Communications
Organometallics, Vol. 24, No. 5, 2005 799
differs markedly from that of a symmetrical π-coordina-
tion as is found, for example, in the (η3-allyl)neodymium
complexes (η3-C3H5)3Nd(DME)9a and [(η3-C3H5)2Nd(µ-
Cl)(THF)]2.9b On the other hand, the bond distances and
angles largely agree with those of the, to our knowledge,
only structurally characterized (η3-azaallyl)lanthanide
complexes, [Me3SiCHC(tBu)N(SiMe3)]2SmI(THF) and
[Me3SiCHC(tBu)N(SiMe3)]2Yb,10 whose π-azaallyl ligands,
however, are not connected by an alkyl bridge.
When the mole ratio of the two reactants 2 and NdBr3-
(THF)3.5 was increased to 2:1, then the nearly colorless,
air- and moisture sensitive neodymium complex 6 was
obtained in 75% yield (Scheme 2). Complex 6 can be
formally considered as a derivative of the ionic com-
pound 4, in which the two bromine ligands are substitu-
ted by a second hexa-1,5-diene-1,6-diamide ligand. There-
fore, it is not much of a surprise that, at least in the
crystalline state, the [(hexa-1,5-diene-1,6-diamide)2Nd]-
Figure 3. Molecular structure of the anion of 6. The hy-
drogen atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): Nd-N1A ) 2.393(3), Nd-
N2A ) 2.364(3), Nd-N1B ) 2.380(3), Nd-N2B ) 2.397(3),
Nd-C1A ) 2.842(4), Nd-C2A ) 3.170(4), Nd-C5B )
3.101(4), Nd-C6 ) 2.834(4), N1A-C1A ) 1.370(5), N2A-
C6A ) 1.374(5), C1A-C2A ) 1.358(6), C2A-C3A ) 1.519(6),
C3A-C4A ) 1.558(6), C4A-C5A ) 1.523(5), C5A-C6A )
1.337(5), N1B-C1B ) 1.382(4), N2B-C6B ) 1.368(5),
C1B-C2B ) 1.335(5), C2B-C3B ) 1.520(5), C3B-C4B )
1.560(5), C4B-C5B ) 1.525(5), C5B-C6B ) 1.356(5);
N1A-Nd-N2A ) 124.4(1), N1B-Nd-N2B ) 125.8(1),
N1A-C1A-C2A ) 124.3(4), N2A-C6A-C5A ) 129.1(4),
N1B-C1B-C2B ) 128.5(3), N2B-C6B-C5B ) 124.1(4).
(8) (a)Crystaldatafor4.ModificationI: [C12H30O6Li]+[C26H34Br2N2Nd]-,
Mr ) 955.91, colorless prism, size 0.10 × 0.08 × 0.06 mm3, monoclinic,
space group P21, a ) 12.1509(3) Å, b ) 28.9797(8) Å, c ) 12.8885(3) Å,
â ) 96.685(2)°, V ) 4507.6(2) Å3, T ) -90 °C, Z ) 4, Fcalcd ) 1.409 g
cm-3, µ(Mo KR) ) 29.65 cm-1, ψ-scan, minimum transmission 0.7559,
maximum transmission 0.8422, F(000) ) 1948, 17 486 reflections in h
(-14 to +15), k (-37 to +24), l (-16 to +12), measured in the range
1.59° e θ e 27.11°, completeness θmax ) 92.7%, 12 240 independent
reflections, Rint ) 0.063, 10 476 reflections with Fo > 4σ(Fo), 896
parameters, 1 restraint, R1obsd ) 0.083, wR2obsd ) 0.201, R1all ) 0.097,
wR2all ) 0.219, GOF ) 1.085, Flack parameter 0.07(2), largest
difference peak/hole 7.089/-1.453 e Å-3. Modification II: triclinic, space
group P1h, a ) 12.1499(7) Å, b ) 12.8905(7) Å, c ) 29.0650(10) Å, R )
86.015(3)°, â ) 88.674(3)°, γ ) 83.328(3)°, V ) 4509.8(4) Å3, T ) -90
°C, Z ) 4, Fcalcd ) 1.787 g cm-3, µ(Mo KR) ) 65 cm-1, ψ-scan, minimum
transmission 0.5626, maximum transmission 0.6244, F(000) ) 2388,
18 964 reflections in h (-12 to +15), k (-16 to +16), l (-27 to +37),
measured in the range 1.59° e θ e 27.45°, completeness θmax ) 98.6%.
The X-ray data of both of the two modifications of compound 4 are of
minor quality. Therefore, only their crystallographic data and the
conformation of 4 are published. Bond lengths and angles are not listed.
anion and the [Li(DME)3]+ cation existsmuch like in the
case of 4sas a solvent-separated ion pair (Figure 3).8
Due to the limited space in the coordination sphere
of the metal center, the two hexa-1,5-diene-1,6-diamide
ligands are forced into the more space-saving enamide
function (η1- and σ-azaallyl, respectively), each at the
expense of one η3-azaallyl function. As a consequence
thereof, the configuration of the double bonds C5AdC6A
and C1BdC2B changes from E to Z and thus prevents
an increase of the ring tension. The result of the crystal
structure analysis furthermore indicates that the Nd-C
distances of the other two η3-azaallyl units are slightly
longer than those of 5 (Nd-C1A ) 2.842(4) Å, Nd-C2A
) 3.170(4) Å, Nd-C6 ) 2.834(4) Å, Nd-C5B ) 3.101(4)
Å). However, the bonding mode of the hexa-1,5-diene-
1,6-diamide ligands in 6 is still best described as η3-
azaally η1-enamide bonding.
Ziegler-Natta catalysts containing neodymium have
been used in the industrial production of poly-cis-1,4-but-
adiene for some time now.11 The above-mentioned (η3-
allyl)neodymium complexes (η3-C3H5)3Nd(dioxane)9a and
[(η3-C3H5)2Nd(µ-Cl)(THF)]2 9b as well as (η3-C3H5)NdCl2-
(THF)2 9b have actually been shown to be extremely ac-
tive and highly selective complex catalysts for the 1,4-cis
polymerization of buta-1,3-diene. To obtain preliminary
information about the catalytic activity of the novel aza-
allyl neodymium complexes 4 and 6, polymerization of
buta-1,3-diene was conducted with them using MMAO
as cocatalyst (molar ratio of about 0.1:30) and cyclohex-
ane as the solvent at 80 °C. For comparison we also stud-
ied the hexa-1,5-diene-1,6-diamide lanthanum complex
7, whose structure was established by 1H NMR and re-
sembles that of 5 (see Experimental Section). The re-
sults of the polymerization experiments are listed in
Table 1. As expected, the coordinatively less saturated
Crystal data for 5:
C60H88Br4Li2N4Nd2O4‚2C4H10O, Mr ) 1699.58,
colorless prism, size 0.10 × 0.09 × 0.06 mm3, triclinic, space group
P1h, a ) 12.3196(5) Å, b ) 13.2774(5) Å, c ) 13.5081(6) Å, R ) 94.649-
(3)°, â ) 112.393(2)°, γ ) 105.774(2)°, V ) 1923.22(14) Å3, T ) -90
°C, Z ) 1, Fcalcd ) 1.467 g cm-3, µ(Mo KR) ) 34.59 cm-1, semiempirical,
minimum transmission 0.623, maximum transmission 0.834, F(000)
) 858, 22 302 reflections in h (-15 to +15), k (-16 to +17), l (-17 to
+13), measured in the range 1.89° e θ e 27.44°, completeness θmax
99.6%, 8743 independent reflections, Rint ) 0.084, 6529 reflections with
Fo > 4σ(Fo), 371 parameters, 0 restraints, R1obsd ) 0.046, wR2obsd
0.097, R1all ) 0.075, wR2all ) 0.110, GOF ) 1.024, largest difference
)
)
peak/hole 0.716/-1.414 e Å-3. Crystal data for 6: [C12H30LiO6]+[C52H68
-
N4Nd]-, Mr ) 1170.64, colorless prism, size 0.10 × 0.10 × 0.09 mm3,
monoclinic, space group P21/c, a ) 10.8383(3) Å, b ) 37.8916(9) Å, c )
15.8874(4) Å, â ) 94.797(1)°, V ) 6501.8(3) Å3, T ) -90 °C, Z ) 4,
Fcalcd ) 1.196 g cm-3, µ(Mo KR) ) 8.47 cm-1, F(000) ) 2484, 40 749
reflections in h (-14 to +13), k (-49 to +35), l (-20 to +20), measured
in the range 1.96° e θ e 27.44°, completeness θmax ) 97.6%, 14 472
independent reflections, Rint ) 0.055, 9932 reflections with Fo > 4σ(Fo),
717 parameters, 0 restraints, R1obsd ) 0.049, wR2obsd ) 0.108, R1all
)
0.088, wR2all ) 0.125, GOF ) 1.007, largest difference peak and hole:
0.875/-0.635 e Å-3. (b) The detailed crystallographic data of this
publication are available as Supplementary Publications CCDC-215583
(5) and CCDC-215584 (6) from the Cambridge Crystallographic Data
conts/retrieving.html (or by postal mail in Great Britain: Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ,
U.K.; fax (+44) 1223-336-033; e-mail deposit@ccdc.cam.ac.uk).
(9) (a) Taube, R.; Windisch, H.; Maiwald, S.; Hemling, H.; Schu-
mann, H. J. Organomet. Chem. 1996, 513, 49-61. (b) Maiwald, S.;
Taube, R.; Hemling, H.; Schumann, H. J. Organomet. Chem. 1998,
552, 195-204. (c) Maiwald, S.; Sommer, C.; Mu¨ller, G.; Taube, R.
Macromol. Chem. Phys. 2000, 202, 1446-1456. See also reports about
allylsamarium complexes which are efficient catalysts for the polym-
erization of methyl methacrylate: (d) Woodman, T. J.; Schormann, M.;
Bochmann, M. Organometallics 2003, 22, 2938-2943. (e) Woodman,
T. J.; Schormann, M.; Hughes, D. L.; Bochmann, M. Organometallics
2003, 22, 3028-3033.
(11) (a) Witte, J. Angew. Makromol. Chem. 1981, 94, 119-124. (b)
Wilson, D. J. Polym. Int. 1996, 39, 235-242. (c) Taube, R.; Sylvester,
G. In Applied Homogeneous Catalysis with Organometallic Compounds;
Cornils, B., Herrmann, W. A., Eds.; VCH: Weinheim, Germany, 1996;
pp 280-318. (d) Thiele, S. K.-H.; Wilson, D. R. J. Macromol. Sci., Part
C-Polym. Rev. 2003, C43, 581-628.
(10) (a) Hitchcock, P. B.; Lappert, M. F.; Tian, S. J. Organomet.
Chem. 1997, 549, 1-12. (b) Lappert, M. F.; Liu, D.-S. J. Organomet.
Chem. 1995, 500, 203-217.