New homoleptic tris(diphosphanylamido) complexes of the lanthanides - Synthesis and structure

Article abstract of DOI:10.1016/j.ica.2005.02.009

New homoleptic diphosphanylamido compounds of the lanthanides, [Ln{N(PPh₂)₂}₃] (Ln = Sm, Gd, Dy), were synthesized and characterized by single crystal X-ray diffraction in the solid state and partly by NMR in solution. In the solid state the complexes solely show a η²-coordination of the {(Ph₂P) ₂N}^- ligand. The dependence of the Ln-N and the Ln-P bond distance on the ion radius of the center metal was investigated.

Full text of DOI:10.1016/j.ica.2005.02.009

Inorganica Chimica Acta 358 (2005) 4172–4176
www.elsevier.com/locate/ica
New homoleptic tris(diphosphanylamido) complexes of
the lanthanides – synthesis and structure
*
Michael T. Gamer, Marcus Rasta¨tter, Peter W. Roesky
Institut fu¨r Chemie, Freie Universita¨t Berlin, Fabeckstraße 34-36, 14195 Berlin, Germany
Received 4 January 2005; accepted 6 February 2005
Available online 14 March 2005
Dedicated to Professor Hubert Schmidtbaur on the occasion of his 70th birthday.
Abstract
New homoleptic diphosphanylamido compounds of the lanthanides, [Ln{N(PPh2)2}3] (Ln = Sm, Gd, Dy), were synthesized and
characterized by single crystal X-ray diffraction in the solid state and partly by NMR in solution. In the solid state the complexes
solely show a g2-coordination of the {(Ph2P)2N}À ligand. The dependence of the Ln–N and the Ln–P bond distance on the ion
radius of the center metal was investigated.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Chelates; Coordination chemistry; Lanthanides; N,P ligands
1. Introduction
ences in terms of correlation of theoretical and experimen-
tal molecular weights as well as polydispersities were
observed depending on the nature of Ln. The single crys-
tal X-ray structures of these complexes solely show a
g2-coordination of the ligand via the nitrogen and one
phosphorous atom. In solution a dynamic behavior of
the ligand is observed, which is caused by the rapid ex-
change of the two different phosphorous atoms. Thus,
the coordination of phosphorous atom to the metal center
is weak and the corresponding bond length is rather long.
So far, we have studied only a limited number of homolep-
tic compounds [Ln{N(PPh2)2}3]. As a result, we are now
interested to see if the Ln–P bond length linearly decreases
with decreasing ion radius of the lanthanide atom as it is
observed in normal r-bonds or if the influence of the crys-
tal packing is superior. Therefore, we wanted to establish
more than the previous reported four data points. Herein,
we report the synthesis and structure of some new homo-
leptic diphosphanylamide complexes of the lanthanides
and establish the relation of the Ln–P bond length to
the ion radius of the center metal.
Recently, there has been a significant research effort in
d- and f-transition metal chemistry to find as an alterna-
tive to the well established cyclopentadienyl ligand [1]
new ancillary ligands for stabilizing high reactive metal
centers. In these regards one approach among others is
the use of phosphines with P–N bonds [2]. Recently, we
have introduced the well known monophosphanylamide,
(Ph2PNPh)À [3] and diphosphanylamide, {(Ph2P)2N}À
[4–6], as ligands in lanthanide chemistry. In dependence
of the steric demand of the ligand either metallate com-
plexes of composition [Li(THF)4][(Ph2PNPh)4Ln]
(Ln = Y, Yb, Lu) [3] or the homoleptic compounds
[Ln{N(PPh2)2}3] (Ln = Y, La, Nd, Er) [4] can be ob-
tained. The later complexes were used as catalysts for
the polymerization of e-caprolactone. Significant differ-
*
Corresponding author. Tel.: +49 308 3854004; fax: +49 308
3852440.
E-mail address: roesky@chemie.fu-berlin.de (P.W. Roesky).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.02.009

M.T. Gamer et al. / Inorganica Chimica Acta 358 (2005) 4172–4176
4173
2. Results and discussion
Reaction of the previously described potassium com-
pound [K(THF)nN(PPh2)2] [4] (1) with anhydrous lantha-
nide trichlorides in a 3:1 molar ratio in THF or reaction of
the homoleptic bis(trimethylsilyl)amides of the lantha-
nides, ([Ln{N(SiMe3)2}3]) [7], with three equivalents of
(Ph2P)2NH in boiling toluene followed by crystallization
from toluene afforded the homoleptic diphosphinoamide
complexes [Ln{N(PPh2)2}3] (Ln = Sm (2a), Gd (2b), Dy
(2c)) as large crystals in good yields (Scheme 1). The
samarium compound 2a was characterized by 1H,
31P{1H} NMR spectroscopy and elemental analysis,
whereas for all other new compounds IR spectra and ele-
mental analysis were obtained. The solid-state structures
of all new compounds were established by single crystal
X-ray diffraction. The NMR spectra of the weekly para-
magnetic samarium complex 2a were investigated. In
1
the H spectrum three well resolved sets of signals for
Fig. 1. Perspective ORTEP view of the molecular structure of 2a.
Thermal ellipsoids are drawn to encompass 30% probability. Selected
bond lengths [pm] or angles [ꢁ] (also given for isostructural 2b–2c): N1–
P1 168.3(3), N1–P2 171.4(2), N2–P3 166.3(3), N2–P4 172.3(3), N3–P5
167.4(3), N3–P6 172.3(2), N1–Sm 234.3(2), N2–Sm 232.7(2), N3–Sm
236.1(2), P1–Sm 286.48(8), P3–Sm 286.41(7), P5–Sm 285.51(8); P1–
N1–P2 121.00(14), P3–N2–P4 124.43(14), P5–N3–P6 118.18(14), P1–
N1–Sm 89.16(10), P2–N1–Sm 149.75(14), P4–N2–Sm 145.24(13),
P5–N3–Sm 88.37(9), P6–N3–Sm 151.67(14), N1–Sm–P1 35.98(6),
N2–Sm–P3 35.50(6), N3–Sm–P5 35.89(6). 2b: N1–P1 167.7(2), N1–
P2 171.4(2), N2–P3 166.5(2), N2–P4 171.2(2), N3–P5 167.7(2), N3–P6
172.1(2), N1–Gd 231.4(2), N2–Gd 230.7(2), N3–Gd 232.8(2), P1–Gd
282.12(7), P3–Gd 282.56(7), P5–Gd 281.61(7); P1–N1–P2 120.85(14),
P3–N2–P(4) 124.79(14), P5–N3–P6 117.35(13), P1–N1–Gd 88.48(9),
P2–N1–Gd 150.53(13), P3–N2–Gd 89.19(10), P4–N2–Gd 145.92(13),
P5–N3–Gd 87.77(9), P6–N3–Gd 153.00(13), N1–Gd–P1 36.45(6), N2–
Gd–P3 36.10(6), P5–Gd–P3 98.62(2). 2c: N1–P1 168.3(2), N1–P2
171.3(2), N2–P3 167.1(2), N2–P4 171.3(2), N3–P5 168.1(2), N3–P6
172.5(2), N1–Dy 228.3(2), N2–Dy 227.3(2), N3–Dy 229.0(2), P1–Dy
279.48(6), P3–Dy 279.75(6), P5–Dy 279.01(6); P1–N1–P2 120.19(12),
P3–N2–P4 124.02(12), P5–N3–P6 116.61(11), P1–N1–Dy 88.27(8),
P2–N1–Dy 151.44(11), P3–N2–Dy 89.01(8), P4–N2–Dy 146.86(10),
P5–N3–Dy 87.87(8), P6–N3–Dy 153.70(10), N1–Dy–P1 37.01(5),
N2–Dy–P3 36.67(5), N3–Dy–P5 37.02(5).
the phenyl protons are observed at d 6.87, 7.07, and
7.45 ppm. Very characteristic is also the 31P{1H} NMR
spectrum. Only one signal for all phosphorous atoms is
observed, showing that the phosphorous atoms in each
case are chemically equivalent in solution. In contrast to
the diamagnetic compounds [Y{N(PPh2)2}3] (d 42.0
ppm) and [La{N(PPh2)2}3] (d 44.6 ppm) the 31P{1H}
NMR signal of compound 2a is strongly shifted upfield
(d À62.7 ppm).
Due to the similar ion radii of the lanthanides used,
the single crystal X-ray structures of 2a–2c are isostruc-
tural to each other and to the previously reported com-
pounds [Ln{N(PPh2)2}3] (Ln = Y, La, Nd, Er). As a
representative example, the structure of 2a is shown in
ꢀ
Fig. 1. 2a–2c crystallize in the trigonal space group P1
having two molecules of 2 and two molecules of toluene
in the unit cell. Three symmetrically chelating (g2)
{(Ph2P)2N}À ligands are coordinated to the lanthanide
atom with the six coordinate LnN3P3 geometry closely
trigonal prismatic (Fig. 1). As observed for other lantha-
PPh2
N
THF
- 3 KCl
Ln = Gd, Dy
3
P
P
+ LnCl3
Ph2P
N
PPh2
PPh2
N
Ln
K(THF)
n
N
Ph2P
Ph2P
Ln = Sm (2a), Gd (2b), Dy (2c)
3
P
P
toluene
+ [Ln{N(SiMe3)2}3]
Ln = Sm
N
H
- 3 HN(SiMe3)2
Scheme 1.

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M.T. Gamer et al. / Inorganica Chimica Acta 358 (2005) 4172–4176
nide complexes having the {(Ph2P)2N}À ligand in the
coordination sphere such as [{(Ph2P)2N}LnCl2(THF)3]
[6] and [{(Ph2P)2N}2Yb(C5Me5)] [8] the diphosphanyl-
amide ligand in 2a–2c is g2-coordinated via the nitrogen
and one phosphorous atom. Thus, one of the phospho-
rous atoms of the ligand binds to the lanthanide center
whereas the other phosphorous atom is bent away.
The average Ln–N1 and Ln–P1 bond lengths are
234.4(2) and 286.13(8) pm (2a), 231.6(2) and
282.10(7) pm (2b), and 228.2(2) and 279.41 pm (2c).
The free electron pair of the nonbonded phosphorous
atom points away from the lanthanide center. In
Fig. 2 a chart of the average Ln–N and Ln–P1 bond dis-
tances versus the effective ionic radii after Shannon [9]
for coordination number six is shown. The average
Ln–N distances increases as expected with increasing
ion radius of the center metal in a linear fashion. A sim-
ilar dependency is observed for the average Ln–P1 bond
distance. Even though the Ln–P interactions are weak
and a dynamic rearrangement is observed in solution
(see above), the Ln–P bond distances do not deviate
from the normal behavior observed.
The average P–N–P angles within the g2-
{(Ph2P)2N}À ligand are 121.20(14)ꢁ (2a), 121.00(14)ꢁ
(2b), and 120.27(12)ꢁ (2c). The deviation from this
average value is significant. For example in compound
2a the angle P3–N2–P4 (124.43(14)ꢁ) is 6.25ꢁ larger
than the angle P5–N3–P6 (118.18(14)ꢁ). Within the li-
gand the P–N bond distance vary. The phosphorous
atom, which binds to the lanthanide metal is slightly
closer located to the nitrogen atom (av. N–Pbonding
167.3(3) pm (2a), 167.33(3) pm (2b), 167.83 pm (2c)
and av. N–Pnonbonding 172.0(2) pm (2a), 171.57(2) pm
(2b), 171.7(2) pm (2c)).
3. Summary
In summary, we have synthesized a number of new
homoleptic diphosphanylamido lanthanide compounds
of the general composition [Ln{N(PPh2)2}3]. The single
crystal X-ray structures of these complexes solely show a
g2-coordination of the ligand, in which only one of the
phosphorus atoms coordinates to the metal center. As
seen by the dynamic behavior of the complex in solution
the Ln–P interaction is weak. In the solid state a long
Ln–P distance is observed. However, the Ln–P bond dis-
tances and the Ln–N bond distance linearly decrease
with decreasing ionic radii.
4. Experimental
4.1. General
All manipulations of air-sensitive materials were per-
formed with the rigorous exclusion of oxygen and mois-
ture in flame-dried Schlenk-type glassware either on a
dual manifold Schlenk line, interfaced to a high vacuum
(10À4 torr) line, or in an argon-filled M. Braun glove
box. THF was predried over Na wire and distilled under
nitrogen from K and benzophenone ketyl prior to use.
Hydrocarbon solvents (toluene and n-pentane) were dis-
tilled under nitrogen from LiAlH4. All solvents for vac-
uum line manipulations were stored in vacuo over
LiAlH4 in resealable flasks. Deuterated solvents were
obtained from Chemotrade Chemiehandelsgesellschaft
mbH (all P99 atom% D) and were degassed, dried,
and stored in vacuo over Na/K alloy in resealable flasks.
300
av. Ln-N1
av. Ln-P1
La
280
260
240
220
200
Nd
Sm
Gd
Dy
Y
Er
104
102
100
98
96
94
92
90
88
effective ionic radii (CN: 6) / pm
Fig. 2. Chart of the effective ionic radii after Shannon [9] (CN: 6) versus the Ln–N, Ln–P1 bond distances of [Ln{N(PPh2)2}3] [4].

M.T. Gamer et al. / Inorganica Chimica Acta 358 (2005) 4172–4176
4175
NMR spectra were recorded on JNM-LA 400 FT-NMR
spectrometer. Chemical shifts are referenced to internal
solvent resonances and are reported relative to tetra-
methylsilane and 85% phosphoric acid (31P NMR),
respectively. IR spectra were obtained on a Shimadzu
FTIR-8400s. LnCl3 [10], [Ln{N(SiMe3)2}3] [7] and
[K(THF)nN(PPh2)2] (n = 1.25, 1.5) [4] were prepared
according to literature procedures.
2a Æ toluene: Stoe IPDS diffractometer (Ag Ka radia-
tion); T = 200(2) K; data collection and refinement:
ꢀ
SHELXS-97 [11], SHELXL-97 [12]; triclinic, space group P1
(No. 2); lattice constants a = 1380.02(10), b = 1383.
92(9), c = 2086.69(13) pm, a = 91.085(8)ꢁ, b = 97.
883(8)ꢁ, c = 118.235(7)ꢁ, V = 3461.8(4) · 106 pm3, Z =
2; l (Ag Ka) = 0.554 mmÀ1; hmax = 24.08; 20744 (Rint
=
0.0511) unique reflections measured, of which 16612
were considered observed with I > 2r(I); maximum
residual electron density 1.825 and À1.076 e/AÀ3; 791
parameters (all nonhydrogen atoms except C33–C35
and C79 were calculated anisotropically; the positions
of the H atoms were calculated for idealized positions)
R1 = 0.0425; wR2 = 0.1040.
4.2. [Sm{N(PPh2)2}3] (2a)
20 ml of toluene was condensed at À196 ꢁC onto a mix-
ture of 270 mg (0.5 mmol) of [Sm{N(SiMe3)2}3] and
650 mg (1.5 mmol) of (Ph2P)2NH. The mixture was re-
fluxed for 6 h, filtered and the solvent taken off in vacuo.
The product was recrystallized from toluene. Yield
564 mg (81%), yellow crystals. 1H NMR (d8-THF,
2b Æ toluene: Stoe IPDS 2T diffractometer (Mo Ka
radiation); T = 200(2) K; data collection and refinement:
ꢀ
SHELXS-97 [11], SHELXL-97 [12]; triclinic, space group P1
(No. 2); lattice constants a = 1365.59(5), b = 1372.38(5),
3
250 MHz, 25 ꢁC): d 6.87 (dd, 24H, m-Ph, J(H,H) = 7.3
and 7.5 Hz), 7.07 (t, 12H, p-Ph, J(H,H) = 7.3 Hz), 7.45
3
c = 2078.37(7) pm,
a = 90.982(3)ꢁ,
b = 98.051(3)ꢁ,
3
(d, 24H, o-Ph, J(H,H) = 7.5 Hz). 31P{1H} NMR (d8-
c = 118.236(2)ꢁ, V = 3382.2(2) · 106 pm3, Z = 2; l (Mo
Ka) = 1.169 mmÀ1; hmax = 29.26; 18199 (Rint = 0.0697)
unique reflections measured, of which 14998 were consid-
ered observed with I > 2r(I); maximum residual electron
density 1.825 and À1.654 e/AÀ3; À1.386 parameters (all
nonhydrogen atoms except C33–C35 and C79 were calcu-
lated anisotropically; the positions of the H atoms were
calculated for idealized positions) R1 = 0.0391;
wR2 = 0.0833.
THF, 101.3 MHz, 25 ꢁC): d À62.7 (br). Anal. Calc. for
C79H68N3P6Sm (2a Æ toluene, 1395.63): C, 67.99; H,
4.91; N, 3.01. Found: C, 67.63; H, 4.92; N, 3.04%.
4.3. [Ln{N(PPh2)2}3] (Ln = Gd (2b), Dy (2c))
4.3.1. General procedure
20 ml of THF was condensed at À196 ꢁC onto a mix-
ture of 750 mg (1.5 mmol) of 1 and 0.5 mmol of LnCl3
and the mixture was stirred for 24 h at room tempera-
ture. The solvent was then evaporated in vacuo and tol-
uene condensed onto the mixture. The mixture was
filtered, and the solvent taken off in vacuo. The product
was recrystallized from toluene.
2b: Yield: 370 mg (79%). IR (KBr [cmÀ1]): 3063 (m,
mC@C–H), 2999 (w, mC–H), 1552 (w, mC@C), 1477
(m), 1431 (s), 1093 (m), 1025 (w, mPC), 997 (w), 950
(s), 919 (s), 907 (s), 738 (s), 710 (s), 693 (s). Anal. Calc.
for C79H68GdN3P6 (2b Æ toluene) (1402.52): C, 67.65;
H, 4.89; N 3.00. Found: C, 67.61; H, 4.92; N, 2.88%.
2c: Yield: 350 mg (75%). IR (KBr [cmÀ1]): 3051 (m,
mC@C–H), 2999 (w, mC–H), 1583 (w, mC@C), 1477
(m), 1431 (s), 1094 (m), 1025 (w, mPC), 996 (w), 944(s),
918 (s), 905 (s), 738 (s), 711 (s), 693 (s). Anal. Calc. for
C79H68DyN3P6 (2c Æ toluene) (1407.77): C, 67.40; H,
4.87; N, 2.98. Found: C, 67.31; H, 4.78; N, 2.96%.
2c Æ toluene: Stoe IPDS 2T diffractometer (Mo Ka
radiation); T = 200(2) K; data collection and refinement:
ꢀ
SHELXS-97 [11], SHELXL-97 [12]; triclinic, space group P1
(No. 2); lattice constants a = 1365.45(6), b = 1371.44(7),
c = 2081.49(10) pm, a = 90.932(4)ꢁ, b = 98.021(4)ꢁ,
c = 118.229(3)ꢁ, V = 3385.5(3) · 106 pm3, Z = 2; l (Mo
Ka) = 1.292 mmÀ1; hmax = 29.22; 17962 (Rint = 0.0381)
unique reflections measured, of which 14802 were con-
sidered observed with I > 2r(I); maximum residual elec-
tron density 1.825 and 1.585 e/AÀ3; À0.926 parameters
(all nonhydrogen atoms except C33–C35 and C79 were
calculated anisotropically; the positions of the H atoms
were calculated for idealized positions) R1 = 0.0309;
wR2 = 0.0681.
5. Supplementary material
4.4. X-ray crystallographic studies of 2a–2c
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Centre as a supplementary publication no. CCDC-
259352 (2a), 259286 (2b), and 259287 (2c). Copies of
the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB21EZ, UK
(fax: +(44)1223-336-033; email: deposit@ccdc.cam.
ac.uk).
Crystals of 2a–2c were grown from a toluene solu-
tion. A suitable crystal was covered in mineral oil
(Aldrich) and mounted on a glass fiber. The crystal
was transferred directly to the À73 ꢁC cold stream of a
STOE IPDS or a STOE IPDS 2T diffractometer. Subse-
quent computations were carried out on an Intel Pen-
tium III or IV Personal Computer.

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M.T. Gamer et al. / Inorganica Chimica Acta 358 (2005) 4172–4176
[3] (a) T.G. Wetzel, S. Dehnen, P.W. Roesky, Angew. Chem. 111
(1999) 1155;
Acknowledgement
(b) T.G. Wetzel, S. Dehnen, P.W. Roesky, Angew. Chem., Int.
Ed. 38 (1999) 1086;
This work was supported by the Deutsche Fors-
chungsgemeinschaft (Graduiertenkolleg: Synthetische,
mechanistische und reaktionstechnische Aspekte von
Metallkatalysatoren) and the Fonds der Chemischen
Industrie.
(c) S. Wingerter, M. Pfeiffer, F. Baier, T. Stey, D. Stalke, Z.
Anorg. Allg. Chem. 626 (2000) 1121.
[4] P.W. Roesky, M.T. Gamer, M. Puchner, A. Greiner, Chem. Eur.
J. 8 (2002) 5265.
[5] M.T. Gamer, G. Canseco-Melchor, P.W. Roesky, Z. Anorg. Allg.
Chem. 629 (2003) 2113.
[6] P.W. Roesky, M.T. Gamer, N. Marinos, Chem. Eur. J. 10 (2004)
3537.
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