Synthesis and molecular structures of zirconium complexes that contain bidentate amido ligands

Article abstract of DOI:10.1016/j.molstruc.2008.11.026

Zirconium complexes that contain bidentate amido ligands, Zr₂{EtN(CH₂)₃NEt}₄ (1), Zr₂{PhN(CH₂)₂NPh}₄ (2), Zr{Me₃SiN(CH₂)₃NSiMe₃

Full text of DOI:10.1016/j.molstruc.2008.11.026

Journal of Molecular Structure 920 (2009) 363–368
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and molecular structures of zirconium complexes that contain
bidentate amido ligands
*
Matthew D. Lococo, Han Lee, Richard F. Jordan
Department of Chemistry, The University of Chicago, 5735 S. Ellis Avenue, Chicago, IL 60637, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 October 2008
Received in revised form 12 November 2008
Accepted 12 November 2008
Available online 21 November 2008
Zirconium complexes that contain bidentate amido ligands, Zr2{EtN(CH2)3NEt}4 (1), Zr2{PhN(CH2)2NPh}4
(2), Zr{Me3SiN(CH2)3NSiMe3}2 (3) and Zr{trans-N,N0-diphenyl-1,2-diaminocyclohexane}Cl2(THF)2 (4),
have been prepared by the reaction of lithium diamido reagents with ZrCl4, and characterized by single
crystal X-ray diffraction. The molecular structures of complexes 1–4 are discussed.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Zirconium (IV) amido complex
Bidentate amido ligands
Chelate ring conformation
Dinuclear complexes
Amine elimination reaction
1. Introduction
ing is disfavored adopt mononuclear tetrahedral structures, as
exemplified by Zr(NPh2)4 (6) [9].
Zirconium (IV) amido complexes are useful precursors to ansa-
zirconocenes and other Zr compounds [1]. Amine elimination reac-
tions of Zr(NR2)4 and HCp0YCp0H [2] compounds provide access to
ansa-(Cp0YCp0)Zr(NR2)2 complexes [3,4], which are important in
stereoselective catalysis and olefin polymerization [5]. The steric
properties of the amido ligands strongly influence the rates and
rac/meso selectivity of these reactions. Homoleptic Zr(NR2)4 com-
pounds are also useful precursors to Zr(NR2)2X2 and Zr(NR2)2X2L2
complexes [6]. Salt elimination reactions of chelated
Zr{RN(CH2)nNR}Cl2(THF)2 (n = 2, 3) complexes and Li2[Cp0YCp0] re-
agents provide access to ansa-(Cp0YCp0)Zr{RN(CH2)nNR} complexes,
which are easily converted to ansa-(Cp0YCp0)ZrCl2 catalysts [7]. The
conformations of the Zr{RN(CH2)nNR} chelate rings control the rac/
meso selectivity in these reactions. In particular, twist conforma-
tions that place the N-R groups on opposite sides of the N–Zr–N
plane favor the formation of rac-(Cp0YCp0)Zr{RN(CH2)nNR} prod-
ucts [7].
The structures of chelated Zr{RNYNR}2 complexes are similar to
those of their non-chelated counterparts, as shown in Fig. 1. The
homoleptic chelated-bisamido Zr complex {Zr[(NiPr)2SiMe2]2}2
(7) has as a dinuclear trigonal bipyramidal structure similar to that
of 5 [10]. In contrast, the bulky N-R groups and larger bisamido li-
gand bite angles of Zr{trans-1,2-(NSiMe3)2-cyclohexane}2 (8) [11]
and Zr{Ph2MeSiN(CH2)3NSiMePh2}2 (9) [12] disfavor formation of
dinuclear species and these complexes adopt distorted tetrahedral
structures similar to that of 6. In both 8 and 9, the N–R groups lie in
their respective N–Zr–N planes.
Several Zr{RN(CH2)nNR}X2 and Zr{RN(CH2)nNR}X2L2 complexes
have been prepared and representative structures are shown in
Fig. 2. Five-membered chelate rings in these systems often adopt
flat conformations, as observed in Zr{Ar2BN(CH2)2NBAr2}Me2,
Ar = 2,4,6-iPr3-Ph (10) and Zr{Cy2BN(CH2)2NBCy2}Et2 (11) [13].
This conformation positions the N–BR2 groups of 10 and 11 in
t
the N–Zr–N plane. The six-membered rings in Zr{Ph2 Bu-
Two general structure types have been observed for simple
Zr(NR2)4 compounds in the solid state (Fig. 1). Complexes with ste-
rically small amido ligands adopt dinuclear, edge-shared, trigonal
bipyramidal structures with two bridging amidos, as exemplified
by Zr2(NMe2)8 (5) [8]. Sterically crowded amidos for which bridg-
SiNCH2CMe2CH2NSitBuPh2}Cl2 (12) [14] and Zr{iPr3SiN(CH2)3N-
SiiPr3}Cl2 (13) [15] adopt boat conformations, in which the N-SiR3
groups again lie in the N–Zr–N plane. In contrast, the chelate ring
in Zr{Me3SiN(CH2)3NSiMe3}Cl2(THF)2 (14) [16] adopts
a pro-
nounced twist conformation, which places the N-SiMe3 groups on
opposite sides of the N–Zr–N plane.
Understanding the structures and conformational properties of
Zr compounds with chelated-bisamido ligands may contribute to
the development of improved methods for the stereoselective
* Corresponding author. Tel.: +1 7737026429; fax: +1 773 702 0805.
E-mail address: rfjordan@uchicago.edu (R.F. Jordan).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.11.026

364
M.D. Lococo et al. / Journal of Molecular Structure 920 (2009) 363–368
gen was purified by passage through activated molecular sieves
NMe2
Zr
Me
Me
and Q-5 oxygen scavenger. Pentane, hexanes, toluene and benzene
were distilled from sodium/benzophenone or purified by passage
through activated alumina and BASF R3-11 oxygen removal cata-
lyst. Benzene-d6 and THF-d8 were distilled from sodium/benzophe-
none and stored under vacuum. ZrCl4 was purchased from Cerac
and sublimed before use. The compounds trans-1,2-diaminocyclo-
hexane, EtNH(CH2)3NHEt and PhNH(CH2)2NHPh were purchased
from Aldrich and used as received. Me3SiNH(CH2)3NHSiMe3 was
prepared by the literature procedure [17].
Me2N
NPh2
Zr
N
NPh2
Me2N
Me
Me
Ph2N
NMe2
N
Zr
NPh2
NMe2
NMe2
5
6
NMR spectra were recorded on Bruker AMX-360, AMX-400 or
AMX-500 spectrometers in flame-sealed or Teflon-valved tubes
at ambient probe temperatures. 1H and 13C chemical shifts are re-
ported relative to SiMe4 and were determined by reference to the
residual 1H and 13C solvent resonances. Coupling constants are gi-
ven in Hz.
Me2Si
iPrN
NiPr
Zr
iPr
SiMe2
N
iPrN
NiPr
Zr
Me2Si
N
iPr
2.1. Synthesis
NiPr
iPrN
2.1.1. Li2[EtN(CH2)3NEt]
SiMe2
A solution of nBuLi in hexanes (5.08 mL, 2.5 M, 13 mmol) was
added to a solution of EtNH(CH2)3NHEt (0.819 g, 6.21 mmol) in
hexanes (50 mL) over 5 min by syringe at ꢀ78 °C. The resulting
slurry was stirred for 24 h during which time the mixture was al-
lowed to warm to 25 °C. The mixture was filtered to yield a white
solid. The solid was washed with hexanes (100 mL) and dried un-
der vacuum (0.80 g, 91%). The same procedure was carried out on a
8.19 g (62.88 mmol) scale with an 81% isolated yield. 1H NMR
(THF-d8): d 3.00 (t, J = 6, 4H, CH2), 2.88 (q, J = 8, 4H, CH2), 1.73
(br, m, 2H, CH2), 1.01 (t, J = 8, 6H, CH3).
7
SiMe3
SiMePh2
N
N
SiMePh2
SiMe3
Zr
Zr
N
N
N
N
N
Me3Si
N
Ph2MeSi
SiMePh2
Me3Si
9
8
2.1.2. Zr2{EtN(CH2)3NEt}4 (1)
Fig. 1. Structures of Zr2(NMe2)8 (5), Zr(NPh2)4 (6), {Zr[(NiPr)2SiMe2]2}2 (7), Zr{trans-
1,2-(NSiMe3)2-cyclohexane}2 (8) and Zr{Ph2MeSiN(CH2)3NSiMePh2}2 (9).
A flask was charged with ZrCl4 (3.13 g, 14.2 mmol) and cooled
to ꢀ78 °C. Et2O (50 mL) was added and the resulting slurry was
stirred for 5 min at –78 °C.
A solution of Li2[EtN(CH2)3NEt]
(4.04 g, 28.4 mmol) in THF (50 mL) was cooled to ꢀ78 °C and
added to the ZrCl4/Et2O slurry by cannula transfer over a 30 min
period. The mixture was stirred overnight while the flask was al-
lowed to warm to 25 °C. The volatiles were removed under vac-
uum. Toluene (60 mL) was added by cannula transfer and the
mixture was stirred overnight at 25 °C. The mixture was filtered
and the filtrate was dried under vacuum to yield an orange solid.
The solid was taken up in benzene (10 mL) and hexanes (100 mL)
was added by cannula transfer. The solution was cooled ꢀ35 °C
overnight and filtered through a medium glass frit to yield white,
X-ray quality crystals (0.965 g, 19%). The NMR spectra of 1 are
complex suggesting that 1 may exist in several forms in solution.
Me
Zr
Et
Zr
BAr2
BCy2
N
N
Me
Et
N
N
BAr2
BCy2
10, Ar = 2,4,6-iPr3-Ph
11
Cl
Zr
Cl
SitBuPh2
SiMe3
SiiPr3
Cl
CH3
Zr
THF
THF
N
N
N
N
Zr
Cl
Cl
Cl
N
N
CH3
SitBuPh2
SiiPr3
2.1.3. Zr2{PhN(CH2)2NPh}4 (2)
SiMe3
The preparation and characterization of 2 were previously
reported [7b]. X-ray quality crystals were obtained by recrystalli-
zation at ꢀ35 °C from a solution of CH2Cl2 layered with hexanes
to yield pale yellow crystals.
12
13
14
Fig. 2. Structures of Zr{Ar2BN(CH2)2NBAr2}Me2 (10), Zr{Cy2BN(CH2)2NBCy2}Et2
(11), Zr{Ph2tBuSiNCH2CMe2CH2NSitBuPh2}Cl2 (12), Zr{iPr3SiN(CH2)3NSiiPr3}Cl2
(13), and Zr{Me3SiN(CH2)3NSiMe3}Cl2THF2 (14).
2.1.4. Zr{Me3SiN(CH2)3NSiMe3}2 (3)
Complex 3 was prepared by a literature method [15]. X-ray
quality crystals were obtained by recrystallization from pentane
at ꢀ78 °C.
synthesis of ansa-zirconocenes [7]. Here we describe the synthesis
and structures of four Zr bisamido complexes, Zr2{EtN(CH2)3NEt}4
(1), Zr2{PhN(CH2)2NPh}4 (2), Zr{Me3SiN(CH2)3NSiMe3}2 (3) [15]
and Zr{trans-N,N0-diphenyl-1,2-diaminocyclohexane}Cl2(THF)2 (4).
2.1.5. Trans-N,N0-diphenyl-1,2-diaminocyclohexane
Trans-N,N0-diphenyl-1,2-diaminocyclohexane was synthesized
by a modified literature method [18]. A flask was charged with
trans-1,2-diaminocyclohexane (1.02 g, 8.97 mmol), bromobenzene
(2.95 g, 18.83 mmol) and toluene (15 mL) by cannula transfer. A
separate flask was charged with Pd(OAc)2 (0.100 g, 0.448 mmol),
BINAP (0.558 g, 0.897 mmol), Na[OtBu] (2.58 g, 26.9 mmol) and
2. Experimental
All reactions were performed under nitrogen or vacuum using
standard Schlenk techniques or in a nitrogen-filled drybox. Nitro-

M.D. Lococo et al. / Journal of Molecular Structure 920 (2009) 363–368
365
Table 1
toluene (30 mL). The two mixtures were stirred for 60 min at room
temperature and the solution containing 1,2-diaminocyclohexane
and bromobenzene was added to the second flask by cannula
transfer. The mixture was heated at 100 °C for 2 h, cooled to
25 °C, and diluted with hexanes (150 mL). The mixture was stirred
for 8 h and filtered through a plug of silica gel. The silica was
washed with CH2Cl2 (25 mL), and the wash and filtrates were com-
bined and dried under vacuum to yield an amber oil. The oil was
purified by column chromatography (silica gel, CH2Cl2 eluent) to
yield an amber gel which was pure enough for use subsequent
reactions (0.708 g, 71%). 1H NMR (CDCl3): d 7.16 (t, J = 8.0, 4H, m-
Ph), 6.70 (t, J = 8.0, 2H, p-Ph), 6.61 (d, J = 8.0, 4H, o-Ph), 3.80 (br s,
2H, NH), 3.19 (m, 2H, CH2), 2.35 (m, 2H, CH2), 1.76 (m, 2H, CH2),
1.40 (m, 2H, CH2), 1.22(m, 2H).
Summary of X-ray diffraction data for Zr2{EtN(CH2)3NEt}4 (1) and
Zr2{PhN(CH2)2NPh}4 (2).
1
2 ꢁ CH2Cl2
C57H58N8Cl2Zr2
1108.49
Triclinic
P
9.9109(6)
11.640(1)
12.677(1)
92.882(1)
109.265(3)
112.284(1)
1349.0(2)
2
Formula
C28H64N8Zr2
695.31
Monoclinic
P21/c
12.052(2)
13.159(3)
21.385(4)
90.0
100.44(3)
90.0
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
(o)
b (o)
c
(o)
V (Å3)
3335.2(1)
4
Z
T (K)
100(2)
173(2)
2.1.6. Li2[trans-N,N0-diphenyl-1,2-diaminocyclohexane]
Crystal color, habit
Transparent, fragment
1.167
R1 = 0.0436, wR2 = 0.0890
Yellow, fragment
1.026
R1 = 0.0248, wR2 = 0.0710
GOF on F2
A solution of nBuLi in hexanes (5.1 mL, 2.5 M, 12.8 mmol) was
added to a solution of trans-N,N0-diphenyl-1,2-diaminocyclohex-
ane (1.7 g, 6.4 mmol) in benzene (150 mL) over 5 min by syringe
at 23 °C. The resulting slurry was stirred for 2 h at 23 °C and fil-
tered to yield a pale yellow solid. The solid was washed with hex-
anes (70 mL) and dried under vacuum to yield a pale yellow solid
(1.65 g, 92%). 1H NMR (THF-d8): d 6.96 (t, J = 8.0, 4H, m-Ph), 6.17 (d,
J = 8.0, 4H, o-Ph), 5.78 (t, J = 8.0, 2H, p-Ph), 2.94 (d, J = 8.0, 2H, CH2),
2.46 (d, J = 8.0, 2H, CH2), 1.73 (obscured by solvent, 2H, CH2), 1.41
(t, J = 8.0, 2H, CH2), 0.08 (br m, 2H, CH2).
R indices (I > 2
r
(I))a
R indices (all data)a
R1 = 0.0507, wR2 = 0.092
R1 = 0.0276, wR2 = 0.0726
ꢂ
ꢂ
ꢃ
ꢂ
ꢃꢃ
1=2
ꢀ
ꢁ
ꢀ
ꢁ
2
2
P
P
a
R1
=
R
||Fo| ꢀ |Fc||/
R
|Fo|; wR2
¼
w
F2o ꢀ F2c
=
w
Fo2
, where
h
ꢀ
ꢁ
iꢀ1
2
w ¼ q r2 F2o þ ðaPÞ þ bP
.
Table 2
Summary of X-ray diffraction data for Zr{Me3SiN(CH2)3NSiMe3}2 (3) and Zr{trans-
N,N0-diphenyl-1,2-diaminocyclohexane}Cl2(THF)2 (4).
2.1.7. Zr{trans-N,N0-diphenyl-1,2-diaminocyclohexane}Cl2(THF)2 (4)
A flask was charged with ZrCl4 (0.420 g, 1.80 mmol) and Li2[-
trans-N,N0-diphenyl-1,2-diaminocyclohexane] (0.500 g, 1.80 mmol).
A mixture of THF and Et2O (1/1 by volume, 175 mL) was added by
vacuum transfer at ꢀ196 °C. The mixture was placed in an ice bath
at 0 °C and stirred for 12 h, during which time it was allowed to
warm to room temperature. The volatiles were removed under
vacuum at 30 °C to yield a yellow solid. Benzene (75 mL) was
added by vacuum transfer at ꢀ196 °C and the mixture was stirred
for 2 h at room temperature. The mixture was filtered through a
3
4
Formula
Formula weight
Crystal system
Space group
a (Å)
C18H48N4Si4Zr
524.18
Monoclinic
C2/c
C26H36N2Cl2O2Zr
662.82
Monoclinic
P21/n
17.159(3)
14.280(2)
b (Å)
10.427(2)
11.044(3)
c (Å)
17.175(3)
111.32(3)
2862.6(10)
4
21.120(4)
107.310(4)
3179.8(1)
b (o)
V (Å3)
Z
4
medium porosity glass frit (10–20 lm pore size) and the volatiles
T (K)
100(2)
100(2)
were removed from the filtrate under vacuum at 35 °C, yielding
an orange solid (0.708 g, 68%). X-ray quality crystals were grown
from a 7/1 (by volume) toluene/hexanes solution at ꢀ35 °C. 1H
NMR (C6D6): d 7.39 (br d, J = 8.0, 4H, o-Ph), 7.19 (t, J = 8.0, 4H, m-
Ph), 6.88 (t, J = 8.0, 2H, p-Ph), 4.70 (br s, 2H) 3.64 (br s, 8H, THF),
1.85 (br d, J = 8.0, 2H, CH2), 1.48 (br d, J = 8.0, 2H, CH2), 1.16 (br
s, 4H, CH2), 1.07 (br s, 8H, THF). 13C{1H} NMR (C6D6) d 149.4,
128.8, 124.7, 122.4, 73.3, 70.8, 30.7, 25.7, 25.1.
Crystal color, habit
Clear, fragment
1.108
R1 = 0.0515, wR2 = 0.1509
R1 = 0.0515, wR2 = 0.1509
Yellow, fragment
1.007
R1 = 0.0263, wR2 = 0.0617
R1 = 0.0330, wR2 = 0.0625
GOF on F2
R indices (I > 2
r
(I))a
R indices (all data)a
ꢂ
ꢂ
ꢃ
ꢂ
ꢃꢃ
1=2
ꢀ
ꢁ
ꢀ
ꢁ
2
2
P
P
a
R1
=
R
||Fo| ꢀ |Fc||/
R
|Fo|; wR2
¼
w
F2o ꢀ F2c
=
w
Fo2
,
where
h
ꢀ
ꢁ
iꢀ1
2
w ¼ q r2 F2o þ ðaPÞ þ bP
.
2.2. X-ray structure determinations
and 7. At Zr(1), N(3) and N(7) occupy the axial positions, and
N(4), N(6) and N(8) occupy the equatorial sites. At Zr(2), N(1)
and N(8) occupy the axial positions and N(2), N(5) and N(7) occupy
the equatorial sites. The N(1)–N(2) bisamido ligand chelates to
Zr(2), and the N(3)–N(4) bisamido chelates to Zr(1). In both cases,
the bisamido ligand occupies an axial and an equatorial site, and as
shown in Fig. 3, the chelate rings have twist conformations. The
N(5)–N(6) bisamido ligand bridges the two Zr centers by mono-
dentate terminal coordination at an equatorial site at each Zr, and
as shown in Fig. 3, has a twist conformation. Finally, the N(7)–
N(8) bisamido ligand forms a double bridge in which each N forms
Crystallographic data are summarized in Tables 1 and 2. ORTEP
plots are drawn at the 50% probability level. Non-hydrogen atoms
were refined with anisotropic displacement coefficients. All hydro-
gen atoms were included in the structure factor calculation at ideal-
ized positions and were allowed to ride on the neighboring atoms
with relative isotropic displacement coefficients. The asymmetric
unit of 2 ꢁ (CH2Cl2) contains a disordered solvent molecule, in which
atom Cl(1) is disordered over two positions in an 85/15 ratio.
a l
2-bridge between the two Zr centers. This bisamido ligand has a
3. Results and discussion
slightly puckered conformation.
3.1. Synthesis and structure of Zr2{EtN(CH2)3NEt}4 (1)
3.2. Synthesis and structure of Zr2{PhN(CH2)2NPh}4 (2)
The reaction of Li2[EtN(CH2)3NEt] with ZrCl4 yields 1. As shown
in Fig. 3, 1 adopts a dinuclear structure comprising two edge-
shared, trigonal bipyramidal units, which is similar to those of 5
The reaction of Li2[PhN(CH2)2NPh] with ZrCl4 yields 2. As shown
in Fig. 4, 2 has a dinuclear structure comprising two edge-shared,

366
M.D. Lococo et al. / Journal of Molecular Structure 920 (2009) 363–368
highly distorted, trigonal bipyramidal Zr units, which are related
by a crystallographically imposed inversion center. This structure
is again grossly similar to those of 5 and 7. N(1) and N(4) occupy
axial positions, and N(2), N(3) and N(4A) occupy equatorial sites.
The principal distortion is a displacement of the ‘‘axial” N(4) atom
toward the equatorial plane by ca. 36°. The connectivity of the Zr
bisamido units and the conformations of the chelate rings in 2
are different from those in 1. The N(1)–N(2) bisamido ligand of 2
chelates to Zr(1), occupies one axial and one equatorial site, and
has a flat envelope conformation. The N(3)–N(4) bisamido ligand
binds in a terminal fashion to Zr(1) via N(3) and in a
l
2-bridging
mode to both Zr centers via N(4). These differences in the struc-
tures of 2 and 1 may be due to the smaller natural bite angle of
Fig. 3. Molecular structure and views of the chelate rings of Zr2{EtN(CH2)3NEt}4 (1).
H atoms are omitted. Bond distances (Å): Zr(1)–N(6) 2.042(2), Zr(1)–N(4) 2.074(2),
Zr(1)–N(3) 2.099(2), Zr(1)–N(7) 2.402(2), Zr(1)–N(8) 2.260(2), Zr(2)–N(1) 2.094(2),
Zr(2)–N(5) 2.046(2), Zr(2)–N(2) 2.069(2), Zr(2)–N(7) 2.286(2), Zr(2)–N(8) 2.367(2).
Bond angles (°): N(4)–Zr(1)–N(3) 100.11(8), N(3)–Zr(1)–N(8) 95.18(8), N(4)–Zr(1)–
N(7) 94.10(8), N(4)–Zr(1)–N(8) 119.15(8), N(1)–Zr(2)–N(2) 88.32(8), N(1)–Zr(2)–
N(8) 146.22(8), N(1)–Zr(2)–N(6) 88.32(8), N(6)–Zr(2)–N(8) 87.24(8). Sums of angles
at N (°): N(1) 353.7(3), N(2) 355.5(4), N(3) 354.0(5), N(4) 352.4(5), N(5) 359.6(3),
N(6) 359.3(3), N(7) 318.2(3), N(8) 338.8. Deviations of atoms from the N(4)–Zr(1)–
N(3) plane (Å): C(13) ꢀ1.000, C(12) 0.940, C(11) 0.296, C(10) ꢀ0.602, C(9) 0.941.
Deviations of atoms from the N(1)–Zr(2)–N(2) plane (Å): C(2) ꢀ0.958, C(3) 0.511,
C(4) 0.409, C(5) ꢀ0.990, C(6) 0.922.
Fig. 4. Molecular structure and views of the chelate rings of Zr2{PhN(CH2)2NPh}4 (2).
H atoms are omitted. Bond distances (Å): Zr(1)–C(23) 2.807(2), Zr(1)–N(1) 2.081(2),
Zr(1)–N(2) 2.049(2), Zr(1)–N(3) 2.150(2), Zr(1)–N(4) 2.302(2). Bond angles (°): N(1)–
Zr(1)–N(2) 84.18(6), N(3)–Zr(1)–N(4) 74.36(5), N(1)–Zr(1)–N(3) 97.59(5), N(1)–
Zr(1)–N(4) 144.25(5), N(2)–Zr(1)–N(3) 113.71(5), N(2)–Zr(1)–N(4) 131.25(5). Sums
of angles at N (°): N(1) 357.1(3), N(2) 359.7(4), N(3) 359.9(5), N(4) 335.1(5). Angles
between planes (°): C(9)–N(2)–C(2)/N(1)–Zr(1)–N(2) 7.2, C(1)–N(1)–C(3)/N(1)–
Zr(1)–N(2) 25.9. Deviations of atoms from the N(1)–Zr(1)–N(2) plane (Å): C(9)
0.176, C(2) ꢀ0.099, C(1) ꢀ0.611, C(3) 0.082. Deviations of atoms from the N(3)–Zr(1)–
N(4) plane (Å): C(23) 1.405, C(16) ꢀ0.602, C(15) 0.262, C(17) 0.194.

M.D. Lococo et al. / Journal of Molecular Structure 920 (2009) 363–368
367
2ꢀ
2ꢀ
the ½PhNðCH2Þ2NPhꢂ ligand versus the ½EtNðCH2Þ3NEtꢂ ligand.
Interestingly, in 2 there is a close contact between Zr and the ipso
carbon of the phenyl ring in the bridging amido unit (Zr(1)–C(23),
2.807(2) Å), and the corresponding Zr–N–Cipso angle is small
(Zr(1)–N(4)–C(23), 95.10(9) deg). These data indicate that a weak
3.4. Synthesis and structure of Zr{trans-N,N0-diphenyl-1,2-
diaminocyclohexane}Cl2(THF)2 (4)
The reaction of Li2[trans-N,N0-diphenyl-1,2-diaminocyclohex-
ane] with ZrCl4 yields 4. As shown in Fig. 6, 4 adopts a monomeric
octahedral structure. The major distortion from ideal octahedral
geometry is the reduced Cl–Zr–Cl angle of 164°. The chelate ring
of 4 adopts a puckered conformation, which places the N–Ph
groups in the N(1)–Zr(1)–N(2) plane. The cyclohexane ring adopts
a normal chair conformation.
Ph–Zr donor interaction is present, analogous to the M-g
2-CH2Ph
interactions commonly observed in unsaturated metal benzyl
complexes [19]. Related donor interactions are observed in
Zr{1,2-(NSiiPr3)2-C6H4}2 [20] and Zr{1,2-(NSiMe3)2-C10H6}2 [21].
Additionally, in 2, the N–Ph rings of N(1), N(4A) and N(2A) are ar-
ranged for staggered p-stacking with an average distance between
the planes of 3.32 Å (Fig. 4) [22].
4. Conclusion
3.3. Synthesis and structure of Zr{Me3SiN(CH2)3NSiMe3}2 (3)
The structures of 1–4 provide useful insights to the nuclearity,
metal coordination geometries and bisamido chelate ring confor-
mations of zirconium amido complexes. The steric bulk of the N–
R groups of the amido ligands influences the preference for mono-
nuclear or dinuclear species. Small N–R groups favor dinuclear
complexes, while large N–R substituents favor mononuclear spe-
cies. The six-membered Zr{EtN(CH2)3NEt} chelate rings in 1 adopt
twist conformations that position the N-Et groups on opposite
sides of their respective N–Zr–N planes. In contrast, the Zr{Me3-
SiN(CH2)3NSiMe3} chelate rings in 3, which contain larger N-SiMe3
groups, adopt an envelope conformation that places the N-SiMe3
groups in the N–Zr–N plane. The five-membered chelate rings in
complexes 2 and 4 adopt slightly puckered conformations that
place the N–R groups close to the N–Zr–N plane.
The reaction of Li2[Me3SiN(CH2)3NSiMe3] with ZrCl4 yields 3. As
shown in Fig. 5, 3 adopts a monomeric, distorted tetrahedral struc-
ture. The major distortion is a 14° reduction of the N–Zr–N angle of
the chelate ring from the ideal tetrahedral angle. The angles be-
tween the N–Zr–N planes (N(1)–Zr–N(2)/N(1A)–Zr–N(2A), 88.4°;
(N(1)–Zr–N(1A)/N(2)–Zr–N(2A), 71.1°) also deviate from the ideal
tetrahedral value of 90°. The chelate ring of 3 adopts an envelope
conformation, which places the N-SiMe3 groups in the N(1)–
Zr(1)–N(2) plane.
Fig. 6. Molecular structure and view of the chelate ring of Zr{trans-1,2-(NPh)2-
cyclohexane}Cl2(THF)2 (4). H atoms are omitted with the exception of H(1A) and
H(2A) in the view at the top right. Bond distances (Å): Zr(1)–N(1) 2.063(2), Zr(1)–
N(2) 2.061(2), Zr(1)–Cl(1) 2.490(7), Zr(1)–Cl(2) 2.489(7), Zr(1)–O(1) 2.300(2), Zr(1)–
O(2) 2.284(2). Bond angles (°): N(1)–Zr(1)–N(2) 80.98(6), O(1)–Zr(1)–O(2) 80.59(5),
Cl(1)–Zr(1)–Cl(2) 164.98(2). Sums of angles at N (°): N(1) 356.6(4), N(2) 356.5(4).
Angles between planes (deg): C(1)–N(1)–C(7)/N(1)–Zr(1)–N(2) 15.3, C(13)–N(2)–
C(2)/N(1)–Zr(1)–N(2) 22.4. Deviations of atoms from the N(1)–Zr(1)–N(2) plane
(Å): C(1) ꢀ0.085, C(2) 0.085, C(13) 0.020, C(7) ꢀ0.281.
Fig. 5. Molecular structure and views of the chelate ring of Zr{Me3SiN(CH2)2NSiM-
e3}2 (3). H atoms are omitted. Bond distances (Å): Zr(1)–N(1) 2.060(4), Zr(1)–N(2)
2.048(4). Bond angles (°): N(1)–Zr(1)–N(2) 98.5(1), N(1)–Zr(1)–N(2A) 116.0(1),
N(1)–Zr(1)–N(1A) 112.0(2). Sums of angles at N (°): N(1) 359.7(4), N(2) 359.9(4).
Angles between planes (°): Si(1)–N(1)–C(4)/N(1)–Zr(1)–N(2) 5.5, Si(2)–N(2)–C(6)/
N(1)–Zr(1)–N(2) 9.0. Deviations of atoms from the N(1)–Zr(1)–N(2) plane (Å): Si(1)
0.091, C(4) ꢀ0.230, C(5) ꢀ0.416, C(1) ꢀ0.132, Si(2) 0.092.

368
M.D. Lococo et al. / Journal of Molecular Structure 920 (2009) 363–368
(e) J.R. Hagadorn, M.J. McNevin, G. Wiedenfeld, R. Shoemaker, Organometallics
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CCDC 704612, 704477, 704493 and 704494 contain the supple-
mentary crystallographic data for 1, 2, 3 and 4. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk.
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Acknowledgements
This work was supported by the National Science Foundation
(Grant CHE-0212210).
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