Donor-functionalized lanthanide terphenyl complexes: Synthesis and structural characterization of 2,6-Di(o-anisol)phenyl compounds of ytterbium, yttrium, and samarium

Article abstract of DOI:10.1021/ic0300161

The syntheses and molecular structures of a number of 2,6-di(o-anisol)phenyl (=Danip-) -based bis(amide) and bis(alkoxide) compounds of ytterbium, yttrium, and samarium are reported. Addtionally, NMR spectroscopic data are reported for the analogous diamagnetic yttrium compounds. Salt metathesis reaction of equimolar amounts of DanipLi and YbCl₃ in tetrahydrofuran at room temperature followed by addition of 2 equiv of KN(SiMe₃)₂ or KN- (SiHMe₂)₂ produces Danip Yb[N(SiMe₃)₂]₂ (1) and Danip Yb[N(SiHMe₂)₂]₂ (2), respectively. The analogous reaction using SmCl₃ and KN(SiHMe₂)₂ produces DanipSm[N(SiHMe₂)₂]₂ (3). Reaction of DanipLi and YbCl₃ in tetrahydrofuran at room temperature followed by addition of 2 equiv of KO(2,6-diisopropylphenyl) produces Danip Yb[O(2,6- diisopropylphenyl)]₂ (4). Our attempts to also prepare the yttrium analogue of complex 4 yielded single-crystalline material of the tetrahydrofuran adduct DanipY(THF)[O(2,6-diisopropylphenyl)]₂ (5). The molecular structures of the complexes 1-4 feature five-coordinate metal atoms and coordination polyhedra which can be described as distorted square-pyramidal rather than trigonal-bipyramidal, with the ipso carbon atom occupying the apical position. On the other hand, the molecular structure of the tetrahydrofuran-solvated yttrium Danip arylalkoxide compound 5 features a six-coordinate metal atom in a distorted trigonal-prismatic coordination environment. In all cases the Danip ligand system adopts the chiral (racemic) d,I form.

Full text of DOI:10.1021/ic0300161

Inorg. Chem. 2003, 42, 3527−3533
Donor-Functionalized Lanthanide Terphenyl Complexes: Synthesis and
Structural Characterization of 2,6-Di(o-anisol)phenyl Compounds of
Ytterbium, Yttrium, and Samarium
,†
Gerd W. Rabe,* Mei Zhang-Presse,† Florian A. Riederer,† and Glenn P. A. Yap‡
Anorganisch-chemisches Institut, Technische UniVersita¨t Mu¨nchen, Lichtenbergstrasse 4,
85747 Garching, Germany, and Department of Chemistry, UniVersity of Ottawa,
10 Marie Curie AVenue, Ottawa, Ontario K1N 6N5, Canada
Received January 13, 2003
The syntheses and molecular structures of a number of 2,6-di(o-anisol)phenyl ()Danip-) -based bis(amide) and
bis(alkoxide) compounds of ytterbium, yttrium, and samarium are reported. Addtionally, NMR spectroscopic data
are reported for the analogous diamagnetic yttrium compounds. Salt metathesis reaction of equimolar amounts of
DanipLi and YbCl3 in tetrahydrofuran at room temperature followed by addition of 2 equiv of KN(SiMe3)2 or KN-
(SiHMe2)2 produces DanipYb[N(SiMe3)2]2 (1) and DanipYb[N(SiHMe2)2]2 (2), respectively. The analogous reaction
using SmCl3 and KN(SiHMe2)2 produces DanipSm[N(SiHMe2)2]2 (3). Reaction of DanipLi and YbCl3 in tetrahydrofuran
at room temperature followed by addition of 2 equiv of KO(2,6-diisopropylphenyl) produces DanipYb[O(2,6-
diisopropylphenyl)]2 (4). Our attempts to also prepare the yttrium analogue of complex 4 yielded single-crystalline
material of the tetrahydrofuran adduct DanipY(THF)[O(2,6-diisopropylphenyl)]2 (5). The molecular structures of the
complexes 1−4 feature five-coordinate metal atoms and coordination polyhedra which can be described as distorted
square-pyramidal rather than trigonal-bipyramidal, with the ipso carbon atom occupying the apical position. On the
other hand, the molecular structure of the tetrahydrofuran-solvated yttrium Danip arylalkoxide compound 5 features
a six-coordinate metal atom in a distorted trigonal-prismatic coordination environment. In all cases the Danip ligand
system adopts the chiral (racemic) d,l form.
Introduction
group 3 elements scandium and yttrium.6-9 We were able
to demonstrate that the use of sterically demanding terphenyl
groups as the only supporting ligand allows for the kinetic
stabilization of novel low-coordinate complexes which are
obtained by simple, straightforward salt methathesis reactions
using different terphenyllithium salts and the corresponding
lanthanide (Ln ) Sm-Lu) or group 3 element trichlorides.
Formation of mono(terphenyl) compounds is observed when
employing the terphenyls Dmp ()2,6-dimesitylphenyl)6,9 and
Dnp [)2,6-di(1-naphthyl)phenyl],7 as well as the donor-
functionalized Danip [)2,6-di(o-anisol)phenyl].8
There is much current interest in the chemistry of terphenyl
element compounds. Still, the vast majority of terphenyl
compounds are based on p block elements, followed by a
number of such compounds of s block elements and some
representatives of the late transition metals.1-5 In recent years
we have been investigating the coordination and reaction
chemistry of terphenyl compounds of the lanthanides and
* To whom correspondence should be addressed. E-mail: g.rabe@
lrz.tum.de.
† Technische Universita¨t Mu¨nchen.
One of the problems we observed in previously studied
nonfunctionalized lanthanide terphenyl systems6,7,9 is the only
‡ University of Ottawa.
(1) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV. Organomet. Chem.
1999, 44, 1 and references therein.
(2) Clyburne, J. A. C.; McMullen, N. Coord. Chem. ReV. 2000, 210, 73
and references therein.
(3) Su, J.; Li, X.-W.; Crittendon. C.; Robinson, G. H. J. Am. Chem. Soc.
1997, 119, 5471.
(6) Rabe, G. W.; Strissel, C. S.; Liable-Sands, L. M.; Concolino, T. E.;
Rheingold, A. L. Inorg. Chem. 1999, 38, 3446.
(7) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A. Inorg. Chem. 2001, 40,
2682.
(4) Stender, M.; Philipps, A. D.; Wright, R. J.; Power, P. P. Angew. Chem.,
Int. Ed. 2002, 41, 1785.
(5) Hardman, N. J.; Wright, R. J.; Philipps, A. D.; Power, P. P. Angew.
Chem., Int. Ed. 2002, 41, 2842.
(8) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A. Inorg. Chem. 2001, 40,
4780.
(9) Rabe, G. W.; Be´rube´, C. D.; Yap, G. P. A.; Lam, K.-C.; Concolino,
T. E.; Rheingold, A. L. Inorg. Chem. 2002, 41, 1446.
10.1021/ic0300161 CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/09/2003
Inorganic Chemistry, Vol. 42, No. 11, 2003 3527

Rabe et al.
SmCl3 instead of YbCl3. In the case of 3 the suspension of SmCl3
in tetrahydrofuran was stirred overnight. After crystallization from
hexanes, complexes 1-3 are insoluble in hexanes, soluble in
aromatic solvents, and well soluble in tetrahydrofuran. We failed
to obtain reasonable combustion analyses data (C, H, N) for 1-3.
The values obtained for both C and N were too low which can
most likely be explained by incomplete combustion of the samples
due to formation of SiC and SiN during the combustion process.
Such incomplete combustion of lanthanide compounds, particularly
with the element combination Ln/N/Si being present, is not
uncommon and has been discussed earlier to explain for the
observation of too low C and N values.12-14
relatively poor stability of lanthanide terphenyl compounds
in the solution state, particularly in tetrahydrofuran solution
at ambient temperature. Considerably more stable products
were obtained with the donor-functionalized terphenyl ligand
Danip,8 a “pincer ligand” with donor groups in the ortho
position of the phenyl substiutents in the 2,6-position. We
were now interested in investigating the reaction chemistry
of Danip-based mono(terphenyl)lanthanide compounds, par-
ticularly the accessibility and structural characterization of
further functionalized Danip-based compounds. Therefore,
efforts were undertaken to explore what other monoanionic
ligand systems can be accommodated vis-a`-vis a Danip
moiety bonded to a lanthanide atom. Here we report on a
simple high-yield preparation and structural characterization
of a number of Danip-based monomeric bis functionalized
lanthanide compounds.
1. IR (Nujol): 1576 w, 1540 w, 1259 m, 1245 s, 1208 w, 1160
m, 1113 w, 1065 w, 980 s, 951 vs, 946 vs, 869 m, 826 s, 740 s,
692 w, 661 m, 608 w, 500 w, 432 w cm-1. Mp: 175-177 °C (dec).
DanipY[N(SiMe3)2]2. 1H NMR (C6D6, 400 MHz, 25 °C): δ 0.24
(s, 36H, Me3Si), 3.78 (s, 6H, OMe) plus sets of signals in the
aromatic region ranging from 6.65 to 7.75 ppm (11H). 13C NMR
(C6D6, 100.4 MHz, 25 °C): δ 2.7 (Me3Si), 61.8 (OMe), 120.8,
126.8, 127.2, 133.2, 138.3, 142.4, 153.7, 185.2 (d, JY-C ) 51 Hz,
ipso C). We failed to detect in the 13C NMR spectrum all signals
that correspond to the terphenyl ligand which is probably due to
overlap of the solvent signal with some of the signals in the aromatic
region. 29Si NMR (C6D6, 79.4 MHz, 25 °C): δ -11.4 (sept, 2JSi-H
) 9 Hz).
2. IR (Nujol): 2021 vs (sh), 1789 w, 1574 m, 1548 w, 1246 vs,
1211 w, 949 vs, 942 vs, 880 vs, 869 vs, 862 vs, 832 s, 799 w, 790
w, 747 m, 745 m, 736 m, 732 m, 722 w, 698 w, 683 w, 678 w,
646 w, 630 w, 626 m, 610 m, 590 m, 578 w, 560 w, 532 w, 496
m cm-1. Mp: 180-182 °C (dec).
Experimental Section
The compounds described below were handled under nitrogen
using Schlenk line double-manifold, high-vacuum, and glovebox
(MBraun, Labmaster 130) techniques. Solvents were dried, and
physical measurements were obtained by following typical labora-
tory procedures. DanipLi was prepared from DanipI and n-
butyllithium in hexanes.8,10,11 KO(2,6-diisopropylphenyl) and KN-
(SiHMe2)2 were prepared by reaction of equimolar amounts of
potassium hydride and the corresponding phenol or amine in
hexanes at room temperature. Both potassium salts are insoluble
in hexanes and toluene but soluble in tetrahydrofuran. KN(SiMe3)2
was purchased as a 0.5 M solution in toluene from Aldrich. The
anhydrous halides YbCl3, YCl3, and SmCl3 were purchased from
Aldrich (packaged under argon in ampules) and were used as
received. NMR spectra were recorded on a JMN-GX 400 instru-
ment. 13C NMR spectra were referenced to the solvent signals
(benzene-d6, 128.0 ppm; THF-d8, 67.4 and 25.2 ppm, respectively).
29Si NMR spectra were referenced to tetramethylsilane.
3. IR (Nujol): 2038 vs (broad sh), 1573 w, 1546 w, 1275 s,
1242 m, 1208 w, 1158 m, 1126 w, 1067 s, 1065 s, 987 m, 884 vs,
880 vs, 837 m, 788 m, 738 vs, 722 vs, 683 m, 633 w, 589 m, 500
w, 446 w cm-1. Mp: 144-146 °C (dec). The samarium compound
1
3 has an uninterpretable H NMR spectrum.
1
DanipY[N(SiHMe2)2]2. H NMR (C6D6, 400 MHz, 25 °C): δ
0.18 (d, 24H, 3JH-H ) 3 Hz, Me2Si), 3.78 (s, 6H, OMe), 4.81 (sept,
4H, 3JH-H ) 3 Hz, Si-H) plus sets of signals in the aromatic region
ranging from 6.95 to 7.70 ppm (11H). 13C NMR (C6D6, 100.4 MHz,
25 °C): δ 3.0 (Me2Si), 64.0 (OMe), 119.3, 126.5, 126.8, 132.9,
137.8, 142.7, 153.2, 186.8 (d, JY-C ) 50 Hz, ipso C). We failed to
detect in the 13C NMR spectrum all signals that correspond to the
terphenyl ligand which is probably due to overlap of the solvent
signal with some of the signals in the aromatic region. 29Si NMR
(C6D6, 79.4 MHz, 25 °C): δ -26.1 (d, sept, 2JSi-H ) 7 Hz, 1JSi-H
) 168 Hz).
DanipYb[N(SiMe3)2]2 (1), DanipYb[N(SiHMe2)2]2 (2), and
DanipSm[N(SiHMe2)2]2 (3). In the glovebox, a colorless suspen-
sion of YbCl3 (279 mg, 1.0 mmol) in 10 mL of tetrahydrofuran
was stirred for several hours. A freshly prepared solution of DanipLi
(296 mg, 1.0 mmol) in 10 mL of tetrahydrofuran was added to the
suspension. The reaction mixture was stirred for 30 min yielding a
red solution. A 0.5 M toluene solution of KN(SiMe3)2 (4.0 mL,
2.0 mmol) was slowly added via syringe. After being stirred for
10 min, the obtained orange suspension was centrifuged. After
removal of the mother liquor, extraction of the residues with
hexanes, and centrifugation, the obtained orange solution was stored
overnight at room temperature, which resulted in almost complete
crystallization of 1 as a yellow microcrystalline material (470 mg,
60%). In the case of 2 a tetrahydrofuran solution of KN(SiHMe2)2
(343 mg, 2.0 mmol) was slowly added via syringe. After being
stirred for 10 min, the obtained orange suspension was centrifuged.
After removal of the mother liquor, extraction of the residues with
hexanes, and centrifugation, the obtained orange solution was stored
overnight at room temperature, which resulted in almost complete
crystallization of 2 as an yellow microcrystalline material (436 mg,
60%). Bright yellow compound 3 is obtained in similar yield using
DanipYb[O(2,6-diisopropylphenyl)]2 (4) and DanipY(THF)-
[O(2,6-diisopropylphenyl)]2 (5). In the glovebox, a colorless
suspension of YbCl3 (279 mg, 1.0 mmol) in 10 mL of tetrahydro-
furan was stirred for several hours. A freshly prepared solution of
DanipLi (296 mg, 1.0 mmol) in 10 mL of tetrahydrofuran was added
to the suspension. The reaction mixture was stirred for 30 min
yielding an orange-red solution. A solution of KO(2,6-diisopropyl-
phenyl) (433 mg, 2.0 mmol) in tetrahydrofuran was slowly added
via pipet. After being stirred for 10 min, the obtained yellow
suspension was centrifuged. After removal of all volatiles and
(12) Fryzuk, M. D.; Jafarpour, L.; Kerton, F. M.; Love, J. B.; Patrick, B.
O.; Rettig, S. J. Organometallics 2001, 20, 1387.
(13) Stults, S. D.; Andersen, R. A.; Zalkin, A. Organometallics 1990, 9,
115.
(10) Rabe, G. W.; Sommer, R. D.; Rheingold, A. L. Organometallics 2000,
19, 5537.
(11) Rabe, G. W.; Zhang-Presse, M.; Yap, G. P. A. Acta Crystallogr. 2002,
E58, m434.
(14) Eppinger, J.; Spiegler, M.; Hieringer, W.; Herrmann, W. A.; Anwander,
R. J. Am. Chem. Soc. 2000, 122, 3080.
3528 Inorganic Chemistry, Vol. 42, No. 11, 2003

Lanthanide Terphenyl Complexes
Table 1. Crystallographic Data for DanipYb[N(SiMe3)2]2 (1), DanipYb[N(SiHMe2)2]2 (2), DanipSm[N(SiHMe2)2]2 (3),
DanipYb[O(2,6-diisopropylphenyl)]2 (4), and DanipY(THF)[O(2,6-diisopropylphenyl)]2 (5)a
param
1
2
3
4
5
formula
fw
C32H53N2O2Si4Yb
783.16
C28H45N2O2Si4Yb
727.06
C28H45N2O2Si4Sm
704.37
C44H51O4Yb
816.89
C48H59O5Y
804.86
space group
a, Å
b, Å
C2/c
P21/c
P21/c
C2/c
P1h
22.208(4)
11.803(3)
14.182(2)
16.5309(16)
10.1709(10)
21.603(2)
16.4865(15)
10.2719(9)
21.860(2)
22.6759(16)
12.3333(9)
17.6237(12)
9.2978(10)
19.631(2)
24.810(3)
87.042(2)
84.740(2)
81.056(2)
4451.3(8)
4
c, Å
R, deg
â, deg
93.870(14)
109.313(2)
109.324(2)
128.0890(10)
γ, deg
V, Å3
3708.6(12)
4
1.403
70(2)
Mo KR (0.710 73)
26.80
5.11
3427.8(6)
4
1.409
70(2)
3493.4(5)
4
1.339
70(2)
3879.2(5)
4
1.399
70(2)
Z
D(calcd), g cm-3
temp, °C
radiation (λ, Å)
µ(Mo KR), cm-1
R1, %
1.201
70(2)
Mo KR (0.710 73)
13.53
5.35
8.86
Mo KR (0.710 73)
Mo KR (0.710 73)
Mo KR (0.710 73)
28.93
2.20
6.24
18.43
4.09
8.56
24.51
1.84
4.74
wR2, %
11.34
a The quantity minimized was wR2 ) ∑[w(Fo - Fc )2]/∑[(wFo )2]1/2; R1 ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|, w ) 1/[σ2(Fo ) + (aP)2 + bP], P ) [2Fc
+
2
2
2
2
2
max(Fo, 0)/3.
extraction of the residues with hexanes followed by repeated
centrifugation (over a period of a couple of hours), the obtained
yellow solution was stored overnight at room temperature, which
resulted in almost complete crystallization of 4 as a bright yellow
microcrystalline material (490 mg, 60%). After crystallization from
hexanes, complex 4 is insoluble in hexanes, soluble in aromatic
solvents, and well soluble in tetrahydrofuran. Colorless
DanipY[O(2,6-diisopropylphenyl)]2 was prepared in a similar
manner. In contrast to the ytterbium compound 4 the crude product
of the yttrium analogue is insoluble in hexanes. We failed to
crystallize the yttrium compound from toluene but managed to
obtain crystalline material of the tetrahydrofuran adduct 5 from a
toluene solution in the presence of small amounts of tetrahydrofuran.
The obtained crystalline material rapidly desolvates when exposed
to vacuum, thereby preventing further characterization of 5. Accord-
ing to 1H and 13C NMR data a completely desolvated compound is
obtained of composition DanipY[O(2,6-diisopropylphenyl)]2.
matrix, least-squares procedures. SADABS absorption corrections
were applied to all data sets. The compound molecule was located
at a 2-fold axis in 1 and 4. One isopropyl moiety in 4 was located
rotationally disordered with a roughly 50/50 refined site occupancy
distribution. Two symmetry unique but chemically identical
compound molecules were located in the asymmetric unit of 5. In
2 and 3 the hydrogen atoms on the silicon atoms were located from
a difference map and refined. All other hydrogen atoms were treated
as idealized contributions.
All software and sources of the scattering factors are contained
in the SHELXTL (5.10) program library (G. M. Sheldrick, Siemens
XRD, Madison, WI).
Results and Discussion
We previously reported the synthesis of the donor-
functionalized terphenyllithium salt DanipLi8,10,11 Danip as
well as its reaction with different lanthanide trichlorides (Ln
) Sm, Y, Yb) which produces two different types of lithium
chloride adducts of composition [DanipLn(µ2-Cl)2(µ3-Cl)-
Li(THF)]2 (Ln ) Yb) or [DanipLn(µ2-Cl)2(µ2-Cl)Li(THF)2]2
(Ln ) Sm, Y), depending on the size of the metal atom being
employed.8 The molecular structures of these compounds are
comprised of dimeric cagelike arrangements.
We here report the one-pot reaction of DanipLi with LnCl3
(Ln ) Sm, Y, Yb) and 2 equiv of different sterically
encumbering potassium amide or alkoxide compounds yield-
ing novel neutral and low-coordinate unsolvated bis substi-
tuted compounds of general composition DanipLnX2 in good
yield. The obtained compounds are toluene soluble, and
under exclusion of air and moisture, toluene solutions of the
presented compounds show no visible signs of decomposition
over several days at ambient temperature. Single-crystalline
material of compounds 1-4 was obtained by extraction of
the obtained crude products with hexanes and slow evapora-
tion of the obtained solutions at room temperature. We note
that after crystallization from hexanes compounds 1-4 are
insoluble in hexanes but soluble in toluene. In the case of
the tetrahydrofuran solvate 5 single-crystalline material was
obtained by slow evaporation of a toluene solution in the
presence of a small amount of tetrahydrofuran. Our repeated
4. Anal. Calcd for C44H51O4Yb: C, 64.69; H, 6.29. Found: C,
64.51; H, 6.10. IR (Nujol): 1926 w, 1893 w, 1645 w, 1585 m,
1262 s, 1258 s, 1252 s, 1205 m, 1170 m, 1103 s, 1040 m, 1016 w,
968 m, 886 s, 860 s, 825 w, 806 m, 796 m, 774 m, 751 s, 743 m,
694 s, 614 w, 570 m, 539 w, 510 m, 439 w, 430 w cm-1. Mp:
245-248 °C (dec).
DanipY[O(2,6-diisopropylphenyl)]2. 1H NMR (C6D6, 400 MHz,
3
25 °C): δ 1.18 (d, 24H, JH-H ) 7 Hz, Me2C), 3.06 (sept, 4H,
3JH-H ) 7 Hz, C-H), 3.42 (s, 6H, OMe) plus sets of signals in the
aromatic region ranging from 6.87 to 7.70 ppm (17H). 13C NMR
(C6D6, 100.4 MHz, 25 °C): δ 24.0 (Me2C), 27.2 (C-H), 65.3
(OMe), 118.1, 122.3, 123.0, 126.4, 127.9, 128.1, 128.5, 132.7,
136.4, 138.7, 143.7, 152.0, 158.1 (d, 1JC-H ) 5 Hz), 183.6 (d, JY-C
) 53 Hz).
General Aspects of X-ray Data Collection, Structure Deter-
mination, and Refinement for Complexes 1-5. Crystal, data
collection, and refinement parameters are given in Table 1. The
systematic absences in the diffraction data are uniquely consistent
for the reported space group for 2 and 3 and consistent for the
space groups Cc and C2/c for 1 and 4. No symmetry higher than
triclinic was observed for 5. The E-statistics suggested the cen-
trosymmetric option, C2/c, for 1 and 4 and P1h for 5, which yielded
chemically reasonable and computationally stable results of refine-
ment. The structures were solved using direct methods, completed
by subsequent difference Fourier syntheses, and refined by full-
Inorganic Chemistry, Vol. 42, No. 11, 2003 3529

Rabe et al.
distance in 1 is shorter than the Yb-O distance [2.376(4)
Å], and the C-Yb-N angle [112.54(12)°] is considerably
larger than the C-Yb-O angle [76.38(19)°]. The distortion
from an ideal square-pyramidal coordination polyhedron can
also be seen by inspecting the two trans and the two cis
interligand angles which belong to the base of the square
pyramid. The O-Yb-O angle [152.8(2)°] is larger than the
N-Yb-N angle [134.9(2)°], and the two O-Yb-N angles
are 91.31(15) and 99.07(15)°, respectively. The Yb-N-Si
angles in 1 are 123.9(2)° [Si(1)] and 115.9(2)° [Si(2)].
However, a closer inspection of the metal‚‚‚carbon distances
reveals that there are no “agostic” interactions present, which
is noteworthy taking into consideration the low coordination
number of the ytterbium atom. Except for the Yb-C(ipso)
distance [2.350(8) Å], there are no Yb‚‚‚carbon distances
shorter than 3.0 Å and the closest Yb‚‚‚C(SiMe3) distance
is 3.334(8) Å [C(16)]. Further interatomic separations and
angles of the molecular structure of 1 can be derived from
Table 2.
Figure 1. ORTEP diagram of DanipYb[N(SiMe3)2]2 (1) showing the atom-
labeling scheme. Thermal ellipsoids are at the 30% level. Hydrogen atoms
were omitted for clarity.
We note that our attempts to also crystallize the corre-
sponding yttrium and samarium compound from different
solvent combinations yielded amorphous material only.
DanipYb[N(SiHMe2)2]2 (2) and DanipSm[N(SiHMe2)2]2
(3). We were interested in investigating how the molecular
structure of Danip-based lanthanide bis(amide) compounds
would vary when using amide ligands with different steric
demands. We therefore decided to employ the slightly smaller
bis(dimethylsilyl)amide ligand. The amine is commercially
available and was first introduced as a ligand in lanthanide
chemistry by Anwander and Herrmann.17
The Yb-C, Yb-N, and Yb-O distances in 2 can
favorably be compared, within the error limits of determi-
nation, with the corresponding distances in compound 1.
Besides the Yb-C(ipso) distance [2.377(2) Å] all other Yb‚‚‚
C distances in 2 are clearly longer than 3.0 Å. As one would
expect, the N-Yb-N angle of 118.85(9)° in 2 is consider-
ably smaller than the corresponding angle in 1 [134.9(2)°].
An observation which can most likely be attributed to the
different steric demand of both ligand systems. On the other
hand, the C-Yb-O and O-Yb-O angles do not differ
much in both compounds (see Table 2). The Yb-N-Si
angles in 2 are within the expected range [Si(1), 113.79-
(12)°; Si(2), 118.95(12)°; Si(3), 111.46(12)°; Si(4), 120.14-
(13)°]. The four Si-H hydrogen atoms were located from a
difference map and refined. The relatively long Yb‚‚‚H(Si-
H) distances [H(1), 3.30(2); H(2), 3.39(2); H(3), 3.25(2);
H(4), 3.40(2) Å] indicate that there is no “agostic” interaction
present despite the relatively low coordination number at the
metal atom.
Figure 2. Side view of complex 1 viewed along the Yb‚‚‚C(ipso) vector.
attempts to obtain crystalline material of hexane-insoluble
DanipYb[O(2,6-diisopropylphenyl)]2 from toluene in the
absence of tetrahydrofuran gave amorphous material only.
1
According to H and 13C NMR data compound 5 becomes
readily and completely desolvated when dried under vacuum.
DanipYb[N(SiMe3)2]2 (1). The molecular structure of
compound 1 (Figure 1) features a C2-symmetric five-
coordinate ytterbium complex in a distorted square-pyramidal
coordination environment with the ipso carbon atom oc-
cupying the apical position. The Danip ligand adopts the
chiral (racemic) d,l form (Figure 2). The Yb-N distance
[2.241(5) Å] is, e.g., somewhat longer than the corresponding
distances in the as well five-coordinate amide compounds
tris((2,6-diisopropylphenyl)amido)bis(tetrahydrofuran)-
ytterbium (average 2.17 Å)15 and {(Me3Si)2N]2Yb(THF)(µ-
Cl)}2 [2.174(5) and 2.108(5) Å, respectively].16 The Yb-N
Since we did not detect any “agostic” interactions in the
solid-state structure of compound 2, we continued our
investigations by choosing a metal of larger size. Previous
investigations from our laboratory6-9 have shown that
lanthanide terphenyl compounds are accessible for the
smaller lanthanide elements and that, so far, the largest
(15) Evans, W. J.; Ansari, M. A.; Ziller, W. J.; Khan, S. I. Inorg. Chem.
1996, 35, 5435.
(16) Aspinall, H. C.; Bradley, D. C.; Hursthouse, M. B.; Sales, K. D.;
Walker, N. P. C.; Hussain, B. J. Chem. Soc., Dalton Trans. 1989,
623.
(17) Herrmann, W. A.; Anwander, R.; Munck, F. C.; Scherer, W.; Dufaud,
V.; Huber, N. W.; Artus, G. R. J. Z. Naturforsch. 1994, 49B, 1789.
3530 Inorganic Chemistry, Vol. 42, No. 11, 2003

Lanthanide Terphenyl Complexes
Table 2. Comparison of Selected Interatomic Separations (Å) and Angles (deg) of Complexes 1-5
param
1 (Ln ) Yb)
2.350(8)
2 (Ln ) Yb)
2.377(2)
2.213(2) [N(1)]
2.204(2) [N(2)]
2.4050(18) [O(1)]
2.3898(18) [O(2)]
3 (Ln ) Sm)
2.484(4)
2.313(3) [N(1)]
2.303(3) [N(2)]
2.512(3) [O(1)]
2.496(3) [O(2)]
4 (Ln ) Yb)
2.379(3)
5 (Ln ) Y)
Ln-C
Ln-N
2.474(3) [Y(1)]/2.468(3) [Y(2)]
2.241(5)
Ln-O
2.376(4)
2.3172(13) [O(1)]
2.0634(13) [O(2)]
2.393(2) [O(1)]/2.397(2) [O(6)]
2.434(2) [O(2)]/2.413(2) [O(7)]
2.127(2) [O(3)]/2.122(2) [O(8)]
2.111(2) [O(4)]/2.100(2) [O(9)]
2.439(2) [O(5)]/2.458(2) [O(10)]
C-Ln-N
C-Ln-O
112.54(12)
76.38(10)
122.75(9) [N(1)]
118.16(9) [N(2)]
74.49(7) [O(1)]
75.18(7) [O(2)]
122.74(13) [N(1)]
117.98(13) [N(2)]
71.66(11) [O(1)]
72.85(11) [O(2)]
76.94(3) [O(1)]
114.72(4) [O(2)]
76.07(9) [O(1)]/74.42(9) [O(6)]
72.61(9) [O(2)]/73.49(9) [O(7)]
105.30(9) [O(3)]/106.99(9) [O(8)]
109.90(9) [O(4)]/105.35(9) [O(9)]
142.64(9) [O(5)]/144.69(9) [O(10)]
N-Ln-N
O-Ln-O
134.9(2)
152.8(2)
118.85(9)
149.67(6)
119.07(13)
144.51(9)
153.89(7) [O(1)/O(1A)] 147.67(7) [O(1)/O(2)]/147.74(8) [O(6)/O(7)]
130.55(8) [O(2)/O(2A)] 82.04(7) [O(1)/O(3)]/82.51(7) [O(6)/O(8)]
102.32(5) [O(1)/O(2)] 87.25(7) [O(1)/O(4)]/90.24(8) [O(6)/O(9)]
88.60(5) [O(1)/O(2A)] 140.38(7) [O(1)/O(5)]/140.33(7) [O(6)/O(10)]
113.76(8) [O(2)/O(3)]/109.93(8) [O(7)/O(8)]
95.87(8) [O(2)/O(4)]/95.15(9) [O(7)/O(9)]
71.88(7) [O(2)/O(5)]/71.91(8) [O(7)/O(10)]
139.37(8) [O(3)/O(4)]/143.46(8) [O(8)/O(9)]
79.04(7) [O(3)/O(5)]/78.77(7) [O(8)/O(10)]
84.99(7) [O(4)/O(5)]/84.64(7) [O(9)/O(10)]
O-Ln-N
91.31(15) [O(1)/N(1)] 107.20(7) [O(1)/N(1)] 108.61(11) [O(1)/N(1)]
99.07(15) [O(1)/N(1A)] 92.98(8) [O(1)/N(2)] 93.96(11) [O(1)/N(2)]
89.68(8) [O(2)/N(1)] 90.41(11) [O(2)/N(1)]
100.78(8) [O(2)/N(2)] 102.70(12) [O(2)/N(2)]
Ln-Cipso- Cortho 122.5(3)
Cipso-Cortho-Cipso′ 121.3(5)
122.30(17) [C(8)]
121.42(17) [C(12)]
121.7(2) [C(8)/C(7)]
122.3(3) [C(8)]
121.5(3) [C(12)]
121.8(4) [C(8)/C(7)]
121.72(12)
121.58(18)
121.8(2) [C(8)]/122.3(2) [C(56)]
122.3(2) [C(12)]/122.0 (2) [C(60)]
122.3(3) [C(8)/C(7)]/122.7(3) [C(56)/C(55)]
122.4(3) [C(12)/C(14)]/121.9(3) [C(60)/C(62)]
121.5(2) [C(12)/C(14)] 121.3(4) [C(12)/C(14)]
lanthanide element that yields stable terphenyl compounds
is samarium. The molecular structure of the samarium
analogue 3 is isomorphic with the ytterbium compound 2.
The Sm-N distances in 3 [2.303(3) and 2.313(3) Å,
respectively] are in the same range as those in the as well
five-coordinate Sm[N(SiHMe2)2]3(THF)2 [2.302(3), 2.327-
(2), and 2.330(3) Å].18 The N-Ln-N angles in both the
ytterbium compound 2 [118.85(9)°] and the samarium
analogue 3 [119.07(13)°] are found to be very similar. The
Sm-N-Si angles in 3 [Si(1), 111.77(19)°; Si(2), 116.99-
(18)°, Si(3), 110.11(18)°; Si(4), 117.3(2)°] can be favorably
compared with the corresponding angles in 2. As was found
in the molecular structure of 2, there are no Sm‚‚‚H(Si-H)
distances in 3 that are significantly shorter than 3.0 Å [H(1),
3.01(2); H(2), 3.23(2); H(3), 3.04(2); H(4), 3.14(2) Å].
Again, this excludes the presence of an “agostic” interaction
in compound 3. Additionally, as one would expect, there
are no Sm‚‚‚C distances shorter than 3.0 Å, besides the Sm-
C(ipso) distance at 2.484(4) Å. The next closest Sm‚‚‚C
distance is 3.271(8) Å [C(19)], and the nearest interaction
with one of the methyl groups on the silicon atoms is 4.627-
(8) Å [C(22)]. The Si-N-Si angles in the bis(dimethylsilyl)
derivatives 2 [Si(1)-N(1)-Si(2), 127.25(14)°; Si(3)-N(2)-
Si(4), 128.30(14)°] and 3 [Si(1)-N(1)-Si(2), 131.2(2)°; Si-
(3)-N(2)-Si(4), 132.5(2)°] are somewhat larger than the
corresponding angle in the bis(trimethylsilyl) compound 1
[Si(1)-N(1)-Si(2), 120.1(3)°]. Further bond distances and
angles of both compounds 2 and 3 are provided in Table 2.
DanipYb[O(2,6-diisopropylphenyl)]2 (4) and DanipY-
(THF)[O(2,6-diisopropylphenyl)]2 (5). We were interested
in the accessibility of other derivatives of general composi-
tion DanipLnX2 and therefore decided to employ a moder-
ately sterically demanding aryloxide ligand, i.e., the 2,6-
diisopropylphenoxide ligand, vis-a`-vis a Danip moiety. This
particular aryloxide ligand was employed first as an ancillary
ligand system for the lanthanides in the early nineties by
Clark and co-workers.19,20 As was found in the case of the
Danip-based bis(amide) compounds 1-3, the molecular
structure of the as well five-coordinate bis(alkoxide) com-
pound 4 (Figure 4) features a distorted square-pyramidal
coordination environment about the metal atom. Besides the
Yb-C(ipso) distance [2.379(3) Å] all other Yb‚‚‚C distances
in 4 are clearly longer than 3.0 Å. The Yb-O(OMe) distance
[2.3172(13) Å] in 4 is noticeably shorter than in the bis-
(amide) compounds 1 [2.376(4) Å] and 2 [2.4050(18) and
2.3898(18) Å, respectively]. The Yb-O(aryloxide) distance
[2.0634(13) Å] is approximately 1/10 of an angstrom longer
than the Yb-O(tert-butoxide) distance in the as well five-
coordinate terphenyl mono(alkoxide) compound DmpYb-
(THF)(OtBu)(µ-Cl2)Li(THF)2 [1.965(5) Å], which is so far
the only other reported terphenyl-based lanthanide alkoxide
compound.9 This observation presumably is as a result of
the increased steric crowding at the metal atom. The Yb-
O(aryloxide) distance of 2.0634(13) Å in 4 can further be
compared, e.g., with the metal-O(aryloxide) distances in the
(19) Clark, D. L.; Watkin, J. G.; Huffman, J. C. Inorg. Chem. 1992, 31,
1556.
(18) Rabe, G. W.; Yap, G. P. A. Z. Kristallogr.-New Cryst. Struct. 2000,
215, 457.
(20) Barnhart, D. M.; Clark, D. L.; Gordon, J. C.; Huffman, J. C.; Vincent,
R. L.; Watkin, J. G.; Zwick, B. D. Inorg. Chem. 1994, 33, 3487.
Inorganic Chemistry, Vol. 42, No. 11, 2003 3531

Rabe et al.
Figure 3. ORTEP diagram of DanipYb[N(SiHMe2)2]2 (2) showing the
atom-labeling scheme. Thermal ellipsoids are at the 30% level. Hydrogen
atoms were omitted for clarity.
Figure 5. ORTEP diagram of DanipY(THF)[O(2,6-diisopropylphenyl)]2
showing the atom-labeling scheme. Only one of the two independent
molecules (5a) is shown. Thermal ellipsoids are at the 30% level. Hydrogen
atoms were omitted for clarity.
Figure 4. ORTEP diagram of DanipYb[O(2,6-diisopropylphenyl)]2 (4)
showing the atom-labeling scheme. Thermal ellipsoids are at the 30% level.
Hydrogen atoms were omitted for clarity.
Figure 6. Central core of 5a showing the distorted trigonal-prismatic
coordination polyhedron.
as well five-coordinate lutetium compound Lu[O(2,6-
diisopropylphenyl)]3(THF)2 (average 2.044 Å),20 taking into
consideration the slightly smaller ionic radius of lutetium-
(III).21 The ytterbium aryloxide moieties in 4 are slightly
bent [Yb-O(2)-C(17), 159.04(12)°], as was previously
observed in the case of tris(2,6-diisopropylphenoxide) com-
pounds of the lanthanides.20 The 2,6-diisopropylphenyl
moieties are not tilted [O(2)-C(17)-C(12), 119.68(16)°;
O(2)-C(17)-C(16), 120.22(17)°]. While the O(OMe)-Yb-
O(OMe) angles in the bis(amide) compound 1 [152.8(2)°]
and in the bis(alkoxide) derivative 4 [153.89(7)°] are very
similar, the O(aryloxide)-Yb-O(aryloxide) angle in 4
[130.55(8)°] is somewhat smaller than the N-Yb-N angle
[134.9(2)°] in 1.
bis(trimethylsilyl)amide analogues of compound 1 but with
yttrium and samarium instead of ytterbium we failed to obtain
single crystalline material. Interestingly, in the molecular
structure of the yttrium bis(alkoxide) compound 5 (Figure
5) additional coordination of one molecule of tetrahydrofuran
is observed, resulting in a coordination polyhedron which
can be described as distorted trigonal-prismatic rather than
octahedral (Figure 6) since there is no interligand angle about
the metal atom close to 180°. Two chemically identical
independent molecules are found in the unit cell of compound
5. The largest interligand angles about the metal atom are
those involving the two methoxy functions, namely 147.67-
(7)° [5a, O(1)-Y(1)-O(2)] and 147.74(8)° [5b, O(6)-
Y(2)-O(7)]. The Y-O(THF) distance [5a, 2.439(2) Å; 5b,
2.458(2) Å] is considerably longer than the Y-O(aryloxide)
distances [5a, 2.111(2) and 2.127(2) Å; 5b, 2.100(2) and
2.122(2) Å] but can favorably compared with the Y-O(OMe)
distances ranging from 2.393(2) to 2.434(2) Å. The smallest
O(THF)-Y-O angle is with one of the O(OMe) atoms
[O(2), 71.88(7)° (5a); O(7), 71.91(8)° (5b), respectively].
Both the Y-O(OMe) and the Y-O(aryloxide) distances in
We were interested in investigating how differences in the
size of the metal atom would affect the molecular structure
of compound 4. In the case of the bis(dimethylsilyl)
compounds 2 and 3 the same structural type was observed
for metals of different size. And in the case of the
(21) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
3532 Inorganic Chemistry, Vol. 42, No. 11, 2003

Lanthanide Terphenyl Complexes
5 are slightly longer (see Table 2) than the corresponding
distances in the ytterbium bis(aryloxide) compound 4, as one
would expect on the basis of Shannon’s radii21 for a
molecular structure with a coordination number 6 instead of
5 at the metal atom and a slightly larger metal atom, i.e.,
yttrium instead of ytterbium. While the O(aryloxide)-Y-
O(aryloxide) angles [5a, 139.37(8)°; 5b, 143.46(8)°] are
larger than the corresponding angle in 4 [130.55(8)°], the
O(OMe)-Y-O(OMe) angles [5a, 147.67(7)°; 5b, 147.74-
(8)°] are noticeably smaller than the same angle in 4 [153.89-
(7)°]. As was found in the molecular structure of compound
4, the yttrium aryloxide moieties in 5 are slightly bent [5a,
168.98(18) and 169.62(19)°; 5b, 165.87(19) and 171.77(19)°]
but to a smaller extent than in 4 [159.04(12)°]. Again, as in
4, the 2,6-diisopropylphenyl moieties are not tilted. Further
interatomic separations and angles of 4 and both independent
molecules of 5 can be derived from Table 2.
air and moisture the compounds are remarkably stable in
the solution state, in contrast to previously reported non-
functionalized lanthanide terphenyl compounds which were
of only limited stability, particularly in tetrahydrofuran
solution at room temperature. The molecular structures of
compounds 1-4 exhibit square-pyramidal coordination
environments about the metal atom. Except for the yttrium
bis(alkoxide) compound 5 all presented complexes are free
of coordinating Lewis bases such as tetrahydrofuran. In all
molecular structures that are reported in this paper, the Danip
ligand adopts the chiral (racemic) d,l form. The usability of
these compounds for, e.g., catalytic applications for a variety
of transformations is currently under investigation.
Acknowledgment. The authors are thankful for financial
support from the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, and the Leonhard-Lorenz
foundation. G.W.R. thanks the Deutsche Forschungsgemein-
schaft for the award of a Heisenberg stipend.
Conclusion
Our work demonstrates that a number of novel low-
coordinate monomeric bis(amide) and bis(arylalkoxide)
compounds of Danip-based lanthanide systems (Ln ) Yb,
Y, Sm) are easily accessible in good yield via simple salt
metathesis reaction in a one-pot synthesis. Our work gives
further insight into structural aspects as well as the reactivity
of Danip-based lanthanide complexes. Under exclusion of
Supporting Information Available: X-ray crystallographic files
in CIF format for the structures of DanipYb[N(SiMe3)2]2 (1),
DanipYb[N(SiHMe2)2]2 (2), DanipSm[N(SiHMe2)2]2 (3), DanipYb-
[O(2,6-diisopropylphenyl)]2 (4), and DanipY(THF)[O(2,6-diiso-
propylphenyl)]2 (5). This material is available free of charge via
the Internet at http://pubs.acs.org.
IC0300161
Inorganic Chemistry, Vol. 42, No. 11, 2003 3533