Rhenium(I), (III) and (V) complexes of tridentate ONX (X = O, N, S)-donor Schiff bases

Article abstract of DOI:10.1016/j.poly.2010.01.013

The reactions of the potentially tridentate Schiff bases 2-[(2-hydroxyphenyl)iminomethyl]phenol (H₂ono) and 2-(2-aminobenzylideneimino)phenol (H₃onn) with trans-[ReOBr₃(PPh₃)₂] were studied, and the complexes [Re^IIIBr(PPh₃)₂(ono)] (1) and [Re^VBr(PPh₃)₂(onn)]Br (2) were isolated. In 1 ono acts as a dianionic tridentate ligand, and in 2 onn is coordinated as a tridentate trianionic imido-imino-phenolate. The complex [Re^I(CO)₃(ons)(Hno)] was isolated from the reaction of [Re(CO)₅Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH₃ group. These complexes were characterized by X-ray crystallography, NMR and IR spectroscopy.

Full text of DOI:10.1016/j.poly.2010.01.013

Polyhedron 29 (2010) 1423–1430
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Rhenium(I), (III) and (V) complexes of tridentate ONX (X = O, N, S)-donor
Schiff bases
P. Mayer a, K.C. Potgieter b, T.I.A. Gerber b,
*
a Department of Chemistry, Ludwig-Maximilians University, D-81377 München, Germany
b Department of Chemistry, Nelson Mandela Metropolitan University, 6031 Port Elizabeth, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of the potentially tridentate Schiff bases 2-[(2-hydroxyphenyl)iminomethyl]phenol
(H2ono) and 2-(2-aminobenzylideneimino)phenol (H3onn) with trans-[ReOBr3(PPh3)2] were studied,
and the complexes [ReIIIBr(PPh3)2(ono)] (1) and [ReVBr(PPh3)2(onn)]Br (2) were isolated. In 1 ono acts
as a dianionic tridentate ligand, and in 2 onn is coordinated as a tridentate trianionic imido-imino-phe-
nolate. The complex [ReI(CO)3(ons)(Hno)] was isolated from the reaction of [Re(CO)5Br] with 2-[(2-
methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate
chelate with a free SCH3 group. These complexes were characterized by X-ray crystallography, NMR and
IR spectroscopy.
Received 11 December 2009
Accepted 12 January 2010
Available online 18 January 2010
Keywords:
Rhenium(I, III, V)
Tridentate Schiff bases
Multidentate imido chelate
X-ray structures
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
One approach to the development of radiopharmaceuticals
containing rhenium and technetium has been the use of Schiff
bases as ligands to stabilize the [MO]3+ core (M = Re, Tc) [1–14].
Schiff bases have been shown to be versatile ligands, especially
in terms of their donor atoms and substituents, thereby providing
the possibility for designing rhenium and technetium complexes
with useful biological properties [2]. Most of these studies included
Schiff bases derived from salicylaldehyde, and various ligand
derivatives were investigated, including bi-, tri-, and tetradentate
versions [4–7].
The geometries of these complexes depend on the nature of
the ligand, that is, the number and type of coordinating atoms,
and the chain length between the coordinating atoms. Pentaden-
tate examples containing the MO3+ core in a square-pyramidal
configuration include [MOCl(OPhsal)] (OPhsal = N-(2-oxidophe-
nyl)salicylideneiminate) [11] and [MOCl(SPhsal)] (SPhsal = N-(2-
sulfidophenyl)salicylideneiminate) [8]. Six-coordinate complexes
containing the MO3+ cores in a distorted octahedral geometry are
represented by [MO(OPhsal)(8-quinolinate)] [12] and [MOCl(Ph-
Concentrating on tridentate Schiff base ligands and rhenium(V),
reactions of the ligand N-(2-hydroxyphenyl)salicylideneimine
(HOPhsalH) with [ReOCl4]- have been investigated [15]. The oxo-
rhenium(V) complexes (Bu4N)[ReOCl3(HOPhsal)], (Bu4N)[ReOCl2-
(OPhsal)], cis-[ReOCl(MeOH)(OPhsal)], trans-[ReOCl(H2O)(OPhsal)],
cis-[ReOCl(PPh3)(OPhsal)] and cis-[ReOCl(PMe2Ph)(OPhsal)] have
been isolated and characterized. Six-coordinate complexes of
rhenium(V) with the general formula [ReO(OPhsal)L] (L = Phsal,
8-quinolinolate) have also been isolated from the reactions of
[ReOCl(MeOH)(OPhsal)] and HL in ethanol [12].
sal)2] (Phsal = phenylsalicylideneiminate) [14], while
l-O[MO-
(sal2pn)]2 (sal2pn = N,N’-propane-1,3-bis(salicylideneiminate) [2]
is an example of a six-coordinate compound containing the
[M2O3]4+ core and possessing a linear O@M–O–M@O bridge.
* Corresponding author. Fax: +27 41 5044236.
E-mail address: thomas.gerber@nmmu.ac.za (T.I.A. Gerber).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.01.013

1424
P. Mayer et al. / Polyhedron 29 (2010) 1423–1430
Here we report on the attempted synthesis of the potentially
2.4. Synthesis of 2-(2-aminobenzylideneimino)phenol (H3onn)
tridentate Schiff base ligand H2OPhsal, which led to the isolation
of the zwitter-ion derivative H2ono. The reaction of H2ono with
trans-[ReOBr3(PPh3)2] surprisingly led to the isolation of the rhe-
nium(III) complex [ReBr(PPh3)2(ono)] (1), in which ono acts as a
dianionic tridentate ligand.
A solution of 0.38 g of 2-aminobenzaldehyde (3.14 mmol) in
20 cm3 of methanol was added to 0.34 g of 2-aminophenol
(3.12 mmol) in 30 cm3 of methanol. The yellow solution
was heated at reflux temperature under nitrogen for an hour.
Upon cooling a yellow solid formed which was filtered and dried
under vacuum. Yield = 65%, m.p. = 115–120 °C. Anal. Calc. for
C13H12N2O: C, 73.56; H, 5.70; N, 13.20. Found: C, 73.45; H, 5.66;
N, 13.31%. IR (m m(C@N) 1606, m(N–H) 3047, m(OH)
max/cmꢀ1):
3375. 1H NMR (295, ppm): 9.17 (s, br, 1H, OH); 8.88 (s, 1H, CH@N);
7.17 (t, 1H, H(7)); 7.05 (d, 1H, H(9)); 6.94 (d, 1H, H(1)); 6.88 (d, 1H,
H(6)); 6.82 (t, 2H, H(3), H(8)); 6.78 (t, 1H, H(2)); 6.73 (d, 1H, H(4));
4.70 (s, br, 2H, NH2).
O
OH
The corresponding tridentate Schiff bases H3onn and Hons were
also synthesized. The reaction of H3onn with trans-[ReOBr3(PPh3)2]
produced the imidorhenium(V) complex salt [ReBr(PPh3)2(onn)]Br
(2), in which onn is coordinated as a dianionic tridentate imidoimi-
nophenolate. The reaction of Hons with [Re(CO)5Br] led to the iso-
lation of the rhenium(I) product [Re(CO)3(ons)(Hno)] (Hno = 2-
aminophenol), with ons coordinated as a monoanionic bidentate
chelate (with a free SCH3 group), and Hno present as a neutral
monodentate ligand with coordination through the amino nitrogen
atom. Pure products could not be isolated from the reaction of
Hons and trans-[ReOBr3(PPh3)2]. With the ligands H2ono and
H3onn, no pure rhenium(I) complexes of sensible formulation
could be isolated.
2.5. Synthesis of 2-[(2-methylthio)benzylideneimino]phenol (Hons)
2-(Methylthio)benzaldehyde (0.31 g) (mtb, 0.95 mmol) in
20 cm3 of methanol was added to 0.10 g of 2-aminophenol
(0.92 mmol) in 30 cm3 of methanol. The yellow solution was
heated at reflux temperature under nitrogen for an hour. The sol-
vent was removed under vacuum to produce a yellow precipitate,
which was dried under vacuum. Yield = 60%, m.p. = 63–65 °C. Anal.
Calc. for C14H13NOS: C, 69.11; H, 5.39; N, 5.76; S, 13.18. Found: C,
69.08; H, 5.32; N, 5.81; S, 13.15%. IR (
m
m m(N–H) 3373,
max/cmꢀ1):
(C@N) 1628. 1H NMR (295, ppm): 9.35 (d, 1H, H(9)); 9.28 (s, 1H,
H(5)); 7.81 (t, 1H, H(7)); 7.74 (d, 1H, H(1)); 7.62 (t, 1H, H(3));
7.49 (d, 1H, H(6)); 7.42 (t, 1H, H(8)); 7.26 (d, 1H, H(4)); 7.18 (t,
1H, H(2)); 2.77 (s, 3H, CH3).
2.6. Synthesis of [ReBr(PPh3)2(ono)] (1)
A
mixture of H2ono (82 mg, 388
lmol) and trans-[Re-
OBr3(PPh3)2] (104 mg, 107
l
mol) was refluxed in 20 cm3 of ethanol
2. Experimental
for 3 h. The brown solution was left to cool to room temperature,
after which the brown precipitate which formed was filtered,
washed with ethanol and diethyl ether, and dried under vacuum.
Red brown needles were obtained by recrystallization from meth-
anol/dichloromethane. Yield = 55%, m.p. = 220–225 °C. Anal. Calc.
for C49H39BrNO2P2Re: C, 58.74; H, 3.92; N, 1.40. Found: C, 58.66;
2.1. Materials
All chemicals were of reagent grade, and solvents were purified
by standard techniques and drying methods. [Re(CO)5Br] was pur-
chased from Aldrich, and trans-[ReOBr3(PPh3)2] was prepared by a
literature method [12].
H, 3.82; N, 1.43%. IR (
(Re–O) 397. 1H NMR (295 K, ppm): 7.36–7.82 (m, 31H, CH@N,
PPh3); 7.17–7.35 (m, 2H, H(5), H(11)); 6.70–7.15 (m, 6H, H(2),
H(3), H(4), H(8), H(9), H(10)). UV–Vis (CH3CN, kmax
, Mꢀ1 cmꢀ1)):
400 (4850), 558 (3050). Conductivity (CH3CN, 10ꢀ3 M):
13 ohmꢀ1 cm2 molꢀ1
m m(C@N) 1596, m(Re–N) 487,
max/cmꢀ1):
m
2.2. Physical measurements
(e
1H NMR spectra were recorded in DMSO-d6 on a Bruker AX
(300 MHz) spectrometer at ambient temperatures, and values are
reported relative to TMS. Infrared spectra were obtained with a
Digilab FTS 3100 Excalibur HE spectrophotometer with solid sam-
ples prepared as KBr disks. Microanalyses were obtained on a Carlo
Erba EA 1108 elemental analyser.
.
2.7. Synthesis of [ReBr(PPh3)2(onn)]Br (2)
A mass of 62 mg of H3onn (292
lmol) was added to trans-[Re-
OBr3(PPh3)2] (102 mg, 106
l
mol) in 20 cm3 of ethanol. The mixture
was heated under refluxed for 3 h. The brown solution was left to
cool to room temperature, after which the brown precipitate which
formed was collected by filtration. Slow evaporation of a dichloro-
methane/ethanol mixture at room temperature produced red crys-
tals suitable for X-ray diffraction study. Yield = 60%, m.p. >300 °C.
Anal. Calc. for C49H39Br2N2OP2Re: C, 54.50; H, 3.64; N, 2.59. Found:
2.3. Synthesis of 2-[(2-hydroxyphenyl)iminomethyl]phenol (H2ono)
A mass of 0.20 g of 2-aminophenol (1.83 mmol) was dissolved
in 50 cm3 of methanol and 0.23 g of salicylaldehyde (1.87 mmol)
was added. The mixture was refluxed under nitrogen for an hour,
after which the yellow solution was filtered whilst hot. The filtrate
was cooled and placed in a cold room at 4 °C overnight, and orange
crystals were obtained which was filtered and dried under vacuum.
Yield = 59%, m.p. = 187–189 °C Anal. Calc. for C13H11NO2: C, 73.23;
C, 54.47; H, 3.59; N, 2.63%. IR (
1094, (Re–N) 471, (Re–O) 396. UV–Vis (CH2Cl2, kmax
ꢀ1 cmꢀ1)): 443 (4260), 464 (4490), 545 (885). Conductivity
(DMF, 10ꢀ3 M): 82 ohmꢀ1 cm2 molꢀ1
m m(C@N) 1637, m(Re@N)
max/cmꢀ1):
m
m
(e,
M
.
H, 5.20; N, 6.57. Found: C, 73.20; H, 5.15; N, 6.58%. IR (
m
max/cmꢀ1):
m
(C@N) 1616, (C@O) 1633, (N–H) 3041,
m
m
m
(OH) 3220. 1H NMR
2.8. Synthesis of fac-[Re(CO)3(ons)(Hno)] (3)
(295, ppm): 8.97 (s, 1H, CH@N); 7.61 (d, 1H, H(9)); 7.33–7.43 (m,
2H, H(1), H(6)); 7.11 (t, 1H, H(4)); 6.94 (t, 2H, H(3), H(7)); 6.88 (t,
2H, H(2), H(8)); 3.42 (s, br, 1H, OH); 3.15 (s, 1H, NH).
A mixture of Hons (120 mg, 493
lmol) and fac-[Re(CO)5Br]
(100 mg, 246
l
mol) was refluxed in 20 cm3 of toluene for 90 min.

P. Mayer et al. / Polyhedron 29 (2010) 1423–1430
1425
Table 1
Crystal and structure refinement data for the complexes.
H2ono
C13H11NO2
[ReBr(PPh3)2(ono)]
[ReBr(PPh3)2(onn)]Br
[Re(CO)3(ons)(Hno)]
Chemical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C49H39NO2P2BrRe
1001.90
monoclinic
P21/c
C49H39N2OP2Br2Re
1076.22
tetragonal
I41/a
C30H27N2O5SRe
713.82
monoclinic
P21/c
213.23
triclinic
ꢀ
P1
9.0414(9)
10.111(1)
12.3332(9)
69.270(5)
89.938(6)
76.929(4)
1023.4(2)
4
23.7123(3)
18.1459(1)
20.9289(2)
90
114.827(1)
90
8173.0(2)
8
1.628
24.9097(2)
24.9097(2)
37.8279(3)
90
90
90
23472.0(3)
16
1.218
3.465
8457
10.1391(4)
13.0964(5)
21.6913(8)
90
98.970(4)
90
2845.1(2)
4
1.666
b (Å)
c (Å)
a
(ꢁ)
b (ꢁ)
c
(ꢁ)
V (Å3)
Z
DCalc (g cmꢀ1
)
1.384
0.094
448
Absorption coefficient (mmꢀ1
F(0 0 0)
)
4.071
3968
4.386
1408
Crystal size (mm)
h Range
Index ranges
0.03 ꢁ 0.07 ꢁ 0.12
0.02 ꢁ 0.04 ꢁ 0.14
3.1–25.3
ꢀ27/28
0.08 ꢁ 0.10 ꢁ 0.16
4.2–26.3
ꢀ12/7
3.3–25.4
ꢀ10 6 h 6 10
ꢀ12 6k 6 11
ꢀ14 6 ‘ 6 14
6443
ꢀ19/21
ꢀ16/8
ꢀ25/25
ꢀ26/25
Reflections measured
55 399
12 385
Independent/observed reflection
Data/parameters
3731/2294
3731/305
1.037
14 889/11 142
14 889/1007
1.04
5763/3887
5763/320
0.89
Goodness-of-fit on F2
Final R indices (I > 2
r(I)]
0.0696/0.1968(wR2)
0.624/ꢀ0.275
0.0283/0.0679
1.01/ꢀ1.71
0.0318/0.0685
0.94/ꢀ0.72
Largest difference in peak/hole (e Åꢀ3
)
The resultant green solution was cooled to room temperature and
the precipitate which formed was filtered, washed with diethyl
ether and dried under vacuum. Orange crystals were obtained by
the slow evaporation of the mother liquor. Yield = 37%,
m.p. = 172–175 °C. Anal. Calc. for ReC23H19N2O5S.C7H8: C, 50.48;
H, 3.81; N, 3.92; S, 4.49. Found: C, 50.42; H, 3.75; N, 3.98; S,
The signal of the imine proton in the 1H NMR spectrum of
H2ono appears as a singlet at 8.97 ppm. The aromatic region has
five signals in the form of a doublet, multiplet, triplet, triplet and
triplet integrating for one, two, one, two and two protons, respec-
tively. The NH proton is found as a broad singlet at 3.15 ppm and
the phenolate proton’s signal is at 3.42 ppm. The IR spectrum of
H2ono is characterized by a strong absorption at 1633 cmꢀ1, as-
4.47%. IR (
m
max/cmꢀ1):
(Re–N) 490, 474;
m
(N–H) 3414, 3471,
m(C@O)fac 2021, 1905,
m
(C@N) 1601,
m
m
(Re–O) 394. 1H NMR (295 K,
signed to the ketone [
m
(C@O)] stretching frequency. The medium
(C@N).
ppm): 10.02 (s, 1H, H(11)); 9.65 (s, br, 1H, OH); 9.41 (d, 1H,
H(9)); 7.74 (t, 1H, H(8)); 7.46–7.60 (m, 2H, H(7), H(6)); 7.38 (d,
1H, H(17)); 7.05–7.30 (m, 3H, H(14), H(15), H(16)); 6.46–6.88 (m,
4H, H(20), H(21), H(22), H(23)); 3.50 (s, br, 1H, NH); 2.23 (s, 3H,
intensity peak at 1616 cmꢀ1 is ascribed to
m
The asymmetric unit of H2ono contains two independent Schiff
base molecules, which are almost identical to each other (Fig. 1). In
each molecule, the two phenyl rings and azomethine group are
practically coplanar, with the two rings making an average dihe-
dral angle of 9.10° with each other in the two molecules. Both mol-
ecules adopt an (E)-configuration about the N(1)–C(7) and N(2)–
C(20) bonds. The N(1)–C(7) and N(2)–C(20) bond distances
[1.296(3) and 1.303(3) Å, respectively] are close to that of a C–N
double bond [1.28 Å] [20]. The bond angles around C(7) and
N(1) [N(1)–C(7)–C(8) = 123.7(3)°, C(6)–N(1)–C(7) = 127.6(2)°] are
slightly larger than that expected for sp2-hybridization of these
atoms. The corresponding values in the second molecule are
123.5(3)° and 127.6(3)°, respectively. There is a significant differ-
ence in the lengths of the C–O bonds in the molecules. The C(1)–
O(1) bond distance of 1.351(4) Å is considerably longer than the
C(9)–O(2) bond [1.301(3) Å], and is typical of C–OH bonds in
similar compounds [21]. However, the shorter C(9)–O(2) and
C(22)–O(4) [1.299(3) Å] bonds are indicative of a double bond.
The C–C bond lengths in the C(8)–C(13) phenyl ring give further
support to the existence of a C@O entity in this ring. Both
the C(10)–C(11) and C(12)–C(13) bond lengths [1.371(5) and
1.362(5) Å, respectively] are significantly shorter than the other
C–C bonds in this ring [C(8)–C(9) = 1.425(4), C(8)–C(13) =
1.410(4), C(11)–C(12) = 1.391(5), C(9)–C(10) = 1.408(5) Å], indicat-
ing that they can be considered as double bonds, with the latter set
of bonds present as single bonds. In the second molecule the
differences are even more dramatic: C(23)–C(24) = 1.368(5),
C(25)–C(26) = 1.367(4) and C(21)–C(22) = 1.431(4), C(21)–C(26) =
1.411(4), C(22)–C(23) = 1.410(5), C(24)–C(25) = 1.396(5) Å, espe-
CH3). UV–Vis (MeOH, kmax (e
, Mꢀ1 cmꢀ1)): 426 (3190). Conductivity
(MeOH, 10ꢀ3 M): 41 ohmꢀ1 cm2 molꢀ1
.
2.9. X-ray crystallography
X-ray diffraction studies on crystals of H2ono, 1, 2 and 3.C7H8
were performed at 200(2) K using a Nonius Kappa CCD diffractom-
eter with graphite monochromated Mo
Ka radiation (k =
0.71072 Å). The structures were solved by direct methods applying
SIR97 [16] and refined by least-squares procedures using SHELXL-97
[17]. All non-hydrogen atoms were refined anisotropically, and
the hydrogen atoms were calculated in idealized geometrical
positions. The data were corrected by a numerical absorption cor-
rection [18] after optimizing the crystal shape with XShape [19].
Crystal and structure refinement data are given in Table 1, with
selected bond distances and angles in Tables 2 and 4–6 for
H2ono, 1, 2 and 3, respectively.
3. Results and discussion
3.1. Synthesis and characterization of H2ono
The zwitter-ion derivative H2ono of 2-[(2-(hydroxyphenyl)-
imino]methylphenol was isolated from the condensation reaction
of 2-aminophenol with two mole equivalents of salicylaldehyde
in methanol.

1426
P. Mayer et al. / Polyhedron 29 (2010) 1423–1430
Table 2
Table 6
Selected bond lengths (Å) and angles (°) for H2ono.
Selected bond lengths (Å) and angles (°) in [Re(CO)3(ons)(Hno)] (3).
N(1)–C(7)
O(2)–C(9)
O(1)–C(1)
C(7)–C(8)
N(1)–C(6)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
C(11)–C(12)
C(12)–C(13)
C(8)–C(13)
C(4)–C(5)
1.296(3)
1.301(3)
1.351(4)
1.410(4)
1.407(4)
1.425(4)
1.408(5)
1.371(5)
1.391(5)
1.362(5)
1.410(4)
1.383(6)
1.386(4)
127.6(3)
123.7(3)
122.2(3)
124.1(3)
N(2)–C(20)
O(4)–C(22)
O(3)–C(14)
C(20–C(21)
1.303(3)
1.299(3)
1.354(4)
1.405(4)
1.411(4)
1.431(4)
1.410(5)
1.368(5)
1.396(5)
1.367(4)
1.411(4)
1.372(6)
1.391(4)
127.6(3)
123.5(3)
122.4(3)
123.4(2)
Re–C(1)
Re–C(2)
Re–C(3)
S(1)–C(5)
O(4)–C(13)
C(1)–Re–N(1)
C(2)–Re–O(4)
C(3)–Re–N(2)
N(1)–Re–O(4)
C(4)–S(1)–C(5)
N(2)–Re–O(4)
1.910(5)
1.908(5)
1.899(6)
1.773(6)
1.337(6)
170.0(2)
172.2(2)
176.3(2)
76.5(1)
Re–N(1)
Re–N(2)
Re–O(4)
2.204(4)
2.248(4)
2.107(4)
1.299(6)
1.346(6)
88.2(2)
88.8(2)
89.9(2)
119.3(4)
82.5(1)
128.4(4)
N(1)–C(11)
O(5)–C(19)
C(1)–Re–C(2)
C(1)–Re–C(3)
C(2)–Re–C(3)
C(11)–N(1)–C(12)
N(2)–Re–N(1)
C(11)–N(1)–Re
N(2)–C(19)
C(21)–C(22)
C(22)–C(23)
C(23)–C(24)
C(24)–C(25)
C(25)–C(26)
C(21)–C(26)
C(17)–C(18)
C(14)–C(15)
C(20)–N(2)–C(19)
N(2)–C(20)–C(21)
O(4)–C(22)–C(23)
O(3)–C(14)–C(15)
103.4(3)
79.5(1)
C(1)–C(2)
C(7)–N(1)–C(6)
N(1)–C(7)–C(8)
O(2)–C(9)–C(10)
O(1)–C(1)–C(2)
atom (see Table 3). These hydrogen-bonds are instrumental in
stabilizing the zwitter-ion conformation of the molecule.
3.2. Synthesis and characterization of [ReBr(PPh3)2(ono)] (1)
Table 3
Hydrogen-bond distances (Å) and angles (°) in H2ono.
The reaction of trans-[ReOBr3(PPh3)2] with a threefold molar ex-
cess of H2ono in ethanol gave the complex 1, which was formed by
the reduction of rhenium(V) to (III), probably according to the
equation:
D–Hꢂ ꢂ ꢂA
D–H
Hꢂ ꢂ ꢂA
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
O(1)–H(1)ꢂ ꢂ ꢂO(4)
N(2)–H(2)ꢂ ꢂ ꢂO(3)
N(2)–H(2)ꢂ ꢂ ꢂO(4)
O(3)–H(3)ꢂ ꢂ ꢂO(2)
N(1)–H(4)ꢂ ꢂ ꢂO(1)
N(1)–H(4)ꢂ ꢂ ꢂO(2)
1.02
0.93
0.93
1.05
0.89
0.89
1.54
2.28
1.84
1.52
2.33
1.84
2.561(3)
2.660(3)
2.597(4)
2.563(3)
2.652(3)
2.596(4)
176
104
137
170
101
142
½ReVOBr3ðPPh3Þ ꢃ þ H2ono ! ½ReIIIBrðPPh3Þ ðonoÞꢃ þ H2O þ Br2
2
2
The reduction of oxo-phosphino-rhenium(V) complexes to rhe-
nium(III) is not unusual [22]. This is usually achieved by the reduc-
tion of the oxo species by dissociated triphenylphosphine (to form
OPPh3), or by disproportionation of the oxorhenium(V) complex to
the rhenium(III) species and perrhenate ([ReO4]ꢀ). Since the yield
of complex 1 was higher than 50%, and since no dissociation of
PPh3 occurred to produce free PPh3, the only possible reducing
agent in the reaction system is bromide, which would be oxidized
to bromine, as indicated in the above reaction equation.
Complex 1 is soluble in a wide variety of solvents including ace-
tone, acetonitrile, DMF and DMSO. It is stable for months in the so-
lid state and is a non-electrolyte in acetonitrile. In its infrared
spectrum the C@N stretching frequency occurs at 1596 cmꢀ1. The
Re–O and Re–N stretches occur at 397 and 487 cmꢀ1, respectively.
The typical Re@O stretch of rhenium(V) complexes in the 890–
020 cmꢀ1 region is absent, implying that the rhenium(III) product
has formed. The 1H NMR spectrum consists of poorly resolved
broad peaks with paramagnetic shifts and line broadening of the
signals. The multiplet in the region 7.36–7.82 ppm integrates for
31 protons and is assigned to the 30 protons of the two triphenyl-
phosphines and the methine proton of the ono chelate. The signals
of the other protons of the ono ligand occur as two multiplets in the
7.17–7.35 ppm and the 6.70–7.15 ppm region, integrating for two
and six protons, respectively.
A perspective view of the asymmetric unit is shown in Fig. 2.
There are two independent and similar structural units in the
asymmetric unit. The rhenium atom is at the center of a distorted
octahedral environment. The basal plane is defined by the imino
nitrogen atom N(11), the two phenolate oxygens O(1) and O(2),
and the bromide. The two phosphorus atoms are in trans axial posi-
tions. In both complexes there is disorder in the bridging HC@N
structural entity. Distortion form an ideal rhenium-centered
octahedron results in a non-linear P(1)-Re-P(2) axis of 176.27(3)°,
with the trans angles Br(1)-Re-N(11) = 170.9(2)° and O(1)–Re–
O(2) = 170.5(1)° also deviating considerably from linearity (Table
4). The metal is shifted slightly out of the mean equatorial plane
formed by NBrO2 by 0.009 Å towards P(2), with the angles P(2)–
Re–Br(1) = 89.66(2)°, P(2)–Re–O(1) = 88.39(9)°, P(2)–Re–O(2) =
91.9(1)°, and P(2)–Re–N(11) = 90.9(2)°. The two bite angles of the
ono chelate are O(1)–Re–N(11) = 74.5(2)° and O(2)–Re–N(11) =
Table 4
Selected bond lengths (Å) and angles (°) in [ReBr(PPh3)2(ono)] (1).
Re–Br(1)
Re–O(1)
Re–O(2)
Re–N(11)
C(12)–C(131)
P(1)–Re–P(2)
O(1)–Re–O(2)
Br(1)–Re–N(11)
Re–N(11)–C6
C(6)–N(11)–C(131)
Br(1)–Re–O1
2.5434(4)
1.978(2)
1.998(3)
2.054(5)
1.431(8)
176.27(3)
170.5(1)
170.9(3)
120.5(3)
114.7(5)
96.45(7)
Re–P(1)
Re–P(2)
2.467(1)
2.476(1)
1.542(7)
1.30(1)
1.334(4)
88.02(9)
91.8(1)
89.2(2)
89.71(2)
74.5(2)
96.0(2)
Re–N(11)–C(6)
N(11)–C(131)
O(1)–C(1)
P(1)–Re–O(1)
P(1)–Re–O(2)
P(1)–Re–N(11)
P(1)–Re–Br
O(1)–Re–N(11)
O(2)–Re–N(11)
Table 5
Selected bond lengths (Å) and angles (°) for [ReBr(PPh3)2(onn)]Br (2).
Re–N(2)
Re–P(1)
Re–Br
N(1)–C(7)
P(1)–Re–P(2)
N(2)–Re–O(1)
N(2)–Re–P(1)
N(2)–Re–P(2)
C(2)–N(1)–C(7)
Br(1)–Re–P(1)
1.74
2.48
2.53
1.29
177.4
161.1
91.7
90.9
120.1
90.8
Re–O(1)
Re–P(2)
Re–N(1)
N(2)–C(9)
Br(1)–Re–N(1)
N(2)–Re–Br(1)
Re–O(1)–C(1)
N(1)–Re–N(2)
N(1)–Re–O(1)
Br(1)–Re–P(2)
1.96
2.48
2.14
1.38
165.9
110.8
118.6
83.3
77.8
87.9
cially when comparing them with the C(7)–C(8) [1.410(4) Å] and
C(20)–C(21) [1.405(4) Å] bonds. The bond lengths in the C(1)–
C(6) [average = 1.386(6) Å] and C(14)–C(19) [average = 1.385(6) Å]
phenyl rings vary little and are indicative of the delocalization of
electron density in the aromatic systems of these two rings.
The two independent molecules in the asymmetric unit interact
through two intermolecular hydrogen-bonds [O(1)–H(1)ꢂ ꢂ ꢂO(4),
O(3)–H(3)ꢂ ꢂ ꢂO(2)]. In the molecules, there are two intramolecular
hydrogen-bonds each, involving the protonated imine nitrogen
p

P. Mayer et al. / Polyhedron 29 (2010) 1423–1430
1427
C16
C3
C15
C2
C17
C4
C5
C14
C18
C1
C19
O3
O4
C6
N1
N2
O1
C20
C7
C22
C21
O2
C9
C8
C26
C23
C10
C13
C25
C12
C11
C24
Fig. 1. ORTEP view of H2ono, showing 40% probability displacement ellipsoids and the atom labelling.
96.0(2)° reflecting the difference in the coordination angles of the
five- and six-membered metallocycles. The two phenyl rings of
ono are coplanar, making an average dihedral angle of 2.35° with
each other in the two molecules. The bond angle C(6)–N(11)–
C(131) = 114.7(5)° is somewhat less than that expected for a
sp2-hybridized nitrogen atom, and can be ascribed to the disorder
around this entity in the molecule. However, the angle Re–N(11)–
C(6) = 120.5(3)° supports the sp2 nature of N(11).
The bond distances of rhenium with the donor atoms support
its oxidation state of +III. The small difference in the Re–
P(1) = 2.467(1) and Re–P(2) = 2.476(1) Å distances can be ascribed
to structural effects in the solid state. The distances Re–O(1)
[1.978(2) Å] and Re–O(2) [1.998(3) Å] are typical of single rhe-
nium–phenolate bonds, and falls in the range found for this type
of bond in similar complexes [21–23]. The Re–N(11) bond length
[2.054(5) Å] is at the lower end of the range observed [2.05–
2.12 Å] for Re–N (imine) bonds [24,25], but is significantly longer
than the average of 2.00(3) Å for Re–N (amide) bonds [21–25].
These data suggest that the ono chelate acts as a tridentate dian-
ionic ligand, with the rhenium in the +III oxidation state. The bond
lengths in the C(1)–C(6) [1.381(8) Å average] and C(7)–C(12) rings
[1.383(8) Å average] are typical aromatic systems.
charge transitions at 443 and 464 nm, ascribed to the ½ppðN2ꢀÞ !
dꢄpðReÞꢃ and the ½ppðBrꢀÞ ! dꢄpðReÞꢃ transitions, and a d–d transition
is observed at 545 nm.
Single crystals of X-ray quality were obtained by the slow
evaporation from the dichloromethane/ethanol mother liquor.
However, the refinement of the data was poor due to the presence
of dichloromethane in the crystal lattice. The dichloromethane was
highly disordered and could not be refined. However, an acceptable
data set could be obtained, and the connectivity and other general
features of the structure were confidently determined, and the
molecular positional parameters of the atoms in the ‘‘inner” core
are well defined.
The rhenium atom lies at the center of a distorted octahedron
(Fig. 3). The basal plane is defined by the bromide Br(1), two phos-
phorus atoms and the imino nitrogen N(1). The doubly deproto-
nated imido nitrogen N(2) and phenolate oxygen O(1) are in
trans axial positions. The two phosphorus atoms are in trans sites
relative to each other. Distortion form an ideal octahedral environ-
ment results in a non-linear N(2)–Re–O(1) axis of 161.1°, with the
other trans angles Br(1)–Re–N(1)
= 165.9° and P(1)–Re–
P(2) = 177.4° also deviating from linearity (Table 5). The rhenium
atom lies 0.17 Å out of the mean equatorial plane towards N(2),
with the angles N(2)–Re–Br(1) = 110.8°, N(2)–Re–N(1) = 83.3°,
N(2) Re P(1) = 91.7° and N(2)–Re–P(2) = 90.9°. The two bite angles
of the onn chelate are O(1)–Re–N(1) = 77.8° and N(1)–Re–
N(2) = 83.3°. The latter angle is considerably larger than the corre-
sponding angle of the six-membered metallocycle in [Re-
Br(PPh3)2(ono)], which is ascribed to the fact that N(2) is doubly
bonded in [ReBr(PPh3)2(onn)]Br, but that the oxygen O(2) is singly
bonded in [ReBr(PPh3)2(ono)]. The two phenyl rings of onn are
coplanar, making a dihedral angle of 4.0° with each other, and a
dihedral angle of 87.6° and 89.7°, respectively, with the mean
equatorial plane.
The average Re-P distance equals 2.48 Å, which is very similar
to the average Re-P length of 2.472(1) Å in [ReBr(PPh3)2(ono)].
The fact that the Re–Br(1) bond length of 2.53 Å is shorter
than the corresponding bond distance in [ReBr(PPh3)2(ono)]
[2.5434(4) Å] is ascribed to the difference in oxidation state of
these two complexes, and the cationic nature of [ReBr(PPh3)2-
3.3. Synthesis and characterization of [ReBr(PPh3)2(onn)]Br (2)
The reaction of a twofold molar excess of H3onn with trans-
[ReOBr3(PPh3)2] in ethanol gave the product 2.
½ReOBr3ðPPh3Þ2ꢃ þ H3onn ! ½ReBrðPPh3Þ2ðonnÞꢃBr þ HBr þ H2O
The complex salt 2 is stable in air for months. It is diamagnetic
and a 1:1 electrolyte in DMF. Its solubility in alcohols and acetoni-
trile is low and it is only soluble in dichloromethane, DMF and
DMSO. There are no intense peaks in the 890–1020 cmꢀ1 region
its IR spectrum, suggesting the absence of the Re@O core, and
the medium intensity band at 1094 cmꢀ1 is assigned to
m(Re@N).
The Re–O (phenolate) and Re–N (imino) stretches occur at 396
and 471 cmꢀ1, respectively. The C@N stretching frequency occurs
at 1637 cmꢀ1. The electronic spectrum shows ligand-to-metal

1428
P. Mayer et al. / Polyhedron 29 (2010) 1423–1430
P2
O2
C9
C8
C10
C11
C7
C12
P1
O1
C6
Re1
C5
N12
B
C4
C3
C131
C132
C1
N11
O1
C5
C3
C6
C2
C1
C4
C7
C8
C2
Br1
N1
C9
Re1
P1
C13
C12
N2
P2
Br2
C10
C11
P4
Fig. 3. ORTEP view of complex 2. Hydrogen atoms were omitted for clarity.
Br2
Re2
3.4. Synthesis and characterization of fac-[Re(CO)3(ons)(Hno)] (3)
P3
Complex 3 was prepared by the reaction of [Re(CO)5Br] with a
two-fold molar excess of Hons in toluene under nitrogen. The
suggested equation for the reaction is
½ReðCOÞ5Brꢃ þ 2Hons þ H2O
! ½ReðCOÞ3ðonsÞðHnoÞꢃ þ 3CO þ HBr þ mtb
The decomposition of a molecule of Hons to form a coordinated
2-aminophenol (Hno) and free 2-(methylthio)benzaldehyde (mtb)
was surprising since all precautions were taken to exclude water
from the reaction mixture. Also, the preferred affinity of the
fac-[Re(CO)3]+ core for an amino nitrogen, rather than the chelated
methylthiolic sulfur atom, is surprising. All our efforts to synthe-
Fig. 2. A perspective view of the asymmetric unit of complex 1.
(onn)]+. The Re–N(2) bond distance of 1.74 Å is similar to and falls
within the range [1.72(1)–1.74(1) Å] observed for ReV–N(imido)
bonds in octahedral geometries [26–28]. The Re–N(2)–C(9) bond
angle of 144.9° illustrates a significant deviation from linearity of
the coordination mode of the imido nitrogen, and illustrates that
the imido is doubly bonded, rather than triply, making the complex
cation a 16-electron species. The Re–O(1) bond length of 1.96 Å is
typical of a phenolate oxygen coordinated trans to oxo or imido
groups in rhenium(V) complexes [26–29]. The Re–N(1) bond dis-
tance is typical of ReV–N(imino) bonds in Schiff-base complexes
of Re(V) [26–29]. The onn ligand therefore acts as a trianionic
tridentate chelate. The intraligand onn distances show that C(7)–
N(1) is a double bond [1.29 Å], with the C(7)–N(1)–C(2) angle of
120.1° exactly what would be expected for the angle around a
sp2-hybridized nitrogen atom. The N(2)–C(9) [1.38 Å] and O(1)–
C(1) [1.37 Å] bonds are single. There is a small difference in the
average C–C distance of the two phenyl rings in onn [ring C(1)–
C(6) = 1.39 Å; ring C(8)–C(13) = 1.40 Å], possibly due to the pres-
ence of the doubly deprotonated N(2) on the latter ring.
size fac-[Re(CO)3(ons)], with ons coordinated as
a tridentate
ONS-donor chelate, were unsuccessful. The synthesis of 3 was also
attempted by the reaction of [Re(CO)5Br] with equimolar quanti-
ties of Hons and Hno in toluene. However, only the complex
fac-[ReI(CO)3(no)(Hno)] was isolated from the reaction mixture.
An X-ray crystal analysis of this product shows that no acts as a
monoanionic bidentate ligand with coordination through the neu-
tral amino nitrogen and phenolate oxygen, and Hno coordinated
only via the amino nitrogen [30].
Complex 3 is stable in air and is a non-electrolyte in methanol.
It is soluble in a wide variety of solvents like methanol, DMF,
DMSO, acetonitrile and acetone. The infrared spectrum is charac-
terized by intense bands at 2021 and 1905 cmꢀ1, typical of
m
(C@O) of the fac-[Re(CO)3]+ unit. The two medium intensity bands
at 490 and 474 cmꢀ1 are assigned to
respectively, and the medium intensity band at 394 cmꢀ1 is attrib-
uted to (C@N) of
(Re–O(4)). The peak at 1601 cmꢀ1 is due to the
the Schiff base, and the two peaks at 3414 and 3471 cmꢀ1 are due
to (N–H) of the amino nitrogen N(2). The imine proton of the ons
ligand appears at 10.02 ppm in the 1H NMR spectrum. The other
m(Re-N(2)) and m(Re–N(1)),
m
m
The closest contact that the Br(2) counter-ion makes with the
complex cation is with the hydrogen atoms attached to C(3)
[2.86 Å], C(7) [2.75 Å] and C(13) [3.05 Å].
m

P. Mayer et al. / Polyhedron 29 (2010) 1423–1430
1429
C4
S1
C6
C22
C23
C5
C7
N2
C10
C
C18
C11
C12
C17
C8
C16
O2
C20
C9
Re1
C19
N1
C13
C2
C15
O5
C14
C1
O4
C3
O1
O3
Fig. 4. Molecular structure of complex 3, with atom labelling.
protons of the ons chelate appear in the 7.0–7.8 ppm range as a
triplet, multiplet, doublet and multiplet integrating for one, two,
one and three protons, respectively. The multiplet in the 6.46–
6.88 ppm region are assigned to the four protons of the Hno ligand.
The broad singlets at 9.65 and 3.50 ppm are due to the phenolate
and amino protons, respectively. The protons of the methylthiol
group appears as a singlet at 2.23 ppm, which integrates for three
protons. The UV–Vis spectrum in methanol shows a ligand-to-me-
tal charge transfer band at 426 nm.
A perspective view of the asymmetric unit is shown in Fig. 4. It
contains a molecule of [Re(CO)3(ons)(Hno)], and a toluene mole-
cule of crystallization. The X-ray results show that the rhenium(I)
complex contains the chemically robust fac-[Re(CO)3]+ core in a
distorted octahedral geometry. The rhenium(I) is coordinated to
three carbonyl donors in a facial orientation, to the imino nitrogen
N(1), the amino nitrogen N(2) and the phenolate oxygen O(4). The
phenolic oxygen O(5) and thioether sulfur S(1) are uncoordinated.
The Re–CO bond distances [average of 1.907(6) Å, Table 6] fall in
the range observed [1.900(2)–1.928(2) Å] for similar complexes
[31,32]. The Re-N(2) bond length of 2.248(4) Å is typical for Re–
N(amino) bonds [33–34]. The Re–N(1) bond distance of
2.204(4) Å, the bond length of N(1–C(11) of 1.299(6) Å (a double
bond), and the C(11)–N(1)–C(12) bond angle of 119.3(4)° leave
no doubt that N(1) is an sp2-hybridized imino-coordinated
nitrogen.
Table 7
Hydrogen-bond distances (Å) and angles (°) in (3).
D–Hꢂ ꢂ ꢂA
D–H
Hꢂ ꢂ ꢂA
Dꢂ ꢂ ꢂA
2.639(5)
2.598(5)
D–Hꢂ ꢂ ꢂA
105
161
N(2)–H(2B)ꢂ ꢂ ꢂO(5)
O(5)–H(5)ꢂ ꢂ ꢂO(4)
0.92
0.84
2.24
1.79
[1.346(6) Å] with the shorter O(4)-C(13) bond [1.337(6) Å] clearly
shows the effect of coordination on this type of bond. The dihedral
angle between the two phenyl rings of ons is 60.5°. The average C–
C distance in the three phenyl rings C(5)–C(10), C(12)–C(17) and
C(18)–C(23) is 1.380(9), 1.383(9) and 1.385(9) Å, respectively.
The larger N(1)–C(12)–C(13)–O(4) torsion angle of ꢀ2.5(7)° than
the N(2)–C(18)–C(19)–O(5) angle of ꢀ1.4(7)° is due to the coordi-
nation of O(4) to the metal.
There are two hydrogen-bonds in the molecule: N(2)Hꢂ ꢂ ꢂO(5)
(intramolecular) and O(5)Hꢂ ꢂ ꢂO(4) (intermolecular) [Table 7].
4. Supplementary data
CCDC 757640, 757638 and 757639 contain the supplementary
crystallographic data for H2ono, 1 and 3. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/cots/retriev-
ing.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.
The distortion from octahedral ideality in the complex is mainly
the result of the trans angles, with C(1)–Re–N(1) = 170.0(2)°, C(2)–
Re–O(4) = 172.2(2)°, and C(3)–Re–N(2) = 176.3(2)°. These distor-
tions are the result of the constraints imposed by the bidentate li-
gand ons, which forms a five-membered [N(1)–Re–O(4) = 76.5(1)°]
metalloring with the rhenium center. This argument is manifested
in the larger (closer to linearity) bond angle between the trans
monodentate ligands/donors C(3)O and N(2)H2. The average C–
Re–C bond angle of 88.6(2)° is close to orthogonality.
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