Synthesis and X-ray Crystal Structure Determination of the First Lanthanide Complexes Containing Primary Phosphide Ligands: Ln[P(H)Mes*]2(thf)4 (Ln = Yb, Eu)

Full text of DOI:10.1021/ic970422i

4914
Inorg. Chem. 1997, 36, 4914-4915
Synthesis and X-ray Crystal Structure Determination of the First Lanthanide Complexes Containing
Primary Phosphide Ligands: Ln[P(H)Mes*]2(thf)4 (Ln ) Yb, Eu)
Gerd W. Rabe,*,† Ilia A. Guzei,‡ and Arnold L. Rheingold‡
Anorganisch-chemisches Institut, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4, 85747 Garching, Germany,
and Department of Chemistry, University of Delaware, Newark, Delaware 19716
ReceiVed April 11, 1997
As part of an effort to investigate the coordination chemistry
of the lanthanides with phosphide ligand systems as well as
the corresponding bonding aspects, we now extended our
systematic studies toward the reactivity of divalent lanthanide
iodide1 complexes of the general formula LnI2(thf)2 (Ln ) Yb,
Eu) with the potassium salt of a primary phosphane, namely
KP(H)Mes* (Mes* ) 2,4,6-tBu3C6H2).2 Earlier work has
demonstrated that different structural types of secondary phos-
phide derivatives of the lanthanides3,4 can be prepared and
structurally characterized.
We now report the synthesis and crystal structure determi-
nation of two novel phosphide derivatives of the lanthanides of
the general formula Ln[P(H)Mes*]2(thf)4 (Ln ) Yb (1), Eu (2)).
LnI2(thf)2 (Ln ) Yb, Eu) reacts immediately with 2 equiv of
KP(H)Mes* in tetrahydrofuran at room temperature to give
complexes 1 and 2, respectively, in 60% yield. Interestingly,
1 and 2 are formed using both a 1:1 and a 1:2 ratio of reagents.
Crystals of both orange-yellow 1 and bright yellow 2 were
obtained from toluene/thf/pyridine at -30 °C.
in 1 range from 76.3(2) to 108.5(1)° (76.0(3) to 111.2(2)° for
the corresponding angles in 2). The molecular structures of
complexes 1 and 2 resemble the structural motif that we
observed earlier in lanthanide bis(phosphido) complexes of the
general formula Ln[PR2]2(L)4 (L ) thf, N-methylimidazole).3g-i
The Yb-P distance in the molecular structure of 1 is 3.025
(2) Å. It can be compared, e.g., with the Yb-P distances in
Yb[PPh2]2(thf)4 (2.991(2) Å)3g and in bis(η5-2,5-diphenylphos-
pholyl)Yb(thf)2 (2.959(1) Å)4b and also with the corresponding
distances reported for the divalent ytterbium phosphinomethanide
complex {(thf)Li[C(PMe2)2(SiMe3)]}2‚YbI2(thf) (2.96(1)-
3.08(1) Å)6 and the tertiary phosphane adducts of divalent
Yb[N(SiMe3)2]2[Me2PCH2CH2PMe2] (3.012(4) Å)7 and trivalent
Yb(C5Me5)2Cl[Me2PCH2PMe2] (2.941(3) Å).8
(5) Crystal data for 1‚2thf: C60H108O6P2Yb, Mr ) 1160.44, monoclinic,
C2/c, a ) 22.4646(3) Å, b ) 19.2702(1) Å, c ) 18.7672(3) Å, â )
126.325(1)°, V ) 6545.5(1) Å3, Z ) 4, Fcalc ) 1.178 g cm -3, F(000)
) 2464, Mo KR radiation (λ ) 0.710 73 Å), T ) 222(2) K, µ(Mo
KR) ) 1.520 mm-1. A total of 11 459 reflections were collected on
a Siemens P4/CCD diffractometer for a yellow crystal with ap-
proximate dimensions 0.55 × 0.10 × 0.10 mm3 in the range 3.1° e
2θ e 56.3°; 6920 reflections were independent, and 5927 reflections
were considered observed. The structure was solved by direct methods
and refined by full-matrix least-squares calculations based on F2 to
final residuals of R1 ) 0.0447 and wR2 ) 0.1308 for 5927 observed
data (I > 2σ(I)) and GOF ) 1.036. Minimal/maximal residual electron
density: 0.888/ -0.692 e Å-3. Crystal data for 2‚2thf: C60H108EuO6P2,
Mr ) 1139.36, monoclinic, C2/c, a ) 22.2985(3) Å, b ) 19.2553(4)
Å, c ) 18.7396(4) Å, â ) 126.290(1)°, V ) 6485.4(2) Å3, Z ) 4,
The molecular structures of 1 and 2 were determined
crystallographically5 as formally hexacoordinated Ln[P(H)-
Mes*]2(thf)4 (Figure 1, Ln ) Yb). Additionally, two tetrahy-
drofuran solvent molecules are present in both crystal lattices.
It is interesting to note that the presence of pyridine is essential
for a successful induction of crystal growth of 1 and 2.
However, pyridine molecules are neither coordinated to the
metal center nor incorporated in the crystal lattice. This
observation is certainly surprising in light of the fact that
pyridine is a stronger base than tetrahydrofuran. Additional
confirmation for the absence of pyridine was obtained from both
F
calc ) 1.169 g cm -3, F(000) ) 2436, Mo KR radiation (λ ) 0.710 73
Å), T ) 222(2) K, µ(Mo KR) ) 1.061 mm-1. A total of 10 619
reflections were collected on a Siemens P4/CCD diffractometer for a
yellow crystal with approximate dimensions 0.55 × 0.40 × 0.40 mm3
in the range 3.1° e 2θ e 56.6°; 5966 reflections were independent,
and 3648 reflections were considered observed. The structure was
solved by direct methods and refined by full-matrix least-squares
calculations based on F2 to final residuals of R1 ) 0.0816 and wR2 )
0.2002 for 3648 observed data (I > 2σ(I)) and GOF ) 1.024. Minimal/
maximal residual electron density: 1.308/-1.453 e Å-3. The function
1
the H NMR and the 13C NMR spectra of crystals of 1 in
tetrahydrofuran-d8.
The isomorphous molecular structures of 1 and 2 display
distorted octahedral environments around the lanthanide cation,
situated at an inversion center, with the two -[P(H)Mes*]
ligands in trans positions (with a P-Yb-P angle of
162.54(6)° and a P-Eu-P angle of 160.5(1)°, respectively).
The deviation from ideal octahedral geometry can best be seen
by examing the interligand angles. The L-Yb-(cis L) angles
minimized was R(wF2) ) ∑[w(Fo - Fc )2]/∑[(wFo )2]1/2, R ) ∑∆/
∑(Fo), ∆ ) |(Fo - Fc)|. The systematic absences in the diffraction
data were consistent for space groups C2/c and Cc. E statistics
suggested the centrosymmetric space group, C2/c, which yielded
chemically reasonable and computationally stable results of refinement.
The structures were solved using direct methods, completed by
subsequent difference Fourier syntheses and refined by full-matrix
least-squares procedures. Structures 1 and 2 are isomorphous. The
complex molecules are each located on a 2-fold axis. The asymmetric
unit also contains a solvent molecule of tetrahydrofuran. In order to
model disorder in the free molecule of THF, it was constrained to the
same geometry as one of the coordinated tetrahydrofuran ligands. One
2
2
2
† Technische Universita¨t Mu¨nchen.
‡ University of Delaware.
(1) Watson, P. L.; Tulip, T. H.; Williams, I. Organometallics 1990, 9,
1999.
(2) Rabe, G. W.; Yap, G. P. A.; Rheingold, A. L. Inorg. Chem. 1997, 36,
1990 and references cited therein.
(3) (a) Rabe, G. W.; Riede, J.; Schier, A. J. Chem. Soc., Chem. Commun.
1995, 577. (b) Rabe, G. W.; Ziller, J. W. Inorg. Chem. 1995, 34, 5378.
(c) Rabe, G. W.; Riede, J.; Schier, A. Organometallics 1996, 15, 439.
(d) Rabe, G. W.; Riede, J.; Schier, A. Inorg. Chem. 1996, 35, 40. (e)
Rabe, G. W.; Riede, J.; Schier, A. Inorg. Chem. 1996, 35, 2680. (f)
Rabe, G. W.; Yap, G. P. A.; Rheingold, A. L. Inorg. Chem. 1997, 36,
3212. (g) Rabe, G. W.; Yap, G. P. A.; Rheingold, A. L. Inorg. Chem.
1995, 34, 4521. (h) Rabe, G. W.; Riede, J.; Schier, A. Main Group
Chem. 1996, 1, 273. (i) Rabe, G. W.; Yap, G. P. A.; Rheingold, A. L.
Inorg. Chim. Acta, in press.
peak from the final difference map of 2 that remained, 1.22 e Å-3
,
was 0.63 Å from the metal and was considered noise. All non-hydrogen
atoms were refined with anisotropic displacement coefficients. The
hydrogen atom on phosphorus was located, and its thermal parameter
was refined while the P-H distance was constrained to 1.400(2) Å.
All other hydrogen atoms were treated as idealized contributions. All
software and sources of scattering factors are contained in the
SHELXTL (5.3) program library (G. Sheldrick, Siemens, XRD,
Madison, WI). Atomic coordinates, bond distances and angles, and
thermal parameters of 1 and 2 have been deposited at the Cambridge
Crystallographic Data Centre (Depository No. CSD-100132).
(6) Karsch, H. H.; Ferazin, G.; Steigelmann, O.; Kooijman, H.; Hiller,
W. Angew. Chem., Int. Ed. Engl. 1993, 32, 1739.
(4) (a) Nief, F.; Ricard, L. J. Organomet. Chem. 1994, 464, 149. (b) Nief,
F.; Ricard, L.; Mathey, F. Polyhedron 1993, 12, 19. (c) Atlan, S.;
Nief, F.; Ricard, L. Bull. Soc. Chim. Fr. 1995, 132, 649.
(7) Tilley, T. D.; Andersen, R. A.; Zalkin, A. J. Am. Chem. Soc. 1982,
104, 3725.
S0020-1669(97)00422-9 CCC: $14.00 © 1997 American Chemical Society

Communications
Inorganic Chemistry, Vol. 36, No. 22, 1997 4915
NMR spectroscopic investigations of the europium species
2 were found to be difficult because of the strong paramagnetism
of europium(II).11 However, the diamagnetic ytterbium deriva-
tive 1 could be studied in solution using mulitnuclear NMR
spectroscopy (1H, 13C, 31P, 171Yb).11 The proton-decoupled 31
P
NMR spectrum of crystals of 1‚2thf in tetrahydrofuran-d8 at
room temperature shows a singlet at -90.1 ppm. Very broad
171Yb satellites were detected with a P-Yb coupling constant
of approximately 650 Hz. The corresponding signal in the
proton-coupled 31P NMR spectrum shows splitting into doublets
with a P-H coupling constant of 179 Hz, thereby documenting
the presence of the P-H proton. The 31P NMR spectrum of 1
at -60 °C consists of a singlet at -88.9 ppm with much better
resolved ytterbium satellites (JP-Yb ) 647 Hz). The 171Yb NMR
spectrum at -60 °C exhibits a triplet at 406.9 ppm (JYb-P
)
647 Hz). Were were unable to detect any signals in the 171Yb
NMR spectrum of complex 1 at room temperature. This
observation might be attributed to a fast interligand exchange.
Figure 1. Molecular structure of Yb[P(H)Mes*]2(thf)4 (1) showing a
distorted octahedral coordination environment around the lanthanide
center. Selected interatomic separations (Å) and angles (deg): Yb-P
) 3.025(2), Yb-O(1) ) 2.480(4), Yb-O(2) ) 2.506(3), P-C(1) )
1.859(4), P-H ) 1.400(2); P-Yb-P ) 162.54(6), Yb-P-C(1) )
121.4(1), O(1)-Yb-O(1A) ) 79.6(3), O(1)-Yb-O(2) ) 152.4(2),
O(1A)-Yb-O(2) ) 76.3(2), O(2)-Yb-O(2A) ) 130.0(2), O(1)-
Yb-P ) 108.5(1), O(1A)-Yb-P ) 85.1(1), O(2)-Yb-P ) 82.8(1),
O(2A)-Yb-P ) 89.4(1)°.
The Eu-P distance in complex 2 (3.143(3) Å) is quite long
compared with the terminal Eu-P distance of 3.034(1) Å3i in
hexacoordinated Eu[PPh2]2(L)4 (L ) N-methylimidazole) and
with the bridging Eu-P distances in four-coordinated Eu[(µ-
PtBu2)2Li(thf)]2 (2)3f ranging from 3.034(1) to 3.068(1) Å
(average: 3.046 (7) Å). Interestingly, the Eu-P distance in
complex 2 is not much shorter than the values ranging from
3.165(2) to 3.249(2) Å reported for the europium phosphane
adduct {Eu[TeSi(SiMe3)3]2(DMPE)2}2(µ-DMPE) (average:
3.20(1) Å), which exhibits the coordination number 7 at the
lanthanide center.9 To the best of our knowlege,10 these are
the only reports on other Eu-P systems that have been
structurally characterized.
The Yb-O distances in 1 are 2.480(4) and 2.506(3) Å
(2.551(7) and 2.587(6) Å for 2, respectively). They are slightly
longer than the corresponding distances which we reported
earlier for Yb[PPh2]2(thf)4 (2.430(4) and 2.437(4) Å).3g The
closest nonbonding Yb‚‚‚C distances in 1 are 3.96(1) Å [C(10)]
and 4.72(1) Å [C(16)]. These distances seem too large even
for very weak agostic interactions in our Ln[P(H)Mes*]2(thf)4
complexes.
The geometry around the phosphorus atom in the Ln[P(H)-
Mes*]2(thf)4 species is distinctly pyramidal; e.g., the sum of
bond angles around the phosphorus atom in 1 is 313°. This
value can be compared with that reported for the molecular
structure of Yb[PPh2]2(thf)4 (∑P ) 332.7°),3g which was found
to exhibit a less pronounced pyramidal environment around the
phosphorus atom. The Yb-P-C angle of 121.4(1)° (1) and
the corresponding angle of 117.1(3)° in 2 can be compared,
e.g., with the corresponding angles of 110.2(1) and 119.4(1)°
reported for Yb[PPh2]2(thf)4.3g
The synthesis of 1 and 2 introduces a novel class of lanthanide
bis(phosphido) complexes, based on primary phosphides. For-
mation of 1 and 2 demonstrates that, with careful control of
stoichiometry, stable lanthanide complexes are accessible using
primary phosphides (e.g. the -P(H)Mes* ligand) as the only
anionic ligands. We were able to show that this ligand system
meets the electrostatic and steric requirements necessary to form
thermally stable, isolable complexes of the lanthanides, without
using sterically demanding supporting ligands such as, e.g.,
pentamethylcyclopentadienyl (Cp*) or cyclooctatetraenyl (COT).
Furthermore, we could prove that the -P(H)Mes* ligand
provides the steric bulk needed to saturate the coordination
environment of the relatively large12 divalent lanthanide cations.
The utility of complexes 1 and 2 as suitable precursors for the
generation of lanthanide phosphinidene species of the type
[(thf)xLndP-R] or related species remains to be determined.
Acknowledgment. The authors thank the Deutsche Fors-
chungsgemeinschaft and the Fonds der Chemischen Industrie,
for financial support. Professor H. Schmidbaur is gratefully
acknowledged for helpful discussions. The University of
Delaware acknowledges the National Science Foundation for
support of the purchase of the CCD-based diffractometer (Grant
CHE-9628768).
Supporting Information Available: Tables listing detailed crystal-
lographic data, atomic positional parameters, bond lengths and angles,
and thermal parameters and an ORTEP diagram of complex 2 (16
pages). Ordering information is given on any current masthead page.
IC970422I
(11) Complexes 1 and 2 are soluble in tetrahydrofuran but insoluble in
toluene. Characterization data for 1 are as follows. 1H NMR (C4D8O,
400 MHz, 25 °C): δ 1.19 (s, 18H), 1.61 (s, 36H), 3.00 (d, JP-H
)
179 Hz, 2H), 7.03 (s, 4H). 31P NMR (C4D8O, 161.9 MHz, 25 °C): δ
-90.1 (d, JP-H ) 179 Hz; JP-Yb ) 650 Hz). 31P NMR (C4D8O, 161.9
MHz, -60 °C): δ -88.9 (d, JP-H ) 184 Hz; JP-Yb ) 647 Hz). 13C
NMR (C4D8O, 100.4 MHz, 25 °C): δ 32.2, 32.3, 32.4, 34.8 (CH3-
C), 38.6 (CH3-C), 120.6 (meta-C), 140.1 (para-C), 148.4 (ortho-C),
149.6 (d, JC-P ) 60 Hz, ipso-C). 171Yb NMR (C4D8O, 70.0 MHz,
-60 °C): δ 406.9 (t, JYb-P ) 647 Hz). IR (Nujol): 2364 s, 1755 w,
1596 m, 1282 m, 1238 m, 1170 m, 1074 s, 1026 s, 918 s, 872 s, 749
m, 723 m, 667 w, 636 w, 593 w, 487 w cm-1. 1 becomes partially
desolvated upon drying. As an example, the remaining residue was
found to analyze as Yb[P(H)Mes*]2(thf)x (x ) 1.3). Anal. Calcd for
Both 1 and 2 desolvate rapidly upon exposure to vacuum,
thus precluding a reliable characterization by elemental analysis.
Analytical data (C, H, P) for both 1 and 2 are consistent with
the formulation Ln[P(H)Mes*]2(thf)x (x < 4), with differing
numbers of tetrahydrofuran molecules, depending on the time
the samples were exposed to vacuum.11
C41.2H70.4O1.3P2Yb: C, 60.23; H, 8.64; P, 7.54. Found: C, 60.54; H,
8.98; P, 7.25. Characterization data for 2 are as follows. IR (Nujol):
2360 s, 1596 w, 1283 m, 1167 m, 1074 s, 1031 s, 916 m, 727 m, 668
w, 635 w cm-1. Magnetic susceptibility: øM293K ) 2.85 × 10-2 cgsu;
µeff ) 8.2 µB. 2 also becomes partially desolvated upon drying. As an
example, the remaining residue was found to analyze as Eu[P(H)-
Mes*]2(thf)x (x ) 0.9). Anal. Calcd for C39.6H67.2EuO0.9P2: C, 61.64;
H, 8.78; P, 8.03. Found: C, 61.93; H, 8.99; P, 7.88.
(8) Tilley, T. D.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1983, 22,
3725.
(9) Cary, D. R.; Arnold, J. Inorg. Chem. 1994, 33, 1791.
(10) Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, O.; Kennard, O.;
Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J. M.; Watson,
D. G. J. Chem. Inf. Comput. Sci. 1991, 31, 187.
(12) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.