Synthesis and characterization of complexes of the {ReO}3+ core with SNS and S donor ligands

Article abstract of DOI:10.1016/S0020-1693(00)00144-4

The reaction of [ReOCl₃(PPh₃)₂] with N,N-bis(2-mercaptoethyl)benzylamine and 4-bromobenzenethiol allowed for the isolation of [ReO{η³-(SCH₂CH₂)₂N(CH₂C₆H₅)}-(η¹ I-C₆H₄Br-4-S)] (1). The reaction of [ReOCL₃(PPh₃)₂] with [(HSCH₂CH₂)₂N(CH₂C₅H₄N)] and the appropriate thiol in chloroform treated with triethylamine has led to the isolation of a series of neutral rhenium complexes of the type [ReO{η³-(SCH₂CH₂)₂N(CH₂C₅H₄N)}(η¹-C₆H₄X-4-S)] (X=Br (2), Cl (3), F (4), and OCH₃ (5)) and [ReO{η³-(SCH₂CH₂)₂N(CH₂C₅H₄N)}(η¹-C₆H₄OCH₃-4-CH₂S)] (6). Likewise, under similar reaction conditions, the use of the related tridentate ligand, [(HSCH₂CH₂)₂N(CH₂CH₂C₅H₄N)], has led to the isolation of a series of rhenium complexes of the type [ReO{η³-(SCH₂CH₂)₂N(CH₂CH₂C₅H₄N)}(η<¹-C₆H₄X-4-S)] (X=Br (7), Cl (8), OCH₃ (9)), as well as [ReO{η³-(SCH₂CH₂)₂N(CH₂CH₂C₅H₄N)}(η¹-C₆H₄C1-4-CH₂S)]·0.5CH₃ (CH₂)₄CH₃ (10). These compounds are extensions of the '3 + 1' approach to the synthesis of materials with the {MO}³⁺ core (M = Tc and Re), which have applications in nuclear medicine. The ligands chosen allow systematic exploration of the consequences of para-substitution on the monodentate thiolate ligand [S] and of derivatization of the substituent R on the tridentate aminodithiol ligand [SNS] of the type (HSCH₂CH₂)₂NR. Such modifications can influence lipophilicity, charge, size and molecular weight of the complex and consequently the biodistribution. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00144-4

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Inorganica Chimica Acta 306 (2000) 30–37
Synthesis and characterization of complexes of the {ReO}3+ core
with SNS and S donor ligands
Frank J. Femia a, Xiaoyuan Chen a, Kevin P. Maresca b, Timothy M. Shoup b,
John W. Babich b, Jon Zubieta a,*
a Department of Chemistry, Syracuse Uni6ersity, Syracuse, NY 13244, USA
b Biostream Inc., 160 Second Street, Cambridge, MA 02142, USA
Received 4 February 2000; accepted 29 March 2000
Abstract
The reaction of [ReOCl3(PPh3)2] with N,N-bis(2-mercaptoethyl)benzylamine and 4-bromobenzenethiol allowed for the isolation
of [ReO{h3-(SCH2CH2)2N(CH2C6H5)}-(h1-C6H4Br-4-S)] (1). The reaction of [ReOCl3(PPh3)2] with [(HSCH2CH2)2N(CH2C5H4N)]
and the appropriate thiol in chloroform treated with triethylamine has led to the isolation of a series of neutral rhenium complexes
of the type [ReO{h3-(SCH2CH2)2N(CH2C5H4N)}(h1-C6H4X-4-S)] (X=Br (2), Cl (3), F (4), and OCH3 (5)) and [ReO{h3-
(SCH2CH2)2N(CH2C5H4N)}(h1-C6H4OCH3-4-CH2S)] (6). Likewise, under similar reaction conditions, the use of the related
tridentate ligand, [(HSCH2CH2)2N(CH2CH2C5H4N)], has led to the isolation of a series of rhenium complexes of the type
[ReO{h3-(SCH2CH2)2N(CH2CH2C5H4N)}(h1-C6H4X-4-S)] (X=Br (7), Cl (8), OCH3 (9)), as well as [ReO{h3-
(SCH2CH2)2N(CH2CH2C5H4N)}(h1-C6H4Cl-4-CH2S)]·0.5CH3(CH2)4CH3 (10). These compounds are extensions of the ‘3+1’
approach to the synthesis of materials with the {MO}3+ core (M=Tc and Re), which have applications in nuclear medicine. The
ligands chosen allow systematic exploration of the consequences of para-substitution on the monodentate thiolate ligand [S] and
of derivatization of the substituent R on the tridentate aminodithiol ligand [SNS] of the type (HSCH2CH2)2NR. Such
modifications can influence lipophilicity, charge, size and molecular weight of the complex and consequently the biodistribution.
© 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structure; Rhenium complexes; Oxo complexes; SNS-donor ligand complexes; S-donor ligand complexes
1. Introduction
life of 17 h and available from a 188W/188Re radionu-
clide generator at no carrier added levels [5], has
become a logical choice for the development of radio-
pharmaceuticals for use in the treatment of cancer [1].
The synthesis of novel compounds, which allow the
systematic exploration of size, shape, molecular weight,
and charge of the metal–thiolate complexes with re-
spect to their biodistribution patterns, provides a driv-
ing force for advances in the radiopharmaceutical
chemistry of rhenium. One approach to the systematic
design of Re(V) complexes with the {ReO}3+ core
exploits the ‘3+1’ concept of ligand addition to a
Group 7 metal-oxo species [6–16]. The methodology is
based on forming a tridentate ‘3’ and a monodentate ‘1’
mixed-thiolate core. The technique uses tridentate dithi-
olates with the (SꢀXꢀS)2− (X=NR, O, S) donor set
and a −2 charge in combination with a monothiol
ligand of −1 charge disposed about a Group 7 metal-
The significant contemporary interest in the coordi-
nation chemistry of rhenium derives from its analogies
to technetium chemistry, as well as its expanding role in
therapeutic nuclear chemistry [1]. The radionuclides of
Re, the Group 7 congener of technetium, are b-emitters
with properties which make them suitable candidates
for therapeutic applications. Rhenium-186 is particu-
larly attractive [2–4] because of its half-life (90 h) and
strong b-emission (imax, 1070 keV), capable of deliver-
ing high radiation doses to tissues. Rhenium-188, also a
b-emitting radionuclide (imax, 2120 keV), with a half-
* Corresponding author. Tel.: +1-315-443 2547; fax: +1-315-443
4070.
E-mail address: jazubiet@syr.edu (J. Zubieta).
0020-1693/00/$ - see front matter © 2306 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00144-4

F.J. Femia et al. / Inorganica Chimica Acta 306 (2000) 30–37
31
O2{C2H5N(CH2CH2S)2}3] [28] and a cationic species,
[ReO{C5H3N(CH2S)2}{C5H4NH-2-S}][Cl] [27].
oxo core, so as to occupy four coordination sites on the
metal with a total formal charge of −3. The ‘3+1’
ligand combination preserves the metal-oxo core and
the formal +5 oxidation state of the metal, thus
conforming to the metal coordination and oxidation
preferences.
In an effort to expand the ‘3+1’ chemistry to the
oxo-rhenium core, our work has concentrated on the
reactions of the tridentate thiol, [(HSCH2CH2)2N-
(CH2C6H5)], and the potentially tetradentate ligands-
[(HSCH2CH2)2N(CH2C5H4N)] and [(HSCH2CH2)2-
N(CH2CH2C5H4N)] with [ReOCl3(PPh3)2], so as to pre-
pare families of compounds with mixed thiol ligands,
and allowing the systematic exploration of the para-
substituted benzenethiol and benzylmercaptan series.
This study continues our development of the coordina-
Over the past decade, thiol based tridentate ligands
have received significant attention in the design of new
Group 7 metal-oxo complexes [8–11,17–31]. One such
series of compounds belongs to the class of [SSS]/[S]
‘3+1’ mixed ligand complexes [10,11,17–21]. Numer-
ous groups have synthesized neutral rhenium and tech-
netium compounds containing 2-mercaptoethyl sulfide
as the tridentate in combination with various monothi-
ols, to produce complexes such as [ReO{(SCH2CH2)2-
S}{SCH2C6H5}] [11], [ReO{(SCH2CH2)2S}{SCH2CH-
(OH)CH(OH)CH2SH}] [17], [ReO{(SCH2CH2)2S}-
{S(CH2)3N(CH3)(CH2)3C6H5}] [18] and [ReO{(SCH2C-
H2)2S}{SCH2CH(CH2CH3)-4-HOC6H5}] [19]. Not only
have such neutral compounds reported but also several
cationic complexes such as [ReO{(SCH2CH2)2S}-
{C5H4NH-2-S}][Br] [20].
Another subclass of compounds includes the class of
[SOS]/[S] ‘3+1’ mixed ligand complexes [11,21,22]. In
most instances of this family of compounds, the triden-
tate 2-mercaptoethylether seems to be the tridentate of
choice, and has been used in the design of such neutral
compounds as [ReO{(SCH2CH2)2O}{SC6H5}] [11] and
[ReO{(SCH2CH2)2O}{SCH2-4-CH3OC6H5}] [22], a cat-
ionic species [ReO{(SCH2CH2)2O}{C5H4NH-2-S}] [22],
and several binuclear complexes, of which [Tc2O2{(SC-
H2CH2)2O}2{SCH2CH2OCH2CH2S}] [21] and [Re2-
O2{(SCH2CH2)2O}2{SCH2CH2OCH2CH2S}] [22] are
representatives.
A third series of ‘3+1’ complexes includes the
[ONS]/[S] mixed ligand complexes [8,9,20,23–27]. One
subclass of this family incorporates the tridentate Schiff
base [HOC6H4C(H)NC6H4SH] and includes complexes
such as [TcO{OC6H4C(H)NC6H4S}{SC6H5}] [9], [TcO-
{OC6H4C(H)NC6H4S}{n-SC8H17}] [8], and a cationic
species [ReO{OC6H4C(H)NC6H4S}{C5H4NH-2-S}][Br]
[23]. Another tridentate ligand type found in the [ONS]/
[S] series is represented by [C5H3N-2-CH2OH-6-
CH2SH], which allows isolation of both neutral
compounds, such as [ReO{C5H3N-2-CH2O-6-CH2S}{S-
4-ClC6H4}] [27], and cationic species, [ReO{C5H3N-2-
CH2O-6-CH2S}{C5H4NH-2-S}][Br] [20].
tion chemistry of the Group
7 metal rhenium
[17,20,22,23,27], in order to provide new materials for
radiolabeling of chemotatic peptides [32]. We report the
synthesis and structural characterization of a series of
oxo-rhenium ‘3+1’ complexes, namely [ReO{h3-(SC-
H2CH2)2N(CH2C6H5)}(h1-C6H4Br-4-S)] (1), [ReO{h3-
(SCH2CH2)2N(CH2C5H4N)}(h1-C6H4X-4-S)] (X=Br
(2), Cl (3), F (4), and OCH3 (5)), [ReO{h3-(SC-
H2CH2)2N(CH2C5H4N)}(h1-C6H4OCH3-4-CH2S)] (6),
[ReO{h3 - (SCH2CH2)2N(CH2CH2C5H4N)}(h1 - C6H4-
X-4-S)] (X=Br (7), Cl (8), OCH3 (9)), and [ReO{h3-
(SCH2CH2)2N(CH2CH2C5H4N)}(h1-C6H4Cl-4-CH2S)]·
0.5CH3(CH2)4CH3 (10).
2. Experimental
2.1. General considerations
NMR spectra were recorded on a Bruker DPX 300
(1H 300.10 MHz) spectrometer in CDCl3 (l 7.27). IR
spectra were recorded as KBr discs with a Perkin–
Elmer series 1600 FT IR. Elemental analysis for car-
bon, hydrogen, and nitrogen were carried out by
Oneida Research Services, Whitesboro, NY. Ammo-
nium perrhenate (Aldrich), triethylamine (Aldrich),
triphenylphosine (Aldrich), benzylamine (Aldrich), 2-
(aminomethyl)pyridine (Aldrich), ethylene sulfide
(Aldrich), 2-(2-aminoethyl)pyridine (Aldrich), 4-bro-
mobenzenethiol
(Aldrich),
4-chlorobenzenethiol
(Aldrich), 4-fluorobenzenethiol (Aldrich), 4-methoxy-
benzenethiol (Aldrich), 4-chlorobenzyl mercaptan
(Aldrich), 4-methoxybenzyl mercaptan (Lancaster) were
used as received without further purification. All other
solvents and reagents were purchased from Aldrich and
used as received, unless otherwise stated. The
The vast majority of the ‘3+1’ Group 7 metal-oxo
complexes belong to the class [SN(R)S]/[S], where the
ꢀR group of the tridentate may be exploited to provide
a variety of derivatives and secondary functionality
[19,28–31]. Examples include [ReO{C5H3N(CH2S)2}{S-
4-C6H4OH}] [19], [ReO{C2H5N(CH2CH2S)2}{S-4-Cl-
C6H4}] [28], [ReO{C2H5SCH2CH2N(CH2CH2S)2}{S-4-
[ReOCl3(PPh3)2]
ethyl)benzylamine [34] were synthesized according to
published procedures.
[33]
and
N,N-bis(2-mercapto-
2.2. Syntheses
2.2.1. [(HSCH2CH2)2N(CH2C5H4N)]
CH3OC6H4}] [29],
a
binuclear complex [Re2-
A similar procedure was employed as for the prepa-

32
F.J. Femia et al. / Inorganica Chimica Acta 306 (2000) 30–37
ration of N,N-bis(2-mercaptoethyl)benzylamine. 1H
NMR (CDCl3, ppm): 1.72 (s, 2H), 2.61 (m, 4H), 2.78
(m, 4H), 3.81 (s, 2H), 7.18 (m, 1H), 7.36, (d, 1H), 7.67
(m, 1H), 8.52 (m, 1H).
C5H4N)}(p1-C6H4F-4-S)] (4). X-ray quality crystals
were grown by slow diffusion of pentane into a
methylene chloride solution of 4 (yield: 0.025 g, 45.6%).
IR (KBr, cm−1): 1654 (m), 1560 (w), 1508 (w), 1263 (s),
1
1154 (m), 1014 (m), 942 (s), 833 (w). H NMR (CDCl3,
2.2.2. [(HSCH2CH2)2N(CH2CH2C5H4N)]
ppm): 2.69 (m, 2H), 2.83 (m, 2H), 3.53 (m, 2H), 3.85
(m, 2H), 5.03 (s, 2H), 7.09 (m, 2H), 7.39 (m, 2H), 7.63
(m, 2H), 7.80 (m, 1H), 8.71 (m, 1H).
A similar procedure was employed as for the prepa-
ration of N,N-bis(2-mercaptoethyl)benzylamine. 1H
NMR (CDCl3, ppm): 1.75 (s, 2H), 2.10-2.90 (m, 12H),
7.18 (m, 1H), 7.20, (d, 1H), 7.60 (t, 1H), 8.50 (d, 1H).
2.2.3.5. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
C5H4N)}(p1-C6H4OCH3-4-S)] (5). X-ray quality crys-
tals were grown by slow diffusion of pentane into a
solution of the compound in methylene chloride (yield:
0.023 g, 41.1%). IR (KBr, cm−1): 1654 (m), 1560 (w),
1508 (w), 1283 (s), 1172 (m), 1028 (m), 941 (s), 828 (w).
1H NMR (CDCl3, ppm): 2.71 (m, 2H), 2.84 (m, 2H),
3.55 (m, 2H), 3.82 (m, 2H), 3.88 (s, 3H), 5.07 (s, 2H),
6.95 (m, 2H), 7.37 (m, 2H), 7.61 (m, 2H), 7.79 (m, 1H),
8.72 (m, 1H).
2.2.3. General synthetic procedure
To a solution of [ReOCl3(PPh3)2] (0.0822 g, 0.0986
mmol) in 1 ml of chloroform was added dropwise a
solution of 1 equiv. (0.0986 mmol) of monothiol (the
HSR donor ligand) and 1 equiv. of the dithiol
[(HSCH2CH2)2NR,
R=CH2C6H5,
CH2C5H4N,
(CH2)2C5H4N] (0.0986 mmol) in 1 ml of chloroform.
The solution remained olive green until the addition of
triethylamine (0.08 ml, 0.574 mmol) whereupon it im-
mediately changed from olive to forest green. The
solution was stirred and refluxed for an additional 30
min and then evaporated to dryness. Crystals for each
of the compounds were grown as indicated.
2.2.3.6. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
C5H4N)}(p1-C6H4OCH3-4-CH2S)] (6). X-ray quality
crystals were grown by slow diffusion of diethylether
into a methylene chloride solution of 6 (yield: 0.027 g,
47.1%). IR (KBr, cm−1): 1654 (m), 1560 (w), 1509 (w),
2.2.3.1. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
C6H5)}(p1-C6H4Br-4-S)] (1). X-ray quality crystals were
grown by slow diffusion of pentane in a solution of the
compound in methylene chloride (yield: 0.021 g, 34.6%).
Anal. Calc. for C17H19NOS3BrRe (mol. wt. 615.62): C,
33.2; H, 3.11; N, 2.28. Found: C, 32.5; H, 3.49; N,
2.16%.
1248 (s), 1104 (m), 1032 (m), 948 (s), 819 (w). H NMR
1
(CDCl3, ppm): 2.61 (m, 2H), 3.01 (m, 2H), 3.53 (m,
2H), 3.81 (s, 3H), 3.87 (m, 2H), 4.89 (s, 2H), 5.00 (s,
2H), 6.84 (m, 2H), 7.34 (m, 2H), 7.41 (m, 2H), 7.76 (m,
1H), 8.71 (m, 1H). Anal. Calc. for C18H23N2O2S3Re
(mol. wt. 581.76): C, 37.2; H, 3.98; N, 4.82. Found: C,
36.8; H, 3.73; N, 4.55%.
2.2.3.2. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
C5H4N)}(p1-C6H4Br-4-S)] (2). X-ray quality crystals
were grown by slow diffusion of pentane in a solution
of the compound in methylene chloride (yield: 0.027 g,
44.4%). IR (KBr, cm−1): 1654 (m), 1560 (m), 1508 (w),
1267 (m), 1080 (m), 1008 (m), 948 (s), 813 (w). 1H NMR
(CDCl3, ppm): 2.73 (m, 2H), 2.85 (m, 2H), 3.52 (m, 2H),
3.85 (m, 2H), 5.03 (s, 2H), 7.26 (m, 2H), 7.38 (m, 2H),
7.53 (m, 2H), 7.80 (m, 1H), 8.71 (m, 1H).
2.2.3.7. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
CH2C5H4N)}(p1-C6H4Br-4-S)] (7). X-ray quality crys-
tals were grown by slow diffusion of pentane into a
methylene chloride solution of 7 (yield: 0.031 g, 49.9%).
IR (KBr, cm−1): 1654 (m), 1578 (w), 1438 (w), 1273 (s),
1
1095 (m), 1029 (m), 943 (s), 846 (w). H NMR (CDCl3,
ppm): 2.76 (m, 2H), 2.91 (m, 2H), 3.31 (t, 2H), 3.42 (m,
2H), 3.68 (m, 2H), 4.19 (m, 2H), 7.24 (m, 2H), 7.32 (m,
2H), 7.51 (m, 2H), 7.67 (m, 1H), 8.56 (m, 1H). Anal.
Calc. for C17H20N2OS3BrRe (mol. wt. 630.64): C, 32.4;
H, 3.20; N, 4.44. Found: C, 32.9; H, 3.36; N, 4.38%.
2.2.3.3. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
C5H4N)}(p1-C6H4Cl-4-S)] (3). X-ray quality crystals
were grown by slow diffusion of diethylether into a
methylene chloride solution of 3 (yield: 0.019 g, 33.9%).
IR (KBr, cm−1): 1654 (m), 1560 (m), 1508 (w), 1266
2.2.3.8. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
CH2C5H4N)}(p1-C6H4Cl-4-S)] (8). Crystals were grown
by slow diffusion of pentane into a solution of the
compound in methylene chloride (yield: 0.024 g, 41.5%).
IR (KBr, cm−1): 1654 (m), 1574 (w), 1472 (w), 1268 (s),
1
(m), 1085 (m), 1012 (m), 949 (s), 818 (w). H NMR
(CDCl3, ppm): 2.72 (m, 2H), 2.83 (m, 2H), 3.52 (m, 2H),
3.86 (m, 2H), 5.03 (s, 2H), 7.35 (m, 2H), 7.41 (m, 2H),
7.73 (m, 2H), 7.82 (m, 1H), 8.71 (m, 1H). Anal. Calc. for
C16H18N2OS3ClRe (mol. wt. 572.15): C, 33.6; H, 3.17;
N, 4.90. Found: C, 34.1; H, 3.55; N, 4.07%.
1
1090 (m), 1009 (m), 947 (s), 816 (w). H NMR (CDCl3,
ppm): 2.79 (m, 2H), 2.89 (m, 2H), 3.31 (t, 2H), 3.42 (m,
2H), 3.68 (m, 2H), 4.20 (m, 2H), 7.22 (m, 2H), 7.33 (m,
2H), 7.55 (m, 2H), 7.68 (m, 1H), 8.57 (m, 1H). Anal.
Calc. for C17H20N2OS3ClRe (mol. wt. 586.19): C, 34.8;
H, 3.44; N, 4.78. Found: C, 33.6; H, 3.21; N, 2.84%.
2.2.3.4. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-

F.J. Femia et al. / Inorganica Chimica Acta 306 (2000) 30–37
33
2.2.3.9. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
CH2C5H4N)}(p1-C6H4OCH3-4-S)] (9). X-ray quality
crystals were grown by slow diffusion of diethylether
into a solution of the compound in methylene chloride
(yield: 0.023 g, 40.1%). IR (KBr, cm−1): 1654 (m), 1577
(m), 1492 (w), 1283 (s), 1171 (m), 1024 (m), 938 (s), 826
1
(w). H NMR (CDCl3, ppm): 2.76 (m, 2H), 2.90 (m,
2H), 3.30 (t, 2H), 3.40 (m, 2H), 3.65 (m, 2H), 3.83 (s,
3H), 4.18 (m, 2H), 6.93 (m, 2H), 7.22 (m, 2H), 7.54 (m,
2H), 7.67 (m, 1H), 8.56 (m, 1H).
2.2.3.10. Preparation of [ReO{p3-(SCH2CH2)2N(CH2-
CH2C5H4N)}(p1-C6H4Cl-4-CH2S)]·0.5CH3(CH2)4CH3
(10). X-ray quality crystals were grown by slow diffu-
sion of hexane into a methylene chloride solution of 10
(yield: 0.028 g, 44.2%). IR (KBr, cm−1): 1650 (m), 1589
(w), 1487 (w), 1263 (s), 1090 (m), 1009 (m), 948 (s), 831
1
(w). H NMR (CDCl3, ppm): 2.71 (m, 2H), 3.01 (m,
2H), 3.30 (t, 2H), 3.43 (m, 2H), 3.69 (m, 2H), 4.15 (m,
2H), 4.83 (s, 2H), 7.19-7.27 (m, 4H), 7.33 (m, 2H), 7.65
(m, 2H), 8.56 (m, 1H).
2.3. X-ray crystallography
All data were collected on a Bruker SMART diffrac-
tometer system using graphite monochromated Mo Ka
,
radiation (u(Mo Ka)=0.71073 A). All the data collec-
tions were carried out at low temperature (87–93 K).
The crystal parameters and other experimental details
of the data collections are summarized in Table 1. A
complete description of the details of the crystallo-
graphic methods is given in Supporting Information.
Data was corrected for Lorentz and polarization ef-
fects, and absorption corrections were made using SAD-
ABS [35]. The structures were solved by direct methods
[36]. Neutral atom scattering factors were taken from
Cromer and Waber [37] and anomalous dispersion cor-
rections were taken from those of Creagh and McAuley
[38]. All calculations were preformed using SHELXTL-96
[36]. Non-hydrogen atoms were refined anisotropically.
No anomalies were encountered in the refinements of
any of the structures. Atomic positional parameters for
the structures have been deposited with the Cambridge
Structural Database (Section 5).
3. Results and discussion
The synthesis of N,N-bis(2-mercaptoethyl)benzylam-
ine employs the route of Schro¨der and coworkers [34],
in which 4 equiv. of ethylene sulfide are reacted with 1
equiv. of benylamine at 65°C for 48 h. A similar
procedure was employed in the synthesis of [(HSCH2-
CH2)2N(CH2C5H4N)] and [(HSCH2CH2)2N(CH2CH2-
C5H4N)] starting from the appropriate amines, 2-
(aminomethyl)pyridine and 2-(2-aminoethyl)pyridine,
respectively.

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F.J. Femia et al. / Inorganica Chimica Acta 306 (2000) 30–37
and (−SCH2CH2N(R)CH2CH2S−). All four of the
multiplets integrate to two protons; however, individual
assignments of the resonances are tenuous at best, due
to the multiplicity of the peaks and the flexibility of the
ligand in solution, as noted by others [6]. In addition,
compounds 2–6 also displayed a single proton reso-
nance integrating to two protons at 5.03 ppm corre-
sponding to the methylene spacer of the tridentate
backbone. Furthermore, [ReO{h3-(SCH2CH2)2N(CH2-
C5H4N)}(h1-C6H4OCH3-4-S)] (5) and [ReO{h3-(SCH2-
CH2)2N(CH2C5H4N)}(h1-C6H4OCH3-4-CH2S)] (6) ex-
hibited an additional singlet at approximately 3.88 and
3.81 ppm, respectively, which is attributed to the three
protons of the methoxy group. The monodentate ben-
zylmercaptan of compound 6 displayed methylene pro-
tons at approximately 4.89 ppm as a single peak, as
anticipated from Sadtler spectra [39].
Fig. 1. A view of the structure of [ReO{h3-(SCH2CH2)2N(CH2C6-
H5)}(h1-C6H4Br-4-S)] (1), showing the atom-labeling scheme and
50% thermal ellipsoids.
The compounds of this study were all prepared read-
ily from the reactions of the appropriate ligands with
[ReOCl3(PPh3)2]. While [Bu4N][ReOBr4(OPPh3)] also
proved to be an effective starting material, there was no
advantage to its use in terms of yield or product purity.
Since the synthesis of [Bu4N][ReOBr4(OPPh3)] is rela-
tively involved and of low yield, the more easily pre-
pared and purified starting material [ReOCl3(PPh3)2]
was used exclusively for the synthesis of 1–10. The
green solid is indefinitely air and moisture stable mak-
ing it suitable for probing the reactivities of a variety of
ligand types. Consequently, the compounds of this
study were synthesized in a straightforward fashion
from the reaction of [ReOCl3(PPh3)2] with one equiva-
lent of the tridentate dithiol ligand (or ‘3’ ligand) and 1
equiv. of the monodentate thiol ligand (or ‘1’ ligand) in
chloroform. An addition of excess triethylamine pro-
duces a forest green solution, which upon workup
yields crystalline products 1–10.
The infrared spectrum of 2–10 are characterized by a
series of ligand bands in the 1008–1654 cm−1 range
and a strong band in the 938–949 cm−1 range at-
tributed to w(ReꢁO). The 1H NMR spectra of com-
pounds 2–6 are unexceptional. All display a series of
multiplets ranging from 6.84 to 8.72 ppm assignable to
the eight aromatic protons, as well as four multiplets at
2.69, 2.87, 3.53, and 3.85 ppm assignable to each CH2
moiety comprising the backbone of the tridentate lig-
1
Similarly, the H NMR spectra for compounds 7–10
contain multiplets at 2.76, 2.93, 3.42, and 3.68 ppm
assignable to each CH2 moiety comprising the back-
bone of the tridentate ligand, as well as series of
multiplets ranging from 6.93 to 8.57 ppm assignable to
the eight aromatic protons. Compounds 7–10 also dis-
played a triplet at 3.31 ppm and a multiplet at 4.18 ppm
each integrating to two protons and corresponding to
the ethylene spacer of the tridentate ligand. In addition,
the monodentate benzylmercaptan of compound 10
displayed methylene protons at approximately 4.83
ppm as a single peak, as anticipated from Sadtler
spectra
[38].
[ReO{h3-(SCH2CH2)2N(CH2CH2C5-
H4N)}(h1-C6H4OCH3-4-S)] (9) exhibited an additional
singlet at approximately 3.83 ppm, which is attributed
to the three protons of the methoxy group. In no case
1
does the H NMR data suggest the presence of syn/anti
isomers with respect to the amine substituent R and the
oxo-group orientations. The crystal structure data, like-
wise, confirm that all compounds adopt the syn geome-
try exclusively.
As shown in Fig. 1, the coordination geometry
around
the
metal
for
[ReO{h3-(SCH2CH2)2-
Table 2
Comparison of selected bond angles a for the rhenium-mixed thiolate complexes of this study
Angle
1
2
3
4
5
6
7
9
10
97.8(2)
O(1)ꢀReꢀN(1)
O(1)ꢀReꢀS(2)
N(1)ꢀReꢀS(2)
O(1)ꢀReꢀS(1)
N(1)ꢀReꢀS(1)
S(2)ꢀReꢀS(1)
O(1)ꢀReꢀS(3)
N(1)ꢀReꢀS(3)
S(2)ꢀReꢀS(3)
S(1)ꢀReꢀS(3)
96.3(2)
93.9(2)
93.71(13)
122.19(11)
83.97(9)
118.14(11)
83.77(9)
118.94(4)
102.86(10)
163.43(9)
87.28(4)
93.10(18)
94.60(14)
94.47(17)
96.23(14)
97.41(10)
118.23(17)
83.31(15)
120.07(17)
83.80(15)
121.23(7)
105.66(17)
157.91(15)
84.05(7)
121.6(2)
84.01(18)
118.6(2)
83.86(18)
119.05(8)
102.8(2)
163.35(17)
87.34(8)
87.97(8)
118.37(14)
84.09(12)
122.05(14)
83.63(12)
118.74(5)
102.89(14)
164.00(12)
88.03(5)
117.24(12)
84.50(10)
122.55(12)
83.16(10)
119.60(4)
103.53(10)
161.85(10)
87.83(4)
119.65(13)
83.11(11)
117.31(13)
83.71(11)
122.21(5)
105.62(13)
159.56(12)
90.02(5)
118.12(11)
83.58(10)
118.15(11)
83.90(11)
123.26(4)
104.07(11)
159.42(10)
83.86(4)
117.78(9)
83.57(8)
117.55(9)
83.46(7)
124.27(3)
104.65(8)
157.78(7)
88.44(3)
84.03(3)
117.36(16)
82.86(14)
117.34(16)
83.43(14)
124.84(6)
105.22(16)
156.50(14)
82.34(6)
87.37(7)
88.21(4)
88.03(5)
86.39(4)
83.75(5)
89.45(4)
90.19(6)
a Angles reported in degrees with e.s.d. values in parentheses.

F.J. Femia et al. / Inorganica Chimica Acta 306 (2000) 30–37
35
(5)), [ReO{h3-(SCH2CH2)2N(CH2C5H4N)}(h1-C6H4O-
CH3-4-CH2S)] (6), [ReO{h3-(SCH2CH2)2N(CH2CH2-
C5H4N)}(h1-C6H4X-4-S)] (X=Br (7), Cl (8), OCH3
(9)), and [ReO{h3-(SCH2CH2)2N(CH2CH2C5H4N)}(h1-
C6H4Cl-4-CH2S)]·0.5CH3(CH2)4CH3 (10) are struc-
turally similar to
1 with the exception of the
para-substituent of the benzenethiol or benzylmercap-
tan, as well as the substitution on the nitrogen of the
tridentate. The core geometry of the five-coordinate
oxo-rhenium complexes containing the tridentate lig-
and, [(HSCH2CH2)2N(CH2C5H4N)], is shown in Fig. 2
for [ReO{h3-(SCH2CH2)2N(CH2C5H4N)}(h1-C6H4Br-
4-S)] (2) and is seen to consist of distorted trigonal
bipyramidal geometry with the oxo group and the
sulfur atoms of the [SNS] ligand defining the equatorial
plane and the axial positions occupied by the sulfur
atom of the monothiol and the nitrogen atom of the
[SNS] ligand. The angles between the atoms in the
equatorial plane are close to the ideal 120° (Table 2),
Fig. 2.
A
view of the structure of [ReO{h3-(SCH2CH2)2-
N(CH2C5H4N)}(h1-C6H4Br-4-S)] (2), showing the atom-labeling
scheme and 50% thermal ellipsoids.
but
a
value of 163.35(17)° observed for the
N(1)ꢀRe(1)ꢀS(3) angle indicates a distortion of the
trigonal bipyramid, which can also be seen in the value
of the trigonality index [51], ~=0.74. The ReꢁO bond
Fig. 3.
A
view of the structure of [ReO{h3-(SCH2CH2)2-
N(CH2CH2C5H4N)}(h1-C6H4Br-4-S)] (7), showing the atom-labeling
,
length is found to be 1.695(6) A, and the ReꢀN bond
scheme and 50% thermal ellipsoids.
,
length [ReꢀN(1)=2.221(7) A] is typical for the
ReꢀNamine single bond in which the nitrogen atom
exhibits sp3 hybridization. The metalꢀsulfur bond
lengths in the equatorial plane are unexceptional
N(CH2C6H5)}(h1-C6H4Br-4-S)] (1) is distorted trigonal
bipyramidal, with the oxo group and the sulfur atoms
of the [SNS] ligand defining the equatorial plane and
the axial positions occupied by the sulfur atom of the
monothiol and the nitrogen atom of the [SNS] ligand.
The angles between the atoms in the equatorial plane
are close to the ideal 120° (Table 2), but a value of
157.91(15)° observed for the N(1)ꢀRe(1)ꢀS(3) angle in-
dicates a distortion of the trigonal bipyramid, which
can also be seen in the value of the trigonality index
[40], ~=0.61. The bond distances in the coordination
environment of the metal are characteristic for this type
of complexation [31]. The ReꢁO bond length is found
,
[ReꢀS(1)=2.270(2), ReꢀS(2)=2.281(2) A], while the
,
ReꢀS(3) axial bond length is 2.313(2) A, a lengthening
phenomena noted by others [24,31,41–52]. The rhe-
,
nium atom is situated 0.0977 A above the equatorial
plane of the trigonal bipyramid in the direction of the
monothiol.
Similarly, the core geometry of the five-coordinate
oxo-rhenium complexes containing the [(HSCH2-
CH2)2N(CH2CH2C5H4N)] tridentate is shown in Fig. 3
for [ReO{h3-(SCH2CH2)2N(CH2CH2C5H4N)}(h1-C6-
H4Br-4-S)] (7) and is also seen to consist of distorted
trigonal bipyramidal geometry. The oxo group and the
sulfur atoms of the [SNS] ligand define the equatorial
plane, while the axial positions are occupied by the
sulfur atom of the monothiol and the nitrogen atom of
the [SNS] ligand. The angles between the atoms in the
equatorial plane are close to the ideal 120° (Table 2),
likewise, a value of 159.42(10)° observed for the
N(1)ꢀRe(1)ꢀS(3) angle indicates a distortion of the
trigonal bipyramid, which can also be seen in the value
of the trigonality index [40], ~=0.60. The ReꢁO and
ReꢀNamine bond lengths are typical for this particular
class of compounds and are found to be 1.694(3) and
,
to be 1.699(5) A, well within the range observed for
other {ReO}3+ complexes [24,31,41–52]. Likewise, the
,
ReꢀN bond length [ReꢀN(1)=2.208(6) A] is typical for
the ReꢀNamine single bond in which the nitrogen atom
exhibits sp3 hybridization [24,31,41–52]. However, in
the case of the metalꢀsulfur bond lengths, those in the
equatorial plane are similar [ReꢀS(1)=2.2794(18),
,
ReꢀS(2)=2.2824(18) A], while for the ReꢀS axial bond
there is an expected lengthening [ReꢀS(3)=2.3097(19)
,
A] [24,31,41–52]. The rhenium atom is situated 0.0817
,
A above the equatorial plane of the trigonal bipyramid
in the direction of the monothiol. This distance is
within the range reported for five-coordinate Re/Tc(V)
complexes with similar distorted trigonal bipyramidal
geometry [31].
,
2.217(4) A, respectively [24,31,39–49,53]. As in the
previous cases, the metalꢀsulfur bond lengths in the
equatorial plane are unexceptional [ReꢀS(1)=
The compounds [ReO{h3-(SCH2CH2)2N(CH2C5-
H4N)}(h1-C6H4X-4-S)] (X=Br (2), Cl (3), F (4), OCH3
2.2758(12), ReꢀS(2)=2.2918(11) A], while the ReꢀS(3)
,
,
axial bond length is slightly lengthened to 2.3144(11) A.

36
F.J. Femia et al. / Inorganica Chimica Acta 306 (2000) 30–37
Table 3
direction of the monothiol group is approximately
The ~ index for the five-coordinate rhenium complexes of this study,
as a measure of geometric distortion from idealized geometries
,
0.0753–0.1087 A as shown in Table 4. The ReꢀNamine
,
distances range from 2.21 to 2.23 A, while the sulfur
a
b
c
distances are all fairly unexceptional, ranging from 2.27
Compound
h
i
~
,
to 2.32 A, well within the range of those reported
[ReO{SN(R1)S}(h1-C6H4Br-4-S)] (1)
[ReO{SN(R2)S}(h1-C6H4Br-4-S)] (2)
[ReO{SN(R2)S}(h1-C6H4Cl-4-S)] (3)
[ReO{SN(R2)S}(h1-C6H4F-4-S)] (4)
121.23(7) 157.91(15) 0.61
119.05(8) 163.35(17) 0.74
118.94(4) 163.43(9) 0.74
118.74(5) 164.00(12) 0.75
previously [52–54]. Tables 2 and 4 compare the relevant
bond angles and lengths for compounds 1–7, 9 and 10,
respectively.
[ReO{SN(R2)S}(h1-C6H4OCH3-4-S)] (5) 119.60(4) 161.85(10) 0.70
[ReO{SN(R2)S}(h1-C6H4OCH3-4-
CH2S)] (6)
122.21(5) 159.56(12) 0.62
4. Conclusions
[ReO{SN(R3)S}(h1-C6H4Br-4-S)] (7)
123.26(4) 159.42(10) 0.60
[ReO{SN(R3)S}(h1-C6H4OCH3-4-S)] (9) 124.27(3) 157.78(7) 0.56
[ReO{SN(R3)S}(h1-C6H4Cl-4-CH2S)] (10) 124.84(6) 156.50(14) 0.53
Exploitation of the thiolate chemistry of the oxo-rhe-
nium(V) core has allowed the preparation of a series of
mononuclear oxo-rhenium-mixed thiolate complexes.
We have demonstrated that the action of the tridentate
[SN(R)S] aminodithiol ligand on a suitable {ReO}3+
precursor in the presence of a monodentate ligand gives
rise to stable, neutral oxo-rhenium complexes of the
‘3+1’ type. This route appears to be a quite general,
facile method for moderate yield synthesis of materials
with the [ReO{SN(R)S}(S)] core. The geometry and
charge of the monodentate thiol ligand may be manipu-
lated easily to produce complexes of various size, shape
and charges for clinical development.
a hꢀthe second largest basal angle.
b iꢀthe largest basal angle.
c ~ꢀ(i−h)/60. SN(R)S=h3-{(SCH2CH2)2N(R)} (R1=CH2C6H5;
R2=CH2C5H4N; R3=(CH2)2C5H4N).
,
The rhenium atom is situated 0.0811 A above the
equatorial plane of the trigonal bipyramid in the direc-
tion of the monothiol.
In all the oxo-rhenium benzenthiolates and benzylmer-
captans (compounds 2–7, 9, 10) the equatorial plane is
defined by the two sulfur donors of the tridentate [SNS]
ligand and the oxo group, while the sulfur atom of the
monothiol and the nitrogen atom of the [SNS] ligand
occupy the axial positions. The Addison ~ indices for the
rhenium mixed thiolate compounds of this study are
listed in Table 3, revealing that compounds 1–7, 9 and
10 actually tend to lie closer to the distorted trigonal
bipyramidal structure, a result that is similar to other
compounds that are members of the oxo-rhenium ‘3+1’
[SNS]/[S] mixed-thiolate family [28–31].
In all cases, one equatorial position is occupied by a
terminal oxo-group with a typical ReꢁO distance ranging
from approximately 1.69–1.71 A. The two other equato-
rial positions are occupied by the two sulfur donors of
the [SNS] tridentate. In the complexes of this study, the
displacement of Re site from the equatorial plane in the
5. Supplementary material
All atomic and thermal parameters and all interatomic
angles are available from the authors upon request.
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as
publication Nos. CCDC 139416–139424. Copies of the
data can be obtained free of charge on application to The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www:http://www.ccdc.cam.ac.uk).
,
Table 4
Comparison of selected bond lengths a for rhenium-mixed thiolate complexes
Complex
ReꢁO
h1-Thiolate
ReꢀS(3)
h3-Donor [S(1)ꢀN(1)ꢀS(2)]
DRe b
ReꢀS(1)
ReꢀN(1)
ReꢀS(2)
1
2
3
4
5
6
7
9
10
1.699(5)
1.695(6)
1.702(3)
1.705(4)
1.697(3)
1.707(4)
1.694(3)
1.703(2)
1.688(5)
2.3097(19)
2.313(2)
2.2794(18)
2.270(2)
2.208(6)
2.221(7)
2.229(3)
2.231(5)
2.234(4)
2.215(5)
2.217(4)
2.220(3)
2.226(5)
2.2824(18)
2.281(2)
0.0817
0.0977
0.1011
0.1087
0.0926
0.1084
0.0811
0.0753
0.0815
2.3087(10)
2.3074(14)
2.3119(11)
2.2983(15)
2.3144(11)
2.3189(8)
2.2954(15)
2.2821(10)
2.2793(13)
2.2876(11)
2.2766(14)
2.2758(12)
2.2889(9)
2.2875(15)
2.2757(10)
2.2772(14)
2.2704(11)
2.2929(14)
2.2918(11)
2.3189(8)
2.2962(16)
a
,
Distances reported in A with e.s.d. values in parentheses.
b DRe, distance of the Re from the least square plane of the equatorial donors.

F.J. Femia et al. / Inorganica Chimica Acta 306 (2000) 30–37
37
[27] X. Chen, F.J. Femia, J.W. Babich, J. Zubieta, Inorg. Chim. Acta
306 (2000) 113–116.
Acknowledgements
[28] M. Papadopoulos, I. Pirmettis, C. Tsoukalas, B. Nock, T.
Maina, C.P. Raptopoulou, H.J. Pietzsch, M. Friebe, H. Spies,
D. Johannsen, E. Chiotellis, Inorg. Chim. Acta 295 (1999) 1.
[29] M. Pelecanou, I.C. Pirmettis, M.S. Papadopoulos, C.P. Rapto-
poulou, A. Terzis, E. Chiotellis, C.I. Stassinopoulou, Inorg.
Chim. Acta 287 (1999) 142.
This work was supported by a grant from the De-
partment of Energy, Office of Health and Environmen-
tal Research (D2-FG02-99ER62791).
[30] M. Pelecanou, I.C. Pirmettis, B.A. Nock, M. Papadopoulos, E.
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[31] M. Papadopoulous, C. Tsoukalas, I. Pirmettis, B. Nock, T.
Maina, Z. Abedin, C.P. Raptopoulou, A. Terzis, E. Chiotellis,
Inorg. Chim. Acta 285 (1999) 97.
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