Syntheses and structures of calcium and ytterbium bis(diphosphanylamido) complexes

Article abstract of DOI:10.1016/j.ica.2006.03.016

Bis(diphosphanylamido) complexes of calcium and ytterbium, [{(Ph₂P)₂N}₂M(THF)₃] (M = Ca (1), Yb (2)), have been prepared by reaction of [K(THF)_nN(PPh₂)₂] (n = 1.25, 1.5) and MI₂. The single crystal X-ray structures of compounds 1 and 2 always show a η²-coordination of the ligand via the nitrogen and one phosphorus atom. In solution a dynamic behavior of the ligand is observed, which is caused by the rapid exchange of the two different phosphorus atoms.

Full text of DOI:10.1016/j.ica.2006.03.016

Inorganica Chimica Acta 359 (2006) 4765–4768
www.elsevier.com/locate/ica
Syntheses and structures of calcium and
ytterbium bis(diphosphanylamido) complexes
*
Tarun K. Panda, Michael T. Gamer, Peter W. Roesky
Institut fu¨r Chemie und Biochemie, Freie Universita¨t Berlin, Fabeckstraße 34-36, 14195 Berlin, Germany
Received 31 January 2006; accepted 16 March 2006
Available online 24 March 2006
Dedicated to Professor Dr. Dr. h.c. Mult. Wolfgang A. Herrmann.
Abstract
Bis(diphosphanylamido) complexes of calcium and ytterbium, [{(Ph2P)2N}2M(THF)3] (M =Ca (1), Yb (2)), have been prepared by
reaction of [K(THF)nN(PPh2)2] (n = 1.25, 1.5) and MI2. The single crystal X-ray structures of compounds 1 and 2 always show a g2-
coordination of the ligand via the nitrogen and one phosphorus atom. In solution a dynamic behavior of the ligand is observed, which
is caused by the rapid exchange of the two different phosphorus atoms.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Calcium; Chelates; Coordination chemistry; Ytterbium; N,P ligands
1. Introduction
dination of the ligand via the nitrogen and one phosphorus
atom. In solution a dynamic behavior of the ligand is
observed, which is caused by the rapid exchange of the
two different phosphorus atoms. Thus, the coordination
of phosphorus atom to the metal center is weak and the
corresponding bond length is rather long.
Recently, there has been a significant research effort in d-
and f-transition metal chemistry to find an alternative to the
well established cyclopentadienyl ligand [1] for stabilizing
high reactive metal centers. In these regards, one approach
among others is the use of phosphines with P–N bonds [2].
In this context, we have introduced the well known mono-
phosphanylamide, (Ph2PNPh)À [3], and diphosphanyla-
mide, {(Ph2P)2N}À [4–6], as ligands in trivalent lanthanide
chemistry. In dependence of the steric demand of the ligand,
either metallate complexes of composition [Li(THF)4][(Ph2-
PNPh)4Ln] (Ln = Y, Yb, Lu) [3] or the homoleptic com-
pounds [Ln{N(PPh2)2}3] (Ln = Y, La, Nd, Er) [4] can be
obtained. The later complexes were used as catalysts for
the polymerization of e-caprolactone. Significant differ-
ences in terms of correlation of theoretical and experimental
molecular weights, as well as polydispersities, were
observed depending on the nature of Ln. The single crystal
X-ray structures of these complexes solely show a g2-coor-
Recently, we also introduced the {(Ph2P)2N}À ligand
into divalent lanthanide and heavy alkaline earth metal
chemistry [7,8]. Whereas to the best of our knowledge,
the {(Ph2P)2N}À ligand was not previously used in group
2 chemistry, the oxidized version, {(Ph2PO)2N}À, was
taken very recently to synthesize complexes of composition
[M{(OPPh2)2N]2 (M =Sr, Ba) [9]. It is well established that
the reactivity and coordination behavior of the divalent
lanthanide metals and the heavier alkaline earth metals
are somewhat related [10]. This similarity in coordination
chemistry originates from the similar ion radii (for CN 6
(pm): Ca2+ 100, Yb2+ 102, Sr2+ 118, Eu2+ 117, Ba2+ 135)
[11]. Bis(diphosphanylamido) complexes of strontium and
europium, [{(Ph2P)2N}2M(THF)3] (M = Sr, Eu), were
obtained by reaction of [K(THF)nN(PPh2)2] (n = 1.25,
1.5) and MI2. The single crystal X-ray structures of these
compounds again show a g2-coordination of the ligand
*
Corresponding author. Tel.: +49 83854004; fax: +49 3083852440.
E-mail address: roesky@chemie.fu-berlin.de (P.W. Roesky).
0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.03.016

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T.K. Panda et al. / Inorganica Chimica Acta 359 (2006) 4765–4768
via the nitrogen and one phosphorus atom. As a result of
the larger ion radius treatment of [K(THF)nN(PPh2)2] with
BaI2 leads to the coordination polymer [{(Ph2P)2N}2-
Ba(THF){(Ph2P)2N}K]n. In the solid state, the infinite
chain is formally held together by p-coordination of the
phenyl rings to the potassium atoms.
Besides the strontium, barium, and europium com-
plexes, now we are interested in synthesizing bis(diphosph-
anylamido) derivatives of the remaining two metals in the
series of divalent lanthanide metals and the heavier alkaline
earth metals, such as calcium and ytterbium.
given in Table 1. As a representative example the solid
structure of compound 1 is shown in Fig. 1. Compound
1 crystallizes in the space group P21/n having four mole-
cules of 1 in the unit cell, whereas compound 2 crystallizes
in the space group C2/c having eight molecules of 2 and 12
molecules of THF in the unit cell. Even more surprising to
us is the fact that the structure of compound 1 is isostruc-
tural to the previously reported europium compound
[{(Ph2P)2N}2Eu(THF)3] [7].
In both compounds 1 and 2, two chelating g2-
{(Ph2P)2N}À ligands and three molecules of THF are
coordinated to the metal atom, resulting in a sevenfold
coordinated metal atom. The {(Ph2P)2N}À ligands coordi-
nate via the nitrogen and one phosphorus atom. In the
coordination polyhedron, the {(Ph2P)2N}À ligands are
bend to each other, thus P1 is opposite to N2. As observed
for the analogous strontium and europium compounds [4],
the bond distances between these two atoms and the metal
atom are longer than the corresponding bond distances of
2. Results and discussion
Reaction of the previously described potassium com-
pound [K(THF)nN(PPh2)2] [4] with anhydrous calcium
diiodide and YbI2(THF)2, respectively, in THF in a 2:1
molar ratio, followed by crystallization from THF/n-pen-
tane (1:2), led selectively to products of composition
[{(Ph2P)2N}2M(THF)3] (M = Ca (1), Yb (2)) in good
yields (Scheme 1). The new complexes have been character-
ized by standard analytical/spectroscopic techniques and
the solid-state structures were established by single crystal
Table 1
Selected bond lengths (pm) and bond angles (°) of [{(Ph2P)2N}2Ca(THF)3]
(1) and [{(Ph2P)2N}2Yb(THF)3] (2)
1
X-ray diffraction. The H and 31P{H} NMR spectra of
1
2
1
both complexes were investigated. The H NMR spectra
˚
Bond lengths (A)
Ca–N1
Ca–N2
Ca–P1
Ca–P3
Ca–O1
Ca–O2
Ca–O3
P1–N1
P2–N1
are not very characteristic. Besides the THF signals, two
multiplets are observed in the aromatic region. In contrast,
the 31P{1H} NMR spectra are very characteristic. Only one
signal for all phosphorus atoms of each compound is
observed at room temperature (d 43.2 ppm (1) and d
44.9 ppm (2)), showing that the phosphorus atoms in each
case are chemically equivalent in solution. A similar
dynamic behavior and chemical shift is seen in
[{(Ph2P)2N}2Sr(THF)3] (d 48.0 ppm). Since the solid state
structures of 1 and 2 (see below) show two non equivalent
phosphorus atoms of each ligand, a dynamic behavior in
solution is anticipated.
Even Ca(II) and Yb(II) have almost the same ionic radii,
and the solid state structures of compounds 1 and 2 look
alike; they crystallize in different unit cells and thus the
respective bond distances and bond angles between 1 and
2 vary a bit. Selected bond lengths and bond angles are
245.5(3)
249.1(3)
294.43(12)
288.09(13)
239.0(3)
241.7(8)a
245.2(3)
166.3(3)
169.5(3)
163.7(4)
170.2(3)
Yb–N1
Yb–N2
Yb–P1
Yb–P3
Yb–O1
Yb–O2
Yb–O3
P1–N1
P2–N1
P3–N2
P4–N2
242.9(3)
247.8(3)
302.29(10)
295.62(10)
246.7(3)
242.0(3)
249.3(3)
166.8(3)
169.8(3)
166.4(3)
169.3(3)
P3–N2
P4–N2
Bond angles (°)
N1–Ca–N2
N1–Ca–P1
N1–Ca–P3
N1–Ca–O1
N1–Ca–O2
N1–Ca–O3
N2–Ca–P1
N2–Ca–P3
N2–Ca–O1
N2–Ca–O2
N2–Ca–O3
O1–Ca–O2
O1–Ca–O3
O2–Ca–O3
O1–Ca–P1
O2–Ca–P1
O3–Ca–P1
O1–Ca–P3
O2–Ca–P3
O3–Ca–P3
P1–Ca–P3
P1–N1–P2
P3–N2–P4
a
134.78(11)
34.38(7)
101.01(8)
96.46(10)
90.1(3)a
125.15(10)
168.01(9)
34.52(8)
94.91(11)
88.2(2)
99.66(11)
167.0(2)a
82.50(10)
84.8(2)
90.77(8)
87.0(2)a
90.77(8)
93.79(8)
95.7(2)a
133.83(8)
135.40(4)
118.8(2)
123.0(2)
N1–Yb–N2
N1–Yb–P1
N1–Yb–P3
N1–Yb–O1
N1–Yb–O2
N1–Yb–O3
N2–Yb–P1
N2–Yb–P3
N2–Yb–O1
N2–Yb–O2
N2–Yb–O3
O1–Yb–O2
O1–Yb–O3
O2–Yb–O3
O1–Yb–P1
O2–Yb–P1
O3–Yb–P1
O1–Yb–P3
O2–Yb–P3
O3–Yb–P3
P1–Yb–P3
P1–N1–P2
P3–N2–P4
133.81(10)
33.44(8)
100.37(8)
94.36(11)
95.11(11)
117.65(10)
166.17(7)
34.25(7)
94.26(10)
91.04(10)
108.53(10)
160.96(10)
80.04(11)
80.93(11)
83.58(7)
95.40(8)
95.40(8)
90.79(7)
103.67(7)
141.31(8)
131.96(3)
120.89(18)
121.88(18)
P
N
P
O
O
THF
- 2 KI
P
P
+ MI2
2
M
P
N
M = Ca, Yb
O
N
K(THF)
P
n
M = Ca (1), Yb (2)
Scheme 1.
Average value of two disordered positions.

T.K. Panda et al. / Inorganica Chimica Acta 359 (2006) 4765–4768
4767
3. Summary
In summary, we have synthesized bis(diphosphanyl-
amide) complexes of calcium and ytterbium of the general
composition [{(Ph2P)2N}2M(THF)3]. The single crystal X-
ray structures of these complexes solely show a g2-coordi-
nation of the ligand, in which only one of the phosphorus
atoms coordinates to the metal center. In solution a
dynamic behavior of the ligand is observed, which is caused
by the rapid exchange of the two different phosphorus
atoms.
4. Experimental
4.1. General
All manipulations of air-sensitive materials were per-
formed with the rigorous exclusion of oxygen and mois-
ture in a 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. N-
pentane was distilled under nitrogen from LiAlH4. All
solvents for vacuum line manipulations were stored in
vacuo over LiAlH4 in resealable flasks. Deuterated sol-
vents were obtained from Chemotrade Chemiehandelsge-
sellschaft mbH (all P99 at.% D) and were degassed,
dried, and stored in vacuo over Na/K alloy in resealable
flasks. The NMR spectra were recorded on JNM-LA 400
FT-NMR spectrometer. Chemical shifts are referenced to
internal solvent resonances and are reported relative to
tetramethylsilane and 85% phosphoric acid (31P NMR),
respectively. Elemental analyses were carried out with
an Elementar vario EL. YbI2(THF)2 [14], and [K(THF)n-
N(PPh2)2] (n = 1.25, 1.5) [4] were prepared according to the
literature procedures. CaI2 was purchased from Aldrich
Inc.
Fig. 1. Solid-state structure of 1 showing the atom labeling scheme,
omitting hydrogen atoms.
P3 and N1 (M–N1 245.5(3) pm (1), 242.9(3) pm (2), and
M–N2 249.1(3) pm (1), 247.8(3) pm (2) and M–P1
294.43(12) pm (1), 302.29(10) pm (2), and M–P3
288.09(13) pm (1), 295.62(10) pm (2)). In compounds 1
and 2, the THF molecules which are located in one plane
are not symmetrically arranged, resulting in a significantly
different O–M–O bond angles; e.g., in 2 O1–Yb–O2
160.96(10)°,
O1–Yb–O3
80.04(11)°,
O2–Yb–O3
80.93(11)°. The M–O bond distances are also non-equiva-
lent. It is obvious that O3, which is located in the most
crowded environment, is also most remote from the metal
center; e.g., the Yb–O distances in complex 2 are Yb–O1
246.7(3) pm, Yb–O2 242.0(3) pm, and Yb–O3 249.3(3)
pm. The Ca–N bond distances (Ca–N1 245.5(3) pm, Ca–
N2 249.1(3) pm) of compound 1 are rather long (e.g.,
233.1(6) pm in [{CH(PPh2N-Mes)2}CaN(SiMe3)2] [12]
and 228.1(9) pm in [(Me3Si)2NCa{l-P(H)SiiPr3}3Ca(thp)3]
(thp = tetrahydropyran) [13]), whereas the Ca–P bond
lengths are in the expected range [13]. The Yb–N and
4.1.1. [{(Ph2P)2N}2Ca(THF)3] (1)
Yb–P bond distances of compound
2
(Yb–N1
20 mL of THF was condensed at À196 °C onto a mix-
ture of 147 mg (0.5 mmol) of CaI2 and 500 mg (1 mmol)
of [K(THF)nN(PPh2)2], and the mixture was stirred for
20 h at room temperature. The mixture was filtered and
the filtrate was concentrated (5 mL). Pentane (10 mL)
was layered on the top of the THF solution. Colorless crys-
tals were obtained after one day.
242.9(3) pm, Yb–N2 247.8(3) pm, Yb–P1 302.29(10) pm,
Yb–P3 295.62(10) pm) are in the range of the mono(di-
phosphanylamido) [{CH(PPh2NSiMe3)2}Yb{N(PPh2)2}Cl]
(Yb–N 241.2(3) pm and Yb–P 294.96(11) pm), which were
recently published by us [8].
Values for the N–M–P bite angles (N1–M–P1 34.38(7)°
(1), 33.44(8)° (2), and N2–M–P3 34.52(8)° (1) and N2–Yb–
P3 34.25(7)° (2)) show that the angles are rather small.
Whereas one of the phosphorus atoms of each ligand binds
to the metal center, the other phosphorus atom is bent
away. The P–N–P angles within the ligand are P1–N1–P2
118.8(2)° (1), 120.89(18)° (2) and P3–N2–P4 123.0(2)° (1),
121.88(18)° (2). Within the ligand the P–N bond distance
varies slightly. The phosphorus atom which binds to the
metal atom is always a bit closer located to the nitrogen
atom.
Yield: 280 mg (54%). 1H NMR (C6D6, 400 MHz, 20 °C):
d 1.37 (br, 12H, THF), 3.61 (br, 12H, THF), 7.01–7.11 (m,
24H, Ph), 7.32–7.35 (m, 16H, Ph). 31P{1H} NMR (C6D6,
161.7 MHz, 20 °C): d 43.2. Anal. Calc. for C60H64Ca-
N2O3P4 (1025.16): C, 70.30; H, 6.29; N, 2.73. Found: C,
69.72; H, 6.09; N, 2.02%.
4.1.2. [{(Ph2P)2N}2Yb(THF)3] (2)
20 mL of THF was condensed at À196 °C onto a mix-
ture of 286 mg (0.5 mmol) of [YbI2(THF)2], and 500 mg

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T.K. Panda et al. / Inorganica Chimica Acta 359 (2006) 4765–4768
(1 mmol) of [K(THF)nN(PPh2)2] and the mixture was stir-
red for 20 h at room temperature. The mixture was filtered
and the filtrate was concentrated (5 mL). Pentane (10 mL)
was layered on the top of the THF solution. Red crystals
were obtained after one day.
Appendix A. Supplementary data
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as a sup-
plementary publication no. CCDC-294422–294423. Copies
of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk). Sup-
plementary data associated with this article can be found,
in the online version, at doi:10.1016/j.ica.2006.03.016.
Yield: 310 mg (53%). 1H NMR (C6D6, 400 MHz, 20 °C):
d 1.24 (br, 12H, THF), 3.45 (br, 12H, THF), 6.94–7.11 (m,
24H, Ph), 7.84 (br, 16H, Ph). 31P{1H} NMR (C6D6,
161.7 MHz, 20 °C): d 44.9. Anal. Calc. for C60H64N2O3-
P4Yb (1158.1): C, 62.23; H, 5.57; N, 2.42. Found: C,
61.92; H, 5.26; N, 2.27%.
4.2. X-ray crystallographic studies of 1 and 2
References
[1] Reviews: (a) F.T. Edelmann, Angew. Chem. 107 (1995) 2647;
(b) F.T. Edelmann, Angew. Chem. Int. Ed. 34 (1995) 2466;
(c) F.T. Edelmann, D.M.M. Freckmann, H. Schumann, Chem. Rev.
102 (2002) 1851.
[2] M.S. Balakrishna, V. Sreenivasa Reddy, S.S. Krishnamurthy, J.F.
Nixon, J.C.T.R. Burckett, St. Laurent, Coord. Chem. Rev. 129
(1994) 1.
Crystals of 1 and 2 were grown from THF/n-pentane
(1:2). 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 2T diffractometer. Subsequent computations
were carried out on an Intel Pentium IV Personal
Computer.
1. (Mo Ka radiation); data collection and refinement:
SHELXS-97 [15], SHELXL-97 [16]; monoclinic, space group
P21/n (no. 14); lattice constants a = 1091.26(6) pm,
[3] (a) T.G. Wetzel, S. Dehnen, P.W. Roesky, Angew. Chem. 111 (1999)
1155;
(b) T.G. Wetzel, S. Dehnen, P.W. Roesky, Angew. Chem. Int. Ed. 38
(1999) 1086;
(c) S. Wingerter, M. Pfeiffer, F. Baier, T. Stey, D. Stalke, Z. Anorg.
Allg. Chem. 626 (2000) 1121.
b = 1234.98(5) pm,
V = 5363.0(5) 106 pm3, Z = 4; l(Mo Ka) = 0.283 mmÀ1
max. = 25.00; 9442 (Rint = 0.0773) unique reflections mea-
c = 3979.4(2) pm,
b = 89.970(4)°,
[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.
;
h
sured, of which 6960 were considered observed with
I > 2r(I); max. residual electron density 1.486 and
[6] P.W. Roesky, M.T. Gamer, N. Marinos, Chem. Eur. J. 10 (2004) 3537.
[7] P.W. Roesky, Inorg. Chem. 45 (2006) 798.
[8] T.K. Panda, A. Zulys, M.T. Gamer, P.W. Roesky, J. Organomet.
Chem. 690 (2005) 5078.
[9] J. Morales-Juarez, R. Cea-Olivares, M.M. Moya-Cabrera, V. Jancik,
V. Garcia-Montalvo, R.A. Toscano, Inorg. Chem. 44 (2005) 6924.
[10] (a) C. Eaborn, P.B. Hitchcock, K. Izod, Z.-R. Lu, J.D. Smith,
Organometallics 15 (1996) 4783;
À0.801 e AÀ3; 624 parameters (all non-hydrogen atoms,
˚
except C50, C51, C53–C56, and O2, were calculated aniso-
tropically; the positions of the H atoms were calculated for
idealized positions) R1 = 0.0681; wR2 = 0.2208.
(2 Æ 2) Æ 3. THF: (Mo Ka radiation); data collection and
refinement: SHELXS-97 [15], SHELXL-97 [16]; monoclinic,
space group C2/c (no. 15); lattice constants
a = 3178.8(2) pm, b = 1986.04(8) pm, c = 2109.38(13) pm,
b = 115.169(4)°, V = 12052.8(11) 106 pm3, Z = 4; l(Mo
Ka) = 1.708 mmÀ1; hmax. = 25.00; 10574 (Rint = 0.0409)
unique reflections measured, of which 6960 were consid-
ered observed with I > 2r(I); max. residual electron density
(b) F. Weber, H. Sitzmann, M. Schultz, C.D. Sofield, R.A. Andersen,
Organometallics 21 (2002) 3139;
(c) H. Schumann, S. Schutte, H.-J. Kroth, D. Lentz, Angew. Chem.
116 (2004) 6335;
(d) H. Schumann, S. Schutte, H.-J. Kroth, D. Lentz, Angew. Chem.
Int. Ed. 43 (2004) 6208;
(e) S. Harder, Angew. Chem. 116 (2004) 2768;
(f) S. Harder, Angew. Chem. Int. Ed. 43 (2004) 2714.
[11] N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, Perga-
mon Press, Oxford, 1984.
0.726 and À0.461 e AÀ3; 656 parameters (all non-hydrogen
˚
atoms, except C55, C57–C60, and the non-coordinated
THF molecules, were calculated anisotropically; the posi-
tions of the H atoms were calculated for idealized posi-
tions) R1 = 0.0315; wR2 = 0.0730.
[12] M.S. Hill, P.B. Hitchcock, Chem. Commun. (2003) 1758.
[13] M. Westerhausen, M.H. Digeser, M. Krofta, N. Wiberg, H. No¨th, J.
Knizek, W. Ponikwar, T. Seifert, Eur. J. Inorg. Chem. (1999) 743.
[14] J.L. Namy, P. Girand, H.B. Kagan, P.E. Caro, in: W.A. Herrmann,
G. Brauer (Eds.), Synthetic Methods of Organometallic and Inor-
ganic Chemistry, vol. 6, Thieme, Stuttgart, 1997, pp. 26–27.
[15] G.M. Sheldrick, SHELXS-97, Program of Crystal Structure Solution,
University of Go¨ttingen, Germany, 1997.
Acknowledgment
This work was supported by the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie.
[16] G.M. Sheldrick, SHELXL-97, Program of Crystal Structure Refinement,
University of Go¨ttingen, Germany, 1997.