is the complex
[Re(CO)3(phen)(pyridine)]+, which was synthesized under harsh
conditions in a two-step process [15]. The fact that complex 2,
[Re(CO)3(Hapa)Br], contains only one Hapa ligand, illustrates that
electronic and steric factors play a role in its dissimilarity to
complex 1.
C8
O1
C9
C1
N2
Re1
C10
C2
C3
C11
3.3. Description of the structure of 2
O2
C15
O3
The asymmetric unit contains four molecules of [Re(CO)3(Ha-
pa)Br]. The rhenium(I) is coordinated to three carbonyl donors in
a facial orientation, to the two amino nitrogens N(1) and N(2),
and a bromide (Fig. 2). The ReAN(2) bond [2.217(5) Å] is signifi-
cantly longer than ReAN(1) [2.202(4) Å], and they are both typical
for ReAN(amino) bonds [11]. The bite angle [N(1)AReAN(2)] of
Hapa is 76.1(2)°, which delineates the trans angles [N(1)AReA
C(3) = 171.7(2)°, N(2)AReAC(1) = 172.9(3)°] (see Table 2). The Re-
N(1)AC(4) and ReAN(2)AC(9) bond angles are 113.6(3)° and
111.7(4)° respectively, with the C(9)AN(2)AC(10) angle at
114.2(5)°.
C14
C12
C13
Fig. 2. Molecular structure of complex 2. Hydrogen atoms have been omitted for
clarity.
The distortion from octahedral ideality is mainly the result of
the trans angles, with N(1)AReAC(13) = 176.3(1)°, N(2)AReAC
(14) = 171.6(1)° and N(3)AReAC(15) = 178.1(2)°. These distortions
are the result of the constraints imposed by the bidentate ligand,
which forms a five-membered [N(1)AReAN(2) = 76.8(1)°] metal-
loring. This argument is manifested in the larger (closer to linear-
ity) bond angle between the trans monodentate ligand/donor
C(15)O and N(3)H2. The average CAReAC bond angle is 88.6(2)°.
A comparison of the N(4)AC(8) bond length [1.41(2) Å] with the
longer N(3)AC(7) one [1.445(4) Å] clearly shows the effect of coor-
dination on this type of bond.
3.4. Description of the structure 3
The crystal structure consists of pi-dimer stacks (Fig. 3) and the
asymmetric unit consists of four of these dimer units. The distance
between the ring centroids of these pi-stacks is 4.419 Å.
Each metal is coordinated to three carbonyl donors in a facial
orientation, to a neutral amino nitrogen (N(2) or N(4) of Hopa)
and to a neutral amino nitrogen (N(1) or N(3)), and a deprotonated
phenolate oxygen (O(1) or O(3)) of opa. The phenolate oxygens
O(2) and O(4) are protonated and uncoordinated.
The bromide counter-ion is involved in a series of hydrogen
bonds in the lattice (see Table 3).
The formation of [Re(CO)3(Hpda)2]Br (1) is surprising since neu-
tral bidentate nitrogen-donor ligands usually form neutral com-
plexes of the type [Re(CO)3(NN)Br] [11–13]. The preparation of
cationic Re(I) complexes (containing the [Re(CO)3]+ core) under
Focussing on the structure around Re(1), there is a notable dif-
ference in the ReANH2 bond lengths [Re(1)AN(1) = 2.213(4) Å;
Re(1)AN(2) = 2.259(4) Å] of the coordinated opa and Hopa ligands.
The Re(1)AO(1) bond length of 2.133(3) Å is considerably longer
Fig. 3. A perspective view of the asymmetric unit of complex 3.

T.I.A. Gerber et al. / Polyhedron 30 (2011) 1739–1745
1743
than that found for bidentate N,O-donor ligands in Re(V) com-
plexes (usually around 2.00 Å), but is similar to other Re(I)AO bond
lengths, which occur in the range 2.120(8)–2.152(9) Å [11,16,17].
The bite angle of opa [N(1)ARe(1)AO(1) = 77.2(1)°] results in
the trans angles falling in the narrow range of 172.6(2)–
174.9(2)°. The packing of the complexes in the unit cell is comple-
mented by an extensive network of hydrogen bonds (Table 3).
[Re(CO)3(opa)(Hopa)] (3) is another example of a ‘2+1’ complex
containing the [Re(CO)3]+ core. In order to obtain neutrality, the
Hopa ligand coordinates via the neutral amino nitrogen, rather
than through the neutral O(2)H group, an example of which is also
shown in complex 4. The preference for the amino nitrogen is
understandable, since the d6 system would have a lower affinity
for the more electronegative oxygen donor atom, which prefers io-
nic interaction with the metal. This feature was observed in the
lengths are practically identical, as are Re(2)AC(5) and Re(2)AC(6)
(see Table 2). The difference between the C(22)AO(22) [1.377(8) Å]
and C(12)AO(12) [1.397(8) Å] lengths are small. The
C(4)ARe(2)AC(6) [90.4(3)°], C(4)ARe(2)AC(5) [91.5(3)°] and
C(4)ARe(2)AC(7) [90.5(3)°] are close to orthogonality.
The potentially bidentate ligand Hspo provides somewhat of a
dilemma for the [Re(CO)3]+ core, since both the OH and SH groups
can be deprotonated. However, in the complex [Re2(CO)7(spo)2]
only the mercapto sulfur atoms are deprotonated. The different
coordination behavior of the two spo ligands is surprising, since
bidentate coordination of both would have led to the symmetrical
complex [Re(CO)3(spo)]2, with sulfide bridges. A second possibility
would be to form the symmetrical dimer [Re(CO)4(spo)]2, with
sulfide bridges and free OH groups. We cannot explain this anom-
alous behavior. Interestingly, with tropolone (Htrp) the anionic
monomer [Re(CO)3(trp)Br]ꢀ was isolated [20].
‘2+1’
complex
[Re(CO)3(ons)(Hopa)]
(Hons = 2-[(2-methyl-
thio)benzylideneimino]phenol; Scheme 1), with ons coordinated
bidentately as a N,Oꢀ-donor, and Hopa monodentately via the
neutral amino nitrogen [18]. Although the deprotonation of phe-
nylamino groups occurs readily in rhenium(V) complexes (due to
the hard acidic properties of Re(V)), it is not observed for the
[Re(CO)3]+ core [18,19].
3.6. Description of the structure of 5
The X-ray results show that the bidentate ligand Htpn is coordi-
nated via the imino nitrogen N(1) and the thioethereal sulfur S(1)
to the metal, which resides in a distorted octahedral environment
(Fig. 5). The ReAN(1) bond length of 2.202(2) Å is typical of rhe-
nium(I)Aimine bonds [12], and the ReAS(1) length of 2.4684(8) Å
is in the range observed for similar bonds [21]. The N(1)AC(11)
bond is double, with a length of 1.287(4) Å, and the angle
C(11)AN(1)AC(12) [114.3(2)°] is slightly smaller than would be
expected around a sp2-hybridized nitrogen atom. The smaller bite
angle of Htpn [N(1)AReAS(1) = 86.18(7)°] results in larger trans
angles [175.2(1)–177.0(1)°], when compared to the other com-
plexes in the study.
3.5. Description of the structure of 4
The structure is shown in Fig. 4. The dimeric molecule has a
rhombic (l-S)2Re2 unit at the center. Each sulfido-bridge is
symmetrical, with unequal ReAS distances of 2.488(1)
[Re(1)AS(11)], 2.522(1) [Re(1)AS(21)], 2.527(1) [Re(2)AS(11)]
and 2.516(1) Å [Re(2)AS(21)]. The ReARe distance across the
rhombus is 3.8038(3) Å, implying no ReARe bonding.
The dimer consists of two different halves. Each rhenium is in a
distorted octahedral environment. Re(1) is coordinated to the car-
bon atoms of three carbonyls, the two charged sulfur atoms S(11)
and S(21), and the phenolic oxygen O(12). The Re(1)AO(12) bond
length of 2.220(5) Å intimates that this oxygen is neutral, and thus
protonated. As stated above for complex 3, the length of a rhe-
nium(I)Aphenoxy bond falls in the range 2.120(8)–2.152(9) Å
[16]. The bite angle of the bidentate ligand is 77.0(1)°
[S(11)ARe(1)AO(12)], leading to trans angles in the range
168.9(2)–174.4(2)°.
One of the hydrogen atoms of the free amino group is involved
in two hydrogen bonds to Br(1) and N(1) (Table 3). These interac-
tions may be responsible for the remarkable value of ꢀ0.2(4)° for
the N(1)AC(12)AC(13)AN(2) torsion angle.
Whereas in complex 5 the potentially tridentate N2S-donor li-
gand Htpn coordinates as a bidentate N,S-donor (with a free amino
group), the very similar NSO-donor ligand Hons (see Scheme 1)
coordinates as a NO-donor (via the imino nitrogen and deproto-
nated oxygen with a free methylthio group) in the complex
[Re(CO)3(ons)(Hopa)] [18]. Complexes with the fac-[Re(CO)3]+ core
have been well studied with potentially tridentate ligands, which
commonly contain N, O and S donor atoms from amine [22],
pyridyl [23], carboxyl [24] or thioether [25] groups in octahedral
In the second half of the molecule Re(2) is bonded to four car-
bonylic carbons and the two sulfido bridging atoms. The O(22)H
group is not coordinated. The Re(2)AC(4) and Re(2)AC(7) bond
O3
C3
O1
C1
Re1
O2
C2
C25
O12
C26
C24
C12
C13
C21
S21
C14
C22
C23
S11
C11
O5
C15
C16
C5
Re2
O22
C6
O6
C7
C4
O7
O4
Fig. 4. Structure of complex 4.

1744
T.I.A. Gerber et al. / Polyhedron 30 (2011) 1739–1745
C16
C7
C17
C8
C15
C11
C4
C6
C12
C14
N1
C9
C13
O3
N2
C5
C10
S1
Re1
C3
Br1
C1
O1
C2
O2
Fig. 5. View of the structure of 5, showing the atom-numbering and 40% thermal ellipsoids.
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This study was a systematic attempt to study the reaction of
[Re(CO)5Br] with a series of potentially bidentate ligands with an
aromatic backbone. The ligands were varied in terms of different
donor atoms, and to be coordinated as neutral, monoanionic or
dianionic chelates in the rhenium(I) complexes. The reaction of
the N,N-donor ligand 1,2-diaminobenzene (Hpda) with [Re(-
CO)5Br] gives the ‘2+1’ complex salt [Re(CO)3(Hpda)2]Br (1).
Increasing the steric bulk of the diamine by using 2-aminodiphen-
ylamine (Hapa) as ligand produces the neutral complex [Re(CO)3
(Hapa)Br] (2). Changing the ligand to the monoanionic bidentate
2-aminophenol (Hopa), the neutral ‘2+1’ complex fac-[Re(CO)3
(opa)(Hopa)] (3) was found. With the dianionic bidentate ligand
2-mercapto-phenol the di(sulfido) bridged species [Re2(CO)7(s-
po)2] (4) was isolated. Giving the [Re(CO)3]+ core a choice of donor
atoms in the ligand Htpn, a thioether sulfur donor atom is
preferred to an amino nitrogen as donor atom in the complex
[Re(CO)3(Htpn)Br] (5).
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