Re2(CO)6(μ-thpymS)2 (thpymSH = pyrimidine-2-thiol) as a versatile precursor to mono- and polynuclear complexes: X-ray crystal structures of fac-Re(CO)3(PPh3) (κ2-thpymS) and two isomers of ReRu3(CO) 13(μ3-thpymS)

Article abstract of DOI:10.1016/j.jorganchem.2012.12.030

The dirhenium complexes Re₂(CO)₆(μ-thpymS) ₂ (1) and eq-Re₂(CO)₉{κ¹-(S)- SN₂C₄H₈} (2) are obtained from the reaction of tetrahydropyrimidine-2-thiol (thpymSH) with Re₂(CO) ₈(NCMe)₂ or Re₂(CO)₁₀. Complex 1 proves to be an excellent precursor to a range of monometallic and cluster complexes acting as a source of Re(CO)₃(thpymS) . Thus, reactions with triphenylphosphine (PPh₃) and bis(diphenylphosphino) methane (dppm) afford mononuclear fac-Re(CO)₃(PPh₃) (κ²-thpymS) (3) and fac-Re(CO)₃(κ¹- dppm)(κ²-thpymS) (4), respectively. A crystal structure of 3 reveals that the pyrimidine-2-thiolate binds in a chelating fashion. Reactions with M₃(CO)₁₂ (M = Ru, Os) at moderate temperatures afford mixed-metal clusters. With Ru₃(CO)₁₂ in boiling thf isomeric tetranuclear butterfly clusters ReRu₃(CO) ₁₃(μ₃-thpymS) (5-6) result which differ in the position of the capping pyrimidine-2-thiolate ligand on the cluster surface. Thus in the kinetic isomer 5, the pyrimidine-2-thiolate caps the ReRu₂ face while in the thermodynamic isomer 6 it caps the Ru₃ face. A similar reaction with Os₃(CO)₁₀(NCMe)₂ in boiling benzene affords predominantly the ReOs₂-capped tetranuclear cluster ReOs₃(CO)₁₃(μ₃-thpymS) (7), together with small amounts of (μ-H)Os₃(CO)₉(μ₃-thpymS) (8) resulting from loss of rhenium. Cluster 7 is stable in refluxing toluene but slowly converts to isomeric 9 in xylene at 140 °C but only in low yields. The crystal structures of isomeric 5-6 have been solved and show only small variations in the cluster core geometry. Density functional calculations show that clusters 6 and 9 are slightly more stable than 5 (ΔG 2.0 kcal mol^-1) and 7 (ΔG 1.5 kcal mol^-1), respectively, and a mechanism is proposed for these conversions in which the pyrimidine-2-thiolate becomes bidentate after release of the pyrimidine group.

Full text of DOI:10.1016/j.jorganchem.2012.12.030

Journal of Organometallic Chemistry 728 (2013) 30e37
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Re2(CO)6(
m
-thpymS)2 (thpymSH ¼ pyrimidine-2-thiol) as a versatile
precursor to mono- and polynuclear complexes: X-ray crystal
structures of fac-Re(CO)3(PPh3)(
of ReRu3(CO)13(m3-thpymS)
k
2-thpymS) and two isomers
,
a,b
Md. Faruque Ahmad a, Jagodish C. Sarker a, Kazi A. Azam a, Shariff E. Kabir a , Shishir Ghosh
,
*
Graeme Hogarth b, Tasneem A. Siddiquee c, Michael G. Richmond d
a Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
b Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK
c Department of Chemistry, Tennessee State University, 3500 John A. Merritt Blvd., Nashville, TN 37209, USA
d Department of Chemistry, University of North Texas, 1155 Union Circle, Box 305070, Denton, TX 76203, USA
a r t i c l e i n f o
a b s t r a c t
The dirhenium complexes Re2(CO)6(m-thpymS)2 (1) and eq-Re2(CO)9{k
1-(S)-SN2C4H8} (2) are obtained
Article history:
Received 20 November 2012
Received in revised form
20 December 2012
from the reaction of tetrahydropyrimidine-2-thiol (thpymSH) with Re2(CO)8(NCMe)2 or Re2(CO)10
.
Complex 1 proves to be an excellent precursor to a range of monometallic and cluster complexes acting
as a source of “Re(CO)3(thpymS)”. Thus, reactions with triphenylphosphine (PPh3) and bis(diphenyl-
Accepted 21 December 2012
phosphino)methane (dppm) afford mononuclear fac-Re(CO)3(PPh3)(
dppm)(
2-thpymS) (4), respectively. A crystal structure of 3 reveals that the pyrimidine-2-thiolate binds
in a chelating fashion. Reactions with M3(CO)12 (M ¼ Ru, Os) at moderate temperatures afford mixed-
metal clusters. With Ru3(CO)12 in boiling thf isomeric tetranuclear butterfly clusters ReRu3(CO)13 m3
k -
2-thpymS) (3) and fac-Re(CO)3(k1
k
Keywords:
Tetrahydropyrimidine-2-thiol
Carbonyls
X-ray structures
Mixed-metal clusters
Cluster isomerization
(
-
thpymS) (5e6) result which differ in the position of the capping pyrimidine-2-thiolate ligand on the
cluster surface. Thus in the kinetic isomer 5, the pyrimidine-2-thiolate caps the ReRu2 face while in the
thermodynamic isomer 6 it caps the Ru3 face. A similar reaction with Os3(CO)10(NCMe)2 in boiling
benzene affords predominantly the ReOs2-capped tetranuclear cluster ReOs3(CO)13
(
m3-thpymS) (7),
together with small amounts of (
m-H)Os3(CO)9(m3-thpymS) (8) resulting from loss of rhenium. Cluster 7 is
stable in refluxing toluene but slowly converts to isomeric 9 in xylene at 140 ꢀC but only in low yields.
The crystal structures of isomeric 5e6 have been solved and show only small variations in the cluster
core geometry. Density functional calculations show that clusters 6 and 9 are slightly more stable than 5
(D D
G 2.0 kcal molꢁ1) and 7 ( G 1.5 kcal molꢁ1), respectively, and a mechanism is proposed for these
conversions in which the pyrimidine-2-thiolate becomes bidentate after release of the pyrimidine group.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
consequently the resultant complexes display a wide range of
structural motifs [21e27].
Transition metal complexes bearing heterocyclic thiolato li-
gands (which contain nitrogen and/or sulphur as hetero atom/s)
have been widely studied to understand the role of metalloproteins
in biological systems [1e5] as well as being precursors for metal-
sulfide materials [6e9]. Heterocyclic thiols are also attractive li-
gands to synthetic chemists as they are capable of coordinating to
the metal centers in a variety of ways [10e20] due to the presence
of both nitrogen and sulphur as potential donating atoms and
We have been studying the reactivity of heterocyclic thiols with
polynuclear metal carbonyls over the past few years and found that
their reactivity towards polymetallic carbonyls depends on both
their structures and the metal carbonyls to which they are treated
[1,13e20,27e36]. For instance, reactions of heterocyclic thiols with
the trimetallic cluster Os3(CO)10(NCMe)2 normally result in the
oxidative addition of the SeH bond to give (
which decarbonylate at elevated temperature to afford (
Os3(CO)9(m3-L), whereas similar reactions with Ru3(CO)12 always
afford only ( -H)Ru3(CO)9(m3-L) [31,33]. Their reactions with Group
7 dinuclear carbonyls, M2(CO)10 (M ¼ Re, Mn), are more diverse
m-H)Os3(CO)10
(m-L)
m-H)
m
* Corresponding author. Tel.: þ880 27791099.
E-mail address: skabir_ju@yahoo.com (S.E. Kabir).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.12.030

Md.F. Ahmad et al. / Journal of Organometallic Chemistry 728 (2013) 30e37
31
compared to trimetallic clusters. For example, reactions of pyri-
dine-2-thiol (pySH) with M2(CO)10 (M ¼ Re, Mn) give dinuclear
M2(CO)6( -pyS)2 [4,26] whereas pyrimidine-2-thiol (pymSH),
which contains an extra nitrogen atom in the aromatic ring, affords
tetranuclear M4(CO)12
2.2. Reaction of 1 with PPh3
m
PPh3 (24 mg, 0.092 mmol) was added to a CH2Cl2 solution
(20 mL) of 1 (35 mg, 0.045 mmol) and the mixture was stirred at
room temperature for 48 h. The solvent was removed under
reduced pressure and the residue separated by TLC on silica gel.
Elution with hexane/CH2Cl2 (4:1, v/v) developed only one band
(m
-pymS)4 (M ¼ Re, Mn) [32]. In contrast, the
five membered heterocyclic thiol, 2-mercapto-1-methylimidazole
(1-MeMID), reacts with Re2(CO)8(NCMe)2 to yield both di- and
tetrarhenium complexes, Re2(CO)6(
1-MeMID)4, together with the trirhenium hydride Re3(CO)8(
CO)( -1-MeMID)2( -H) [18].
m
-1-MeMID)2 and Re4(CO)12
(
m
m
-
-
which afforded fac-Re(CO)3(PPh3)(k
2-thpymS) (3) (32 mg, 54%) as
colourless crystals after recrystallization from hexane/CH2Cl2
m
m
at 4 ꢀC.
The reactivity of some of the resultant Group 7 di- and tetra-
nuclear complexes with various mono- and bidentate ligands as
well as with metal carbonyls had been investigated which reveals
that they are versatile precursors for mono- and polynuclear
complexes possessing M(CO)3(L) fragment [18e20,28,29]. In
a continuation of our previous work on the reactivity of heterocy-
clic thiols with polynuclear carbonyls, we have now prepared the
Data for 3: Anal. Calcd. for C25H22N2O3ReS: C, 46.36; H, 3.42; N,
4.33. Found: C, 46.47; H, 4.54; N, 3.46%. IR (nco, CH2Cl2): 2017 vs,
1916 s, 1887 s cmꢁ1 1H NMR (CDCl3):
d 7.65 (m, 6H), 7.40 (m, 9H),
4.42 (s, br, 1H), 2.94 (m, 2H), 2.55 (m, 1H), 2.44 (m, 1H), 1.63 (m, 1H),
1.36 (m, 1H). 31P{1H} NMR (CDCl3):
617 (Mþ).
d 19.9 (s). FAB MS (m/z):
dirhenium complex Re2(CO)6(
m-thpymS)2 (2) and examined its
2.3. Reaction of 1 with dppm
reactivity towards various phosphines and polynuclear carbonyls
which are the subject of this article.
To a cyclohexane (20 mL) solution of 1 (35 mg, 0.045 mmol) was
added dppm (35 mg, 0.091 mmol) and the mixture was heated to
reflux for 20 h. The solvent was removed under reduced pressure
and the residue chromatographed by TLC on silica gel. Elution with
hexane/CH2Cl2 (4:1, v/v) developed three bands. The first and third
bands were unconsumed dppm and 1 respectively. The second
2. Experimental
All manipulations were carried out under nitrogen using
standard Schlenk techniques. Terahydropyrimidine-2-thiol (thpy-
mSH), triphenylphosphine (PPh3) and bis(diphenylphosphino)
methane (dppm) were purchased from Aldrich and used as
received. Metal carbonyls were purchased from Strem Chemicals
Inc. and used without further purification. Re2(CO)8(NCMe)2 and
Os3(CO)10(NCMe)2 were prepared according to literature methods
[14,37]. Reagent-grade solvents were dried and distilled by stan-
dard methods prior to use. Infrared spectra were recorded on
a Shimadzu FTIR 8101 spectrophotometer. NMR spectra were
recorded on a Bruker DPX 400 instrument. Elemental analyses
were performed by Wazed Miah Science Research Center, Jahan-
girnagar University, Dhaka. Preparative thin layer chromatography
was carried out on 1 mm plates prepared from silica gel GF254
(type 60, E. Merck).
band afforded Re(CO)3(k k
1-dppm)( 2-thpymS) (4) (20 mg, 57%) as
colourless crystals after recrystallization from hexane/CH2Cl2
at 4 ꢀC.
Data for 4: Anal. Calcd. for C31H29N2O2ReP2S: C, 50.19; H, 3.94; N,
3.78. Found: C, 50.30; H, 4.11; N, 3.86%. IR (nco, CH2Cl2): 2016 vs,
1915 s, 1886 s cmꢁ1 1H NMR (CDCl3):
d 7.59 (m, 2H), 7.53 (m, 2H),
7.36e7.16 (m, 16H), 4.59 (s,br, 1H), 3.71 (ddd, J ¼ 12, 8, 4 Hz, 1H),
3.35 (ddd, J ¼ 12, 8, 4 Hz,1H), 2.95 (m,1H), 2.80 (dt, J ¼ 16, 4 Hz,1H),
2.56 (m, 1H), 2.06 (m, 1H), 1.51 (m, 1H), 1.01 (m, 1H). 31P{1H} NMR
(CDCl3):
d
11.4 (d, J ¼ 74.5 Hz, 1P), e25.6 (d, J ¼ 74.5 Hz, 1P). FAB MS
(m/z): 742 (Mþ).
2.4. Reaction of 1 with Ru3(CO)12
2.1. Reaction of Re2(CO)10 or Re2(CO)8(MeCN)2 with thpymSH
A thf (20 mL) solution of 1 (50 mg, 0.065 mmol) and Ru3(CO)12
(21 mg, 0.033 mmol) was heated to reflux for 30 min. The solvent
was removed under reduced pressure and the residue chromato-
graphed by TLC on silica gel. Elution with hexane/CH2Cl2 (9:1, v/v)
developed three bands. The first band was unconsumed Ru3(CO)12
and the third and second third bands gave two isomers of
A
benzene (30 mL) solution of Re2(CO)8(NCMe)2 (100 mg,
0.15 mmol) and thpymSH (23 mg, 0.28 mmol) was heated to reflux
for 6 h. The solvent was removed under reduced pressure and the
residue chromatographed by TLC on silica gel. Elution with hexane/
CH2Cl2 (7:3, v/v) developed three bands. The second band afforded
ReRu3(CO)13(m3-thpymS) (5, 30 mg, 24%; 6, 10 mg, 8%) as deep red
eq-Re2(CO)9{
k
1-(S)eSN2C4H8} (2) (12 mg, 11%) as yellowish green
and pink crystals respectively after recrystallization from hexane/
crystals and the third band gave Re2(CO)6(
m
-thpymS)2 (1) (36 mg,
CH2Cl2 at 4 ꢀC.
32%) as colourless crystals after recrystallization from hexane/
CH2Cl2 at 4 ꢀC. The content of the first band was too small for
characterization. Alternatively, Me3NO (63 mg, 0.84 mmol) was
added dropwise to an acetone (30 mL) solution of Re2(CO)10
(200 mg, 0.31 mmol) and thpymSH (72 mg, 0.62 mmol) and the
mixture was stirred at room temperature for 48 h. A similar workup
and chromatographic separation described as above developed two
bands on TLC plate which afforded 2 (12 mg, 5%) and 1 (80 mg,
34%), respectively, in order of elution.
Data for 5: Anal. Calcd. for C17H7N2O13Ru3ReS: C, 21.08; H, 0.73;
N, 2.89. Found: C, 21.32; H, 0.95; N, 3.05%. IR (nco, CH2Cl2): 2101 m,
2041 vs, 2021 m, 2007 m 1965 m, 1910 m cmꢁ1. 1H NMR (CDCl3):
d
6.76 (s,br, 1H), 4.12 (m, 2H), 3.47 (m, 2H), 2.01 (m, 2H). FAB MS (m/
z): 969 (Mþ).
Data for 6: Anal. Calcd. for C17H7N2O13Ru3ReS: C, 21.08; H, 0.73;
N, 2.89. Found: C, 21.27; H, 0.96; N, 3.01%. IR (nco, CH2Cl2): 2092 w,
2059 s, 2027 s, 2008 m, 1976 m, br. cmꢁ1 1H NMR (CDCl3):
.
d
6.42 (s,br, 1H), 3.57 (m, 2H), 3.36 (m, 2H), 1.94 (m, 2H). FAB MS (m/
Data for 1: Anal. Calcd. for C14H14N4O6Re2S2: C, 21.81; H, 1.83; N,
7.27. Found: C, 22.06; H, 1.98; N, 7.40%. IR (nco, CH2Cl2): 2031 m,
z): 969 (Mþ).
2006 vs, 1923 m, br cmꢁ1. 1H NMR (CD2Cl2):
d
5.50 (s, 2H), 3.36 (m,
2.5. Conversion of 5 to 6
8H), 1.83 (m, 4H). FAB MS (m/z): 770 (Mþ).
Data for 2: Anal. Calcd. for C13H8N2O9Re2S: C, 21.08; H, 1.09; N,
3.78. Found: C, 21.42; H,1.14; N, 3.86%. IR (nco, CH2Cl2): 2104 m, 2023
A thf (10 mL) solution of 5 (20 mg, 0.021 mmol) was heated to
reflux for 2 h. A similar workup and chromatographic separation
described as above furnished two bands on TLC plate. The first band
gave 6 (8 mg, 40%), while the second was unconsumed 5 (3 mg).
vs, 2004 vs, 1956 m, 1915 m cmꢁ1. 1H NMR (d6-acetone):
d
8.51 (s,
1H), 6.64 (s, 1H), 3.65 (m, 4H), 3.26 (m, 2H). FAB MS (m/z): 740 (Mþ).

32
Md.F. Ahmad et al. / Journal of Organometallic Chemistry 728 (2013) 30e37
2.6. Reaction of 1 with Os3(CO)10(NCMe)2
Data for 9: Anal. Calcd. for C17H7N2O13Os3ReS: C, 16.52; H, 0.57;
N, 2.27. Found: C, 16.71; H, 0.67; N, 2.36%. IR (nco, CH2Cl2): 2107 w,
2094 m, 2061 vs, 2041m, 2027 vs, 2008 m, 1984 m, br. cmꢁ1
To a benzene (20 mL) solution of 1 (35 mg, 0.045 mmol) was
added Os3(CO)10(NCMe)2 (22 mg, 0.026 mmol) and the mixture
was refluxed for 40 min. The solvent was removed under reduced
pressure and the residue chromatographed by TLC on silica gel.
Elution with hexane/CH2Cl2 (7:3, v/v) developed four bands. The
first band was Os3(CO)12 (trace). The second and third bands
.
2.8. X-ray crystallography
Single crystals of 3, 5 and 6 suitable for X-ray diffraction were
grown by slow diffusion of hexane into a dichloromethane solution
at 4 ꢀC. Crystallographic data was collected on a Rigaku Mercu-
ry375 R/M CCD (XtaLAB mini) diffractometer using graphite mon-
afforded (m-H)Os3(CO)9(m3-thpymS) (8) (8 mg, 8%) as yellow crys-
tals and ReOs3(CO)13
(
m3-thpymS) (7) (23 mg, 45%) as red crystals
after recrystallization from hexane/CH2Cl2 at 4 ꢀC. The fourth band
was too small for characterization.
ochromated Mo-Ka radiation. All calculations were carried out
using the WinGX package [38] and all datasets were corrected for
absorption using DIFABS [39]. The structures were solved by direct
methods (SHELXS-97) [40] and refined on F2 by full-matrix least-
squares (SHELXL-97) [41] using all unique data. Non-hydrogen
atoms were refined anisotropically and hydrogen atoms on C-
atoms were fixed at calculated positions and refined using a riding
model. Hydrogen atoms connected to N atoms were located in
difference Fourier maps and refined isotropically with the NeH
Data for 7: Anal. Calcd. for C17H7N2O13Os3ReS: C, 16.52; H, 0.57;
N, 2.27. Found: C, 16.77; H, 0.69; N, 2.41%. IR (nco, CH2Cl2): 2107 s,
2041 vs, 2022 s, 2007 s, 1982 s, 1961 m, br, 1910 w, br. cmꢁ1. 1H NMR
(CDCl3):
d 6.62 (s, br, 1H), 4.23 (m, 2H), 3.35 (m, 2H), 1.98 (m, 2H).
FAB MS (m/z): 1236 (Mþ).
Data for 8: Anal. Calcd. for C13H8N2O9Os3S: C, 16.63; H, 0.86; N,
2.98. Found: C, 16.82; H, 0.99; N, 3.15%. IR (nco, CH2Cl2): 2083 w,
2051 vs, 2023 vs, 1994 s, 1982 sh, 1942 w,br. cmꢁ1. 1H NMR (CDCl3):
ꢀ
distances being restrained to 0.90(3) A. All pertinent crystal data
major isomer: d 5.79 (s, br, 1H), 3.49 (m, 2H), 3.09 (m, 2H), 1.78 (m,
and other experimental conditions and refinement details are
summarized in Table 1.
2H), ꢁ15.25 (s, 1H); minor isomer:
d 5.50 (s, br, 1H), 3.35 (m, 2H),
3.13 (m, 2H), 1.68 (m, 2H), ꢁ12.44 (s, 1H). FAB MS (m/z): 939 (Mþ).
2.7. Thermolysis of 7
2.9. Computational methodology and modelling details
The reported calculations were performed with the hybrid DFT
functional B3LYP, as implemented by the Gaussian 09 program
package [42]. This functional utilizes the Becke three-parameter
exchange functional (B3) [43], combined with the correlation
functional of Lee, Yang and Parr (LYP) [44]. The Os, Re, and Ru atoms
were described by StuttgarteDresden effective core potentials
(ecp) and an SDD basis set, while the 6-31G(d0) basis set was
employed for the remaining atoms. The geometries found for
clusters 5, 6, 7, and 9 were fully optimized and the analytical Hes-
sian afforded only positive eigenvalues for the ground-state
A xylene solution of (10 mL) of ReOs3(CO)13(m3-thpymS) (7)
(13 mg, 0.01 mmol) was refluxed for 1 h. The colour of the reaction
mixture changed from red to pale yellow. The solvent was removed
under reduced pressure and the residue was chromatographed by
TLC on silica gel. Elution with hexane/CH2Cl2 (7:3, v/v) developed
two bands. The first band was unconsumed ReOs3(CO)13
thpymS) (7) (1.5 mg) and the second band gave ReOs3(CO)13
(
(
m3
m3
-
-
thpymS) (9) (1 mg, 8%) as yellow crystals after recrystallization
from hexane/CH2Cl2 at 4 ꢀC.
Table 1
Crystallographic data and structure refinement for 3, 5 and 6.
Compound
3
5
6
Empirical formula
Formula weight
Temperature (K)
C25H22N2O3P1Re1S1
647.68
293(2)
C17H7N2O13Ru3ReS
968.72
293(2)
C17H7N2O13Ru3ReS
968.72
293(2)
ꢀ
Wavelength (A)
0.71075
0.71075
0.71075
Crystal system
Space group
Monoclinic
P 2l/c
Monoclinic
P 2l/c
Monoclinic
P 2l/c
Unit cell dimensions
ꢀ
a (A)
10.4490(8)
14.788(1)
16.173(1)
101.934(7)
19.346(2)
9.391(1)
13.671(2)
90.445(6)
10.231(3)
16.344(2)
15.628(2)
108.84(2)
ꢀ
b (A)
ꢀ
c (A)
b
(ꢀ)
3
ꢀ
Volume (A )
2445.1(3)
2483.5(5)
2473.2(8)
Z
4
4
4
Density (calculated) (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
1.759
5.150
1264
2.591
6.799
1796
2.602
6.827
1800
0.12 x 0.11 x 0.09
3.02e27.48
)
Crystal size (mm3)
q
0.34 ꢂ 0.21 ꢂ 0.10
0.11 ꢂ 0.08 ꢂ 0.04
range for data collection (ꢀ)
3.04e27.48
2.98e27.48
Index ranges
ꢁ13 ꢃ h ꢄ 13
ꢁ19 ꢃ k ꢄ 19
ꢁ21 ꢃ l ꢄ 21
25,010
ꢁ25 ꢃ h ꢄ 24
ꢁ12 ꢃ k ꢄ 12
ꢁ17 ꢃ l ꢄ 17
25,437
ꢁ13 ꢃ h ꢄ 13
ꢁ21 ꢃ k ꢄ 21
ꢁ20 ꢃ l ꢄ 20
25,955
Reflections collected
Independent reflections
Refinement method
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
5605 [R(int) ¼ 0.0545]
Full-matrix least-squares on F2
0.6269 and 0.2734
5605/0/298
5680 [R(int) ¼ 0.1331]
Full-matrix least-squares on F2
0.7727 and 0.5217
5680/0/334
5662 [R(int) ¼ 0.1086]
Full-matrix least-squares on F2
0.5786 and 0.4946
5662/0/338
1.048
1.030
1.080
Final R indices [I > 2
R indices (all data)
s
(I)]
R1 ¼ 0.0292, wR2 ¼ 0.0621
R1 ¼ 0.0393, wR2 ¼ 0.0656
1.619 and ꢁ0.786
R1 ¼ 0.0557, wR2 ¼ 0.0846
R1 ¼ 0.1089, wR2 ¼ 0.0971
1.209 and ꢁ1.044
R1 ¼ 0.0626, wR2 ¼ 0.1368
R1 ¼ 0.1042, wR2 ¼ 0.1542
2.886 and ꢁ2.272
Largest diff. peak and hole (eÅꢁ3
)

Md.F. Ahmad et al. / Journal of Organometallic Chemistry 728 (2013) 30e37
33
H
N
H
H
N
N
N
N
S
H
OC
OC
CO
Re
CO
S
CO
CO
N
SH
Re2(CO)8(NCMe)2
(OC)
(CO)3
3 Re
Re
+
OC
Re
C6H6
80oC
S
N
OC
CO
N
1
H
2
Scheme 1. Reaction of Re2(CO)8(NCMe)2 with tetrahydropyrimidine-2-thiol.
minima. The computed frequencies were used to make zero-point
and thermal corrections to the electronic energies, and the repor-
ted free energies are quoted in kcal/mol relative to the specified
standard.
and dppm affords fac-Re(CO)3(PPh3)(
Re(CO)3(
1-dppm)( 2-thpymS) (4) in 54 and 57% yields, respec-
k
2-thpymS) (3) and fac-
k
k
tively (Scheme 2). The reaction with PPh3 proceeded smoothly at
room temperature, but addition of dppm was very slow under these
conditions and was carried out in boiling cyclohexane. The greater
reactivity of 1 towards PPh3 as compared to dppm suggests that the
reaction is associative in nature, with the approach of the larger
diphosphine to compound 1 having a higher activation barrier.
Characterisation was relatively straightforward, the IR spectra
of both showing three strong carbonyl bands characteristic of
complexes containing a fac-Re(CO)3 fragment [32]. The 31P NMR
3. Results and discussion
3.1. Reaction of Re2(CO)8(NCMe)2 or Re2(CO)10 with thpymSH:
formation of dirhenium complexes
Treatment of Re2(CO)8(NCMe)2 with thpymSH in boiling ben-
spectrum of 3 consists only of a singlet at
shows two equally intense doublets at
d
19.9, whilst that of 4
11.4 and ꢁ25.6
zene afforded two dirhenium complexes, namely Re2(CO)6(
m-
1-(S)eSN2C4H8} (2), in 32 and 11%
d
thpymS)2 (1) and eq-Re2(CO)9{
k
(J ¼ 74.5 Hz). A single crystal X-ray analysis of 3, the results of
which are summarised in Fig. 1, confirms the formulation. The
molecule consists of a single rhenium atom coordinated by three
carbonyls, a PPh3 ligand, and a chelating tetrahydropyrimidine-2-
thiolato ligand. The carbonyls are arranged in a facial fashion and
the thiolato ligand is bonded to rhenium using its exocyclic sul-
phur atom and sp2-hybridized nitrogen. The NeReeS chelate angle
is very acute [64.05(9)ꢀ] which causes major distortion from the
octahedral arrangement of ligands around rhenium. The ReeP, Ree
S and ReeN bond distances are similar to those reported for related
complexes [32].
yields, respectively (Scheme 1). Both were also obtained from
a direct reaction between Re2(CO)10 and thpymSH in the presence
of Me3NO at room temperature [yield e 1 (34%); 2 (5%)].
The target complex 1 was readily characterized by comparing its
IR spectrum with similar dirhenium and dimanganese complexes
[4,18,28]. The 1H NMR spectrum shows a singlet at
d
5.50 and two
multiples at
d 3.36 and 1.83 with the intensity ratio 1:4:2 which are
attributable to the NꢁH and methylene protons of the heterocyclic
ligands. The FAB mass spectrum displays a parent molecular ion at
m/z 770 together with ions due to the successive loss of six car-
bonyls in accord with the proposed structure.
Complex 2, a rare example of dirhenium carbonyl complexes
containing a thiolato ligand coordinated in a
been characterized both spectroscopically and crystallographically
[46]. The 1H NMR spectrum displays two broad singlets at
8.51
and 6.64 (each integrating to 1H) attributable to the NꢁH protons
together with two multiplets at 3.65 (4H) and 3.26 (2H) due to the
k
1-fashion [45], has
3.3. Reactions of 1 with M3(CO)10L2 (M ¼ Ru, Os; L ¼ CO, MeCN):
formation of mixed-metal clusters
d
It has been shown that the structural analogues of 1 are excel-
lent precursors for the synthesis of tetranuclear mixed-metal
d
methylene protons of the heterocyclic ring. The FAB mass spectrum
exhibits a parent molecular ion at m/z 740 and other ions due to
sequential loss of nine carbonyls.
clusters M3Re(CO)13
(
m3-L) (M ¼ Os, Ru; L ¼ heterocyclic thiolato
ligand) [19,20,28,29,32]. Treatment of 1 with Ru3(CO)12 in refluxing
thf afforded two isomeric tetranuclear butterfly clusters 5 and 6 in
24 and 8% yield, respectively (Scheme 3). In separate control ex-
periments we found that cluster 5 transforms into 6 under the same
conditions, while thermolysis of the latter cluster in thf results in
slow decomposition which suggests that 5 is the kinetic product of
this reaction.
3.2. Reaction of 1 with PPh3 and dppm: formation of mononuclear
complexes
As observed for related complexes of the type M2(CO)6(m-L)2
(M ¼ Re, Mn; L ¼ heterocyclic thiolato ligand), dirhenium 1 un-
dergoes facile ReeS bond scission to afford mononuclear complexes
when treated with phosphines. Thus reaction of 1 with PPh3
IR spectra of 5 and 6 are very similar and the FAB mass spectrum
of each exhibits a molecular ion peak at m/z 969. The 1H NMR
spectra are not particularly informative as each of them displays
OC
OC
OC
OC
N
OC
OC
N
PPh3
CH2Cl2, 25oC
dppm
C6H12, 82oC
Re
NH
Re
NH
1
S
S
PPh2
PPh3
P
3
Ph2
4
Scheme 2. Reaction of Re2(CO)6(m-thpymS)2 (1) with PPh3 and dppm.

34
Md.F. Ahmad et al. / Journal of Organometallic Chemistry 728 (2013) 30e37
Fig. 2. X-ray structure of ReRu3(CO)13(m3-thpymS) (5) showing the atom labelling
scheme used. The hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn
ꢀ
ꢀ
at 50% probability level. Selected interatomic distances (A) and angles ( ):Ru(1)ꢁRu(2)
2.841(1), Ru(1)ꢁRu(3) 2.760(1), Ru(2)ꢁRu(3) 2.847(1), Re(1)ꢁRu(1) 2.9131(9), Re(1)ꢁ
Ru(3) 2.922(1), Re(1)ꢁN(1) 2.189(7), Ru(1)ꢁS(1) 2.380(3), Ru(3)ꢁS(1) 2.380(3), N(1)ꢁ
Re(1)ꢁRu(1) 85.1(2), N(1)ꢁRe(1)ꢁRu(3) 84.9(2), Ru(1)ꢁRe(1)ꢁRu(3) 56.47(2), S(1)ꢁ
Ru(1)ꢁRu(3) 54.55(6), S(1)ꢁRu(1)ꢁRu(2) 81.81(7), Ru(3)ꢁRu(1)ꢁRu(2) 61.08(3), S(1)ꢁ
Ru(1)ꢁRe(1) 81.09(6), Ru(3)ꢁRu(1)ꢁRe(1) 61.92(2), Ru(2)ꢁRu(1)ꢁRe(1) 119.69(3),
Ru(1)ꢁRu(2)ꢁRu(3) 58.06(3), S(1)ꢁRu(3)ꢁRu(1) 54.56(6), S(1)ꢁRu(3)ꢁRu(2) 81.67(6),
Ru(1)ꢁRu(3)ꢁRu(2) 60.86(3), S(1)ꢁRu(3)ꢁRe(1) 80.92(6), Ru(1)ꢁRu(3)ꢁRe(1)
61.61(3), Ru(2)ꢁRu(3)ꢁRe(1) 119.19(3), Ru(3)ꢁS(1)ꢁRu(1) 70.89(7).
Fig. 1. X-ray structure of fac-Re(CO)3(PPh3)(k
2-thpymS) (3) showing the atom labelling
scheme used. The hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn
ꢀ
ꢀ
at 50% probability level. Selected interatomic distances (A) and angles ( ): Re(1)eP(1)
2.483(1), Re(1)eS(1) 2.554(1), Re(1)eN(1) 2.156(3), Re(1)eC(3) 1.923(4), Re(1)eC(2)
1.896(4), Re(1)eC(1) 1.940(4), N(1)eRe(1)eP(1) 89.64(9), N(1)eRe(1)eS(1) 64.05(9),
P(1)eRe(1)eS(1) 84.20(3), C(7)eS(1)eRe(1) 78.5(1), C(7)eN(1)eRe(1) 105.5(3), C(4)e
N(1)eRe(1) 132.9(3), N(1)eC(7)eN(2) 124.8(4), N(1)eC(7)eS(1) 112.0(3), N(2)eC(7)e
S(1) 123.2(3).
parameters of these isomeric clusters are very similar to each other
and are within the range reported for related compounds
[19,20,28].
four resonances attributed to the methylene and NeH protons of
the pyrimidine-2-thiolato ligand. However, we were able to grow
single crystals of both and carried out X-ray diffraction analyses the
results of which are summarized in Figs. 2 and 3, respectively. Both
products contain 62 valence electrons and exhibit a butterfly
skeleton of four metal atoms with the rhenium atom at a wingtip
position in both isomers. The observed four-vertex butterfly
framework in 5 and 6 is consistent with Polyhedral Skeletal Elec-
tron Pair (PSEP) Theory. The metallic core is ligated by 13 carbonyls
and a tetrahydropyrimidine-2-thiolato ligand that functions as
a five-electron donor ligand. In both clusters, the carbonyls are all
terminally bonded to the metal centers and the tetrahydropyr-
imidine-2-thiolato ligand is coordinated regioselectively to one of
the two convex faces of the butterfly. In 5 the heterocyclic ligand
caps the ReRu2 triangle, whereas it caps the homometallic Ru3 face
in 6; the capping of different triangular faces by the ancillary tet-
rahydropyrimidine-2-thiolato ligand serves as the major differ-
entiating point of these two clusters. In both clusters, the
rutheniumeruthenium hinge is slightly shorter than the other
two rutheniumeruthenium vectors within the molecule. Move-
ment of the tetrahydropyrimidine-2-thiolato ligand does not
change the dihedral angle at the hinge vector significantly, being
159.39(3)ꢀ in 5 and reducing to 157.56(4)ꢀ in 6. Likewise, bonding
Isomer 5 is clearly the kinetic product of the reaction, being
converted into the thermodynamically more stable 6. In order to
probe the relative energy differences between the two we have
carried out density functional studies on both, and we find a free
energy difference of 2.0 kcal molꢁ1 in favour of cluster 6 that is in
keeping with the control experiments. The computed ground-state
structures for 5 and 6 closely matched the X-ray diffraction struc-
tures. Initial formation of 5 presumably results from addition of
a putative 16-electron “Re(CO)3(thpymS)” fragment to the trir-
uthenium centre via insertion into the rheniumesulphur bond.
While the nature of the cluster isomerisation is not fully under-
stood at this time, a plausible route is shown in Scheme 4. Here
initial cleavage of the rheniumenitrogen bond leads to a decrease
in the skeletal electrons from 7 SEP to 6 SEP, and this is compen-
sated by the formation of a new RueRe bond as the molecular
polyhedron undergoes an arachno-to-nido transformation [47].
Accompanying this reaction is the formation of a bridging CO group
at the new metalemetal bond. Subsequent rotation about the
sulphurecarbon bond (or proton transfer between nitrogen atoms),
followed by coordination of nitrogen to the initial wingtip ruthe-
nium results and cleavage of this newly formed RueRe bond and
concomitant migration of the transient m2-CO group to the
(CO)
Re
3
(CO)3
(OC)3Ru
(CO)3
Ru
Ru
Ru
(OC)4
Re(CO)4
Ru3(CO)12
1
N
thf
thf
N
S
H
Ru
67oC
67oC
S
Ru
(CO)3
(CO)3
N
N
5
H
6
Scheme 3. Reaction of Re2(CO)6(m-thpymS)2 (1) with Ru3(CO)12.

Md.F. Ahmad et al. / Journal of Organometallic Chemistry 728 (2013) 30e37
35
rhenium, completes the formal transfer of the face-capping tetra-
hydropyrimidine-2-thiolato ligand to the Ru3 face. Such a process is
attractive since the intermediate is an electron-precise tetrahedral
cluster (60 valence electrons) and might thus be expected to pro-
vide a relatively low energy pathway.
A similar reaction between 1 and Os3(CO)10(NCMe)2 gave
Os3Re(CO)13
Os3(CO)9(m3-thpymS)(
(
m3-thpymS) (7) as major product (45%) together with
-H) (8) (8%) (Scheme 5). Cluster 7 was
m
characterized by comparing its IR spectrum with that of 5, specif-
ically the highest frequency carbonyl vibration at 2107 cmꢁ1 is
consistent with that found in 5 (2101 cmꢁ1) but not 6 (2092 cmꢁ1).
The FAB mass spectrum shows a parent molecular ion at m/z 1236
together with ions due to the successive loss of 13 carbonyls. The 1H
NMR spectrum displays three multiplets
integrating to 2H) and a broad singlet at
d
4.23, 3.35, 1.98 (each
d
6.62 (integrating to 1H)
assigned to the methylene and NeH protons of the pyrimidine-2-
thiolato ligand.
Under the reaction conditions described above (refluxing ben-
zene), a second isomer of 7 was not observed and even when we
heated 7 in toluene for a prolonged period this was also the case.
However, in xylene the slow transformation of 7 was observed.
Thus, heating for 1 h led to the loss of ca. 90% of 7 and formation of
isomeric 9 in low (6.5%) yield (Scheme 6). DFT calculations were
performed on 7 and 9, and the latter cluster was found to lie
1.5 kcal molꢁ1 lower in energy, paralleling the trend found in
clusters 5 and 6. Given the favourable thermodynamics for the
formation of cluster 9, the observed decomposition that accom-
panies this isomerization reflects the higher activation barrier for
the isomerization in the ReOs3 system. Importantly trinuclear 8 was
not generated under these conditions. Due to the small amounts of
9, characterization was made on the basis of IR spectroscopy and
elemental analysis with the former being quite distinct from that of
7. The high temperature, low yield isomerisation of 7 to 9 is in
contrast to that noted for the analogous Ru3Re system. Presumably
the nature of the rheniumenitrogen bond in 7 is very similar to that
in 5, likewise formation of a new osmium-rhenium bond should
also be favourable. It is well-known that carbonyl bridging across
bonds between the heavier transition elements is not favoured and
thus we suggest that it may be for this reason that isomerisation is
not facile in this case [48].
Fig. 3. X-ray structure of ReRu3(CO)13
scheme used. The hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn
(m3-thpymS) (6) showing the atom labelling
ꢀ
ꢀ
at 50% probability level. Selected interatomic distances (A) and angles ( ):Ru(1)ꢁRu(2)
2.786(1), Ru(1)ꢁRu(3) 2.819(1), Ru(2)ꢁRu(3) 2.832(1), Re(1)ꢁRu(1) 2.898(1), Re(1)ꢁ
Ru(2) 2.920(1), Ru(3)ꢁN(2) 2.16(1), Ru(1)ꢁS(1) 2.372(3), Ru(2)ꢁS(1) 2.371(3), Ru(1)ꢁ
Re(1)ꢁRu(2) 57.22(3), N(2)ꢁRu(3)ꢁRu(1) 87.9(3), N(2)ꢁRu(3)ꢁRu(2) 86.6(3), Ru(1)ꢁ
Ru(3)ꢁRu(2) 59.07(4), S(1)ꢁRu(1)ꢁRu(2) 54.02(8), S(1)ꢁRu(1)ꢁRu(3) 80.44(8), Ru(2)ꢁ
Ru(1)ꢁRu(3) 60.69(4), S(1)ꢁRu(1)ꢁRe(1) 82.93(8), Ru(2)ꢁRu(1)ꢁRe(1) 61.79(3),
Ru(3)ꢁRu(1)ꢁRe(1) 118.61(4), S(1)ꢁRu(2)ꢁRu(1) 54.05(8), Ru(1)ꢁRu(2)ꢁRu(3)
60.24(4), S(1)ꢁRu(2)ꢁRu(3) 80.18(8), S(1)ꢁRu(2)ꢁRe(1) 82.46(8), Ru(1)ꢁRu(2)ꢁRe(1)
60.99(3), Ru(3)ꢁRu(2)ꢁRe(1) 117.45(4), Ru(2)ꢁS(1)ꢁRu(1) 71.93(9).
O
C
Re
Ru
Re
Re CO
Ru
Ru
OC Ru
Ru
Ru
N
Ru
N
S
H
Ru
N
S
Ru
5
S
N
N
H
H
6
N
Scheme 4. A plausible pathway for the isomerisation of 5 to 6.
H
N
Re (CO)3
(CO)3
N
(OC)4Os
Os
S
Os3(CO)10(NCMe)2
+
Os
Os
(OC)3
N
(CO)3
1
S
H
Os
C6H6
80oC
(CO)3
H
Os
(CO)3
N
7
8
Scheme 5. Reaction of Re2(CO)6(m-thpymS)2 (1) with Os3(CO)10(NCMe)2.

36
Md.F. Ahmad et al. / Journal of Organometallic Chemistry 728 (2013) 30e37
(CO)
Re
3
(CO)3
Os
(OC)3Os
(CO)3
Os
Os
(OC)4
Re(CO)4
xylene
140 oC
N
N
S
H
Os
(CO)3
S
Os
(CO)3
N
N
7
H
9
Scheme 6. Isomerisation of Os3Re(CO)13(m3-thpymS) (7) to 9 upon heating in xylene.
Cluster 7 is stable in both refluxing benzene and toluene but in
xylene at 140 ꢀC it slowly converts into isomeric 9, although yields
are poor due to accompanying decomposition. The reason(s) for
this reactivity difference between the Ru3Re and ReOs3 clusters is
not fully understood but we speculate that the isomerism proceeds
via an intermediate containing a bridging carbonyl and such species
are known to be unfavourable across metalemetal bonds formed
from the heavier transition elements.
H
H
N
N
N
N
S
S
Os
(OC)3
Os (CO)3
H
Os
Os
(CO)3
(OC)3
Os
(CO)3
H
Os
(CO)3
8a
8b
Chart 1. Two isomers of Os3(CO)9(m3-thpymS)(m-H) (8).
Acknowledgements
The second product of the reaction, namely 8, results from
This research has been jointly sponsored by the Ministry of
Science and Information & Communication Technology and Min-
istry of Education, Government of the People’s Republic of Ban-
gladesh. We thank the Commonwealth Scholarship Commission for
the award of a Commonwealth Scholarship to SG. Financial support
from the Robert A. Welch Foundation (Grant B-1093-MGR) and the
NSF (CHE-0741936) is acknowledged and we would like to thank
the Title-III fund of the US Department of Education for providing
support for the purchase of the diffractometer at Tennessee State
University.
complete transfer of the tetrahydropyrimidine-2-thiolato ligand
from rhenium to osmium. Its identity is readily determined from
the IR spectrum, the pattern of which closely resembles other
Os3(CO)9(m3-L)(m-H) complexes [31]. The FAB mass spectrum dis-
plays a parent ion at m/z 939 and further ions due to stepwise loss
of nine carbonyls. The 1H NMR shows two sets of resonances in 3:1
ratio indicating that 8 exists in two isomeric forms in solution
(Chart 1). The isomerism in this type of cluster occurs due to
disposition of the hydride ligand across different osmiumeosmium
edges and both isomeric forms have been structurally characterized
for Os3(CO)9(m3-L)(
[31]. The relationship between 7 and 8 is unclear.
m
-H)
(
L
-H ¼ 2-mercapto-1-methylimidazole)
Appendix A. Supplementary material
CCDC 880835 for 3, CCDC 880834 for 5 and CCDC 890659 for 6
contain supplementary crystallographic data for this paper. These
data may be obtained free of charge from The Cambridge Crys-
tallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
Atomic coordinates and DFT-computed energies for clusters 5, 6, 7,
and 9 are available from MGR upon request.
4. Summary and conclusions
The synthesis and reactivity of the dirhenium complex
Re2(CO)6(
thpymSH with either Re2(CO)8(NCMe)2 or Re2(CO)10 gives the
expected dirhenium complex Re2(CO)6( -thpymS)2 (1) in moderate
yields (32e34%) along with small amounts of eq-Re2(CO)9{
1-(S)e
SN2C4H8} (2) (5e11%). Complex 2 is a rare example of dirhenium
complex containing a
1-thiolato ligand. Reactions of 1 with mono-
m-thpymS)2 (2) have been investigated. Reactions of
m
k
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