Synthesis and structure of an aminoethyl-functionalized cyclopentadienyl vanadium(i) dinitrogen complex

Article abstract of DOI:10.1039/c0dt00499e

Reduction of a V(iii) complex [(η⁵,η¹-C ₅H₄CH₂CH₂NMe₂)VCl ₂(PMe₃)] in the presence of diphenylacetylene under nitrogen atmosphere yields a novel V(i) dinitrogen-bridged complex {[η⁵-(C₅H₄CH₂CH ₂NMe₂)]V(PhCCPh)(PMe₃)}₂(μ-N ₂).

Full text of DOI:10.1039/c0dt00499e

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Synthesis and structure of an aminoethyl-functionalized cyclopentadienyl
vanadium(I) dinitrogen complex†
Guohua Liu,*a Xiaohui Liang,a Auke Meetsmab and Bart Hessenb
Received 19th May 2010, Accepted 8th July 2010
First published as an Advance Article on the web 26th July 2010
DOI: 10.1039/c0dt00499e
5
1
Reduction of a V(III) complex [(g ,g -C5H4CH2CH2NMe2)-
diphenylacetylene using an excess of magnesium as a reducing
agent under N2 atmosphere. Its molecular structure is determined
and the pendant amino functionality to bind or to dissociate from
the vanadium center is observed.
Aminoethyl-functionalized monocyclopentadienyl V(III) com-
plex 1, used as a synthetic precursor, was prepared ac-
cording to the reported method.7a Two-electron reduction
VCl2(PMe3)] in the presence of diphenylacetylene under nitro-
gen atmosphere yields a novel V(I) dinitrogen-bridged com-
5
plex
N2).
{[g -(C5H4CH2CH2NMe2)]V(PhC CPh)(PMe3)}2(l-
Transition metal dinitrogen complexes have received considerable
attention due to the activation and functionalization of molecular
dinitrogen,1 which presents a unique opportunity to establish
structure–reactivity relationships for nitrogen fixation and offer
the possibility to discover new transformations. Although research
on transition metal dinitrogen complexes have been documented
with almost all metals,2 so far, only a few reports on dinitrogen
vanadium complexes are available.3 Possible reasons are mainly
due to the intrinsic properties of extremely air- and moisture-
sensitive paramagnetic compounds and inherent instability asso-
ciated with vanadium analogues. A cyclopentadienyl ligand with
additional pendant Lewis basic functionality possesses remarkable
versatility, such as chelate effect and hemilabile behavior. The
chelate effect of pendant functionality can obviously enhance
the stability of metal complexes, while the hemilabile behavior
of pendant functionality can reversibly dissociate from the metal
center. These features often lead to produce highly interesting new
species.4 We have been interested in the chemistry of vanadium
complexes,5 especially those of amino-functionalized cyclopenta-
dienyl vanadium complexes.6–7 Recently, we report a vanadium(III)
complex (h ,h -C5H4CH2CH2NMe2)VCl2(PMe3)7a containing an
amino-functionalized pendant chain, which it is a suitable starting
material for the synthesis of a range of organometallic vanadium
derivatives, not only of V(III) but also of V(II) and V(V).7b Thus, the
discovery of thermally stable, isolable dinitrogen vanadium species
do not only provide a unique opportunity to study dinitrogen
coordination and to enrich the chemistry of vanadium complexes,
but also explore the influence of ligand exchange between pendant
amino functionality and dinitrogen on vanadium centers.
of the V(III) complex
1 with an excess of magnesium
in THF afforded the red V(I) dinitrogen-bridged com-
5
plex {[h -(C5H4CH2CH2NMe2)]V(PhC CPh)(PMe3)}2(m-N2) (2,
Scheme 1) in 31% isolated yield. Complex 2 is a diamagnetic,
extremely air-sensitive red crystalline. The well-resolved NMR
spectra, together with elemental analysis are consistent with its
structure. The IR spectrum shows the useful information with
coordinated PMe3 (947.92, 1278.68, 1298.92 cm-1). Also the C–H
vibration bands at 2760.83 and 2813.79 cm-1 are consistent with
the presence of non-coordinated NMe2 groups.7,8 The relatively
high frequency of the nC C vibration (1717 cm-l) indicates that the
alkyne has less p-back-donation when compared to the alkyne with
2
more p-back-donation in CpV(PMe3)2(h -PhC CPh) (nC
=
C
1600 cm-l).5b In addition, the high thermostability at room
temperature suggests that 2 is more electronically favorable rather
than sterically though extremely large steric hindrance around the
vanadium center. Crystal structure determination (Fig. 1, selected
bond lengths and angles in Table 1) shows that complex 2 has
an idealized C2 symmetry with the principal axis bisecting the
N(2)–N(3) bond, in which two identical vanadium fragments
5
1
5
[(h -C5H4CH2CH2NMe2)V(PhC CPh)(PMe3)] are linked by a
Scheme 1 Preparation of the V(I) dinitrogen complex 2.
In this contribution, we present
a novel aminoethyl-
functionalized monocyclopentadienyl vanadium(I) dinitrogen
5
complex {[h -(C5H4CH2CH2NMe2)]V(PhC CPh)(PMe3)}2(m-
N2) (2), which is synthesized via the reduction of
5
1
(h ,h -C5H4CH2CH2NMe2)VCl2(PMe3) in the presence of
aThe Key Laboratory of Resource Chemistry of Ministry of Education,
Shanghai Normal University, Shanghai, China. E-mail: ghliu@shnu.edu.cn;
Tel: + 86 21 64321819
bCenter for Catalytic Olefin Polymerization, Stratingh Institute for Chem-
istry and Chemical Engineering, University of Groningen, Nijenborgh 4, 9747
AG, Groningen, The Netherlands
† Electronic supplementary information (ESI) available: Experimental
procedures and crystallographic data. CCDC reference number 778191.
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c0dt00499e
5
Fig. 1 Molecular structure of {[h -(C5H4CH2CH2NMe2)]V(PhC CPh)-
(PMe3)}2(m-N2) (2): thermal ellipsoids are drawn at the 50% probability
level.
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◦
5
˚
Table 1 Selected bond lengths (A) and angles ( ) for 2
complex [(h -C5H4CH2CH2NMe2)V(PhC CPh)(PMe3)]2(m-N2),
which not only produces a new species and enriches organometal-
lic vanadium chemistry, but can also offer an opportunity to
compare its isostructural analogue. More importantly, it has been
recognized that the pendant amino functionality can reversibly
dissociate from the vanadium center.
V1–N2
V2–N3
N2–N3
V1–P1
V2–P2
V1–C16
V1–C17
1.761(6)
1.773(6)
1.212(8)
2.385(2)
2.373(3)
1.996(7)
2.059(7)
V2–C42
V2–C43
V1–N2
1.978(7)
2.063(7)
1.761(6)
1.773(6)
1.292(10)
1.285(10)
V2–N3
C16–C17
C42–C43
We are grateful to China National Natural Science Foundation
(20673072), Shanghai Sciences and Technologies Development
Fund (10jc1412300, 10dj1400103), and Shanghai Municipal Edu-
cation Commission (08YZ71) for financial supports.
Characterization method: NMR spectra were recorded on
Varian VXR-300 (300 MHz) spectrometers in NMR tubes sealed
with a Teflon (Young) stopcock. IR spectra were recorded in
a Mattson-4020 Galaxy FT-IR spectrometer from Nujol mulls
between KBr disks unless stated otherwise. Elemental analyses
were performed by Kolbe Analytical Laboratories, Mu¨lheim a.d.
Ruhr, Germany.
V1–N2–N3
V2–N3–N2
P1–V1–C16
P2–V2–C42
P1–V1–C17
175.4(6)
174.5(5)
120.1(2)
120.2(2)
83.9(2)
P2–V2–C43
84.1(2)
N2–V1–C16
N3–V2–C42
C15–C16–C17
C41–C42–C43
102.0(3)
101.4(3)
138.4(7)
138.6(7)
bridging dinitrogen ligand. The coordination geometry can be
best described as two lean square-pyramidal piano-stool config-
urations around two vanadium centers, in which each pendant
amino functionality is not coordinated to the vanadium atom.
The bridging dinitrogen ligand has a N(2)–N(3) bond distance
of 1.212(8) A, which is obviously elongated as compared to
terminal N2 ligands (1.1111(17) A ). The V–N bond distances
[1.761(6) and 1.773(6) A] are obviously shorter than general V–
N single bonds and slightly longer than general V N double
bonds. Overall these bond lengths in the core of the molecule
confirm that the bridging dinitrogen are consistent with medium-
activated dinitrogen ligand.1b These values are strongly similar
to those of dinitrogen-bridged vanadium complex, where the N–
N distance of 1.222(4) A and the V–N distances of 1.770(3) A
are observed in {K(digly)3(m-Mes)3V}2(m-N2).3a In addition, the
alkyne’s C(16)–C(17) and C(42)–C(43) distances of 1.292 (10)
5
[(h -C5H4CH2CH2NMe2)V(PhC CPh)(PMe3)]2(m-N2) (2): to
0.8 g activated Mg (33.3 mmol) was added a solution of
(C5H4CH2CH2NMe2)VCl2(PMe3) (1.10 g, 3.29 mmol), together
with PhC CPh (0.56 g, 3.13 mmol) in 20 mL of THF at
-30 ◦C. The solution was allowed to warm to 0 ◦C and was stirred
for another 30 min at this temperature. The solution changed from
purple to deep-red. The solvent was removed in vacuo and the
residue stripped with two portions of 5 mL of pentane. The dark-
red solid was repeatedly extracted with 30 of pentane and 30 mL of
ether. Concentrating to 5 mL and cooling the solution to -30 ◦C
yielded 0.44 g (0.49 mmol, 31.1%) of red crystals. The suitable
crystals for X-ray experiment were obtained by recrystallization in
pentane. IR (Nujol Mull): 697.33, 720.48, 764.33, 793.36, 947.92,
1023.04, 1043,06, 1067.36, 1096.50, 1261.79, 1278.68, 1298.92,
1377.36, 1461.17, 1587.02, 1707.71, 2760.83, 2813.79, 2853.14,
˚
2c
˚
˚
˚
˚
˚
and 1.285(10) A, together with the C–C–C(Ph) angles [C(15)–
C(16)–C(17) = 138.4(7)◦ and C(41)–C(42)–C(43) = 138.6(7)◦] of
around 139◦ are consistent with an obviously lesser extent of p-
2923.35, 2954.31, 3049.58, 3060.15 cm-1; H NMR (benzene-d6,
1
20 ◦C, 300 MHz): d 7.80 (s, 2H, Ph), 7.23–6.60 (m, 8H, Ph),
5.71, 5.66 (d, 2H, Cp), 5.18, 5.14 (d, 2H, Cp), 2.63–2.47 (m, 4H,
CpCH2CH2N), 2.21 (s, 6H, NMe2), 0.82, 0.79 (d, 9H, JPH = 7.5 Hz,
PMe3); 13C NMR (benzene-d6, 20 ◦C, 75.4 MHz): d 16.91, 17.15 (q,
JPC = 72.9 Hz, PMe3), 28.96 (t, CpCH2), 45.71 (q, NMe2), 61.57 (t,
NCH2), 97.66, 99.44, 101.06, 101.95, (all s, C C), 117.97, 123.88,
124.52, 125.98, 126.14, 126.71, 130.27, 139.32, 149.12, 151.15,
164.33, 176.96 (all d, Ph C); Anal. Calcd for C52H66N4P2V2: C,
68.56; H, 7.30; N, 6.15. Found: C, 68.54; H, 7.36; N, 5.98.
2
back-donation in 2 than that in the V(I) complex CpV(PMe3)2(h -
PhC CPh),5b where the related parameters are 1.328(3) A and
˚
136◦.
For comparison, the experiment under argon atmosphere was
also carried out with similar reaction conditions. As a result,
an extremely air-sensitive red crystalline was obtained in an
acceptable yield. Attempts to get the crystals were unsuccessful.
However, the well-resolved H NMR and 13C NMR indicated
1
that this compound was also a diamagnetic compound. The C–H
absorptions of 2760.83 and 2813.79 cm-1 in the IR spectrum and
the signals of PMe3 protons in the 1H NMR spectrum disappeared
completely,7 suggesting that this compound was a phosphine-
free complex with the coordinated NMe2 groups. Overall these
characterizations speculated that this compound might be for-
mulated as (h ,h -C5H4CH2CH2NMe2)V(PhC CPh).7b In order
to explore the reactivity of the V(I) dinitrogen-bridged complex,
stirring 2 in THF solution at ambient temperature was carried out.
A Toepler pump experiment showed only traces of nitrogen were
pumped-off during several evacuation cycles in a high-vacuum
line, suggesting the coordination of N2 was quite robust. The
equivalent of dinitrogen could be released quantitatively by the
addition of a few drops of CH3OH via an NMR-tube experiment,
in which the diphenylacetylene is produced at the same time.
In conclusion, the dimethylaminoethylcyclopentadienyl V(III)
Crystal data: formula C52H66N4P2V2, Mr = 910.95 g mol-1,
triclinic, P1, a = 12.182(2) A, b = 14.323(3) A, c = 14.344(3) A,
˚
˚
◦
˚
3
¯
◦
◦
˚
a = 79.989(3) , b = 83.952(3) , g = 88.051(3) , V = 2450.6(8) A ,
Z = 2, Dx = 1.234 gcm-3, F(000) = 964, m = 4.85 cm-1, q(max) =
24.11◦. A red colored needle-shaped crystal with dimensions of
0.30 ¥ 0.065 ¥ 0.035 mm was mounted on top of a glass fiber,
by using inert-atmosphere handling techniques, and aligned on
a Bruker SMART APEX CCD diffractometer (Platform with
full three-circle goniometer). The diffractometer was equipped
with a 4 K CCD detector set 60.0 mm from the crystal. The
crystal was cooled to 100(1) K using the Bruker KRYOFLEX low-
temperature device. Intensity measurements were performed using
graphite monochromated Mo-Ka radiation from a sealed ceramic
diffraction tube (SIEMENS). SMART was used for preliminary
determination of the unit cell constants and data collection
control. Data integration and global cell refinement was performed
with the program SAINT. The final unit cell was obtained from the
5
1
dichloride complex was
a suitable organometallic vana-
dium starting material for development of a V(I) dinitrogen
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xyz centroids of 2436 reflections after integration. Intensity data
were corrected for Lorentz and polarization effects, scale variation,
for decay and absorption: a multi-scan absorption correction was
applied, based on the intensities of symmetry-related reflections
measured at different angular settings (SADABS9), and reduced
to Fo2. The program suite SHELXTL10 was used for space
group determination (XPREP). The structure was solved by
Patterson methods and extension of the model was accomplished
by direct methods applied to difference structure factors using the
program DIRDIF.11 The positional and anisotropic displacement
parameters for the non-hydrogen atoms were refined. Some atoms
showed unrealistic displacement parameters when allowed to vary
anisotropically, suggesting dynamic disorder (dynamic means that
the smeared electron density is due to fluctuations of the atomic
positions within each unit cell). Hydrogen atoms were constrained
to idealized geometries and allowed to ride on their carrier atoms
with an isotropic displacement parameter related to the equivalent
displacement parameter of their carrier atoms. Final refinement on
F2 carried out by full-matrix least-squares techniques converged
at wR(F2) = 0.1761 for 7680 reflections and R(F) = 0.0776 for
3226 reflections with Fo ≥ 4.0s (Fo) and 551 parameters and
360 restraints. The positional and anisotropic displacement pa-
rameters for the non-hydrogen atoms and isotropic displacement
parameters for hydrogen atoms were refined on F2 with full-matrix
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ꢀ
2
least-squares procedures minimizing the function Q = h[w(|(Fo
)
- k(Fc )|)2], where w = 1/[s (Fo2) + (aP)2 + bP], P = [max(Fo2,0) +
2
2
2
2Fc ]/3, Fo and Fc are the observed and calculated structure factor
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Reduction of 1 in the presence of diphenylacetylene under
argon atmosphere with the similar reaction condition. Red solid,
yield: 54.6%; IR (Nujol Mull): 698.30, 726.21, 800.59, 1026.43,
1041.96, 1074.63, 1094.90, 1261.07, 1376.96, 1460.98, 1483.40,
1588.21, 2854.59, 2923.71, 2953.59 cm-1;1H NMR (benzene-d6,
◦
20 C, 300 MHz) d 6.89, 6.86 (d, 4H, Ph), 6.71 (t, 2H, Ph), 6.55
(t, 2H, Ph), 6.19 (s, 2H, Ph), 6.02, 6.04 (d, 2H, Cp), 5.73, 5.71
(d, 2H, Cp), 3.05 (t, 2 H, J = 6.9 Hz, CH2Cp), 2.67 (t, 2 H,
J = 6.9 Hz, CH2N), 2.22 (s, 6 H, NMe2); 13C NMR (benzene-d6,
20 ◦C, 75.4 MHz): d 28.64 (t, CpCH2), 45.65 (q, NMe2), 60.17
(t, NCH2), 105.86, 106.35 (all s, C C), 124.07, 126.11, 126.74,
126.92, 127.25, 131.56, 142.31, 158.67 (all d, Ph, Cp, C C); Anal.
Calcd for C23H24NV: C, 75.60; H, 6.62; N, 3.83. Found: C, 75.38;
H, 6.65; N, 3.45.
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This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 7891–7893 | 7893
©