Novel metal complexes containing a chiral trinitrogen isoindoline-based pincer ligand: In situ synthesis and structural characterization

Article abstract of DOI:10.1039/c0dt00869a

The first synthesis and characterization of metal coordinated complexes containing in situ prepared chiral trinitrogen 1,3-bis(4,5-dihydrooxazol-2- ylimino)isoindoline-based pincer ligands are reported. Two zinc complexes, isolated as Zn(L)₂, w

Full text of DOI:10.1039/c0dt00869a

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Novel metal complexes containing a chiral trinitrogen isoindoline-based pincer
ligand: in situ synthesis and structural characterization†
Jessica L. Cryder,a Andrew J. Killgore,b Curtis Moore,c James A. Golen,d Arnold L. Rheingoldc and
Christopher J. A. Daley*a
Received 19th July 2010, Accepted 25th August 2010
DOI: 10.1039/c0dt00869a
The first synthesis and characterization of metal coordinated complexes containing in situ prepared
chiral trinitrogen 1,3-bis(4,5-dihydrooxazol-2-ylimino)isoindoline-based pincer ligands are reported.
Two zinc complexes, isolated as Zn(L)2, where L = 1,3-bis(4,5-dihydro-4-(R)-phenyloxazol-2-ylimino)-
isoindoline ((R,R)-5) or 1,3-bis(4,5-dihydro-4-(S)-iso-propyloxazol-2-ylimino)isoindoline ((S,S)-6),
respectively, are reported. Complexes Zn((R,R)-5)2 and Zn((S,S)-6)2 were prepared in situ through the
condensation of phthalonitrile with enantiopure 2-amino-4-(R)-phenyloxazoline ((R)-3) or
2-amino-4-(S)-iso-propyloxazoline ((S)-4) in the presence of ZnCl2 at 80 ◦C in dry toluene over
3–4 days. The characterizations of Zn((R,R)-5)2 and Zn((S,S)-6)2 in both the solid (X-ray
crystallography) and solution (multinuclear NMR spectroscopy) states are reported.
Introduction
Tridentate nitrogen donor ligands have played an impor-
tant role in inorganic chemistry in recent years. The fac-
coordinating ligand systems, such as the tris(pyrazolyl)borates
(Tp),1 tris(pyrazolyl)methanes (Tpc),2 and triazacyclanones
(tacn),3 have found applications as metalloenzyme synthetic
analogues and as ligands in metal-mediated organic catalysis re-
actions. The corresponding mer-coordinating ligand systems have
also been reported with the 1,3-bis(2-arylimino)isoindoline pincer
ligands4 (e.g. aryl = pyridine) having been studied for over 40 years.
The study of the latter systems has found a resurgence recently due
in part to their rich palladium chemistry,5 their formation of zwit-
terionic metal coordination complexes6 that display intramolecu-
lar proton transfer properties, and their successful use in catalysis
(including oxidation of alcohols7 and hydrocarbons,8 hydrogena-
tion of alkenes,9 and radical polymerizations10). Only a few mer-
tridentate ligands have been developed for use in enantioselective
catalysis including Gade’s bis(oxazolinylmethyl)pyrrole ligands
(Fig. 1: A),11 Nakada’s bis(oxazolinyl)carbazole ligands (Fig. 1:
B),12 Bro¨ring’s13 and Gade’s14 chiral bis(pyridylimino)isoindoline
ligands (Fig. 1: C), and most notably Nishiyama’s highly suc-
cessful chiral C2 symmetric 2,6-bis(2-oxazolinyl)pyridine (‘pybox’)
ligand15 (Fig. 1: D), which has become a standard in the
chiral “tool kit” of stereodirecting ligands. Noting Bro¨ring’s
and Gade’s success in enantioselective catalysis with chiral
bis(pyridylimino)isoindoline ligands (C) and observing 1,3-bis(2-
Fig. 1 Examples of chiral tridentate meridionally coordinating ligands.
Ligands A–D have been successfully isolated and reported while ligand E
is our target ligand.
aDepartment of Chemistry and Biochemistry, University of San Diego, 5998
Alcala´ Park, San Diego, USA. E-mail: cjdaley@sandiego.edu; Tel: +1 619-
260-4033
pyridylimino)isoindoline’s structural similarity to the highly suc-
cessful pybox ligand (D) we pursued the synthesis of a new
class of chiral mer-coordinating tridentate nitrogen donor ligands,
1,3-bis(4,5-dihydrooxazol-2-ylimino)isoindolines (Fig. 1: E), for
potential use in enantioselective catalysis. The choice of replacing
the 2-aminopyridine units of 1,3-bis(2-pyridylimino)isoindoline
for enantiopure 2-amino-4-substituted-oxazoline units stems
from the fact that the oxazolines (i) are readily available in
bDepartment of Chemistry, Western Washington University, 516 High Street,
Bellingham, WA, USA
cDepartment of Chemistry and Biochemistry, University of California, San
Diego, 9500 Gilman Drive, MC 0332, La Jolla, CA, USA
dDepartment of Chemistry and Biochemistry, University of Massachusetts
Dartmouth, 285 Old Westport Road, North Dartmouth, MA, USA
† CCDC reference numbers 783916 [Zn((R,R)-5)2] and 783917 [Zn((S,S)-
6)2]. For crystallographic data in CIF or other electronic format see DOI:
10.1039/c0dt00869a
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enantiopure form either commercially or from established
synthetic protocols using enantiopure aminoalcohols, and (ii)
have had enormous success in the field of enantioselective
catalysis as exemplified by the bis(oxazoline),16 bis(oxazolinyl-
methyl)pyrrole,11 bis(oxazolinyl)carbazole,12 and pybox15 ligand
systems.
Herein we report the first major developments toward this new
class of chiral 1,3-bis(4,5-dihydrooxazol-2-ylimino)isoindoline lig-
and system (E) through the synthesis, isolation, and characteriza-
tion in both the solution and solid state, of two zinc(II) com-
plexes (Zn((R,R)-5)2 and Zn((S,S)-6)2). These complexes contain
the desired ligands 1,3-(3-bis(4,5-dihydro-4-(R)-phenyloxazol-2-
ylimino)-isoindoline ((R,R)-5) and 1,3-(3-bis(4,5-dihydro-4-(S)-
iso-propyloxazol-2-ylimino)isoindoline ((S,S)-6)) coordinated in
their deprotonated state.
Results and discussion
Synthesis of metal complexes
The chiral oxazoline units, 2-amino-4-substituted-oxazolines (R)-
3 and (S)-4 were prepared following an improved procedure
reported by Agami et al.17 Enantiopure amino alcohol ((R)-
1 or (S)-2) was reacted with cyanogen bromide in refluxing
ethanol to produce the desired oxazolines ((R)-3 and (S)-4) in
high yields after basic (pH > 8) workup (Scheme 1: reaction
1). Our initial strategy was to prepare the new class of chiral
tridentate 1,3-bis(4,5-dihydrooxazol-2-ylimino)isoindoline-based
ligands ((R,R)-5 and (S,S)-6) following the well established
procedures (Scheme 1; reaction 2: top) reported for the analo-
gous 1,3-bis(2-pyridylimino)isoindoline (7) that included reaction
of phthalonitrile with the desired 2-aminopyridine in high-
boiling alcohol solvent (butanol, hexanol) using CaCl2 as catalyst
(Scheme 1; reaction 2: top).18 However, under those conditions,
specifically the elevated temperatures, the 2-amino-4-substituted-
oxazolines decompose into numerous byproducts and no isolation
of the desired ligands (R,R)-5 or (S,S)-6 (Scheme 1; reaction 2:
bottom) was obtained. Attempts with reported shorter reaction
time microwave conditions were also unsuccessful yielding un-
reacted starting material and/or decomposition products of the
oxazolines. Attempts were then made to prepare the ligand in
situ as part of a metal complex, specifically zinc, as was reported
by Siegl18d for the 1,3-bis(2-pyridylimino)isoindolines. Again,
elevated temperatures and protic solvents produced poor results.
However, using the condensation conditions reported by Heinrich
et al.19 for the formation of 1,2-(oxazole)benzene where ZnCl2
was found to be an active catalyst, the syntheses of Zn((R,R)-5)2
and Zn((S,S)-6)2 were successfully completed. On reacting ph-
thalonitrile with 2.5 equiv. of either (R)-3 or (S)-4 in refluxing dry
toluene for 3–4 days with ZnCl2, Zn((R,R)-5)2 or Zn((S,S)-6)2 was
obtained, respectively. In each complex, two equiv. of the chiral
tridentate isoindoline-based ligand ((R,R)-5 or (S,S)-6), formed in
situ during the reaction, are bonded in their monoanionic forms
in the overall 6-coordinated neutral Zn(L)2 complexes (Scheme 1:
reaction 3: L = (R,R)-5 or (S,S)-6). Oxazoline ring decomposition
was still observed under the initial conditions of 110 ◦C, however
we have determined that the reaction proceeds in a similar manner
at 80 ◦C with minimal thermal decomposition of the oxazoline
ring. Complexes Zn((R,R)-5)2 and Zn((S,S)-6)2 were purified and
isolated by column chromatography in modest yields of 15% each.
Scheme
1
Reaction schemes for (1) synthesis of enantiopure
2-amino-4-substituted-oxazoline precursors, (2) synthesis of bis(2-pyridyl-
imino)isoindoline ligands, and (3) synthesis of complexes Zn((R,R)-5)2 and
Zn((S,S)-6)2.
Solid state characterizations
Solid state structural characterizations of the complexes were
performed by single crystal X-ray diffraction analyses. Needle
crystals of Zn((R,R)-5)2 and Zn((S,S)-6)2 were grown separately,
via evaporation of a concentrated solution of the corresponding
complex in CH2Cl2 : acetone (5 : 1). Several crystals of Zn((R,R)-
5)2 and Zn((S,S)-6)2 were examined and ones that gave suitable
diffraction were used for X-ray measurements (Fig. 2 and Tables 1
and 2). Using standard X-ray analysis software, the structures
were refined to final R values of R1 = 0.0395 and wR2 = 0.1095
for Zn((R,R)-5)2 and R1 = 0.0604 and wR2 = 0.1852 for Zn((S,S)-
6)2. At this stage in the refinement there were void volumes with
unmodeled electron density in each structure. The SQUEEZE
program was used to model 5/3 and 7/3 acetone molecules per
Zn((R,R)-5)2 and Zn((S,S)-6)2, respectively. Their formulae were
added to the formula for the unit cell and the electron density was
removed for final refinement. We chose to model the voids with
acetone based on the fact that acetone was one of the solvents
used during the crystallization process. However, we note that
modeling CH2Cl2 molecules or combinations of solvents may also
10672 | Dalton Trans., 2010, 39, 10671–10677
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Table 1 Selected crystal data for Zn((R,R)-5)2 and Zn((S,S)-6)2
Compound
Formula
Zn((R,R)-5)2
Zn((S,S)-6)2
C52H40N10O4Zn·
5/3C3H6O
1031.11
Trigonal
P3121
19.3476(6)
19.3476(6)
11.5041(4)
90
90
120
3729.4(2)
3
120(2)
C40H48N10O4Zn·
7/3C3H6O
933.77
Trigonal
P3221
18.788(5)
18.788(5)
11.730(6)
90
90
120
3586(2)
3
123(2)
Fw (g mol-1)
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (◦)
b (◦)
g (◦)
3
˚
V (A )
Z
T (K)
m (mm-1)
Total reflns
1.199 (Cu Ka)
22080
0.572 (Mo Ka)
31203
Independ. reflns 4172
GOF 1.030
4261
1.051
Final R indicesa R1 = 0.0264, wR2 = 0.0672 R1 = 0.0287, wR2 = 0.0697
Flack c
0.003(17)
-0.006(9)
a Refinement by full-matrix least squares on F2 (all data): R for I > 2s(I),
2
R1 = R(|Fo| - |Fc|)/R|Fo|); wR2 = [Rw(Fo - Fc2)2/Rw(Fo2)2]1/2
.
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for Zn((R,R)-5)2 and
Zn((S,S)-6)2
Zn((R,R)-5)2
Zn((S,S)-6)2
Zn–N1/N1i
Zn–N3/N3i
Zn–N5/N5i
N1–Zn–N3
N1–Zn–N5
N3–Zn–N5
N1–Zn–N3i
N1–Zn–N1i
N1–Zn–N5i
N5–Zn–N5i
N1i–Zn–N5
N3–Zn–N3i
2.1832 (15)
2.1210 (13)
2.1525 (15)
83.31 (6)
167.49 (5)
84.34 (5)
94.92 (6)
99.12 (10)
83.91 (6)
2.1592 (18)
2.1743 (18)
2.1811 (18)
82.85 (7)
165.72 (6)
82.91 (6)
98.52 (7)
95.58 (9)
85.49 (7)
96.99 (10)
85.49 (7)
95.76 (8)
83.91 (6)
177.27 (8)
177.97 (10)
of Zn((R,R)-5)2 showed 2 equiv. of (R,R)-5 in its deprotonated
state bound to a zinc(II) center in a meridional fashion, resulting
in an overall approximate octahedral geometry (Fig. 2: top). The
angles between the two ligands (median planes defined by N1, N3,
and N5 of each ligand with Zn) are distorted from the ideal 90◦
for octahedral to 83.2 and 96.8◦. This distortion likely occurs to
minimize the steric interactions between the phenyl substituents
of the oxazoline arms, which are located in the same quadrant of
space (the larger 96.9◦ quadrant), on the two adjacent ligands in
Zn((R,R)-5)2. The corresponding interactions between the proton
on the chiral center (CH2–C(Ph)(H)–N) of the oxazoline ring of
one ligand with the neighboring diastereomeric protons (CH2–
C(Ph)(H)–N) of the oxazoline ring on the adjacent ligand are less
severe and thus they can accommodate a closer interaction (the
smaller average 83.2◦ quadrant) to relieve the congestion about
the phenyl substituents. Of note, one of the phenyl substituents on
each of the ligated (R,R)-5 ligands shows disorder that has been
satisfactorily modeled as being in two positions (50 : 50).
Fig. 2 X-Ray crystallographic structures of complexes Zn((R,R)-5)2 (top)
and Zn((S,S)-6)2 (bottom). Ellipsoids are shown at 50% probability.
Hydrogen atoms are not shown for clarity. All but one of the oxazoline
phenyl rings have been removed for clarity in Zn((R,R)-5)2 except for the
first carbon atoms. Two of the phenyl rings are disordered modeled as
50 : 50 in two positions (shown) while the other two rings do not show the
disorder. All of the isopropyl groups in Zn((S,S)-6)2 have been removed
for clarity except for the first carbon atom.
account for the observed void volumes and electron density in
these complexes. Following this procedure the final R values were
R1 = 0.0264, wR2 = 0.0672 and R1 = 0.0287, wR2 = 0.0697 for
Zn((R,R)-5)2 and Zn((S,S)-6)2, respectively. The X-ray analysis
The X-ray structure of Zn((S,S)-6)2 revealed it to be isostruc-
tural to Zn((R,R)-5)2 containing 2 equiv. of (S,S)-6 bound in its
deprotonated state to the zinc(II) center in a meridional fashion
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with an overall approximate octahedral geometry. The angles
between the two ligands (median planes defined by N1, N3, and
N5 of each ligand with Zn) were distorted to 84.6◦ and 95.4◦
with the substituent isopropyl groups of the ligands occupying
the larger quadrants of space around the zinc center likely to
reduce the steric interactions between ligands as in Zn((R,R)-5)2.
Analysis of bond distances show that the Zn–N(isoindoline) bond
(S,S)-6 had been deprotonated. As with Zn((R,R)-5)2, the 1H
NMR spectrum indicated that (S,S)-6 was bound meridionally to
the zinc(II) metal center in a C2-symmetric fashion as noted by the
appearance of only eight signals: two for the backbone isoindoline
aromatic protons, three for the oxazoline ring protons, one for the
methine proton of the isopropyl group, and two for the methyl
protons of the isopropyl groups. All proton and carbon atoms have
been assigned via a suite of multidimensional and multinuclear
NMR analyses including HSQC, HMBC, and ROESY and com-
parison to the assignments in Zn((R,R)-5)2 (Fig. 3: assignments
shown). As with Zn((R,R)-5)2, the diastereomeric protons H-3
and H-3¢ were assigned based on the ROE correlation between the
methyl groups of the isopropyl arm and H-3¢.
˚
distances of Zn((R,R)-5)2 (Zn–N3: 2.1205 (14) A) and Zn((S,S)-6)2
˚
(Zn–N3: 2.1743 (18) A) are longer than those reported for similar
bis[2-(4-methylpyridyl)imino]isoindoline (8) zinc complex (Zn(8)2:
5a
˚
2.038 (2) and 2.053 (2) A). Also, the Zn–N(oxazoline) bond
distances in Zn((R,R)-5)2 (Zn–N1: 2.1840 (16) and Zn–N5: 2.1519
˚
(16) A) and Zn((S,S)-6)2 (Zn–N1: 2.1592 (18) and Zn–N5: 2.1811
˚
(18) A) are longer than those reported by Gade for the structurally
similar bis(2-oxazolinylmethyl)pyrrole (9) zinc chloride distorted
Conclusions
tetrahedral complex Zn(9)Cl (1.9936 (13), 2.0020 (13), 2.0176 (14),
11c
˚
2.0257 (14) A).
The isolation of Zn((R,R)-5)2 and Zn((S,S)-6)2 represents the first
observation of chiral mer-coordinating 1,3-bis(4,5-dihydrooxazol-
2-ylimino)isoindoline pincer ligands. In addition, the successful
coordination of (R,R)-5 and (S,S)-6 to zinc(II) and the similar
projection of their chiral auxiliaries (Ph and iPr groups) about the
metal center as compared to reported pybox complexes make them
good candidates for isolation and use in enantioselective catalysis
studies. The synthesis and isolation of the free ligands (R,R)-5
and (S,S)-6, as well as other related 4-substituted analogues, are
currently underway.
In both cases (Zn((R,R)-5)2 and Zn((S,S)-6)2), the C–N bond
distances for the isoindoline carbon atoms (C4 and C11) adja-
cent to the imine (N2 and N4) and isoindoline (N3) nitrogens
are consistent with those found in other reported 1,3-bis(2-
pyridylimino)isoindoline metal complexes. While it is noted that
the Zn–N(oxazoline) bond lengths in Zn((R,R)-5)2 and Zn((S,S)-
6)2 differ between the two oxazoline arms of (R,R)-5 and (S,S)-6,
respectively, along with their ring conformations (i.e. ligand is
not C2-symmetric about Zn), this inequivalence is not observed
in solution based on NMR analysis in CDCl3 between 253 and
323 K.
Methods and materials
Chemicals and analysis. All reagents were purchased from
commercial sources and used as received. Solvents (Et2O and
CH2Cl2) were dried bypassing throughanInnovative Technologies
solvent purification system and collected just prior to use. Toluene
(EMD: DriSolv) was deoxygenated by bubbling with a stream
of N2 for 30 min prior to use. NMR spectra were collected on
a 400 MHz or 500 MHz Varian NMR spectrometer. 1H and
Solution state characterizations
Multinuclear NMR analyses were used to identify the solution
structures of Zn((R,R)-5)2 and Zn((S,S)-6)2. 1H NMR analysis of
Zn((R,R)-5)2 indicated that (R,R)-5 was in its deprotonated form
bound to zinc based on the number of signals, integration, and
the chemical shifts (Fig. 3: top). The absence of the isoindoline
N–H proton resonance indicated (R,R)-5 had been deprotonated.
1
13C{ H} NMR chemical shifts are referenced to TMS. Column
1
Furthermore, the H signals of the phenyl groups were found
chromatography was performed on a Biotage Sephora Flash
system.
in the range of 6.6–7.1 ppm whereas we expected these signals
to appear in the 7.2–7.4 ppm range for free (R,R)-5 based on
1
(R)-3 having its phenyl H signals between 7.25 and 7.35 ppm.
The H NMR spectrum also indicated that ligand (R,R)-5 was
Ligand synthesis and characterization
1
bound meridionally to the zinc(II) metal center in a C2-symmetric
fashion as noted by the appearance of only eight signals: two
for the backbone isoindoline aromatic protons, three for the
o-, m-, and p-aromatic protons of the phenyl substituents in
the oxazoline rings, and three for the oxazoline ring protons
themselves. All proton and carbon atoms have been assigned
via a suite of multidimensional and multinuclear NMR analyses
including HSQC, HMBC, and ROESY (Fig. 3: assignments
shown). ROESY was key in differentiating the diastereomeric
protons H-3¢ and H-3 on C-3. Cross-peaks were observed from
the ortho-phenyl protons (H-9) of the ligand to protons on C-3,
which were thus assigned as H-3¢ owing to their proximity to the
phenyl protons relative to H-3.
Synthesis of 2-amino-4-(R)-phenyloxazoline ((R)-3). Com-
pound (R)-3 was prepared in a similar fashion to that reported.17
(R)-Phenylglycinol (1; 10.0 g, 72.9 mmol) was dissolved with
stirring in ethanol (250 mL) in a 250 mL round bottom flask.
Cyanogen bromide (9.35 g, 89.9 mmol: caution: toxic fumes –
weigh in a fume hood) was added to the solution. The solution
was heated to reflux and stirred for 20 h under N2. The solvent was
removed under reduced pressure. The solid residue was redissolved
CH2Cl2 (75 mL) and transferred to a 500 mL separatory funnel
along with 1 M NaOH (160 mL). The organic phase was separated
and the aqueous phase was extracted with CH2Cl2 (3 ¥ 30 mL).
The combined organic phases were evaporated to dryness on a
rotary evaporator to yield (R)-3 as an off-white solid (10.82 g,
66.70 mmol) in 93% yield. Product identification was confirmed
1H NMR analysis of Zn((S,S)-6)2 indicated that (S,S)-6 was
in its deprotonated form bound to zinc based on the number of
signals, integration, and chemical shifts (Fig. 3: bottom). Again,
the absence of an isoindoline N–H proton resonance indicated
1
by comparison to H NMR to reported spectrum.20 1H NMR
(CDCl3 400 MHz) d 7.26 (5 H, m), 5.12 (1 H, dd), 4.64 (1 H, dd),
4.08 (1 H, dd), signals for N-H2 exchanged with H2O in solvent.
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Fig. 3 1H NMR spectra of Zn((R,R)-5)2 (top) and Zn((S,S)-6)2 (bottom) in CDCl3 and assignments. Residual NMR solvent, CH2Cl2, Et2O, and water
1
are denoted with “¥”. Assignments were made from a combination of 1H, 13C{ H}, COSY, HMBC, HSQC, and ROESY analyses.
Synthesis of 2-amino-4-(S)-iso-propyloxazoline ((S)-4). Com-
pound (S)-4 was prepared in a similar fashion as (R)-3. (S)-
2-Amino-3-methyl-1-butanol ((S)-2; 10.00 g, 76.82 mmol) was
dissolved with stirring in ethanol (125 mL) in a 250 mL round
bottom flask. Cyanogen bromide (9.77 g, 92.2 mmol: caution:
toxic fumes – weigh in a fume hood) was added to the solution.
The solution was heated to reflux and stirred for 16 h under
N2. The solvent was removed under reduced pressure. The solid
residue was redissolved CH2Cl2 (70 mL) and transferred to a
500 mL separatory funnel along with 1 M NaOH (60 mL). The
organic phase was separated and the aqueous phase was extracted
with CH2Cl2 (3 ¥ 30 mL). The combined organic phases were
evaporated to dryness on a rotary evaporator to yield (S)-4 as an
off-white solid (9.0532 g, 70.674 mmol) in 92% yield. The product
was used without further purification. 1H NMR (CDCl3 500 MHz)
d 4.30 (1 H, t, –OCH2CHiPr–), 3.95 (1 H, t, –OCH2CHiPr–),
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3.74 (1 H, q, –OCH2CHiPr–), 1.65 (1 H, m, –CH(CH3)2), 0.96
X-Ray structural characterizations
1
(3 H, d, –CH(CH3)2), 0.85 (3 H, d, –CH(CH3)2).13C{ H} NMR
X-Ray structure analysis of Zn((R,R)-5)2. Crystals suitable for
single crystal X-ray analysis were prepared via slow evaporation
of a concentrated acetone : CH2Cl2 (1 : 5) solution of Zn((R,R)-
5)2. A yellow rod 0.44 ¥ 0.13 ¥ 0.12 mm3 in size was mounted
on a Cryoloop with Paratone-N oil. The data were collected on a
(CDCl3 126 MHz) d 160.8 (–CNH2), 71.2 (–OCH2CHiPr–), 69.9
(–OCH2CHiPr–), 33.3 (–CH(CH3)2), 18.95 (–CH(CH3)2), 18.3
(–CH(CH3)2).
Complex synthesis and characterization
˚
Bruker Apex II CCD system with a copper source (l = 1.54178 A)
in a nitrogen gas stream at 120 (2) K and was 98.6% complete
to 65.78◦ in theta. Data were collected in a series of phi and
omega scans using 0.50◦ oscillations with 10 s exposures. A total
of 22 080 reflections were collected covering the indices, -22 ꢀ h
ꢀ 22, -21 ꢀ k ꢀ 18, -12 ꢀ l ꢀ 13. 4172 reflections were found
to be symmetry independent, with an Rint = 0.0524. The data
were integrated using the Bruker SHELXTL21 software program
and scaled using the SADABS22 software program. The structure
was solved by direct methods (SHELXS) and all non-hydrogen
atoms were refined anisotropically by full-matrix least-squares on
F2 (SHELXL-97).23 SQUEEZE found one void that has been
modeled as containing 5 disordered acetone molecules. Their
formula was added to the formula for the unit cell and the electron
density removed. All hydrogen atoms were constrained relative
to their parent atom using the appropriate HFIX command in
SHELXL-97. The compound was determined to be chiral with
atoms C1 and C14 being both R-configuration with a Flack24
parameter of -0.002 (18). The maximum and minimum peaks
on the final difference Fourier map corresponded to 0.191 and
Synthesis of Zn((R,R)-5)2. To a 200 mL side arm flask
was added (R)-3 (1.50 g, 9.25 mmol), phthalonitrile (0.395 g,
3.08 mmol), and zinc chloride (0.413 g, 3.03 mmol). The flask
had a stirbar added and was then sealed with a septum and placed
under N2 atmosphere. Toluene (150 mL; dried by passing through
Innovative Technologies solvent purification system) was added
via cannula to dissolve the reactants. The mixture was stirred
and allowed to react at 80◦ C for 3 days. The reaction mixture
was vacuum filtered through a column of Celite (1¢ ¥ 1¢) and the
Celite washed with minimal hot toluene. The filtrate solvent was
removed under reduced pressure to yield an orange solid. Column
chromatography of the residue (hexane : ethyl acetate – 20% to
35% EtOAc over 9 column volumes (CV), 35% to 80% EtOAc
over 7 CV, 80% to 100% over 0.5 CV, 100% EtOAc for 3 CV)
was performed to isolate Zn((R,R)-5)2 as a yellow solid (3rd peak:
1
0.210 g, 0.239 mmol) after solvent evaporation in 15% yield. H
NMR (500 MHz, CDCl3) d 7.70 (4 H, dd, J = 5.4, 3.0, H-10), 7.55
(4 H, dd, J = 5.4, 3.0, H-11), 7.04 (4 H, tt, J = 7.4, 1.6, H-1), 6.90
(8 H, ‘t’, J = 7.7, H-2), 6.71 (8 H, dd, J = 7.8, 1.6, H-3), 4.67 (4
H, dd, J = 10.1, 8.4, H-5), 4.45 (4 H, dd, J = 10.1, 8.4, H-6a), 3.94
-3
˚
-0.220 e A , respectively.
1
(4 H, t, J = 8.4, H-6b). 13C{ H} NMR (500 MHz, CDCl3) d 68.3
X-Ray structure analysis of Zn((S,S)-6)2. Crystals suitable for
single crystal X-ray analysis were prepared via slow evaporation
of a concentrated acetone : CH2Cl2 (1 : 5) solution of a mixture
of Zn((S,S)-6)2. Data were collected on a Bruker Apex II CCD
(C-5), 73.2 (C-6), 122.2 (C-10), 126.5 (C-3), 127.7 (C-1), 128.1 (C-
2), 131.4 (C-11), 139.6 (C-9), 140.9 (C-4), 165.5 (C-7), 173.7 (C-8).
Assignments confirmed by HSQC, HMBC, and ROESY analyses
(see Fig. 3 for labels).
˚
system with a molybdenum source (l = 0.71073 A) in a nitrogen
gas stream at 123 (2) K and was 99.5% complete to 25.00◦ in
theta. Data were collected in a series of phi and omega scans using
0.50◦ oscillations with 10 s exposures. A total of 31 203 reflections
were collected covering the indices, -22 ꢀ h ꢀ 22, -22 ꢀ k ꢀ
22, -14 ꢀ l ꢀ 14. 4261 reflections were found to be symmetry
independent, with an Rint = 0.0539. The data were integrated using
the Bruker SHELXTL21 software program and scaled using the
SADABS22 software program. The structure was solved by direct
methods (SHELXS) and all non-hydrogen atoms were refined
anisotropically by full-matrix least-squares on F2 (SHELXL-97).23
SQUEEZE found one void that has been modeled as containing
7 disordered acetone molecules. Their formula was added to the
formula for the unit cell and the electron density removed. All
hydrogen atoms were constrained relative to their parent atom
using the appropriate HFIX command in SHELXL-97. The
compound was determined to be chiral with atoms C1 and C14
being both S-configuration with a Flack24 parameter of -0.006(9).
The maximum and minimum peaks on the final difference Fourier
Synthesis of Zn((S,S)-6)2. To a 200 mL side arm flask
was added (S)-4 (1.00 g, 7.81 mmol), phthalonitrile (0.4999 g,
3.095 mmol), and zinc chloride (0.2661 g, 1.953 mmol). The flask
had a stirbar added and was then sealed with a septum and placed
under N2 atmosphere. Toluene (150 mL; dried by passing through
Innovative Technologies solvent purification system) was added
via cannula to dissolve the reactants. The mixture was stirred
and allowed to react at 80◦ C for 3 days. The reaction mixture
was vacuum filtered through a column of Celite (1¢ ¥ 1¢) and
the Celite washed with minimal hot toluene. The filtrate solvent
was removed under reduced pressure to yield an orange solid.
Column chromatography of the residue (hexane : ethyl acetate –
20% to 35% EtOAc over 9 column volumes (CV), 35% to 80%
EtOAc over 7 CV, 80% to 100% over 0.5 CV, 100% EtOAc for
3 CV) was performed to isolate Zn((S,S)-6)2 as a yellow solid
(3rd peak: 0.2342 g, 0.2933 mmol) in 15% yield after solvent
1
evaporation. H NMR (500 MHz, CDCl3) d 7.91 (1 H, m, H-
-3
˚
9), 7.57 (1 H, m, H-10), 4.23 (1 H, dd, J 8.8, 4.5, H-5a), 4.07
(1 H, t, J 9.3, H-5b), 3.78 (1 H, m, H-4), 1.66 (1 H, ddd, J
28.4, 17.4, 11.3, F), 0.68 (3 H, d, J 6.7, G), 0.41 (3 H, d, J 7.0,
map corresponded to 0.179 and -0.246 e A , respectively.
Acknowledgements
1
H). 13C{ H} NMR (126 MHz, CDCl3) d 174.0 (C-7), 164.7 (C-
6), 138.6 (C-8), 132.0 (C-10), 122.5 (C-9), 68.8 (C-4), 66.2 (C-
5), 30.9 (C-3), 19.3 (-CH(CH3)2), 15.0 (-CH(CH3)2). Assignments
confirmed by HSQC, HMBC, and ROESY analyses (see Fig. 3 for
labels).
We would like to thank the American Chemical Society Petroleum
Research Fund for the major financial support of this re-
search. J.L.C. would like to thank the University of San Diego’s
Summer Undergraduate Research Experience (SURE) program
10676 | Dalton Trans., 2010, 39, 10671–10677
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The Royal Society of Chemistry 2010
©

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for summer financial support. We would also like to thank Western
Washington University and the University of San Diego for
financial support of this project.
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