Neodymium(III) phosphinidene complexes supported by pentamethylcyclopentadienyl and hydrotris(pyrazolyl)borate ligands

Article abstract of DOI:10.1039/c001839b

Synthesis of new neodymium(iii) phosphinidene complexes from a neodymium(iii) phosphinidene iodide [(μ-PC₆H₃-2,6- ⁱPr₂)Nd(i)(THF)₃]₂ (1) was studied. The metathesis reaction of 1 with KC₅Me₅ (KCp*) gave a neodymium(iii) pentamethylcyclopentadienyl phosphinidene complex [(μ-PC₆H₃-2,6-ⁱPr₂)(C ₅Me₅)Nd(THF)]₂ (2), and that with potassium hydrotris(pyrazolyl)borate KHB(3-phenylpz)₃ (KTp^Ph) generated a neodymium(iii) hydrotris(pyrazolyl)borate phosphinidene complex [(μ-PC₆H₃-2,6-ⁱPr₂)(Tp ^Ph*)Nd(THF)]₂ (3) and a C-H bond activation byproduct [κ⁴(N,N′,N″,C^Ph)-Tp ^Ph]Tp^PhNd (4). Complexes 2-4 have been characterized by single-crystal X-ray diffraction analysis. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c001839b

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www.rsc.org/dalton | Dalton Transactions
Neodymium(III) phosphinidene complexes supported by
pentamethylcyclopentadienyl and hydrotris(pyrazolyl)borate ligands†
Peng Cui,a Yaofeng Chen*a and Maxim V. Borzovb
Received 27th January 2010, Accepted 15th June 2010
First published as an Advance Article on the web 28th June 2010
DOI: 10.1039/C001839B
Synthesis of new neodymium(III) phosphinidene complexes from a neodymium(III) phosphinidene
iodide [(m-PC6H3-2,6-iPr2)Nd(I)(THF)3]2 (1) was studied. The metathesis reaction of 1 with KC5Me5
(KCp*) gave a neodymium(III) pentamethylcyclopentadienyl phosphinidene complex
[(m-PC6H3-2,6-iPr2)(C5Me5)Nd(THF)]2 (2), and that with potassium hydrotris(pyrazolyl)borate
KHB(3-phenylpz)3 (KTpPh) generated a neodymium(III) hydrotris(pyrazolyl)borate phosphinidene
complex [(m-PC6H3-2,6-iPr2)(TpPh*)Nd(THF)]2 (3) and a C–H bond activation byproduct
4
[k (N,N¢,N¢¢,CPh)-TpPh]TpPhNd (4). Complexes 2–4 have been characterized by single-crystal X-ray
diffraction analysis.
Herein, we report the preparation of Nd(III) phosphinidene
complexes supported by pentamethylcyclopentadienyl (Cp*) and
Introduction
Alkyl, amide, and phosphide complexes of lanthanide metals have
hydrotris(pyrazolyl)borate (Tp) ligands obtained from 1 along
been extensively explored during the last three decades. These
with the crystal structures of the corresponding metal complexes.
complexes have diverse coordinating properties and reactivities,1–3
and have been widely used in organic4 and polymer syntheses.5,6
However, chemistry of their counterparts, the alkylidene, imido,
Results and discussion
and phosphinidene complexes are in their infancy. On the other
hand, the alkylidene, imido, and phosphinidene complexes of
other early transition metals have received great attention in
recent years, and studies on them have revealed their rich
coordination chemistry and reactivities.7–9 The scarcity of the
alkylidene, imido, and phosphinidene complexes of lanthanide
metals is due to the relative mismatch in LUMO/HOMO orbital
energy between the Ln3+ (d0) ions and the alkylidene (imido,
or phosphinidene) groups and the lack of synthetic approaches
towards these complexes.10 Up until now, only a few examples
of lanthanide alkylidene11 and imido12 complexes have been
reported, and the lanthanide phosphinidene complexes are even
more sparse. Only two examples of lanthanide phosphinidene
complexes have been reported to date. Kiplinger and coworkers
reported a late lanthanide Lu(III) phosphinidene complex [{2-
(R2P)C6H4}2NLu(m-PMes)]2,13 which was prepared by a-hydrogen
abstraction of {2-(R2P)C6H4}2NLu(CH2SiMe3)2 with MesPH2
at 80 ◦C, and our group reported an early lanthanide Nd(III)
phosphinidene complex [(m-PC6H3-2,6-iPr2)Nd(I)(THF)3]2 (1),14
which was obtained by reaction of NdI3(THF)3.5 with K[(2,6-iPr2)-
C6H3PSiMe3] via a silyl-group exchange. Because 1 possesses a
Nd–I bond, it can serve as a suitable synthetic precursor of other
Nd(III) phosphinidene complexes simply via metathesis reactions.
At first, the metathesis reaction of 1 with KC5Me5 (KCp*) was
studied. The reaction gave the desired complex 2, in which the
I ligand in 1 was replaced by Cp* (Scheme 1). Complex 2 is
readily soluble in THF, toluene and benzene, and nearly insoluble
in hexane.
Scheme 1 Reaction of 1 with KCp*.
The molecular structure of 2 is given in Fig. 1. It presents
a centrosymmetric dimer, with the metal atoms bridged by two
phosphinidene ligands. Each Nd(III) center in 2 is in a distorted
tetrahedron coordination environment (assuming the Cp* ring
occupies one coordination site and not considering far Nd–
˚
NdA contact, 4.1164(5) A). The distances from Nd(III) ion to
the carbon atoms on the Cp* ring range from 2.691(4) through
˚
˚
to 2.784(4) A, the average distance (2.738(4) A) being close to
aState Key Laboratory of Organometallic Chemistry, Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road,
Shanghai, 200032, China. E-mail: yaofchen@mail.sioc.ac.cn; Fax: +86-21-
64166128
the analogous Nd–C distances in (Cp*)(h-C5H4SiMe3)NdI(py)
15
˚
˚
(2.72 A) and (Cp*)NdI2(py)3 (2.76 A). The Cp*-ring r.m.s.
plane through atoms C21–25 and a plane through Nd, P1, NdA,
and P1A atoms (denoted as PL1 and PL2, respectively) form a
dihedral angle of 38.4(1)◦. Similarly to 1, 2 has slightly non-
bKey Laboratory of Synthetic and Natural Chemistry of the Ministry of
Education, College of Chemistry and Material Science, the North-West
University of Xi’an, Taibai Bei avenue 229, Xi’an, 710069, Shaanxi prov,
China
˚
equivalent Nd–P bonds of 2.7456(11) and 2.7827(10) A, with
the average bond distance, 2.764 A, being close to that in 1
(2.753 A). The phosphorus atom in 2 is somewhat more tetrahedral
˚
† CCDC reference numbers 763478–763480. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c001839b
˚
6886 | Dalton Trans., 2010, 39, 6886–6890
This journal is The Royal Society of Chemistry 2010
©

Scheme 2 Reaction of 1 with KTpPh
.
TpPh ligand undergoes a “1,2-borotropic” shift to switch the phenyl
substituent on it (the C32–37 ring in Fig. 2) from the 3rd to the 5th
position to alleviate the steric congestion around the metal center
(Scheme 3). Such isomerization of the ligand has been observed in
some other pyrazolylborate metal complexes.17 The Nd(III) center
adopts a pseudo-octahedron geometry with two phosphinidene
groups and two pyrazolyl groups forming the equatorial plane,
and a pyrazolyl group and a THF molecule occupying the apical
positions. The distance from the Nd(III) ion to the nitrogen atom
Fig. 1 Two views of the molecular structure of 2 with thermal el-
lipsoids at the 30% probability level. Isopropyl groups at the aryl
substituents and hydrogen◦atoms are omitted for clarity. Selected bond
˚
lengths (A) and angles ( ): Nd–P1 2.7827(10), Nd–P1A 2.7456(11),
Nd–NdA 4.1164(5), Nd–O1 2.486(3), Nd–C21 2.714(4), Nd–C22 2.770(4),
Nd–C23 2.784(4), Nd–C24 2.732(4), Nd–C25 2.691(4), ∠Nd–P1–NdA
96.25(3), ∠P1–Nd–P1A 83.75(3) ∠C1–P1–Nd 128.82(14), ∠C1–P1–NdA
124.14(13), The ‘A’ denoted atoms are at the symmetrically equivalent
positions (-x, -y, -z).
˚
of 5-substituted pyrazolyl group is 2.497(5) A, falling within the
[C1–P1–Nd = 128.82(14)◦, Nd–P1–NdA = 96.25(3)◦, C1–P1–
ꢀ
NdA = 124.14(13)◦,
(
= 349.2(3)◦] in comparison to that in 1
ꢀ
= 359.1◦). The dihedral angle between the Ph-ring r.m.s. plane
(atoms C1–6; denoted as PL3) and PL2 (67.1◦) is significantly
smaller than that in 1 (81.29◦), which can be accommodated
by a Cp*–iso-propyl repulsions. Coordinated THF molecule is
disordered between two positions with site occupancy factors (sof-
s) of 0.596(14) and 0.404(14). THF–iso-propyl repulsions are also
significant, which causes considerable deviation of the O1–Nd–
NdA–P1 torsion angle (105.8(1)◦) from 90◦.
Lanthanide complexes with terminal phosphinidene ligands still
remain unknown. The hydrotris(pyrazolyl)borate ligands have a
protective pocket of varying size and shape,16 and a crowded
ligand of this type could probably force the cleavage of the bis(m-
phosphinidene) structure and the formation of the lanthanide
terminal phosphinidene complex. Thus, the reaction of 1 with
potassium hydrotris(pyrazolyl)borate, KHB(3-Butpz)3, in THF
was carried out. However, all attempts to obtain any crystalline
product from this reaction mixture failed. Application of another
hydrotris(pyrazolyl)borate, KHB(3-phenylpz)3 (KTpPh), in the
same reaction gave complex 3 as dark red crystalline blocks and
complex 4 as brown prisms (Scheme 2).
Fig. 2 Two views of the molecular structure of 3 with thermal el-
lipsoids at the 30% probability level. Isopropyl groups at the aryl
substituents and hydrogen atoms are omitted for clarity. Selected
The molecular structures of 3 and 4 are shown in Fig. 2
and 3, respectively. Complex 3 presents a centrosymmetric dimer
and retains the bis(m-phosphinidene)dineodymium structural unit.
It crystallizes as a solvate adduct with one molecule of THF
which is disordered around the inversion center (0, 1/2, 0) and
bond lengths (A) and angles (◦): Nd1–P1 2.7808(16), Nd1–P1A
˚
2.7911(15), Nd1–N1 2.714(5), Nd1–N3 2.497(5), Nd1–N5 2.707(5),
Nd1–O1 2.460(4), ∠Nd1–P1–Nd1A 103.25(5), ∠P1–Nd–P1A 76.75(5),
∠C1–P1–Nd1 128.01(19), ∠C1–P1–Nd1A 127.67(19), The ‘A’ denoted
atoms are at the symmetrically equivalent positions (2 - x, 2 - y, 1 - z).
¯
equivalents (space group P1). One of the pyrazolyl groups of the
This journal is The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6886–6890 | 6887
©

The crystal of 4 is presented by two components with
sof-s 0.905(2) and 0.095(2) (only the main of the two
disordered components is discussed).‡ In 4, there is a seven-
coordinated Nd(III) center bound by one monoanionic hydrotris-
(pyrazolyl)borate ligand and one dianionic hydrotris-
(pyrazolyl)borate ligand. In the latter one Ph-group ortho-
proton is removed and the deprotonated Ph-ring becomes
s-bonded to the Nd center. The distances from Nd(III) ion to
the nitrogen atoms on the TpPh ligands are quite different due
to formation of the five member Nd1/N2B/C3B/C4B/C5B
˚
metallacycle. The Nd1–N2B bond (2.487(6) A) is the shortest
one, while the Nd1–N4B and Nd1–N6B bonds (2.722(6)
Fig. 3 Molecular structure of 4 with thermal ellipsoids at the 30%
˚
and 2.646(6) A) are longer than the Nd1–N4A and Nd1–
probability level. Minor component and all hydrogen atoms are omitted for
˚
N6A ones (2.564(5) and 2.529(5) A). The Nd1–N2A bond
˚
clarity. Selected bond lengths (A) (for only the main of two disordered com-
˚
(2.868(5) A) is noticeably elongated, most likely, due to steric
ponents): Nd1–N2A 2.868(5), Nd1–N4A 2.564(5), Nd1–N6A 2.529(5),
Nd1–N2B 2.487(6), Nd1–N4B 2.722(6), Nd1–N6B 2.646(6), Nd1–C5B
2.569(7).
interactions between the phenyl groups. The Nd1–N4A and
Nd1–N6A bond lengths are close to those in the less hindered
19a
˚
Nd(III) complexes [Nd(HB(pz)3)2Cl(H2O)] (2.566–2.613 A) and
[NdCl(HB(pz)3)2(Hpz)] (2.57–2.59 A).19b Formation of 4 is a result
˚
of a rather unusual aromatic o-C–H bond activation. The Nd–CPh
˚
distance of 2.569(7) A in 4 is close to those in the only reported
complex containing s-Nd–Ph bond [(C5H5)3NdC6H5][Li(DME)3]
20
˚
(2.593(17), 2.613(13) and 2.601(13) A). To the best of our
knowledge, 4 represents the first example of C–H bond activation
of a TpPh ligand for the lanthanide complexes. Similar C–H
bond activation at phenyl substituent of TpPh ligand has
been reported for some transition metal complexes, such as
[Rh(H)(CO){HB(C3H2N2 C6 H3 OCH3 )(C3 H2 N2 C6 H4 OCH3)2}]21a
and [IrHB(C3H2N2C6H3)(C3H2N2C6H4)2(H)( C(CH2)3O)].21b
Conclusions
Our study demonstrated that new neodymium(III) phosphinidene
complexes can be synthesized by using a neodymium(III)
phosphinidene iodide [(m-PC6H3-2,6-iPr2)Nd(I)(THF)3]2 (1) as
the precursor via metathesis reactions. In this way, the
lanthanide phosphinidene complexes supported by pen-
tamethylcyclopentadienyl and hydrotris(pyrazolyl)borate ligands,
[(m-PC6H3-2,6-iPr2)(C5Me5)Nd(THF)]2 (2) and [(m-PC6H3-2,6-
iPr2)(TpPh*)Nd(THF)]2 (3), have been prepared and structurally
characterized. Complexes 2 and 3 both possess the bridging
phosphinidene structure, and in 3 one pyrazolyl group of the TpPh
ligand undergoes a “1,2-borotropic” shift to minimize the steric
congestions around the metal center. The lanthanide terminal
phosphinidene complex is still not accessible, and the synthesis
of this complex is under investigation.
Scheme 3 Isomerization of TpPh ligand via a 1,2-borotropic shift
˚
range of 2.46 to 2.52 A reported for the less hindered mono-
hydrotris(pyrazolyl)borate Nd(III) complexes.18 The distances
from the Nd(III) ion to the nitrogen atoms on 3-substituted pyra-
˚
˚
zolyl groups, 2.714(5) A and 2.707(5) A, are significantly longer.
The same observation was reported for Co(II)[HB(3-iPrpz)2(5-
iPrpz)]2,17a Zn(II)I[HB(3-mesitylpz)2(5mesitylpz)],17c M(II)[HB(4-
CN-3-Phpz)2(4-CN-5-Phpz)]2(M = Mn, Fe, Co),17e which can be
ascribed to steric effects. Unlike in 1 and 2, 3 has nearly equivalent
Experimental
General Procedures
˚
Nd–P bonds (2.7808(16) and 2.7911(15) A), and the average bond
˚
˚
All operations were carried out under an atmosphere of argon
using Schlenk techniques or in a nitrogen gas filled glovebox.
THF was distilled from Na-benzophenone ketyl and degassed
prior to use, toluene and hexane were dried over Na/K alloy.
C6D6 were purchased from Cambridge Isotopes, dried over Na/K
length (2.786 A) is slightly longer than those in 1 (2.753 A) and
˚
2 (2.764 A). Interestingly, the dihedral angle between the 2,6-
(diisopropyl)phenyl ring and the Nd1–P1–Nd1A–P1A plane in
3 (50.2◦) is much smaller than those in 1 (81.3◦) and 2 (67.1◦). The
geometry of the phosphorus atom in 3 is very close to trigonal
planar (C1–P1–Nd1 = 128.01(19)◦, Nd1–P1–Nd1A = 103.25(5)◦,
ꢀ
C1–P1–Nd1A = 127.67(19)◦, = 358.9(4)◦). The Nd-coordinated
THF molecule in 3 is disordered between two positions with sof-s
0.47(2) and 0.53(2).
‡ For model definition, restrains applied, and exhaustive structural discus-
sion of complex 4 including the details of packing, see the corresponding
sections of the provided CIF file.
6888 | Dalton Trans., 2010, 39, 6886–6890
This journal is
The Royal Society of Chemistry 2010
©

alloy, distilled under vacuum and stored in a glovebox. [(m-
PC6H3-2,6-iPr2)Nd(I)(THF)3]2 (1) was synthesized as we reported
was stirred overnight at room temperature. The precipitate was
removed by centrifugation. The dark red filtrate was concentrated
to approximately 2 mL, and then 9 mL of hexane was layered to
give dark-red crystalline blocks of 3 and brown crystalline prisms
of 4. The well-formed crystals of 3 and 4 are fine distinguished
from each other and were separated manually. The yield of 3 is
about 10~15 mg and that of 4 is about 30~40 mg. 3: Anal. Calcd
for C86H94B2N12Nd2O2P2: C, 60.77; H, 5.57; N, 9.89. Found: C,
59.82; H, 5.72; N: 10.10. The NMR signals are very broad and
not informative. The complex is thermal instable in C6D6. 4: Anal.
Calcd for C54H43B2N12Nd: C, 63.22; H, 4.22; N, 16.38. Found: C,
62.27; H, 4.95; N: 15.98. 1H NMR (400 MHz, C6D6, 25 ◦C) : d =
57.61 (bs, 1H), 34.94 (bs, 2H), 25.44 (bs, 1H), 24.19 (s, 1H), 18.45
(bs, 1H), 17.29 (bs, 1H), 15.21 (bs, 1H), 14.77 (bs, 2H), 13.43 (bs,
1H), 12.68 (bs, 1H), 11.55 (bs, 1H), 9.76 (bs, 2H), 7.36 (bs, 3H),
6.96 (bs, 1H), 5.71 (bs, 2H), 4.65 (bs, 3H), 2.84 (bs, 2H), 2.42 (bs,
2H), 1.62 (bs, 2H), 1.24 (bs, 1H), 0.57 (bs, 4H), -0.48 (bs, 4H),
-1.78 ppm (bs, 4H).
previously.14 KC5Me5,22 KHB(3-Butpz)3 and KHB(3-phenylpz)3
23
1
were prepared according to the literature procedures. H NMR
spectra were recorded on a Varian Mercury 400 spectrometer,
chemical shifts were reported in d (ppm) units with references
to the residual solvent resonance of the deuterated solvents.
Elemental analyses was performed by Analytical Laboratory of
Shanghai Institute of Organic Chemistry.
[(l-PC6H3-2,6-iPr2)(C5Me5)Nd(THF)]2 (2)
KC5Me5 (19 mg, 0.10 mmol) and 1 (69 mg, 0.05 mmol) were mixed
in 4 mL of toluene. The dark red mixture was stirred overnight
at room temperature and filtered. The dark red filtrate was
concentrated to approximately 0.5 mL, and then 3 mL of hexane
was layered to give 2 as a dark red solid (28 mg, 52% yield). Anal.
Calcd for C52H80Nd2O2P2: C, 57.42; H, 7.41. Found: C, 54.48; H,
7.06. The found carbon content is somewhat low, the same was
also reported for some other lanthanide complexes derived from
P-atom-containing ligands.24 The NMR signals are very broad
and not informative. The complex is thermal instable in C6D6.
X-Ray crystallography†
Single crystals suitable for X-ray diffraction analysis were obtained
by slow diffusion of hexane into toluene (complex 2) or THF (com-
plexes 3 and 4) solutions, mounted under argon in thin-walled glass
capillaries that were sealed off. Data collection were performed
on a Bruker SMART diffractometer (graphite-monochromatized
[(l-PC6H3-2,6-iPr2)(TpPh*)Nd(THF)]2 (3) and
[j4(N,N’,N’’,CPh)-TpPh]TpPhNd (4)
KHB(3-phenylpz)3 (57 mg, 0.118 mmol) and
1 (80 mg,
◦
˚
0.059 mmol) were mixed in 7 mL of THF. The dark red mixture
Mo-Ka radiation, 0.71073 A) using w scan mode at 20(2) C. The
Table 1 Crystal data and refinement parameters for 2–4
2
3
4
Empirical formula
Formula weight
Colour, habit
Crystal size/mm
Crystal system
Space group
C52H80Nd2O2P2
1087.58
Red block
0.30 ¥ 0.21 ¥ 0.16
Monoclinic
P21/n
C86H94B2N12Nd2O2P2·C4H8O
1771.88
Red block
C54H43B2N12Nd
1025.86
Brown prism
0.38 ¥ 0.25 ¥ 0.19
Monoclinic
P21/c
0.36 ¥ 0.34 ¥ 0.26
Triclinic
¯
P1
Cell dimensions
˚
a/A
11.3913(10)
18.0366(16)
12.6070(11)
90
97.184(2)
90
2569.9(4)
2
1.405
11.9838(16)
14.2191(19)
14.739(2)
98.263(2)
109.668(2)
109.723(2)
2130.4(5)
1
11.719(2)
18.458(3)
21.719(4)
90
94.824(4)
90
4681.4(15)
4
1.456
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
Density (calc.)/g cm-3
Absorption coeff./mm-1
F(000)
1.381
1.30
910
2.10
1116
1.16
2084
Min./max. transmission
q range/
0.572/0.730
1.98 – 25.10
-13 £ h £ 13
-21 £ k £ 18
-14 £ l £ 15
12923
0.652/0.729
1.86 – 25.10
-14 £ h £ 14
-16 £ k £ 13
-16 £ l £ 17
10502
0.667/0.810
1.88 – 25.10
-13 £ h £ 13
-22 £ k £ 19
-18 £ l £ 25
23265
Index ranges
Reflections collected
Independent reflections (Rint
Reflections with I > 2s(I)
Data/restraints/parameters
Goodness of fit
)
4570 (0.0286)
3961
4570/79/290
1.06
R1 = 0.0347
wR2 = 0.0813
R1 = 0.0415
wR2 = 0.0841
99.8%
7428 (0.0375)
5860
7428/159/550
0.98
R1 = 0.0535
wR2 = 0.1179
R1 = 0.0727
wR2 = 0.1247
97.9%
8312 (0.0633)
6023
8312/720/904
1.07
R1 = 0.0613
wR2 = 0.1323
R1 = 0.0905
wR2 = 0.1416
99.8
R indices [I > 2s(I)]
R indices (all data)
Completeness to q = 25.1◦
-3
˚
Largest diff. peak/hole/e A )
0.71/-0.67
1.43/-0.79
1.51/-1.05
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6886–6890 | 6889
©

SMART program package25 was used to determine the unit-cell
parameters. Data reduction were performed with the SAINT+
program package.26 In all cases, the absorption corrections were
performed semi-empirically from equivalents.27 The structures
were solved by direct methods and refined on F2 by full-matrix
least squares techniques with anisotropic thermal parameters for
non-hydrogen atoms.28 H-atoms, except BH in 3 and 4, were placed
at calculated positions and refined isotropically using the riding
model. Borohydride H-atoms in 3 and 4 were found from difference
Fourier synthesis and refined isotropically. Details on the restrains
applied can be found in the ESII (corresponding sections of CIF
files for complexes 2–4).† Crystal data and refinement parameters
for 2–4 are listed in Table 1.
Organometallics, 2006, 25, 1329; (f) S. T. Liddle, J. McMastera, J. C.
Green and P. L. Arnold, Chem. Commun., 2008, 1747; (g) D. P. Mills,
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant Nos. 20872164 and 20821002), and
Chinese Academy of Sciences.
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6890 | Dalton Trans., 2010, 39, 6886–6890
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