# Molybdenum and Tungsten Tricarbonyl Complexes of  Isatin with Triphenylphosphine

Authors: M. M. H. Khalil; F. A. Al-Seif
Journal: Research Letters in Inorganic Chemistry
 (2008)

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## Abstract

Reaction ofM(CO)6; M = Mo or W with isatin in the presence of triphenylphosphine in THF under reduced pressure gave the tricarbonyl derivatives complexes [M(CO)3(isatH)(PPh3)]. The two complexes were characterized by elemental analysis, infrared, mass and 1H NMR spectroscopy. The spectroscopic studies show that the two complexes exist in fac- and mer-isomers in solutions through exchange the CO group and PPh3. The Uv-Vis spectra of the complexes in different solvents were  studied.


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## Body

## 1. Introduction

Isatin (2,3-dihydroindole-2, 3-dione) is a
versatile lead  molecule for designing potential bioactive agents, and its
derivatives were reported to possess broad-spectrum antiviral activity [1, 2]. In the
previous reports, the synthesis and characterization of group 6 and 8 complexes of isatin
and 5-methylisatin in absence and presence of bipyridine were investigated [3, 4]. In this article, we
report the synthesis and characterization of molybdenum and tungsten complexes
of isatin in the presence of PPh3. The aim of these reactions is the
synthesis and study of mixed-ligand complexes, where the metal is surrounded by
different donor atoms in the coordination sphere, that is, the oxygen from
isatin and phosphorous atom from the triphenylphosphine (PPh3). PPh3 is different from the carbonyl group since it is a strong σ-donor and weak π-acceptor ligand. Furthermore, the organic
phosphenes increase the stability of the transition metal complexes in the low-oxidation
state.  Taking into account the electronic
spectra the combination of a reducing metal and an acceptor ligand generates a
metal-to-ligand charge transfer (MLCT) excited state which may appear in
absorption and emission [5, 6].


## 2. Experimental

### 2.1. Reagents

Mo(CO)6, W(CO)6, isatin, and PPh3 were supplied from (Sigma Aldrich, St. Louis, USA).
All the solvents were reagent grade and purified
prior to use.


### 2.2. Instruments

IR measurements were recorded
as KBr pellets on a Unicam-Mattson 1000 FT-IR spectrometer. Electronic
absorption spectra were measured on a Unicam UV2-300 UV-vis spectrophotometer.H1-NMR
measurements were performed on a Varian-Mercury 300 MHz spectrometer. Samples were dissolved in (CD3)2SO
with TMS as internal reference. The complexes were also characterized by
elemental analysis (Perkin-Elmer 2400 CHN elemental analyzer) and mass
spectroscopy (Finnigan MAT SSQ 7000). Table 1 gives the elemental analyses and mass
spectrometry data for the complexes.Table 1
Elemental analysis and mass spectrometric data for the molybdenum and tungsten complexes.
ComplexCalculatedFoundMass spectroscopy%C%H%N%C%H%NMwtm/z(P+)[Mo(CO)3(isatH)(PPh3)]59.093.422.3758.573.423.05589.39590[W(CO)3(isatH)(PPh3)]51.422.982.0652.053.062.39677.29678[Mo(CO)3(isatH)(PPh3)]
Mo(CO)6 (0.20 g;  0.76 mmol), isatin (0.06 g; 0.33 mmol), and
PPh3 (0.09 g; 0.33 mmol) were mixed in ca 30 ml
tetrahydrofuran. The mixture was degassed and heated to reflux for 4 hours,
where the color of the solution changed from yellow to dark red. The reaction
mixture was cooled and the solvent was removed under vacuum. The obtained solid
was washed several times with hot benzene and petroleum ether to give brown
crystals with a yield of 55% based on the metal.[W(CO)3(isatH)(PPh3)]
A similar procedure was performed as in the case of[Mo(CO)3(isatH)(PPh3)] but the reaction time was 11 hours
(reddish brown powder, yield 48%).


## 2.1. Reagents

Mo(CO)6, W(CO)6, isatin, and PPh3 were supplied from (Sigma Aldrich, St. Louis, USA).
All the solvents were reagent grade and purified
prior to use.


## 2.2. Instruments

IR measurements were recorded
as KBr pellets on a Unicam-Mattson 1000 FT-IR spectrometer. Electronic
absorption spectra were measured on a Unicam UV2-300 UV-vis spectrophotometer.H1-NMR
measurements were performed on a Varian-Mercury 300 MHz spectrometer. Samples were dissolved in (CD3)2SO
with TMS as internal reference. The complexes were also characterized by
elemental analysis (Perkin-Elmer 2400 CHN elemental analyzer) and mass
spectroscopy (Finnigan MAT SSQ 7000). Table 1 gives the elemental analyses and mass
spectrometry data for the complexes.Table 1
Elemental analysis and mass spectrometric data for the molybdenum and tungsten complexes.
ComplexCalculatedFoundMass spectroscopy%C%H%N%C%H%NMwtm/z(P+)[Mo(CO)3(isatH)(PPh3)]59.093.422.3758.573.423.05589.39590[W(CO)3(isatH)(PPh3)]51.422.982.0652.053.062.39677.29678[Mo(CO)3(isatH)(PPh3)]
Mo(CO)6 (0.20 g;  0.76 mmol), isatin (0.06 g; 0.33 mmol), and
PPh3 (0.09 g; 0.33 mmol) were mixed in ca 30 ml
tetrahydrofuran. The mixture was degassed and heated to reflux for 4 hours,
where the color of the solution changed from yellow to dark red. The reaction
mixture was cooled and the solvent was removed under vacuum. The obtained solid
was washed several times with hot benzene and petroleum ether to give brown
crystals with a yield of 55% based on the metal.[W(CO)3(isatH)(PPh3)]
A similar procedure was performed as in the case of[Mo(CO)3(isatH)(PPh3)] but the reaction time was 11 hours
(reddish brown powder, yield 48%).


## 3. Results and Discussion

### 3.1. IR and NMR Studies

Reactions ofM(CO)6; M=Mo or
W with isatin in the presence of PPh3 resulted in the formation of
[M(CO)3(isatH)(PPh3)] complexes. The IR spectra of the
complexes exhibited characteristic bands of the isatin and PPh3 ligands with the corresponding shifts, Table 2. In addition, the IR spectra of
the complexes showed that the νCO of isatin ligand exerted 20–45 cm−1 shift to lower frequency suggesting that the coordination of isatin occurred in
the range of ketoform in both complexes. On the other hand, the IR spectra of
the two complexes exhibited three bands in the metal terminal carbonyl region
[7] with shifts toward the low-frequency region, Table 2. Also, the IR spectra exhibited two
medium bands at 1099, 1102 cm−1 characteristic
ν(P–CPh)
bands indicates the presence of coordinated PPh3 in the complexes, similar to the literature trend [8] and suggesting
similarity of the structure of the two complexes. It is generally difficult to
determine the stretching frequency υ(M-P) that contains PPh3 because it has many stretching frequencies in the lower-frequency region [9].
However, the IR spectra of the two complexes showed interesting differences. The νCO of the three terminal carbonyls
in the tungsten complex exhibit more shift to lower frequencies than that of
the molybdenum complex.  This can be
contributed to the difference in the metal and arrangements of the ligands in
the two complexes. From the positions of the three CO groups and their
intensities, it can be concluded that the complex [Mo(CO)3(isatH)(PPh3)] could be presented in the meridional (mer)-isomer in the solid state and tungsten complex in the facial (fac)-isomer as shown in Scheme 1.Table 2
Important IR data for isatin and its complexes.
CompoundIR data(cm−1)aν(NH)ν(C=C)+δCHν(CO)IsatH3191(s)1615(vs),1748(sh), 1727(vs)1461(s)[Mo(CO)3(isatH)(PPh3)]3184(w)1619(s)2013(m),1943(m), 1887(vs), 1725 (sh),
1703(s)1462(m)1435(m)[W(CO)3(isatH)(PPh3)]3186(m)1619(m)1935(m), 1879(s), 1810(w), 1727(s), 1703(s)1463(m)1435(m)avs, very strong; s, strong; m, medium; w, weak; sh, shoulder.Scheme 1TheH1 NMR
spectrum of isatH in deuterated DMSO showed signals at 6.9(d), 7.06(t),
7.5(t), 7.61(d) ppm due to protons of the benzene ring and a signal at 10.98(s)
ppm due to proton of NH group [3]. The H1 NMR spectrum of PPh3 showed multiplets in the range of
6.93–7.24 ppm. H1 NMR spectra of the
molybdenum complex exhibited two broad singlet signals at 11.02 and 10.86 ppm
due to NH and appearance of a new doublet signal at 9.05 ppm due to one proton in the isatin phenyl
ring, in addition to the shifts of isatin and PPh3 as a result of
coordination. The ratios of the signals at 11.02 and 10.86 ppm were of
(1:3) and 2:1 for molybdenum and tungsten complexes, respectively, suggesting that
the complex present in two-tautomeric structure. The appearance of the new signal and change in
the chemical shift of NH proton is essentially related to the presence of the
PPh3 and its effect on the chemical shifts of the isatin protons.
This shift may be due to mutual anisotropic deshielding between the phenyl
group of PPh3 and one proton of the benzene ring of isatin which can
affect the signal of NH. This effect is due to magnetic field through space and
not through chemical bond by inductive effect [10]. This indicates the
possibility of exchange between CO and PPh3 groups in the solution
in the axial position [11, 12] .X-ray studies ofcis-RuCl2(trpy)(PPh3);
where trpy=terpyridine,  showed that the
PPh3 has two phenyl rings parallel to the trpy while the third
phenyl ring nearly perpendicular to the external pyridine of trpy and this lead
to low-field shift of the parallel pyridine proton by 1.09 ppm. This was not observed for trans-RuCl2(tepy)(PPh3)
[13]. From the spectroscopic data, we can conclude that the complexes
can exist in mer- and fac-isomers in solution as shown in Scheme 2.Scheme 2Table 3
Absorption data of isatin and its complexes in different solvents.
CompoundSolventλ (nm)IsatinDMSO334, 418Ethanol249, 296, 420Toluene295, 405CH2CL2249, 296, 415[Mo(CO)3(isatH)(PPh3)]DMSO284, 363,389a, 481Ethanol265, 353, 363, 393, 491Toluene282, 349, 361, 387, 473CH2CL2263, 291, 365, 473[W(CO)3(isatH)(PPh3)]DMSO248, 349, 365, 358, 448Ethanol243, 261,290a, 389, 481Toluene289, 345, 357, 387, 452CH2CL2263, 297, 343, 379,  446ashoulderThe UV-vis spectra of the (a)[Mo(CO)3(isatH)(PPh3)],
(b) [W(CO)3(isatH)(PPh3)] complexes in different solvents.
(a)(b)


### 3.2. UV-Vis Studies

The absorption spectra of isatin and its complexes were measured in
ethanol. Isatin displayed three bands at 249, 296, and 420 nm due toπ-π* and n-π* transitions, Table 3. The
solvent effect on the position of the longer wavelength absorption band of
isatin indicates that the nπ* transition has some charge
transfer (CT) character; the nitrogen atom being the electron donor and the β-carbonyl group the acceptor. Absorption
spectra of the complexes obtained from the reaction of M(CO)6; M=Cr or Mo with isatin only as a ligand showed a shift or disappearance  of  the
CT band due to complexation through carbonyl group in isatin [3]. The electronic spectra of the
complexes showed new bands in the range 360–387 nm due to
complexation and a weak band in the range of 445–490 nm. The
longer wavelength band could be attributed to metal-to-ligand charge transfer
transitions. The charge
transfer bands for the [Mo(CO)3(isatH)(PPh3)] were appeared at longer
wavelength than the [W(CO)3(isatH)(PPh3)] Figure 1.
This trend was observed for the complexes [Mo(CO)3(pbiH)(PPh3)]
and [W(CO)3(pbiH)(PPh3)]; pbiH=2-(2′-pyridyl)benzimidazole [14].


## 3.1. IR and NMR Studies

Reactions ofM(CO)6; M=Mo or
W with isatin in the presence of PPh3 resulted in the formation of
[M(CO)3(isatH)(PPh3)] complexes. The IR spectra of the
complexes exhibited characteristic bands of the isatin and PPh3 ligands with the corresponding shifts, Table 2. In addition, the IR spectra of
the complexes showed that the νCO of isatin ligand exerted 20–45 cm−1 shift to lower frequency suggesting that the coordination of isatin occurred in
the range of ketoform in both complexes. On the other hand, the IR spectra of
the two complexes exhibited three bands in the metal terminal carbonyl region
[7] with shifts toward the low-frequency region, Table 2. Also, the IR spectra exhibited two
medium bands at 1099, 1102 cm−1 characteristic
ν(P–CPh)
bands indicates the presence of coordinated PPh3 in the complexes, similar to the literature trend [8] and suggesting
similarity of the structure of the two complexes. It is generally difficult to
determine the stretching frequency υ(M-P) that contains PPh3 because it has many stretching frequencies in the lower-frequency region [9].
However, the IR spectra of the two complexes showed interesting differences. The νCO of the three terminal carbonyls
in the tungsten complex exhibit more shift to lower frequencies than that of
the molybdenum complex.  This can be
contributed to the difference in the metal and arrangements of the ligands in
the two complexes. From the positions of the three CO groups and their
intensities, it can be concluded that the complex [Mo(CO)3(isatH)(PPh3)] could be presented in the meridional (mer)-isomer in the solid state and tungsten complex in the facial (fac)-isomer as shown in Scheme 1.Table 2
Important IR data for isatin and its complexes.
CompoundIR data(cm−1)aν(NH)ν(C=C)+δCHν(CO)IsatH3191(s)1615(vs),1748(sh), 1727(vs)1461(s)[Mo(CO)3(isatH)(PPh3)]3184(w)1619(s)2013(m),1943(m), 1887(vs), 1725 (sh),
1703(s)1462(m)1435(m)[W(CO)3(isatH)(PPh3)]3186(m)1619(m)1935(m), 1879(s), 1810(w), 1727(s), 1703(s)1463(m)1435(m)avs, very strong; s, strong; m, medium; w, weak; sh, shoulder.Scheme 1TheH1 NMR
spectrum of isatH in deuterated DMSO showed signals at 6.9(d), 7.06(t),
7.5(t), 7.61(d) ppm due to protons of the benzene ring and a signal at 10.98(s)
ppm due to proton of NH group [3]. The H1 NMR spectrum of PPh3 showed multiplets in the range of
6.93–7.24 ppm. H1 NMR spectra of the
molybdenum complex exhibited two broad singlet signals at 11.02 and 10.86 ppm
due to NH and appearance of a new doublet signal at 9.05 ppm due to one proton in the isatin phenyl
ring, in addition to the shifts of isatin and PPh3 as a result of
coordination. The ratios of the signals at 11.02 and 10.86 ppm were of
(1:3) and 2:1 for molybdenum and tungsten complexes, respectively, suggesting that
the complex present in two-tautomeric structure. The appearance of the new signal and change in
the chemical shift of NH proton is essentially related to the presence of the
PPh3 and its effect on the chemical shifts of the isatin protons.
This shift may be due to mutual anisotropic deshielding between the phenyl
group of PPh3 and one proton of the benzene ring of isatin which can
affect the signal of NH. This effect is due to magnetic field through space and
not through chemical bond by inductive effect [10]. This indicates the
possibility of exchange between CO and PPh3 groups in the solution
in the axial position [11, 12] .X-ray studies ofcis-RuCl2(trpy)(PPh3);
where trpy=terpyridine,  showed that the
PPh3 has two phenyl rings parallel to the trpy while the third
phenyl ring nearly perpendicular to the external pyridine of trpy and this lead
to low-field shift of the parallel pyridine proton by 1.09 ppm. This was not observed for trans-RuCl2(tepy)(PPh3)
[13]. From the spectroscopic data, we can conclude that the complexes
can exist in mer- and fac-isomers in solution as shown in Scheme 2.Scheme 2Table 3
Absorption data of isatin and its complexes in different solvents.
CompoundSolventλ (nm)IsatinDMSO334, 418Ethanol249, 296, 420Toluene295, 405CH2CL2249, 296, 415[Mo(CO)3(isatH)(PPh3)]DMSO284, 363,389a, 481Ethanol265, 353, 363, 393, 491Toluene282, 349, 361, 387, 473CH2CL2263, 291, 365, 473[W(CO)3(isatH)(PPh3)]DMSO248, 349, 365, 358, 448Ethanol243, 261,290a, 389, 481Toluene289, 345, 357, 387, 452CH2CL2263, 297, 343, 379,  446ashoulderThe UV-vis spectra of the (a)[Mo(CO)3(isatH)(PPh3)],
(b) [W(CO)3(isatH)(PPh3)] complexes in different solvents.
(a)(b)


## 3.2. UV-Vis Studies

The absorption spectra of isatin and its complexes were measured in
ethanol. Isatin displayed three bands at 249, 296, and 420 nm due toπ-π* and n-π* transitions, Table 3. The
solvent effect on the position of the longer wavelength absorption band of
isatin indicates that the nπ* transition has some charge
transfer (CT) character; the nitrogen atom being the electron donor and the β-carbonyl group the acceptor. Absorption
spectra of the complexes obtained from the reaction of M(CO)6; M=Cr or Mo with isatin only as a ligand showed a shift or disappearance  of  the
CT band due to complexation through carbonyl group in isatin [3]. The electronic spectra of the
complexes showed new bands in the range 360–387 nm due to
complexation and a weak band in the range of 445–490 nm. The
longer wavelength band could be attributed to metal-to-ligand charge transfer
transitions. The charge
transfer bands for the [Mo(CO)3(isatH)(PPh3)] were appeared at longer
wavelength than the [W(CO)3(isatH)(PPh3)] Figure 1.
This trend was observed for the complexes [Mo(CO)3(pbiH)(PPh3)]
and [W(CO)3(pbiH)(PPh3)]; pbiH=2-(2′-pyridyl)benzimidazole [14].



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*Source: 746058-2008-11-09.xml*