Zirconium complexes of symmetric and of chiral diketiminate ligands: Synthesis, crystal structures, and reactivities

Article abstract of DOI:10.1021/om900852y

Reaction of N,N-dialkyl-2-amino-4-iminopent-2-enes (nacnac^RH; R = Bn (1a), Cy (1b), R-CH(Me)Ph (1c)) with nBuLi afforded the lithium salts nacnac^RLi(THF), 2a-c. Further reaction with ZrCl₄ or ZrCl₄(THF)₂ yielded the cis-dichloride complexes nacnac^R₂ZrCl₂, 3a-c. As a side reaction in the synthesis of 3c, CH activation of CH(Me)Ph under formal HCl elimination was observed. Complex 3a could also be obtained by reaction of nacnac^BnH with nBu₂ZrCl₂. nacnac^Bn₂ZrMe ₂, 5, was formed in reactions of 3a with MeLi in the presence of excess AlMe₃ and was isolated from the reaction of Me ₂ZrCl₂ with 2a. Complex 5 reacts with aluminum chloride compounds, but not with lithium chloride, to form the dichloride complex 3a and with ethanol to form nacnac^Bn₂Zr(OEt)₂, 6. X-ray diffraction studies have been performed for 3a-c, 5, and 6.

Full text of DOI:10.1021/om900852y

Organometallics 2010, 29, 1551–1559 1551
DOI: 10.1021/om900852y
Zirconium Complexes of Symmetric and of Chiral Diketiminate Ligands:
Synthesis, Crystal Structures, and Reactivities
Ibrahim El-Zoghbi, Saıda Latreche, and Frank Schaper*
ꢀ ꢀ ꢀ ꢀ ꢀ
Departement de Chimie, Universite de Montreal, Montreal, Quebec, H3C 3J7, Canada
Received October 1, 2009
Reaction of N,N-dialkyl-2-amino-4-iminopent-2-enes (nacnacRH; R = Bn (1a), Cy (1b), R-CH-
(Me)Ph (1c)) with nBuLi afforded the lithium salts nacnacRLi(THF), 2a-c. Further reaction with
ZrCl4 or ZrCl4(THF)2 yielded the cis-dichloride complexes nacnacR2ZrCl2, 3a-c. As a side reaction
in the synthesis of 3c, CH activation of CH(Me)Ph under formal HCl elimination was observed.
Complex 3a could also be obtained by reaction of nacnacBnH with nBu2ZrCl2. nacnacBn2ZrMe2, 5,
was formed in reactions of 3a with MeLi in the presence of excess AlMe3 and was isolated from the
reaction of Me2ZrCl2 with 2a. Complex 5 reacts with aluminum chloride compounds, but not with
lithium chloride, to form the dichloride complex 3a and with ethanol to form nacnacBn2Zr(OEt)2, 6.
X-ray diffraction studies have been performed for 3a-c, 5, and 6.
Introduction
was focused mostly on their application in olefin, notably
ethylene, polymerization5,9-11 or on investigations of the
ligand coordination mode,4,6-8,15,16 which varies between in-
plane κ2-coordination and out-of-plane η4/5-coordination.
With a single exception,12 ligands with aryl substituents on
nitrogen were employed, as is the case in most diketiminate
metal complexes. Variations in the ligand framework were
limited by the fact that ortho-substitution of both N-aryl
substituents impedes the coordination of a second diketimi-
nate ligand to zirconium,6-8 although the use of unsymme-
trical ligands allowed the substitution of at least one phenyl
ring.11 Complexation of the bulky bis(trimethylsilyl) diketi-
minate (nacnacTMS) to Zr resulted in a rearrangement of
one nacnacTMS ligand.10 Coordination of two diketiminate
ligands to a ZrX2 fragment should favor the formation of
C2-symmetric cis-complexes, with two homotopic Zr-X
sites, whose environment is strongly influenced by the sub-
stituent on nitrogen. We present in the following the synthe-
ses of zirconium bis(diketiminate) complexes with aliphatic
substituents on nitrogen, which increase the possibilities of
steric variations in these complexes and allow easy introduc-
tion of chirality, the investigation of their solid state and
solution structures, and (attempted) applications in catalysis.
β-Diketiminate (“nacnac”) ligands have gained increasing
popularity since the mid 1990s due to their suitability as
spectator ligands.1 Zirconium complexes with diketiminate
ligands (based on 2,4-diiminopentane)2,3 appeared in the
literature in 1994 with the work of Lappert and co-workers,4
followed by more extensive work in the groups of Collins,5,6
Smith,7,8 Novak,9 and others.10-16 Interest in these complexes
*Corresponding author. E-mail: Frank.Schaper@umontreal.ca.
(1) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
102, 3031.
(2) For other structures, for example incorporating a pyridyl moiety,
see: Deelman, B.-J.; Hitchcock, P. B.; Lappert, M. F.; Leung, W.-P.;
Lee, H.-K.; Mak, T. C. W. Organometallics 1999, 18, 1444.
(3) Cortright, S. B.; Huffman, J. C.; Yoder, R. A.; Coalter, J. N.;
Johnston, J. N. Organometallics 2004, 23, 2238.
(4) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. Chem. Commun.
1994, 2637.
(5) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.; Taylor,
N. J.; Collins, S. Organometallics 2000, 19, 2161.
(6) Rahim, M.; Taylor, N. J.; Xin, S.; Collins, S. Organometallics
1998, 17, 1315.
(7) Kakaliou, L.; Scanlon, W. J.; Qian, B.; Baek, S. W.; Smith, M. R.;
Motry, D. H. Inorg. Chem. 1999, 38, 5964.
(8) Qian, B.; Scanlon, W. J.; Smith, M. R.; Motry, D. H. Organome-
tallics 1999, 18, 1693.
(9) Jin, X.; Novak, B. M. Macromolecules 2000, 33, 6205. Novak,
B. M.; Jin, X.; Tanaka, H. Polym. Prepr. (Am. Chem. Soc., Div. Polym.
Chem.) 2000, 41, 399.
(10) Shaviv, E.; Botoshansky, M.; Eisen, M. S. J. Organomet. Chem.
2003, 683, 165.
(11) Gong, S.; Ma, H.; Huang, J. J. Organomet. Chem. 2008, 693,
3509.
(12) Franceschini, P. L.; Morstein, M.; Berke, H.; Schmalle, H. W.
Inorg. Chem. 2003, 42, 7273.
(13) Basuli, F.; Kilgore, U. J.; Brown, D.; Huffman, J. C.; Mindiola,
D. J. Organometallics 2004, 23, 6166.
Results and Discussion
nacnac2ZrCl2 Complexes. Diketimine ligands 1a-c were
obtained from condensation of acetylacetone and the res-
pective amine in the presence of stoichiometric amounts of
para-toluenesulfonic acid. Synthesis of 1a and 1c by this
method has been previously described.17,18 Ligand 1b has
been prepared previously using TiCl4 as an activator in 29%
yield.19 Deprotonation with nBuLi in THF yielded the THF-
coordinated lithium salts 2a-c, which were used without
(14) Hamaki, H.; Takeda, N.; Tokitoh, N. Organometallics 2006, 25,
2457.
ꢀ
(15) Fortune, R.-V.; Verguet, E.; Oguadinma, P. O.; Schaper, F. Acta
Crystallogr. 2007, E63, m2822.
(16) Verguet, E.; Fortune, R.-V.; Oguadinma, P. O.; Schaper, F. Acta
Crystallogr. 2007, E63, m2539. Verguet, E.; Oguadinma, P. O.; Schaper, F.
Acta Crystallogr. 2007, E63, m2541.
(17) Oguadinma, P. O.; Schaper, F. Organometallics 2009, 28, 4089.
(18) Oguadinma, P. O.; Schaper, F. Organometallics 2009, 28, 6721.
(19) Clegg, W.; Coles, S. J.; Cope, E. K.; Mair, F. S. Angew. Chem.,
Int. Ed. 1998, 37, 796.
ꢀ
r
2010 American Chemical Society
Published on Web 02/26/2010
pubs.acs.org/Organometallics

1552 Organometallics, Vol. 29, No. 7, 2010
El-Zoghbi et al.
Scheme 1
In the Λ-isomer, rotation around the N1-C20 and N4-C50
bonds places the phenyl rings of each diketiminate in a syn-
orientation, comparable to the Cs-symmetric ligand confor-
mation observed in 3a (Figure 1). Consequently, methyl
groups C27 and C57 instead of hydrogen atoms are oriented
toward the Zr center, causing an increased distortion from
octahedral geometry, increased Zr1-Cl distances, and a
reduced Cl1-Zr1-Cl2 angle in Λ-3c compared to Δ-3c
(Table 1).
The zirconium atom in 3a-c is bent significantly out of the
mean plane of the ligand (bending angles of 34-49°,
Table 1), as commonly observed in sterically encumbered
diketiminate complexes.1 Since the nitrogen atoms retain
P
their planar geometry (e.g., for 3a: (X-N1-Y) = 359°,
P
(X-N2-Y) = 359°), the alkyl substituents on N are
displaced out of the ligand mean plane (Figure 3). In all
cases, the remaining ligand framework adopts a boat-like
conformation, which reduces the distance between the elec-
tron-rich central carbon atom of the ligand backbone and the
further purification (Scheme 1). Reaction of 2a-c with ZrCl4
or ZrCl4(THF)2 in toluene afforded the respective bis-
(diketiminate) complexes nacnacBn2ZrCl2, 3a, nacnacCy
-
2
ZrCl2, 3b, and (R,R-nacnacMeBn)2ZrCl2, 3c, in moderate
yields (Scheme 1). The choice of zirconium starting material
or the solvent (toluene, THF) did not seem to influence
reaction yields. Following an alternative synthetic route,20
reaction of nBu2ZrCl2, generated in situ by reaction of nBuLi
with ZrCl4, with the neutral ligand 1a in toluene at 90 °C
improved the yield of 3a from 35% to 75%. Similar reactions
with 1b and 1c in toluene or hexane at various temperatures
and reaction times led only to unidentified product mixtures,
which did not contain 3b or 3c in significant amounts.
Reactions of diketiminate ligands with secondary alkyl
substituents on nitrogen seem to be too slow with respect
to the instability of nBu2ZrCl2.
zirconium center.4 In diketiminate Zr complexes with a η4/5
-
coordinated nacnac ligand, distances of the metal center to
5-7,13,16
˚
the central carbon atom are less than 2.8 A.
The
˚
rather longer respective distances in 3a-c (3.1-3.3 A)
indicate, as expected for octahedral coordinated Zr com-
plexes, the absence of significant coordinative interactions
between Zr and the central carbon atom (C3 in Figure 3).
Similar ligand conformations in nacnac Sc complexes have
likewise been ascribed to steric origins.22 Leaving aside
potential pN-d donation, diketiminate ligands in 3a-c thus
act as κ2-coordinated, 4 e--donor ligands.
Yellow crystals of 3c were consistently contaminated with
a minor amount of red crystalline material, which could not
be isolated in sufficient quantity for characterization. X-ray
analysis identified the contamination as the CH-activation
product 4 (Scheme 1, Figure 4). The complex is nonsym-
metric and its geometry best described as distorted square
pyramidal with N1 and C27 sharing the apical position
(X-Zr-X angles (X = Cl1, N2-N4) = 84-89°, X-Zr-Y
angles (Y=centroid N1/C27) =96-112°). The two nacnac
ligands are coordinated differently. The CH-activated ligand
is planar with an anti-orientation of the phenyl rings and the
Zr atom coordinated in the ligand mean plane. In the second
ligand, Zr is found to be bent quite strongly (62°) out of the
mean ligand plane. Zr-C distances to the ligand backbone
X-ray diffractions studies of complexes 3a-c (Figures 1
and 2, Table 1) show distorted octahedral coordination
geometries around the zirconium center (X-Zr-X angles
of 78-107°). In all cases the expected cis-geometry of the
ZrCl2 fragment is found. Complexes 3a and 3b contain a
crystallographic C2-axis, while chiral complex 3c crystallizes
with two diastereomers in the asymmetric unit, which, how-
ever, approach C2-symmetry. The structural features of
3a-c seem to be governed by steric interactions between
the alkyl substituent on nitrogen and the atoms coordinated
to the metal center. The complex distorts in a way to place the
N-substituent between two chloride ligands (or between
chloride and nitrogen) instead of the eclipsed placement
expected from an idealized geometry. Similar distortions
were observed, sometimes to a lesser extent, in related octa-
hedral bis(diketiminato) zirconium complexes,6,7,12 while
they are mostly absent in zirconium complexes with two
aminoketone (acnac) ligands, where the oxygen atom occu-
pies the position trans to the chloride (or amide) ligands.7,12,21
For all complexes, the N-alkyl substituents are oriented away
from the chloride ligands, indicating stronger steric interac-
tions of the alkyl substituent with the chloride ligand than
with the methyl group in the ligand backbone.
˚
˚
are shorter than those in 3c (4: 2.8-2.9 A, 3c: 3.0-3.3 A), but
still noticeably longer than those observed in η4/5-coordi-
5-7,13,16
˚
nated nacnac ligands (2.5-2.8 A).
The shortened
Zr-Cnacnac distances are thus most likely due to steric
reasons, i.e., the increased out-of-plane bending of the Zr
atom.
The formation of 4 as a result of formal HCl elimination
was surprising and only observed as a side reaction during
the preparation of 3c. Treatment of complexes 3a-c with
excess (1-2 equiv) of bases such as NaOtBu, NEt3, pyridine,
Na(NSiMe3)2, or nBuLi showed no reaction (or decomposi-
tion upon heating).
Dynamic Behavior in Solution. NMR spectra of complexes
3a-c indicate that the complexes do not retain their con-
formation in solution. The 1H NMR spectrum of 3a in
CDCl3 at room temperature displays two doublets for
diastereotopic hydrogen atoms of the benzyl CH2 groups,
The diastereomeric Δ- and Λ-isomers of 3c can both be
found in the asymmetric unit. Changes in the Δ/Λ-confor-
mation of the complex are accompanied by changes in the
conformation of the diketiminate ligand. In the Δ-isomer,
the diketiminate ligands retain a C2-symmetric conforma-
tion with the phenyl substituents anti toward each other.
(20) Eisch, J. J.; Owuor, F. A.; Otieno, P. O. Organometallics 2001,
20, 4132.
(21) Jones, D.; Roberts, A.; Cavell, K.; Keim, W.; Englert, U.;
(22) Hayes, P. G.; Piers, W. E.; Lee, L. W. M.; Knight, L. K.; Parvez,
M.; Elsegood, M. R. J.; Clegg, W. Organometallics 2001, 20, 2533.
Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1998, 255.

Article
Organometallics, Vol. 29, No. 7, 2010 1553
Figure 1. Crystal structures of 3a and 3b. Thermal ellipsoids are drawn at the 50% probability level. Most hydrogen atoms are omitted
for clarity.
Figure 2. Crystal structures of Λ-3c (left) and Δ-3c (right), both found in the same asymmetric unit. Thermal ellipsoids are drawn at the
50% probability level. Most hydrogen atoms are omitted for clarity.
one singlet for the CH groups in the ligand backbone, and
one singlet for the ligand methyl groups. Below -50 °C, four
doublets for benzyl CH2, two singlets for the methyl groups,
but still only one sharp singlet for the backbone CH groups
are obtained (Figure 5). The low-temperature spectrum is
thus in agreement with the observed solid-state structure: a
symmetric complex, in which unsymmetrically coordinated
nacnac ligands are connected by a C2-axis. The observed
spectral changes on heating can be explained with an iso-
merization between the Δ- and Λ-enantiomer, which at the
same time exchanges trans chloride and trans nitrogen sites
(Scheme 2). Rahim et al. proposed a Bailar-twist mechanism
for a similar fluxional behavior in nacnacPh2ZrCl2.6 That two
doublets are observed for the benzyl CH2 group even at
higher temperature indicates that the Cs-symmetric isomer
with trans chloride ligands is not obtained, even as a short-
lived intermediate at high temperatures.
The Bailar-twist is significantly slower for cyclohexyl-
substituted 3b, resulting in exchange-broadened peaks close
to coalescence at room temperature. The presence of six
signals for the cyclohexyl ring in 13C spectra of 3b at higher
temperatures again indicates that isomerization occurs

1554 Organometallics, Vol. 29, No. 7, 2010
El-Zoghbi et al.
a
˚
Table 1. Selected Bond Distances [A] and Bond Angles [deg] for 3a-c, 5, and 6
3b Λ-3c Δ-3c
3a
5
6
Zr-N1b
Zr-N2c
Zr-Xd
2.201(3)
2.190(2)
2.455(1)
2.235(2)
2.181(2) and 2.205(2) 2.177(3) and 2.183(2) 2.203(3) and 2.217(3) 2.288(2)-2.305(2)
2.213(3) and 2.246(3) 2.221(3) and 2.247(3) 2.289(3) and 2.295(3) 2.225(2)-2.232(2)
2.499(1) and 2.516(1) 2.483(1) and 2.487(1) 2.290(4) and 2.297(4) 1.939(2)-1.954(2)
2.197(2)
2.483(1)
1.339(3) and
1.331(2)
1.397(3) and
1.410(3)
34
N1-C2/N2-C4 1.325(4) and
1.339(4)
1.321(4)-1.357(4)
1.394(5)-1.408(4)
47-49
1.328(4)-1.348(4)
1.398(4)-1.413(4)
36-42
1.328(5)-1.338(5)
1.314(3)-1.336(3)
C2-C3/C3-C4 1.410(5) and
1.388(5)
1.380(6)-1.403(5)
1.388(4)-1.416(4)
complex bendinge 37
31
74.56(11) and
74.81(11)
32-34
76.65(7)-77.52(8)
N1-Zr-N2f
78.06(9)
80.52(6)
83.71(9) and 85.46(9) 82.28(9) and
82.44(9)
N-Zr-Ng
X1-Zr-X2
N-Zr-Xd
86.71(13)-87.28(9) 86.7(1)-89.2(1)
93.58(5) 93.36(3)
90.11(7)-97.54(7) 90.07(5)-95.48(4) 83.53(6)-92.51(7)
91.32(9)-106.81(9) 91.31(9)-98.60(9)
77.31(11)-127.20(12) 83.20(7)-87.37(8)
116.36(15) 97.12(7) and 98.72(7)
78.34(13)-94.59(12) 87.78(7)-102.55(8)
88.52(3)
90.59(3)
88.95(7)-91.41(7)
a Atom numeration according to 3a. Values were provided for analogous atoms in other structures, independent of the numeration in the respective
complex. b Nitrogen atoms trans to Cl, numeration differs between complexes. c Nitrogen atoms trans to N, numeration differs between complexes. d X=
Cl (3a-c), C (5), O (6). e Angle(s) between the least-squares planes defined by N1,N2,C2-C4 and Zr1,N1,N2 in 3a or respective atoms in other
complexes. f cis-angle(s) between nitrogen atoms of the same ligand. g cis-angle(s) between nitrogen atoms of different ligands.
Figure 3. Boat-like conformation of the diketiminate ligand in 3a.
Figure 5. Variable-temperature 1H NMR spectra of 3a.
˚
Table 2. Selected Bond Distances [A] and Bond Angles [deg] for 4
Zr1-Cl1
Zr1-N1
Zr1-N2
Zr1-N3
Zr1-N4
Zr1-C27
N1-C27
2.477(1)
2.031(3)
2.318(4)
2.230(3)
2.196(4)
2.305(5)
1.410(7)
N1-C25
1.330(6)
1.366(8)
1.437(7)
1.323(6)
76.6(2)
C24-C25
C23-C24
N2-C23
N1-Zr1-N2
N3-Zr1-N4
N1-Zr1-N4
83.5(1)
109.1(2)
100 °C. In contrast to 3a and 3b, coalescence into a fully
symmetric spectra requires two different Bailar-twists for 3c.
The mechanism depicted in Scheme 2 will exchange groups
trans to N in the Δ-isomer (short: Δ-N, Scheme 3) with
groups trans to Cl in the Λ-isomer (short: Λ-Cl). Since the
pairs Δ-N/Λ-Cl and Λ-N/Δ-Cl are enantiomeric in 3a and
3b, only one resonance is observed for these groups. This is
not the case for diastereomeric Δ-3c and Λ-3c, and a second
Bailar-twist mechanism is required to exchange Δ-N with
Δ-Cl (or Λ-N with Λ-Cl, respectively). Since this requires one
diketiminate ligand to bridge the two trigonal faces of the
prismatic transition state (Scheme 3), the latter is probably of
higher energy.23 The presence of two, eventually overlapping
Figure 4. Crystal structure of complex 4 with 50% probability
thermal ellipsoids depicted. Hydrogen atoms, other than H35,
are omitted for clarity.
between Δ- and Λ-enantiomers, but not between cis- and trans-
isomers. The isomerization is even slower in 3c. Resonances
1
in the H and 13C spectra are broadened by exchange, but
show the presence of two diastereomeric complexes. Cooling
of a CDCl3 solution below 0 °C resulted in two signal sets in a
2:1 ratio for Δ-(R,R-nacnacMeBn)ZrCl2, Δ-3c, and Λ-(R,R-
nacnacMeBn)ZrCl2, Λ-3c. A spectrum in the fast exchange
region was not obtained in CDCl3 or even in toluene-d8 at
(23) For 3a, the second Bailar-twist would lead to an exchange of Ha
and Hb (Scheme 2). That two doublets are observed for the diastereo-
topic CH2 hydrogens of 3a at room temperature is in agreement with a
higher activation barrier for this isomerization.

Article
Organometallics, Vol. 29, No. 7, 2010 1555
Scheme 2
Figure 6. Eyring plots of the exchange rates for isomerizations
of 3a-c and 6 (hollow data points not used in linear regression
analysis).
Scheme 3. Exchange of Δ-Cl First with Λ-N, Then with Δ-N
exchange process. The activation entropy of 18(3) J/(mol K)
3
for 3a is significantly more positive than those previously
observed (-39 to -56 J/(mol K))6,7,12 and might be indica-
3
tive for a dissociation/recoordination mechanism instead of
a Bailar-twist mechanism for 3a. However, a negative activa-
tion entropy is obtained for 3b, although its crystal structure
indicates increased steric interactions in the presence of a
cyclohexyl substituent on nitrogen, and 3b would be ex-
pected to be even more prone to follow a dissociation/
recoordination mechanism than 3a. In addition, as will be
discussed below, alkylation of 3a can be aided by partial
dissociation of diketimine. The inactivity of 3a-c toward
alkylation (vide infra) indicates that a five-coordinated inter-
mediate is not present with sufficient lifetime to allow
chloride-alkyl exchange. While a dissociation mechanism
for 3a can thus not be excluded, it seems incompatible with
additional data. An alternative explanation would involve a
less restricted rotation around the N-CH2 bond in the
prismatic transition state, which is blocked in the Δ/Λ-
ground state. In agreement with this, the activation entropy
obtained for 3b, which has only one hydrogen on the
secondary alkyl substituent and no other accessible rotamers,
is comparable to those in N-aryl-substituted complexes.
nacnac2ZrMe2 Complexes. Attempts to prepare alkyl de-
rivatives of 3a-c using alkylating agents such as MeLi,
MeMgBr, BnMgBr, ZnEt2, tBuLi, or nBuLi in a variety of
solvents and reaction conditions did not meet with success.
NMR spectra of reaction products showed only the presence
of starting material or, under forcing conditions such as
prolonged heating, decomposition products. Since alkyla-
tion seemed impossible after complexation of the nacnac
ligand, we decided to introduce the methyl group prior to
complexation.24 Indeed, the dimethyl analogue 5 was obtai-
ned in moderate yield (60%) by reaction of ZrCl4 first with
2 equiv of MeLi and then with the lithium salt 2a (Scheme 4).
Only 5 was accessible by this pathway. As observed for the
synthesis of the dichloride complexes, ligands with second-
ary alkyls on N, i.e., 2b and 2c, did not react fast enough to
compete with the decomposition of the zirconium alkyl
chloride complex.
Table 3. Activation Parameters Determined from Eyring Plots of
a
k
obs for the Isomerization of nacnacR2ZrX2
ΔHq
ΔSq
k298K
[ꢀ 103 s-1
complex
R/X
[kJ mol-1
]
[J mol-1 K-1
]
]
3
3
3
3a
3b
6
Bn/Cl
Cy/Cl
Bn/OEt
51(1)
48(2)
48(1)
18(3)
-27(9)
-16(6)
60
1
3
a Temperature range used for determination of ΔHq and ΔSq: 223-
283 K (3a), 233-318 K (3b), 223-298 K (6).
exchange processes might explain the lack of coalescence
even at higher temperatures. The presence of four CH-
(Me)Ph resonances in the 1H NMR spectrum of 3c at room
temperature and two HC(dN)2 resonances in its 13C spec-
trum indicates that even the first Bailar-twist, which leads to
Δ-Λ-isomerization, is slow on the NMR time scale at room
temperature. Nevertheless, the chiral diketiminate complex
3c does not have the configurational stability exhibited, for
example, by the chiral “IAN amino” zirconium complexes
of Johnston and co-workers,3 since, in contrast to those,
Δ-Λ-isomerization in 3c does not require ligand enantio-
merization.
1
Simulation of the line shape of selected peaks in the H
NMR spectra of 3a-c allowed the determination of ex-
change rates (kobs) at different temperatures (see Experimen-
tal Section) Activation parameters were obtained from
Eyring plots of these rate constants (Figure 6, Table 3).
While satisfactory linear plots and identical values from
different pairs of exchanging nuclei were obtained for 3a
and 3b, a smaller temperature window and difficulties in the
determination of exchange constants made the determina-
tion rather unreliable for 3c. Activation enthalpies for 3a and
3b (Table 3) are slightly higher than that of nacnacPh2ZrCl2
(38 kJ/mol),6 but comparable to those in other nac(n)ac2ZrX2
complexes (36-57 kJ/mol),7,12 which undergo the same
(24) Park, J. T.; Woo, B. W.; Yoon, S. C.; Shim, S. C. J. Organomet.
Chem. 1997, 535, 29.

1556 Organometallics, Vol. 29, No. 7, 2010
El-Zoghbi et al.
Figure 8. Chemical displacement of the averaged methyl reso-
nance in 5/AlMe3 mixtures in C6D6.
Scheme 5
Figure 7. Crystal structure of complex 5. Thermal ellipsoids are
drawn at the 50% probability level, and most H atoms are
omitted for clarity.
Scheme 4
or benzaldehyde. Surprisingly with regard to the failed at-
tempts to exchange chloride against alkyl ligands, 5 reacted
fast with AlCl3-xMex (x=0-2) in C6D6 solution to yield the
dichloride complex 3a. To investigate this further, a C6D6
solution of 5 was titrated with AlMe3 (0-1.8 equiv). 1H NMR
spectra, recorded after each addition, showed no change in the
diketiminate ligand resonances, but only one averaged reso-
nance for Zr- as well as Al-bound methyl groups, which shifted
from 0.32 (Al/Zr = 0) to -0.23 ppm (Al/Zr = 1.8) as the
concentration of AlMe3 increased (Figure 8). Interpolation of
the linear regression line yielded a reasonable value of δ -0.36
ppm for pure AlMe3 in C6D6. Exchange of methyl groups
between Al and Zr centers is thus occurring fast on the NMR
time scale, in contradiction with the problems encountered in
the alkylation of these complexes. This might indicate that
alkylation of 3a-c is a thermodynamic, rather than a kinetic,
problem. Alternatively, interaction of AlMe3 with a diketimi-
nate ligand might loosen its coordination to zirconium, render-
ing the methyl ligands in 5 more accessible for exchange
processes (Scheme 5). Additional experiments support the
latter explanation: Reaction of C6D6 solutions of 5 with excess
LiCl did not lead to the formation of the dichloride complex 3a,
and methyl against chloride exchange is thus no more feasible
than chloride against methyl.28 On the other hand, when C6D6
solutions of the dichloride complex 3a were reacted with
The solid-state structure of 5 shows the octahedral cis-
geometry previously observed (Figure 7), but with a signifi-
cantly more pronounced deviation from ideal geometry
(N-Zr-N/X angles of 75-127°), while the bending angle
of 31° is the smallest observed (Table 1). A possible reason
for the increased deviation might lie in the shorter Zr-Me
˚
distance in 5 (2.290(4) and 2.297(4) A), when compared to
˚
Zr-Cl in 3a (2.454(1) A). The closer distance to the benzyl
CH2 group (C30 and C50, Figure 7) results in a widening of
the X-Zr-X angle by 23° (3a, Cl1-Zr1-Cl1: 93.6(1)°; 5,
C16-Zr1-C17: 116.4(2)°) and subsequent distortion of the
octahedral geometry.
Reactions of styrene with 3a-c/AlCl3-xMex (x=1-3),25
3a/AlMe3/H2O,26 5/AlCl3-xMex (x=0-3), or 5/B(C6F5)3,27
in polar or apolar solvents, at room temperature or upon
heating, showed no evidence for insertion of the olefin into
the Zr-Me bond (NMR, GC-MS). No insertion was likewise
observed in reactions of 5/B(C6F5)3 with diphenylacetylene
(25) Kondakov, D. Y.; Negishi, E. J. Am. Chem. Soc. 1996, 118, 1577.
(26) Wipf, P.; Ribe, S. Org. Lett. 2000, 2, 1713.
(27) Reaction of 5 with B(C6F5)3 in C6D6 solution yielded NMR
spectra in agreement with the formation of the ion pair
[(nacnacBn)2ZrMe][MeB(C6F5)3]: only one peak each is observed for
1
all CH2, CH, or Me groups of the diketiminate ligands in H and 13C
(28) Minor amounts of 3a (ca. 5%) were attributed to the presence of
traces of water and excess LiCl. These amounts increased if aged LiCl,
not kept from moisture, is used.
spectra, while the former ZrMe2 group splits into two signals. The ion-
pair is only metastable in solution and rapidly separates as a red oil.

Article
Organometallics, Vol. 29, No. 7, 2010 1557
substituents readily form bis(diketiminate) zirconium com-
plexes, even with bulky secondary alkyls, and offer access to
an easy modification of the steric environment. Steric crowd-
ing caused by the N-substituent seems the most likely cause
for the inactivity of the dichloride complexes toward ligand
exchange. It does not impede fast complex racemization,
however, most probably by a Bailar-twist mechanism. While
structural analyses confirm the targeted proximity of the
alkyl substituent and the reactive coordination sites and the
potential utility of the ligand framework in catalysis, the
dimethyl complex 5 does not insert styrene, diphenylacety-
lene, or benzaldehyde when activated with AlMe3-xClx or
B(C6F5)3, which might be due again to steric crowding or a
too low Lewis acidity of the metal center. Complex racemi-
zation proved to be too fast to impart selectivity in lactide
polymerizations. We are currently investigating the effects of
interligand bridging to control complex racemization and to
improve the reactivity of this class of compounds.
Experimental Section
All reactions, except ligand synthesis, were carried out under
an inert atmosphere using Schlenk and glovebox techniques
under a nitrogen atmosphere. nacnacBnH (1a),18 R,R-nacnacMeBn
H
Figure 9. Crystal structure of 6. Only one of two independent
molecules is shown. Thermal ellipsoids are drawn at the 50%
probability level. The minor occupied positions of the disor-
dered ethyl groups and most H atoms are omitted for clarity.
30
(1c),17 and ZrCl4(THF)2 were prepared according to literature
procedures. All other chemicals were purchased from common
commercial suppliers and used without further purification. THF
was distilled from sodium/benzophenone; all others solvents were
dried by passage through activated aluminum oxide (MBrown SPS)
and deoxygenated by repeated extraction with nitrogen. C6D6 was
dried over sodium, CDCl3 was dried over CaH2, and both were
distilled under reduced pressure and then degassed by three freeze-
methyllithium in the presence of 10 equiv of AlMe3, the
obtained reaction mixtures contained up to 90% of the dimeth-
yl complex 5 (Scheme 5). Ligand exchange between 3a and 5 is
thus most likely aided by a loosening of the diketiminate
coordination with AlMe3.
pump-thaw cycles. Styrene and ethanol were evacuated under
1
vacuum and dried over 4 A molecular sieves. H and 13C NMR
˚
While 3a did not undergo ligand exchange with NaOEt,
reaction of 5 with 2 equiv of ethanol afforded the dialkoxide
complex nacnacBn2Zr(OEt)2, 6.29 Despite Zr-O distances
spectra were acquired on a Bruker AMX 300 or Bruker AV 400
spectrometer. 19F NMR spectra were acquired on a Bruker Avance
300. Chemical shifts were referenced to the residual signals of the
˚
even shorter (1.939(2)-1.954(2) A) than Zr-Me in 5
1
deuterated solvents (C6D6: H: δ 7.16 ppm, 13C: δ 128.38 ppm;
˚
(2.290(4) and 2.297(4) A), its crystal structure (Figure 9) is
CDCl3: 1H: δ 7.26 ppm, 13C: δ 77.00 ppm; C7D8: 1H: δ 2.09 ppm,
13C: δ 20.40 ppm). Low-temperature NMR spectra were recorded
using a Bruker AV 500 spectrometer. NMR data at low or high
temperatures are given in the Supporting Information. Exchange
rates were obtained by comparison of experimental and simulated
spectra with the WINDNMR program.31 Elemental analyses were
again very similar to that of the dichloride complex 3a, with
O-Zr-O angles of 97.12(7)° and 98.72(7)° and a slightly
distorted octahedral coordination environment (Table 1).
This might be related to the smaller vdW radius of oxygen
compared to chloride and methyl, which can accommodate a
shorter Zr-O distance: shortest distances between a benzyl
ꢀ
ꢀ
ꢀ
performed by the Laboratoire d’Analyse Elementaire (Universite de
ꢀ
˚
Montreal).
hydrogen and the Zr-X ligand (3a, d(H-Cl) = 2.9 A; 5,
2-Cyclohexylamino-4-cyclohexyliminopent-2-ene, nacnacCyH,
1b.19 Acetylacetone (1.00 g, 10 mmol), para-toluenesulfonic
acid monohydrate (1.9 g, 10 mmol), and cyclohexylamine (1.0
g, 10 mmol) were combined with toluene (100 mL). The resulting
white suspension was refluxed for 3 h with the help of Dean-
Stark apparatus to afford a colorless solution. After cooling
to room temperature, a second equivalent of cyclohexylamine
(1.0 g, 10 mmol) was added and the reaction mixture was refluxed
for 3 days. A colorless precipitate appeared upon cooling to
room temperature, which was separated by filtration and com-
bined with 100 mL of ether and 100 mL of an aqueous solution
of KOH (5.6 g, 100 mmol). Phases were separated and the
aqueous phase was extracted with ether. The combined phases
were dried over Na2SO4 and filtered, and the solvent was
evaporated. The obtained yellow liquid was allowed to cool
slowly to room temperature to yield colorless crystals (1.8 g,
69%). The crude product contained ca. 5% impurities according
to NMR, but was used without further purification in subse-
quent reactions. Recrystallization from ethanol afforded analy-
tically pure compound.
˚
˚
d(H-C) = 2.8 A; 6, d(H-O) = 2.5 A) are in all three
complexes only slightly shorter than the sum of their vdW
˚
˚
˚
radii (H-Cl: 3.0 A, H-C: 2.9 A, H-O: 2.7 A). Again, a
fluxional process was observed by NMR. In addition to the
changes observed for 3a and 5, the quartet of the CH2O
group splits into two multiplets of equal intensity at -50 °C,
confirming again that the fluxional process is associated with
a racemization of the complex. Activation parameters
yielded an activation enthalpy comparable to 3a, but an
activation entropy lower by 34 J/(mol K) (ΔSq = -16(6) J/
(mol K), Table 3), which might indicate reduced rotational
freedom of the ethoxy substituents in the transition state.
3
3
Conclusions
While not accessible with ortho-substituted N-aryl diketi-
minate ligands, β-diketiminates with aliphatic N-alkyl
(29) Complex 6 can be employed as initiator for the polymerization of
rac-lactide in molten monomer (Zr/lactide = 1:200, 130 °C, 98%
conversion in 0.5 h), but yielded essentially atactic polymer (Pr =0.6).
(30) Manzer, L. E. Inorg. Synth. 1982, 21, 135.
(31) Reich, H. J. WinDNMR; J. Chem. Educ. Software 3D2, 1996.

1558 Organometallics, Vol. 29, No. 7, 2010
El-Zoghbi et al.
1H NMR (CDCl3, 400 MHz, 298 K): δ 11. 72 (bs, 1H, NH),
4.44 (s, 1H, CH(CdN)2), 3.32-3.35 (m, 2H,CH(Cy)), 1.90 (s,
6H, Me(CdN)), 1.80-1.35 (m, 20H, Cy). 13C{1H} NMR
(CDCl3, 101 MHz, 298 K): δ 158.4 (CdN), 93.7(CH(CdN)2),
54.1 (CHCy), 34.6 (CH2a), 25.7 (CH2b), 25.7 (CH2c), 18.8 (CH3).
Anal. Calcd for C17H30N2: C, 77.80; H, 11.52; N, 10.62. Found:
C, 77.60; H, 11.24; N, 10.85.
yielding 3a as a yellow powder (1.5 g, 75%). Crystals suitable for
X-ray diffraction studies were obtained by slow diffusion of
hexane into a THF solution of the complex at 25 °C.
1H NMR (CDCl3, 400 MHz, 298 K): δ 7.20-7.30 (m, 20H,
Ph), 5.65 (bs, 2H, CH2Ph), 5.62 (bs, 2H, CH2Ph), 5.32 (s, 2H,
CH(CdN)2), 4.61 (bs, 2H, CH2Ph), 4.56 (bs, 2H, CH2Ph), 1.92
(s, 12H, Me(CdN)). 13C{1H} NMR (CDCl3, 101 MHz, 298 K):
δ 167.1 (CdN), 139.5 (ipso Ph), 128.2 (ortho Ph), 127.2 (para
Ph), 126.5 (meta Ph), 108.1 (CH(CdN)2), 54.9 (CH2Ph), 23.2
(Me(CdN)). Anal. Calcd for C38H42ZrN4Cl2: C, 63.66; H, 5.91;
N, 7.82. Found: C, 63.00; H, 6.19; N, 7.69.
NacnacBnLi(THF), 2a. A hexane solution of nBuLi (1.36 mL,
2.9 M, 3.95 mmol) was added over 25 min at room temperature
to a yellow THF solution of 1a (1.0 g, 3.6 mmol). The yellow-
orange solution was allowed to stir for 4 h. The volatiles were
removed, and the remaining solid was washed with 2 ꢀ 5 mL of
hexane. The solid was dried under reduced pressure to yield a
colorless powder (1.25 g, 90%) and used without further puri-
fication.
nacnacCy2ZrCl2, 3b. In a dry Schlenk, ZrCl4 (0.34 g, 1.5 mmol)
and 2b (1.0 g, 3.0 mmol) were mixed and toluene (10 mL) was
added under stirring. After 24 h of stirring at room temperature
the obtained orange mixture was filtered. The red filtrate was
concentrated to half its volume, and the desired product was
precipitated by addition of 15 mL of hexane. The white pre-
cipitate separated by filtration was dried at a vacuum line to
yield 3b (0.35 g, 35%). Crystals suitable for X-ray diffraction
studies were obtained by slow diffusion of hexane into a THF
solution of the complex at 25 °C.
1H NMR (CDCl3, 400 MHz): δ 7.22-7.30 (m, 10H, Ph), 4.54
(s, 1H, CH(CdN)2), 4.42 (s, 4H, CH2Ph), 3.74 (m, 4H, THF),
1.93 (s, 6H, Me(CdN)), 1.83 (m, 4H, THF). H NMR (C6D6,
1
400 MHz): δ 7.00-7.30 (m, 10H, Ph), 4.82 (s, 1H, CH(CdN)2),
4.60 (s, 4H, CH2Ph), 2.86 (m, 4H, THF), 2.09 (s, 6H, Me-
(CdN)), 0.98 (m, 4H, THF). 13C{1H} NMR (CDCl3, 101 MHz):
δ 161.0 (CdN), 140.9 (ipso Ph) 128.3 (ortho Ph), 127.2 (para Ph),
126 (meta Ph), 95.1 (CH(CdN)2), 67.9 (THF), 50.7 (CH2(Ph)),
25.6 (THF), 19.6 (Me(CdN)). 13C{1H} NMR (C6D6, 101
MHz): δ 165.8 (CdN), 145.4 (ipso Ph) 128.5 (ortho Ph), 127.5
(para Ph), 126.0 (meta Ph), 93.8 (CH(CdN)2), 67.5 (THF), 50.7
(CH2(Ph)), 25.1 (THF), 22.0 (Me(CdN)).
1H NMR (CDCl3, 500 MHz, 298 K): δ 5.15 (s, 2H, CH-
(CdN)2), 4.25 (bm, 4H, Cy CH), 1.91 (bs, 12H, CH3), 2.16-1.19
(m, 40H, Cy CH2). 13C{1H} NMR (CDCl3, 75 MHz, 298 K):
Peaks severely broadened. For low- and high-temperature
spectra see the Supporting Information Anal. Calcd for
C34H58ZrN4Cl2: C, 59.62; H, 8.53; N, 8.18. Found: C, 58.98;
H, 8.75; N, 7.71.
nacnacCyLi(THF), 2b. To a yellow THF solution of 1b (1.5 g,
5.8 mmol) was added gradually a hexane solution of nBuLi
(2 mL, 2.9 M, 5.8 mmol) at room temperature. After 4 h of
stirring the solution turned orange. The volatiles were removed
under reduced pressure to yield 2b as a yellow solid (1.9 g, 96%),
which was used without further purification.
R,R-nacnacMeBn2ZrCl2, 3c. To a mixture of ZrCl4(THF)2
(0.77 g, 2.04 mmol) and 2c (1.57 g, 4.08 mmol) was added
toluene under stirring. The obtained orange mixture was al-
lowed to react for 3 days at room temperature. The mixture was
filtered, the orange filtrate concentrated to half its volume, and
the desired product precipitated by addition of 15 mL of hexane.
Recrystallization by slow diffusion of hexane into a saturated
toluene solution gave yellow crystals of 3c (1.1 g, 65%), con-
taminated with isolated red crystals of 4 (insufficient quantity
for full characterization), which were separated by hand.
1H NMR (CDCl3, 400 MHz, 298 K) (peaks severely broa-
dened; for low-temperature spectra of both diastereomers, see
Supporting Information): δ 7.08-7.4 (m, 20H, Ph), 6.74 (bm,
2H, b CH(Me)Ph), 6.64 (bm, 2H, a CH(Me)Ph), 6.14 (bm, 2H,
a CH(Me)Ph), 5.26 (bs, aþb CH(CdN)2), 4.48 (bm, 2H, b CH-
(Me)Ph), 2.15-1.63 (m, 24H, Me). 13C{1H} NMR (CDCl3,
75 MHz, 298 K) (peaks severely broadened, many not observed
or overlapping; for low-temperature spectra of both diastereo-
mers, see Supporting Information): δ 168.1 (CdN), 167 (CdN),
162.9 (CdN), 143.9 (ipso Ph), 143.4 (ipso Ph), 110.8 (CH-
(CdN)2), 104.3 (CH(CdN)2), 62 (CH(Me)Ph), 59.4 (CH(Me)-
Ph), 57.6 (CH(Me)Ph), 27.2 (CH(Me)Ph), 25.3 (CH(Me)Ph),
19.8 (Me(CdN)), 18.2 (Me(CdN)), 17 (Me(CdN)). Anal. Calcd
for C42H50N2ZrCl2: C, 65.26; H, 6.52; N, 7.01. Found: C, 64.93;
H, 6.70 ; N, 7.13.
1H NMR (C6D6, 400 MHz, 298 K): δ 4.56 (s, 1H, CH(CdN) 2),
3.40-3.44 (m, 6H, Cy CH and CH2O), 2.16 (s, 6H, CH3),
1.77-1.3 (m, 24H, THF and Cy CH2). 13C{1H} NMR (C6D6,
101 MHz, 298 K): δ 158.0 (CdN), 95.0 (CH(CdN)2), 54.6 (THF),
54.4 (Cy CH), 34.6 (CH2a), 25.7 (CH2b), 25.7 (CH2c), 24.5 (THF),
18.8 (CH3).
R,R-nacnacMeBnLi(THF), 2c. A solution of nBuLi in hexane
(2.9 M, 0.9 mmol) was added gradually over 10 min to a yellow
THF solution of 1c (0.25 g, 0.82 mmol). The yellow-orange
solution was allowed to stir for 4 h at room temperature, vola-
tiles were evaporated, and a brown oil was obtained (0.30 g,
92%), which was used without further purification.
1H NMR (400 MHz, C6D6): δ 7.16-7.42 (m, 10H, Ph), 4.81
(q, 2H, J=7 Hz, CH(Me)Ph), 4.71 (s, 1H, CH(CdN)2), 3.00 (m,
4H, THF), 2.07 (s, 6H, Me(CdN)), 1.44 (d, 6H, J = 7 Hz,
CH(Me)Ph), 0.97 (m, 4H, THF). 13C{1H} NMR (C6D6, 101
MHz): δ 161.0 (CdN), 150.2 (ipso Ph), 128.4 (ortho Ph), 126.6
(para Ph), 125.8 (meta Ph), 93.7 (CH(CdN)2), 67.6
(CH(Me)Ph), 57.2 (THF), 25.5 (THF), 24.6 (CH(Me)Ph), 22.3
(Me(CdN)).
nacnacBn2ZrMe2, 5. ZrCl4 (0.42 g, 1.8 mmol) was dissolved
in THF (60 mL). An ether solution of MeLi (2.5 mL, 1.6 M, 4.0
mmol) was added at -78 °C under exclusion of light. The
obtained white suspension was allowed to stir for 30 min in
order to generate Me2ZrCl2. To the obtained mixture was added
2a (1.28 g, 3.6 mmol), affording a yellow suspension. The mix-
ture was allowed to warm to room temperature during 18 h,
upon which it turned red. The volatiles were evaporated under
reduced pressure to give an orange solid film. The product was
extracted with CH2Cl2 (20 mL), and the resulting red solution
was evaporated to dryness to yield 5 as a yellow powder (0.70 g,
63%). Crystals suitable for X-ray diffraction analysis were
obtained by slow diffusion of hexane into a saturated toluene
solution at -20 °C.
nacnacBn2ZrCl2, 3a. Method A. In a dry Schlenk tube, ZrCl4
(0.34 g, 1.4 mmol) and 2a (1.0 g, 2.8 mmol) were mixed. Toluene
(10 mL) was added under stirring. After 24 h at room tempera-
ture, the obtained orange mixture was filtered. The yellow
filtrate was concentrated to half its volume, and the desired
product was precipitated by addition of 15 mL of hexane. The
yellow precipitate was separated by filtration and dried at a
vacuum line to yield 3a (0.35 g, 0.50 mmol, 35%).
Method B. A hexane solution of nBuLi (2.9 M, 5.4 mmol) was
added to a toluene suspension of ZrCl4 (0.62 g, 2.7 mmol) at
-78 °C. The mixture was allowed to warm to room temperature
and then stirred for another 12 h. To the obtained brown
mixture was gradually added 15 mL of a toluene solution of
1a (5.4 mmol, 1.5 g). The mixture was stirred for 2 days at 90 °C,
during which it turned yellow. After cooling to room tempera-
ture, 20 mL of dichloromethane was added and the mixture was
filtered. The combined volatiles were removed under vacuum,
1H NMR (C6D6, 400 MHz, 298 K): δ 7.60-7.06 (m, 20H, Ph),
4.94 (s, 2H, CH(CdN)2), 4.77 (bs, 8H, CH2), 1.76 (s, 12H,
Me(CdN)), 0.32 (s, 6H, Me-Zr). 13C{1H} NMR (C6D6, 101

Article
Organometallics, Vol. 29, No. 7, 2010 1559
Table 4. Details of X-ray Diffraction Studies
3a
3b
3c
4
5
6
formula
Mw (g/mol); F(000)
C38H42Cl2N4Zr
716.88; 1488
yellow block
C34H58Cl2N4Zr
684.96; 1456
colorless block
C42H50Cl2N4Zr
772.98; 1616
yellow fragment
C42H49ClN4Zr
736.52; 772
red plate
C40H48N4Zr
676.04; 1424
yellow plate
C42H52N4O2Zr
736.10; 3104
colorless plate
cryst color and form
cryst size (mm)
T (K); wavelength
cryst syst
0.12 ꢀ 0.06 ꢀ 0.03 0.60 ꢀ 0.28 ꢀ 0.10 0.10 ꢀ 0.08 ꢀ 0.04 0.06 ꢀ 0.06 ꢀ 0.04 0.06 ꢀ 0.05 ꢀ 0.02 0.06 ꢀ 0.04 ꢀ 0.02
200; 0.71073
tetragonal
P43212
150; 1.54178
monoclinic
C2/c
150; 1.54178
monoclinic
P21
150; 1.54178
monoclinic
P21
150; 1.54178
monoclinic
P21/n
150; 1.54178
orthorhombic
P212121
space group
unit cell: a (A)
˚
8.7244(5)
8.7244(5)
47.453(6)
90
20.2320(8)
9.0276(4)
22.539(1)
91.250(2)
13.6460(3)
20.5189(5)
14.4588(4)
108.891(1)
13.5011(18)
9.1289(11)
15.1108(18)
95.413(7)
15.2045(13)
9.6321(8)
24.0981(19)
97.213(4)
11.6079(9)
15.7760(12)
42.516(3)
90
˚
b (A)
˚
c (A)
β (deg)
3
V (A ); Z; dcalcd. (g/cm3)
3611.9(6); 4;1.318 4115.7(3); 4; 1.105a 3830.41(16);4; 1.340 1854.1(4); 2; 1.319 3501.3(5); 4; 1.283 7785.8(10); 8; 1.256
˚
θ range (deg); completeness
collected reflns; Rσ
unique reflns; Rint
1.7-27.6; 1.0
99 235; 0.070
4177; 0.144
0.484; multiscan
0.039; 0.069
0.075; 0.078
0.920
3.9-72.3; 0.99
53 603; 0.021
4013; 0.036
3.554; multiscan
0.034; 0.098
0.034; 0.098
1.113
3.2-58.0; 0.99
60 497; 0.025
10 532; 0.046
3.893; multiscan
0.025; 0.064
0.027; 0.065
1.029
2.9-68.1; 0.98
27 516; 0.082
6510; 0.079
3.348; multiscan
0.050; 0.127
0.058; 0.131
0.793
3.3-67.5; 1.0
54 484; 0.063
6282; 0.116
2.813; multiscan
0.045; 0.101
0.076; 0.117
1.013
2.1-67.9; 1.0
137 856; 0.027
14 075; 0.060
2.611; multiscan
0.027; 0.072
0.029; 0.073
1.026
μ (mm-1); abs corr
R1(F); wR(F2) (I > 2σ(I))
R1(F); wR(F2) (all data)
GoF(F2)
-
3
˚
residual electron density (e /A ) 0.28
0.40
0.53
1.28
0.88
0.31
a Co-crystallized solvent removed with SQUEEZE.
MHz, 298 K): δ 163.5 (CdN), 140.2 (ipso Ph), 128.1 (ortho Ph),
126.6 (para Ph), 126.1 (meta Ph), 100.5 (CH(CdN)), 52.1
(CH2Ph), 41.2 (Me-Zr), 21.4 (Me(CdN)). Anal. Calcd for
C40H48N4Zr: C, 71.06; H, 7.16; N, 8.29. Found: C, 71.59; H,
7.28; N, 8.29.
Reaction of 5 with B(C6F5)3. To a C6D6 solution of B(C6F5)3
(7.5 mg, 0.0148 mmol) in a J. Young NMR tube was added 0.5
mL of a yellow C6D6 solution of 5 (2.96 ꢀ 10-3 M, 0.0148 mmol)
in portions of 0.1 mL every 5 min to give [nacnacBn2ZrMe]-
[MeB(C6F5)3]. A red oil separated from the solution upon
standing.
Supporting Information. Exchange rates were obtained by
simulation of the experimental spectra with the WINDNMR
program.31 Temperature range, exchange simulated: 3a,
223-298 K, Me(CN) and both diastereotopic NCH2Ph; 3b,
223-328 K, N-CHd(CH2)5; 3c, 223-328 K, Me(CN) and both
diastereotopic CH(Me)Ph; 6, 223-298 K, Me(CN) and both
diastereotopic MeCH2O.
X-ray Diffraction Studies. Diffraction data for complexes 3a
were recorded on a Bruker Smart APEXII (Mo radiation)
diffractometer, for complex 4 on a Bruker Smart 6000 (Cu
rotating anode), and for all others on a Bruker Proteum X8/
Microstar (Cu radiation), using the APEX2 software package.32
Data reduction was performed with SAINT;33 absorption cor-
rections with SADABS.34 Structures were solved with direct
methods (SHELXS97).35 All non-hydrogen atoms were refined
anisotropically using full-matrix least-squares on F2, and hydro-
gen atoms were refined with fixed isotropic U using a riding
model (SHELXL97).35 For 3b, the cocrystallized solvent was
identified as a disordered hexane (in agreement with NMR
data), but could not be resolved and thus was suppressed by
application of SQUEEZE.36 For further details see Table 4 and
the Supporting Information.
1H NMR (C6D6, 400 MHz, 298 K): δ 7.37-7.06 (m, 20H, Ph),
4.89 (bs, 2H, CH(CdN)2), 4.54 (bs, 8H, CH2), 1.77 (bs, 12H,
Me(CdN)), 0.43 (s, 3H, MeB), 0.19 (s, 3H, MeZr). 13C{1H}
NMR (C6D6, 101 MHz, 298 K): δ 191.0 (CdN), 136.9 (ipso Ph),
129.3 (B(C6F5)3) 128.3 (B(C6F5)3), 128.1 (ortho Ph), 128.05
(para Ph), 127.9 (meta Ph), 126.9 (B(C6F5)3), 93.2 (CH-
(CdN)), 31.9 (CH2Ph), 23.0 (MeB), 21.4 (Me(CdN)), 14.4
(MeZr).
nacnacBn2Zr(OEt)2, 6. Ethanol (37.5 mg, 0.81 mmol) was
added to a yellow ether solution of 5 (250 mg, 0.37 mmol), upon
which gas formation (CH4) was observed. The yellow solution
was evaporated to dryness, and the obtained yellow solid was
extracted with 15 mL of hexane. Evaporation of the volatiles
yielded a colorless powder, which contained mostly 6 and the
free ligand 1a. Recrystallization from a saturated ethanol solu-
tion at -20 °C gave colorless crystals of 6 (136 mg, 50%).
1H NMR (CDCl3, 400 MHz, 298 K): δ 7.30-7.06 (m, 20H,
Ph), 5.10 (bs, 4H, CH2), 4.86 (s, 2H, CH(CdN)2), 4.54 (bs, 4H,
CH2), 3.69 (q, 4H, CH2O), 1.83 (bs, 12H, Me(CdN)), 0.72 (t,
6H, MeCH2O). 13C{1H} NMR (C6D6, 400 MHz, 298 K): δ
163.5 (CdN), 142.1 (ipso Ph), 127.9 (ortho Ph), 127.2 (para Ph),
125.8 (meta Ph), 102.7 (CH(CdN)), 64.7 (CH2O), 53.6 (CH2Ph),
22.2 (MeCH2O), 19.8 (Me(CdN)). Anal. Calcd for
C42H48N4O2Zr: C, 68.53; H, 7.12; N, 7.61. Found: C, 68.13;
H, 7.45; N, 7.68.
Acknowledgment. We thank Sylvie Bilodeau for vari-
able-temperature NMR measurements and appreciate
helpful discussions with Dr. Peter Burger and Dr.
Marc-Heinrich Prosenc.
Supporting Information Available: Variable-temperature
NMR data and crystallographic information files (CIF). This
material is available free of charge via the Internet at http://
pubs.acs.org.
(32) APEX2, Release 2.1-0; Bruker AXS Inc.: Madison, WI, 2006.
(33) SAINT, Release 7.34A; Bruker AXS Inc.: Madison, WI, 2006.
(34) Sheldrick, G. M. SADABS; Bruker AXS Inc.: Madison, WI, 1996
and 2004.
(35) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(36) Spek, A. L. PLATON; Utrecht University: Utrecht, The Netherlands,
2008.
Variable-Temperature NMR Measurements. Variable-tem-
perature NMR spectra were recorded using a Bruker AV 500
spectrometer with CDCl3 solutions of complexes 3a-c and 6.
NMR data at low or high temperatures are given in the