Synthesis and characterisation of trigonal C2-chiral di- and tetra-substituted bis(oxazoline) alkyl zinc complexes and their reactivity towards protic reagents

Article abstract of DOI:10.1039/c0dt01252a

A series of zinc(ii) alkyl complexes stabilised by the C₂-chiral bis(oxazoline) ligand (R₁,R₂BOX, with R₁ = (4S)-tBu, R₂ = H (a); R₁ = (4S)-Ph, R₂ = H (b); R₁ = (4R)-Ph, R₂ = (5S)-Ph (c)), has been synthesised and structurally characterised. (R₁,R₂BOX)H ligands react with ZnEt₂ in toluene to give the heteroleptic three-coordinate compounds of (R₁,R₂BOX)ZnEt, 1a, 1b and 1c in high yield. However, when the addition of (BOX)H ligands (a-b) over ZnEt₂ is "uncontrolled", the formation of homoleptic four-coordinate compounds are favoured (2a-b), but not for the more sterically crowded ligand (c). The zinc-ethyl derivatives (1a-c) react readily with protic reagents such as acetic acid (HOAc) and methanol (MeOH). For compounds 1a-c a redistribution of ligands is observed leading preferentially to homoleptic compounds, except for the bulkier ligand c providing a three-coordinate complex identified as ( ^Ph,PhBOX)Zn(OMe), 4c. The reaction of acetylacetone (acacH) with compounds 1a-c leads straightforwardly to the more stable four-coordinate compounds corresponding to (R₁,R₂BOX)Zn(η²- acac), 5a-c. The potential of these compounds as initiators for the copolymerisation of epoxides with CO₂ was investigated.

Full text of DOI:10.1039/c0dt01252a

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PAPER
Synthesis and characterisation of trigonal C -chiral di- and tetra-substituted
2
bis(oxazoline) alkyl zinc complexes and their reactivity towards protic
reagents†
Erwan Le Roux,* Nicolas Merle and Karl W. T o¨ rnroos
Received 17th September 2010, Accepted 22nd November 2010
DOI: 10.1039/c0dt01252a
R
,R
2
1
A series of zinc(II) alkyl complexes stabilised by the C
4S)-tBu, R = H (a); R = (4S)-Ph, R = H (b); R = (4R)-Ph, R
and structurally characterised. ( BOX)H ligands react with ZnEt
2
-chiral bis(oxazoline) ligand (
= (5S)-Ph (c)), has been synthesised
in toluene to give the heteroleptic
three-coordinate compounds of ( 1 BOX)ZnEt, 1a, 1b and 1c in high yield. However, when the
addition of (BOX)H ligands (a–b) over ZnEt is “uncontrolled”, the formation of homoleptic
BOX, with R =
1
(
2
1
2
1
2
R
,R
2
1
2
R
,R
2
2
four-coordinate compounds are favoured (2a–b), but not for the more sterically crowded ligand (c). The
zinc-ethyl derivatives (1a–c) react readily with protic reagents such as acetic acid (HOAc) and methanol
(
MeOH). For compounds 1a–c a redistribution of ligands is observed leading preferentially to
homoleptic compounds, except for the bulkier ligand c providing a three-coordinate complex identified
Ph,Ph
as ( BOX)Zn(OMe), 4c. The reaction of acetylacetone (acacH) with compounds 1a–c leads
straightforwardly to the more stable four-coordinate compounds corresponding to
R
,R
2
1
2
(
BOX)Zn(h -acac), 5a–c. The potential of these compounds as initiators for the copolymerisation
of epoxides with CO was investigated.
2
Introduction
imine-oxazoline (IOx) and anilido-aldimine/imine (AI) ligands
for example, have been widely studied and imparted a substantial
impact on the catalytic intramolecular hydroamination of func-
Since the 90s the bis(oxazoline) ligands (BOX) and their derivatives
have become readily synthetically accessible and commercially
available with a wide range of backbones and substituents.
Combined with main group, rare-earth and transition metals, their
conformationally constrained framework with bulky substituents
7
tionalised aminoalkenes and aminoalkynes, and ring-opening
1
8
8h
polymerisation of meso- and rac-lactides, e-caprolactone, b-
9
butyrolactone and g-valerolactone, copolymerisation of lactide
10
11
12
with styrene, epoxides with CO
2
or with cyclic anhydrides, and
and C
2
-symmetric axis of the stereogenic centres in close vicinity
terpolymerisation of epoxides/diglycolic anhydride or lactide with
of the metals centres are the driving force in many enantioselective
13
CO
2
.
The accessibility of vacant Lewis acid sites such as those
1b
catalytic transformations. With respect to main group chemistry
supported by mono-anionic bis(oxazoline), the preventive isola-
tion of these enantioselective catalysts, often efficiently prepared
found in tri-coordinated (LX)Zn-X¢ (X¢ = alkyl, OtBu, N(SiMe
NiPr , OSiPh , Cl, Br, OTf) or “masked” tri-coordinated with
a weakly coordinated additional donor ligand (L¢) (LX)Zn-
X¢L¢ (X¢/L¢ = m-OR, m-OC(R)O), m-OS(Et)O), OSiPh /THF) on
3
)
2
,
2
3
1d,1k
in situ, were not determinant for their success,
and for this
3
reason few protocols of their preparation and characterisation
were reported. Few anionic bis(oxazoline) compounds of the
main group have been X-ray structurally reported and fully
characterised (Mg, Zn, B, Al, Ga ). Moreover, mono-anionic
bidentate N,N¢-chelating ligands (LX) in organozinc chemistry,
such as aminotroponiminate (ATI), b-diketiminato (BDI), hybrid
mono-anionic bidentate N,N¢ zinc complexes, in synergy with the
steric and electronic parameters, have been a key factor in the
aforementioned catalysis. Furthermore, the capacity of the BDI
ligands, bearing bulkier aryl substituents, favouring the equilib-
rium of weakly bonded dimer in solution over the monomeric
form and avoiding formation of homoleptic zinc compounds,
were successfully identified and brought a real breakthrough
2
3
4
5
6
Department of Chemistry, University of Bergen, All e´ gaten 41, N-5007,
Bergen, Norway. E-mail: Erwan.LeRoux@kj.uib.no; Fax: +47 555 89490;
Tel: +47 555 89854
in epoxides/CO
and/or m-OR bimetallic zinc species as a key step intermediate).
2
copolymerisation (involving a bridged m-OAc
11
†
Electronic supplementary information (ESI) available: Parameters and
Although the bis(oxazoline) zinc chemistry seems to be trivial,
we were interested to investigate furthermore this field for their
1
X-ray structure of the 2nd conformer of 1b and 2b, VT H NMR
1
experiments (4b/4b¢/2b and 4c) and H NMR spectra of polymers. CCDC
use in epoxides/CO copolymerisation. A bis(oxazoline) zinc
2
reference numbers 791883 (1b); 791884 (2a) and 791885 (2b). For ESI
tBu,H
complex such as (
BOX)Zn(N(SiMe ) ) has been previously
3
2
and crystallographic data in CIF or other electronic format see DOI:
1
0.1039/c0dt01252a
developed by the Coates group and was found to be inactive in
1
768 | Dalton Trans., 2011, 40, 1768–1777
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copolymerisation of epoxides/CO
2
, despite of presenting struc-
) or
Table 1 Comparison of principal infrared frequencies of bis(oxazoline)
a
zinc(II) compounds
tural analogy with the active initiators as (BDI)Zn(N(SiMe
)
3 2
11b
(
IOx)Zn(N(SiMe
3
)
2
). Such a BOX-Zn system is believed to de-
b
Compounds
n
(C N)
n
(C C), d(C CH)
n
(C O), n(C C)
tBu,H
compose either into (a) a homoleptic zinc complex (
BOX) Zn
2
or (b) zinc aggregates at the earlier stage of the polymerisation,
which are in both cases detrimental for catalysis.
1a
1595
1600
1602
1590
1596
1599
1589
1585
1584
1539
1532
1536
1540
1531
1539
1536/1518
1523
1524
—
—
—
—
—
—
1388
1388
1381
1
1
2
2
b
c
a
b
Thus, we report herein the preparation and structural char-
acterisation of zinc(II) alkyl compounds supported by mono-
anionic bidentate bis(oxazoline) ligands with different substituents
in position C(4) and C(5). Then a survey to examine the steric
effects on BOX-Zn systems for accessing heteroleptic compounds
4c
c
c
c
b
5
5
5
a
b
c
R
,R
2
1
(
BOX)ZnX, having one nucleophilic ligand X (X = OMe, OAc,
a
In cm-1 (resolution ±4 cm ). From acetylacetonate ligand. Overlapping
-1
b
c
acac), and their stability towards ligand redistribution is presented.
Next, we assessed their use as initiators for the copolymerisation
of propylene oxide (PO) and of cyclohexene oxide (CHO) with
with stretching bands of n(C O), n(C C) and d(C CH)
.
CO .
2
of quartets (0.04/-0.03 and 0.00/-0.02 ppm, respectively) due
to the diastereotopic protons induced by the chiral BOX ligands
conformation (Scheme 1). Such a diastereotopic splitting has
already been reported in symmetric chiral aminotroponiminate
Results and discussion
Heteroleptic and homoleptic BOX zinc complexes synthesis
7
c
zinc complex [(S,S)-{i-PrATI)
2
diph}(ZnEt)
2
] (0.49/0.55 ppm).
R
,R
2
1
The heteroleptic ethyl zinc(II) compounds (
BOX)ZnEt 1a, 1b
= (4S)-Ph, R = H
= (5S)-Ph (1c) (Scheme 1), were obtained
in high yield (92–95%) by slow addition of one equivalent of
Attempts to crystallise compounds 1a–c failed in a variety of
1
4
16
◦
and 1c, (R
1
= (4S)-tBu, R
2
= H (1a); R
1
2
solvents (toluene, hexane, CH Cl , toluene–hexane) at -35 C or
2
2
(
1b); R = (4R)-Ph, R
1
2
at room temperature, except for 1b which gives two independent
◦
molecules at -35 C in toluene. Compound 1b crystallises in the
R
,R
2
neutral ligand ( 1 BOX)H onto ZnEt
in hexane (1a) or in toluene
2
chiral orthorhombic space group P2 2 2 with eight molecules in
1 1 1
(
1b–c) at room temperature. Compounds 1b–c were characterised
the unit cell (Table 2). The structures determined for 1b show that
the zinc metal centre adopts a slightly distorted trigonal geometry
(Fig. 1, see also Fig. S1† for the 2nd conformer). The main
difference between both independent molecules lies in the spa-
2
1
13
1
by DRIFT and H/ C{ H} NMR spectroscopies. Infrared data
show the imine stretching band, n(C N) from oxazolinyl ring, which
-
1
is shifted at lower frequencies (ª1600 cm ) relative to the free
ligands (ª1670 cm ) and the appearance in the region of 1540 cm
for n(C C) and d(C CH) from aromatic ring vibrations (Table 1),
-
1
-1
tial orientation of Zn-Et in C -symmetric (non-crystallographic)
◦
conformers that is a deviation of 5.15 (on the right, between
3
b,15
indicating their coordination to the zinc.
planes defined by C(9)–C(8)–Zn(1) and C(8)–Zn(1)–C(2)) and
◦
2
.75 (on the left, between planes defined by C(30)–C(29)–Zn(2)
and C(29)–Zn(2)–C(23)) are observed. In addition, the oxazolinyl
rings are slightly twisted for both conformers as shown by
◦
the interplanar angles of ∠C(3)–N(1)–C(5)–C(4) = -15.85 and
◦
∠
C(1)–N(2)–C(7)–C(6) = -12.10 for the 1st conformer, and
Scheme
1
Synthesis of heteroleptic three-coordinate
2
C -chiral
bis(oxazoline) ethyl zinc(II) compounds 1a–c and representative projection
of diastereotopic proton.
1
13
1
The H and C{ H} NMR spectra of 1a–c show the expected set
of signals for the chiral BOX ligands, with an overall shift in lower
field for HC
1
4
1
protons upon coordination. Among compounds
a–c, a deshielding effect of HC protons is observed (4.74 (1a);
.93 (1b); 5.31 (1c) ppm) according to the electronic nature of
1
substituents in C(4) and C(5) positions. Thus, the additional
weakly electron-withdrawing substituent in C(5) (Ph > H) and the
substituent in C(4) (Ph > tBu) in oxazolinyl rings seem greatly
to strengthen the delocalised p-electron system on the newly
Fig.
1
Molecular structures of 1b shown with atomic displace-
ment parameters at the 50% level. Selected bond lengths ( A˚ )
◦
and angles ( ) for the 1st conformer of 1b: Zn(1)–C(8) 1.960(3),
Zn(1)–N(1) 1.964(3), Zn(1)–N(2) 1.970(3), N(1)–C(3) 1.322(4), N(2)–C(1)
formed six-membered ring. Although the Zn–CH
2
CH
3
proton
1
.315(4), C(1)–C(2) 1.392(5), C(3)–C(2) 1.391(5), N(1)–Zn(1)–N(2)
signal of 1a is overlapping with the tBu groups, the Zn–CH
2
CH
3
93.31(11), N(1)–Zn(1)–C(8) 133.46(14), N(2)–Zn(1)–C(8) 133.05(14),
C(1)–C(2)–C(3) 121.7(3), C(2)–Zn(1)–C(8) 176.12(13).
proton signals shifted upfield of 1b–c clearly show two doublets
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 1768–1777 | 1769

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Table 2 Crystallographic data for 1b, 2a and 2b
1
b
2a·1/2(toluene)
Zn
2b
Formula
Formula weight
C
21
H
22
N
2
O
2
Zn
C
33.50
H
54.50
N
4
O
4
38 34 4 4
C H N O Zn
399.78
103(2)
0.71073
642.68
103(2)
0.71073
676.06
100(2)
0.71073
T/K
Wavelength/A˚
Crystal size/mm
Crystal system
0.18 ¥ 0.17 ¥ 0.05
0.35 ¥ 0.28 ¥ 0.22
0.49 ¥ 0.38 ¥ 0.24
Orthorhombic
Monoclinic
Orthorhombic
Space group
P2
1
2
1
2
1
(No. 19)
C
2
(No. 5)
1
C222 (No. 20)
a/A˚
5.4113(7)
21.983(3)
31.330(4)
90
90
90
3726.9(8)
8
1.425
1664
1.335
17.0744(9
10.7322(6)
19.3548(10)
90
10.3033(7)
16.6104(11)
75.385(5)
90
90
90
12901.5(15)
16
1.392
5632
0.890
b/A˚
c/A˚
◦
a ( )
◦
b ( )
107.6540(1)
90
3379.7(3)
4
1.263
1382
0.768
2.21 to 30.70
28634
10241 [Rint = 0.0266]
10084
◦
g ( )
V/A˚
3
Z
3
D
c
/g cm-
F(000)
Absorption coefficient/mm-
1
◦
q range for data collection/
Reflections collected
Independent reflections
Reflections with I > 2s(I)
Data/restraints/parameters
1.85 to 25.15
42494
6679 [Rint = 0.0715]
6227
6679/0/470
1.108
1.62 to 30.59
110073
19733 [Rint = 0.0422]
19509
19733/0/847
1.290
10241/6/403
1.069
2
Goodness-of-fit on F
Final R indices [I > 2s(I)]
R
1
1
= 0.0376, wR
2
2
= 0.0908
= 0.0929
R
1
= 0.0203, wR
2
2
= 0.0548
= 0.0550
R
1
= 0.0673, wR
2
2
= 0.1484
= 0.1487
R indices (all data)
R
= 0.0415, wR
R
1
= 0.0206, wR
R
1
= 0.0679, wR
Largest diff. peak and hole/e A˚
Flack parameter
3
1.236 and -0.365
0.003(10)
0.656 and -0.263
0.014(4)
1.181 and -1.377
0.088(10)
◦
18
∠
C(24)–N(4)–C(26)–C(25) = 12.45 and ∠C(22)–N(3)–C(28)–
along the formation of 1c. An addition of excess of ZnEt
2
on
◦
C(27) = -17.7 for the 2nd conformer.
The Zn–C distances in both conformers are in a similar
range (Zn(1)–C(8) 1.960(3) A and Zn(2)–C(29) 1.961((3) A)
comparable to (BDI) or (ATI)Zn-Et compounds with a trigonal
geometry. The Zn–N distances are in expected range of anionic
this reaction mixture allows the complete transformation of 2c
into 1c after 24 h, indicating that the reverse reaction is possible
by disproportionation (Scheme 2). Upon heating at 80 C, no
ligand redistribution is observed with 1c indicating its highstability
toward ligand redistribution.
8l
◦
˚
˚
8,11
bidentate N,N¢-chelating to zinc ethyl compounds: (Zn(1)–N(1)
1
.964(3), Zn(1)–N(2) 1.970(3) and Zn(2)–N(3) 1.967(3), Zn(2)–
10
˚
N(4) 1.971(2) A). The six-membered rings are almost coplanar
with Zn(1)/Zn(2) atoms which are only displaced (a) from
˚
0
.021/0.030 A above the plane defined by N(1)/N(3), N(2)/N(4)
and C(2)/C(23) with a C(2)/C(23)–Zn–C(8)/C(29) angle close
◦
◦
˚
to 180 (176.12/176.99(13) ), and (b) from 0.047/0.051(2) A
above the plane defined by N(1)/N(3), N(2)/N(4) and C(8)/C(29)
◦
◦
with coplanar ZnN
and 359.78 ). The two conformers show also a narrower bite
angle defined by N–Zn–N angle (b
2
C core atoms close to 360 (sum 359.82
◦
Scheme 2 Reaction completion in 1c compound by addition of ZnEt
excess onto hetero-/homoleptic 1c/2c mixture 50/50.
2
◦
n
= 93.31(11) and 94.00(10) ),
exhibiting more the zinc metal centre compared to most trigonal
compounds such as (AI), (BDI) or (IOx) Zn–X, independently of
The IR spectra of homoleptic zinc compounds 2a and 2b display
a slight shift to lower frequencies of the imine stretching (Dn = 4–
5 cm ), which reflects a bond shortening due to the reinforcement
◦
11
the X ligands nature (b
n
= 94.48–99.26(3) ).
-
1
Note that, when the addition of sterically less demanding
BOX)H ligands (a–b) over ZnEt is not carefully controlled (here
fast addition) under same aforementioned conditions (diluted
(
2
of the electron density around the metal, consistent with an
1
13
1
additional electron-rich BOX ligand. The H and C{ H} NMR
R
,R
2
systems: ª20–50 mM), the homoleptic ( 1 BOX)
a and 2b (R = (4S)-tBu, R = H (2a); R = (4S)-Ph, R
2b) were obtained, albeit the synthesis of 2a proceed more cleanly
Zn compounds
= H
2
spectra of 2a–b corroborate the preliminary observation with the
2
(
1
2
1
2
chemical resonance of HC shifted in upfield region with Dd =
1
0.14 and 0.36 ppm for 2a and 2b, respectively, in comparison with
1a–b.
17
in high yield with a ratio of 2 : 1. In the case of sterically more
crowded ligand (c), unidentifiable product mixtures were obtained
The molecular structures of 2a–b have been determined by
X-ray diffraction, as illustrated in Fig. 2. Compound 2a crystallises
1
Ph,Ph
by H NMR. The homoleptic compound ( BOX)
2
Zn 2c could
partially be observed in solution (ª45–50%) by slow addition
in the chiral monoclinic space group C with four molecules and
two molecules of toluene in the unit cell, while 2b crystallises in the
2
Ph,Ph
of a concentrated solution of ( BOX)H (85 mM) over ZnEt
2
1
770 | Dalton Trans., 2011, 40, 1768–1777
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to be favourably oriented in order to minimise steric interactions.
This arrangement affects the overall Zn–N distances, which are
slightly longer than in most homoleptic BOX-zinc compounds i.e.
19
Zn–N = 2.0073(8)–2.0239(8).
19
As already observed, the compound 2b displays similar
structural features to 2a, except that (a) the Zn–N distances are
slightly shorter (Zn–N = 1.964(3)–1.998(3) for the 1st conformer
and Zn–N = 2.017(4)–1.953(3) for the 2nd conformer), (b) the bite
◦
angles N–Zn–N are narrower (b
1
n
= 94.00(13)/95.39(14) for the
◦
st conformer and 94.22(14)/92.43(14) for the 2nd conformer)
and (c) the six-membered rings show increased folding about
◦
◦
1
.60/15.01 (for the 1st conformer) and 9.36/26.54 for the 2nd
conformer. These effects are principally attributed to the steric and
electronic effect of the phenyl groups (Fig. S2 and S3†).
Fig.
2
Molecular structure of 2a shown with atomic displace-
ment parameters at the 50% level. Hydrogen atoms and the
Reactivity of BOX ethyl zinc complexes with protic reagents
toluene molecule are omitted for clarity. Selected bond lengths
◦
(
A˚ ) and angles ( ): Zn(1)–N(1) 2.0239(8), Zn(1)–N(2) 2.0170(8),
Although Zn-alkyl compounds are known to be inactive as
tBu,H
11b
Zn(1)–N(3) 2.0189(8), Zn(1)–N(4) 2.0073(8), N(1)–C(1) 1.3150(12),
N(2)–C(9) 1.3117(12), N(3)–C(22) 1.3214(13), N(4)–C(24) 1.3153(12),
C(1)–C(8) 1.3936(14), C(8)–C(9) 1.3973(13), C(22)–C(23) 1.3988(15),
C(23)–C(24) 1.3987(15), N(1)–Zn(1)–N(2) 97.29(3), N(3)–Zn(1)–N(4)
well as (
BOX)Zn(N(SiMe ) ) in the copolymerisation of
3
2
epoxides/CO
2
, we tried to convert 1a–c into the putative catalytic
intermediates by replacing the ethyl group by acetate or alkoxide
groups. The reaction with protic reagents such as acetic acid
or methanol with heteroleptic 1a compounds did not yield
the targeted compounds i.e. either in monomeric or dimeric
9
7.29(3), N(1)–Zn(1)–N(4) 126.50(3), N(1)–Zn(1)–N(3) 104.73(3),
N(2)–Zn(1)–N(3) 130.75(3), N(2)–Zn(1)–N(4) 104.00(3), C(1)–C(8)–C(9)
24.19(9), C(22)–C(23)–C(24) 123.85(8).
1
tBu,H
tBu,H
forms of (
BOX)Zn(OAc) or (
BOX)Zn(OMe), respectively.
chiral orthorhombic space group C222
1
with sixteen molecules in
The resulting ligand redistribution is observed leading to the
the unit cell (Table 2). As reported for other chiral BOX homoleptic
zinc compounds, the zinc atoms of 2a are coordinated in a
homoleptic zinc compound 2a next to the most likely zinc
acetate or methoxide species (Scheme 3). Such rearrangement
19
20
distorted tetragonal fashion (interplanar angle between N(1)–
Zn(1)–N(2) and N(3)–Zn(2)–N(4) = 70.60(3) ). In addition, for
one of the BOX ligand, one oxazolinyl ring is more twisted and
the six-membered chelate ring is more folded than the opposite
BOX ligand. The results are that (a) the oxazolinyl rings are
is believed to occur through a ligand protonation mechanism
◦
releasing a (BOX)H ligand which in turn reacts with 1a to give
21
homoleptic 2a compound. Such reactions have been previously
reported, mainly for sterically undemanding diketiminates N-
(ortho-monosubstituted) aryl, N-benzyl and tris(pyrazolyl)borate
◦
◦
8h,8l,11c,22
twisted about -17.18(11) and 8.06(10) as shown by the torsion
angles of ∠C(22)–N(3)–C(16)–C(21) and ∠C(24)–N(4)–C(26)–
ligands.
When contacting 1b with AcOH, only the formation of ho-
moleptic 2b compound is observed, while upon reaction with
◦
◦
C(25) respectively compared to -1.21(11) and 1.37(10) (∠C(1)–
1
N(1)–C(2)–C(3) and ∠C(9)–N(2)–C(11)–C(10), respectively) and
MeOH three distinct sets of new signals are observed by H
◦
13
1
(
b) the six-membered rings are folded about 10.88(16) (defined by
and C{ H} NMR spectroscopy. One set is attributed to the
the planes N(3)–Zn(2)–N(4) and C(22)–C(23)–C(24)) compared to
homoleptic compound 2b (ª10%). The two others given sets
◦
1
3
.37(21) (defined by the planes N(1)–Zn(1)–N(2) and C(1)–C(8)–
of signals ( H NMR: HC
1
3
= 4.87/4.82 ppm and Zn–OCH =
3
1
1
C(9)). This specific ligand distortion allows the tert-butyl groups
2.99/2.98 ppm (splitting); C{ H} NMR: C
2
= 174.0/173.8 ppm)
R1 ,H
Scheme 3 Reactivity of ( BOX)ZnEt 1a–b compounds with acetic acid and methanol.
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Ph,H
are believed to belong to monomeric ( BOX)Zn(OMe) 4b and
addition of 5 equivalents of THF to 61 mM of 4c (in C
6
D ) leads to
6
Ph,H
dimeric [( BOX)Zn(m-OMe)]
2
4b¢ species with a ratio close to
a new resonance for HC at 5.06 ppm along with the appearance of
1
2
: 1at room temperature, which can existinequilibrium in solution
coordinated-THF to the zinc complex (and free THF), attributed
11c
1
Ph,Ph
(
Scheme 3). Variable temperature (VT) H NMR experiment on
to the formation of ( BOX)Zn(OMe)(THF) adduct. In parallel,
23
◦
◦
1
◦
◦
this mixture, from 10 C → 80 C (Fig. S4†), showed the complete
VT H experiments from 10 C → 80 C, are also consistent with
the existence of tri-coordinated 4c compounds in solution (Fig.
S5†), where no equilibrium is observed with its dimeric form (no
disappearance of dimeric species 4b¢ yielding to the monomeric
4b species and increasing the amount of 2b obtained by ligand
◦
redistribution. After heating the same solution for 15 min at 80 C,
shift of HC in upfield region). Note that, for both experiments,
1
2
b became the major product in the solution (ª45%), shifting
decomposition of 4c into three products is observed, increasing
with time, after 24 h of reaction with THF or upon heating at 70 C
for 3 h. In each case, these products have been identified as the
◦
also the equilibrium between both species 4b/4b¢ upon cooling
where 4b is now favoured at 25 C (ª40%). Such a shift in the
◦
equilibrium and the formation of the homoleptic compound at
high temperature shows that the 4b/4b¢ are highly susceptible to
concentration and temperature.
homoleptic 2c, zinc methoxide (Zn-OCH = 3.09 ppm) compounds
3
20
(minor), and the third product could be assigned to the formation
Ph,Ph
of ( BOX)Zn(OMe) aggregates (major), with an integral ratio
The scenario partially differs when supplementary substituents
corresponding to 2 : 1 : 2 : 3 for HC
determined by H NMR spectroscopy.
5
:HC
1
:HC
4
:OCH moieties
3
1
27
in the C(5) position on oxazolinyl rings are introduced as in
Ph,Ph
(
BOX) ligand c. Indeed, the protonolysis reaction of 1c with
The distinct behaviour of this zinc complex bearing the anionic
c ligand, compared to the other ligands a–b, is mainly attributed
to the reduced ability of c to allow the formation of corresponding
homoleptic zinc compound 2c. We tentatively propose that a
short distance between Zn ◊ ◊ ◊ Zn atoms, generates substantial
steric interactions between m-OMe bridges with the orthogonally
oriented phenyl groups in C(4) and C(5) positions, favouring
significantly the destabilisation of a dimer allowing preferential
formation of 4c in solution (Scheme 4). Such destabilisation is
less pronounced with the less sterically crowded BOX ligand b
allowing a partial equilibrium between monomer and dimer 4b/4b¢
species. Whereas most of anionic bidentate N,N-chelating ligands
in zinc(II) chemistry bearing a primary alcohol are found to be
in their dimeric form in solid-state as well as in solution, this
equilibrium in favour of the monomeric species in a rare example
HOAc at low temperature leads principally to the formation of
Ph,Ph
1
heteroleptic ( BOX)Zn(OAc) (ª50%, determined by H NMR),
20
homoleptic 2c and white insoluble solid (presumably zinc acetate)
compounds. Although ( BOX)Zn(OAc) was unisolatable, the
Ph,Ph
24
1
◦
◦
VT H NMR experiments, from 10 C → 80 C with different
25
concentrations, exhibit only one very broad resonance for HC
1
(
4.35 → 4.45 ppm) which has been attributed to the dimer
Ph,Ph
2
[(
BOX)Zn(m-h -OAc)]
2
3c¢ compound in solution without
Ph,Ph
2
observable equilibrium with its monomeric form ( BOX)Zn(h -
OAc) 3c. At 10 C, the molecular motion of 3c¢ is reduced
◦
showing better resolved signals with the splitting of HC
5
and HC
4
3
protons into two doublets ( JC–H = 7.8 Hz) at 5.58 and 4.69 ppm,
1
3
1
respectively. The C{ H} NMR spectroscopy is consistent with
the presence of 3c¢ next to 2c, although the carbonyl peak related to
acetate unit is missing due to its low solubility in dichloromethane-
11h
of tri-coordinate zinc methoxide.
26
d
2
.
In contrast, a longer Zn ◊ ◊ ◊ Zn distance, induced by the m-OAc
bridges, tolerates the formation of the highly stable dimer 3c¢
(ª50%), where the interactions between phenyl groups are reduced
for BOX ligand c. While the use of sterically less demanding
BOX ligands a–b on zinc systems, which easily undergo ligand
redistribution in presence of HOAc, leads to the formation of
homoleptic zinc(II) compounds (2a–b). Without clear structural
evidences, it seems that the steric congestion around the metal
centre is more pronounced for c.
The reaction between 1c and one equivalent of MeOH at low
temperature leads to the formation of either to the monomer
Ph,Ph
Ph,Ph
(
BOX)Zn(OMe) 4c (Scheme 4) or the dimer [( BOX)Zn(m-
OMe)]
2
4c¢ (not shown) species. In order to differentiate
monomeric/dimeric species, two experiments were carried out: a)
1
addition of donor ligand (THF) and b) VT H experiments. The
In parallel, we have found that a mono-anionic bidentate O,O¢-
chelating “flat” and bulkier ligand such acetylacetone (acacH)
can be introduced in the coordination sphere of compounds 1a–c.
The addition of one equivalent of acacH to 1a–c leads straight-
forwardly without specific treatment to the four-coordinate com-
R
,R
2
1
2
pounds (
BOX)Zn(h -acac) 5a–c (Scheme 5). Infrared data
Ph,Ph
Scheme 4 Reactivity of (
BOX)ZnEt 1c complex with acetic acid and
R1 ,R2
methanol showing ligand redistribution and formation of monomeric 4c
Scheme
5
Reactivity of
(
BOX)ZnEt 1a–c compounds with
species.
acetylacetone.
1
772 | Dalton Trans., 2011, 40, 1768–1777
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2
show a strong shift of n(C N), n(C O), n(C C) and d(C CH) in lower
active species, i.e. either [(BOX)Zn(m-OMe)]
OAc)]
2
or [(BOX)Zn(m-h -
frequencies indicating the coordination of the six-membered acac
2
, is possible with BOX ligands without leading necessarily
1
13
1
ring (Table 1). The H and C{ H} NMR spectra of all compounds
a–c confirm the coordination of acac ligand by the appearance
of a new sets of signals related to the acac ligand and by the
shift of chemical resonance of HC protons upfield. Although,
to the inactive homoleptic or agglomerated species. A balance
between Zn ◊ ◊ ◊ Zn distance and BOX ligand bulkiness should be
found to generate the weakly coordinated m-OR bridges bimetallic
zinc system. It is hoped that future investigations on chiral BOX
ligands, with different substituents on C(4)/C(5) and/or even in
C(1) positions, will accomplish active and stereoselective catalytic
5
1
an X-ray analysis was not successful, it is assumed that 5a–c
are stabilised by the six-membered acac ring, as the isostructural
compounds 2a–b. Furthermore, the coordination of the “flat”
bidentate O,O¢-chelating acac ligand seems to be not hampered by
steric hindrance, indicating again that the supplementary phenyl
groups on the ligand c are the main factors disfavouring the
formation of homoleptic 2c compounds.
species for copolymerisation of epoxides/CO .
2
Experimental
General considerations
All operations were performed with rigorous exclusion of
air and water, using standard Schlenk, high-vacuum and
glove box techniques (MB Braun MB200B-G; <1 ppm
Catalysis
Copolymerisation experiments of epoxides with CO were per-
formed by using mixture of 3c¢/2c, 4b/4b¢ and isolated 4c
compounds as putative catalysts. The copolymerisation of neat PO
2
O
2
, <1 ppm H
were purified by using Grubbs columns (MB Braun Sol-
vent Purification System 800). Benzene-d , toluene-d and
dichloromethane-d (99.96 atom% D) were obtained from
Aldrich, dried over sodium or CaH , vacuum transferred, de-
gassed and filtered prior used. 2,2¢-Methylenebis[(4S)-4-tert-butyl-
-oxazoline], 2,2¢-methylenebis[(4S)-4-phenyl-2-oxazoline], 2,2¢-
2
O). Dichloromethane, hexane and toluene
with CO shows no formation of polymer or cyclic carbonate from
2
6
8
the aliquot of the crude materials taken from the reaction mixture
or after treatment (conditions: 8 bar of CO
2
◦
2
at 30 C; or at 20 bar
2
◦
of CO
2
at 10, 30 or 50 C). Only traces of polymer (yield <2%, with
1
a selectivity in carbonate linkages ª5% determined by H NMR
spectroscopy, Fig. S6†), were observed with [( BOX)Zn(m-h -
2
Ph,Ph
2
methylenebis[(4R,5S)-4,5-diphenyl-2-oxazoline], glacial acetic
acid (99.99%), acetylacetone (>99%), anhydrous methanol
◦
OAc)]
2
(condition: 8 bar of CO
2
at 50 C). As reported by Coates
group, the lack of steric bulk (4b/4b¢), the tightly bound dimer
3c¢) and the monomer inept of dimerisation or susceptible of
decomposition (4c) for zinc compounds are given as reasons for
(
99.8%), chloroform-d (99.96% atom% D) and ZnEt
hexane) were purchased from Aldrich and used as received. CO
from Yara Praxair AS, purity grade: 99.999%) was purified
2
(1 M in
(
2
(
11
the inability to perform copolymerisation reactions. Compounds
a–c show no activity probably due to the high stability of the six-
through two stainless steel cylinders (48.2 ¥ 597 mm) filled with
activated copper(II) oxide on alumina (14–20 mesh loading 13%
from Aldrich) and 3 A molecular sieves (pellets 1.6 mm from
5
membered acac ring.
˚
Aldrich). Propylene oxide (PO) and cyclohexene oxide (CHO) and
were purchased from Aldrich and were distilled from CaH under
2
Conclusion
vacuum following three freeze–pump–thaw cycles and stored at
◦
Heteroleptic mono-anionic bidentate bis(oxazoline) zinc(II) alkyl
compounds 1a–c can be obtained straightforwardly under con-
trolled conditions by slow addition of a diluted neutral di- or
-35 C in a glove box.
The NMR spectra of air and moisture sensitive compounds
◦
were recorded by using J. Young valve NMR tubes at 25 ± 1 C
1
tetra-substituted C
2
-chiral bis(oxazoline) solution into a diluted
on a Bruker-AVANCE-DMX400 spectrometer (5 mm BB, H:
1
3
ZnEt solution. Their reactivity towards protic reagents greatly
2
400.13 MHz; C: 100.62 MHz) and a Bruker-BIOSPIN-AV500
1
13
1
13
depends on the substituents of the BOX ligand from the sterically
undemanding BOX ligand a–b to the sterically crowded BOX
ligand c as well as the nature of protic reagents. When the sterically
undemanding ligand is used, the formation of homoleptic 2a–b
(5 mm BBO, H: 500.13 MHz; C: 125.77 MHz). H and
C
shifts are referenced to internal solvent resonances and reported
in parts per million relative to TMS.
IR spectra were recorded on a Nicolet FT-IR Prot e´ g e´ 460
R
,R
TM
1
2
(
BOX)
leads to a mixture of [( BOX)Zn(OMe) 4b, [( BOX)Zn(m-
OMe)] 4b¢ and 2b in solution. In contrast, the use of the
2
Zn compounds are favoured, excepted for 1b which
spectrometer with a DRIFT collector (Spectra-Tech Collector
Ph,H
Ph,H
TM
II from Thermo Scientific), and the samples were prepared in a
2
glovebox and mixed in a KBr powder matrix before to be loaded in
the micro-cup. Then the cup is mounted onto a micro-cup holder
and placed into the DRIFT dome (equipped with KBr windows).
The spectra were averaged over 256 scans; the resolution was
bulkier ligand c, with an additional phenyl substituent in C(5)
positions onto oxazonyl rings, changes the stability towards
AcOH and MeOH reagents. This leads preferentially to a tightly
Ph,Ph
2
-1
bound dimer [( BOX)Zn(m-h -OAc)]
2
3c¢ or to the monomer
±4 cm . Elemental analyses of C, H and N were performed on
Ph,Ph
(
BOX)Zn(OMe) 4c which is incapable of dimerisation. The
an Elementar Vario EL III.
addition of the “flat” and bulkier (compare to AcOH and
MeOH) bidentate O,O¢-chelating acac ligand to 1a–c is possible
without ligand redistribution and the resulting four-coordinate
compounds ( 1 BOX)Zn(h -acac) 5a–c are greatly stabilised by
Syntheses
R
,R
2
tBu,H
2
(
BOX)ZnEt (1a). To a solution of ZnEt (0.48 mL of a
2
the formation of a new six-membered ring. Although, these
1 M solution in hexane, 0.48 mmol) in hexane (5 mL) was added
tBu,H
compounds are not active in epoxides/CO
2
copolymerisation,
dropwise a solution of (
BOX)H (127.9 mg, 0.48 mmol) in
we demonstrated that the formation of “presumed” bimetallic
hexane (10 mL). The colourless solution was stirred at ambient
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temperature for 3 h, and then the reaction mixture was dried
in vacuo, leading to white solid. Yield: 173.3 mg (92%). H NMR
(10 mL). Upon addition, the colourless solution turned quickly to
a white solution before becoming a white suspension. The reaction
mixture was stirred at ambient temperature for 3 h, and then the
reaction mixture was dried in vacuo, leading to white solid. Yield:
90 mg (99%). Procedure 2. To a solution of 1a (66.3 mg, 191
mmol) in cold toluene (5 mL) was added dropwise a solution of
glacial acetic acid (0.095 M, 191 mmol) in cold toluene (3 mL). The
colourless solution was stirred at ambient temperature for 4 h. The
reaction mixture was solubilised in <1 mL of cold hexane, filtrated
and dried in vacuo (repeated three times). Then the white solid was
solubilised in 2 mL of toluene, filtrated and concentrated to ca.
1
◦
(
8
8
400.13 MHz, C
6
D
6
, 25 C): d 4.74 (s, 1 H, HC
1
); 3.86 (dd, 2 H, J =
); 3.41 (dd, 2 H, J =
.6, 3.2 Hz, H
a
C
5
); 3.62 (t, 2 H, J = 8.6 Hz, HC
); 1.60 (t, 3 H, J = 8.2 Hz, Zn–CH
4
.6, 3.2 Hz, H
b
C
5
2
CH ); 0.7–0.8
3
1
3
1
(
(
bs, 18 H + 2 H, C–(CH
3
◦
)
3
+ Zn–CH
2
CH
, 25 C): d 174.0 (C
); 35.0 (C–(CH ); 26.2 (C–(CH
.1 (Zn–CH CH
3
) ppm. C{ H} NMR
100.62 MHz, C
6
D
6
2
); 72.4 (C
4
); 68.9 (C
CH
5
);
);
5
3
7.3 (C
1
3
)
3
3
)
3
); 13.3 (Zn–CH
2
3
-
1
2
3
) ppm. IR (KBr, n/cm : 2961 m, 2935 m, 2904
m, 2853 s, 1595 s, 1539vs, 1470 m, 1452 m, 1394w, 1364w, 1345w,
1
1
7
326w, 1316w, 1266w, 1235 m, 1210w, 1151 m, 1087 s, 1052 m,
024 m, 997 m, 979w, 951vw, 929vw, 851vw, 823vw, 778w, 754w,
◦
1 mL. Colourless crystals of 2a were isolated at -35 C after 4 days.
1
◦
46 m, 713vw, 666 m, 630vw, 527w. Anal. calcd for C17
H
30
N
2
O
2
Zn
Yield: 51 mg (45%). H NMR (400.13 MHz, C
6
D
6
, 25 C): d 4.60
(
359.82): C, 56.75; H, 8.40; N, 7.79; O, 8.89; Zn, 18.17%. Found:
(s, 1 H, HC
(CH
1
); 3.95–3.70 (m, 6 H, H
2
C
5
+ HC
4
); 0.88 (s, 18 H, C–
1
3
1
◦
C, 56.35; H, 8.07; N, 7.71%.
3
)
3
) ppm. C{ H} NMR (100.62 MHz, C
6
D
6
, 25 C): d 174.4
(
(
C
CH
2
); 73.9 (C
4
); 67.6 (C
5
); 55.3 (C
1
); 34.5 (C–(CH ) ); 26.4 (C–
3
3
Ph,H
(
BOX)ZnEt (1b). Following the procedure described
-1
3
)
3
) ppm. IR (KBr, n/cm : 2958 m, 2900 m, 2869 m, 1652w,
Ph,H
above, ( BOX)H (80 mg, 0.26 mmol) in toluene and ZnEt
(
1
2
crystals of 1b were isolated at -35 C after one week. Yield: 97.6 mg
(
ArH); 4.93 (s, 1 H, HC
4
1
2
1
1
1
590 s, 1540vs, 1483 m, 1467 m, 1394w, 1363w, 1350vw, 1340vw,
313vw, 1283w, 1265w, 1227 m, 1195w, 1179vw, 1157w, 1087 m,
057 m, 1024 m, 996 m, 748w, 657vw, 479vw, 426vw. Anal. calcd
0.26 mL of a 1 M solution in hexane, 0.26 mmol) in toluene gave
b as a pale yellow–orange solid. Then the solid was solubilised in
mL of toluene, filtrated and concentrated to ca. 1 mL. Colourless
for C30
H
50
N
4
O
4
Zn (1.2 C
6
H
5
CH ): C, 65.26; H, 8.50; N, 7.93%.
3
◦
Found: C, 65.3; H, 9.32; N, 8.02%. (presence of toluene confirmed
1
◦
94%). H NMR (400.13 MHz, C
6
D
6
, 25 C): d 7.2–7.0 (m, 10 H,
1
by H NMR).
1
); 4.49 (dd, 2 H, J = 8.8, 6.8 Hz, H
.01 (t, 2 H, J = 8.8 Hz, HC ); 3.41 (dd, 2 H, J = 8.8, 6.8 Hz, H
.60 (t, 3 H, J = 8.2 Hz, Zn–CH CH
a
C
5
);
);
4
b
C
5
Ph,H
(
BOX)
2
Zn (2b). To a solution of ZnEt (0.26 mL of a 1 M
2
2
3
); 0.04 and -0.03 (dq, 2 H,
solution in hexane, 0.26 mmol) in toluene (5 mL) was added
quickly a solution of ( BOX)H (80 mg, 0.26 mmol) in toluene
1
3
1
J = 8.2 Hz, Zn–CH
C
a
H
b
CH
3
) ppm. C{ H} NMR (100.62 MHz,
Ph,Ph
◦
6
D
6
, 25 C): d 173.6 (C
2
); 144.2 (ipso-CAr); 129.4 (ortho-CAr);
(
10 mL). The orange solution was stirred at ambient temperature
for 3 h, and then the reaction mixture was dried in vacuo, leading to
b as a pale orange solid. Then the solid was solubilised in 2 mL
1
1
3
1
1
8
28.4 (meta-CAr); 127.4 (para-CAr); 74.7 (C
4
); 67.3 (C
5
); 57.2 (C
1
-
);
1
2.7 (Zn–CH CH ); -0.7 (Zn–CH CH
2
3
2
3
) ppm. IR (KBr, n/cm :
2
116vw, 3086vw, 3061w, 3027w, 2891 m, 2852 m, 2802vw, 1600 s,
532vs, 1492 m, 1469 m, 1451 m, 1384w, 1356 m, 1312w, 1255 m,
233 m, 1179vw, 1154 m, 1074 m, 1038 m, 1002w, 983w, 952vw,
51vw, 754 m, 735 m, 699 m, 668w, 604vw, 537w, 411vw. Anal.
of toluene, filtrated and concentrated to ca. 1 mL. Colourless
crystals of 2b were isolated at -35 C after two weeks. Yield:
◦
1
◦
8
6 mg (49%). H NMR (400.13 MHz, C
6
D
6
, 25 C): d 7.1–6.8
(
m, 20 H, ArH); 4.57 (s, 2 H, HC
1
); 4.48 (t, 4 H, J = 8.3 Hz,
calcd for C21
8
H
22
N
2
2
O Zn (399.8): C, 63.09; H, 5.55; N, 7.01; O,
H
H
a
C
C
5
); 3.98 (t, 4 H, J = 8.3 Hz, HC
) ppm. C{ H} NMR (100.62 MHz, C
4
); 3.62 (t, 4 H, J = 8.3 Hz,
.00; Zn, 16.36%. Found: C, 62.61; H, 5.30; N, 6.88%.
13
1
◦
b
5
6
D
6
, 25 C): d 173.4
Ph,Ph
(C
(para-CAr); 73.9 (C
106vw, 3084vw, 3060w, 3028w, 2984vw, 2961w, 2899w, 2886 m,
2
); 142.3 (ipso-CAr); 129.2 (ortho-CAr); 128.3 (meta-CAr); 127.5
(
BOX)ZnEt (1c). Following the procedure described
-
1
Ph,Ph
4
); 67.3 (C
5
); 56.0 (C ) ppm. IR (KBr, n/cm :
1
above, ( BOX)H (80 mg, 0.17 mmol) in toluene and ZnEt
0.17 mL of a 1 M solution in hexane, 0.17 mmol) gave 1c as
2
3
(
1
2854 m, 2807vw, 1596 s, 1531vs, 1492 m, 1476 m, 1452 m, 1376w,
1355 m, 1314w, 1259 m, 1226 m, 1226w, 1178vw, 1150 m, 1072 m,
a white solid. Yield: 91 mg (95%). H NMR (400.13 MHz, C
2
5
6
6
D ,
◦
5 C): d 7.0–6.8 (m, 20 H, ArH); 5.55 (d, 2 H, J = 8.7 Hz, HC
5
);
); 0.89 (t, 3 H,
); 0.05 and 0.01 (dq, 2 H, J = 8.3 Hz, Zn–
1
6
052w, 1031 m, 1003w, 972w, 883vw, 754w, 744 m, 733w, 699 m,
64w, 664vw, 584vw, 531w, 404vw. Anal. calcd for C38 Zn
.30 (s, 1 H, HC
1
); 5.05 (d, 2 H, J = 8.7 Hz, HC
CH
4
H
34
N
4
O
4
J = 8.3 Hz, Zn–CH
2
1
3
1
3
◦
(676.09): C, 67.51; H, 5.07; N, 8.29; O, 9.47; Zn, 9.67%. Found: C,
7.11; H, 4.89; N, 8.15%.
CH
d 173.7 (C
Ar); 127.9 (ortho-C¢Ar); 127.7 (meta-CAr); 127.6 (meta-C¢Ar); 126.6
para-CAr and para-C¢Ar); 84.6 (C ); 71.4 (C ); 57.2 (C ); 12.2 (Zn–
CH CH ); -1.3 (Zn–CH CH ) ppm. IR (KBr, n/cm : 3108vw,
a
H
b
CH
3
) ppm. C{ H} NMR (100.62 MHz, C
6
D
6
, 25 C):
6
2
); 139.8 (ipso-CAr); 136.9 (ipso-C¢Ar); 128.0 (ortho-
C
(
Ph,Ph
2
[
(
BOX)Zn(l,g -OAc)]
2
(3c¢). To a solution of 1c (70 mg,
4
5
1
-
1
126 mmol) in cold toluene (5 mL) was added dropwise a solution
of glacial acetic acid (0.1 M, 126 mmol) in cold toluene (4 mL).
The white suspension initially formed in solution disappeared
upon stirring after few minutes. The colourless solution was stirred
at ambient temperature for 4 h. The reaction mixture was dried
in vacuo leading to 3c¢ as a white solid. Yield: ª 50% (based on
2
3
2
3
3
2
1
1
6
085vw, 3062w, 3028 m, 2995vw, 2953w, 2932 m 2893 m, 2862 m,
801vw, 1602 s, 1585 m, 1536vs, 1496 m, 1452 m, 1340 m, 1286w,
265 m, 1241w, 1213w, 1181vw, 1151 m, 1084 m, 1065 m, 1040 m,
023 m, 954vw, 921vw, 869vw, 783vw, 767w, 744 m, 728w, 720w,
97 m, 676vw, 638vw, 601vw, 575vw, 547vw, 520vw, 497vw. Anal.
1
◦
NMR). H NMR (400.13 MHz, 9.6 mg in 0.5 mL CD
d 7.2–6.6 (m, 40 H, ArH); 5.59 (db, 4 H, HC ); 4.72 (db, 4 H,
HC ); 4.38 (sb, 2 H, HC ); 1.05 (sb, 6 H, –OCO–CH ) ppm.
, 25 C): d C{ H} NMR
); 139.0, 136.7 (ipso-
); 22.6 (-OCO-CH ) ppm.
2
Cl
2
, 10 C):
calcd for C33
5
H
30
N
2
2
O Zn (551.99): C, 71.80; H, 5.48; N, 5.07; O,
5
.80; Zn, 11.85%. Found: C, 71.60; H, 5.24; N, 4.90%.
4
1
3
tBu,H
13
1
◦
13
1
(
BOX)
2
Zn (2a). Procedure 1. To a solution of ZnEt
2
C{ H} NMR (100.62 MHz, CD
2
Cl
2
◦
(
0.15 mL of a 1 M solution in hexane, 0.15 mmol) in hexane (5 mL)
(100.62 MHz, CD
2
Cl
2
, 25 C): d 173.3 (C
2
tBu,H
was added 2 equiv. of (
BOX)H (80 mg, 0.30 mmol) in hexane
C
Ar/Ar¢); 84.5 (C
4
); 70.4 (C
5
); 55.1 (C
1
3
1
774 | Dalton Trans., 2011, 40, 1768–1777
This journal is © The Royal Society of Chemistry 2011

View Article Online
Peaks related to the homoleptic compounds 2c and zinc acetate
are also present (vide supra).
calcd for C20
H
32
N
2
O
4
Zn (429.87): C, 55.88; H, 7.50; N, 6.52; O,
20
14.89; Zn, 15.21%. Found: C, 56.21; H, 6.18; N, 6.42%.
Ph,H
2
(
BOX)Zn(g -acac) (5b). Following the procedure de-
Ph,H
Ph,H
(
BOX)Zn(OMe)/[( BOX)Zn(l-OMe)] (4b/4b¢). To a
2
scribed above, 1b (50 mg, 125 mmol) and acetylacetone (0.032 M,
solution of 1b (50 mg, 125 mmol) in toluene (5 mL) was added
dropwise a solution of anhydrous methanol (0.138 M, 125 mmol) in
toluene (4 mL). The white suspension initially formed in solution
disappeared upon stirring after few minutes. The colourless
solution was stirred at ambient temperature for 1 h. The reaction
1
25 mmol) in toluene gave 5b as a yellowish solid. Yield: 57 mg
1
◦
(
95%). H NMR (400.13 MHz, C
6
D
6
, 25 C): d 7.1–6.9 (m, 10 H,
ArH); 4.91 (s, 1 H, HC
1
); 4.71 (s, 1 H, HC(CO-CH
3
)
2
); 4.66 (dd, 2
H, J = 8.8, 8.0 Hz, HaC
5
4
); 3.68 (t, 2
1
3
1
H, J = 8.0 Hz, HbC
5
); 1.52 (s, 6 H, HC(CO–CH
mixture was dried in vacuo leading to 4b/4¢b as an orange solid.
NMR (100.62 MHz, C
6
D
3 2
)
); 173.9
1
Yield: ª 90% (based on NMR). H NMR (500.13 MHz, C
6
D ,
6
(
(
C
2
); 143.1 (ipso-CAr); 128.9 (ortho-CAr); 128.0 (para-CAr); 127.6
meta-CAr); 99.7 (HC(CO-CH ); 74.5 (C ); 66.8 (C ); 56.2 (C );
) ppm. IR (KBr, n/cm : 3084vw, 3061w,
◦
2
7
2
5 C, with M = monometallic, B = bimetallic; ratio = 65 : 35): d
.5–6.8 (m, 30 H, ArH, M + B); 4.87 (s, 1 H +, HC
H, HC , B); 4.10–3.80 (m, 6 H +12 H, HC + HC
3
)
2
4
5
1
1
, M); 4.82 (s,
-
1
2
3
1
1
7
8.0 (HC(CO-CH
)
3 2
1
4
5
, M+B); 2.99
030w, 3004w, 2994vw, 2996w, 2919w, 2901 m, 2855vw, 1585 s,
529 s, 1523vs, 1493vw, 1469 m, 1452 m, 1388 s, 1311vw, 1262w,
235w, 1195vw, 1153w, 1078 m, 1036 m, 1002vw, 985vw, 931w,
71w, 749w, 735w, 700 m, 660w, 573vw, 538vw, 449vw, 412vw.
1
3
1
(
(
(
(
s, 3 H, -OCH
125.75 MHz, C
3
, M); 2.98 (s, 6 H, -OCH
3
, B) ppm. C{ H} NMR
, M); 173.8 (C , B); 145.8
, M); 74.2 (C , B); 64.9
, B); 21. 4 (-OCH , M
B) ppm. Peaks related to the homoleptic compounds 2b and
◦
6
D
6
, 25 C): d 174.0 (C
2
2
(ipso-CAr, M); 144.8 ((ipso-CAr, B); 75.0 (C
4
4
C
5
, B); 65.8 (C , M); 55.6 (C , M); 54.6 (C
5
1
1
3
Anal. calcd for C24
H
24
N
2
4
O Zn (469.85): C, 61.35; H, 5.15; N, 5.96;
+
O, 13.62; Zn, 13.92%. Found: C, 61.61; H, 5.91; N, 5.73%.
20
zinc methoxide are also present (vide supra).
Ph,Ph
2
(
BOX)Zn(g -acac) (5c). Following the procedure de-
Ph,Ph
(
BOX)Zn(OMe) (4c). To a solution of 1c (50 mg, 90 mmol)
scribed above, 1c (50 mg, 90 mmol) and acetylacetone (0.032 M,
90 mmol) in toluene gave 5c as a white solid. Yield: 54 mg (96%).
in toluene (5 mL) was added dropwise a solution of anhydrous
methanol (0.138 M, 90 mmol) in toluene (4 mL). The white
suspension initially formed in solution disappeared upon stirring
after few minutes. The colourless solution was stirred at ambient
temperature for 1 h. The reaction mixture was dried in vacuo
1
◦
H NMR (400.13 MHz, C
5.45 (d, 2 H, J = 8.7 Hz, HC
H, J = 8.7 Hz, HC ); 4.59 (s, 1 H, HC(CO-CH
HC(CO–CH
d 193.4 (HC(CO-CH
C¢Ar); 128.2 (ortho-CAr); 128.0 (ortho-C¢Ar); 127.8 (meta-CAr); 127.6
(meta-C¢Ar); 127.0 (para-CAr and para-C¢Ar); 99.7 (HC(CO-CH );
) ppm. IR (KBr,
6
D
6
, 25 C): d 7.0–6.7 (m, 20 H, ArH);
5
); 5.28 (s, 1 H, HC ); 5.18 (d, 2
1
4
3
)
2
); 1.49 (s, 6 H,
1
3
1
◦
3
)
2
) ppm. C{ H} NMR (100.62 MHz, C
); 174.4 (C
6
D
6
, 25 C):
1
leading to 4c as a white sticky solid. Yield: 52 mg (99%). H
3
)
2
2
); 138.9 (ipso-CAr); 137.4 (ipso-
◦
NMR (500.13 MHz, C
6
D
6
, 25 C): d 7.2–6.7 (m, 20 H, ArH);
5
.29 (d, 2 H, J = 8.0 Hz, HC
5
); 5.08 (s, 1 H, HC
1
); 4.68 (d, 2
)
3 2
1
3
1
H, J = 8.0 Hz, HC
4
); 3.04 (s, 3 H, -OCH
, 25 C): d 174.0 (C
3
) ppm. C{ H} NMR
84.8 (C
4
); 71.2 (C
5
); 56.5 (C
1
); 27.9 (HC(CO-CH
)
3 2
◦
-1
(125.75 MHz, C
6
D
6
2
); 140.22 (ipso-CAr); 136.7
n/cm : 3110vw, 3088vw, 3064w, 3032w, 3007vw, 2958vw, 2936 m
2875w, 2856vw, 2801vw, 1608 m, 1584 s, 1524vs, 1496 m, 1471w,
1452 m, 1381 s, 1357w, 1344w, 1306vw, 1285w, 1263 m, 1229w,
1158 m, 1089 m, 1070 m, 1038 m, 1024 m, 1002vw, 950vw, 932vw,
867vw, 839vw, 800vw, 783vw, 765w, 745 m, 723 m, 695 m, 682vw,
(
ipso-C¢Ar); 128.1; 127.9; 127.8; 127.6; 127.3; 126.9 (o-CAr, m-CAr
); 70.4 (C ); 55.8 (C ); 54.8 (-O-CH ) ppm. IR
KBr, n/cm : 3111vw, 3087vw, 3062w, 3029 m, 3004vw, 2920 m,
and p-CAr); 84.9 (C
(
4
5
1
3
-
1
2
1
1
8
5
881w, 2862 m, 2801 m, 1599 s, 1585 m, 1539vs, 1494 m, 1465 m,
452 m, 1342 m, 1309w, 1286w, 1259 m, 1244w, 1214w, 1178vw,
151 m, 1087 s, 1072 s, 1035 m, 1025 m, 1001 m, 952vw, 922vw,
69vw, 848vw, 803vw, 765w, 747 m, 721 m, 697 m, 668vw, 637vw,
575w, 544vw, 502vw, 450vw, 412vw. Anal. calcd for C36
H
32
N
2
4
O Zn
(622.04): C, 69.51; H, 5.19; N, 4.50; O, 10.29; Zn, 10.51%. Found:
C, 69.58; H, 6.79; N, 4.35%.
76w, 543w, 515vw, 500w, 474w. Anal. calcd for C32
H
28
N
2
3
O Zn
General procedure for PO or CHO/CO copolymerisation
2
(
553.97): C, 69.38; H, 5.09; N, 5.06; O, 8.66; Zn, 11.80%. Found:
C, 69.79; H, 5.13; N, 4.79%.
In a glovebox, an oven-dried scintillation vial, equipped with a
magnetic stir bar, was filled with 39.5 mmol of monometallic
complex (or 19.75 mmol of bimetallic complex) which was then
dissolved in 4 mL of PO (59.25 mmol) or CHO (39.5 mmol), and
placed in an autoclave reactor. The mixture was stirred at the
desired pressure and temperature adjusted with a heated oil bath.
After 24 h, the pressure was released and an aliquot of the solution
tBu,H
2
(
BOX)Zn(g -acac) (5a). To a solution of 1a (50 mg, 128
mmol) in toluene (5 mL) was added a solution of acetylacetone
0.032 M, 128 mmol) in toluene. The colourless solution was stirred
(
at room temperature for 12 h, and then the reaction mixture was
dried in vacuo, leading to white solid 5a. Yield: 52 mg (95%). H
1
◦
NMR (400.13 MHz, C
6
D
6
, 25 C): d 5.26 (s, 1 H, HC(CO-CH
3
)
2
);
); 3.67 (t,
); 3.60 (dd, 2 H, J = 8.6, 5.6 Hz, HbC ); 1.86
1
was taken for the characterisation of crude material by H NMR
4
2
.72 (s, 1 H, HC
H, J = 8.6 Hz, HC
1
); 3.77 (dd, 2 H, J = 8.6, 5.6 Hz, HaC
5
in CDCl . Subsequently, the reaction was quenched by 20 mL of
3
4
5
3
MeOH and dried in vacuo until constant weight.
1
1
(
s, 6 H, HC(CO–CH
3
)
2
); 0.74 (s, 18 H, C-(CH
3
)
3
) ppm. C{ H}
); 174.2
); 55.9 (C ); 34.5
) ppm. IR (KBr,
◦
NMR (100.62 MHz, C
6
D
6
, 25 C): d 193.7 (HC(CO-CH
3 2
)
Crystallography
(
(
C
2
); 100.6 (HC(CO-CH
3
)
2
); 72.4 (C
4
); 68.6 (C
5
1
C-(CH ); 28.4 (HC(CO-CH
3
)
3
3
)
2
); 25.9 (C-(CH
3
)
3
Details of the crystal data, intensity collection and refinement
for compounds 1a, 2a and 2b are given in Table 2 and further
details are available in the ESI.† Crystals were selected in a
glovebox and mounted inside a nylon loop containing Paratone-
N cryoprotectant oil (Hampton Research). Data were collected
-
1
n/cm : 2988 m, 2956 m, 2910 m, 2870 m, 1589 s, 1536vs, 1518 s,
1477 s, 1447 m, 1388 s, 1366 m, 1350 m, 1327w, 1278 m, 1264w,
1245 m, 1214w, 1191w, 1158 m, 1090 s, 1053 m, 1029 m, 1019w,
1003w, 953vw, 927w, 775w, 742w, 661w, 565w, 440vw, 409vw. Anal.
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 1768–1777 | 1775

View Article Online
on a Bruker APEXII Ultra CCD diffractometer. Raw data were
absorption corrected using faced indexed numerical methods.
Structure solution by direct methods and model refinement were
Lobkovsky and G. W. Coates, Angew. Chem., Int. Ed., 2002, 41, 2599;
(
e) S. D. Allen, D. R. Moore, E. B. Lobkovsky and G. W. Coates, J. Am.
Chem. Soc., 2002, 124, 14284; (f) R. Eberhardt, M. Allmendinger, G. A.
Luinstra and B. Rieger, Organometallics, 2003, 22, 211; (g) K. Yu and
C. W. Jones, Organometallics, 2003, 22, 2571; (h) D. R. Moore, M.
Cheng, E. B. Lobkovsky and G. W. Coates, J. Am. Chem. Soc., 2003,
28
performed using SHELXTL.
1
25, 11911; (i) D. R. Moore, S. D. Allen and G. W. Coates, Polym.
Prepr., 2003, 44, 735; (j) C. M. Byrne, S. D. Allen, E. B. Lobkovsky and
G. W. Coates, J. Am. Chem. Soc., 2004, 126, 11404; (k) J.-S. Herrmann,
G. A. Luinstra and P. W. Roesky, J. Organomet. Chem., 2004, 689, 2720;
(l) G. W. Coates and D. R. Moore, Angew. Chem., Int. Ed., 2004, 43,
6618; (m) W. J. van Meerendonk, R. Duchateau, C. E. Koning and
G.-J. M. Gruter, Macromol. Rapid Commun., 2004, 25, 382; (n) C. M.
Byrne and G. W. Coates, Polym. Prepr., 2005, 46, 162; (o) M. Kr o¨ ger,
C. Folli, O. Walter and M. D o¨ ring, Adv. Synth. Catal., 2005, 347, 1325;
Acknowledgements
We thank the University of Bergen (program Nanoscience@UiB)
for generous support. N. M. is grateful to the Norwegian Research
Council (project No. 182536) for post-doctoral fellowships.
(
p) B. Y. Lee, H. Y. Kwon, S. Y. Lee, S. J. Na, S. I. Han, H. Yun,
H. Lee and Y. W. Park, J. Am. Chem. Soc., 2005, 127, 3031; (q) W. J.
Van Meerendonk, R. Duchateau, C. E. Koning and G.-J. M. Gruter,
Macromolecules, 2005, 38, 7306; (r) T. Bok, H. Yun and B. Y. Lee,
Inorg. Chem., 2006, 45, 4228; (s) M. Kr o¨ ger and M. D o¨ ring, Catal.
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Hultzsch and B. Ziemer, Organometallics, 2007, 26, 3668; (u) D. F.-J.
Piesik, S. Range and S. Harder, Organometallics, 2008, 27, 6178.
12 R. C. Jeske, A. M. DiCiccio and G. W. Coates, J. Am. Chem. Soc., 2007,
129, 11330.
13 M. Kr o¨ ger, C. Folli, O. Walter and M. D o¨ ring, Adv. Synth. Catal., 2006,
348, 1908; R. C. Jeske, J. M. Rowley and G. W. Coates, Angew. Chem.,
Int. Ed., 2008, 47, 6041.
14 For the synthesis of similar (BDI)Zn-R compounds (R = Me, Et, tBu,
Ph), see ref. 11 and J. Prust, A. Stasch, W. Zheng, H. W. Roesky, E.
Alexopoulos, I. Us o´ n, D. B o¨ hler and T. Schuchardt, Organometallics,
2001, 20, 3825.
Notes and References
1
(a) C. Bolm, Angew. Chem., Int. Ed. Engl., 1991, 30, 542; (b) A. Pfaltz,
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G. Muller and M. Rocamora, Coord. Chem. Rev., 1999, 193–195,
7
69; (e) K. A. Jørgensen, M. Johannsen, S. Yao, H. Audrain and
J. Thorhauge, Acc. Chem. Res., 1999, 32, 605; (f) J. S. Johnson and
D. A. Evans, Acc. Chem. Res., 2000, 33, 325; (g) F. Fache, E. Schutz,
M. L. Tommasino and M. Lemaire, Chem. Rev., 2000, 100, 2159;
(
h) D. Rechavi and M. Lemaire, Chem. Rev., 2002, 102, 3467; (i) G.
Desimoni, G. Faita and P. Quadrelli, Chem. Rev., 2003, 103, 3119;
j) H. A. McManus and P. J. Guiry, Chem. Rev., 2004, 104, 4151; (k) G.
Desimoni, G. Faita and K. A. Jørgensen, Chem. Rev., 2006, 106, 3561;
l) H. Nishiyama, Chem. Soc. Rev., 2007, 36, 1133.
(
(
2
3
E. J. Corey and Z. Wang, Tetrahedron Lett., 1993, 34, 4001; V. Schulze
and R. W. Hoffmann, Chem.–Eur. J., 1999, 5, 337.
(a) M. Nakamura, A. Hirai and E. Nakamura, J. Am. Chem. Soc.,
15 M. L. Niven and G. C. Percy, Transition Met. Chem., 1978, 3, 267; I.
Diaz-Acosta, J. Baker, W. Cordes and P. Pulay, J. Phys. Chem. A, 2001,
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A, 2001, 105, 238.
1
7
996, 118, 8489; (b) R. P. Singh, Bull. Soc. Chim. Fr., 1997, 134,
65.
4
5
6
7
M. Bandini, P. G. Cozzi, M. Monari, R. Perciaccante, S. Selva and A.
Umani-Ronchi, Chem. Commun., 2001, 1318.
16 Compounds 1a–c are all soluble in CH
2
Cl
2
and in toluene and only 1a
S. Dagorne, S. Bellemin-Laponnaz and R. Welter, Organometallics,
is soluble in hexane.
tBu,H
2
004, 23, 3053.
17 The reaction between (
BOX)H and ZnEt in 1 : 1 ratio in hexane at
2
S. Dagorne, S. Bellemin-Laponnaz, A. Maisse-Fran c¸ ois, M.-N. Rager,
L. Jug e´ and R. Welter, Eur. J. Inorg. Chem., 2005, 4206.
room temperature shows a mixture of 1a (minor) and 2a (major) iden-
tified by NMR spectroscopy in comparison with the pure compounds
2a obtained with the 2 : 1 ratio.
A. Zulys, M. Dochnahl, D. Hollmann, K. L o¨ hnwitz, J.-S. Herrmann,
P. W. Roesky and S. Blechert, Angew. Chem., Int. Ed., 2005, 44, 7794;
M. Dochnahl, J.-W. Pissarek, S. Blechert, K. L o¨ hnwitz and P. W.
Roesky, Chem. Commun., 2006, 3405; N. Meyer and P. W. Roesky,
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W. Pissarek, M. Biyikal, P. W. Roesky and S. Blechert, Organometallics,
1
18 NMR spectra of compound 2c observed in solution: H NMR
◦
(400.13 MHz, C
6
D
5
6
, 25 C): d 7.0-6.8 (m, 20 H, ArH); 5.29 (d, 4
H, J = 8.6 Hz, HC
); 5.11 (d, 4 H, J = 8.6 Hz, HC
4
); 4.78 (s, 2 H, HC
1
)
13
1
◦
ppm. C{ H} NMR (100.62 MHz, C
6
D
6
, 25 C): d 173.8 (C
2
); 140.1
(ipso-CAr); 137.1 (ipso-C¢Ar); 128-127 (ortho-CAr/C¢Ar + meta-CAr/C¢Ar);
126.6 (para-CAr + para-C’Ar); 84.1 (C ); 70.4 (C ); 56.2 (C ) ppm.
19 For homoleptic (BOX) M compounds see: for copper, R. E. Lowenthal,
2
010, 29, 2637.
4
5
1
8
(a) M. Cheng, A. B. Attygalle, E. B. Lobkovsky and G. W. Coates,
J. Am. Chem. Soc., 1999, 121, 11583; (b) M. H. Chisholm, J. C. Huffman
and K. Phomphrai, J. Chem. Soc., Dalton Trans., 2001, 222; (c) B. M.
Chamberlain, M. Cheng, D. R. Moore, T. M. Ovitt, E. B. Lobkovsky
and G. W. Coates, J. Am. Chem. Soc., 2001, 123, 3229; (d) M. H.
Chisholm, J. Gallucci and K. Phomphrai,, Inorg. Chem., 2002, 41,
2
A. Abiko and S. Masamune, Tetrahedron Lett., 1990, 31, 6005; for zinc:
M. Jiang, S. Dalgarno, C. A. Kilner, M. A. Halcrow and T. P. Kee,
Polyhedron, 2001, 20, 2151; J. M. Takacs, D. S. Reddy, S. A. Moteki, D.
Wu and H. Palencia, J. Am. Chem. Soc., 2004, 126, 4494; J. M. Takacs,
P. M. Hrvatin, J. Atkins, D. S. Reddy and J. Clark, New J. Chem., 2005,
29, 263.
2
3
785; (e) M. H. Chisholm and K. Phomphrai, Inorg. Chim. Acta, 2003,
50, 121; (f) A. P. Dove, V. C. Gibson, E. L. Marshall, A. J. P. White
20 To mimic the formation of zinc acetate in solution, two equivalents
◦
and D. J. Williams, Dalton Trans., 2004, 570; (g) K. Yu and C. W.
Jones, J. Catal., 2004, 222, 558; (h) H.-Y. Chen, B.-H. Huang and
C.-C. Lin, Macromolecules, 2005, 38, 5400; (i) M. H. Chisholm, J. C.
Gallucci and K. Phomphrai, Inorg. Chem., 2005, 44, 8004; (j) C. A.
Wheaton, P. G. Hayes and B. J. Ireland, Dalton Trans., 2009, 4832;
of AcOH were slowly added at -35 C to a solution of ZnEt
2
in
toluene, resulting in the formation of colourless and viscous solution
attributed to [(ZnEt (Zn(OAc) ] or [ZnEt(OAc)] . The isolation of
2
)
x
2
)
y
z
such a compound, after removing all volatiles in vacuo, is hampered by
its complexity (polymeric nature) and its low solubility in most common
solvents. Nevertheless, NMR spectra have been obtained despite of its
(
k) C. N. Ayala, M. H. Chisholm, J. C. Gallucci and C. Krempner,
1
◦
Dalton Trans., 2009, 9237; (l) F. Drouin, P. O. Oguadinma, T. J. J.
Whitehorne, R. E. Prud’homme and F. Schaper, Organometallics, 2010,
2
low solubility in CDCl
3
: H NMR (400.13 MHz, CDCl
CH
3
, 25 C): d 1.85
(–OCO–CH
3
); 0.89 (t, 3 H, J = 8.3 Hz, Zn–CH
2
3
); 0.01 (q, 2 H,
13
1
9, 2139.
J = 8.3 Hz, Zn–CH
2
CH
3
) ppm. C{ H} NMR (100.62 MHz, CDCl
); 12.2 (Zn–CH CH ); -1.3
) ppm. For zinc methoxide synthesised from ZnEt with
3
,
◦
9
L. R. Rieth, D. R. Moore, E. B. Lobkovsky and G. W. Coates, J. Am.
Chem. Soc., 2002, 124, 15239.
25 C): d 180.0 (C O); 22.6 (–OCO–CH
3
2
3
(Zn–CH
2
CH
3
2
1
1
0 V. Poirier, M. Duc, J.-F. Carpentier and Y. Sarazin, ChemSusChem,
010, 3, 579.
1 (a) M. Cheng, E. B. Lobkovsky and G. W. Coates, J. Am. Chem. Soc.,
998, 120, 11018; (b) M. Cheng, N. A. Darling, E. B. Lobkovsky and
G. W. Coates, Chem. Commun., 2000, 2007; (c) M. Cheng, D. R. Moore,
J. J. Reczek, B. M. Chamberlain, E. B. Lobkovsky and G. W. Coates,
J. Am. Chem. Soc., 2001, 123, 8738; (d) D. R. Moore, M. Cheng, E. B.
MeOH (1 : 2) see: M. Ishimori and T. Tsuruta, Makromol. Chem., 1963,
64, 190; G. Allen, J. M. Bruce, D. W. Farren and F. G. Hutchinson,
J. Chem. Soc. B, 1966, 799; T. Tsuruta, J. Polym. Sci.,Part D, 1972,
6, 176; T. Hagiwara, J. Sato, H. Hamana and T. Narita, Makromol.
Chem., 1987, 188, 1825.
2
1
21 No formation of a homoleptic compound was observed in solution
after standing for several days. See also ref. 8l.
1
776 | Dalton Trans., 2011, 40, 1768–1777
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2
2 A. Looney, R. Han, I B. Gorrell, M. Cornebise, K. Yoon, G. Parkin and
A. L. Rheingold, Organometallics, 1995, 14, 274; A. Looney, R. Han,
I. B. Gorrell, M. Cornebise, K. Yoon, G. Parkin and A. L. Rheingold,
Organometallics, 1995, 14, 274.
25 VT NMR experiments in CD
2
Cl
2
(0.5 mL) with 9.6 mg or 20.8 mg
of 3c:2c (50 : 50). The insoluble materials have been solubilised by
◦
ultrasonification (during 30 min at 30 C).
13
1
◦
26 C{ H} NMR (100.62 MHz, CD
2
Cl
2
, 25 C): d 173.3 (C
2
); 139.0, 136.7
) ppm.
);
2
2
3 VT NMR experiments in C
6
D
6
(0.5 mL) with 14.6 mg of 4b/4b¢:2b
(ipso-CAr/Ar¢); 84.5 (C
4
); 70.4 (C
5
); 55.1 (C
1
); 22.6 (–OCO–CH
3
◦
1
◦
(
ratio of 90 : 10 initially observed at 25 C).
27 H NMR (400.13 MHz, C
6
D
6
, 25 C): d 5.38 (d, 2 H, J = 7.8 Hz, HC
5
Ph,Ph
4 The obtained mixture of (
BOX)Zn(OAc), 2c and zinc acetate
4.03 (d, 2 H, J = 7.8 Hz, HC
ppm.
4
1
3
); 4.98 (s, 1 H, HC ); 3.16 (s, 3 H, –OCH )
compounds are not soluble in most common hydrocarbons sol-
vents (hexane, benzene, toluene) and slightly in chlorinated solvents
28 Bruker, SHELXTL v. 6.14, Bruker AXS Inc., Madison, Wisconsin,
(
dichloromethane and chloroform).
USA, 2005.
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 1768–1777 | 1777