Zinc complexes of chiral ligands obtained from methylbenzylamine

Article abstract of DOI:10.1016/j.inoche.2011.07.018

Condensation of S-methylbenzylamine with 2 equiv. of 2,4-tert-butylphenol yielded the chiral tridentate ligand 2H₂, which formed the dimetallic complex (2)(k-N,(μ-O)₂ZnEt)((μ-O)₂ZnEt), 3, upon reaction with ZnEt₂

Full text of DOI:10.1016/j.inoche.2011.07.018

Inorganic Chemistry Communications 14 (2011) 1737–1741
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Inorganic Chemistry Communications
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Zinc complexes of chiral ligands obtained from methylbenzylamine
⁎
María Frutos Pastor, Todd J.J. Whitehorne, Paul O. Oguadinma, Frank Schaper
Département chimie, Université de Montréal, Montréal, Québec, Canada H3C 3J7
a r t i c l e i n f o
a b s t r a c t
Article history:
Condensation of S-methylbenzylamine with 2 equiv. of 2,4-tert-butylphenol yielded the chiral tridentate
ligand 2H2, which formed the dimetallic complex (2)(k-N,(μ-O)2ZnEt)((μ-O)2ZnEt), 3, upon reaction with
ZnEt2. Reaction of the chiral Schiff base ligand, 4H, obtained from condensation of salicylaldehyde and S-
methylbenzylamine, with ZnEt2 yielded (4)2Zn, 5, or (4)ZnEt, 6, respectively. Deprotonation of 4H with NaH
afforded tetrameric {(4)Na}4, 7. Complexes 3, 5 and 7 were characterized by single crystal diffraction studies
and tested as initiators in the polymerization of rac-lactide. Complexes 3 and 5 showed only low to moderate
activity. All complexes yielded essentially atactic polymers with minor contents of heterotactic enchainment.
© 2011 Elsevier B.V. All rights reserved.
Received 29 April 2011
Accepted 26 July 2011
Available online 2 August 2011
Keywords:
Schiff base ligand
Zinc complexes
Chiral ligands
Lactide polymerization
While the utility of chiral ligands in asymmetric catalysis is undoubted,
enantiopure ligands often require elaborate synthesis and/or are highly
expensive. In recent years, we and others became interested in the
selective polymerization of rac-lactide [1–7]. Given the potential
applications of polylactide (PLA) for disposable packaging, low costs of
the catalyst are a prerequisite for potential applications. We thus
investigated the performance of enantiopure complexes with ligands
based on methyl-benzylamine, one of the cheapest sources of chirality
available, in rac-lactide polymerization. Harder and our group reported
the synthesis of a diketimine ligand with N,N’-S-methylbenzylamine
substituents [8,9]. Rac-lactide polymerizations catalyzed by the corre-
sponding Zn alkoxide complex 1 (Scheme 1), however, yielded
heterotactic PLA due to the prevalence of chain-end control in
diketiminate zinc alkoxide complexes [6]. In the following we present
the preparation of several metal complexes bearing simple, chiralN,N,O-
and N,O-ligands, based onS-methylbenzylamine. Unfortunately, noneof
the obtained complexes displayed any selectivity when applied in rac-
lactide polymerization.
(N,O,O)-ligand. The tridentate ligand 2H2 was obtained by conden-
sation of 2,4-ditertbutylphenol, S-methylbenzylamine and formalde-
hyde, in adaption of literature procedures (Scheme 2) [10,11]. Similar
compounds with different chiral N-substituents have been reported
previously and employed as ligands for Zr [12] and V complexes [13].
2H2 was obtained as a yellow oil, in good yields and reasonable purity
(one spot TLC, N90% estimated from NMR), and proved to be soluble in
most organic solvents (hexane, toluene, methanol, ethanol, diethyl
ether, dichloromethane etc.). The molecular formula was confirmed
by HR–MS, but we were unable to remove the remaining impurities
by column chromatography (SiO2, Al2O3), recrystallization or adap-
tion of the reaction conditions. While the obtained purity was
sufficient for subsequent reaction, no analytically pure sample could
be obtained (ΔC≈1%).
Silvernail et al. obtained related bis(phenolato)amine complexes
LZn (lacking a chiral N-substituent) as dimers {LZn}2 by reaction of
LH2 with one equivalent of Zn{N(SiMe3)2}2 [14]. Identical reactions
with 2H2, however, gave only unresolved product mixtures. Reaction
of 2H2 with ZnEt2 yielded the bimetallic zinc complex 2(ZnEt)2, 3
(Scheme 2). While the four NCH2 protons in the free ligand 2H2
appeared as two doublets due to the fast inversion of the nitrogen
center, coordination to zinc prevents this inversion in 3 and the NCH2
protons split consequently into four doublets. Complex 3 did not
undergo further protonation reactions with alcohols.
In the crystal structure of 3 (Fig. 1, Table 1), one zinc atom is found
in a tetrahedral environment, coordinated by two phenolates, an ethyl
group and the bridging amine. The second zinc ethyl group is likewise
coordinated to the two bridging phenolates and thus adopts a
trigonal–planar coordination geometry with Σ X−Zn1/3−X=360°,
despite the reduced O―Zn1/3―O bite angle of 85°, and without
apparent intermolecular interactions. Zn―O, but not Zn―C bond
lengths are shorter by 0.08(1) Å for trigonal–planar Zn1/3 than for
tetrahedral Zn2/4, which can be attributed to the increased Lewis
acidity of the three-coordinated Zn center and the involvement of p–p
donation from oxygen. Zn2/4―O and Zn2/4―N bond lengths in 3 are
slightly longer (0.05 and 0.14 Å, respectively) than the corresponding
bond lengths in {LZn}2 dimers obtained by Silvernail et al. [14],
indicating a slightly more strained structure for 3, but are well at the
longer end of the range generally observed in tetrahedral zinc
complexes (Zn―OAr: 1.99(4) Å, n=61; Zn—NR3: 2.04(7) Å,
n=221) [15].
Bimetallic 3 was obtained even in the presence of excess 2H2 and
under variation of reaction conditions (solvent, order of reagent addition,
etc.). A reduced lability of the second Zn ethyl group towards protonation
⁎
Corresponding author.
E-mail address: Frank.Schaper@umontreal.ca (F. Schaper).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.07.018

1738
M.F. Pastor et al. / Inorganic Chemistry Communications 14 (2011) 1737–1741
Table 1
Bond distances [Å] and angles [°] in the X-ray structure of complex 3.
Zn2/4―Na
2.191(5); 2.188(5)
1.933(4)–1.987(4)
2.037(4)–2.062(4)
1.944(7); 1.953(7)
1.962(6); 1.953(6)
84.9(2); 84.6(2)
80.4(2); 81.1(2)
89.3(2)–90.0(2)
Zn1/3―Ob
Zn2/4―Oa
Zn1/3―C51/151b
Zn2/4―C41/141a
O―Zn1/3―Ob
O―Zn2/4―Oa
N―Zn2/4―Oa
Scheme 1. Lactide polymerization with 1.
a
Tetrahedral zinc center: Zn2, Zn3.
Trigonal–planar zinc center: Zn1, Zn4.
b
favors the heteroleptic complex 6. Upon addition of alcohol, ZnEt2 is
removed from the equilibrium in the form of Zn(OiPr)Et and 6 is
transformed into 5. NMR-scale experiments showed complete conver-
sion of equimolar mixtures of 5 and ZnEt2 into the heteroleptic complex
6 in 30 min, demonstrating the accessibility of the proposed pre-
equilibrium.
Complex 5 was further characterized by an X-ray diffraction(Table 2,
Fig. 3). The asymmetric unit contains two independent molecules of
essentially identical geometry. The coordination geometry around the
Zn centers is distorted tetrahedral due to the reduced N―Zn―O bite
angle (95–97°). Both independent molecules adopt a Δ-configuration.
The same relative configuration was observed in a previous room-
temperature X-ray diffraction study of the Λ,R,R-enantiomer of 5 [21].
The stereoselectivity of bis(N-1-phenylethylsalicylideneiminato) zinc
complexes to adopt a Λ,R,R or a Δ,S,S configuration [20–22] was
previously attributed to a steric preference of the methyl group to
occupy an axial position (predicted from NMR data) [20]. However,
none of the crystal structures displays the methyl group in this position
(although the situation might be different in solution). Based on X-ray
data, attractive hydrogen bonding between the methyl group and oxygen
and CH–π interactions (i.e. C15―O1 and C9H―(C25–C27) in Fig. 3) have
been offered as explanation for the observed stereoselectivity [21]. The
hydrogen bonding is, however, rather weak (d(C―O)=3.4 Å) and there
is no indication that comparable interactions would be absent in the Δ,S,S
diastereomer. Furthermore, crystal structures of compounds similar to 5,
but carrying additional nitro, dichloro or methoxy substituents on the
phenol [22,23], might not show any hydrogen bonding (d(C―O)N4 Å),
but conserve the selectivity for Λ,R,R configurations. These structures
display to varying degrees π-stacking interactions between phenol and
the phenyl substituent (interplanar distances of 3.3–3.5 Å), which are
sterically only possible in the Λ,R,R or Δ,S,S configuration. We propose
that these interactions, albeit absent in the solid state for 5, are at least
partially responsible for the observed stereoselectivity. It should be noted
that π-stacking between phenol and phenyl also places the methyl group
in the axial position, predicted from NMR data for these compounds [20].
Scheme 2. Synthesis of complex 3.
by alcohols has been noted before by us and others [6,16–18], but it was
nevertheless unexpected for a bidentate diphenolate ligand. Some
rational for the preferred formation of a dinuclear zinc complex can be
obtained from the crystal structure of 3: it seems likely that the putative
intermediate of the reaction between 2H2 and ZnEt2, (2H)ZnEt, would
adopt a structure comparable to 3, in which the three-coordinated ZnEt
fragment is replaced by hydrogen (Fig. 2). Protonation of the second
ethyl group would thus be hindered by the stable tetrahedral
coordination geometry of the zinc center and the hydrogen bonding
between O1 and O2, which places the hydrogen pointing away from the
ethyl group and might explain its low reactivity towards protonation.
(N,O)-ligand. The bidentate ligand 4H was obtained following
reported procedures [19]. Reaction of 4H with Zn{N(SiMe3)2}2 afforded
the homoleptic complex (4)2Zn, 5 [20–22], independent from reaction
conditions and in the presence of excess Zn{N(SiMe3)2}2 (Scheme 3).
Reaction of 4H with ZnEt2 was more controlled and yielded the
heteroleptic complex (4)ZnEt, 6 (Scheme 3). Attempts to react the
second Zn ethyl group with isopropanol or benzyl alcohol yielded,
however, again the homoleptic complex 5. Formation of 5 most likely
proceeds by way of a pre-equilibrium between 6, 5 and ZnEt2, which
Fig. 1. X-ray structure of 3. Hydrogen atoms, minor part of disordered atom C52 and the
second independent molecule are omitted for clarity. Thermal ellipsoids are drawn at
the 50% probability level.
Fig. 2. Potential structure of intermediate (2H)ZnEt. O1―H2A=2.5 Å.

M.F. Pastor et al. / Inorganic Chemistry Communications 14 (2011) 1737–1741
1739
Scheme 3. Synthesis of 5 and 6.
For the sake of comparison, a more ionic compound, the sodium salt
(4)Na, 7, was prepared in slight variation from reported procedures by a
simple reaction of 4H with NaH [24]. Complex 7 crystallizes as a cubic
tetramer (Fig. 4, Table 2), essentially isostructural to the structure of the
diethyl ether adduct of its R,R,R,R-enantiomer [24]. While sodium was
described as four-coordinated in the reported diethyl ether adduct, in 7
short Na―CPh distances of 2.8 to 3.0 Å are found to the meta position of
the phenylethyl substituent. These are notably smaller than the sum of
the vdW radii of Na and C (4.0 Å) and in the normal range observed for
Na–π interactions. Coordination geometry around Na1, Na2 and Na4 is
thus best described as distorted square–pyramidal, with the O, N and C
atom of the same ligand in the equatorial plane. The absence of a sixth
ligand leads to an increase of the X―Na―O angles to the apical oxygen
atom (N: 109–134°, C: 109–129°). For Na3, short intermolecular
distances to a second phenyl ring (d(Na3―C14a/C15a)=3.7 Å) com-
plete an octahedral coordination and C/N―Na3―O angles closer to ideal
geometry (89° and 96°, respectively) are observed.
Lactide polymerization. Complexes 3, 5 and 7 were tested for
potential enantioselectivity in rac-lactide polymerization (Table 3).
Complex 3 proved inactive in initiating lactide polymerizations in
CDCl3 at ambient temperature, but prolonged reaction times at 50 °C
led to essentially complete conversion. Low rates of insertion into Zn
ethyl groups have been observed before [25] and, given the low rate of
polymerization, neither insertion in Zn―OAr nor activation of 3 by
trace impurities can be excluded. The polymer microstructure showed
a slight, but notable bias for heterotacticity, typically observed for
tetrahedral zinc complexes due to a chain-end control mechanism.
The value is higher than that observed for Zn(OiPr)2, which yields
atactic PLA (Pr =0.50) [26]. While this indicates that the ligand
remains coordinated to Zn in the active species, its function seems to
be limited to providing moderate steric bulk without any chiral
induction from the methylbenzyl substituent.
Fig. 3. X-ray structure of Δ,S,S-5. Hydrogen atoms and the second independent
molecule are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability
level.
steric saturation of the zinc center, which prevents insertion into the
Zn―OAr group. The sodium salt 7, on the other hand, effectively
initiated lactide polymerization in CDCl3 at ambient temperature,
leading to 85% monomer conversion in 2 h. Not surprisingly, the use of
an enantiopure initiator, which might not remain bound to the
sodium counter cation, did not affect the polymer microstructure and
essentially atactic PLA was obtained.
In summary, incorporation of enantiopure S-methylbenzylamine is
a very economic way to enantiopure metal complexes containing a
chiral center. Asymmetric induction from the chiral center, however,
was not observed in rac-lactide polymerizations, which might be
related to the small steric differences between methyl and phenyl
close to the metal center and/or to the high degree of flexibility
provided by rotation around the N-C single bond.
Experimental section. All reactions, except ligand synthesis, were
carried out under nitrogen atmosphere using Schlenk or glove box
techniques. Solvents were dried by passage through activated aluminum
oxide (MBraun SPS) and de-oxygenated by repeated extraction with
nitrogen. C6D6 was distilled from Na and de-oxygenated by three freeze–
pump–thaw cycles. CDCl3 was dried over activated molecular sieves. All
other chemicals were obtained from commercial suppliers and used as
Bischelate complex 5 proved to be inactive towards lactide
polymerization even at 50 °C. Under forcing conditions (molten
monomer, 180 °C), polymerization was achieved in 30 min, but we
cannot exclude that catalyst decomposition precedes initiation under
these conditions. The obtained polymer was atactic, with a negligible
heterotactic bias. This lack of reactivity seems to be related to the
Table 2
Bond distances [Å] and angles [°] in the X-ray structures of complexes 5 and 7.
5 (M=Zn)
7 (M=Na)
M―N
M―O
M―O
2.012(2)–2.020(2)
1.926(2)–1.948(2)
2.399(1)–2.459(1)
2.259(1)–2.293(1)
2.306(1)–2.441(2)
75.93(4)–78.81(4)
96.56(4)–164.60(5)
a
N―M―Ob
N―M―Oc
N―M―N
O―M―O
94.91(9)–97.41(9)
110.85(8)–113.69(7)
126.62(7); 124.80(9)
111.16(7); 118.71(10)
83.10(4)–97.46(4)
a
7: Oxygen is part of the six-membered metallacycle, e.g. Na3, N3, C49–C51, O3.
Ligand bite angles, e.g. 5: O1―Zn1―N1; 7: N3―Na3―O3.
Angles between N and O atoms of different ligands.
b
c
Fig. 4. X-ray structure of 7. Hydrogen atoms are omitted for clarity. Thermal ellipsoids
are drawn at the 50% probability level. Atoms C10a–C15a are generated by x−1, y, z.

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M.F. Pastor et al. / Inorganic Chemistry Communications 14 (2011) 1737–1741
Table 3
(50 mL) are heated to reflux for 6 h. The reaction mixture is filtered
Rac-lactide polymerization results.
and the solvent removed to yield a yellow oil, which is washed with
cold methanol and dried under vacuum to yield 1.8 g (90%) of 4H.
1H-RMN (C6D6, 400 MHz): δ 13.76 (s, 1H, OH), 7.82 (s, 1H,
N=CH), 7.22–7.06 (m, 7H, Ph), 6.89 (dd, J=2 Hz, J=8 Hz, 1H, m-Ph),
6.70 (td, J=7 Hz, J=1 Hz, 1H, p-Ph), 4.04 (q, J=7 Hz, 1H, CH(CH3)
Ph), 1.32 (d, J=7 Hz, 3H, CH(CH3)Ph). C-RMN (C6D6, 101 MHz): δ
169.39 (N=CH), 161.02 (Ph), 143.77 (Ph), 132.24 (Ph), 131.34 (Ph),
128.63 (Ph), 127.22 (Ph), 126.35 (Ph), 118.79 (Ph), 118.58 (Ph),
116.93 (Ph), 68.41 (CH(CH3)Ph), 24.93 (CH(CH3)Ph). Anal. calcd. for
a
Initiator
[Lactide]/initiator
T
Time
Conversion
Pr
3
3
5
5
5
7
200:1
100:1
100:1
100:1
100:1
200:1
23 °C
50 °C
23 °C
50 °C
180 °Cb
23 °C
2 h
20 h
2 h
24 h
0.5 h
2 h
–
–
91%
–
0.59
–
–
–
95%
85%
0.52
0.56
Conditions: CDCl3, [lactide]/[initiator]=100:1, [initiator]=5–7·10−6 M.
a
Pr is the probability for alternating monomer insertion, determined from decoupled 1
H
C15H15NO: C, 79.97; H, 6.71; N, 6.22. Found: C, 80.05; H, 6.85; N, 6.18.
NMR: Pr=2·I1/(I1+I2), with I1=5.20–5.25 ppm (rmr, mmr/rmm), I2=5.13–5.20 ppm
(mmr/rmm, mmm, mrm) [25].
(4)2Zn, 5. a) A solution of 4H (100 mg, 0.44 mmol) in toluene
b
No solvent.
(6 mL) was added to Zn{N(SiMe3)2}2 (171 mg, 0.44 mmol). After 5 h
stirring at ambient temperature, the solution is concentrated to 1/3 of
its volume and the product precipitated by addition of hexanes (4 mL).
Decantation of the solvent, washing with hexane and drying yielded
107 mg (95%) of 5 as a slightly yellow powder, which could be further
purified by recrystallization from toluene/hexane.
b) To a solution of ZnEt2 (100 mg, 1.1 mmol) in diethyl ether was
added a solution of 4H (500 mg, 2.2 mmol) in diethyl ether. After 20 h
stirring at ambient temperature, the solvent was decanted from the
formed precipitate, which was washed with hexane and recrystallized
from toluene/hexane (208 mg, 37%).
received. Elemental analyses were performed by the Laboratoire
d'Analyse Élémentaire (Université de Montréal). NMR spectra were
recorded on a Bruker DRX 400 MHz spectrometer and referenced to
residual solvent (C6D6, 1H: δ 7.15, 13C: δ 128.02; CDCl3, 1H: δ 7.26, 13C: δ
77.0).
2,2'-({[(1S)-1-phenylethyl]imino}dimethanediyl)bis(2,4-di-
tert-butylphenol), 2H2. A mixture of 2,4-di-tert-butylphenol (10.0 g,
49 mmol), formaldehyde (3.7 mL, 37% in water, 49 mmol) and S-1-
phenyethylamine (2.9 g, 24 mmol) in water (30 mL) was heated to
reflux for 18 h. After cooling to room temperature, two phases formed.
The crude reaction mixture was extracted twice with hexane. The
combined organic phases were washed with water, dried over Na2SO4
and evaporated, to yield a light-yellow sticky solid in ca. 90% purity
(13.1 g, 97%).
1H NMR (C6D6,400 MHz): 7.52 (s, 2H, N=CH), 7.26–6.74 (m, 4H,
Ph), 6.91 (d, J=7 Hz, 2 H, Ph), 6.85 (t, J=7 Hz, 4H, Ph), 6.81 (d,
J=7 Hz, 2H, Ph), 6.74 (d, J=7 Hz, 4H, Ph), 6.57 (t, J=7 Hz, 2 H, Ph),
3.81 (q, J=7 Hz, 2H, CH(CH3)Ph), 1.28 (d, J=6 Hz, 6H, CH(CH3)Ph).
13C NMR (C6D6, 101 MHz): δ 171.7 (N=CH), 169.0 (Ph), 140.7 (Ph),
136.2 (Ph), 135.3 (Ph), 129.3 (Ph), 128.7 (Ph), 125.7 (Ph), 124.0 (Ph),
118.9 (Ph), 114.2 (Ph), 69.4 (CH(CH3)Ph), 22.0 (CH(CH3)Ph). Anal.
calcd. for C30H30O2N2: C, 69.84; H, 5.86; N, 5.43. Found: C, 69.90; H,
5.77; N, 5.25.
(4)ZnEt, 6. To a solution of ZnEt2 (57 mg, 0.47 mmol) in toluene
(1 mL) was added a solution of 4H (100 mg, 0.41 mmol) in toluene
(1 mL). After stirring for 5 h at ambient temperature, the solution is
concentrated under vacuum. The slightly yellow precipitate formed is
washed with hexane to yield a colorless powder (94 mg, 71%).
1H-RMN (C6D6, 400 MHz): δ 7.71 (s, 1H, N=CH), 7.28 (d, J=8 Hz,
2H, Ph), 7.19–7.10 (m, 4H, Ph), 7.05 (t, J=7 Hz, 1H, Ph), 6.73 (dd,
J=2 Hz, J=10 Hz, 1H, Ph), 6.58 (td, J=10 Hz, J=2 Hz, 1H, Ph), 4.28
(q, J=7 Hz, 1H, CH(CH3)Ph ), 1.68 (d, J=7 Hz, 3H, CH(CH3)Ph), 1.24 (t,
J=8 Hz, 3 H, ZnCH2CH3), 0.28 (q, J=8 Hz, 2 H, ZnCH2CH3). 13C-RMN
(C6D6,101 MHz): δ 168.95 (N=CH), 167.27 (Ph), 141.97 (Ph), 135.56
(Ph), 134.29 (Ph), 128.63 (Ph), 127.63 (Ph), 127.31 (Ph), 122.68 (Ph),
121.07 (Ph), 116.93 (Ph), 68.34 (CH(CH3)Ph), 22.40 (CH(CH3)Ph), 12.79
(ZnCH2CH3), −0.61 (ZnCH2CH3). Anal. calcd. for C17H19NOZn: C, 64.06,
H, 6.01, N, 4.39. Found: C, 63.90, H, 6.15, N, 4.44.
1H-RMN (CDCl3, 300 MHz): 7.42–7.26 (m, 5H, Ph), 7.20 (d,
J=2 Hz, 2H, Ph), 6.91 (d, J=2 Hz, 2H, Ph), 4.12 (q, J=7 Hz, 1H, CH
(CH3)Ph), 3.63 (bs, 4H, CH2N), 1.52 (d, J=7 Hz, 3H, CH(CH3)Ph), 1.42
(s, 18 H, tBu), 1.25 (s, 18 H, tBu). 1H-RMN (C6D6, 300 MHz): 7.54 (bs,
2H, Ph), 7.47 (d, J=2 Hz, 2H, Ph), 7.28–7.10 (m, 3H, Ph), 6.93 (d,
J=2 Hz, 2H, Ph), 4.06 (q, J=7 Hz, 1H, CH(CH3)Ph), 3.55 (d, J=14 Hz,
2H, CH2N), 3.33 (d, J=14 Hz, 2H, CH2N), 1.61 (s, 18 H, tBu), 1.33 (s, 18
H, tBu), 1.10 (d, J=7 Hz, 3H, CH(CH3)Ph). 13C-RMN (CDCl3, 75 MHz):
δ 152.3 (Ph), 141.4 (Ph), 140.0 (Ph), 135.9 (Ph), 128.6 (Ph), 128.4
(Ph), 127.8 (Ph), 127.4 (Ph), 125.1 (Ph), 123.5 (Ph), 121.5 (Ph), 56.2
(CH2), 52.1 (CH2), 34.9 (C(CH3)3), 34.1 (C(CH3)3), 31.6 (C(CH3)3),
29.6 (C(CH3)3), 11.3 (CH(CH3)Ph), 1.03 (CH(CH3)Ph). HR–MS: calcd.
for C38H56NO2 (MH+): 558.4306. Found: 558.4304.
(2)(ZnEt)2, 3. To a solution of ZnEt2 (22 mg, 0.18 mmol) in hexane
(1 mL) were added a solution of 2H2 (0.10 g, 0.18 mmol) in hexane
(3 mL). After 3 h of stirring, the solvent is removed by decantation
and the remaining solid washed with hexane. Recrystallization
from a toluene/hexane mixture yielded 51 mg (77%) of colorless
crystals.
(4)Na, 7. To a suspension of NaH (0.02 g, 0.9 mmol) in toluene, a
solution of 4H (0.2 g, 0.9 mmol) in toluene was added. After 4 h of
stirring at ambient temperature, the solution was filtered and the
solvent removed by evaporation. Recrystallization from toluene/hexane
yielded 170 mg (78%) of 7.
1H NMR (C6D6, 300 MHz): 7.56 (d, J=3 Hz, 1H, Ph), 7.50 (d,
J=2 Hz, 1H, Ph), 7.30 (d, J=7 Hz, 2H, Ph), 7.20–7.11 (m, 3H, Ph), 6.96
(d, J=2 Hz, 1H, Ph), 6.95 (d, J=2 Hz, 1H, Ph), 4.05 (q, J=7 Hz, 1H, CH
(Me)Ph), 4.08 (d, J=15 Hz, 1H, NCH2), 3.85 (d, J=15 Hz, 1H, NCH2),
3.84 (d, J=15 Hz, 1H, NCH2), 3.53 (d, J=15 Hz, 1H, NCH2), 1.66 (s, 9
H, tBu), 1.64 (s, 9 H, tBu), 1.43 (t, J=8 Hz, 3 H, ZnCH2CH3), 1.39 (d,
J=7 Hz, 3H, CH(Me)Ph), 1.35 (s, 9 H, tBu), 1.33 (s, 9 H, tBu), 1.07 (t,
J=8 Hz, 3 H), 0.58 (q, J=8 Hz , 2H, ZnCH2), 0.57 (q, J=8 Hz, 2H,
ZnCH2). 13C NMR (C6D6, 75 MHz): δ 159.6 (Ph), 158.7 (Ph), 130.6
(Ph), 128.6 (Ph), 126.5 (Ph), 125.3 (Ph), 125.1 (Ph), 124.5 (Ph), 64.7
(CH(CH3)Ph), 62.5 (NCH2), 58.7 (NCH2), 35.8 (C(CH3)3), 35.7, (C
(CH3)3), 34.4 (C(CH3)3), 34.3 (C(CH3)3), 32.0 (C(CH3)3), 30.8 (C
(CH3)3), 21.3 (CH(CH3)Ph), 12.9 (ZnCH2CH3), 11.6 (ZnCH2CH3), 0.92
(ZnCH2CH3), 0.25 (ZnCH2CH3). Anal. calcd. for C42H63NO2Zn2: C,
67.73; H, 8.53; N, 1.88. Found: C, 68.08; H, 8.12; N, 1.84.
1H NMR (C6D6, 400 MHz): δ 7.89 (s, 1 H, N=CH), 7.24 (td, J=8 Hz,
J=2 Hz, 1H, Ph), 7.18–7.12 (m, 4 Hz, Ph), 6.86 (dd, J=2 Hz, J=7 Hz, 2
H, Ph), 6.70 (t, J=7 Hz, 1H, Ph), 5.73 (d, J=8 Hz, 1H, Ph), 3.78 (q,
J=7 Hz, 1H, CH(CH3)Ph ), 1.12 (d, J=7 Hz, 3H, CH(CH3)Ph). 13C-RMN
(C6D6, 101 MHz): δ 171.2 (N=CH), 165.9 (Ph), 144.9 (Ph), 137.0 (Ph),
132.7 (Ph), 129.7 (Ph), 127.5 (Ph), 126.5 (Ph), 123.5 (Ph), 123.0 (Ph),
112.4 (Ph), 69.9 (CH(CH3)Ph), 22.7 (CH(CH3)Ph). Anal. calcd. for
C15H14NONa: C, 72.86; H, 5.71; N, 5.66. Found: C, 72.52; H, 5.67; N,
5.62.
X-ray diffraction studies. Data sets for 5 and 7 were recorded on a
Bruker SMART 6000 diffractometer with Helios optics, equipped with a
rotating anode source for Cu Kα radiation (λ=1.54178 Å). Data for 3
was collected on a Bruker Smart APEX2 with graphite monochromatized
Mo Kα radiation (λ=0.71073 Å). Cell refinement and data reduction
Ligand 4H. Following a previous procedure [19], a mixture of
salicylaldehyde (1.0 g, 8.3 mmol), S-1-phenylethylamine (1.0 g,
8.3 mmol) and Na2SO4 (4 g) as a drying agent in dry methanol

M.F. Pastor et al. / Inorganic Chemistry Communications 14 (2011) 1737–1741
1741
Table 4
Appendix A. Supplementary data
Details of X-ray structures studies.
Supplementary data to this article can be found online at doi:10.
1016/j.inoche.2011.07.018.
3
5
7
Formula
C
42H63NO2Zn2
C30H28N2O2Zn
C60H56N4O4Na4
Mw (g/mol); dcalcd. (g/cm3)
T (K); F(000)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
744.67; 1.238
200; 796
Triclinic
513.91; 1.315
150; 2144
Orthorhombic
P212121
989.05; 1.245
150; 2080
Orthorhombic
P212121
10.0993(2)
21.9355(5)
23.8247(5)
90
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P1
10.5215(7)
11.4562(8)
16.8967(11)
88.579(1)
89.501(1)
78.849(1)
1997.6(2); 2
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9.890(1)
17.737(2)
29.588(3)
90
90
90
5190.1(10); 8
2.9–72.0; 1.0
67349; 0.027
10084; 0.038
1.535
0.031; 0.080
0.034; 0.081
1.04; 0.00(2)
0.33; −0.27
90
90
γ (°)
V (Å3); Z
5278.0(2); 4
2.7–72.3; 0.99
68375; 0.019
10358; 0.033
0.902
0.030; 0.082
0.032;0.083
1.02; 0.00(3)
0.14; −0.21
θ range (°); completeness
Collected refl.; Rsigma
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μ (mm−1
)
IN2σ(I): R1(F); wR(F2)
All data: R1(F); wR(F2)
GoF(F2); flack
0.047; 0.103
0.066; 0.110
0.93; 0.00(3)
0.45; −0.27
Res. elec. dens.
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Acknowledgments
We like to thank Elena Nadezhina and Francine Bélanger for assistance
with the combustion analyses, and Alexandra Furtos and Marie-Christine
Tang for assistance with mass spectroscopy. Funding was provided by the
Natural Sciences and Engineering Research Council of Canada (NSERC)
and the Centre in Green Chemistry and Catalysis (CCVC/CCGC).