Vanadium complexes incorporating the β-diketiminato ligand L. Syntheses and structures of LV(OSO2CF3)2 and LVPPh2

Article abstract of DOI:10.1039/b303196a

The reaction of LLi (where L = N,N′-bis(2-diethylaminoethyl)-2,4-pentanediimine-ate(-1)) with VCl₃·3THF yielded LVCl₂, which was characterized by EI-MS and elemental analysis. Subsequent reactions of LVCl₂ with AgOSO₂

Full text of DOI:10.1039/b303196a

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Vanadium complexes incorporating the ꢀ-diketiminato ligand L.
Syntheses and structures of LV(OSO2CF3)2 and LVPPh2
Dante Neculai,a Ana Mirela Neculai,a Herbert W. Roesky,*a Regine Herbst-Irmer,a
Bernhard Walfortb and Dietmar Stalkeb
a Institut für Anorganische Chemie der Universität Göttingen, Tammannstr. 4, D-37077,
Göttingen, Germany. E-mail: hroesky@gwdg.de; Fax: ϩ49-551-393373; Tel: ϩ49-551-393001
b Institut für Anorganische Chemie der Universität Würzburg, Am Hubland, D-97074,
Würzburg, Germany
Received 20th March 2003, Accepted 4th June 2003
First published as an Advance Article on the web 23rd June 2003
The reaction of LLi (where L = N,NЈ-bis(2-diethylaminoethyl)-2,4-pentanediimine-ate(-1)) with VCl3ؒ3THF yielded
LVCl2, which was characterized by EI-MS and elemental analysis. Subsequent reactions of LVCl2 with AgOSO2CF3
and KPPh2 afforded two new complexes, LV(OSO2CF3)2 and LVPPh2 which were characterized by 19F, 31P NMR
spectroscopy, EI-MS, elemental analysis, and single crystal X-ray structural analysis.
Göttingen. The conjugated acid of the ligand L, (2-diethyl-
Introduction
aminoethyl)[3-(2-diethylaminoethylimino)-1-methylbut-1-enyl]-
Recently, the groups of Theopold, Gibson, and Budzelaar have
amine, and its lithium salt were prepared according to the
exploited the multifariousness of the β-diketiminato ligands to
literature protocols.6 The following substances were purchased
prepare various complexes of Cr(),1 V(),2,1b and Ti().1b,2,3
from Aldrich and used as received: VCl3ؒ3THF, AgOSO2CF3,
Also, it has been shown that such systems might act as para-
and 0.5 M THF solution of KPPh2.
magnetic homogeneous catalysts for the polymerization of
small olefins (ethylene, propene etc.).1,2 In spite of all these
LVCl2
efforts the β-diketiminato chemistry of such metals is not
A solution of LLi (2.23 g, 7.37 mmol), freshly prepared, in
toluene (40 mL) was allowed to react with a toluene (30 mL)
suspension of VCl3ؒ3THF (2.75 g, 7.37 mmol) at room temper-
ature overnight. After the solvent removal and extraction in
CH2Cl2, followed by subsequent CH2Cl2 removal and washing
the remaining green substance with cold hexane, 1.80 g of
LVCl2 (58%) were obtained. Melting point: 156 ЊC. Anal. Calc.
for C17H35Cl2N4V (%): C, 48.93; H, 8.45; N, 13.42. Found: C,
48.74; H, 8.45; N, 13.55. EI-MS: m/z (rel. int.%): 416 [Mϩ, 5],
381 [Mϩ Ϫ Cl, 2], 86 [C5H12N, 100].
adequately developed. Previously we have reported the
synthesis and structural characterization of new derivatives
of titanium LTiX2 (L = N,NЈ-bis(2-diethylaminoethyl)-2,4-
pentanediimineate(1Ϫ), X = Cl, FؒSnMe3Cl), belonging to a
novel class of metal complexes containing a β-diketiminato-
based ligand which possesses two dangling arms.4 Herein we
report the synthesis of LVCl2 and subsequent reactions with
different nucleophiles, other than alkyls, that were carried
out. The structure of LV(OSO2CF3)2, which represents the first
vanadium() triflate derivative structurally characterized,
and the structure of LVPPh2 which represents the first
neutral heteroleptic terminal diorganophosphido complex of
vanadium(), are also described.
LV(OSO2CF3)2
A mixture of 0.80 g (1.91 mmol) 1 and 0.985 g (3.83 mmol) of
AgOSO2CF3 in a 100 mL Schlenk flask in toluene (40 mL) was
stirred for two days. The suspension was filtered. The resulting
clear green solution was concentrated under reduced pressure
to obtain yellow crystals of LV(OSO2CF3)2, which were
collected by filtration, and washed with pentane (10 mL). Yield
0.98 g (81%). Melting point: 195 ЊC. Anal. Calc. for C19H35F6-
N4O6S2V (%): C, 35.40; H, 5.47; N, 8.69. Found: C, 35.60; H,
5.91; N, 7.81. 19F NMR (188.28 MHz, C6D6): δ Ϫ136 (s, CF3).
EI-MS: m/z (rel. int.%): 644 [Mϩ, 79], 495 [Mϩ Ϫ SO3CF3, 100],
558 [Mϩ Ϫ C5H12N, 5].
Experimental
General methods
All manipulations were performed on a dual-manifold line or
in a glove box under a purified N2 atmosphere, using Schlenk
techniques with rigorous exclusion of moisture and air. The
samples for spectral measurements were prepared inside a
MBraun MB 150-GI glove-box where the O2 and H2O levels
were normally maintained below 1 ppm. Commercial grade
solvents were purified and freshly distilled following usual
procedures prior to their use.5 Melting points of all new com-
pounds were measured in sealed capillaries and are reported
uncorrected. 19F and 31P NMR spectra (C6D6) were recorded on
a Bruker MSL-400 instrument. The chemical shifts are reported
in ppm with reference to external standards, more explicitly:
C6F6/CFCl3 for 19F nuclei and 85% H3PO4 for 31P nuclei. The
LVP(C6H5)2
30 mL of dry THF were added to 0.46 g (1.1 mmol) of 1 in a
100 mL Schlenk flask. The mixture was cooled to Ϫ78 ЊC and
a solution of 4.41 mL (0.5 M, 2.2 mmol) KPPh2 in THF was
added dropwise. The mixture was stirred for 2 h at Ϫ78 ЊC, and
then stirred overnight at room temperature. After the solvent
removal and extraction in toluene (25 mL), the resulting
solution was concentrated to 15 mL and cooled at Ϫ26 ЊC. The
formed dark red crystals were filtered off. Yield 0.24 g (41%).
Melting point: 160–163 ЊC. Anal. Calc. for C29H45N4PV (%): C,
1
heteroatom NMR spectra were measured in the H-decoupled
mode. The downfield shifts from the reference are quoted
positive and the upfield shifts are reported as negative values.
The C6D6 for NMR measurements was dried over K or CaH2
and trap-to-trap distilled prior to use. Mass spectra were
obtained on a Finnigan MAT 8230 instrument by EI technique.
Elemental analyses were performed at the Analytisches Labor
des Instituts für Anorganische Chemie der Universität
65.52; H, 8.53; N, 10.54. Found: C, 65.14; H, 8.31; N, 9.70. 31
P
NMR (200.13 MHz, C6D6): δ Ϫ40.27 (s, VP(C6H5)). EI-MS:
m/z (rel. int.%): 641 [Mϩ ϩ C6H5PH, 30], 460 [Mϩ Ϫ C5H12N,
2], 371 [(C6H5)4P2, 100].
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 2 8 3 1 – 2 8 3 4
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Table 1 Crystal data and summary of X-ray data collection for LV(OSO2CF3)2ؒ2C7H8 and LVP(C6H5)2
Empirical formula
Mr
C33H51F6N4O6S2V
828.84
C29H45N4PV
531.60
T /K
λ/Å
173(2)
0.71073
Monoclinic
P21/c
100(2)
1.54178
Monoclinic
P21
Crystal system
Space group
Unit cell dimensions
a/Å
15.329(2)
12.740(3)
b/Å
c/Å
13.388(2)
19.652(3)
14.466(3)
15.247(3)
β/Њ
97.77(3)
3995.8(11), 4
1.378
93.55(3)
2804.6(10), 4
1.259
3.667
V/Å3, Z
Dc/g cmϪ3
µ/mmϪ1
0.426
F(000)
1736
0.4 × 0.3 × 0.1
1.34–28.22
Ϫ20 to 19, 0 to 17, 0 to 24
30036
1140
0.2 × 0.2 × 0.1
3.48–59.67
Ϫ13 to 14, Ϫ16 to 16, Ϫ15 to 16
Crystal size/mm
θ Range for data collection/Њ
Index ranges, hkl
Reflections collected
17902
Independent reflections (Rint
Completeness to θ = θmax (%)
Refinement method
)
9058 (0.0315)
91.8
7400 (0.0197)
95.0
Full-matrix least-squares on F 2
9058/0/477
Data/restraints/parameters
7400/1/645
1.153
Goodness-of-fit on F 2
1.032
Final R indices [I > 2σ(I )]
R indices (all data)
R1 = 0.0514, wR2 = 0.1273
R1 = 0.0723, wR2 = 0.1392
0.613, Ϫ0.428
R1 = 0.0264, wR2 = 0.0647
R1 = 0.0264, wR2 = 0.0648
0.351, Ϫ0.360
Largest diff. peak, hole/e ÅϪ3
General aspects of X-ray data collection, structure determin-
ation, and refinement for complexes LV(OSO2CF3)2 and
LVP(C6H5)2
paramagnetic nature of the vanadium nucleus. The 51V NMR
spectrum could not be recorded. Unfortunately the poor
quality of the crystals of LVCl2 precluded an X-ray diffraction
experiment. Further proofs showing the readiness of LVCl2
to participate in substitution reactions have been given by the
following experiments.
Suitable crystals were mounted on glass fibers in rapidly cooled
perfluoropolyether.7 Data for the crystal structure of LV-
(OSO2CF3)2 was collected on a Bruker Smart Apex CCD
diffractometer and for LVP(C6H5)2 was collected on a Bruker
three-circle diffractometer equipped with a SMART 6000 CCD
detector. The data for both compounds were collected at
low temperature (the temperatures for individual compounds
are mentioned in Table 1) using graphite Mo-Kα or Cu-Kα
radiation. Crystal data collection details, and the solution and
refinement procedures are summarized in Table 1. All structures
were solved by direct methods, SHELXS-97,8 and refined
against F 2 using SHELXL-97.9 Heavy atoms were refined
anisotropically. Hydrogen atoms were included using the riding
model with Uiso tied to Uiso of the parent atoms. The structure
of LVP(C6H5)2 was refined as a racemic twin (the fractional
contribution of the second domain 0.503(3)). There is a
pseudo-inversion center on 0.262, 0.369, 0.255. Refinement
on P21/n leads to a disordered model with high R-values (R1 ≈
0.15).
(1)
LVCl2 reacted with AgSO3CF3 to yield the expected product
LV(OSO2CF3)2 due to the oxophilic nature of vanadium and
the thermodynamically favored formation of AgCl (eqn. (2)).
LV(OSO2CF3)2 is a green solid which is very soluble in aromatic
solvents and THF, and it has been characterized by 19F NMR,
EI-MS, elemental analysis and single crystal X-ray diffraction.
The 19F NMR spectrum shows, as expected, only one sharp
resonance due to the equivalency of the CF3 groups.
LV(OSO2CF3)2 constitutes the first vanadium() triflate
derivative to be structurally characterized (two triflate con-
taining complexes of vanadium() were structurally character-
CCDC reference numbers 206412 and 206413.
See http://www.rsc.org/suppdata/dt/b3/b303196a/ for crystal-
lographic data in CIF or other electronic format.
12
ized, namely V(py)4(OSO2CF3)2 and V(H2O)6(OSO2CF3)2).13
LV(OSO2CF3)2 is expected to be a superior starting material
than LVCl2 for further substitution reactions owing to the weak
nucleophilicity of the CF3SO3 anion, which is a better leaving
group compared to the Cl anion.12
Results and discussion
Treatment of LLi with an equivalent amount of VCl3ؒ3THF
in toluene at room temperature afforded LVCl2 in good yield
(eqn. (1)). VCl3ؒ3THF constitutes the usual common entry for
many vanadium complexes in different oxidation states due to
the straightforward accessibility and hence relatively low cost.10
LVCl2 is well soluble in toluene, dichloromethane and THF,
respectively. It is thermally very stable, but moisture- and
air-sensitive, and represents facile entry into the vanadium()
chemistry of the β-diketiminato ligand L. Mass spectrometry
and elemental analysis showed that LVCl2 is monomeric and
contains neither coordinated lithium salt nor coordinated THF.
It may be compared with [Sc{(N(CH2CH2NEt2)C(Me))2CH}-
Cl2] which is a similar compound of a highly electrophile
metal.11 The 1H NMR spectrum could not be interpreted
because it exhibits a broad NMR resonance due to the
(2)
Suitable single crystals of LV(OSO2CF3)2 for an X-ray
structural analysis were obtained from toluene at Ϫ26 ЊC within
several hours. LV(OSO2CF3)2 crystallizes in the monoclinic
D a l t o n T r a n s . , 2 0 0 3 , 2 8 3 1 – 2 8 3 4
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Table 2 Selected bond lengths (Å) and angles (Њ) of LV(OSO2CF3)2
Table 3 Selected bond lengths (Å) and angles (Њ) for LVP(C6H5)2
V(1)–N(3)
V(1)–N(1)
V(1)–N(2)
V(1)–N(4)
C(2)–N(1)
C(2)–C(3)
C(3)–C(4)
C(4)–N(3)
V(1)–O(1)
V(1)–O(4)
O(1)–S(1)
O(4)–S(2)
2.0080(18)
2.0090(18)
2.3223(18)
2.3379(19)
1.327(3)
1.401(4)
1.408(4)
N(3)–V(1)–N(1)
N(3)–V(1)–N(4)
N(1)–V(1)–N(2)
N(2)–V(1)–N(4)
O(1)–V(1)–O(4)
S(2)–O(4)–V(1)
S(1)–O(1)–V(1)
C(2)–N(1)–V(1)
C(4)–N(2)–V(1)
N(3)–C(4)–C(3)
C(2)–C(3)–C(4)
N(1)–C(2)–C(3)
89.13(8)
82.09(7)
81.39(7)
107.40(7)
167.89(6)
130.27(10)
132.67(10)
128.80(16)
128.66(16)
122.7(2)
Molecule a
V(1)–N(2)
V(1)–N(1)
V(1)–N(3)
V(1)–N(4)
V(1)–P(1)
N(1)–C(2)
C(2)–C(3)
C(3)–C(4)
N(3)–C(4)
2.3253(18)
2.0446(17)
2.0499(17)
2.3078(17)
2.5752(9)
1.337(3)
1.398(3)
1.399(3)
1.332(2)
N(2)–V(1)–N(1)
N(1)–V(1)–N(3)
N(3)–V(1)–N(4)
N(2)–V(1)–N(4)
N(1)–C(2)–C(3)
N(3)–C(4)–C(3)
C(4)–C(3)–C(2)
C(2)–N(1)–V(1)
C(4)–N(3)–V(1)
77.89(6)
89.73(7)
78.21(7)
108.19(6)
123.26(19)
123.57(18)
128.87(17)
127.29(14)
127.09(14)
1.327(3)
2.0606(16)
2.0637(16)
1.4733(16)
1.4788(16)
127.3(2)
122.7(2)
Molecule b
V(2)–N(5)
V(2)–N(6)
V(2)–N(8)
V(2)–N(7)
V(2)–P(2)
N(5)–C(31)
N(6)–C(33)
C(33)–C(32)
C(31)–C(32)
2.0392(17)
2.0511(17)
2.2781(18)
2.2882(18)
2.5600(9)
1.333(3)
1.337(3)
1.395(3)
1.402(3)
N(5)–V(2)–N(6)
N(6)–V(2)–N(8)
N(5)–V(2)–N(7)
N(8)–V(2)–N(7)
N(6)–C(33)–C(32)
N(5)–C(31)–C(32)
C(33)–C(32)–C(31)
C(31)–N(5)–V(2)
C(33)–N(6)–V(2)
89.58(7)
79.50(6)
79.01(6)
103.80(6)
123.07(18)
122.79(18)
129.30(18)
127.88(14)
127.27(14)
of vanadium in different oxidation states (tBuN᎐V(NiPr )[P-
᎐
2
(SiMe3)2]2,15 tBuN᎐V[P(SiMe ) ] ,16 [Li(DME)V(P(C6H11)2)4]17)
᎐
3
2 3
have been previously published, none has been structurally
characterized.
(3)
LVP(C6H5)2 has been characterized by 31P NMR, EI-MS,
elemental analysis, and single crystal X-ray diffraction. Support
for the reaction pathway has been given by confirmation of
[Ph2P]2 by multinuclear NMR spectroscopy. This type of
reduction is not unusual when diorganophosphides are
involved. Previously, a similar reaction has been reported for
LnI3ؒ3THF (Ln = Sm, Yb) giving as the major product
Ln[P(C6H5)2]2ؒ4THF.18 In the precedent not so numerous
examples, ligands of composition PR2 mainly act as bridging
units (µ-PR2).19 There are only a few complexes of transition
metals structurally characterized where the bonding pattern
is terminal.20 Interestingly, a terminal diorganophosphido-
platinum() complex has found application as a catalyst in the
asymmetric hydrophosphination of acrylonitrile.20c
Single crystals of LVP(C6H5)2 have been obtained from
toluene at Ϫ26 ЊC and crystallize in the monoclinic P21 space
group (Fig. 2) with two crystallographically independent but
chemically equivalent molecules in the unit cell (Tables 1 and 3).
The crystal structure analysis reveals that, unlike for LV-
(OSO2CF3)2, the vanadium atom in LVP(C6H5)2 is penta-
coordinated (four coordination positions being occupied by the
tetradentate ligand) with a square-pyramidal geometry. The
vanadium atom lies on the NC3N β-diketiminato backbone
plane (the mean deviation from the plane is 0.09 and 0.05 Å for
the two molecules). However the vanadium atom is placed
about 0.38 Å (av.) above the plane formed by the four nitrogen
atoms of the ligand. Similarly to LV(OSO2CF3)2, the V–N
(belonging to the ligand core) bond lengths are comparable
to those found in literature,2,14 although they are slightly
longer due to the larger vanadium() radius. As expected the
delocalization of the π-electrons is reflected by the C–C and
C–N bond lengths of the backbone. The phosphido ligands
are substantially pyramidalyzed with large V–P bond lengths
Fig. 1 Molecular structure of LV(OSO2CF3)2 showing 50% probability
ellipsoids (the hydrogen atoms are omitted for clarity).
space group P21/c together with two molecules of toluene (the
toluene molecules are omitted in Fig. 1 for clarity).
The crystal structure reveals that the vanadium atom in
LV(OSO2CF3)2 is hexacoordinated (ligand is tetradentate) with
a pseudo-octahedral geometry and the triflate anions are
arranged in the apical positions (O(4)–V–O(1) 167.89(6)Њ)
(Table 2). This distortion might be attributable to the existence
of the C–H–X (X = O, F) hydrogen bond like interaction
between the discrete molecules (F ؒ ؒ ؒ H 2.48 Å, O ؒ ؒ ؒ H 2.57
Å). From sterical and electronical reasons the triflate groups
are not coordinated to vanadium in a chelate fashion, they
bind rather as monodentate through an oxygen atom. The V–O
distances (av. 2.06 Å) in LV(OSO2CF3)2 are slightly shorter
than those reported for V(py)4(OSO2CF3)2 (2.127(6) Å)12 or
for V(H2O)6(OSO2CF3)2 (2.129(6) Å)13 as a consequence of
a smaller radius of vanadium() compared to that of
vanadium(). The NC3N atoms of the β-diketiminato back-
bone as well as the nitrogen atoms of the ligand arms are
almost coplanar. The deviation of the vanadium atom from the
NC3N plane (0.09 Å) clearly indicates a σ-bond interaction (η2)
between vanadium and the β-diketiminato ligand. The V–N
(belonging to the ligand core) bond lengths are comparable to
those found in literature2,14 (e.g. 1.963(2) and 1.940(2) Å for
[V{(N(C6H3iPr2-2,6)C(Me))2CH}Cl2]).2b
Surprisingly, the reaction of LVCl2 with 2 equivalents of
KPPh2 in THF yielded, after removal of the THF and extrac-
tion in toluene, complex LVP(C6H5)2 as an unexpected product
which represents the first neutral heteroleptic terminal di-
organophosphido-complex of vanadium() (eqn. (3)). Even
though the synthesis of some diorganophosphido complexes
D a l t o n T r a n s . , 2 0 0 3 , 2 8 3 1 – 2 8 3 4
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Fig. 2 Molecular structure of one LVP(C6H5)2 molecule showing 50%
probability ellipsoids (the hydrogen atoms are omitted for clarity).
(2.5752(9) and 2.5600(9) Å). These V–P distances are notably
longer than those reported for a diphosphene vanadium()
complex, trans-[{V(η5-C5H5)(CO)3}2(PMes)2]21 (2.397(1) Å)
or a phospinidene vanadium complex, [V2(CO)4(η5-C5H5)2-
{µ-P(2,4,6-(tBu)3C3H2)}]22 (2.268(1) and 2.243(1) Å).
Intriguingly, they are also longer than the V–P distances
found in some complexes that contain coordinated phosphine,
such as V(N-2,6-iPr2C6H3)Cl3(depe) (2.520(2) Å) (depe =
Et2PCH2CH2PEt2).23 This can be attributed to the larger
radius of vanadium() compared to vanadium(), and to a
greater extent of the ionic character of the V–P bond in
LVP(C6H5)2.
16 F. Preuss and F. Tabellion, Z. Naturforsch., Teil B, 2000, 55,
735–737.
17 R. T. Baker, P. J. Krusic, T. H. Tulip, J. C. Calabrese and S. S.
Wreford, J. Am. Chem. Soc., 1983, 105, 6763–6765.
18 G. W. Rabe, G. P. A. Yap and A. L. Rheingold, Inorg. Chem., 1995,
34, 4521–4522.
Conclusions
In this study it has been shown that the ligand L functions as an
ancillary system for vanadium, thereby providing an easy access
to a novel class of β-diketiminato vanadium complexes. Not
only does the β-diketiminato ligand L provide a suitable
coordination environment for vanadium() or vanadium()
cations but its built-in amine donor allows the isolation of
base- and salt-free complexes. While the substitution reaction
of LVCl2 with AgOSO2CF3 follows a well established pattern,
the reaction of LVCl2 with KPPh2 is interesting due to its
product formation, which constitutes the first structurally
characterized terminal vanadium phosphido complex that
features a remarkably long V–P bond length.
19 (a) C. J. Adams, M. I. Bruce, B. W. Skelton and A. H. White,
J. Chem. Soc., Dalton Trans., 1999, 2451–2460; (b) F. A. Cotton,
E. V. Dikarev and M. A. Petrukhina, Inorg. Chem., 1998, 37,
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C. Fortuno, F. Duran and A. Martin, Organometallics, 2002, 21,
2226–2234.
20 (a) R. Melenkivitz, D. J. Mindiola and G. L. Hillhouse, J. Am.
Chem. Soc., 2002, 124, 3846–3847; (b) M. A. Zhuravel,
D. S. Zakharov, N. Lev and A. L. Rheingold, Organometallics, 2002,
21, 3208–3214; (c) D. K. Wicht, I. Kovacik, D. S. Glueck,
L. M. Liable-Sands, C. D. Incarvito and A. L. Rheingold,
Organometallics, 1999, 18, 5141–5151.
21 R. A. Bartlett, H. V. R. Dias and P. P. Power, J. Organomet. Chem.,
1989, 362, 87–94.
22 A. M. Arif, A. H. Cowley, N. C. Norman, A. G. Orpen and
M. Pakulski, Organometallics, 1988, 7, 309–318.
23 F. Montilla, A. Monge, E. Gutiérrez-Puebla, A. Pastor, D. del Rio,
N. C. Hernandez, Y. F. Sanz and A. Galindo, Inorg. Chem., 1999, 38,
4462–4466.
Acknowledgements
Dedicated to Professor Friedrich Hensel on the occasion of his
70th birthday. We are thankful to the Deutsche Forschungs-
gemeinschaft for financial support.
D a l t o n T r a n s . , 2 0 0 3 , 2 8 3 1 – 2 8 3 4
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