The pyrrole ring η2-hapticity bridged binuclear tricarbonyl Mo(0) and W(0) complexes: catalysis of regioselective hydroamination reactions and DFT calculations

Article abstract of DOI:10.1039/c6dt04458a

Following the report of the ferrocene structure, metal complexes containing the heteroatom-substituted cyclopentadienyl (Cp) analogue, that is the η⁵ pyrrolyl ligand, have been reported. While the Cp ligand continues to be a favorite ligand in

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Received 00th January
2
20xx,
The Pyrrole Ring η -Hapticity Bridged Binuclear Tricarbonyl Mo(0)
and W(0) Complexes: Catalysis of Regioselective Hydroamination
Reactions and DFT Calculations
,
a
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Vikesh Kumar Jha, Ganesan Mani,* Yogeswara Rao Davuluri and Anakuthil Anoop
Following the report of ferrocene structure, metal complexes containing the heteroatom substituted cyclopentadienyl (Cp)
5
analogue, that is, η pyrrolyl ligand, have been reported. While the Cp ligand continues to be a favorite ligand in
organometallics, the transition metal chemistry of pyrrolyl ligand is still in the developing stage. In view of this, we carried
out the reaction between the multidentate ligand 2,3,4,5-tetrakis(3,5-dimethylpyrazolylmethyl)pyrrole (LH) and Mo(CO)
6
2
2
4
or [W(CO)
3
(CH
3
CN)
2
3
] and isolated two new binuclear tricarbonyl Mo(0) and W(0) complexes, [Mo
2
(CO)
6
(μ-η :η -LH-κ N)] 1
2
4
and [W (CO)
2
6
(μ-η :η -LH-κ N)] 2. Their X-ray structural analyses showed the metal centers are bridged by the double
2
2
bonds of the central pyrrole ring (ꢀ-η :η ), a rarely observed coordination mode. Interestingly, complex 1 is a catalyst
precursor for the hydroamination reactions of phenylacetylene with a series of secondary amines at room temperature
offering the regioselectively formed anti-Markovnikov product in excellent yields. In addition, DFT calculations were
performed to understand the bonding nature of the pyrrole ring in 1 and 2 and to estimate the energy of six different
conformations
of
LH.
1
4
complexes have been reported. As a continuation of our
work on this ligand, herein we report the synthesis, structural
characterization of molybdenum(0) and tungsten(0)
tricarbonyl complexes bearing LH in which the pyrrole ring
possesses the new bridging coordination mode. We also report
the catalysis of hydroamination reactions of phenylacetylene
with secondary amines using the LH molybdenum complex and
the DFT calculations for both complexes and ligand.
Introduction
1
Since the report of the X-ray structure analysis of ferrocene,
cyclopentadienyl ligands played major role in the
development of the transition metal organometallic chemistry.
a
5
Cyclopentadienyls adopts not only the ubiquitous
2
η
,
3
3
coordination mode, but also bonding modes such as
4
σ
,
η
4
and
η
isoelectronic
.
Conversely, metal complexes containing the
electron donor pyrrolyl ligand
6
azacyclopentadienyls have not been extensively studied,
5
Results and discussion
though a large progress has been done. In addition to their
5
6
Synthesis and Structure of Mo and W Complexes
most common bridging mode
7
κ
lanthanide metals, sandwich complexes containing one or
N-
η
found in transition and
8
LH reacts with two equiv of Mo(CO)
conditions or photolysis to give the binuclear Mo(0) carbonyl
complex containing one neutral ligand LH in about 50% yield
Scheme 1). The H NMR spectrum of complex
showed well-resolved resonances, indicating the rigid
structure of maintained in solution. The pyrrolic NH
resonance appears at 9.26 ppm as a broad singlet, which is
shifted downfield as compared to that of the free ligand. The
diastereotopic methylene protons of LH in appears as two
well separated AB pattern with J(H ) = 15.2 Hz. This is in
6
in THF under reflux
9
5
10
two
η pyrrolyl and half sandwich complexes have been
3
11
reported. It also displayed bonding modes such as
η
,
and
Further, Floriani and co-workers have
reported the lithium complex of meso-octaethylcalix[4]pyrrole
1
2
12
1
bridging
κN-η .
(
1 in CDCl
3
2
13
in which the pyrrole ring adopts the
η bonding mode.
We recently reported the direct synthesis of multidentate
1
δ
ligand,
2,3,4,5-tetrakis(3,5-dimethylpyrazolylmethyl)pyrrole
(LH). It is a source of azacyclopentadienyl anion containing
1
four neutral pyrazole nitrogen donors upon the deprotonation
of the pyrrole NH, and its binuclear and multinuclear
A B
H
contrast to the two broad singlets observed for the free ligand.
In addition, four singlet resonances corresponding to the four
different methyl groups were observed and their integrated
intensity values are in accord with the structure. The FT-IR
a.
Department of Chemistry, Indian Institute of Technology – Kharagpur, Kharagpur,
West Bengal, India 721 302, Fax: +91 3222 282252, E-mail:
gmani@chem.iitkgp.ernet.in.
spectrum showed strong ν(CO) stretching frequency bands at
−
1
Electronic Supplementary Information (ESI) available: Experimental procedure,
NMR, IR spectra, crystallographic data (CIF) and DFT calculations data and
coordinates. CCDC 1518990-1518991, See DOI: 10.1039/x0xx00000x
1909, 1793 and 1778 cm , suggesting the presence of three
terminal COs.
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CO
N
N
N
N
N
N
N
M
[
Mo(CO) ] (or)
6
N
OC
W(CO) (CH CN)
CO
3
3
3
N
N
THF, reflux/ h
ν
N
H
N
N
N
H
N
N
N
M
CO
N
LH
M = Mo, 1 (50%) and W, 2 (18%)
OC
CO
Scheme 1. Synthesis of the Mo(0) 1 and W(0) 2 complexes of LH.
Table 1. Selected bond lengths (Å) and angles (deg) for complex 1 and 2.
Mo complex 1
W complex 2
C(1)-Mo
C(2)-Mo
C(3)-Mo
N(3)-Mo
N(5)-Mo
C(4)-Mo
C(5)-Mo
1.942(2)
1.950(3)
1.940(2)
2.2805(19)
2.2659(18)
2.614(2)
2.563(2)
C(1)-Mo-N(5)
C(2)-Mo-N(3)
C(3)-Mo-C(1)
C(3)-Mo-N(5)
N(5)-Mo-N(3)
C(1)-Mo-N(3)
178.61(8)
169.52(8)
84.70(9)
96.10(8)
83.63(6)
95.12(8)
C(1)-W
C(2)-W
C(3)-W
N(3)-W
N(5)-W
C(4)-W
C(5)-W
1.936(3)
1.950(4)
1.949(4)
2.248(3)
2.247(3)
2.567(3)
2.511(3)
C(1)-W-N(5)
C(2)-W-N(3)
C(1)-W-C(3)
C(3)-W-N(5)
N(5)-W-N(3)
C(1)-W-N(3)
177.80(12)
169.52(12)
85.39(13)
95.11(12)
83.37(10)
94.44(11)
unit constitutes one half of the molecule and thf. The X-ray
structure revealed that the molecule consists of two ‘Mo(CO)3’
units bridged by one neutral ligand LH. Each Mo(CO) unit is
3
coordinated by two pyrazolyl nitrogens, creating a nine-
membered ring having a ‘tub’ shape with a deep cavity. This
conformation facilities the pyrrole ring to bind to the metal
atoms via its double bond π-electrons and to bridge the two
metal centers on either side, representing a rarely observed
2
2
coordination mode
ring -coordination is treated as the tail of a scorpion, then the
coordination mode of ligand LH is reminiscent of the famous
ꢀ-η :η of the pyrrole ring. If the pyrrole
π
1
5
polypyrazolylborate scorpionate ligand and indicates its
flexibility. The resulting coordination environment causes the
pyrazole moieties as well as the two Mo(CO) units lie above
3
and below the pyrrole ring plan, which is similar to the
conformation LH adopted in the structures of reported
4
1
Figure 1. ORTEP diagram (50% thermal ellipsoids) of complex 1. Most hydrogen atoms
binuclear Pd(II) and Ag(I) complexes. The geometry around
the molybdenum atom is a distorted octahedron with
...
...
...
are omitted for clarity. N1 O4 2.782(4) Å, H1N O4 2.05(4) Å, N1−H1N O4 180.0°.
Symmetry transformations used to generate equivalent atoms: (i) −x+2, y, −z+1/2, (ii)
C1
−
−
Mo
Mo
−
−
N5 angle of 178.61(8)
°
N3 angle value of 169.52(8)
being larger than the
probably because of
−
x+3, y, −z + ½, (iii) x−1/2, y−1/2, z.
C2
°
The X-ray structure of complex
1
is given in Figure 1, and steric hinderance of two pyrazole methyl groups and the
selected metric parameters and refinement data are given in constraint, created by the presence of one rigid methylene
Table 1 and Table 3, respectively. The molecule crystallizes in group between the pyrazole and pyrrole rings, with which the
the centrosymmetric space group C2/c and the asymmetric pyrazolyl nitrogens coordinate. This steric effect causes the
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8
pyrrole ring C
−
Mo
π
-bond distances 2.614(2) Å and 2.563(2) Å complex
(COD)] (2.462(6) to greater than that of Mo (1.54(5) Å). However, these W
.497(6) Å), indicating that they are relatively weaker bonds. distances are longer than those found in the reported alkene
In addition, this is reflected in the Mo CO distances which are bound complexes such as [W(CO) (P(OMe) )(COD)]
almost identical (1.940(2) Å, 1.942(2) Å and 1.950(3) Å). Ideally (2.395(5) to 2.424(6) Å), [{Tp’W(CO) ){(Cp)Ru(PPh )}]
-norbornadiene)W(CO)
1 because the covalent radius of W (1.62(7) Å) is
to be longer than those found in [Mo(CO)
4
−C
1
6
2
−
W
3
3
1
9
2
}(C
2
S
2
3
2
0
4
Mo
to be longer than the other two distances (Mo
Mo O) lie trans to the donor pyrazole nitrogen atoms and 2.510(15) Å). As found for
because usually simple alkenes are weaker -acceptors than double bond distance (1.404(5) Å) is also longer than that
CO. Nevertheless, the pyrrole ring C double bond distance (1.359(6) Å) found in the structure of 2,5-bis(3,5-
is elongated to 1.396(3) Å as compared to the corresponding dimethylpyrazolylmethyl)pyrrole. In addition, the W
C-C distance (1.359(6) Å) found in the structure of 2,5-bis(3,5- distance (1.949(4) Å) trans to the pyrrole -bond is slightly
−
C
3
O distance lies trans to the pyrrole
π
-bond is supposed (2.066(7) Å and 2.049(6) Å), [(
η
4
]
2
1
2
−
C
1
O and (2.403(6) to 2.419(5) Å) and [W(CO)
5
(
η
7
-C H10)] (2.497(16)
2
2
−
C
2
σ
1
, the pyrrole ring C −C
4 5
π
4 5
−C
3 3
−C O
π
1
7
dimethylpyrazolylmethyl)pyrrole. Eventually, the substitution longer than the Mo
of three COs in Mo(CO)6 by three donors results in the for the metal back bonding with the pyrrole ring
formation of complex containing three different Mo CO
groups. In addition, the two pyrazole N Mo bond distances
N3 Mo = 2.2805(19) Å and N5 Mo = 2.2659(18) Å) are
−
C O distance in
1
and the C O competes
3
3
3
3
π
bond.
−
−
Hydroamination Reactions
(
−
−
slightly different. The pyrrole ring NH is strongly hydrogen
bonded to the lattice THF molecule as shown by the distance
and angle, and as a result the NH hydrogen atom was located
in the X-ray structure.
The hydroamination of C-C multiple bonds is an atom efficient
process and provides bulk and fine chemicals, and versatile
intermediates for further reactions. A large number of
catalysts based on metals across the periodic table have been
2
3,24,25,26,27,28
known
for
mediating
these
reactions.
Hydroamination reactions involving ammonia as the amine
2
9,30
31
partner,
and energy efficient room temperature catalysis
have also been reported. Nevertheless, the field continues to
attract the attention of researchers because of the challenges
in developing catalysts for selective anti-Markovnikov
3
2
hydroamination of aliphatic olefin,
and regioselective
addition of ammonia to olefins. In this industrially important
research field, McDonald et. al. reported the [Mo(CO) (Et N)]
catalyzed intramolecular hydroamination of alkynylamines.
3
3
5
3
3
4
Recently, Szymańska-Buzar and co-workers have reported the
first hydroamination reaction of terminal alkynes in the
presence
W(CO) (piperidine)
We found complex
terminal alkyne PhCCH with a series of secondary amines; the
of
tungsten
carbonyl
complex
3
5
[
4
2
].
1
catalyzes the hydroamination of
Figure 2. ORTEP diagram (50% thermal ellipsoids) of complex 2. Most hydrogen atoms optimized reaction conditions and yields are given in Table 2.
...
...
...
are omitted for clarity. N1 O4 2.779(5) Å, H1N O4 1.95(6) Å, N1−H1N O4 180.0°. In cases of morpholine and piperazine, the reactions go cleanly
Symmetry transformations used to generate equivalent atoms: −x, y, −z + 1/2.
at room temperature with very high yields of the stereo- and
regioselectively formed anti-Markovnikov product, E-isomer,
The analogous tungsten complex
2 was obtained from the
in the presence of ∼0.4 mol% of the pre-catalyst 1. Products
reaction of [W(CO) (CH CN) ] with LH under reflux conditions
3
3
3
were obtained in almost pure form by just removing the
volatiles from the resulting reaction mixture. However, an
elevated temperature is required to obtain the best yields of
the anti-Markovnikov products formed in the piperidine and
pyrrolidine reactions, as shown in Table 2. The reactions with
1
in poor yield. The H NMR spectrum is similar to that of the
molybdenum complex , suggesting a similar structure. The
presence of terminal COs is shown by the FT-IR spectrum
1
−
1
featuring strong
which are lower than those for complex
crystallized from the same solvent, THF/petroleum ether,
ν(CO) bands at 1899, 1791 and 1773 cm ,
1
. Complex was
2
1
these two amines at room temperature are slow and their H
NMR spectra showed unreacted starting materials. To test the
which was used for complex
show that the crystal lattice of
1
2
and the unit cell parameters
is isomorphous to . The X-ray
efficiency of the catalytic activity of complex
between PhCCH and morpholine or phenylpiperazine was
carried out in the presence of Mo(CO) (1 mol%) as catalyst
1, the reaction
1
structure of
structure of complex
slightly different owing to their covalent radii difference. The
2
is given in Figure 2; it closely resembles the
6
1. However, its metric parameters are
under reflux conditions and we found that a mixture of
36
products including the anti-Markovnikov (20%) and the
2
bridging pyrrole ring
η hapticity found in this structure
possesses the W C distances of 2.567(3) Å and 2.511(3) Å,
phenylacetylene dimer were formed. In addition, the starting
1
materials were not consumed, as shown by their H NMR and
−
which are shorter and hence stronger than those in the Mo
GCMS data. Besides, there is no product formed for the same
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Table 2. Hydroamination of PhCCH with secondary amines catalyzed by the Mo catalyzes the formation of anti-Markovnikov
3 slowly at room
complex 1.
temperature.
In an attempt to understand the mechanism of the
1
catalysis, the reaction was monitored by H NMR method. The
Complex 1
NR2
Ph
R NH
2
1
H NMR spectrum of complex
1 with one equiv of PhCCH in
No sovent
r.t
Ph
CD
2
Cl showed no change in the spectral pattern. However,
2
the spectrum recorded after 24 h for the same solution in the
presence of one equiv of morpholine showed the
disappearance of the pyrrolic NH proton and appearance of
Amine
Product
1,
mol%
t,
h
T,
Yield
(%)
(
PhCCH :
amine)
°C
two singlets at
ligand. In addition, the spectrum also showed the presence of
the intact complex , starting materials and negligible amount
δ 4.82 and 5.02 ppm, which is for the free
Ph
1
H
N
of the product. This indicates the catalyst decomposes via the
deprotonation of the pyrrole NH proton and the product
formation is very slow in CH Cl at room temp. On the other
N
O
3
1
2
0.4
0.4
96
96
28
92
90
2
2
O
1
hand, the H NMR spectrum recorded for a mixture of PhCCH,
morpholine and kept at room temp for 3 days, giving solid
(
(
(
2:1)
1
Ph
and then dissolved in C6D6 showed the disappearance of
starting materials and cleanly formed anti-Markovnikov
product. In addition, it showed a different complex formation
as indicated by the pyrrolic NH peak appearing around 10 ppm
H
N
N
4
28
N
and shifted AB quartets similar to complex
in the negative region for possible formation of [Mo-H] species
(see ESI, Fig. S18). Hence, complex is the precatalyst and
cleanly catalyzes at room temperature. It is likely that the
mechanism could involve the decoordination of the pyrrole
1; there is no peak
Ph
2:1)
N
Ph
1
Ph
H
N
π-
bond and the coordination of the incoming PhCCH followed by
the nucleophilic attack of the secondary amine and
protonolysis to give the product.
N
N
5
N
3
0.43
96
28
89
H
4:1)
Computational Studies
Ph
DFT calculations based on the hybrid exchange-correlation
functional were performed to better understand the nature of
bonding, the electronic structure and the conformations LH
Ph
H
N
6
N
N
4
5
0.41
0.42
5
3
80
80
70
36
(
(
1:1)
H
N
Ph
7
2:1)
reaction at room temperature for 12 h. This emphasizes the
importance of the role played by ligand LH coordinated to the
Mo atom in complex
can be ascribed to the binuclear nature of complex
However, complex failed to selectively yield the desired
1. Further, the observed catalytic activity
1.
1
hydroaminated product even under reflux conditions for
alkynes such as 1-hexyne and 1-phenyl-1-propyne and for
styrene, which gave a mixture of products. This indicates
complex
1 is selective toward the hydroamination of
phenylacetylene with the examined secondary amines to give Figure 3. Molecular orbital diagrams showing metal-pyrrole π-bonds for 1 and 2
(
B3LYP/def2-SVP level).
the anti-Markovnikov product. Furthermore, complex
2 also
4
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Figure 4. DFT (B3LYP/def2-SVP level) optimized six different possible conformations of LH based on the orientation of the pyrazolyl rings about the pyrrole ring plane. Their relative
energies (kcal/mol) are given in parenthesis below each structure.
adopt in complex
are in close agreement with their X-ray structures. The HOMO– with the t2g set d orbitals being lower in energy than the e
LUMO energy gap, calculated at B3LYP/def2-SVP level, is 3.72 orbitals. Among the t2g orbitals, the occupancies of the dxy and
1
and
2. The geometry optimized structures simple crystal field theory model for an octahedral geometry
g
set
eV and 3.52 eV for
1
and
2, respectively. From the QTAIM
d
yz orbitals are higher than the dxz orbital.
analyses, the nature of bonding between the metal and the
The extended charge decomposition analysis (ECDA) was
ligating atoms is described as coordinate bond as characterized performed to quantify the net amount of charge transferred
by positive values for both the electron density (ρ(r ) > 0) and between two fragments of the given complex (see ESI, Table
) > 0), and negative value T7). The theory of CDA is based on the molecular orbitals of
c
2
the Laplacian electron density (
of the Cremer–Kraka electron energy density (H(r
bond strength estimations showed the M
the weakest (for example, 39.5 and
among the metal-ligand bonds in and
bond indices are 0.1736 (Mo-C ), 0.2079 (Mo-C
) and 0.2153 (W-C ), which are consistent with their complex
relatively longer M pyrrole bond distances observed in their X- estimated for the carbonyl group (C
ray structures. However, the pyrrole ring C double bond pyrazolyl nitrogen atom, though they are isostructural. In
distances found in the optimized structures of (1.401 Å addition, frequency calculations were performed, which
B3LYP), 1.418 Å (BP86) and 1.398 Å (M06)) and (1.404 Å closely match with the experimental (CO) values. The (CO)
B3LYP), 1.421 Å (BP86) and 1.403 Å (M06)) are longer than value decreases in the order C > C > C and the higher
the double bond distance 1.383 Å (B3LYP), 1.394 Å (BP86) and value of (C ) is due to its trans position to the coordinated
.376 Å (M06)) in the optimized free ligand structure conf-2 pyrrole ring bond which compete for backing bonding from
owing to coordination to the metal atoms. The MO diagrams the metal atom with CO.
∇ ρ(r
c
3
7
c
) < 0). The complex composed by the linear combination of the donor and
bonds are acceptor fragment orbitals (FO). The highest magnitude of net
45.5 kJ/mol for charge transfer (0.1519) was estimated for the carbonyl ligand
and their Wiberg (C ) lying trans to the pyrrole ring -bond among the
), 0.1758 (W- carbonyl ligands in complex . Conversely, in the case of
, the highest net charge transfer 0.5286 was
) lying trans to the
−
−
C
pyrrole
π
−
1)
1
2
3
O
3
π
4
5
1
C
4
5
2
−
C
2 2
O
4 5
−C
1
(
2
ν
ν
(
3
O
3
1
O
1
2 2
O
ν
3 3
O
1
π
corresponding to these pyrrole ring
in Figure 3.
π interactions are shown
Conformations of LH
The occupancies of the metal valence orbitals were
analyzed using Natural Population Analysis (NPA) method (see
ESI, Table T6). The Mo atom possesses 6.507 valence electrons
For the pyrrole molecule LH containing substitutents in all
α
and β-positions, the 3,5-dimethylpyrazolyl ring can lie above
with a natural partial charge of −1.11, and those for W atom
are 6.697 and 0.68, respectively. The valence electronic
or below the pyrrole ring plane. The four pyrazolyl rings can be
arranged in six different orientations about the pyrrole ring
plane, giving the six different possible conformations
−
configuration for Mo is 4d (6.12) and that for W is 5d (5.81).
The d orbitals energy level ordering is consistent with the
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represented as conf-1 to conf-6 and their optimized residual protons present in the deuterated solvents. Chemical
geometries are given in Figure 4. Their relative energy shifts are in parts per million, and coupling constants are in Hz.
increases in the order, conf-1
conf-1 possesses the lowest energy (0.00 kcal/mol) owing to High Resolution Mass Spectra (ESI) were recorded using the
the presence of the stabilizing , N- and H-bond Xevo G2 Tof mass spectrometer (Waters). GC-MS analyses
< 2 < 4 < 6 < 3 < 5. Among these, FTIR spectra were recorded using Perkin-Elmer Spectrum Rx.
π
-π
π
interactions in the structure as indicated in Figure 4. The were performed on a ThermoScientific TRACE 1300 system
conformation conf-5 has the highest energy (5.21 kcal/mol) as with ISQ mass detector and the capillary column of TG-5MS
it exhibits less number of or weak stabilization interactions as (30 m
compared to others. Interestingly, conf-1 conf-2 conf-3 and 330/350
conf-5 have been observed in the X-ray structures of Pd(II), 125W medium pressure mercury lamp supplied by SAIC (India).
×
0.25 mm
× 0.25 ꢀm, 5% phenyl methylpolysiloxane,
,
,
°
C). The photolysis reaction was carried out using
1
4
2
2
4
Ag(I) and Cu(I) complexes bearing LH reported previously.
Synthesis of [Mo
Method a: A Schlenk flask equipped with water condenser was
charged with Mo(CO) (0.106 g, 0.40 mmol) and 2,3,4,5-
2 6
(CO) (ꢀ-η :η -LH-κ N)] 1
Conformations conf-4 and conf-6 lie in the middle of the
energy level ordering and were not observed to date. In
6
complex
1 or 2, LH adopts one of the lowest energy forms
tetrakis(3,5-dimethylpyrazol-1-ylmethyl)pyrrole (0.100 g, 0.20
mmol). To this was added THF (20 mL) and the resulting
solution was refluxed for 36 h. The solution color changed to a
dark brownish yellow. The resulting clear solution was cooled
to room temperature, transferred to another Schlenk tube and
conf-2. Although metals could direct and bind with their own
preferred conformations, it is interesting to investigate why
the other two conformations have not been observed to date.
then layered with petroleum ether. Yellow crystals of
1 were
Conclusions
formed over a period of two weeks. The crystals were
The formation of two similar binuclear Mo(0) and W(0) separated and dried under vacuum (0.093 g, 0.10 mmol). Yield:
1
carbonyl complexes presented here and the multinuclear 50%. H NMR(600 MHz, CDCl ):
δ
= 9.26(br s, 1H, NH), 5.83(s,
3
14
complexes previously reported by us
tetrakis(dimethylpyrazolylmethyl)pyrrole molecule is
versatile and flexible ligand for transition metal chemistry. To J(H H ) = 14.4, CH ), 3.75(m, 4H, THF), 2.86(d, 2H, J(H H ) =
show that the 2H, pyrazole CH), 5.76(s, 2H, pyrazole CH), 5.51(d, 2H, J(H H )
A
B
a
2 A B 2
= 15.2, CH ), 5.25(d, 2H, J(H H ) = 15.2, CH ), 4.28(d, 2H,
A
B
2
A B
the best of our knowledge, the bridging mode of the pyrrole 14.0, CH ), 2.51(s, 6H, Me), 2.23(s, 6H, Me), 1.87(s, 6H, Me),
2
2
2
13
1
ring via
has not been reported to date. Although the
occupies one of the coordination sites of an octahedron, it is a 151.6(C3 of Pz ), 141.3(C5 of Pz ), 139.8(C of Pz ),
η :η hapticity found in these complexes is new and 1.85(m, 4H, THF), 1.72(s, 6H, Me). C{ H}NMR(153.9 MHz,
2
Me2
η
hapticity CDCl ): δ = 227.2(CO), 226.6(CO), 226.4(CO), 151.9(C of Pz ),
3 3
Me2
Me2
Me2
5
Me2
weaker bond, as shown by the DFT calculations and can be 123.5(
α
-C of pyrrole ring), 107.1(CH of Pz ), 106.6(CH of
labile. Interestingly, in contract to the poor catalytic activity of Pz ), 104.8(
-C of pyrrole ring), 68.0(THF), 46.8(CH ),
of the binary carbonyl Mo(CO) , the LH carbonyl complex is 44.0(CH ), 25.8(THF), 16.5(Me of Pz ), 14.4(Me of Pz ),
Me2
β
2
Me2
Me2
Me2
6
1
2
Me2
−1
the better catalyst precursor for the selective hydroaminations 12.0(Me of Pz ), 11.7(Me of Pz ). FTIR (KBr, cm ): ν =
of phenylacetylene with a series of secondary amines. In most 3173(w), 3103(w), 2920(w), 1909(vs), 1793(vs), 1778(vs),
cases, the products are formed in excellent yields with a low 1552(m), 1463(m), 1437(m), 1385(w), 1372(w), 1291(w),
catalyst loading at room temperature probably because of the 1262(w), 1090(w), 1045(m), 877(w), 802(m), 686(w), 658(w),
multidentate nature of LH ligand which stabilizes the actual 626(w), 594(w), 532(w), 515(w), 477(w). HRMS(+ESI): m/z
+
catalyst formed in situ and the catalysis reactions are selective. calcd for [M + H ] C H Mo N O 864.1048, found 864.1088.
3
4
38
2 9 6
The energy of each possible conformations of LH based on the Method b: A Schlenk flask equipped with water condenser was
pyrazolyl ring orientations depends on the number of charged
with 2,3,4,5-tetrakis(3,5-dimethylpyrazol-1-
stabilizing interactions it possesses, as shown by DFT ylmethyl)pyrrole (0.050 g, 0.1 mmol) and Mo(CO) (0.053 g, 0.2
6
calculations. Other metal complexes of LH and their properties mmol). THF (20 mL) was added and the solution was exposed
are under progress.
to UV light (
transferred to another Schlenk tube and layered with
petroleum ether. Yellow crystals of complex were collected
after 15 days and dried under vacuum (0.030 g, 0.03 mmol).
λ ≥ 360 nm) for 2h. The reaction mixture was
1
Experimental Section
All reactions were carried out under nitrogen atmosphere Yield: 32%.
2
2
4
2 6
using Schlenk line techniques or nitrogen-filled glove box. Synthesis of [W (CO) (ꢀ-η :η -LH-κ N)] 2
1
4
2
,3,4,5-Tetrakis(3,5-dimethylpyrazol-1-ylmethyl)pyrrole
3
and
A Schlenk flask equipped with water condenser was charged
with [W(CO) (CH CN) ] (0.110 g, 0.28 mmol) and 2,3,4,5-
8
3 3 3
[W(CO) (CH CN) ]
were synthesized accordingly to the
3
3
3
reported procedures. Other chemicals were obtained from
commercial sources and used as received. Solvents were
tetrakis(3,5-dimethylpyrazol-1-ylmethyl)pyrrole (0.070 g, 0.14
mmol). To this was added THF (20 mL) and the resulting
solution was refluxed for 24 h. The solution color changed to a
dark brownish yellow. The resulting clear solution was cooled
to room temperature, transferred to another Schlenk tube and
1
distilled before use by following the standard procedures. H
1
NMR (400 MHz or 600 MHz) and C NMR (153.9 MHz) spectra
3
1
13
were recorded at room temperatures. H NMR and C NMR
chemical shifts were referenced with the chemical shift of the
then layered with petroleum ether. Yellow crystals of
1 were
6
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ARTICLE
1
formed over a period of one month. The crystals were Yield: ~18%. H NMR(CDCl
separated and dried under vacuum (0.030 g, 0.026 mmol).
3
, 600 MHz):
δ
= 8.90(br s, 1H, NH),
Table 3. Crystal Data and Structure Refinement for 1 and 2.
1
·THF
2·1.5THF
Empirical formula
Formula weight
Wavelength (Å)
Temperature (K)
Crystal system
Space group
a/Å
C
38
H
45Mo
2
N
9
O
7
40 49 9 7.5 2
C H N O W
931.71
0.71073
100(2)
1143.58
0.71073
100(2)
Monoclinic
C2/c
Monoclinic
C2/c
14.506(2)
14.760(2)
20.139(3)
90.00
14.4325(9)
14.7737(9)
20.2936(13)
90.00
b/Å
c/Å
α/degree
β/degree
98.609(4)
90.00
99.005(2)
90.00
γ/degree
3
Volume (Å )
4263.3(12)
4
4273.7(5)
4
Z
-
3
D
calcd, g cm
1.452
1.777
-1
µ/mm
F(000)
range (degree)
0.644
5.439
1904
2240
θ
1.980 to 25.000
−16<=h<=17, −17<=k<=17, −23<=l<=23
25081 / 3759
1.985 to 24.999
Limiting indices
−17<=h<=16, −17<=k<=17, −21<=l<=24
25049 / 3773
Total/ unique no. of reflns.
R
int
0.0485
0.0310
Data / restr./params.
3759 / 0 / 259
3773 / 0 / 259
2
GOF (F )
1.050
1.094
R1, wR2
0.0259, 0.0638
0.0209, 0.0514
0.0229, 0.0524
1.091 and −1.054
R indices (all data) R1, wR2
0.0308, 0.0659
Largest different peak and hole (e Å–3)
0.459 and −0.264
5.81(s, 2H, pyrazole CH), 5.73(s, 2H, pyrazole CH), 5.41(d, J = Single crystal X-ray diffraction data collections for complex 1
1
8.0, 2H, CH
CH ), 3.75(m, 4H, THF CH
H, CH
2
), 5.33(d, J = 18.0, 2H, CH
), 2.78(d, J = 12.0, 2H, CH
), 1.85(m, 4H, THF CH
2
), 4.29(d, J = 12.0, 2H, and
2
were performed using Bruker-APEX-II CCD
2
2
2
), 2.55(s, diffractometer with graphite monochromated Mo Kα radiation
6
3
), 2.23(s, 6H, CH
3
1
2
), 1.82(s, 6H,
(
λ
): δ = obtained by XPREP program. The structures were then solved
= 0.71073 Å). The space group for every structure was
3
1
CH
3
), 1.73(s, 6H, CH
3
). C{ H}NMR(153.9 MHz, CDCl
3
Me2
of Pz ), 151.5(C
40
41
2
22.0(CO), 220.0(CO), 219.4(CO), 152.6(C
3
3
by SIR-92
or SHELXS-97
available in WinGX, which
Me2
of Pz ), 141.2(C
Me2
of Pz ), 139.9(C
Me2
Me2
of Pz ), 119.6(α-C of successfully located most of the non-hydrogen atoms.
5
5
Me2
2
pyrrole ring), 107.1(CH of Pz ), 106.3(CH of Pz ), 100.3(β-C Subsequently, least square refinements were carried out on F
2 2
of pyrrole ring), 68.2(THF), 47.3(CH ), 45.4(CH ), 25.8(THF), using SHELXL-2014 to locate the remaining non-hydrogen
Me2
Me2
Me2
1
1
1
1
1
7.3(Me of Pz ), 14.6(Me of Pz ), 12.2(Me of Pz ), atoms. Non-hydrogen atoms were refined with anisotropic
Me2
−
1
2.0(Me of Pz ). FT-IR (KBr, cm ):
ν = 3422(m), 2925(w), displacement parameters. All NH protons were located from
899(vs), 1793(vs), 1773(vs), 1551(m), 1457(m), 1435(m), the Difference Fourier Map. The displacement parameters of
420(m), 1388(m), 1292(w), 1258(w), 1231(w), 1155(w), the NH hydrogen atoms were made dependent on the
052(w), 1038(w), 873(w), 803(w), 581(w). HRMS (+ESI): calcd respective parent atom (1.2 times for the pyrrolic hydrogens).
+
m/z for [M−H ] C34
H
W
N
O
6
: 1036.1958, found: 1036.2024.
In the case of structure 2·1.5THF, the unit cell contains one
38
2
9
General Procedure for the Hydroamination Reactions
and half molecule of THF. This half THF molecule has been
treated as a diffuse contribution to the overall scattering
The typical procedure for the hydroamination reactions
involves stirring the appropriate mixture consisting of
4
2
without specific atom positions by SQUEEZE/PLATON. The
refinement data for all the structures are summarized in Table
phenylacetylene, amines and complex
1 taken in a Schlenk
3.
flask at room temperature or refluxed for the time period
Computational Details
mentioned in Table 2. The volatiles were removed under
1
vacuum to give the product, which was analyzed by H NMR The presented calculations are based on the density functional
and GCMS methods showing essentially the anti-Markovnikov theory (DFT) formalism. The approach is based on the hybrid
3
5,39
product and compared with the literature spectra.
exchange-correlation functional proposed by Becke, Lee, Yang
4
3
44
X-ray Crystallography
and Parr (B3LYP) and the applied basis set is def2-SVP
including dispersion. In addition, density functionals BP86
4
5
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Journal Name
4
6
and M06 were also being used to compare the results with
B3LYP functional. The minimum character of the stationary
points obtained by geometry optimizations was checked by
vibrational frequency calculations. Natural bond orbital (NBO)
analysis was performed to explain the binding properties of
complexes. The computed geometries were visualised using
the GaussView 3.09 program and the computations were
4
7
carried out using the GAUSSIAN 09 suite. The wavefunction
.wfn) file obtained from gaussian-09 software was used as an
input file to perform multiwfn program package for quantum
(
4
8
theory atom in molecules (QTAIM).
9
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Acknowledgements
We thank the CSIR and DST (New Delhi, India) for financial
support and for the X-ray, and NMR facilities. We thank
Sanghamitra Das, Department of Chemistry, IIT-Kharagpur for
recording a few NMR spectra.
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ARTICLE
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For Table of Contents
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Journal Name
CO
N
NR2
Ph
2
R NH
N
N
M
N
Ph
OC
CO
Regioselective
anti-Markovnikov
N
N
N
r.t.
N
N
H
M
CO
M = Mo and W
OC CO
The new pyrrole ring π-bonds bridged binuclear Mo
complex catalyzes the regioselective hydroamination of
phenylacetylene with a series of secondary amines at
room temperature giving the products in very high
yields.
1
0 | J. Name., 2012, 00, 1-3
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