Photochemical reactions of cis-[(η4-NBD)M(CO)4] (NBD = norbornadiene; M = Cr, Mo) olefin complex with ligand, containing S and N donor atoms

Article abstract of DOI:10.1134/S1070328407120032

New complexes cis-[M(CO)₄-DABRd] (M = Cr(I), Mo(II) and fac-[M(CO)₃-SAT] (M = Cr(III), Mo(IV)) have been synthesized by the photochemical reactions of cis-[(η⁴-NBD)M(CO)₄] (NBD is norbornadiene; M=Cr, Mo) with 5-(4-dimethylaminobenzylidene) rhodanine (DABRd) and salicylidene-3-amino-1,2,4-triazole (SAT) ligands and characterized by elemental analysis, FT-IR and ¹H NMR spectroscopy, and mass spectrometry. The spectroscopic studies show that the DABRd ligand acts as a bidentate ligand coordinating via both NH-(S)C=S sulfur donor atoms in I and II and SAT ligand behaves as a tridentate ligand coordinating via its all imine nitrogen-C=N-donor atoms in III and IV to the metal center.

Full text of DOI:10.1134/S1070328407120032

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2007, Vol. 33, No. 12, pp. 886–890. © Pleiades Publishing, Ltd., 2007.
Photochemical Reactions of cis-[(h4-NBD)M(CO)4]
(NBD = Norbornadiene; M = Cr, Mo) Olefin Complex
with Ligand, Containing S and N Donor Atoms1
E. Subasia, S. Karahana, and A. Ercagb
a Department of Chemistry, Faculty of Science and Literature, Dokuz Eylul University, 35160 Izmir, Turkey
b Department of Chemistry, Faculty of Engineering, Istanbul University, 34850 Istanbul, Turkey
e-mail: elif,subasic@deu.edu.tr
Received August 17, 2006
Abstract—New complexes cis-[M(CO)4-DABRd] (M = Cr(I), Mo(II) and fac-[M(CO)3-SAT] (M = Cr(III),
Mo(IV)) have been synthesized by the photochemical reactions of cis-[(η4-NBD)M(CO)4] (NBD is norborna-
diene; M = Cr, Mo) with 5-(4-dimethylaminobenzylidene) rhodanine (DABRd) and salicylidene-3-amino-
1,2,4-triazole (SAT) ligands and characterized by elemental analysis, FT-IR and 1H NMR spectroscopy, and
mass spectrometry. The spectroscopic studies show that the DABRd ligand acts as a bidentate ligand coordi-
nating via both NH–(S)C=S sulfur donor atoms in I and II and SAT ligand behaves as a tridentate ligand coor-
dinating via its all imine nitrogen –C=N– donor atoms in III and IV to the metal center.
DOI: 10.1134/S1070328407120032
1
INTRODUCTION
Initially, here we describe a particularly convenient
photochemical route to the synthesis of cis-[(η4-
NBD)M(CO)4] (M = Cr, Mo). Then we investigated the
behavior of cis-[(η4-NBD)M(CO)4] (M = Cr, Mo) with
the title ligands 5-(4-dimethylaminobenzylidene)rhoda-
nine (DABRd) and salicylidene–3-amino–1,2,4-tria-
zole (SAT) which contain the pentagonal heterocycle
rhodanine and 1,2,4-triazole ring, respectively. New
complexes cis-[M(CO)4-DABRd] (M = Cr (I), Mo (II))
and fac-[M(CO)3-SAT] (M = Cr (III), Mo (IV)) have
been synthesized by the photochemical reactions of
[(η4-NBD)M(CO)4] (M = Cr, Mo) with DABRd and
SAT ligands and characterized by elemental analysis,
FT-IR and 1H NMR spectroscopy, and mass spectrome-
try. The spectroscopic studies show that DABRd ligand
acts as a bidentate ligand coordinating via both sulfur
NH–(S)C = S donor atoms in I and II, and SAT ligand
behaves as a tridentate ligand coordinating via its all
imine nitrogen –C = N– donor atoms in III and IV to the
metal center.
Photosubstitution of group VI metal carbonyls is a
highly efficient process which provides convenient
access to a large variety of mono- and polysubstituted
derivatives [1]. Carbonyl compounds with sulfur and
nitrogen donor ligands continue to attract considerable
attention not only on account of their fascinating struc-
tural chemistry but also because of their ability to act
as electron reservoirs and their potential in catalysis
[2]. Features of the chemistry of these molecules
which are currently of interest include the mechanisms
and sites of substitution as well, as the modification
of reactivity accompanying carbonyl replacement by
donor ligands [3].
Photosubstitutions of CO with the formation of
M(CO)5L (M = Cr, Mo, W) from VIB group metal car-
bonyls M(CO)6 were studied with a variety of σ-donor
ligands L (L are Schiff base derivatives) [4]. In order to
contribute to these studies, we tried to substitute these
ligands to the metal center as bi- or polydentate che-
lates. Along with our continued interest in the photo-
chemical synthesis and structural aspects of VIB group
metal carbonyls led us to launch an exploratory investi-
gation into the photolytic behavior of the cis-[(η4-
NBD)M(CO)4] (NBD is norbornadiene) complexes in
the presence of ligands containing sulfur and nitrogen
donor atoms [5].
EXPERIMENTAL
Materials and methods. All reactions and manipu-
lations were carried out under argon and in argon-satu-
rated solvents using Schlenk techniques. All solvents
were dried and degassed using standard techniques [6].
All organic solvents and silica gel were purchased from
Merck and M(CO)6 (M = Cr, Mo, W) were from Ald-
rich. DABRd [7] and SAT [8] were prepared by litera-
1
The article was submitted by the authors in English.
886

PHOTOCHEMICAL REACTIONS
887
M(CO)6 + NBD Hexane cis-[(η4-NBD)M(CO)4]
+ [W(CO)5]2(µ-NBD).
hν
ture methods. Elemental analyses were performed on a
LECOCHNS-O–9320 instrument at the Technical and
Scientific Research Council of Turkey, (TUBITAK).
FT-IR spectra of samples were recorded in KBr at the
Dokuz Eylul University on a Varian 1000 FT spectro-
photometer. 1H NMR spectra were recorded in DMSO
on a 500 MHz High Performance Digital FT-NMR
instrument at the Ege University and chemical shifts
were referenced to tetramethylsilane (TMS). Electron
impact mass spectra (Micromass VG Platform-II
LC-MS) were recorded at the TUBITAK. Photochem-
ical reactions in a preparative scale were carried out in
a water-cooled quartz-walled immersion well reactor
equipped with a Philips HPK 125-W high-pressure
mercury lamp [9].
(2)
M = W.
These complexes were prepared by similar methods,
for example, a method for cis-[M(CO)4-DABRd] is the
following. Cr(CO)6 (0.22 g, 1 mmol) and NBD
(0.276 g, 3 mmol) were dissolved in hexane (70 ml) and
the solution was irradiated for 2 h using a 125 W
medium-pressure mercury lamp through a quartz-
walled immersion well reactor. During the irradiation,
the solution changed from colorless to yellow. After
irradiation the solvent was evaporated under the vac-
uum yielding a yellow solid. After subliming out any
traces of unreacted white hexa-carbonylchromate(0) at
25–50°C, the probe is cleaned and the sublimation is
continued at 70–90°C to give 0.16 g (72%) yield of
bright golden yellow crystalline [(η4-NBD)Cr(CO)4].
Synthesis of the [(η4-NBD)M(CO)4] [M = Cr, Mo,
W] complexes were carried out by the photochemical
reactions of [M(CO)6] (M = Cr, Mo, W) with NBD. The
yields were 56–72%.
Syntheses of the cis-[M(CO)4-DABRd] (M = Cr (I),
Mo (II)) and fac-[M(CO)3-SAT] (M= Cr (III), Mo (IV))
complexes were carried out by the photochemical reac-
tions of cis-[(η4-NBD)M(CO)4] (M Cr, Mo) DABRd
and SAT. The yields were 40–60%.
hν
M(CO)6 + NBD
cis-[(η4-NBD)M(CO)4],
Hexane
–2CO
(1)
M = Cr, Mo
O
HN
C
C
C
CH3
CH3
hν
THF
–NBD
cis-[(η4-NBD)M(CO) ] DABRd
(3)
+
CH
N
4
M = Cr, Mo
S
S
OC
OC
M
CO
CO
cis-[M(CO)4-DABRd],
M = Cr (I); Mo (II)
HN
HC
N
C
OH
hν
THF
–NBD, –CO
cis-[(η4-NBD)M(CO) ]
(4)
+ SAT
4
N
CH
M = Cr, Mo
N
M
CO
CO
OC
fac-[M(CO)3-SAT],
M = Cr (III); Mo (IV)
These complexes were prepared by similar methods, walled immersion well reactor. During the irradiation,
for example, a method for [Cr(CO)4-DABRd] is the fol- the solution changed from yellow to lightbrown. After
lowing. The cis-[(η4-NBD)Cr(CO)4] complexe the irradiation and cooling system was cut off from the
(0.256 g, 1 mmol) were dissolved in THF (80–100 ml), photochemical reactor, DABRd (0.27 g, 1 mmol) was
and the solution was irradiated for 1.5 h using a 125 W added to the solution and mixed under argon atmo-
medium-pressure mercury lamp through a quartz- sphere for 3 h. Then solvent was evaporated under vac-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 12 2007

888
SUBASI et al.
Table 1. The elemental analysis data and physical properties for olefin and I–IV complexes
Content (found/calcd), %
Yield,
%
Complex
Empirical formula (M.w.)
CrC11H8O4 (256)
Color
C
H
N
S
[(η4-NBD)Cr(CO)4]
50.95/51.56 3.10/3.13
43.67/44.00 2.56/2.66
[(η4-NBD)W(CO)4] + WC11H8O4 + W2C17H8O10 29.67/29.78 1.36/1.42
Yellow
Yellow
Yellow
72
66
56
[(η4-NBD)Mo(CO)4] MoC11H8O4 (300)
+ [W(CO)5]2(µ-NBD) (388 + 740)
I
II
III
IV
C16H12O5CrN2S2 (428)
C16H12O5MoN2S2 (472)
C12H8O4CrN4 (324)
44.77/44.86 2.75/2.80 6.60/6.54 14.05/14.95 Brown
40.37/40.68 2.35/2.54 5.60/5.93 13.05/13.56 Brown
62
54
60
47
44.37/44.44 2.35/2.45 17.06/17.28
38.87/39.13 1.95/2.17 18.06/18.48
Brown
Brown
C12H8O4MoN4 (368)
uum yielding a brown solid, which was extracted with DABRd and SAT ligands and characterized by elemen-
CH2Cl2 (10 ml). Addition of petroleum ether (50 cm3) tal analysis, FT-IR and H NMR spectroscopy, and
1
resulted in precipitation of a dark brown solid, which
was washed with petroleum ether, dried under vac-
uum, and shown to be [Cr(CO)4-DABRd] (I). The
yield was 62%.
mass spectrometry. The photochemical reactions of
[(η4-NBD)M(CO)4] (M = Cr, Mo) with DABRd and
SAT proceed in this expected manner to yield the hith-
erto unknown series of complexes I–IV Eqs. (1), (2).
The analytical results and some physical properties of
the novel complexes I–IV are summarized in Table 1.
The complexes are air-stable and soluble in chlorinated
solvents.
RESULTS AND DISCUSSION
Treatment of the photochemically produced
M(CO)5. The intermediates with the ligands in THF led
to the expected monosubstituted complexes [10]. These
16-electron M(CO)5 fragments react avidly with any
available donor to form M(CO)5L species, where L is a
chelating bidentate ligand, and rapid continuation to the
chelating M(CO)4L or bridging M2(CO)10L products
can occur. Moreover, photochemical occurence of
M(CO)4 (M = Re), M(CO)3, and M(CO)2 (M = Mn)
from [Re(CO)5Br] and [Mn(CO)3Cp] have been done
[11]. In this photochemical complexation study, we
considered it worthwhile to irradiate cis-[(η4-
NBD)M(CO)4] (M = Cr, Mo, W) in the presence of
rhodanine and 1,2,4-triazole derivative ligands,
because they have never been investigated and can be
interesting examples for substitution reactions.
As shown in Table 2, the FT-IR spectrum of I, for
example, exhibits four prominent bands at 2014 m,
1939 s, 1893 v.s, and 1832 s cm–1 in the CO stretching
vibrational region. The four ν(CO) patterns indicate the
local C2ν (2A1 + B1 + B2 + E) symmetry of the M(CO)4
skeleton. These modes shift to lower wave numbers
when compared with that of Cr(CO)6 [13]. The FT-IR
spectra of II exhibit essentially the same ν(CO) absorp-
tion pattern as that observed for I. Important FT-IR
spectral data of III and IV are presented in Table 2 as
well. As anticipated, the chromium and molybdenum
complexes exhibit a two-band pattern in the ν(CO) IR
region at 1870 s and 1731 v.s cm–1, which is consistent
with a tricarbonyl derivative of approximately C C3ν
(A1 + E) symmetry of the M(CO)3 unit (M = Cr, Mo).
The ν(CO) modes of III and IV move to lower wave
numbers when compared with the starting M(CO)6
(M = Cr, Mo) molecules [13]. The changes observed in
the FT-IR spectra of the free ligands upon coordination
can be compared with the spectral changes in 5-substi-
tuted rhodanine and 1,2,4-triazole in its metal carbonyl
complex. The ν(N–H) ligand bands at 3150 and
3060 cm–1 appear, as expected for N–H of DABRd in
the complexes I and II. Both complexes exhibit no
changes in the intensity or position of the bands in the
range 1695–1690 cm–1 that are indicative of coordina-
tion via ν(C=O), this is in keeping with that there are no
metal–oxygen interactions in these complexes. The
stretching vibrations of C–Sring observed at 810 cm–1 in
the free ligands shift to lower wave numbers in the
Photolysis of M(CO)6 (M = Cr, Mo, W) in the pres-
ence of NBD afforded high yields of the olefin-substi-
tuted derivatives cis-[(η4-NBD)M(CO)4] (M = Cr, Mo,
W). The relatively stable cis-[(η4-NBD)M(CO)4] (M =
Cr, Mo) complexes could be isolated as pure solids (eq.
(1)), while the cis-[(η4-NBD)W(CO)4] complex was
found to be contaminated with [W(CO)5]2(µ-NBD)
(Eq. (2)). Therefore, only the cis-[(η4-NBD)M(CO)4]
(M = Cr, Mo) complexes were reacted with the title
ligands as shown in Eq. (1). Assignments of the FT-IR
spectra were made by reference to literature data and
the data is in accord with the previous publications on
the related complexes [12].
New complexes cis-[M(CO)4-DABRd] (M = Cr (I),
Mo (II)) and fac-[M(CO)3-SAT] (M = Cr (III),
Mo (IV)) have been synthesized by the photochemical spectra of I and II. The divisions between strong sym-
reactions of [(η4-NBD)M(CO)4] (M = Cr, Mo) with metric and asymmetric stretching vibrations of C = S in
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PHOTOCHEMICAL REACTIONS
889
Table 2. Important IR absorption bands (cm–1) of olefin complexes, free ligands and their complexes I–IV
ν(C=S)
Compound*
DABRda
ν(CO)
ν(NH)
ν(C=O) ν(C–Sring) ν(OH)
ν(C=N)
ν(C–O)
(asym, sym)
685 s, 610 s 3150 m, 3060 m 1690 s 810 s
2937 s
SATb
2033 m, 1960 s,
1944 v.s, 1915 s
3400 s 1573 s, 1514 s, 1290 s
1615 s
[(η4-NBD)Cr(CO)4] 2032 m, 1980 s,
1923 v.s, 1875 s
[(η4-NBD)Mo(CO)4] 2071 m, 2014 m,
1980 s, 1972 m,
1945 m, 1920 v.s,
1870 s
[η4-NBD)W(CO)4] 2014 m, 1939 s,
1893 m, 1832 m
+
W(CO)5](µ-NBD)
I
2014 m, 1940 s, 697 s, 594 s 3123 m, 3057 m 1690 s 804 s
1892 m, 1830 m
II
1870 s, 1731 v.s 703 s, 591 s 134 m, 3054 m 1690 s 805 s
III
1874 s, 1732 v.s
2936
3990 s 1564 s, 1501 s, 1290 s
1596 s
IV
2940
3985 s 1565 s, 1508 s, 1290 s
1603 s
a
b
* Taken: from [7] from [8].
Table 3. 1H NMR data for the free ligands and I–IV complexes in DMSO-d6 solution
δ, ppm
Compound
HC=N
0H
CHAr
NH
N(3)–H
C(6)–H
DABRd*
13.56 s, 1H
7.49 s, 1H
SAT*
I
II
8.96 s, 6.30 s, 2H 12.82 s, 1H
6.80–7.90 m, 2H
13.55 s, 1H
13.55 s, 1H
7.48 s, 1H
7.48 s, 1H
III
IV
9.97 s, 7.23 s, 2H 12.85 s, 1H
10.03 s,7.34 s, 2H 12.85 s, 1H
6.80–7.90 m, 2H 6.60 s, 1H
6.80–7.90 m, 2H 6.60 s, 1H
* Taken from [7] and [8].
DABRd are increased in the spectra of I and II, show- assigned to the stretching vibrations of ring NH and
phenolic C–O, respectively, and show no shift upon
ing that the DABRd ligands coordinate to the metal via
both sulfur NH–(S)C = S donor atoms in I and II. The
FT-IR spectra of complexes III and IV displayed the
characteristic bands of SAT with the appropriate shifts
due to complex formation. The strong bands at 1615,
1573, and 1514 cm–1 in the FT-IR spectra of free SAT
belong to the C=N stretching vibrations. These bands
shift toward lower frequency in compounds III and IV
showing that the SAT ligand behaves as a tridentate
ligand coordinating via its all imine nitrogen –C=N–
donor atoms to the metal center. The shifts have been
assessed as weakening of the all C = N bonds resulting
from the transfer of electron density from the nitrogen
atoms to the metal atom. The sharp bands in the FT-IR
complex formation in III and IV.
The 1H NMR spectral data in DMSO-d6 solutions of
compounds I and II are presented together with the
assignments of the signals in Table 3. The presence of
the low-field N–H signal in the 1H NMR spectra of the
complexes indicates that deprotonation of the ligands
from their N–H on coordination to the organometallic
moiety is not possible. It was clearly seen from the
1H NMR spectra that no signal belongs to the thiol pro-
ton confirming the maintenance of the thione form of
the ligand in solution, because conversion to the thiol
form would result in stronger shielding as in the S-coor-
dinated methyl- and phenylmercury(II) complexes of
1
spectrum of the SAT at 2937 and 1290 cm–1 are rhodanine [HgR(Rd)] [14]. The H NMR data in
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 33 No. 12 2007

890
SUBASI et al.
Table 4. The mass spectral data for I–IV
Complexes
M.w.
Relative intensities of ions, m/z
I
II
III
IV
428
472
324
368
428.00 (10), [M+]; 372.00 (15) [M+ – 2(CO)]; 316.00 (23), [M+ – 4(CO)]
472.00 (7), [M+]; 416.00 (11) [M+ – 2(CO)]; 360.00 (22), [M+ – 4(CO)]
324.00 (12), [M+]; 296.00 (08) [M+ – CO]; 268.00 (14), [M+ – 2(CO)]; 240.00 (22), [M+ – 3(CO)]
368.00 (17), [M+]; 340.00 (06) [M+ – CO]; 312.00 (23), [M+ – 2(CO)]; 284.00 (12), [M+ – 3(CO)]
For the mass spectral data relative intensities are given in parentheses; probable assignments are given in square brackets.
DMSO-d6 solutions of compounds III and IV are col-
lected. Except for the chemical shift of –HC=N– imine
protons, all of the other proton signals of the coordi-
nated SAT ligand of compounds III and IV have almost
similar values to those of the free ligand. In the
1H NMR spectra of the compounds OH and NH, pro-
tons of the free ligand at 12.82 and 6.59 ppm remains
approximately unchanged in the complexes and show
that the OH and NH groups do not participate in coor-
dination. As expected, the down-field shift of the
HC=N imine protons can be related to a decrease in the
π-electron density in the C=N bonds with complex for-
mation in III and IV.
ACKNOWLEDGMENTS
We thank Research Foundation of Dokuz Eylul Uni-
versity for funds. We thank TUBITAK for allocation of
time at the Mass spectra and Elemental analyses. We
thank Dr.YurdanurYayla for obtaining 1H NMR spectra
at the Ege University. This work was also supported by
the Research Fund of the Istanbul University (project
no. 818/190496) and Dokuz Eylul University (project
no. 2005.KB.FEN.019).
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