Binuclear magnesium, calcium, and zinc complexes based on nitrogen-nitrogen-coupled salicylaldiminate and ss-diketiminate ligands

Article abstract of DOI:10.1002/ejic.200900435

The diprotic bis(salicylaldimine) ligand N,N′-bis(3,5-di- tBusalicylidene)diimine, (1-NN)H₂, was smoothly deprotonated by reaction with two equivalents of a metal amide M[N(SiMe₃) ₂]2 (M = Mg, Ca or Zn) to form a bimetalli

Full text of DOI:10.1002/ejic.200900435

FULL PAPER
DOI: 10.1002/ejic.200900435
Binuclear Magnesium, Calcium, and Zinc Complexes Based on
Nitrogen–Nitrogen-Coupled Salicylaldiminate and β-Diketiminate Ligands
Dirk F. -J. Piesik,[a] Robert Stadler,[a] Sven Range,[a] and Sjoerd Harder*[a]
Keywords: Alkaline earth metals / Magnesium / Calcium / Zinc / Bimetallic complexes
The diprotic bis(salicylaldimine) ligand N,NЈ-bis(3,5-di-tBu-
salicylidene)diimine, (1-NN)H2, was smoothly deprotonated
tonated only under much harsher reaction conditions. At-
tempted synthesis of (2-NN)[Mg(nBu)]2 gave after ligand ex-
change the homoleptic species (2-NN)Mg and Mg(nBu)2. For
Ca, the complexes [(2-NN)Ca]2 and (2-NN)[CaN(SiMe3)2·
thf]2 both have been prepared and structurally characterized
by X-ray diffraction. The latter heteroleptic complex is in
by reaction with two equivalents of
a metal amide
M[N(SiMe3)2]2 (M = Mg, Ca or Zn) to form a bimetallic metal
amide complex (1-NN)[MN(SiMe3)2]2. This heteroleptic com-
plex was only stable in the case of Mg and (1-
NN)[MgN(SiMe3)2·thf]2 was structurally characterized by X- benzene solution in equilibrium with [(2-NN)Ca]2 and Ca[N-
ray diffraction. For Ca and Zn homoleptic products could be
obtained: (1-NN)Ca·(thf)2 and (1-NN)Zn. The latter crys-
tallized as a trimer with approximate C3-symmetry. The di-
protic N–N coupled bis(β-diketimine) ligand [RHN–
C(Me)=C–C(Me)=N–N=C(Me)–C=C(Me)–NHR, R = 2,6-di-
(SiMe3)2]2·(thf)2. Reaction of (2-NN)H2 with excess of Et2Zn
gave the heteroleptic complex (2-NN)[ZnEt]2 and is stable
towards ligand exchange reactions. The complex is not
active in CO2/cyclohexene oxide copolymerization.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
iPr-C6H3], which is abbreviated as (2-NN)H2, can be depro- Germany, 2009)
Here we introduce a series of Mg, Ca and Zn complexes
Introduction
in which anionic salicylaldiminate or β-diketiminate units
are directly connected through N–N bonding. Lack of a
bridging spacer in these ligands, which in their protonated
form are abbreviated as (1-NN)H2 and (2-NN)H2
(Scheme 1), could give rise to very small metal···metal dis-
tances. The influence of this direct connection on the struc-
tures of the metal complexes, and its possible consequences
for Schlenk equilibria and for catalytic CO2/cylohexene ox-
ide copolymerization, are discussed.
The increasing interest in bimetallic catalysis[1] and in the
use of benign and cheap main-group metal catalysts[2]
prompted us to introduce various bis(salicylaldiminate)[3]
and bis(β-diketiminate)[4] complexes of group 2 metals (Mg,
Ca) and the group 12 metal Zn. The N,O- or N,N-chelating
mono-anionic units in our ligands are connected through a
variety of rigid spacers (Scheme 1; ligands are abbreviated
according to the bridge). The nature of this bridging spacer
not only tunes the metal···metal distances but also the elec-
tronic properties.
Results and Discussion
Bis(salicylaldiminate)metal Complexes
The bis(salicylaldimine) ligand (1-NN)H2 has been pre-
pared according to a literature procedure[5] that involves
condensation of two equivalents of 3,5-di-tBu-salicylalde-
hyde with one equivalent of hydrazine. Such O,N,N,O-li-
gands have been used earlier in the chemistry of various
metals (Ti, Ru, Fe, Cu and Zn)[6] but hitherto no binuclear
alkaline-earth metal complexes have been described. We are
particularly interested in heteroleptic complexes of the type
(1-NN)[MR]2 in which M is either Mg, Ca or Zn and R is
a reactive group (amide or alkyl) for catalytic activity.
Like the other diprotic bis(salicylaldimine) ligands in
Scheme 1, (1-NN)H2 reacts smoothly with two equivalents
of Mg[N(SiMe3)2]2·(thf)2 to the bimetallic heteroleptic
Scheme 1.
[a] Anorganische Chemie, Universität Duisburg-Essen,
Universitätsstraße 5–7, 45117 Essen, Germany
E-mail: sjoerd.harder@uni-due.de
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D. F. -J. Piesik, R. Stadler, S. Range, S. Harder
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Scheme 2.
magnesium amide complex (1-NN)[MgN(SiMe3)2·thf]2 chelated by two O and two N atoms of one single O,N,N,O-
(Scheme 2). This complex is, also in benzene solution, stable ligand and solvated by two thf ligands. The (1-NN)Ca·
against ligand exchange by the Schlenk equilibrium. Yellow (thf)2 molecules dimerize by mutual Ca···N–N bonding
crystals could be obtained from cold hexane. The crystal (Scheme 2). Although a detailed structure description can
structure shows a crystallographically centrosymmetric not be given at this stage, the eightfold coordination of Ca2+
molecule (Figure 1, a). The center of inversion on the N–N illustrates its considerable size. The latter is responsible for
axis renders both nearly flat salicylaldiminate units copla- the ligand distribution reactions that often plague organ-
nar and gives rise to a trans-geometry. This contrasts with ocalcium chemistry[13] and also have been observed for (1-
the structure of (1-PARA)[MgN(SiMe3)2·thf]2 which crys- PARA)[CaN(SiMe3)2·(thf)2]2.[4]
tallized with C2 symmetry and perpendicularly oriented sal-
Likewise, reaction of (1-NN)H2 with two equivalents of
icylaldiminate units.[4] Despite this trans-conformation, the Zn[N(SiMe3)2]2 gave exclusively access to the homoleptic
Mg···MgЈ distance of 5.2276(9) Å in (1-NN)[MgN(SiMe3)2· species (1-NN)Zn. Similar problems have been observed for
thf]2 is shorter than that in (1-PARA)[MgN(SiMe3)2·thf]2 the other bridged salicylaldiminate ligands in Scheme 1.
[8.186(2) Å]; this is due to lack of a spacer unit. Other se- Different than (1-PYR)Zn, which through self-organization
lected bond lengths and angles (Table 1) are comparable.
formed a cyclic tetramer,[4] the current complex crystallized
Reaction of (1-NN)H2 with two equivalents of Ca[N- as the cyclic trimer [(1-NN)Zn]3 (Figure 1, b–c). The asym-
(SiMe3)2]2·(thf)2 in THF gave an immediate colour change metric unit contains two trimers, which essentially show
from yellow to red and overnight large orange-red crystal- equal geometries. Although the overall structure is roughly
line blocks of (1-NN)Ca·(thf)2 crystallized. The poor solu- C3-symmetric, merely crystallographic C2-symmetry can be
bility and precipitation of this product directs the Schlenk observed. The Zn···ZnЈ distances, however, are in a very
equilibrium to the homoleptic side. Crystals of (1-NN)- narrow range of
4.8126(8)–4.8483(7) Å [average:
Ca·(thf)2 are of poor quality and additional twinning prob- 4.8328(8) Å]. Like in [(1-PYR)Zn]4, each Zn atom coordi-
lems result in a structure determination that only allows for nates to two mutual perpendicular N,O-chelating ligands, a
a qualititative description. The Ca2+ ion in this complex is structural motiv that allows for formation of cyclic aggre-
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Binuclear Magnesium, Calcium, and Zinc Complexes
the preparation of our previously published bis(β-diket-
imine) ligands:[4] i.e. stepwise reaction of (2,6-iPr2–C6H3)-
–
N=C(Me)–CH=C(Me)–OH with Et3O+BF4 followed by
the addition of 0.5 equiv. of the diamine (hydrazine). Al-
though a large variety of connected β-diketimine ligands
has been reported,[5,8] this particular linkage of ligands was
hitherto unknown.
The crystal structure of (2-NN)H2 shows a non-crystallo-
graphically centrosymmetric molecule (Figure 2). The
acidic hydrogen atoms, which could be located and have
been refined, are connected to the outer nitrogen atoms and
form strong N–H···N hydrogen bridges to the inner imine
nitrogen atoms. This results in extended conjugation
(RHN–C=C–C=N–N=C–C=C–NHR) which is responsible
for the coplanarity of the two β-diketimine units and the
short N–N bond of 1.389(3) Å. The C–N and C–C bond
lengths and alternation in (2-NN)H2 is comparable to that
in
the
unlinked
(2,6-iPr2C6H3)NH–C(Me)=C(H)–
C(Me)=N(2,6-iPr2C6H3) (DIPP-nacnacH).[9]
The reaction of the bis(β-diketimine) ligand (2-NN)H2
with two equivalents of Mg[N(SiMe3)2]2·(thf)2 is very slug-
gish and, even at elevated temperatures, proceeds slowly. In
benzene at 70 °C, we observed after three days only 15%
mono-deprotonation. This contrasts strongly with the reac-
tivity of the corresponding unbridged β-diketimine ligand
(DIPP-nacnacH) which in toluene at 80 °C was fully depro-
tonated by Mg[N(SiMe3)2]2·(thf)2 overnight.[10] The ex-
tended conjugation of C=C and C=N bonds in (2-NN)H2
should make this ligand more acidic. Therefore, the reluc-
tance of (2-NN)H2 to be deprotonated might be attributed
to steric shielding of the acidic N–H. Twofold deproton-
ation of the ligand with the stronger base (nBu)2Mg gave,
instead of (2-NN)[Mg(nBu)]2, the homoleptic complex (2-
NN)Mg.
Even deprotonation of (2-NN)H2 with the considerably
more reactive Ca[N(SiMe3)2]2·(thf)2 is slow: in benzene at
80 °C reaction times of 3 days are needed. Use of the polar
solvent THF did not give a significant acceleration of this
deprotonation reaction. The desired product, the heterolep-
tic dinuclear complex (2-NN)[CaN(SiMe3)2·thf]2, is not
stable towards ligands exchange and only homoleptic (2-
NN)Ca could be isolated as
a crystalline product
(Scheme 3). Despite the poor crystal quality we have been
able to reveal its structure as the dimer [(2-NN)Ca]2 (Fig-
ure 3, b). This dimer, of approximate D2 symmetry, does
not show any crystallographic symmetry. The N–Ca bonds
to the outer N atoms in the ligand [average: 2.375(5) Å] are
slightly longer than those to the inner N atoms [2.330(5) Å].
The β-diketiminate units within one ligand are oriented
nearly perpendicular in respect to each other [75.2(3)° and
85.6(4)°]. This results in rather long N–N bonds of 1.446(6)
and 1.457(7) Å [cf. 1.389(3) Å in (2-NN)H2]. The Ca···CaЈ
distance measures 4.341(3) Å.
Figure 1. Crystal structures (hydrogen atoms omitted for clarity) of
(a) (1-NN)[MgN(SiMe3)2·thf]2 (b) [(1-NN)Zn]3 (tBu groups omit-
ted for clarity); view direction perpendicular on the crystallo-
graphic twofold rotation axis and (c) [(1-NN)Zn]3; view along the
approximate threefold axis. Selected geometric parameters for both
structures have been summarized in Table 1.
gates.[7] The average metal–ligand bond lengths and angles
in [(1-NN)Zn]3, given in Table 1, compare well to those in
[(1-PYR)Zn]4.
The attempted synthesis of the comparable mononuclear
complex (DIPP-nacnac)CaN(SiMe3)2·thf by reaction of a
DIPP-nacnacH with Ca[N(SiMe3)2]2·(thf)2 also gave im-
Bis(β-diketiminate)metal Complexes
The N,N-coupled bis(β-diketimine) ligand (2-NN)H2 can pure products on account of ligand distribution reac-
be prepared by a standard condensation route also used for tions.[11] In this case the desired product could be obtained
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D. F. -J. Piesik, R. Stadler, S. Range, S. Harder
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Table 1. Selected bond lengths [Å] and angles [°] for the bimetallic complexes; numbers given in ϽbracketsϾ represent average values.
(1-NN)[MgN(SiMe3)2·thf]2
Mg1–N1
Mg1–N2
Mg1–O1
Mg1–O2
2.134(2)
1.978(2)
1.885(2)
2.041(12)[a]
N1–Mg1–O1
N2–Mg1–O2
N1–Mg1–N2
O1–Mg1–N2
90.41(7)
115.9(4)[a]
121.9(1)
126.5(1)
O1–Mg1–O2
N1–Mg1–O2
100.9(4)[a]
94.3(4)[a]
[(1-NN)Zn]3
Zn–O
Zn–N
1.872(3)–1.888(3) Ͻ1.879(3)Ͼ
2.018(3)–2.030(3) Ͻ2.022(3)Ͼ
O–Zn–OЈ
N–Zn–NЈ
122.1(1)–123.8(1) Ͻ123.1(1)Ͼ
98.9(1)–101.2(2) Ͻ100.0(1)Ͼ
(2-NN)[CaN(SiMe3)2·thf]2
Ca1–N1
Ca1–N2
Ca1–N3
Ca1–O1
2.369(2)
N1–Ca1–N2
N1–Ca1–N3
N2–Ca1–N3
82.6(1)
113.9(1)
140.7(1)
N1–Ca1–O1
N2–Ca1–O1
N3–Ca1–O1
131.7(1)
98.96(9)
95.28(9)
2.366(2)
2.296(2)
2.393(2)
[(2-NN)Ca]2
Ca1–N1
Ca1–N2
Ca1–N5
Ca1–N6
2.336(5)
2.365(5)
2.318(5)
2.376(5)
Ca2–N3
Ca2–N4
Ca2–N7
Ca2–N8
2.314(5)
2.390(5)
2.353(5)
2.371(5)
N1–Ca1–N5
N2–Ca1–N6
N3–Ca2–N7
N4–Ca2–N8
131.7(1)
98.96(9)
131.7(1)
98.96(9)
(2-NN)[ZnEt]2
Zn1–N1
Zn1–N2
Zn1–C35
1.950(2)
1.957(2)
1.945(5)
Zn2–N3
Zn2–N4
Zn2–C37
1.968(2)
1.950(2)
1.939(5)
N1–Zn1–N2
Zn1–C35–C36
N3–Zn2–N4
Zn2–C37–C38
95.3(1)
120.7(4)
95.2(1)
123.1(5)
[a] Average value from thf molecule disordered over two positions.
Figure 2. Crystal structure of (2-NN)H2; only the NH hydrogen
atoms (located and refined) are depicted. The C–C/C–N bond al-
teration is shown (distances given in Å). Average N–H···NЈ hydro-
gen bond geometry: N···NЈ 2.652(3), N–H 0.89(3), H···NЈ 1.91(3),
N–H···NЈ 140(2)°.
by reacting the β-diketimine ligand in THF with two equiv-
alents of KN(SiMe3)2 and one equivalent of CaI2. Similar
to this procedure, reaction of (2-NN)K2 with two equiva-
lents of KN(SiMe3)2 and two equivalents of CaI2 allowed
the isolation of (2-NN)[CaN(SiMe3)2·thf]2 in the form of
orange crystals (37% yield). The crystal structure (Figure 3,
a) shows a centrosymmetric heteroleptic complex. The in-
version center on the N–N bond results in coplanarity and
trans-orientation of the β-diketiminate units. The Ca atoms
are considerably bend out of the β-diketiminate plane: the
average C(H)–C(Me)–N–Ca torsion angle is 34.8(1)°. This
structural feature was also observed in the mononuclear
Scheme 3.
complex (DIPP-nacnac)CaN(SiMe3)2·thf, but to a much the ligand prohibits an in-plane metal position on account
smaller extent: the average C(H)–C(Me)–N–Ca torsion an- of repulsion with the methyl group in the ligand’s backbone.
gle is 26.5(1)°.[11] It is likely that the trans-conformation of The Ca···CaЈ distance measures 5.8291(8) Å.
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Binuclear Magnesium, Calcium, and Zinc Complexes
highly active catalyst in the copolymerization of cyclohex-
ene oxide (CHO) and CO2. In contrast to the mononuclear
catalyst, (DIPP-nacnac)ZnEt, conversion of the ZnEt func-
tionality in an initiating group (ZnOR or ZnO2S) is not
needed.[1g,10,12] Under the same conditions, (2-NN)[ZnEt]2
was found to be inactive in the CHO/CO2 copolymeriza-
tion.
Conclusions
The metal amide reagents of Mg, Ca and Zn react fast
and efficiently with a N–N coupled bis(salicylaldimine) li-
gand: (1-NN)H2. Only in the case of Mg a well-defined het-
eroleptic complex, (1-NN)[MgN(SiMe3)2·thf]2, could be ob-
tained. For Ca and Zn homoleptic products have been iso-
lated and were structurally characterized.
Twofold deprotonation of a N–N-coupled bis(β-diket-
imine) ligand, (2-NN)H2, is not easily accomplished and
more reactive reagents combined with harsher reaction con-
ditions are a necessity. This is likely due to a steric shielding
of the acidic N–H functionalities [as can be seen in the crys-
tal structure of (2-NN)H2]. Heteroleptic complexes of the
type (2-NN)[MR]2 with M = Mg and Ca are not stable and
in Schlenk equilibrium with their homoleptic counterparts.
The heteroleptic complex (2-NN)[ZnEt]2, however, shows
good stability against ligand distribution reactions. In con-
trast to other bridged β-diketiminate zinc ethyl complexes,[4]
(2-NN)[ZnEt]2 is not active as a catalyst in the copolymer-
ization of CO2 and cyclohexene oxide. Apparently, this par-
ticular ligand geometry is not suitable for the cyclic bimetal-
lic polymerization process. We are currently investigating
the use of the here presented stable heteroleptic bimetallic
complexes in catalysis and as initiators in the polymeriza-
tion of other polar monomers.
Figure 3. Crystal structures (hydrogen atoms omitted for clarity) of
(a) (2-NN)[CaN(SiMe3)2·thf]2, (b) [(2-NN)Ca]2 (iPr groups omitted
for clarity), (c) (2-NN)[ZnEt]2. Selected geometric parameters for
both structures have been summarized in Table 1.
Experimental Section
General: All manipulations were performed under a dry and oxy-
gen-free atmosphere (argon or nitrogen) using Schlenk line and
glove box techniques and freshly dried solvents. Following com-
plexes have been prepared according to literature: (1-NN)H2,[5]
Mg[N(SiMe3)2]2·(thf)2,[14] Ca[N(SiMe3)2]2·(thf)2,[14] and Zn[N-
(SiMe3)2]2.[15]
Also the reaction of (2-NN)H2 with Zn[N(SiMe3)2]2 is
extremely slow. Refluxing these reagents in toluene (1:2 ra-
tio, respectively) gave after two days only mono-deproton-
ation but no defined products could be isolated. Use of
Et2Zn, however, gave under milder reaction conditions
(benzene, 70 °C, 2 d) the desired bimetallic complex (2-
NN)[ZnEt]2 which crystallized as light-yellow blocks from
hexane. The crystal structure (Figure 3, c) shows a complex
of approximate C2-symmetry in which the β-diketiminate
(1-NN)[MgN(SiMe3)2·thf]2: To a solution of Mg[N(SiMe3)2]2·(thf)2
(501 mg, 1.02 mmol) in hexane (10 mL) was added (1-NN)H2
(238 mg, 512 µmol). Upon heating a yellow solid precipitated. The
solid was washed two times with 2 mL of hexane and dried under
vacuo. Yield 384 mg, 77%. 1H NMR (500 MHz, C6D6, 25 °C): δ =
4
units within the ligand are oriented nearly perpendicular in 9.38 (s, 2 H, CCHN), 7.75 [d, JH,H = 1.2 Hz, 2 H, HAryl], 7.54 [d,
4JH,H = 1.2 Hz, 2 H, HAryl], 3.48 (m, 8 H, thf), 1.72 (s, 18 H, tBu),
respect to each other [angle between least-squares planes:
1.43 (s, 18 H, tBu), 0.93 (m, 8 H, thf), 0.45 (s, 36 H, SiMe3) ppm.
87.1(1)°]. This originates in a relatively short Zn···ZnЈ dis-
13C{1H} NMR (125 MHz, C6D6, 25 °C): δ = 168.8 (NCHC), 167.3
tance of 3.9676(5) Å and a long N–N bond of 1.442(3) Å.
(COMg), 141.8, 137.3, 132.1, 130.3, 117.9 (CAryl), 70.1 (thf), 36.0
The Zn–N and Zn–C bond lengths are comparable to those
(CMe3), 34.6 (CMe3), 31.9 (CMe3), 29.9 (CMe3), 24.9 (thf) ppm.
[4]
in (2-PYR)[ZnEt]2 or (DIPP-nacnac)ZnEt.[10] The dinu-
Crystals for X-ray measurement were grown by the following pro-
cedure: to a solution of Mg[N(SiMe3)2]2·(thf)2 (50.1 mg, 102 µmol)
in hexane (300 µL) was added (1-NN)H2 (23.8 mg, 51.2 µmol).
Cooling of the solution to 7 °C, gave yellow single crystals.
clear complex (2-NN)[ZnEt]2 is in a benzene solution also
at higher temperatures stable towards ligand exchange.
The availability of a dinuclear Zn complex invited for a
preliminary investigation of its catalytic activity. The dinu-
C50H94Mg2N4O4Si4 (976.3): calcd. C 61.51, H 9.71; found C 61.84,
clear Zn complex (2-META)[ZnEt]2 was found to be a H 9.87.
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D. F. -J. Piesik, R. Stadler, S. Range, S. Harder
[(1-NN)Ca·(thf)2]2: To a solution of Ca[N(SiMe3)2]2·(thf)2 (60.6 mg, [CH(CH3)2], 24.5 [CH(CH3)2], 22.9 (CH3CN), 21.1 (CH3CN) ppm.
FULL PAPER
120 µmol) in THF (0.10 mL) was added (1-NN)H2 (28.2 mg,
60.7 µmol). The solution turned red immediately. Over night red
crystals precipitated from the solution. The crystals were washed
two times with 0.1 mL portions of hexane and dried under vacuo.
Yield 26.7 mg, 69%. 1H NMR (300 MHz, [D8]THF, 25 °C): δ =
C34H48K2N4 (591.0): calcd. C 69.10, H 8.19; found C 69.46, H 8.35.
Synthesis of (2-NN)Mg: A solution of (nBu)2Mg (0.5  in heptane,
10 mL, 5.0 mmol) was added to a solution of (2-NN)H2 (2.13 g,
4.14 mmol) in benzene (12 mL) over a period of one hour. The
yellow solution turned to orange-red and was stirred for two hours
at ambient temperature. After removing the solvent under vacuum,
the crude product was crystallized from hot hexane to obtain (2-
NN)Mg (1.66 g, 75%) as yellow needless. 1H NMR (300 MHz,
C6D6, 25 °C): δ = 7.11–6.94 (m, 6 H, CHN-aryl), 4.71 (s, 2 H,
4
8.00 (s, 2 H, CCHN), 7.14 [d, JH,H = 1.2 Hz, 2 H, HAryl], 6.74 [d,
4JH,H = 1.2 Hz, 2 H, HAryl], 3.52 (m, 8 H,thf), 1.73 (m, 8 H,thf),
1.46 (s, 18 H, tBu), 1.17 (s, 18 H, tBu) ppm. 13C{1H} NMR
(75 MHz, [D8]THF, 25 °C): δ = 168.4 (NCHC), 164.4 (COCa),
139.0, 132.3, 129.2, 127.9, 120.7 (CAryl), 68.8 (thf), 36.0 (CMe3),
34.2 (CMe3), 32.2 (CMe3), 30.4 (CMe3), 24.9 (thf) ppm.
C76H116Ca2N4O8 (1294.0): calcd. C 70.55, H 9.04; found C 69.98,
H 9.21.
CH3CNCH), 3.17 [m,
2 H, CH(CH3)2], 2.56 [sept, 2 H,
CH(CH3)2], 2.09 (s, 6 H, CH3CN), 1.40 (s, 6 H, CH3CN), 1.34 [d,
3
3J(H,H) = 6.7 Hz, 6 H, CH(CH3)2], 1.17 [d, J(H,H) = 6.7 Hz, 6
H, CH(CH3)2], 1.10 [d, 3J(H,H) = 6.7 Hz, 6 H, CH(CH3)2], 0.45 [d,
3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2] ppm. 13C NMR {1H} (75 MHz,
C6D6, 25 °C): δ = 169.3 (Cq), 167.3 (Cq), 150.0 (Cq), 143.6 (Cq),
142.3 (Cq), 126.0 (CHN-aryl), 124.8 (CHN-aryl), 124.0 (CHN-aryl), 93.3
(CH3CNCH), 30.1 [CH(CH3)2], 29.4 [CH(CH3)2], 26.7 [CH-
(CH3)2], 25.4 [CH(CH3)2], 24.9 [CH(CH3)2], 24.6 (CH3CN), 22.3
(CH3CN) ppm. C34H48MgN4 (537.1): calcd. C 76.04, H 9.01; found
C 75.75, H 9.23.
[(1-NN)Zn]3: To a solution of Zn[N(SiMe3)2]2 (46.3 mg, 120 µmol)
in toluene (0.20 mL) was added (1-NN)H2 (28.2 mg, 60.7 µmol).
Cooling of the solution to –27 °C, gave after 96 h single crystals
suitable for X-ray diffraction. Yield 16.6 mg, 52%. 1H NMR
2
(300 MHz, C6D6, 25 °C): δ = 8.17 (s, 2 H, CCHN), 7.14 [d, JH,H
4
= 2.4 Hz, 2 H, HAryl], 6.36 [d, JH,H = 2.4 Hz, 2 H, HAryl], 1.77 (s,
18 H, tBu), 1.17 (s, 18 H, tBu) ppm. 13C{1H} NMR (75 MHz, [D8]-
THF): δ = 168.0 (NCHC), 167.5 (COZn), 141.3, 137.5, 132.0,
128.0, 116.2, (CAryl), 35.9 (CMe3), 34.1 (CMe3), 31.8 (CMe3), 29.9
(CMe3) ppm. C90H126N6O6Zn3 (1584.2): calcd. C 68.24, H 8.02;
found C 68.70, H 8.14.
Synthesis of [(2-NN)Ca]2:
A solution of (2-NN)H2 (1.00 g,
1.94 mmol) and Ca[N(SiMe3)2]2·(thf)2 (1.55 g, 7.77 mmol) dis-
solved in benzene (15 mL) was heated to 80 °C for 70 h. After re-
moving the solvent under vacuum, the crude product was washed
with hexane (10 mL) to obtain [(2-NN)Ca]2 (680 mg, 63%) as a
1
Synthesis of (2-NN)H2: Triethyloxonium tetrafluoroborate (14.1 g,
65.9 mmol) dissolved in dichloromethane (60 mL) was added over
a period of 20 min to a stirred solution of 2-hydroxy-4-(2,6-diisop-
ropylphenyl)imino-2-pentene (17.1 g, 65.9 mmol) in dichlorometh-
ane (80 mL) under an argon atmosphere. The mixture was stirred
overnight. An equimolar portion of triethylamine (6.53 g,
64.5 mmol) was slowly added to the red-brown solution after which
the solution turned dark-red. After stirring for 20 min, a solution
of hydrazine monohydrate (1.65 g, 32.9 mmol) and triethylamine
(25 mL) was added. The mixture was stirred for 80 h at ambient
temperature. All volatiles were removed in vacuo and the crude
product was washed three times with ethanol (150 mL) to yield (2-
NN)H2 (8.53 g, 50%) as a yellow powder. 1H NMR (300 MHz,
C6D6, 25 °C): δ = 12.0 (s, 2 H, NH), 7.22–7.12 (m, 6 H, CHN-aryl),
4.88 (s, 2 H, CH3CNCH), 3.43 [m, 4 H, CH(CH3)2], 2.23 (s, 6 H,
CH3CN), 1.66 (s, 6 H, CH3CN), 1.22 [d, 3J(H,H) = 6.9 Hz, 12
yellow powder. H NMR (300 MHz, C6D6, 25 °C): δ = 7.08–6.97
(m, 12 H, CHN-aryl), 4.61 (s, 4 H, CH3CNCH), 3.12 [sept, 4 H,
CH(CH3)2], 2.87 [sept, 4 H, CH(CH3)2], 2.08 (s, 12 H, CH3CN),
1.59 (s, 6 H, CH3CN), 1.23 [ps-t, 24 H, CH(CH3)2], 1.08 [d,
3J(H,H) = 6.9 Hz, 12 H, CH(CH3)2], 0.50 [d, 3J(H,H) = 6.9 Hz, 12
H, CH(CH3)2] ppm. 13C{1H} NMR (75 MHz, C6D6, 25 °C): δ =
164.7 (Cq), 162.3 (Cq), 147.9 (Cq), 142.6 (Cq), 142.1 (Cq), 125.0
(CHN-aryl), 124.7 (CHN-aryl), 124.4 (CHN-aryl), 92.2 (CH3CNCH),
29.4 [CH(CH3)2], 29.3 [CH(CH3)2], 26.2 [CH(CH3)2], 25.1
[CH(CH3)2], 25.0 [CH(CH3)2], 24.3 [CH(CH3)2], 24.1 (CH3CN),
21.9 (CH3CN) ppm. C68H96Ca2N8 (1105.7): calcd. C 73.87, H 8.75;
found C 73.36, H 8.39.
Synthesis of (2-NN)[CaN(SiMe3)2·thf]2: A suspension of (2-NN)K2
(455 mg, 770 µmol), CaI2 (445 mg, 1.51 mmol) and K[N(SiMe3)2]
(311 mg, 1.56 mmol) in THF (10 mL) was stirred at ambient tem-
perature for 18 h. After centrifugation, the solvent was removed
under vacuum. The reddish brown residue was extracted with hex-
ane (20 mL). The hexane solution was concentrated to 5 mL and
slowly cooled to –28 °C. (2-NN)[CaN(SiMe3)2·thf]2 was obtained
as orange crystals (760 mg, 37%). 1H NMR studies in C6D6
showed a highly complex mixture of signals in which those of the
homoleptic complexes [(2-NN)Ca]2 and Ca[N(SiMe3)2]2·(thf)2
could be recognized. Therefore, (2-NN)[CaN(SiMe3)2·thf]2 is in
solution not stable on account of the Schlenk equilibrium. The
ratio between homoleptic and the heteroleptic species is circa 1/2.
C54H100Ca2N6O2Si4 (1057.9): calcd. C 61.31, H 9.53; found C
60.98, H 9.67.
3
H, CH(CH3)2], 1.15 [d, J(H,H) = 6.8 Hz, 12 H, CH(CH3)2] ppm.
13C{1H} NMR (75 MHz, C6D6, 25 °C): δ = 161.7 (Cq), 153.4 (Cq),
147.6 (Cq), 136.9 (Cq), 128.4 (CHN-aryl), 124.2 (CHN-aryl), 95.7
(CH3CNCH), 29.2 [CH(CH3)2], 25.7 [CH(CH3)2], 23.4 [CH-
(CH3)2], 20.9 (CH3CN), 20.2 (CH3CN) ppm. C34H50N4 (514.8):
calcd. C 79.33, H 9.79; found C 79.04, H 9.87.
Synthesis of (2-NN)K2: A solution of (2-NN)H2 (2.00 g, 3.89 mmol)
and K[N(SiMe3)2] (1.55 g, 7.77 mmol) in benzene (30 mL) was
stirred at ambient temperature for 4 h. After removing the solvent
under vacuum, pure (2-NN)K2 was obtained in quantitative yield.
1H NMR (300 MHz, C6D6, 25 °C): δ = 7.04–6.95 (m, 6 H,
CHN-aryl), 4.36 (s, 2 H, CH3CNCH), 3.12 [sept, 2 H, CH(CH3)2], Synthesis of (2-NN)[ZnEt]2: A solution of (2-NN)H2 (853 mg,
2.67 [sept, 2 H, CH(CH3)2], 1.78 (s, 6 H, CH3CN), 1.70 (s, 6 H,
1.66 mmol) and diethylzinc (1  in hexane, 4.5 mL, 4.5 mmol) in
CH3CN), 1.25 [d, 3J(H,H) = 6.9 Hz, 6 H, CH(CH3)2], 1.11 [d, benzene (10 mL) was stirred at 70 °C for 42 h. After removing the
3
3J(H,H) = 6.9 Hz, 6 H, CH(CH3)2], 1.09 [d, J(H,H) = 7.0 Hz, 6 solvent under vacuum, pure (2-NN)[ZnEt]2 was obtained in quanti-
3
H, CH(CH3)2], 0.37 [d, J(H,H) = 6.9 Hz, 6 H, CH(CH3)2] ppm.
13C{1H} NMR (75 MHz, C6D6, 25 °C): δ = 162.2 (Cq), 159.0 (Cq),
151.0 (Cq), 140.3 (Cq), 139.7 (Cq), 125.1 (CHN-aryl), 123.5
(CHN-aryl), 122.8 (CHN-aryl), 86.8 (CH3CNCH), 30.4 [CH(CH3)2],
27.1 [CH(CH3)2], 25.5 [CH(CH3)2], 25.2 [CH(CH3)2], 24.5
tative yield as a yellow powder. Light coloured yellow crystals suit-
able for X-ray analysis could be obtained by slowly cooling a hot
hexane solution to 5 °C. 1H NMR (300 MHz, C6D6, 25 °C): δ =
7.10 (s, 6 H, CHN-aryl), 4.75 (s, 2 H, CH3CNCH), 3.15 [sept, 4 H,
CH(CH3)2], 1.96 (s, 6 H, CH3CN), 1.64 (s, 6 H, CH3CN), 1.37 [t,
3574
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 3569–3576

Binuclear Magnesium, Calcium, and Zinc Complexes
3J(H,H) = 8.1 Hz, 6 H, CH2CH3], 1.22 [d, 3J(H,H) = 7.0 Hz, 12 Crystal Structure Determinations: All data were collected on a Sie-
H, CH(CH3)2], 1.17 [d, 3J(H,H) = 7.0 Hz, 6 H, CH(CH3)2], 1.14 mens SMART CCD APEX II diffractometer (Table 2). The struc-
3
3
[d, J(H,H) = 6.9 Hz, 6 H, CH(CH3)2], 0.49 [q, J(H,H) = 8.1 Hz,
tures have been solved by direct methods (SHELXS-97)[16] and
4 H, CH2CH3] ppm. 13C{1H} NMR (75 MHz, C6D6, 25 °C): δ = were refined with SHELXL-97.[17] The geometry calculations and
166.3 (Cq), 166.2 (Cq), 145.4 (Cq), 142.3 (Cq), 142.1 (Cq), 126.4 graphics have been performed with PLATON.[18]
(CHN-aryl), 124.3 (CHN-aryl), 123.9 (CHN-aryl), 93.1 (CH3CNCH),
28.8 [CH(CH3)2], 28.7 [CH(CH3)2], 24.8 [CH(CH3)2], 24.7
The crystal structure solution of [(1-NN)Zn]3 was complicated by
[CH(CH3)2], 23.8 [CH(CH3)2], 23.6 [CH(CH3)2], 23.4 (CH3CN), cocrystallized toluene molecules. A total of 4.5 toluene molecules
21.5 (CH3CN), 12.9 (CH2CH3), –1.54 (CH2CH3) ppm. per asymmetric unit, i.e. per trimeric [(1-NN)Zn]3, has been esti-
C38H58N4Zn2 (701.7): calcd. C 65.05, H 8.33; found C 64.74, H
8.27.
mated. Two of these molecules were relatively ordered and could
be refined, the remaining 2.5 molecules were completely disordered
Table 2. Crystal data.
(1-NN)[MgN(SiMe3)2·thf]2
[(1-NN)Zn]3
(2-NN)H2
Formula
C50H94Mg2N4O4Si4
976.27
C90H126N6O6Zn3·(C7H8)2
1768.41
0.1ϫ0.1ϫ0.1
monoclinic
C2/c
C34H50N4
514.78
0.3ϫ0.3ϫ0.3
monoclinic
P21/c
MW
Crystal size [mm3]
0.45ϫ0.15ϫ0.10
triclinic
Crystal system
Space group
¯
P1
a [Å]
b [Å]
c [Å]
α
10.2419(5)
12.4802(5)
13.5319(6)
111.806(2)
101.290(2)
99.473(2)
1520.39(12)
1
31.5897(17)
24.4156(13)
32.8376(17)
90
112.964(3)
90
17.2928(8)
13.1564(7)
16.0570(7)
90
114.996(2)
90
3311.0(3)
4
1.033
β
γ
V [Å3]
23320(2)
8
Z
ρ [gcm–3]
1.066
0.159
1.138[a]
µ (Mo-Kα) [mm–1]
0.658
0.060
T [°C]
θ (max.)
–70
26.0
–70
26.1
–100
25.4
Reflections total, unique
Rint
51246, 5967
0.045
383583, 23089
0.129
13341, 6040
0.036
Obsd. reflections [IϾ2σ(I)]
Parameters
4605
458
11976
1089
3613
411
R1
wR2
GOF
0.0541
0.1595
1.05
–0.43/0.46
0.0610
0.1650
0.95
–0.44/0.50
0.0679
0.2088
1.06
Min./max. residual e– density [eÅ–3]
–0.21/0.14
Compound
(2-NN)[CaN(SiMe3)2·thf]2
[(2-NN)Ca]2
(2-NN)[ZnEt]2
Formula
C54H100Ca2N6O2Si4·(C6H6)2
C68H96Ca2N8
1105.69
0.5ϫ0.4ϫ0.3
orthorhombic
P212121
9.563(5)
22.047(12)
31.120(15)
90
C38H58N4Zn2
701.62
0.5ϫ0.3ϫ0.3
monoclinic
P21/n
15.2419(3)
16.6230(3)
15.7753(3)
90
MW
1214.14
0.5ϫ0.4ϫ0.3
monoclinic
P21/n
13.9606(4)
15.5500(5)
17.9974(5)
90
Crystal size [mm3]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α
β
γ
101.808(2)
90
3824.3(2)
2
1.054
0.253
90
90
6561(6)
8
1.119
94.796(1)
90
3982.9(1)
4
1.170
1.232
V [Å3]
Z
ρ [gcm–3]
µ (Mo-Kα) [mm–1]
0.218
T [°C]
θ (max.)
+20
25.0
–70
26.1
–70
25.5
Reflections total, unique
Rint
46522, 6746
0.045
47563, 11555
0.156
53094, 7411
0.056
Obsd. reflections [IϾ2σ(I)]
Parameters
4327
333
8075
728
4934
411
R1
wR2
GOF
0.0530
0.1663
1.02
0.0906
0.2078
1.10
0.0429
0.1189
1.02
Min./max. residual e– density [eÅ–3]
–0.27/0.45
–0.34/0.34
–0.38/0.47
[a] Density corrected for the additional 2.5 toluene molecules which have been treated with SQUEEZE.
Eur. J. Inorg. Chem. 2009, 3569–3576
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3575

D. F. -J. Piesik, R. Stadler, S. Range, S. Harder
FULL PAPER
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gram PLATON.[18]
(2-NN)[CaN(SiMe3)2·(thf)2]2 cocrystallized with two molecules of
benzene which were disordered over two positions and have been
refined as regular hexagons.
[(2-NN)Ca]2 crystallized in the chiral space group P212121 and has
been checked for the correct absolute structure [Flack parameter
0.049(54)]. The complex has no crystallographic symmetry but ap-
proximate D2 symmetry. No higher crystal symmetry could be
found. The somewhat poor crystal quality led to weak diffraction
and subsequently somewhat higher R values (wR2 = 0.2078, R1 =
0.0906).
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CCDC-729095 {for (1-NN)[MgN(SiMe3)2·thf]2}, -729096 {for [(1-
NN)Zn]3}, -729097 {for (2-NN)[CaN(SiMe3)2·thf]2}, -729098 {for
(2-NN)[ZnEt]2}, -729099 {for [(2-NN)Ca]2}, -729100 [for (2-NN)
H2] contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
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Received: May 12, 2009
Published Online: July 21, 2009
3576
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Eur. J. Inorg. Chem. 2009, 3569–3576