Unique formation of mono-, tetra- and nona-nuclear zinc complexes from protonolysis reactions of [Zn(dmpzm)Et2]

Article abstract of DOI:10.1039/b819637k

Protonolysis reactions of [Zn(dmpzm)Et₂] (1) with acetic or formic acid in different molar ratios gave rise to four mononuclear zinc complexes [ZnEt(dmpzm)(L)] (2: L = OAc; 3: L = HCOO) and [Zn(dmpzm)(L) ₂] (4: L = OAc; 5: L = HCOO),

Full text of DOI:10.1039/b819637k

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Unique formation of mono-, tetra- and nona-nuclear zinc complexes from
protonolysis reactions of [Zn(dmpzm)Et2]†
Mei-Ling Cheng,a Hong-Xi Li,a Lei-Lei Liu,a Hui-Hui Wang,a Yong Zhanga and Jian-Ping Lang*a,b
Received 5th November 2008, Accepted 16th December 2008
First published as an Advance Article on the web 29th January 2009
DOI: 10.1039/b819637k
Protonolysis reactions of [Zn(dmpzm)Et2] (1) with acetic or formic acid in different molar ratios gave
rise to four mononuclear zinc complexes [ZnEt(dmpzm)(L)] (2: L = OAc; 3: L = HCOO) and
[Zn(dmpzm)(L)2] (4: L = OAc; 5: L = HCOO), one nonanuclear zinc complex [Zn(m4-O)2(ZnEt)6-
(m3-OAc)4(m¢3-OAc)2{Zn(dmpzm)Et}2] (6), and one tetranuclear zinc complex [Zn4(m4-O)(dmpzm)3Et3]
(7). Compounds 1–7 were characterized by elemental analysis, IR spectra, 1H NMR spectra, and the
crystal structures of 1, 3, 4, 6, and 7 were determined by single-crystal X-ray crystallography. In the
structures of 1, 3, and 4, the central Zn atom is tetrahedrally coordinated by two N atoms of one
dmpzm and two C atoms of two Et groups (1), or one C atom of one Et group and one O atom of
formate ligand (3), or two O atoms of two acetates (4). In the structure of 6, a heptanuclear
[Zn(m4-O)2(ZnEt)6(m3-OAc)4] core is connected with two [Zn(dmpzm)Et]+ fragments via a pair of
m¢3-OAc ligands. Compound 7 consists of a Zn4(m4-O) tetrahedron in which three Zn atoms are further
saturated by two N atoms from dmpzm ligands and an ethyl group while one Zn center is coordinated
by three C atoms from the methylene group of the three dmpzm ligands.
The resulting mononuclear zinc complexes with a possible N2O2
coordination sphere may resemble those found in the active sites of
Introduction
thermolysin or carboxypeptidase.3a,b,7 To this end, we carried out
reactions of 1 with acetic and formic acids to prepare our expected
zinc model complexes. However, such reactions were complicated
and four mononuclear zinc complexes [ZnEt(dmpzm)(L)] (2: L =
OAc; 3: L = HCOO) and [Zn(dmpzm)(L)2] (4: L = OAc;
5: L = HCOO) along with one unusual nonanuclear zinc complex
[Zn(m4-O)2(ZnEt)6(m3-OAc)4(m¢3-OAc)2{Zn(dmpzm)Et}2] (6) and
one tetranuclear zinc complex [Zn4(m4-O)(dmpzm)3Et3] (7) were
isolated. We herein report the intriguing reactivity of 1 towards the
two acids along with the isolation and structural characterization
of 1–7.
Alkylzinc compounds are found to be of importance in catalysis,
organic synthesis, and materials.1 Some alkylzinc compounds
have been employed to react with donor ligands to form various
mononuclear adducts and polynuclear zinc complexes.2–4 Among
the mononuclear Zn adducts, those containing N-donor ligands
are useful precursors to form other interesting zinc complexes.3,4
Some of them were used as model complexes to mimic the
structures or functions of the active site of zinc enzymes3 or
as special catalysts for the ring-opening polymerization of rac-
lactide,4a,g and for the copolymerization of carbon oxide and
epoxides.1b,4b Currently, most of the mononuclear adducts are
engaged in the utilization of the 3 N tripodal ligands such
as hydridotris(pyrazol-1-yl)borate and some mixed ligands that
incorporate histidine-like nitrogens and one or more thioether,
thiolate, aldehyde, methoxy, carboxyl and phenolate donor atoms.
Their reactivity towards H2O, ROH, and RCOOH have been
extensively investigated.3,4g Although the mononuclear adducts of
the 2 N bipodal ligands have also been described,5 studies on
the reactivity of those of the neutral 2 N bipodal ligands are
less explored.1b,4c In this context, we deliberately chose diethylzinc
(ZnEt2) to react with a neutral 2 N bipodal ligand bis(3,5-
dimethylpyrazolyl)methane (dmpzm)6 and isolated their adduct
[Zn(dmpzm)Et2] (1). Complex 1 has two terminal ethyl groups that
may be protonated by carboxylic acids to form ethane molecules.
Experimental
Materials and methods
All manipulations were carried out under high purity nitrogen us-
ing standard Schlenk techniques. Solvents were dried by refluxing
over sodium-benzophenone (THF, toluene, and n-hexane), P2O5
(MeCN) and freshly distilled prior to use. The ligand bis(3,5-
dimethylpyrazol-1-yl)methane (dmpzm) was prepared according
to the literature method.6 Other chemicals and reagents were
obtained from commercial sources and used as received. 1H
NMR spectra were recorded at ambient temperature on a Varian
UNITYplus-400 spectrometer. 1H NMR chemical shifts were
referenced to the solvent signal in C6D6. Elemental analyses
for C, H, and N were performed on a Carlo-Erbo CHNO–S
microanalyzer. The IR spectra (KBr disc) were recorded on a
Nicolet MagNa-IR550 FT-IR spectrometer (4000–400 cm-1).
aCollege of Chemistry, Chemical Engineering and Materials Science, Suzhou
University, Suzhou, 215123, P. R. China. E-mail: jplang@suda.edu.cn;
Fax: 86-512-65880089
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 200032,
P. R. China
Synthesis of [Zn(dmpzm)Et2] (1). To a solution of ZnEt2
(3.0 mL of a 1M solution in hexane, 3.0 mmol) in THF (10 mL) was
† CCDC reference numbers 704329–704333. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b819637k
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added a solution of dmpzm (0.61 g, 3 mmol) in THF (10 mL). The
colorless solution was stirred at ambient temperature for 5 h, and
was concentrated to ca. 5 mL. Colorless crystals of 1 were isolated
by cooling the solution to -26 ◦C for 2 days. Yield: 0.75 g (76%).
Anal. Calcd. for C15H26N4Zn: C, 54.96; H, 7.80; N, 17.09; Found:
C, 54.58; H, 7.65; N, 17.43%. IR (KBr disk): 2977 (m), 2924 (m),
1558 (s), 1486 (s), 1471 (m), 1464 (m), 1456 (m), 1417 (m), 1384
(s), 1353 (s), 1313 (m), 1267 (s), 1139 (m), 1084 (m), 1035 (m),
970 (w), 809 (s), 783 (m), 712 (m), 673 (s), 627 (s) cm-1. 1H NMR
(400 MHz, ppm): (C6D6) d -5.457 (s, 2H, -CH), 5.372(s, 2H, -CH2),
2.240 (s, 6H, -CH3), 1.675 (s, 6H, -CH3), 1.565 (t, 3J = 8.0 Hz, 6H,
-ZnCH2CH3), 0.636 (q, 3J = 12.4 Hz, 4H, -ZnCH2CH3).
(400 MHz, ppm): (C6D6) d -5.601(s, 2H, -CH), 5.554(s, 2H, -CH2),
2.254 (s, 6H, -CH3), 2.152 (s, 6H, -CH3), 1.905 (s, 6H -CH3COO).
Synthesis of [Zn(dmpzm)(HCOO)2] (5). To a solution of 1
(0.66 g, 2.20 mmol) in 20 mL toluene was added HCOOH
(0.17 mL, 4.40 mmol) at room temperature. After the evolution
of gas ceased, some insoluble white precipitate was formed. The
resulting solution was further stirred overnight at room tempera-
ture and then filtered. n-Hexane (15 mL) was allowed to diffuse
into the filtrate. Then the white solid of Zn(dmpzm)(HCOO)2 (5)
was formed, which were collected by filtration, washed by absolute
hexane and dried in vacuo. Yield: 0.53 g (67%). Anal. Calcd. for
C13H18N4O4Zn: C, 43.41; H, 5.04; N, 15.58; Found: C, 43.19; H,
5.45; N, 15.47%. IR (KBr disk): 3133 (w), 3012 (w), 2942 (w), 2926
(m), 2895 (s), 2834 (s), 2752 (m), 2692 (w), 1629 (s), 1589 (s), 1558
(s), 1469 (m), 1435 (s), 1421 (s), 1384 (s), 1318 (s), 1286 (s), 1233
(m), 1044 (m), 1007 (m), 978 (w), 921 (w), 808 (s), 705 (w), 678
Synthesis of [ZnEt(dmpzm)(OAc)] (2). To a solution of 1
(0.62 g, 1.90 mmol) in 15 mL toluene was added a solution of
HOAc (0.11 mL, 1.90 mmol) at room temperature. After the
evolution of gas ceased, the mixture was stirred overnight and then
filtered. n-Hexane (15 mL) was allowed to diffuse into the filtrate.
Then the white solid of 2 were formed, which were collected by
filtration, washed by dry hexane and dried in vacuo. Yield: 0.59 g
(87%). Anal. Calcd. for C15H24N4O2Zn: C, 50.36; H, 6.76; N, 15.66;
Found: C, 49.69; H, 6.65; N, 15.17%. IR (KBr disk): 3138 (w), 3019
(w), 2962 (w), 2947 (m), 2926 (m), 2890 (s), 2844 (s), 1615 (s), 1579
(s), 1558 (s), 1468 (m), 1445 (s), 1421 (s), 1375 (s), 1322(s), 1286 (s),
1235 (m), 1044 (m), 1004 (m), 973 (w), 920 (w), 810 (s), 706 (w), 678
1
(s), 600 (m), 510 (m) cm-1. H NMR (400 MHz, ppm): (C6D6) d
-8.413 (br, 2H, -HCOO), 5.787 (s, 2H, -CH), 5.614 (s, 2H, -CH2),
2.217 (s, 6H, -CH3), 2.139 (s, 6H, -CH3).
Synthesis
of
[Zn(l4-O)2(ZnEt)6(l3-OAc)4(l¢3-OAc)2{Zn-
(dmpzm)Et}2]·2C7H8 (6·2C7H8). To a solution of 1 (0.93 g,
2.84 mmol) in 15 mL toluene was added HOAc (81.8 mL,
1.42 mmol) at room temperature. Gas evolution was observed.
The solution was stirred at ambient temperature for 30 min. After
this time, gas evolution had ceased, the reaction mixture was
further stirred overnight at room temperature. Then the solution
was reduced in vacuo to 8 mL. Colorless crystals of 6·2C7H8 was
formed by cooling the solution to -26 ◦C for 1 month. Yield:
0.081 g (17%). Anal. Calcd. for C64H106N8O14Zn9: C, 42.70; H,
5.94; N, 6.22; Found: C, 42.56; H, 6.01; N, 6.43%. IR (KBr disk):
3137 (m), 3015 (m), 2979 (m), 2925 (s), 2891 (s), 2844 (s), 1614
(s), 1579 (s), 1557 (s), 1464 (s), 1383 (s), 1353 (s), 1322(s), 1286
(s), 1268 (s), 1235 (m), 1139 (m), 1043 (s), 1005 (s), 985 (m), 971
(m), 953 (m), 920 (m), 827 (m), 810 (s), 783 (s), 776 (m), 673
1
(s), 600 (m), 510 (m) cm-1. H NMR (400 MHz, ppm): (C6D6) d
-5.763(s, 2H, -CH), 5.484(s, 2H, -CH2), 2.238 (s, 6H, -CH3), 2.156
(s, 6H, -CH3), 1.934 (s, 3H -CH3COO), 1.752 (t, 3J = 8.2 Hz, 3H,
-ZnCH2CH3), 0.780 (q, 3J = 10.0 Hz, 2H, -ZnCH2CH3).
Synthesis of [ZnEt(dmpzm)(HCOO)] (3). Compound
3
(0.47 g, 83%) was isolated as colorless crystals from the reaction
of 1 (0.54 g, 1.66 mmol) with HCOOH (62.9 mL, 1.66 mmol) in
10 mL toluene and 10 mL CH3CN followed by a similar workup
to that used in the isolation of 2. Anal. Calcd. for C14H22N4O2Zn:
C, 48.92; H, 6.45; N, 16.30; Found: C, 49.29; H, 6.64; N, 15.93%.
IR (KBr disk): 3132 (w), 3005 (m), 2927 (m), 2903 (m), 2851 (m),
2797 (m), 2720 (m), 2687 (w), 1626 (s), 1593 (s), 1557 (s), 1467 (m),
1425 (s), 1391 (m), 1383 (m), 1312(s), 1286 (s), 1233 (m), 1160 (w),
1150 (w), 1116 (w), 1048 (s), 1005 (w), 985 (w), 922 (w), 828 (m),
812 (m), 780 (s), 703 (m), 679 (s), 630 (m), 601 (s), 506 (m) cm-1.
1H NMR (400 MHz, ppm): (C6D6) d -8.426 (br, 1H, -HCOO),
5.867 (s, 2H, -CH), 5.507(s, 2H, -CH2), 2.196 (s, 6H, -CH3), 2.136
(s, 6H, -CH3), 1.777 (t, 3J = 8.4 Hz, 3H, -ZnCH2CH3), 0.797 (q,
3J = 10.0 Hz, 2H, -ZnCH2CH3).
1
(s), 628 (s), 614 (m), 600 (m), 509 (m), 470 (m) cm-1. H NMR
(400 MHz, ppm): (C6D6) d -5.863(s, 4H, -CH), 5.435(s, 4H,
-CH2), 2.138 (s, 12H, -CH3), 2.106 (s, 12H, -CH3), 2.011 (s, 18H
3
-CH3COO), 1.821 (t, J = 8.0 Hz, 18H, -ZnCH2CH3), 1.731 (t,
3
3J = 12.0 Hz, 6H, -ZnCH2CH3), 0.901 (q, J = 10.0 Hz, 12H,
3
-ZnCH2CH3), 0.720 (q, J = 8.0 Hz, 4H, -ZnCH2CH3). On the
other hand, white solid of 2 was obtained by slowly diffusing
n-hexane (10 ml) into the toluene solution, which were collected
by filtration, washed twice with absolute n-hexane and dried in
vacuo. Yield: 0.19 g (39%).
Synthesis of [Zn4(dmpzm)3Et3(l4-O)] (7).
Synthesis of [Zn(dmpzm)(OAc)2](4). To a solution of 1 (0.69 g,
2.10 mmol) in 25 mL toluene was added HOAc (0.25 mL,
4.20 mmol) at room temperature. Gas evolution was observed.
The solution was stirred at ambient temperature for 40 min. After
this time, the evolution of gas ceased, and the reaction mixture was
further stirred overnight at room temperature and then filtered.
The filtrate was kept at ambient temperature for one week to
form colorless crystals of 4. Yield: 0.68 g (83%). Anal. Calcd. for
C15H22N4O4Zn: C, 46.46; H, 5.72; N, 14.45; Found: C, 46.53; H,
6.05; N, 14.37%. IR (KBr disk): 3129 (w), 3014 (w), 2968 (w),
2937 (m), 2919 (m), 2894 (s), 2837 (s), 1585 (s), 1560 (s), 1463 (m),
1439 (s), 1410 (s), 1390 (s), 1338(m), 1285 (m), 1049 (w), 1018 (w),
967 (w), 923 (w), 829 (m), 682 (s), 627 (m), 479 (w) cm-1. 1H NMR
Method 1. To a solution of 1 (0.85 g, 2.60 mmol) in 10 mL
toluene was added HCOOH (49.3 mL, 1.30 mmol) at room
temperature. After the evolution of gas ceased, some insoluble
white precipitate was formed. The resulting solution was further
stirred overnight at room temperature and then filtered. The filtrate
was kept at -26 ◦C for one month to form colorless crystals of 7.
Yield: 0.15 g (20%). Anal. Calcd. for C39H60N12OZn4: C, 48.06;
H, 6.20; N, 17.25; Found: C, 47.89; H, 6.53; N, 17.44%. IR (KBr
disc): 2945(w), 2923 (m), 2880 (w), 2838 (m), 1555 (s), 1459 (m),
1418 (s), 1384 (s), 1353 (m), 1314(w), 1267 (s), 1211 (w), 1140
(w), 1041 (m), 1033 (m), 971 (w), 922 (w), 844 (w), 805 (m), 776
(s), 713 (w), 673 (s), 628 (w), 587 (m), 470 (s) cm-1. H NMR
1
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Table 1 Crystal data and structure refinement parameters for complexes 1, 3, 4, 6·2C7H8 and 7
Compounds
1
3
4
6·2C7H8
7
Formula
C15H26N4Zn
327.77
Monoclinic
C14H22N4O2Zn
343.73
Triclinic
¯
P1
7.8314(16)
10.326(2)
11.652(2)
106.46(3)
106.65(3)
102.01(3)
821.7(3)
193
C15H22N4O4Zn
387.74
Monoclinic
C64H106N8O14Zn9
1800.08
Monoclinic
C39H60N12OZn4
974.47
Cubic
Formula weight
Crystal system
Space group
P21/n
P21/c
C2/m
P213
˚
a/A
8.3359(17)
14.195(3)
14.467(3)
13.681(3)
8.2077(16)
15.815(3)
23.993(5)
13.776(3)
15.394(3)
16.5114(19)
16.5114(19)
16.5114(19)
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
103.53(3)
97.97
128.64(3)
3
˚
V/A
T/K
Z
1664.4(6)
193
4
1.308
696
1.473
15690
1758.7(6)
193
4
1.464
808
1.423
16535
3974(2)
193
2
1.504
1856
2.725
19491
4501.4(9)
193
4
1.438
2024
2.150
44810
2
Dc/g cm-3
1.389
360
1.504
8100
F(000)
m(Mo Ka)/mm-1
Total reflections
Unique reflections
No. of observations
No. of parameters
Flack parameters
Ra
3023 (Rint = 0.0427)
2983 (Rint = 0.0396)
3215 (Rint = 0.0349)
3781 (Rint = 0.0605)
2757 (Rint = 0.1013)
2451
187
2455
2832
211
3082
232
2654
195
175
0.42(4)
0.0449
0.0986
1.071
0.038
0.107
1.062
0.0557
0.1144
1.097
0.0656
0.1644
1.116
0.064
0.1308
1.139
wRb
GOFc
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
1/2
2
a R = ꢀFo| - |Fc|/ |Fo|. b wR = { w(Fo - Fc2)2/ w(Fo2)2}
p = total number of parameters refined.
.
c GOF = { [w((Fo - Fc2)2)/(n - p)}1/2, where n = number of reflections and
(400 MHz, ppm): (C6D6) d -5.587 (s, 6H, -CH), 5.568(s, 3H,
-CH), 2.277 (s, 18H, -CH3), 2.1149 (s, 18H, -CH3), 1.790 (t, 3J =
8.0 Hz, 9H, -ZnCH2CH3), 0.799 (q, 3J = 8.2 Hz, 6H, -ZnCH2CH3).
On the other hand, the white solid was re-dissolved in MeCN (10
ml) to give a colorless solution. Colorless crystals of 3 were isolated
by cooling the solution to -26 ◦C for one week. Yield: 0.26 g (35%).
transmission factors ranging from 0.452 to 0.643 for 1, from 0.416
to 0.796 for 3, from 0.572 to 0.655 for 4, from 0.410 to 0.612 for
6·2C7H8, from 0.466 to 0.631 for 7. The reflection data were also
corrected for Lorentz and polarization effects.
The structures of 1, 3, 4, 6·2C7H8, and 7 were solved by
direct methods and refined by full matrix least-squares on F2.8
In the case of 6·2C7H8, one Zn atom and two C atoms from an
acetyl group were found to be disordered over two sites with an
occupancy factor of 0.48/0.52 for Zn(1)/Zn(1A), C(11)/C(11A)
and C(12)/C(12A). Because the single crystal used rapidly lost
solvent upon removal from its mother liquor and thus was
weakly diffracting, especially at high angles, those from toluene
solvent molecule and C(9) in 6·2C7H8 were refined isotropically.
All other non-H atoms in these five compounds were refined
anisotropically. All hydrogen atoms were placed in geometrically
Method 2. To a solution of 1 (0.88 g, 2.68 mmol) in 15 mL
toluene was added a solution of H2O (0.67 mmol) in THF
(0.13 mL) at room temperature. After the evolution of gas ceased,
the mixture was stirred overnight and then filtered. The filtrate
was kept at room temperature for 3 days to form colorless crystals
of 7. Yield: 0.57 g (87%).
X-Ray crystallography
˚
idealized positions (C–H = 0.98 A for methyl groups, C–H =
All measurements were made on a Rigaku Mercury CCD X-ray
diffractometer (3 kV, sealed tube) at 193 K by using graphite
˚
˚
0.99 A for methylene groups or C–H = 0.95 A for phenyl groups)
and constrained to ride on their parent atoms with Uiso(H) =
1.2Ueq(C), or 1.5 Ueq(C) for methyl groups. All the calculations
were performed on a Dell workstation using the CrystalStructure
crystallographic software package (Rigaku and MSC, Ver.3.60,
2004). A summary of the important crystallographic information
for 1, 3, 4, 6·2C7H8, and 7 are tabulated in Table 1.
˚
monochromated Mo Ka (l = 0.71073 A). Single crystals of 1, 3, 4,
6·2C7H8 and 7 were obtained directly from the above preparations.
A colorless chunk of 1 with dimensions 0.55 ¥ 0.50 ¥ 0.30 mm,
a colorless chunk of 3 with dimensions 0.60 ¥ 0.20 ¥ 0.15 mm,
a colorless prism of 4 with dimensions 0.40 ¥ 0.40 ¥ 0.30 mm, a
colorless prism of 6·2C7H8 with dimensions 0.36 ¥ 0.20 ¥ 0.18 mm,
a colorless prism of 7 with dimensions 0.40 ¥ 0.30 ¥ 0.21 mm were
mounted into a glass capillary. Diffraction data were collected
at w mode with a detector distance of 35 mm to the crystals. A
total of 720 oscillation images for each were collected in the range
Results and discussion
Synthetic and spectral aspects
6.40◦ < 2q < 50.60◦ for 1, 6.82◦ < 2q < 50.69◦ for 3, 6.01◦
<
2q < 50.69◦ for 4, and 6.40◦ < 2q < 50.69◦ for 6·2C7H8, 6.04◦ <
2q < 50.69◦ for 7. The collected data were reduced by using the
program CrystalClear (Rigaku and MSC, Ver. 1.3, 2001), and an
absorption correction (multi-scan) was applied, which resulted in
As shown in Scheme 1, complex 1 was prepared in 76% yield
from reactions of the solution of ZnEt2 in hexane with equimolar
dmpzm in THF. Treatment of 1 with HOAc in a 1 : 1 or 1 : 2
molar ratio afforded colorless crystals of 2 in 87% yield and 4 in
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Scheme 1
1
83% yield. Under similar conditions the use of HCOOH led to
the formation of analogous products 3 (78% yield) and 5 (72%
yield). Intriguingly, treatment of a toluene solution of 1 with
1/2 equiv. of HOAc at ambient temperature produced not only
colorless crystals of 2 in 39% yield, but also a rare nonanuclear
zinc carboxylate oxide complex 6 in 17% yield. The preparation
for 6 was reproducible, though its yield was always relatively low.
Similarly, reactions of 1 with 1/2 equiv. of HCOOH formed 3 in
35% yield and a tetranuclear carboxylate oxide complex 7 in 20%
yield. This complex could also be isolated in 87% yield from the
reactions of 1 with 1/4 equiv. of water in toluene/THF.
1, 2, 3, 6 and 7 were highly air and moisture sensitive, and were
readily soluble in toluene, THF, DME, MeCN, while 4 and 5 were
soluble in DME, THF, toluene, and MeCN. Elemental analyses of
1–7 were consistent with the formulas. The 1H NMR spectrum of
1 showed the methyl and methylene protons of ethyl groups at d =
1.565 and 0.636 ppm. Other peaks can be assigned to be those of
the dmpzm ligand. In the 1H NMR spectra of 2 and 3, resonances
related to the methyl and methylene protons of the ethyl group
were at d = 1.752/0.780 ppm (2) and d = 1.777/0.797 ppm (3).
For 2 and 4, a singlet realted to the OAc group was observed at
d = 1.934 ppm (2) and 1.905 ppm (4) while a broad singlet at d =
8.426 ppm (3) or 8.133 ppm (5) may ascribed to the proton of
HCOO- group. In the 1H NMR spectrum of 6, two sets of signals
(d = 1.821/0.901 and 1.731/0.720 ppm) were observed due to the
two different ethyl groups while one singlet at d = 2.011 ppm was
assigned to be the methyl protons of the OAc group. In the H
NMR spectrum of 7, two signals at d = 1.790 and 0.799 ppm were
assigned to be the methyl and methylene protons of the Et group.
Besides, the singlet at d = 5.568 ppm belongs to the deprotonated
methylene group of the dmpzm ligands. The identities of 1, 3, 4, 6
and 7 were further confirmed by X-ray analysis.
Crystallography
Crystal structure of 1. Compound 1 crystallizes in the mono-
clinic space group P21/n and the asymmetric unit contains one
[Zn(dmpzm)Et2] molecule. The Zn center of 1 is tetrahedrally
coordinated by two N atoms from one dmpzm ligand and two
C atoms from two Et groups (Fig. 1a). The mean Zn–C bond
2
˚
distance (2.000(3) A) (Table 2) is close to that in [{h -B(3-
Bu pz)2}ZnC(CH3)3] (3-Bu pz = 3-C3N2Bu H2, 1.995(7) A).4c The
t
t
t
˚
˚
mean Zn–N bond length is 2.267(3) A, which is comparable
to that of the corresponding one of [(tmeda)ZnEt2] (temda =
9
˚
N,N,N¢,N¢-tetramethylenediamine, 2.294(5) A), and somewhat
2
t
4c
˚
longer than that in [{h -B(3-Bu pz)2}ZnC(CH3)3] (2.042(5) A).
The adjacent [Zn(dmpzm)Et2] molecules are stacked in a face-to-
˚
face fashion with a separation of 3.651 A between the centroids of
the two pyrazolyl rings, indicating the existence of the significant
intermolecular p–p interactions.
Crystal structure of 3. Compound 3 crystallizes in the triclinic
space group P1 and the asymmetric unit of 3 contains one
¯
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◦
˚
Table 2 Selected bond distances (A) and angles ( ) for 1, 3, 4, 6·2C7H8
and 7
Compound 1
Zn(1)–C(12)
1.998(4) Zn(1)–C(14)
2.003(3)
Zn(1)–N(1)
2.263(3) Zn(1)–N(3)
2.271(3)
C(12)–Zn(1)–C(14)
C(14)–Zn(1)–N(1)
C(14)–Zn(1)–N(3)
138.89(15)C(12)–Zn(1)–N(1)
104.00(12)C(12)–Zn(1)–N(3)
105.19(12)N(1)–Zn(1)–N(3)
108.76(13)
102.34(15)
83.94(10)
Compound 3
Zn(1)–C(12)
1.975(5) Zn(1)–O(1)
2.098(4) Zn(1)–N(4)
119.94(18)C(12)–Zn(1)–N(1)
96.58(13) C(12)–Zn(1)–N(4)
97.37(13) N(1)–Zn(1)–N(4)
1.997(3)
2.106(3)
124.5(2)
123.04(19)
87.60(13)
Zn(1)–N(1)
C(12)–Zn(1)–O(1)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(4)
Compound 4
Zn(1)–O(3)
1.946(5) Zn(1)–O(1)
2.081(4) Zn(1)–N(3)
136.8(2) O(3)–Zn(1)–N(1)
97.14(17) O(3)–Zn(1)–N(3)
102.17(19)N(1)–Zn(1)–N(3)
1.955(5)
2.110(4)
116.4(2)
104.67(18)
88.88(15)
Zn(1)–N(1)
O(3)–Zn(1)–O(1)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(3)
Compound 6·2C7H8
Zn(1)–C(8)
1.956(9) Zn(1)–O(1)
2.085(5) Zn(4A)–C(10)
1.957(5) Zn(2)–O(4)
1.940(4) Zn(3)–C(14)
2.089(3) Zn(4)–C(11)
2.031(3) Zn(4)–O(2)
1.885(4) Zn(4A)–C(11A)
2.037(5)
2.520(10)
2.178(4)
1.974(7)
1.898(15)
2.199(8)
1.934(14)
121.5(3)
95.67(17)
95.67(17)
180.0(3)
180.0(2)
90.9(3)
Zn(1)–N(1)
Zn(2)–O(3)
Zn(3)–O(3)
Zn(3)–O(5)
Zn(4)–O(3)
Zn(4)a–O(3)
O(3)–Zn(4A)–O(2)a
C(8)–Zn(1)–N(1)a
C(8)–Zn(1)–N(1)
N(1)a–Zn(1)–N(1)
O(3)–Zn(2)–O(4)
O(3)–Zn(2)–O(4)e
O(3)–Zn(2)–O(4)a
O(3)b–Zn(2)–Zn(4A)
O(4)e–Zn(2)–Zn(4A)
O(3)–Zn(2)–Zn(4A)b
O(4)–Zn(2)–Zn(4A)
O(4)–Zn(2)–Zn(4A)e
O(3)b–Zn(2)–Zn(4)
O(4)e–Zn(2)–Zn(4)
Zn(4A)b–Zn(2)–Zn(4)
Zn(4A)e–Zn(2)–Zn(4)
Zn(4A)–Zn(2)–Zn(4)b
O(3)–Zn(3)–O(5)
O(5)–Zn(3)–O(5)a
C(11)–Zn(4)–O(4)b
C(11)–Zn(4)–O(2)
O(4)b–Zn(4)–O(2)
O(2)–Zn(4)–Zn(2)
O(2)–Zn(4A)–C(11A)
C(11A)–Zn(4A)–O(2)a
C(11A)–Zn(4A)–O(4)b
85.6(2)
C(8)–Zn(1)–O(1)
122.40(18)O(1)–Zn(1)–N(1)a
122.40(18)O(1)–Zn(1)–N(1)
91.7(3)
O(3)b–Zn(2)–O(3)
96.51(14) O(4)b–Zn(2)–O(4)
83.49(14) O(4)–Zn(2)–O(4)e
96.51(14) O(4)–Zn(2)–O(4)a
142.42(10)O(4)–Zn(2)–Zn(4A)
83.29(16) O(4)a–Zn(2)–Zn(4A)
89.1(3)
134.05(11)
96.71(16)
142.42(10)Zn(4A)–Zn(2)–Zn(4A)b 180.0(14)
96.71(16) O(3)–Zn(2)–Zn(4A)e
142.42(10)
83.29(16) Zn(4A)–Zn(2)–Zn(4A)e 131.32(16)
138.55(8) O(4)–Zn(2)–Zn(4)
97.18(15) O(4)a–Zn(2)–Zn(4)
135.05(10)
82.82(15)
166.04(3) Zn(4A)a–Zn(2)–Zn(4) 61.22(15)
118.78(15)O(3)–Zn(2)–Zn(4)b
166.04(3) O(3)–Zn(3)–C(14)
102.42(13)C(14)–Zn(3)–O(5)
138.55(8)
124.1(3)
113.03(16)
146.2(5)
82.71(18)
80.1(2)
Fig. 1 (a) Molecular structure of 1. (b) Molecular structure of 3.
(c) Molecular structure of 4. The thermal ellipsoids are drawn at the 50%
probability level and all H atoms are omitted for charity.
98.3(2)
C(11)–Zn(4)–O(3)
122.4(5) O(3)–Zn(4)–O(4)b
120.7(5) O(3)–Zn(4)–O(2)
85.5(3)
92.2(2)
C(11)–Zn(4)–Zn(2)
O(2)–Zn(4A)–O(3)
145.9(5)
107.1(3)
monomeric [ZnEt(dmpzm)(HCOO)] molecule. The Zn center is
tetrahedrally coordinated by two N atoms from the dmpzm
ligand, an ethyl group and a monodentate acetate group (Fig. 1b).
109.3(5) O(3)–Zn(4A)–C(11A) 131.1(5)
126.9(5) O(3)–Zn(4A)–O(4)b
85.56(18)
113.9(5) O(2)–Zn(4A)–Zn(4A)a 58.3(2)
C(11A)–Zn(4A)–Zn(4A)a 148.5(5) O(3)–Zn(4A)–C(10)
125.1(3)
93.3(3)
111.3(3)
94.4(2)
˚
The mean Zn–N bond length (2.102(3) A) is in-between that
C(11A)–Zn(4A)–C(10)
99.3(5)
O(4)b–Zn(4A)–C(10)
O(2)–Zn(4A)–Zn(2)
of the thermolysin7e (2.09 A) and that of 1 while the Zn–O
˚
Zn(4A)a–Zn(4A)–C(10) 77.3(2)
˚
˚
length (1.997(3) A) is shorter than that in thermolysin (2.08 A).
C(11A)–Zn(4A)–Zn(2)
C(10)–Zn(4A)–Zn(2)
138.6(5) O(2)a–Zn(4A)–Zn(2)
115.5(3) O(2)–Zn(4A)–O(4)b
The Zn–C length is close to those of 1. The Zn–O distance
106.0(3)
2
t
˚
(1.997(3) A) is close to those in [{h -H2B(3-Bu pz)2}Zn(m-OH)]3
Compound 7
4c
Zn(1)–C(12)
1.968(8) Zn(1)–O(1)
2.138(7) Zn(1)–N(4)
1.986(8) Zn(2)–C(6)
121.9(4) C(12)–Zn(1)–N(1)
106.2(2) C(12)–Zn(1)–N(4)
1.975(5)
2.143(6)
2.074(7)
119.0(3)
120.4(4)
84.8(2)
105.57(19)
105.57(19)
113.07(16)
˚
(1.909(21) A). In the crystal of 3, an intramolecular hydrogen
Zn(1)–N(1)
Zn(2)–O(1)
bonding interaction between the coordinated O atom of the
HCOO group and the methylene group, and two intermolecular
hydrogen bonding interactions between the uncoordinated O atom
of the HCOO group and methyl group, methylene group of
the dmpzm ligand producing a dimer of 3. The distances of
these hydrogen bonds are in the range of 2.29–2.54 A, which
are comparable to those found in zinc enzymes.10 The adjacent
[ZnEt(dmpzm)(HCOO)] molecules are also stacked in a face-to-
face fashion with a separation of 3.677 A between the centroids of
C(12)–Zn(1)–O(1)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(4)
O(1)–Zn(2)–C(6)d
C(6)d–Zn(2)–C(6)
C(6)d–Zn(2)–C(6)e
97.0(2)
N(1)–Zn(1)–N(4)
105.57(19)O(1)–Zn(2)–C(6)
113.07(16)O(1)–Zn(2)–C(6)e
113.07(16)C(6)–Zn(2)–C(6)e
˚
a x, -y + 1, z. b -x + 1, -y + 1, -z. c -x + 1, y, -z. d -z + 3/2, -x + 1, y +
1/2. e -y + 1, z-1/2, -x + 3/2.
˚
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the two pyrazolyl rings, indicating the existence of the significant
intermolecular p–p interactions.
Crystal structure of 4. Compound 4 crystallizes in the mon-
oclinic space group P21/c and the asymmetric unit of 4 consists
of one monomeric [Zn(dmpzm)(OAc)2] molecule. The Zn atom
is coordinated by a dmpzm ligand and a pair of monodentate
acetate groups, forming a distorted tetrahedral ZnN2O2 geometry
(Fig. 1c), which closely resembles those of the zinc active sites in
zinc enzymes.3a,b,7 The average Zn–N and Zn–O bond lengths in
˚
˚
4 (2.096(4) A vs 1.950(5) A) are slightly shorter than those of the
corresponding ones in 3. In the crystals of 4, two intramolecular H
bonding interactions between the coordinated O atoms of the OAc
groups and the methyl group or the methylene group, and three
intermolecular H bonding interactions between the uncoordinated
O atoms of the OAc groups and the pyrazolyl C–H group of
the dmpzm ligand, and the methyl groups and, affording a 3D
hydrogen-bonded network. The distances of these hydrogen bonds
Fig. 3 View of the [Zn7(m4-O)2] skeleton of 6 showing the vertex shared
double tetrahedron.
by two m4-O atoms (occupying the axial positions) and four O
atoms from four acetate groups (locating on the equatorial plane),
thus forming a distorted octahedral coordination geometry. Such
a [Zn7(m4-O)2] double tetrahedron core in 6 resembles those found
in the known discrete complexes12 and polymeric structures.13 The
difference between the [Zn7O2(RCO2)10] motif in those reported
complexes and the [Zn(m4-O)2(ZnEt)6(m3-OAc)4] core in 6 is that
the former has ten caboxylate groups around its Zn7(m4-O)2 core
while the peripheral ligation around the latter core is provided by
four acetate groups along with six ethyl groups.
For each Zn(m4-O)(ZnEt)3 unit, a m4-O3 or m4-O3A atom
connects Zn2 and three ZnEt fragments. Each Zn in these ZnEt
fragments exhibit a distorted tetrahedral environment and is
saturated by an ethyl group and two O atoms from acetate groups.
For each [Zn(dmpzm)Et]+ fragment, Zn1 or Zn1A is tetrahedrally
coordinated by a C atom from ethyl groups and a O atom from
acetate group and two N atoms from dmpzm groups. It is noted
that there are two kinds of triply-bridging OAc ligands. One links
Zn2, Zn3A, Zn4 (or Zn4A) or Zn2, Zn3, Zn4B (or Zn4C) while
the other disordered over two positions and bridges Zn1, Zn4 (or
Zn4A) or Zn1A, Zn4B (or Zn4C). The mean Zn–N, Zn–O znd
Zn–C bond lengths are normal.
˚
are in the range of 2.40–2.50 A, which are comparable to those
found in zinc enzymes.10
Crystal structure of 6·2C7H8. Compound 6·2C7H8 crystal-
lizes in the monoclinic space group C2/m and its asymmet-
ric unit contains one-fourth of a [Zn(m4-O)2(ZnEt)6(m3-OAc)4(m¢3-
OAc)2{Zn(dmpzm)Et}2] molecule and one-half of one toluene
solvent molecule. This molecule has a mirror plane going through
the Zn1, O1, C6, C7, C8, Zn2, O3, Zn3, C13, C14, and their
symmetry-related atoms (Fig. 2). It consists of a heptanuclear
[Zn(m4-O)2(ZnEt)6(m3-OAc)4] core and two [Zn(dmpzm)Et]+ frag-
ments that are held together by a pair of m¢3-OAc ligands. To
our knowledge, such a polynuclear Zn structure in 6 is un-
precedented, though several other nonanuclear zinc complexes3a,11
i
such as [Zn6{(RNH)3(RN)3P3N3}2Zn3O3] (R = Bu, nPr)3a and
[Zn9(2poap-2H)3(2poap-H)3](NO3)9 (2poap = 2,6-bis(4-amino-
4-(pyrid-2-yl)-1-oxy-2,3-diazabuta-1,3-dienyl)pyridine)11a were re-
ported. The former example contains a planar (ZnO)3 ring between
two cyclic hexamer [Zn3{(RNH)3(RN)3P3N3}] fragments, while
the latter has a [Zn9(m-O)12] plane.
Crystal structure of 7. Compound 7 crystallizes in the cubic
space group P213 and its asymmetric unit has one-third of a
[Zn4(m4-O)(dmpzm)3Et3] molecule. The whole molecule possesses
a C3 axis running along the Zn2–O1 bond (Fig. 4). The m4-O
atom lies at the center of the Zn4 tetrahedron and interacts with
four Zn atoms, with Zn–m4-O lengths ranging from 1.974(2) to
˚
1.986(8) A. The Zn4(m4-O) tetrahedron is slightly irregular with
˚
the Zn ◊ ◊ ◊ Zn distances being between 3.167 and 3.284 A. Each Zn
atom in this tetrahedron displays a distorted tetrahedral geometry.
Zn1, Zn1A or Zn1B is saturated by two N atoms from dmpzm
ligands and an ethyl group, while Zn2 binds to three C atoms
from the methylene group of the three dmpzm ligands. This is
quite unusual that one methylene proton of the dmpzm ligand
was removed during the reactions. The Zn2–C6 bond distance
Fig. 2 Perspective view of 6 showing 30% thermal probability ellipsoids.
The disordered moieties, solvent molecules and hydrogen atoms are
omitted for charity.
˚
˚
(2.074(7) A) is longer than that of Zn1–C12 bond (1.968(8) A),
The [Zn(m4-O)2(ZnEt)6(m3-OAc)4] core in 6 has a [Zn7(m4-
O)2] double tetrahedron core in which two tetrahedral Zn(m4-
O)(ZnEt)3 units share a vertex via the Zn2 atom and are linked
by four m3-OAc bridges (Fig. 3). The central Zn2 is coordinated
but within the range for Zn–C-alkyl distances.9 The mean Zn–N
˚
bond length (2.140(6) A) is somewhat shorter than that in 1. The
adjacent [Zn4(m4-O)(dmpzm)3Et3] molecules are stacked in a face-
to-face fashion with a separation of 3.684 A between the centroids
˚
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SooChow Scholar Program and Program for Innovative Research
Team of Suzhou University. We are grateful to the editor and the
reviewers for their helpful suggestions.
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Fig. 4 Perspective view of 7 showing 30% thermal probability ellipsoids.
All hydrogen atoms are omitted for charity.
of the two pyrazolyl rings, showing the existence of the significant
intermolecular p–p interactions.
For 6 and 7, two important phenomena deserve comment. One
is that both contain one or two m4-O atoms in their structures.
These m4-O atoms may be derived from the small amount of water
in organic acids used in the reactions. In fact, the direct addition
of 1/4–1/10 equiv. of water into the mixture of 1 and acetic acid
always produced 6 in low yields, while 7 could be readily obtained
in relative high yields from reactions of 1 with 1/4–1/8 equiv. of
H2O in toluene. The other is that during the protonolysis reaction
some Zn centers still retained one Et group while some lost the
dmpzm ligand. In 6, the central Zn2 atom lost two Et groups and
the dmpzm ligands while Zn3 and Zn4 and their symmetry-related
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group and one dmpzm ligand. In 7, the central Zn2 lost all Et
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Conclusions
In this paper, we have demonstrated that the protonolysis reaction
of 1 with acetic or formic acid was stoichiometric-dependent.
Only the 1 : 2 mixture of 1 and the acid could afford the desired
[ZnN2O2] complexes (4 and 5) while those with other molar ratios
could produce mononuclear complexes (2 and 3) and polynculear
complexes (6 and 7). These results may provide interesting insight
into the reactivity of similar alkylzinc complexes toward acids and
a useful route to other zinc model complexes mimicking the active
sites in some zinc-containing enzymes.
Acknowledgements
8 G. M. Sheldrick, SHELXS-97 and SHELXL-97, Program for the X-ray
Crystal Structure Solution, University of Go¨ttingen, Germany,
1997.
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This work was supported by the National Natural Science
Foundation of China (20525101 and 20871088), and the State Key
Laboratory of Organometallic Chemistry of Shanghai Institute
of Organic Chemistry (08–25), the Qing-Lan Project, and the
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This journal is
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View Article Online
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