Mendeleev Commun., 2010, 20, 197–199
electron-rich YbII central atom, thus, to compounds that are
less susceptible toward protolytic and oxidative degradation.
These properties render the CpPN building unit an ideal spectator
ligand for functionalized lanthanide complexes such as hetero-
leptic amides and alkyls.
Table 1 Selected bond lengths (Å) and angles (°) for the Δ- and Λ-enantio-
mers of 4·1/2Et2O.
Δ-enantiomer
Λ-enantiomer
Yb(2)–N(2)
N(2)–P(2)
P(2)–C(32)
Yb(2)–Z(2)
Yb(1)–N(1)
N(1)–P(1)
P(1)–C(1)
Yb(1)–Z(1)
2.537(2)
1.597(2)
1.758(3)
2.622(1)
2.618(2)
1.596(2)
1.763(3)
2.563(1)
K.A.R. akcnowledges Deutsche Akademischer Austausch
Dienst (DAAD) for funding a research fellowship at Philipps-
Universität Marburg within the Ostpatnerschaftsprogramm. This
study was supported by DFG (SPP-1166).
N(1)–Yb(1)–C(1)
N(1)–Yb(1)–Z(1)
N(1)–P(1)–C(1)
N(1)–Yb(1)–N(1)'
Z(1)–Yb(1)–Z(1)'
60.2(1)
85.2(1)
103.1(1)
122.1(1)
133.6(1)
N(2)–Yb(2)–C(32)
N(2)–Yb(2)–Z(2)
N(2)–P(2)–C(32)
N(2)–Yb(2)–N(2)'
Z(2)–Yb(2)–Z(2)'
59.6(1)
85.2(1)
102.7(1)
127.8(1)
131.5(1)
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.mencom.2010.06.004.
CpPN chelate ligand and by the helical configuration of both.
The molecular bonding distances and angles of the CpPN
ligand are closely related to those found in the structure of the
[{η5,η1-Me2P(C5Me4)NAd}Lu(CH2SiMe3)2] complex.1(c) How-
ever, a further investigation into the ligand bonding mode, by
comparison of Lu3+ and Yb2+ complexes, reveals characteristic
differences. Although the ionic radius of ytterbium(II) (0.159 Å)6
is larger than that of lutetium(III), the average Yb–N bond
length is significantly greater [2.578(4) Å] than that of the
corresponding Lu–N bond in the lutetium complex [{η5,η1-
Me2P(C5Me4)NAd}Lu(CH2SiMe3)2] [2.278(3) Å]. On the one
hand, the value is better comparable with those found in closely
related ytterbocenes with σ-donating nitrogen ligands (e.g.,
2.486, 2.514 Å in [{η5-1,3-(Me3Si)2C5H3}2Yb(Phen)],7 2.544,
2.586 Å in [{η5-C5Me5}2Yb(py)2]8 and av. 2.579 Å in [{η5,η1-
C5H4(CH2)2NMe2}2Yb]9). On the other hand, the average Yb–Z
distance of 2.593(2) Å is unexpectedly long and falls out of the
range typical of ytterbocenes. For instance, in ytterbocenes
with the polysubstituted cyclopentadienyl ligands, the Yb–Z
distance of av. 2.466(3) Å was found in [{η5-C5Me5}2Yb(py)2]8
and 2.443(2) Å in [{η5-C5Me5}2Yb(terpy)].10 Note that the Yb–Z
distances in complexes with a non-substituted Cp moiety are,
in general, significantly shorter; the distance of only 2.408(1) Å
was found in [{η5-C5H5}2Yb(dme)]11 and av. 2.376(2) Å in
[{η5-C5H5}2Yb(thf)].12 The elongation of the Yb-Z distance
in the structure of complex 4 can be attributed to the significant
electron withdrawing –I and/or –M effects of the iminophos-
phorane moiety. The comparison of the average P–CPh bond length
[av. 1.835(3) Å] in 4 with the closely related Ph2P(C5H4)Me
(av. 1.808 Å)13 and Ph3P(C5H4) (av. 1.806 Å)14 is in accordance
with this assumption.
References
1
(a) K. A. Rufanov, B. Ziemer, M. Hummert and S. Schutte, Eur. J.
Inorg. Chem., 2004, 4759; (b) K. A. Rufanov, B. Ziemer and M. Meisel,
Dalton Trans., 2004, 3808; (c) K. A. Rufanov, A. R. Petrov, V. V. Kotov,
F. Laquai and J. Sundermeyer, Eur. J. Inorg. Chem., 2005, 3805;
(d) A. R. Petrov, K. A. Rufanov, B. Ziemer, P. Neubauer, V. V. Kotov
and J. Sundermeyer, Dalton Trans., 2008, 909; (e) K. A. Rufanov and
A. Spannenberg, Mendeleev Commun., 2008, 18, 32.
2
3
(a) P. J. Shapiro, E. E. Bunel, W. P. Schaefer and J. E. Bercaw, Organo-
metallics, 1990, 9, 867; (b) P. J. Shapiro, W. D. Cotter, W. P. Schaefer,
J. A. Labinger and J. E. Bercaw, J. Am. Chem. Soc., 1994, 116, 4623;
(c) W. E. Piers, P. J. Shapiro, E. E. Bunel and J. E. Bercaw, Synlett,
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Top. Curr. Chem., 1991, 160, 97.
(a) J. C. Stevens, F. J. Timmers, G. W. Rosen, G. W. Knight and
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4
5
G. Blasse and B. C. Grabmaier, Luminescent Materials, Spriger-Verlag,
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A. V. Khvostov, A. I. Sizov, B. M. Bulychev, S. Ya. Knjazhanski and
V. K. Belsky, J. Organomet. Chem., 1998, 559, 97.
6
7
R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751.
M. Schultz, J. M. Boncella, D. J. Berg, T. D. Tilley and R. A. Andersen,
Organometallics, 2002, 21, 460.
8
9
T. D. Tilley, R. A. Andersen, B. Spencer and A. Zalkin, Inorg. Chem.,
1982, 21, 2647.
T. D. Tilley, R. A. Andersen, B. Spencer and A. Zalkin, Inorg. Chim.
Acta, 1998, 280, 138.
10 C. J. Kuehl, R. E. Da Re, B. L. Scott, D. E. Morris and K. D. John,
Chem. Commun., 2003, 2336.
Thus, not only steric but also electronic effects of the CpPN
ligands are responsible for the unique stability of the above
compounds with respect to dioxygen. The ligands reveal an
ambident character; the monoanionic charge is partially localized
on the Cp ring, as well as on the nitrogen atom of the phos-
phazene unit (Scheme 3). Due to the negative-hyperconjugative
stabilizing effect15 of the phosphorus(V) σ* orbitals and the
characteristic charge distribution, CpPN ligands can be con-
sidered as much weaker donors than classical ligands [C5R5]–
or [NPR3]–, which are well established in lanthanide chemistry.
Both the weaker donor character and charge distribution lead
to less polar metal carbon and metal nitrogen bonds and a less
11 J. Jin, S. Jin and W. Chen, J. Organomet. Chem., 1991, 412, 71.
12 T. D. Tilley, R. A. Andersen, B. Spencer, H. Ruben, D. H. Templeton
and A. Zalkin, Inorg. Chem., 1980, 19, 2999.
13 J. H. Brownie, H. Schmider and M. C. Baird, Organometallics, 2007,
26, 1433.
14 P. Laavanya, B. S. Krishnamoorthy, K. Panchanatheswaran and
M. Manoharan, J. Mol. Struct. THEOCHEM, 2005, 716, 149.
15 T. Leyssens and D. Peeters, J. Org. Chem., 2008, 73, 2725 and
references cited therein.
16 C. Giacovazzo, Z. Kristallogr., 1993, 206, 161.
17 G. M. Sheldrick, SHELXS 97, Program for Solution of Crystal Structures,
Universität Göttingen, 1997.
18 K. Brandenburg, Diamond 3.0a, Crystal Impact GbR, Bonn, Germany,
1997–2004.
Me4
Me4
Me4
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R
R
R
R
R
R
P
P
P
N
N
N
Yb
Yb
Yb
R
R
R
R
R
R
N
N
N
P
P
P
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Me4
Me4
Me4
Scheme 3 Valence bond description of the title complexes.
Received: 10th February 2010; Com. 10/3464
– 199 –