Simple synthesis and structure characterization of a phosphoniomethylidyne tantalum(V) complex

Article abstract of DOI:10.1016/j.inoche.2012.10.017

A high-valent phosphoniomethylidyne tantalum complex [(C₅Me ₄H)Ta(C-PPh₃)(CH-PPh₃)Cl] (3) was obtained via transylidation reactions of (C₅Me₄H)TaCl₄ with 5 equivalents of the phosphorus ylide Ph₃P = CH₂. The addition of strong base Li(N(SiMe₃)₂ is beneficial to the transylidation reaction and improves the yield of complex 3. The ylide adduct complex [(C₅Me₄H)TaCl₄(CH₂PPh ₃)] (4) as the reaction intermediate was isolated through the reaction of (C₅Me₄H)TaCl₄ with one equivalent of the phosphorus ylide Ph₃P = CH₂. Both complexes 3 and 4 were structurally characterized by X-ray single crystal diffraction. A comparison on the preparation and properties of the phosphoniomethylidyne tantalum complexes with different supporting ligands, [CpTa(C-PPh ₃)(CH-PPh₃)Cl] (1) (Cp = cyclopentadieneyl ligand), [(C₅Me₄H)Ta(C-PPh₃)(CH-PPh₃)Cl] (3) (C₅Me₄H = tetramethylcyclopentadienyl ligand) (3) and [Cp^*Ta(C-PPh₃)(CH-PPh₃)Cl] (2) (Cp ^* = pentamethylcyclopentadienyl ligand) was discussed.

Full text of DOI:10.1016/j.inoche.2012.10.017

Inorganic Chemistry Communications 27 (2013) 36–39
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Simple synthesis and structure characterization of a phosphoniomethylidyne
tantalum(V) complex
1
1
⁎
Nazhen Liu , Gengyu Zhu , Hongjian Sun, Xiaoyan Li
School of Chemistry and Chemical Engineering, Shandong University, Shanda Nanlu 27, 250100 Jinan, People's Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A high-valent phosphoniomethylidyne tantalum complex [(C5Me4H)Ta(`C-PPh3)(_CH-PPh3)Cl] (3) was
obtained via transylidation reactions of (C5Me4H)TaCl4 with 5 equivalents of the phosphorus ylide Ph3P=CH2.
The addition of strong base Li(N(SiMe3)2 is beneficial to the transylidation reaction and improves the yield of
complex 3. The ylide adduct complex [(C5Me4H)TaCl4(CH2PPh3)] (4) as the reaction intermediate was isolated
through the reaction of (C5Me4H)TaCl4 with one equivalent of the phosphorus ylide Ph3P=CH2. Both complexes
3 and 4 were structurally characterized by X-ray single crystal diffraction. A comparison on the preparation and
properties of the phosphoniomethylidyne tantalum complexes with different supporting ligands, [CpTa(`C-
Received 28 August 2012
Accepted 9 October 2012
Available online 22 October 2012
Keywords:
Phosphoniomethylidyne complex
Tantalum
Tetramethylcyclopentadiene
Phosphorus ylide
PPh3)(_CH-PPh3)Cl] (1) (Cp
= cyclopentadieneyl ligand), [(C5Me4H)Ta(`C-PPh3)(_CH-PPh3)Cl] (3)
⁎
⁎
(C5Me4H = tetramethylcyclopentadienyl ligand) (3) and [Cp Ta(`C-PPh3)(_CH-PPh3)Cl] (2) (Cp
=
pentamethylcyclopentadienyl ligand) was discussed.
© 2012 Elsevier B.V. All rights reserved.
The study on metal carbyne complex is always an interesting topic
in current research of organometallic chemistry. Metal carbyne com-
plexes can be used in alkyne metathesis reaction. Compared to the
chemistry of metal carbene complexes, the chemistry of metal carbyne
complexes is less developed because they are more difficult to synthe-
size than carbene complexes. The first bridged dinuclear titanium(IV)
phosphonio carbyne complex was obtained from titanium tetrachloride
via transylidation reaction [1]. Employing the transylidation method,
we successfully prepared the phosphoniomethylidyne complex of tung-
sten [2], rhenium [3] and niobium [4] with a d0 electron configuration.
We prepared the phosphoniomethylidyne complex of tantalum
with a d0 electron configuration, [(CpTa(`C-PPh3)(_CH-PPh3)Cl]
(1) [5], supported by cyclopentadienyl ligand. This is the first report
of a stable tantalum complex with a terminal [Ta`C-PR3] function
(Eq. (1)).
Under similar reaction conditions, the transylidation reaction of
Cp*TaCl4 with the ylide Ph3P=CH2 did not occur. The expected
phosphoniomethylidyne complex [(Cp Ta(`C-PPh3)(_CH-PPh3)Cl]
(2) was not obtained (Eq. (2)) [6]. Complex 2 was only formed with
the participation of a strong base, LiN(SiMe3)2 (Eq. (3)) [6].
⁎
CH2
ð2Þ
Ph P
5
+
Ta
3
Ta
Ph3P
C
H
Cl
C
Cl
Cl
PPh3
Cl
Cl
2
CH2
Ph P
+ 5
3
Ta
[Ph P-CH ]Cl
+ 3
3
3
Ta
Ph3P
C
H
Cl
C
Cl
3 LiN(SiMe )
+
3
2
PPh3
Cl
Ta
Cl
Cl
3
LiCl
2 HN(SiMe )
+
+
Ta
3
Ph3P = CH2
Ph3P
3
2
+
Cl
C
Cl
C
[Ph3PCH3][N(SiMe3)2]
Cl
Cl
PPh3
1
Cl
H
ð1Þ
2
ð3Þ
In order to clarify the influence of the substituents on the
cyclopentadienyl ring upon the synthesis and stability of the correspond-
ing phosphoniomethylidyne tantalum complexes, herein we report our
progress in the synthesis and characterization of a new tantalum
⁎
Corresponding author. Tel.: +86 531 88361350; fax: +86 531 88564464.
E-mail address: xli63@sdu.edu.cn (X. Li).
The first two authors contributed equally to this work.
1
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2012.10.017

N. Liu et al. / Inorganic Chemistry Communications 27 (2013) 36–39
37
phosphoniomethylidyne complex [(C5Me4H)Ta(`C-PPh3)(_CH-PPh3)
Cl] (3) with tetramethylcyclopentadienyl group as supporting ligand.
The reaction of (C5Me4H)TaCl4 with 5 equivalents of the phospho-
rus ylide Ph3P=CH2 lead to phosphoniomethylidyne tantalum com-
plex 3 (Eq. (4)) [7]. Crystallization in pentane at 0 °C afforded 3 as
orange crystals with a 30% yield.
Ta
Ta
Ph P = CH
Ph3P
5
+
3 [Ph PMe]Cl
3
2
+
PPh3
3
Cl
C
H
Cl
C
Cl
Cl
Cl
3
ð4Þ
Complex 3 was characterized by NMR spectroscopy. In the 1H
NMR spectra the proton signal of C5Me4H appears at 5.46 ppm as a
singlet. The metal-bound α-CH function (Ta=CH) is located at
4.50 ppm as a triplet with |2JPH + 4JPH|=2.7 Hz. Two types of protons
of the methyl groups on the cyclopentadienyl ring appear at 2.13
and 2.06 ppm, respectively. The 31P NMR spectra of complex 3
show two doublets for [Ta=CH-PPh3] and [Ta`C-PPh3] at 22.3
Fig. 1. Molecular structure of 3 and selected bond distances (Å) and angles (°): Ta1–
C47 2.060(4), Ta1–C46 1.880(5), Ta1–Cl1 2.4060(13), C47–P4 1.697(4), C46–P5
1.684(5), Ta1–C37 2.375(5), Ta1–C38 2.445(5), Ta1–C39 2.563(5), Ta1–C40 2.551(5),
Ta1–C41 2.430(5), Ta1–C47–P4 134.3(3), Ta1–C46–P5 155.7(3), C46–Ta1–Cl1
103.29(15), and C47–Ta1–Cl1 105.04(13).
4
and −25.9 ppm with a coupling constant JPP =5.5 Hz. In compar-
ison with the chemical shifts of the phosphorus resonances of com-
plexes [CpTa(`CPPh3)(=CH-PPh3)Cl] (1) (23.7, −21.7 ppm) [5]
and [Cp*Ta(`C-PPh3)(=CH-PPh3)Cl] (2) (22.0, −30.0 ppm) [6],
the corresponding values of complex 3 are between them. This
trend is also reflected in the data of the 13C NMR spectra of com-
plexes 3, 2 and 1. The 13C NMR resonance for carbyne carbon
([Ta`C-PPh3]) shows at 208.0 (1) [5], 202.1 (3) and 198.6 (2)
ppm [6], respectively.
with 2 equivalents of Ph3P=CH2 in toluene. From the experimental
results it was found that the transylidation reaction and the formation
yield of the phosphoniomethylidyne tantalum complexes strongly
depend upon the substituents on the cyclopentadienyl ring. Complex
1 without substituent on the Cp ring was obtained in 4 d in the yield
of 34% [5], complex 3 with four methyl groups on the Cp ring was
obtained in 15 d in the yield of 30%, but complex 2 with five methyl
groups on the Cp ring could not be formed through the transylidation
reaction of Cp*TaCl4 with 5 equivalents of Ph3P=CH2 [6]. This result
is consistent with the decreasing of the acidity of ylide methylene
protons of the ylide adducts from [CpTa(CH2-PPh3)Cl4], [(C5Me4H)
Ta(CH2-PPh3)Cl4] to [Cp*Ta(CH2-PPh3)Cl4], with the increase in the
number of methyl groups on the cyclopentadienyl ring. This trend is
The molecular structure of complex 3 is shown in Fig. 1 with selected
bond distances and angles [8]. The Ta atom is tetra-coordinated with the
center of tetramethylcyclopentadienyl group acting as one vertex
of the tetrahedron. The Ta1–C47 distance of 2.060(4) Å in the moiety
of [Ta=CH-PPh3] is comparable with the tantalum–carbon double
bond (2.040(6) Å in complex 1 [5]. The Ta1–C46 distance of
1.880(5) Å in the moiety of [Ta`C-PPh3] lies within the range of the
expected values for a metal–carbon triple bond (1.849(8) Å in
[Cp*Ta(`C-Ph)(PMe3)2Cl] [9], 1.850(5)
Å
in [Ta(`C-CMe3)(H)
(dmpe)2(ClAlMe3)] [10] and 1.853 Å in 1 [5]. Due to the stronger
electron-donating ability of the four methyl groups on the tetra-
methylcyclopentadienyl ring in comparison to the cyclopentadienyl
group, the bond distances of Ta`C, Ta_C in complex 3 are longer
than those in complex 1 [5].
Upon the basis of our previous investigation [2–6], the transylidation
reaction is likely to proceed via the hexa-coordinate classical ylide
adduct [(C5Me4H)TaCl4(CH2-PPh3)] (4) (Scheme 1). Complex 4 is
deprotonated by 2 equivalents of Ph3P=CH2 molecules to provide
phosphoniomethylidyne complex 5 and methyltriphenyl phosphonium
chloride. In the presence of another 2 equivalents of Ph3P=CH2 com-
plex 5 was transformed to the end product 3.
In order to catch intermediate 4 the reaction of (C5Me4H)TaCl4
with one equivalent of Ph3P=CH2 was carried out in toluene [11].
After the workup complex 4 was isolated as yellow crystals. The mo-
lecular geometry is shown in Fig. 2 with selected bond distances and
angles [12]. X-ray single crystal diffraction studies show that complex
4 has a hexa-coordinate octahedron geometry. The four chloride li-
gands are in the equatorial plane while the ylide carbon atom and
the tetramethylcyclopentadienyl ligand are in the axial positions.
The bond length Ta1–C1 (2.337(3) Å) in complex 4 is longer than
those (Ta1–C47 2.060(4) Å and Ta1–C46 1.880(5) Å) in complex 3.
This distinction indicates that the Ta1–C1 bond is a single bond in
complex 4.
Ph P = CH
+
3
2
Ta
Ta
Cl
Cl
Ph3P
Cl
Cl
Cl
Cl
Cl
Cl
4
2 Ph P = CH
+
3
2
[Ph PMe]Cl
2
3
2 Ph P = CH
+
3
2
Ta
Ta
Ph3P
[Ph3PMe]Cl
Cl
C
C
Cl
PPh3
Cl
H
PPh3
3
5
The efforts to isolate intermediate 5 failed when complex 2 was
treated with 3 equivalents of Ph3P=CH2 or when complex 4 reacted
Scheme 1. Proposed formation mechanism of complex 3.

38
N. Liu et al. / Inorganic Chemistry Communications 27 (2013) 36–39
Appendix A. Supplementary material
CCDC-793860 (3) and CCDC-793859 (4) contain the supplementary
crystallographic data for complexes 3 and 4. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/conts/retrieving.html. Supplementary data
associated with this article can be found, in the online version at
http://dx.doi.org/10.1016/j.inoche.2012.10.017.
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[7] Synthesis of 3. Method a: To the solution of (C5Me4H)TaCl4 [13–15] (1.2 g,
2.70 mmol) in 30 mL of toluene was added Ph3P=CH2 [16] (3.7 g, 13.40 mmol)
in 30 mL of toluene at 0 °C. After 15 d of stirring at room temperature, the resulting
suspension was filtered. Toluene was evaporated under vacuo and the residue
was extracted with pentane and diethyl ether. The product was crystallized as
orange crystals from pentane. Yield: 0.72 g (30%). Anal. calcd for C47H44TaClP2
(3; 887.21 g/mol): C, 63.63; H, 5.00. Found: C, 63.82; H, 4.99. 1H NMR (300 MHz,
Fig. 2. Molecular structure of 4 and selected bond distances (Å) and angles (°): Ta1–C1
2.337(3), C1–P1 1.773(3), P1–C14 1.802(4), P1–C8 1.827(3), P1–C2 1.804(4), Ta1–Cl1
2.4073(9), Ta1–Cl2 2.4289(9), Ta1–Cl3 2.4516(12), Ta1–Cl4 2.4045(12), Ta1–C1–P1
132.22(18), C1–Ta1–Cl1 80.74(9), C1–Ta1–Cl2 74.96(9), C1–Ta1–Cl3 78.68(10), C1–
Ta1–Cl4 77.55(10), C1–P1–C2 115.90(16), C1–P1–C8 107.86(15), and C1–P1–C14
114.53(17).
4
5
C6D6, 300 K, ppm): 2.06 (d, JHH=8.1 Hz, 6H, C5Me4H), 2.13 (d, JHH=3.6 Hz, 6H,
C5Me4H), 4.50 (t′, |2JPH+4JPH|=2.7 Hz, 1H, Ta=CH), 5.46 (s, 1H, C5Me4H),
6.96–8.04 (m, 30H, PPh3). 31P NMR (121 MHz, C6D6, 300 K, ppm): −25.9
4
4
(d, JPP=5.5 Hz, 1P, TaCPPh3), 22.3 (d, JPP=5.5 Hz, 1P, TaCHPPh3). 13C NMR
(75 MHz, C6D6, 300 K, ppm): 11.4 (s, C5Me4H), 14.1 (s, C5Me4H), 65.8 (s, CMe,
C5Me4H), 99.4 (s, CH, C5Me4H), 112.2 s, 113.8 s, 117.6 s, 118.4 s, 119.0 s, 119.7 s,
4
4
3
130.0 (d, JP,C =2.3 Hz), 130.3 (d, JP,C =3.0 Hz), 133.2 (d, JP,C =9.0 Hz),
also in accordance with the strength of basicity of the cyclopentadienyl
ligands.
3
4
4
134.2 (d, JP,C =9.0 Hz), 135.1 (d, JP,C =2.0 Hz), 135.4 s, 136.2 (d, JP,
C =2.0 Hz),136.5 s, 202.2 (t′, |1JP,C 3JP,C|=12.8 Hz,Ta`C). Method b: To a sus-
+
pension of (C5Me4H)TaCl4 (0.90 g, 2.03 mmol) in 30 mL of toluene was added
1.68 g (6.08 mmol) of Ph3P=CH2 in 20 mL of toluene at 0 °C. The reaction mix-
ture was stirred at room temperature for 3 h, and the resulting suspension was
treated with a solution of 1.02 g (6.09 mmol) LiN(SiMe3)2 in 20 mL of toluene at
−78 °C. The reaction solution was allowed to warm slowly to room tempera-
ture and stirred for an additional 12 h. Removal of the precipitate by filtration
furnished a bright red solution containing 3 analyzed by 31P NMR spectroscopy.
Yield: 100% confirmed by 31P NMR.
A strong base, LiN(SiMe3)2, was added to the reaction of (C5Me4H)
TaCl4 with Ph3P=CH2 to improve the yield of complex 3 because the
basicity of the phosphorus ylide Ph3P=CH2 is weaker than that of
LiN(SiMe3)2 (Eq. (5)) [7]. With the addition of 3 equivalents of
LiN(SiMe3)2 and 3 equivalents of Ph3P=CH2 complex 3 could be
quantitatively obtained within 12 h.
[8] Crystallographic data for 3. C47H44TaClP2, Mr=887.21, monoclinic, space group
P2(1)/n, a=10.7345(10) Å, b=27.758(3) Å, c=14.4496(14) Å, V=4095.9(7)
Å3, T=298 K, Z=4, Dc=1.439 g/cm3, μ=2.858 mm−1. A total of 22,717 reflec-
tions were collected, 8458 unique (Rint=0.0287), R1=0.0293 (for 8458 reflec-
tions with I>2 sigma(I)), wR2=0.0712 (all data). The structure was solved by
direct methods and refined with full-matrix least-squares on all F2 (SHELXL-97)
with non-hydrogen atoms anisotropic.
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3 LiN(SiMe )
+
3
2
Ta
3
2 HN(SiMe )
LiCl
+
+
Ta
3
Ph3P = CH2
Ph3P
3
2
+
Cl
C
H
Cl
C
[Ph3PCH3][N(SiMe3)2]
Cl
Cl
PPh3
Cl
3
ð5Þ
In conclusion, a high-valent phosphoniomethylidyne tantalum
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of LiN(SiMe3)2 and 3 equiv of Ph3P=CH2 complex 3 could be
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as an intermediate through the reactions of (C5Me4H)TaCl4 with
one equivalent of Ph3P=CH2. Complexes 3 and 4 were structural-
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[11] Synthesis of 4. To the solution of (C5Me4H)TaCl4 (0.60 g, 1.35 mmol) in 20 mL of
toluene was added PPh3P=CH2 (0.37 g, 1.35 mmol) in 20 mL of toluene at 0 °C.
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analysis. Yield: 0.68 g (70.6%). Anal. calcd for C28H30TaCl4P (4; 720.24 g/mol): C,
46.69; H, 4.20. Found: C, 47.01; H, 4.02. 1H NMR (300 MHz, C6D6, 300 K, ppm):
2
2.22 (s, 6H, CH3), 2.56 (s, 6H, CH3), 4.01 (d, JP,H=15.9 Hz, 2H, PCH2), 5.84 (s,
1 H, C5Me4H), 6.90–7.80 (m, 15H, PPh3). 31P NMR (121 MHz, C6D6, 300 K,
ppm): 34.1 (s, PPh3).
⁎
[12] Crystallographic data for 4. C28H30TaCl4P, Mr=720.24, monoclinic, space group
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were collected, 5474 unique (Rint =0.0887), R1=0.0228 (for 5474 reflections
with I>2 sigma(I)), wR2=0.0645 (all data). The structure was solved by direct
methods and refined with full-matrix least-squares on all F2 (SHELXL-97) with
non-hydrogen atoms anisotropic.
and 2 with Cp ) was discussed.
Acknowledgment
This work was supported by NSFC no. 21172132/20972087.

N. Liu et al. / Inorganic Chemistry Communications 27 (2013) 36–39
39
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