Synthesis and structures of zinc alkoxo, aryloxo and hydroxo complexes with an amidodiamine ligand

Article abstract of DOI:10.1016/j.poly.2010.06.029

The synthesis and characterization of zinc complexes bearing an amidodiamine ligand, (EtO)₄Zn₃[N(CH₂CH ₂NMe₂)₂]₂ (1), [(Et ₃CO)ZnN(CH₂CH₂NMe₂) ₂]₂ (2) and [(2,6-ⁱPr₂C ₆H₃O)ZnN(CH₂CH₂NMe₂) ₂]₂ (3), [(Me₃Si)₂N]Zn[N(CH ₂CH₂NMe₂)₂] (4) and [(Me ₃Si)₂N]₂Zn₂(OH)[N(CH ₂CH₂NMe₂)₂] (5), are reported. Compounds 1-3 are synthesised in the reactions of {Zn[N(CH₂CH ₂NMe₂)₂]₂}₂ with 2 equiv. of ethanol, 3-ethyl-3-pentanol and 2,6-diisopropylphenol, respectively. Compound 4 is obtained by the reaction of Zn[N(SiMe₃) ₂]₂ with HN(CH₂CH₂NMe ₂)₂, and compound 5 is synthesised by reacting 4 with 1 equiv. of H₂O. Compound 4 is characterized by NMR and MS while all of the other compounds are characterized with NMR, MS, elemental analysis and single-crystal X-ray diffraction. Compound 1 is a trinuclear species containing a Zn₃N₂O₂ core. Compounds 2 and 3 are dimeric with planar Zn₂N₂ rings. Compound 5 is dimeric with a planar Zn₂NO ring.

Full text of DOI:10.1016/j.poly.2010.06.029

Polyhedron 29 (2010) 2795–2801
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and structures of zinc alkoxo, aryloxo and hydroxo complexes
with an amidodiamine ligand
*
Bing Luo, Benjamin E. Kucera, Wayne L. Gladfelter
Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and characterization of zinc complexes bearing an amidodiamine ligand,
(EtO)4Zn3[N(CH2CH2NMe2)2]2 (1), [(Et3CO)ZnN(CH2CH2NMe2)2]2 (2) and [(2,6-iPr2C6H3O)ZnN(CH2CH2
NMe2)2]2 (3), [(Me3Si)2N]Zn[N(CH2CH2NMe2)2] (4) and [(Me3Si)2N]2Zn2(OH)[N(CH2CH2NMe2)2] (5), are
reported. Compounds 1–3 are synthesised in the reactions of {Zn[N(CH2CH2NMe2)2]2}2 with 2 equiv. of
ethanol, 3-ethyl-3-pentanol and 2,6-diisopropylphenol, respectively. Compound 4 is obtained by the
reaction of Zn[N(SiMe3)2]2 with HN(CH2CH2NMe2)2, and compound 5 is synthesised by reacting 4 with
1 equiv. of H2O. Compound 4 is characterized by NMR and MS while all of the other compounds are char-
acterized with NMR, MS, elemental analysis and single-crystal X-ray diffraction. Compound 1 is a trinu-
clear species containing a Zn3N2O2 core. Compounds 2 and 3 are dimeric with planar Zn2N2 rings.
Compound 5 is dimeric with a planar Zn2NO ring.
Received 29 January 2010
Accepted 30 June 2010
Available online 14 July 2010
Keywords:
Alkoxo amido zinc
Aryloxo amido zinc
Hydroxo amido zinc
Zn alkoxides
Zn hydroxide
Ó 2010 Elsevier Ltd. All rights reserved.
Tridentate nitrogen ligand
1. Introduction
we react {Zn[N(CH2CH2NMe2)2]2}2 [45] with a series of alcohols
to obtain several crystalline compounds having an alkoxy or aryl-
Zinc alkyls such as diethyl zinc are the most widely used pre-
cursors in vapor phase deposition of ZnO films. Because zinc alkyls
are pyrolytic, alternative precursors including carbarmates such as
Zn4O(CO2NEt2)6 [1,2], zinc acetylacetonate derivatives [3,4], b-
ketoiminates and b-iminoesterates [5], alkyl zinc alkoxides such
as (MeZnOiPr)4 and (MeZnOtBu)4 [6] and a methyl zinc aminoalk-
oxide [7] have been adopted in the ZnO film preparation.
The dialkoxides Zn(OR)2 [8] and diamides Zn(NR2)2 [9,10] with
short-chain alkyl R groups, presumably polymeric, are nonvolatile
and insoluble. Soluble dialkoxides [11–19] and diamides [20–29],
typically having a monomeric or dimeric structure, are obtained
using bulky ligands. Most of them have a low volatility. Exceptions
are the bis(trimethylsilyl)amido zinc complexes, such as
Zn[N(SiMe3)2]2 [26] that is volatile and has been used in the depo-
sition of SiO2-containing ZnO films [30] and Zn3N2 films [31].
In contrast to the dialkoxides, alkyl zinc alkoxides are soluble
even for the smallest alkyl groups [9,32–34] and some, as indicated
above, are volatile. These compounds have also been used in nano-
crystalline ZnO synthesis [35–39]. Analogously, a number of solu-
ble and/or volatile alkyl zinc amide compounds exist [10,40–42].
Their applications in materials synthesis have yet to be explored.
Only a few Zn complexes bearing both amido and alkoxy li-
gands were reported, and all contain bulky ligands [12,43,44]. To
study the ZnO precursor chemistry in this group of compounds,
oxy ligand and the amidodiamine ligand N(CH2CH2NMe2)2. The
synthesis and structures of these compounds are reported in this
paper. The N(CH2CH2NMe2)2 ligand and its corresponding amine
HN(CH2CH2NMe2)2 were previously used in the preparation of vol-
atile Al, Ga and Sr compounds [46–48]. Several Zn complexes bear-
ing this ligand were also reported [45], one of which, the diamide
{Zn[N(CH2CH2NMe2)2]2}2, is used as a reactant in the present
study. It is prepared by ligand exchange from [Zn(NiBu2)2]2 [45].
We have also attempted the reaction of Zn[N(SiMe3)2]2 with
HN(CH2CH2NMe2)2 and only the mono-substituted complex,
[(Me3Si)2N]Zn[N(CH2CH2NMe2)2], is obtained. Interestingly, this
complex reacts with H2O forming a hydroxo Zn complex in a mod-
erate yield.
2. Experimental
2.1. Materials and general procedures
The solvents and reactants are obtained from Aldrich. Toluene
and hexanes are dried with alumina in an MBraun solvent purifica-
tion system. Diethyl ether, pentane, diisobutylamine, benzene-d6,
toluene-d8 and deuterated chloroform are dried over calcium hy-
dride under nitrogen. Ethanol and 3-ethyl-3-pentanol (Et3COH)
are dried over 4 A molecular sieves and 2,6-diisopropylphenol
(2,6-iPr2C6H3OH) is recrystallized from pentane at ꢀ50 °C.
{Zn[N(CH2CH2NMe2)2]2}2 [45] and Zn[N(SiMe3)2]2 [49] are pre-
pared according to the methods described in the literature. All
* Corresponding author.
E-mail address: wlg@umn.edu (W.L. Gladfelter).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.06.029

2796
B. Luo et al. / Polyhedron 29 (2010) 2795–2801
experiments are conducted under an oxygen-free, dry-nitrogen
atmosphere using standard Schlenk and glovebox techniques.
Except for the otherwise indicated, all NMR spectra are obtained
in benzene-d6 solutions at room temperature on a Varian INOVA
300 spectrometer. The residual proton at 7.15 ppm and the carbon
resonance at 128.39 ppm in benzene-d6 are used as the internal
standards for 1H and 13C NMR, respectively. When CDCl3 is used
as the NMR solvent, the residual proton at 7.27 ppm and the carbon
resonance at 77.23 ppm in CDCl3 are the internal standards. When
toluene-d8 is used as the solvent, one of the residual aromatic pro-
tons at 7.00 ppm and one carbon resonance at 137.86 ppm are used
as the internal standards. The IR spectra (KBr pellets) are recorded
on a Nicolet MAGNA-IR 560 spectrometer. Chemical-ionization (CI)
mass spectra are acquired on a Finnigan Mat 95 spectrometer using
a direct insertion probe. The samples are evaporated at 150 °C and
the ionization gas mixture is methane with 4% ammonia. Melting
points are measured in sealed glass capillaries and were uncor-
rected. The elemental analyses are performed by Columbia Analyt-
ical Services, Tucson, AZ.
(CH2CH2NMe2)2ꢀMe]+, 12), 160 ([H2N(CH2CH2NMe2)2]+, 36). Anal.
Calc. for C30H70N6O2Zn2: C, 53.17; H, 10.41; N, 12.40. Found: C,
52.88; H, 10.74; N, 12.62%.
2.4. Synthesis of [(2,6-iPr2C6H3O)ZnN(CH2CH2NMe2)2]2 (3)
To
a stirred solution of {Zn[N(CH2CH2NMe2)2]2}2 (1.20 g,
1.57 mmol) in 40 mL of toluene at room temperature is added
2,6-iPr2C6H3OH (0.56 g, 3.1 mmol) via a syringe. A clear solution
forms and is stirred for 2 h. After the solution is concentrated to
10 mL and stored at ꢀ20 °C, colorless, crystalline compound 3 pre-
cipitates and is isolated (0.60 g). The toluene and as-formed
HN(CH2CH2NMe2)2 inthemotherliquorareremovedundervacuum,
and 4 mL of toluene is added to dissolve the residue. The solution is
storedatꢀ20 °C forafewdaystoyieldasecondcropoftheproduct. A
total yield of 0.66 g (50% yield) of compound 3 is obtained. M.p.:
210 °C, decomposed. 1H NMR: d 1.44 (24H, d, CHMe2), 2.05 (24H, s,
NMe2), 2.37 (8H, t, CH2NMe2), 2.97 (8H, t, CH2CH2NMe2), 3.61 (4H,
heptet, CHMe2), 6.97 (2H, t, para-H in C6H3O), 7.26 (4H, d, meta-H
in C6H3O). 13C NMR: d 24.2 (CHMe2), 28.0 (CHMe2), 46.3 (NMe2),
52.6 (CH2NMe2), 62.0 (CH2CH2NMe2), 115.9 (para-C in C6H3O),
123.2 (meta-C in C6H3O), 136.8 (ortho-C in C6H3O), 162.1 (C bonded
to O in C6H3O). Anal. Calc. for C40H74N6O2Zn2: C, 59.91; H, 9.30; N,
10.48. Found: C, 60.04; H, 9.30; N, 10.71%.
2.2. Synthesis of (EtO)4Zn3[N(CH2CH2NMe2)2]2 (1)
To
a stirred solution of {Zn[N(CH2CH2NMe2)2]2}2 (2.50 g,
3.28 mmol) in 30 mL of toluene at room temperature is added
EtOH (0.30 g, 6.6 mmol) via a syringe. A white solid formed upon
the addition of EtOH, which is quickly dissolved affording a color-
less solution. The solution is stirred for 2 h. The volatiles are then
removed under vacuum affording a wet, white solid. Pentane
(30 mL) is added to dissolve the solid and filtered. After the filtrate
is concentrated to ca. 8 mL and stored at ꢀ20 °C for a few days, col-
orless, crystalline compound 1 precipitates and is isolated (1.05 g,
70% yield). M.p.: 88.0–90.0 °C. 1H NMR: d 1.48 (6H, t, CH2CH3), 1.67
(6H, t, CH2CH3), 2.30 (24H, s, NMe2), 2.00, 2.46, 2.79 and 2.97 (total
16H, overlapping broad multiplets, CH2CH2NMe2), 4.18 (4H, q,
CH2CH3), 4.51 (4H, q, CH2CH3). 13C NMR: d 22.3 and 24.7 (CH2CH3),
45.7 (NMe2), 52.8 (broad, CH2NMe2), 60.8 (broad, CH2CH2NMe2),
62.4 and 64.0 (CH2CH3). CI MS (assignment, % relative intensity):
693 ([1+H]+, 2.1), 647 ([1ꢀOEt]+, 12), 537 ([1ꢀZn(OEt)2+H]+, 21),
491 ([1ꢀZn(OEt)2ꢀOEt]+, 26), 381 ({Zn[N(CH2CH2NMe2)2]2+H}+,
58), 378 ([1ꢀZn(OEt)2ꢀN(CH2CH2NMe2)2]+, 23), 268 ([(EtO)ZnN
(CH2CH2NMe2)2+H]+, 17), 160 ([H2N(CH2CH2NMe2)2]+, 100). Anal.
Calc. for C24H60N6O4Zn3: C, 41.56; H, 8.73; N, 12.13. Found: C,
41.50; H, 8.85; N, 12.26%.
2.5. Synthesis of [(Me3Si)2N]Zn[N(CH2CH2NMe2)2] (4)
To a stirred solution of Zn[N(SiMe3)2]2 (2.00 g, 5.18 mmol) in
10 mL of Et2O at room temperature is added a solution of
HN(CH2CH2NMe2)2 (0.825 g, 5.18 mmol) in 10 mL of Et2O. A clear
solution forms and is stirred for 1 h. The volatiles are removed under
vacuum affording an oil. The 1H NMR spectrum of this crude product
shows that over 90% is compound 4. Hexanes (10 mL) are added to
dissolvethe oil. Upon cooling at ꢀ78 °C, colorlessneedles precipitate
from the solution and are isolated at low temperatures. When
warmedto room temperature, the crystallinematerial melts to a col-
orless liquid, which slowly solidifies over a period of 24 h to yield a
colorless, glassy solid (1.42 g, 71% yield). M.p.: 49.0–62.0 °C. 1H
NMR: d 0.30 (18H, s, SiMe3), 1.96 (12H, s, NMe2), 2.27 (4H, t,
CH2NMe2), 3.05 (4H, t, CH2CH2NMe2). 13C NMR: d 6.3 (SiMe3), 45.0
(NMe2), 52.3 (CH2NMe2), 62.5 (CH2CH2NMe2). CI MS (assignment,
% relative intensity): 770 (fZn½NðSiMe3Þ2ꢁ2g2þ, 0.2), 768 (f½ðMe3SiÞ2
NꢁZn½NðCH2CH2 NMe2Þ2ꢁg2þ, 0.2), 612 (fZn2½NðSiMe3Þ2ꢁg3þ, 0.5),
449 ({[(Me3Si)2N] Zn2[N(CH2CH2NMe2)2]ꢀH}+, 1.5), 384 (Zn½N
ðSiMe3Þ2ꢁ2þ, 2.0), 382 ({[(Me3Si)2N]Zn[N(CH2CH2NMe2)2]}+, 2.0),
380 ({Zn[N(CH2CH2 NMe2)2]2}+, 2.0), 369 ({Zn[N(SiMe3)2]2ꢀMe}+,
20), 324 ({[(Me3Si)2N]Zn[N(CH2CH2NMe2)2]ꢀCH2NMe2}+, 70), 275
2.3. Synthesis of [(Et3CO)ZnN(CH2CH2NMe2)2]2 (2)
To
a stirred solution of {Zn[N(CH2CH2NMe2)2]2}2 (1.20 g,
1.57 mmol) in 30 mL of toluene at room temperature is added Et3-
COH (0.37 g, 3.1 mmol) via a syringe. A clear solution forms and is
stirred for 2 h. Volatiles are then removed under vacuum to afford
a white solid. Pentane (20 mL) is added to dissolve the solid. After
the pentane solution is stored at ꢀ20 °C overnight, colorless, crys-
talline compound 2 precipitates and is isolated (0.53 g, 50% yield).
M.p.: 70.0–73.0 °C. 1H NMR (in toluene-d8, 22 °C): d 0.86, 1.01 and
1.05 (total 18H, overlapping multiplets, CH2CH3), 1.25, 1.45 and
1.58 (total 12H, overlapping multiplets, CH2CH3), 2.05, 2.12, and
2.24 (total 24H, overlapping broad singlets, NMe2), 2.40, 2.70,
2.96 and 3.20 (total 16H, overlapping broad multiplets,
CH2CH2NMe2). 13C NMR: d 9.8, 10.3 and 10.6 (CH2CH3), 33.8 and
35.5 (CH2CH3), 45.9, 46.7 (broad) and 47.0 (NMe2), 51.7, 52.2,
53.8 and 55.6 (CH2NMe2), 52.3, 62.8 (broad), 63.1 and 64.8
(CH2CH2NMe2), 72.6 (broad) and 73.0 (OCEt3). The low-tempera-
ture NMR results will be discussed below. CI MS (assignment, % rel-
ative intensity): 679 ([2+H]+, 0.8), 563 ([2ꢀOCEt3]+, 14), 520
([2ꢀN(CH2CH2NMe2)2]+, 100), 381 ([{Zn[N(CH2CH2NMe2)2]2}2+H]+,
73), 338 ([(Et3CO)ZnN(CH2CH2NMe2)2+H]+, 24), 322 ([(Et3CO)ZnN
({[(Me3Si)2N] Zn(NH3)3}+, 85), 224 ({Zn[N(SiMe3)2]}+, 70), 146
({HN(SiMe3)2ꢀ Me}+, 95),130 (NSi2Me4þ, 98), 72 (CH2CH2NMe2
,
þ
83), 58 (SiMe2þ, 100).
2.6. Synthesis of [(Me3Si)2N]2Zn2(OH)[N(CH2CH2NMe2)2] (5)
To a stirred solution of Zn[N(SiMe3)2]2 (2.02 g, 5.23 mmol) in
10 mL of Et2O at room temperature is added a solution of
HN(CH2CH2NMe2)2 (0.833 g, 5.23 mmol) in 10 mL of Et2O. A clear
solution forms and is stirred for 1 h. Then the solvent and as-
formed HN(SiMe3)2 are removed under vacuum. Toluene (20 mL)
is added to dissolve the residue. The solution is cooled at ꢀ78 °C
and H2O (0.094 mL, 5.2 mmol) is added via a syringe. The mixture
is warmed to room temperature and stirred for 1.5 h to yield a
cloudy solution. Filtration removes a solid (0.43 g), which is not
characterized. The volatiles in the filtrate are removed under
vacuum and the residue is dissolved in 10 mL of pentane. Upon
cooling at ꢀ78 °C, colorless, crystalline compound 5 precipitates
and is isolated (0.68 g, 42%). M.p.: 148.0–150.0 °C. IR: mOH
,

B. Luo et al. / Polyhedron 29 (2010) 2795–2801
2797
3709 cmꢀ1. CI MS (assignment, % relative intensity): 610 ([5ꢀOH]+,
5.5), 465 ([5ꢀN(SiMe3)2]+, 19), 162 ([(Me3Si)2NH2]+, 100), 160
([H2N(CH2CH2NMe2)2]+, 52). Anal. Calc. for C20H57N5OSi4Zn2: C,
38.32; H, 9.16; N, 11.17. Found: C, 38.08; H, 9.05; N, 11.05%. 1H
NMR (in C6D6, 22 °C): d 0.28 (36H, s, SiMe3), 1.96 (16H, broad s,
NMe2 and CH2NMe2), 2.64 (4H, broad s, CH2CH2NMe2). 13C NMR
(in C6D6, 22 °C): d 6.8 (SiMe3), 45.1 and 48.2 (broad peaks,
NMe2), 50.5 (CH2NMe2), 62.6 (CH2CH2NMe2). 1H NMR (in CDCl3,
22 °C): d 0.01 (36H, s, SiMe3), 2.41 (12H, broad s, NMe2), 2.66
(4H, broad s, CH2NMe2), 2.89 (4H, broad s, CH2CH2NMe2). 13C
NMR (in CDCl3): 22 °C: d 6.2 (SiMe3), 45.5 and 48.1 (broad peaks,
NMe2), 50.1 (CH2NMe2), 62.6 (CH2CH2NMe2); 0 °C: d 6.1 (SiMe3),
45.2 and 48.5 (NMe2), 50.0 (CH2NMe2), 62.3 (CH2CH2NMe2);
ꢀ20 °C: d 6.1 (SiMe3), 45.1 and 48.4 (NMe2), 49.9 (CH2NMe2),
62.2 (CH2CH2NMe2); ꢀ40 °C: d 6.0 (SiMe3), 45.0 and 48.4 (NMe2),
49.8 (CH2NMe2), 62.0 (CH2CH2NMe2).
pentanol and 2,6-diisopropylphenol (Scheme 1), and are character-
ized using NMR, IR, MS, elemental analysis and single-crystal X-ray
diffraction.
The three compounds are colorless crystalline materials soluble
in nonpolar and weakly polar organic solvents. They do not sub-
lime when heated to 100 °C under vacuum. The elemental analyses
of the three compounds are satisfactory, and the chemical ioniza-
tion mass spectra for compounds 1 and 2 exhibit the molecular
ions (plus 1).
The 1H and 13C NMR spectra of compound 3 show a set of
N(CH2CH2NMe2)2 and 2,6-iPr2C6H3O resonances, consistent with
its X-ray crystal structure given below. The NMR results for com-
pounds 1 and 2, however, differ from those expected based on their
X-ray crystal structures. For 1, while the bridging and terminal EtO
ligands are clearly identified by two sets of 1H and 13C resonances,
the 1H and 13C NMR peaks of the N(CH2CH2NMe2)2 ligands are sub-
stantially broadened. This is perhaps due to the existence of a dy-
namic process involving the NMe2 bonding and nonbonding to Zn.
Variable temperature NMR spectra of compound 2 are collected in
toluene-d8 from room temperature to ꢀ85 °C. In all 1H and 13C
spectra, multiple broad, overlapping N(CH2CH2NMe2)2 resonances
exist. From the relatively better resolved OCEt3 peaks, we can esti-
mate that more than three isomers of 2 exist at all temperatures.
Specifically, according to the crystal structure of 2 shown below,
the OCEt3 ligand should only afford one set of resonances, but in
all 1H spectra, at least three sets of resonances are observed and
the relative intensities vary with the temperatures. We are not able
to assign the structures of these isomers. In view of the bulkiness of
the OCEt3 ligand, it is possible that three-coordinate Zn isomers are
present in solution as a result of dissociation of the NMe2 group
from Zn. In addition, monomers of 2 could exist.
2.7. X-ray data collection, structure solution and refinement
The detailed experimental procedures and structure solution
methods are described elsewhere [50]. A Siemens Smart system
is used for compounds 1 and 3 and a Bruker Smart system is used
for compounds 2 and 5. The final cell constants are calculated from
3987 strong reflections for 1, 2491 for 2, 3573 for 3, and 2540 for 5.
For all structures, all non-hydrogen atoms are refined with aniso-
tropic displacement parameters. All hydrogen atoms are placed
in ideal positions and refined as riding atoms with relative isotro-
pic displacement parameters. For the OH group in compound 5, the
largest difference Fourier peak in the E-map (without the H) is ca.
0.6 Å from the oxygen atom. In the modeling, the hydroxyl proton
is placed on the twofold axis at 0.84 Å from the O atom. For com-
pound 1, each of the ethoxy groups O(1)–C(17)–C(18) and O(4)–
C(23)–C(24) is modeled as disordered over two positions with
occupancy ratios of 52:48 and 92:8, respectively. The experimental
conditions and unit cell information for compounds 1–3 and 5 are
summarized in Table 1.
While the synthesis of compounds 2 and 3 can be understood as
a ligand metathesis, the formation of 1 is unexpected. Possible
reactions leading to 1 could involve the formation of the mono eth-
oxide intermediate [(EtO)ZnN(CH2CH2NMe2)2]2 and a subsequent
ligand redistribution reaction.
Compound 1 crystallizes in space group P21/c with one mole-
cule in the asymmetric unit. The molecule (Fig. 1) has a trinuclear
Zn3N2O2 center formed by joining two Zn2NO rings through a com-
mon Zn atom. Selected bond lengths and angles are given in Ta-
ble 2. The two Zn2NO rings are slightly twisted as evidenced by
the small torsion angles of N(2)–Zn(1)–O(2)–Zn(2) (3.63(5)°) and
N(5)–Zn(2)–O(3)–Zn(3) (1.79(6)°). The central Zn(2) atom adopts
3. Results and discussion
3.1. Synthesis and characterization of compounds 1–3
Compounds 1–3 are isolated in good yields from the reactions
of {Zn[N(CH2CH2NMe2)2]2}2 with 2 equiv. of ethanol, 3-ethyl-3-
Table 1
Crystallographic data of compounds 1–3 and 5.
Chemical formula
C24H60N6O4Zn3 (1)
C30H70N6O2Zn2 (2)
C40H74N6O2Zn2 (3)
C20H57N5OSi4Zn2 (5)
Formula weight
Crystal size (mm3)
Crystal system
Space group
a (Å)
692.89
677.66
801.79
626.81
0.35 ꢂ 0.35 ꢂ 0.10
monoclinic
P21/c
9.0047(7)
15.6337(11)
24.1295(18)
90
98.2370(10)
90
3361.8(4)
4
0.15 ꢂ 0.15 ꢂ 0.15
0.30 ꢂ 0.30 ꢂ 0.10
monoclinic
P21/c
10.9912(12)
18.248(2)
11.1383(12)
90
99.131(2)
90
2205.7(4)
2
0.22 ꢂ 0.20 ꢂ 0.09
monoclinic
C2/c
17.6141(17)
9.0592(8)
21.714(2)
90
97.178(2)
90
3437.8(6)
4
triclinic
ꢀ
P1
8.8904(13)
9.3616(14)
11.3156(17)
94.612(2)
98.423(2)
94.345(2)
924.9(2)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
1
T (°C)
k (Å)
ꢀ100
ꢀ100
ꢀ100
ꢀ100
0.71073
0.71073
0.71073
0.71073
18 913
Total reflections
Unique reflections (Rint
Observed reflections
Completeness to theta
38 909
7737(0.0278)
6711
27.51°, 99.9%
0.0253, 0.0593
11 160
4217 (0.0314)
3717
27.54°, 98.7%
0.0270, 0.0728
25 695
5072 (0.0438)
4161
27.50°, 99.9%
0.0401, 0.0755
)
3931 (0.0272)
3491
27.52°, 99.6%
0.0267, 0.0622
R1 [I > 2
r
(I)], wR2 (all data)a
P
P
P
P
2
2
2
kFoj ꢀ jFck= jFoj and wR2 ¼ f ½wðFo2 ꢀ Fc2Þ ꢁ= ½wðFo2Þ ꢁg1=2, where w ¼ q=½r2ðF2oÞ þ ða ꢃ PÞ þ b ꢃ P þ d þ e ꢃ sinðhÞꢁ; P ¼ ðFo2 þ 2F2c Þ=3.
a
R1
¼

2798
B. Luo et al. / Polyhedron 29 (2010) 2795–2801
ligation to the two NMe2 groups of a tridentate N(CH2CH2NMe2)2
ligand and a terminal EtO ligand. Compounds containing a similar
trinuclear Zn3O4 structure are known, including Me2Zn3(OSiiPr3)4,
[(Me3Si)2N]2Zn3(OSiMe3)4, [(Me3Si)2N]2Zn3(OSiEt3)4, (C6F5)2Zn3(O-
CHiPr2)4 and (p-CF3C6H4)2Zn3(OCHiPr2)4 [43,51].
ꢀ
Compounds 2 and 3 crystallize in P1 and P21/c, respectively. The
structures of 2 and 3 are shown in Figs. 2 and 3, respectively. Both
molecules are dimeric with a crystallographically imposed inver-
sion center. In both structures, the Zn atoms are bridged by the
amide N atoms in the N(CH2CH2NMe2)2 ligands, one NMe2 group
in each N(CH2CH2NMe2)2 is bonded to a Zn atom forming a five-
member ring, and the alkoxy or aryloxy ligand is bonded to a Zn
atom at the terminal position. In the previously reported structures
of {Zn[N(CH2CH2NMe2)2]2}2 and [EtZnN(CH2CH2NMe2)2]2, the
bridging N(CH2CH2NMe2)2 ligands are bonded in a similar manner
as in 2 and 3 [45].
The selected bond lengths and angles are given in Tables 3 and 4
for compounds 2 and 3, respectively. The Zn–O bond lengths
(1.8625(12) Å for 2 and 1.8852(14) Å) for 3 are comparable to the
terminal Zn–O bond length in the four-coordinate Zn complex
[(2,6-F2C6H3O)2Zn(THF)]2 (1.869(4) Å) [16]. These bond lengths are
between the terminal Zn–O bond lengths in the three-coordinate
complex [(2,6-tBuC6H3O)2Zn]2 (1.831(2) and 1.839(2) Å) [18] and
those in the five-coordinate Zn complexes [(F5C6O)2Zn(THF)2]2
(1.918(3) Å) [19] and compound 1 (1.910(9) and 1.8897(16) Å).
Scheme 1.
Fig. 1. Structure of 1 showing 20% thermal ellipsoids. Only the major disordered
positions of the terminal ethoxy ligands are shown. The hydrogen atoms are
omitted for clarity.
Table 2
Selected bond lengths (Å) and angles (°) for 1.
Zn(1)–O(1)
Zn(1)–O(2)
Zn(1)–N(1)
Zn(1)–N(2)
Zn(1)–N(3)
Zn(2)–O(2)
Zn(2)–O(3)
1.910(9)
Zn(2)–N(2)
Zn(2)–N(5)
Zn(3)–O(3)
Zn(3)–O(4)
Zn(3)–N(4)
Zn(3)–N(5)
Zn(3)–N(6)
2.0386(13)
2.0302(14)
1.9975(12)
1.8897(16)
2.2685(15)
2.1249(15)
2.2906(15)
1.9958(12)
2.2601(15)
2.1382(14)
2.2709(15)
1.9649(12)
1.9684(12)
Fig. 2. Structure of 2 showing 20% thermal ellipsoids. The hydrogen atoms are
omitted for clarity.
O(1)–Zn(1)–O(2)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(2)
O(1)–Zn(1)–N(3)
O(2)–Zn(1)–N(1)
O(2)–Zn(1)–N(2)
O(2)–Zn(1)–N(3)
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(3)
N(2)–Zn(1)–N(3)
O(2)–Zn(2)–O(3)
O(2)–Zn(2)–N(2)
O(2)–Zn(2)–N(5)
O(3)–Zn(2)–N(2)
O(3)–Zn(2)–N(5)
N(2)–Zn(2)–N(5)
O(3)–Zn(3)–O(4)
114.7(4)
O(3)–Zn(3)–N(4)
O(3)–Zn(3)–N(5)
O(3)–Zn(3)–N(6)
O(4)–Zn(3)–N(4)
O(4)–Zn(3)–N(5)
O(4)–Zn(3)–N(6)
N(4)–Zn(3)–N(5)
N(4)–Zn(3)–N(6)
N(5)–Zn(3)–N(6)
Zn(1)–N(2)–Zn(2)
Zn(1)–O(2)–Zn(2)
Zn(2)–N(5)–Zn(3)
Zn(2)–O(3)–Zn(3)
Zn(1)–N(2)–C(4)
Zn(1)–N(2)–C(5)
Zn(3)–N(5)–C(12)
Zn(3)–N(5)–C(13)
103.52(5)
98.9(3)
158.6(5)
88.5(3)
85.42(5)
101.83(5)
99.74(8)
155.33(8)
87.10(7)
80.86(6)
146.60(6)
79.86(6)
89.56(5)
95.98(5)
90.06(5)
95.70(5)
109.63(5)
85.34(5)
99.88(5)
80.05(5)
142.77(5)
80.26(5)
108.98(5)
88.89(5)
126.21(6)
123.78(5)
88.78(5)
123.09(6)
117.94(9)
111.69(10)
110.64(10)
111.00(11)
110.65(11)
a distorted tetrahedral geometry with similar N(2)–Zn(2)–O(2)
(88.89(5)°) and N(5)–Zn(2)–O(3) (88.78(5)°) bond angles. Each Zn
atom on the sides of the core is five-coordinate with additional
Fig. 3. Structure of 3 showing 20% thermal ellipsoids. The hydrogen atoms are
omitted for clarity.

B. Luo et al. / Polyhedron 29 (2010) 2795–2801
2799
Table 3
CH2 NMe2)2]. No resonances of Zn[N(SiMe3)2]2, {Zn[N(CH2CH2
NMe2)2]2}2 or HNCH2CH2NMe2 are present. In the CI mass
spectrum, the most abundant Zn-containing fragments are {Zn
[N(SiMe3)2]2–Me}+, {[(Me3Si)2N]Zn[N(CH2CH2NMe2)2]–CH2NMe2}+,
{[(Me3Si)2N]Zn(NH3)3}+ and {Zn[N(SiMe3)2]}+. The detection of
Zn[N(SiMe3)2]2-related ions suggests that a ligand redistribution
reaction can occur, as depicted in Eq. (1), possibly during the evapo-
ration of 4 in the mass spectrometer. Consistent with this, the peak
intensities in the 380–388 mass region could be assigned as a com-
Selected bond lengths (Å) and angles (°) for 2.
Zn(1)–O(1)
Zn(1)–N(2)
1.8625(12)
2.0931(13)
117.16(5)
103.90(5)
134.85(5)
88.01(5)
Zn(1)–N(3)
2.1693(14)
2.0313(13)
91.99(5)
Zn(1)–N(2A)a
O(1)–Zn(1)–N(2)
O(1)–Zn(1)–N(3)
O(1)–Zn(1)–N(2A)a
Zn(1)–N(2)–Zn(1A)a
Zn(1)–N(2)–C(5)
N(2)–Zn(1)–N(2A)a
N(2)–Zn(1)–N(3)
N(3)–Zn(1)–N(2A)a
Zn(1)–N(3)–C(6)
Zn(1)–O(1)–C(9)
85.43(5)
112.61(5)
101.13(9)
131.83(10)
107.60(10)
a
Symmetry transformations used to generate equivalent atoms: ꢀx, ꢀy + 2,
bination of {Zn[N(CH2CH2NMe2)2]2}+ (m/e = 380), {[(Me3Si)2N]Zn
ꢀz + 2.
[N(CH2CH2NMe2)2]}+ (m/e = 382) and fZn½NðSiMe3Þ2ꢁ2g
(m/e =
þ
2
384). The intensities of these ions are only ca. 2% of that of the most
intense ion, SiMe2þ. Even less in intensity (ca. 0.2%) are the ions
Table 4
þ
Selected bond lengths (Å) and angles (°) for 3.
fZn½NðSiMe3Þ2ꢁ2g2 (m/e = 770) and f½ðMe3SiÞ2NꢁZn ½NðCH2CH2
þ
NMe2Þ2ꢁg2 (m/e = 768).
Zn(1)–O(1)
Zn(1)–N(2)
1.8852(14)
1.9979(16)
111.44(6)
112.42(7)
119.79(7)
93.55(6)
88.78(7)
122.34(7)
140.57(14)
Zn(1)–N(3)
2.0920(17)
2.0824(16)
86.45(6)
113.74(12)
103.60(12)
122.26(13)
113.98(13)
112.40(16)
Zn(1)–N(2A)a
O(1)–Zn(1)–N(2)
O(1)–Zn(1)–N(3)
O(1)–Zn(1)–N(2A)a
N(2)–Zn(1)–N(2A)a
N(2)–Zn(1)–N(3)
N(3)–Zn(1)–N(2A)a
Zn(1)–O(1)–C(1)
Zn(1)–N(2)–Zn(1A)a
Zn(1)–N(2)–C(16)
Zn(1)–N(2)–C(17)
Zn(1A)–N(2)–C(16)a
Zn(1A)–N(2)–C(17)a
C(16)–N(2)–C(17)
2½ðSiMe3Þ2NꢁZn½NðCH2CH2NMe2Þ2ꢁꢀZn½NðSiMe3Þ2ꢁ2
þ Zn½NðCH2CH2NMe2Þ2ꢁ2
ð1Þ
The broad melting point (49.0–62.0 °C) of the solid sample of 4
suggests it exists as a mixture, perhaps of a monomer and dimer or
as a mixture of the compounds in Eq. (1). Whatever the nature of
the solid, the solution NMR spectrum requires that 4 exists as a
pure compound or a rapidly interconverting equilibrium mixture.
When compound 4 reacts with 1 equiv. of H2O, as shown in the
second step of Scheme 2, crystalline 5 is obtained in 42% yield. The
elemental analysis is satisfactory. In the high mass region of its CI
mass spectrum, the [5ꢀOH]+ and [5ꢀN(SiMe3)2]+ ions are detected
as the major fragments. The IR spectrum of 5 exhibits a sharp OH
absorption at 3709 cmꢀ1. Variable temperature 1H NMR spectros-
copy provides valuable insight into the fluxional processes of 5
(Fig. 4). At ꢀ40 °C two resonances each for the –SiMe3 and –
NMe2 hydrogens are observed at ꢀ0.01 and ꢀ0.11 ppm and 2.29
and 2.46 ppm, respectively. This is consistent with the crystal
structure. The methylenes of the amidodiamine ligand exhibit a
complex pattern centered around 2.8 ppm. Definitive assignment
of the hydroxyl hydrogen is complicated by the presence of a sec-
ond set of resonances corresponding to an impurity (the relative
integration of the peaks attributed to the impurity ranges from
5% to 8% at different temperatures). As the temperature is raised
a
Symmetry transformations used to generate equivalent atoms: ꢀx + 1, ꢀy, ꢀz.
The bond lengths and angles of the four-membered Zn2N2 rings in 2
and 3 are close to those in {Zn[N(CH2CH2NMe2)2]2}2, [EtZnN(CH2
CH2NMe2)2]2, [RZnNMe(CH2)2NMe]2 (R = Me or Et) and {RZnN[CH2
(2-pyridyl)]2}2 (R = Me or CH(SiMe3)2) [41,45,52].
3.2. Syntheses and characterization of compounds 4 and 5
The diamide reactant in the above synthesis, {Zn[N(CH2CH2
NMe2)2]2}2, is prepared by a complete ligand exchange from [Zn(Ni-
Bu2)2]2 [45]. When Zn[N(SiMe3)2]2 is reacted with 2 equiv. of
HN(CH2CH2NMe2)2 in Et2O for 4 h at room temperature, the major
product is the partial ligand exchange compound [(Me3-
Si)2N]Zn[N(CH2CH2NMe2)2] (4). When Zn[N(SiMe3)2]2 is reacted
with 1 equiv. of HN(CH2CH2NMe2)2 (as shown in the first step of
Scheme 2), compound 4 is isolated in 71% yield. This compound
is isolated initially via recrystallization at low temperatures as a
colorless, crystalline solid. It melts at room temperature, then
slowly solidifies over a period of 24 h to form a glassy solid having
a broad melting point. We emphasize that the room temperature
1H and 13C NMR spectra of this sample exhibit well resolved peaks
showing a 1:1 molar ratio of N(CH2CH2NMe2)2 and N(SiMe3)2,
consistent with the empirical formula [(Me3Si)2N]Zn[N(CH2
Scheme 2.
Fig. 4. Variable-temperature 1H NMR spectra of 5 obtained in CDCl3.

2800
B. Luo et al. / Polyhedron 29 (2010) 2795–2801
to ꢀ20 °C, the two resonances due to the trimethylsilyl substitu-
ents coalesce due to rotation about the Zn–N bond of the –
N(SiMe3)2 ligand. At higher temperatures, both the methyl and
methylene hydrogens of the amidodiamine ligand broaden, and
by room temperature the methyls have coalesced into one broad
resonance at 2.4 ppm. One set of methylenes has collapsed almost
into the baseline while the other is clearly visible, but broadened.
The changes are consistent with reversible dissociation of the –
NMe2 arms, coupled with rotation about the CH2–NMe2 bond
and inversion at the nitrogen. Exchange of the –NMe2 ligands be-
tween the two zinc ions could also be involved as suggested in
Scheme 3.
Compound 5 crystallizes in space group C2/c with half of a mol-
ecule in the asymmetric unit and selected bond lengths and angles
are given in Table 5. The OH and the amido N atom in the
N(CH2CH2NMe2)2 bridge the two Zn atoms forming a ZnNZnO ring
(Fig. 5). A crystallographic C2 axis passes through the N atom and
the OH group. The two NMe2 groups in the N(CH2CH2NMe2)2 are
bonded to the two Zn atoms. The N(SiMe3)2 ligands are bonded
to Zn at the terminal positions. The Zn atoms and the N atoms in
N(CH2CH2NMe2)2 are four-coordinate adopting distorted tetrahe-
dral geometries. The geometry on the O atom was trigonal planar
and that of the three-coordinate N(SiMe3)2 is nearly planar with
Scheme 4.
a sum of the bond angles around the N atom being 359.3(3)°. Con-
sistent with the sharp OH absorption in IR, no hydrogen bonding is
found for OH. The bond angles in the ZnNZnO ring, e.g. Zn(1)–N(2)–
Zn(1A) (90.02(8)°), Zn(1)–O(1)–Zn(1A) (95.33(7)°) and O(1)–
Zn(1)–N(2) (87.33(5)°), are very close to the corresponding bond
angles in the ZnNZnO rings in compound 1.
A number of hydroxyl Zn compounds have been structurally
characterized, most of which are the synthetic analogs of Zn en-
zymes [53,54]. Other known structures include dimers [(Me2Ph-
Si)3CZn(OH)]2 [55] and [(NHC)Zn(OH)(OC6H2-2,4,6-Me3)]2 (NHC =
1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) [56], a cyclic
trimer {[g
2-H2B(3-tert-butylpyrazolyl)2]Zn(OH)}3 [57] and a cub-
ane, [(2,4,6-(CF3)3C6H2)Zn(OH)]4 [58]. Recently, Jaime et al. re-
ported a compound with a structure similar to 5, [(SiMe3)2CH]2
Zn2(OH){N[CH2(2-pyridyl)]2} (7) [52]. This compound was ob-
tained as a minor product from the hydrolysis of the alkyl Zn amide
(6) as illustrated in Scheme 4. In compound 7, the tridentate
bis(pyridyl)amido ligand and the hydroxyl ligand are bonded to
the Zn atoms in the same manner as in compound 5. Perhaps be-
cause of the rigidity of the pyridyl group, the ZnNZnO ring in 7 is
nonplanar as evidenced by a large N–Zn–O–Zn torsion angle
(13.28(7)°). The bond angles in the Zn2NO ring of 7, Zn–N–Zn
(87.90(7)°), Zn–O–Zn (91.77(7)°) and N–Zn–O (88.75(7)° and
88.58(7)°), are somewhat different from those in compound 5.
Density functional theory (DFT) calculations conducted by
Jaime et al. on the reaction between H2O and the methyl Zn analog
of compound 6 were consistent with their experimental results
[52]. It was found that cleavage of the amido ligand by H2O was
preferred over cleavage of the alkyl ligand. The computations sug-
gest that the lowest energy reaction path involves initial activation
of H2O by the uncomplexed pyridine. It is reasonable to expect in
our experiments the conversion of 4 to 5 occurs by a similar path.
One might speculate that the more basic NMe2 substituent in 4
should facilitate the reaction with H2O, leading to the better yield
of compound 5.
Scheme 3.
Table 5
Selected bond lengths (Å) and angles (°) for 5.
Zn(1)–O(1)
Zn(1)–N(1)
1.9746(11)
2.1722(16)
102.72(4)
87.33(5)
85.07(5)
114.37(6)
142.27(5)
116.76(5)
95.33(7)
Zn(1)–N(3)
Zn(1)–N(2)
1.9255(14)
2.0639(14)
90.02(8)
105.42(9)
122.47(8)
110.8(2)
114.42(7)
120.96(8)
123.90(8)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(3)
N(2)–Zn(1)–N(3)
O(1)–Zn(1)–N(3)
Zn(1)–O(1)–Zn(1A)a
Zn(1)–N(2)–Zn(1A)a
Zn(1)–N(2)–C(4)
Zn(1)–N(2)–C(4A)a
C(4)–N(2)–C(4A)a
Zn(1)–N(3)–Si(1)
Zn(1)–N(3)–Si(2)
Si(1)–N(3)–Si(2)
a
Symmetry transformations used to generate equivalent atoms: ꢀx + 1, y, ꢀz + 1/2.
4. Conclusions
The synthesis and structures of several alkoxo, aryloxo and hy-
droxo Zn complexes stabilized with the amidodiamine ligand
N(CH2CH2NMe2)2 are reported. In the reactions of {Zn[N(CH2CH2
NMe2)2]2}2 with alcohols in a 1:1 Zn to alcohol ratio, a trinuclear
compound, 1, is obtained from the less bulky EtOH. When using
the bulky alcohols Et3COH and 2,6-iPr2C6H3OH, stoichiometric
ligand substitution takes place forming dimeric compounds 2
and 3. In the reactions of Zn[N(SiMe3)2]2 with HN(CH2CH2NMe2)2
either in a 1:1 or 1: 2 molar ratio, only the mono-substituted prod-
uct [(Me3Si)2N]Zn[N(CH2CH2NMe2)2] (4) is isolated. When com-
pound 4 is reacted with H2O, the cleavage of the amidodiamine
Fig. 5. Structure of 5 showing 20% thermal ellipsoids. The hydrogen atoms are
omitted for clarity.

B. Luo et al. / Polyhedron 29 (2010) 2795–2801
2801
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CCDC 763490, 763491, 763492 and 763493 contain the supple-
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data can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online version,
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