Reactivity of (β-diketiminato)zinc hydride toward lewis bases, heterocumulenes and cyclohexene oxide

Article abstract of DOI:10.1002/ejic.201200378

The reaction of LZnH (1) {L = Mesnacnac = [(2,4,6-Me₃C ₆H₂)NC(Me)]₂CH} with 4-(dimethylamino)pyridine (dmap) yielded the Lewis acid-base adduct LZn(H)dmap (2), whereas LZn(Cl)dmap (3) was obtained from the equim

Full text of DOI:10.1002/ejic.201200378

Job/Unit: I20378
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Date: 29-06-12 09:33:00
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FULL PAPER
DOI: 10.1002/ejic.201200378
Reactivity of (β-Diketiminato)zinc Hydride toward Lewis Bases,
Heterocumulenes and Cyclohexene Oxide
Georg Bendt,[a] Stephan Schulz,*[a] Jan Spielmann,[a] Sarah Schmidt,[a] Dieter Bläser,[a] and
Christoph Wölper[a]
Dedicated to Professor Dieter Fenske on the occasion of his 70th birthday
Keywords: N ligands / Zinc / Insertion / Cumulenes / Lewis acids
The reaction of LZnH (1) {L = Mesnacnac = [(2,4,6-Me3C6H2)-
NC(Me)]2CH} with 4-(dimethylamino)pyridine (dmap)
yielded the Lewis acid–base adduct LZn(H)dmap (2),
whereas LZn(Cl)dmap (3) was obtained from the equimolar
reaction of LZnCl with dmap. In addition, reactions of 1 with
di-tert-butylcarbodiimide [C(NtBu)2] and tert-butyl thioiso-
cyanate (tBuNCS) proceeded with insertion of the hetero-
cumulene into the Zn–H bond and formation of
[LZn(tBuNC(H)NtBu)] (4) and [LZn(tBuNC(H)S)] (5),
whereas 1 reacted with Me3SiN3 with the elimination of Me3-
SiH and formation of [LZnN3]2 (6). Moreover, the reaction of
1 with cyclohexene oxide (CHO) occurred with ring opening
and formation of [LZnOCy]2 (7) (Cy = cyclohexyl). Com-
plexes 2–7 were characterized by multinuclear NMR (1H,
13C) and IR spectroscopy, elemental analyses and by single-
crystal X-ray diffraction (2, 3, 6, 7).
sponding zinc hydride RZnH.[6] MesnacnacZnH (1) was
found to readily react with heterocumulenes such as CO2,
carbodiimides and isocyanates with insertion into the Zn–
H bond and subsequent formation of the corresponding
formato, formamidinato and formamido complexes, respec-
tively.[12] Moreover, its reaction with DippnacnacAl(Me)-
OH proceeded with elimination of H2 and formation of
a heterodimetallic, μ-O-bridged Al–Zn oxide complex,
MesnacnacZnOAl(Me)Dippnacnac.[13]
Herein, we report on the reactions of MesnacnacZnH
(1) with the strong Lewis base 4-(dimethylamino)pyridine
(dmap), which occurred with adduct formation. In ad-
dition, reactions of MesnacnacZnH with di-tert-butyl-
Introduction
Zinc hydride ZnH2 and hydridozincates such as LiZnH3
and Li2ZnH4 are powerful reducing reagents widely used in
organic and inorganic chemistry.[1] However, the rather low
thermal stability of ZnH2 and its insolubility in organic sol-
vents prompted the interest in more suitable heteroleptic
organozinc hydrides of the general type RZnH.[2] Even
though simple alkylzinc hydrides also show a limited ther-
mal stability, they can be stabilized by coordination of an
additional Lewis base as was found for RZnH(pyridine) (R
= Et, Ph).[3] Moreover, chelating organic ligands such as
scorpionato (Tpp-Tol,Me [4]
and β-diketiminato (MesЈnacnac
)
= [HC{C(Me)N(2,6-Me2C6H3)}2],[5] Mesnacnac,[6] Dipnac-
nac[7]) as well as sterically demanding terphenyl substituents
[ArЈ = C6H3-2,6-(C6H3-2,6-iPr2)2][8] were found to stabilize
the desired class of compounds. In addition, a tetranuclear
hydridozinc alkoxide complex (HZnOtBu)4 was reported by
Driess et al.,[9] whereas a tetranuclear amidinatozinc hy-
dride complex {C[C(NiPr)2ZnH]4} was synthesized in our
group by the reaction of the Cl-substituted derivative
{C[C(NiPr)2ZnCl]4} with CaH2.[10]
carbodiimide
[C(NtBu)2],
tert-butyl
thioisocyanate
(tBuN=C=S), trimethylsilyl azide (Me3SiN3) and cyclohex-
ene oxide (CHO) are reported.
Results and Discussion
We recently reported on the synthesis of (β-diket-
iminato)zinc halide complexes,[11] which were found to be
suitable starting reagents for the synthesis of the corre-
Equimolar amounts of 1 and dmap were stirred at ambi-
ent temperature for 30 min and then stored at –30 °C for
48 h, yielding colourless crystals of LZn(H)dmap (2) in al-
most quantitative yield. An analogous reaction of LZnCl
with an equimolar amount of dmap yielded the Cl-substi-
tuted adduct LZn(Cl)dmap (3) in quantitative yield
(Scheme 1).
[a] Institute of Inorganic Chemistry, University of Duisburg-Essen,
45117 Essen, Germany
Fax: +49-201-1834635
E-mail: stephan.schulz@uni-due.de
Eur. J. Inorg. Chem. 0000, 0–0
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FULL PAPER
Scheme 1. Synthesis of 2 and 3.
1
The H NMR spectra of 2 and 3 in C6D6 showed the
expected resonances from the β-diketiminato ligand and the
dmap base in the expected 1:1 molar ratio. In addition, the
resonance of the Zn–H group, which was found at δ =
4.57 ppm for 1, was observed at δ = 4.50 ppm. The IR spec-
trum of 2 did not show an absorption band from the Zn–
H group as was observed for 1. Pulsed gradient spin echo
(PGSE) diffusion measurements of a solution of 2 at 25 °C
in [D8]toluene and [D8]THF yielded hydrodynamic radii of
5.66(24) and 5.65(26) Å, respectively, which are slightly
larger than that observed for 1 in [D8]THF [5.26(26) Å].
Moreover, a second diffusion constant was measured
[3.30(05) Å], which corresponds to that of pure dmap
[3.53(15) Å]. These results indicate that 1 forms an equilib-
rium in solution between the dmap-coordinated adduct 2,
uncomplexed dmap and LZnH (1). Since the 1H NMR
spectrum of 2 only shows one set of resonances of the or-
ganic ligands, the exchange between the uncomplexed
and complexed form in solution is fast on the NMR time
scale.
Figure 1. Solid-state structure of 2 (thermal ellipsoids are shown at
50% probability levels); H atoms are omitted for clarity except for
Zn–H1. Selected bond lengths [Å] and angles [°]: Zn(1)–N(1)
2.0188(14), Zn(1)–N(2) 2.0121(14), Zn(1)–N(3) 2.0979(14), N(1)–
C(1) 1.320(2), C(1)–C(2) 1.407(2), N(2)–C(3) 1.323(2), C(2)–C(3)
1.405(2); N(2)–Zn(1)–N(1) 94.58(6), N(2)–Zn(1)–N(3) 101.57(6),
N(1)–Zn(1)–N(3) 98.46(5).
Single crystals of 2 and 3 were obtained from solutions
in toluene at ambient temperature. Complex 2 (Figure 1)
crystallizes together with a toluene molecule in the mono-
clinic space group P21/n, whereas 3 (Figure 2) crystallizes
without any additional solvent molecules in the space group
Figure 2. Solid-state structure of 3 (thermal ellipsoids are shown at
50% probability levels); H atoms are omitted for clarity. Selected
bond lengths [Å] and angles [°]: Zn(1)–N(1) 1.9956(9), Zn(1)–N(2)
2.0037(9), Zn(1)–N(3) 2.0468(9), Zn(1)–Cl(1) 2.2337(3), N(1)–C(1)
1.3270(14), N(2)–C(3) 1.3258(13), C(1)–C(2) 1.4066(14), C(2)–C(3)
1.4077(14); N(1)–Zn(1)–N(2) 97.77(3), N(1)–Zn(1)–N(3) 105.19(4),
N(2)–Zn(1)–N(3) 109.07(4), N(1)–Zn(1)–Cl(1) 120.74(3), N(2)–
Zn(1)–Cl(1) 118.44(3), N(3)–Zn(1)–Cl(1) 104.74(3).
¯
P1. The central bond lengths and bond angles within the
Mesnacnac ligands in 2 and 3 are almost identical to those
previously observed for 1 as well as LZnX (X = I, OMe,
OEt, OiPr) and L2Zn.[14] The Zn–N bonds of the Mesnac-
nac ligand [2: 2.0188(14), 2.0121(14); 3: 1.9956(9),
2.0037(9) Å] are significantly shorter than the Zn–Ndmap
bond [2: 2.0979(14); 3: 2.0468(9) Å], as was expected be-
cause of the dative character of the latter. Moreover, the
increased Lewis acidity of the Zn atom in 3 compared with
Because of our interest in reactions of organozinc com-
2, which results from the more electronegative chlorine sub- plexes with heterocumulenes, we treated 1 with di-tert-but-
stituent, significantly influences the Zn–Ndmap bond length ylcarbodiimide [C(NtBu)2] and tert-butyl isocyanate
as was expected. The endocyclic N1–Zn1–N2 bond angle (tBuNCS). The reactions proceeded with insertion of the
[2: 94.58(6)°; 3: 97.77(3)°] is smaller than the exocyclic N1– heterocumulene into the Zn–H bond and formation of the
Zn1–N3 and N2–Zn1–N3 bond angles [2: 98.46(5), formamidinato {LZn[(tBuN)2CH] (4)} and thioformamido
101.57(6)°; 3: 105.19(4), 109.07(4)°], hence leading to a dis- {LZn[RN(S)CH] (5)} complexes, respectively, as was pre-
torted tetrahedral coordination sphere at the Zn atom. In viously observed with (iPrN)2C, tBuNCO and CO2. In con-
addition, the higher steric demand of the Cl atom in 3 leads trast, the reaction of 2 with trimethylsilyl azide (Me3-
to wider Zn1–N1/2-C13/22 bond angles in 3 compared with SiN3) occurred with the elimination of Me3SiH and forma-
2 [2: 116.39(10), 117.27(10)°; 3: 121.68(6), 122.66(7)°].
tion of the azido-bridged dimer [LZnN3]2 (6) (Scheme 2).
2
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Reactivity of (β-Diketiminato)zinc Hydride
Single crystals of 6 were obtained from a solution in tolu-
ene at ambient temperature. Complex 6 (Figure 3) crys-
¯
tallizes in the triclinic space group P1. The molecule is lo-
cated on a centre of inversion. The C3N2Zn ring in 6 is
almost planar (r.m.s. deviation from best plane 0.037 Å)
with the Zn atoms slightly out of the plane [0.3938(12) Å
deviation from the plane] as was observed in 1, 2 and 3
as well as in [MesЈnacnacZn(μ-H)]2,[5] DippnacnacZnH,[7]
[21]
DippnacnacZnN(SiMe3)2
and DippnacnacZn(μ-H)2-
BH2.[22] The C–C and C–N bond lengths as well as the N–
C–C and C–C–C bond angles within the β-diketiminato
backbone are nearly unchanged compared to those in
LZnH (1), 2 and 3. In contrast, the Zn1–N1 and Zn1–N2
bonds in 6 [1.9480(9) 1.9497(9) Å] are shorter than those in
2 [2.0188(14), 2.0121(14) Å], 3 [1.9956(9), 2.0037(9) Å] and
the two polymorphs of dimeric [LZnH]2 (1) [1.971(2),
1.975(2) Å; 2.0046(16), 2.0056(17) Å].[6] The azide group
adopts an asymmetrically bridging μ-1,1 binding mode as
Scheme 2. Synthesis of 4–6.
1
The H NMR spectra of 4 and 5 in C6D6 showed the was expected from the IR spectrum, with the Zn1–N3 and
expected resonances from the Mesnacnac ligand and the Zn1–N3#1 bond lengths differing by 0.04 Å [2.0652(9),
tert-butyl groups of the carbodiimide and thioisocyanate 2.0265(9) Å]. The azide groups are almost linear [N3–N4–
substituents. In addition, single resonances at δ = 7.30 (4) N5 179.30(13)°], and the Nα–Nβ [1.2117(13) Å] and Nβ–Nγ
and 8.40 (5) ppm, which are characteristic for a C–H group bond lengths [1.1391(14) Å] indicate a covalently bound
of a formamidinato and thioformamido backbone, respec- azide, in accordance with the high energy of the asymmetric
tively, clearly proved that the reactions proceeded with in- stretching mode in the IR spectrum (Δd = 0.0726 Å). Com-
sertion of the heterocumulenes into the Zn–H bond. Com- parable Zn–N and N–N bond lengths were previously re-
parable findings were previously reported for reactions of ported for zinc azides.[20b,20c,23] A CSD database search
[15]
[DippnacnacMgH]2 with C(NCy)2
and Dippnacnac- gave 26 zinc azides with bridging azide moieties.[24] The Zn–
SnH[16] as well as [DippnacnacFeH]2 with C(NiPr)2.[17] Nα bond length ranged from 1.946 to 2.249 Å, with a mean
These reactions also occurred with insertion into the metal– value of 2.089 Å. The central Zn2N2 four-membered ring in
H bond and subsequent formation of the corresponding 6 is planar (inversion centre within the ring), and the Zn
formamidinato complexes, in which the formamidinato atoms adopt a distorted tetrahedral environment. The en-
groups adopt an η2-chelating binding mode. In contrast,
the corresponding organocalcium hydride complex
[DippnacnacCaH(thf)]2 did not react with CO2, C(NR)2 or
RNCO.[18]
The reaction of 1 with Me3SiN3 was expected to either
proceed with insertion into the Zn–H bond and subsequent
formation of the triazenido complex or with formation of
a zinc azide complex as was recently reported by Holland
et al. for the reaction of [LFeH]2 with organic azides.[17]
However, the 1H NMR spectrum of 6 in C6D6 only showed
the resonances from the Mesnacnac substituent, whereas
the expected singlet for the trimethylsilyl group was not ob-
served, indicating the formation of a zinc azide complex.
Moreover, the IR spectrum of 6 showed two absorption
bands from the asymmetric N–N–N stretching frequency
νas(N3) (2160, 2115 cm–1), indicating the presence of an
asymmetrically bridging μ-1,1-azido group.[19] Comparable
Figure 3. Solid-state structure of 6 (thermal ellipsoids are shown at
values have been reported previously for zinc azide com-
50% probability levels), asymmetric unit highlighted in dark bonds;
plexes.[20] Since the energy of the νas(N3) band to a first
H atoms and solvent molecules are omitted for clarity. Selected
bond lengths [Å] and angles [°] (#1: –x + 2, –y + 1, –z + 1): Zn(1)–
approximation only depends on the degree of the symmetry
of the azide group, the high energy indicates a large differ-
ence between the Nα–Nβ and Nβ–Nγ distances (Δd). The
expected bands from the symmetric N–N–N stretching fre-
quency (around 1300 cm–1) and the N–N–N deformation
mode (around 640 cm–1) are overlapped by the absorption
bands of the β-diketiminato group.
N(1) 1.9480(9), Zn(1)–N(2) 1.9497(9), Zn(1)–N(3)#1 2.0265(9),
Zn(1)–N(3) 2.0652(9), N(1)–C(1) 1.3344(13), N(2)–C(3) 1.3283(13),
N(3)–N(4) 1.2117(13), N(4)–N(5) 1.1391(14), C(1)–C(2)
1.4051(15), C(2)–C(3) 1.4081(15); N(1)–Zn(1)–N(2) 99.49(4), N(1)–
Zn(1)–N(3)#1 124.39(4), N(2)–Zn(1)–N(3)#1 116.04(4), N(1)–
Zn(1)–N(3) 117.35(4), N(2)–Zn(1)–N(3) 119.71(4), N(3)#1-Zn(1)–
N(3) 81.28(4), N(5)–N(4)–N(3) 179.30(13).
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docyclic N1–Zn1–N2 bond angle [99.49(4)°] is significantly [95.68(10), 95.90(9)°] and comparable to the endocyclic N–
larger than the endocyclic N3–Zn1–N3#1 bond angle Zn–N bond angle [81.28(4)°] observed for 6. The Zn–O–Zn
[81.28(4)°].
bond angles [97.23(9), 98.13(8)°] in 7 and the Zn–N–Zn
In order to reveal the mechanism for the formation of 7, bond angle [98.72(4)°] in 7 are also comparable.
the reaction of MesnacnacZnH with an excess of Me3SiN3
was monitored in situ by 29Si{1H} NMR spectroscopy. Af-
ter 2 h, a sharp resonance from the formation of Me3SiH
at δ = –16.3 ppm was observed. In contrast, the reaction
between [LFeH]2 and Me3SiN3 proceeded with the forma-
tion of Me3SiSiMe3, most likely by a coupling reaction of
two trimethylsilyl radicals, whereas that with AdN3 (Ad =
adamantyl) yielded the triazenido complex LFe(η2-
HNNNAd).[17]
Zinc complexes have found wide technical application in
CO2/epoxide copolymerization reactions in the last dec-
ade.[25] In order to investigate the capability of 1 to serve as
a catalyst in CO2/CHO (cyvlohexene oxide) copolymeriza-
tion reactions, several reactions were performed. Unfortu-
nately, 1 did not show any catalytic activity in these reac-
tions. However, the reaction of 1 with CHO yielded a
1
colourless crystalline solid 7. The H NMR spectrum of 7
in C6D6 showed the expected resonances from the Mesnac-
nac substituent and a cyclohexane group in a 1:1 molar
ratio (Scheme 3).
Scheme 3. Synthesis of 7.
Figure 4. Solid-state structure of 7 (thermal ellipsoids are shown at
50% probability levels), asymmetric unit highlighted in dark bonds;
H atoms are omitted for clarity. The arrangement of the molecules
does not represent their actual arrangement in the crystal packing.
Single crystals of 7 were obtained from a solution in tolu-
ene at 50 °C upon slow cooling to ambient temperature.
Complex 7 (Figure 4) crystallizes in the monoclinic space
group P21/c. The asymmetric unit contains two indepen-
dent molecules placed on inversion centres. Complex 7
forms an asymmetrically alkoxido-bridged dimer in the so-
lid state with a (necessarily) planar four-membered Zn2O2
ring and fourfold-coordinated Zn atoms, which adopt a dis-
torted tetrahedral coordination sphere. Analogous struc-
tural motifs were observed in simple Mesnacnac zinc alk-
oxide complexes LZnOR (R = Me, Et, iPr).[14b] The central
bond lengths and bond angles within the envelope-shaped
C3N2Zn heterocycles [r.m.s. deviation from C3N2 best
plane: 0.039 Å, 0.0455 Å; deviation Zn from best plane:
Zn1 0.633(3) Å, Zn2 0.690(3) Å] are comparable to those
observed for 2 and 6 and values previously reported for (β-
diketiminato)zinc complexes. In addition, the Zn–O bond
lengths [2.008(2), 1.952(2), 2.000(2), 1.9447(19) Å] in 7,
which are comparable to the Zn–N bond lengths [1.994(2),
1.995(2), 1.990(2), 2.002(2) Å], are typical for dimeric zinc
Selected bond lengths [Å] and angles [°] (#1: –x, –y + 2, –z; #2:
–x + 1, –y + 1, –z): Zn(1)–O(1) 2.008(2), Zn(1)–O(1)#1 1.952(2),
Zn(1)–N(1) 1.995(2), Zn(1)–N(2) 1.994(2), N(1)–C(1) 1.331(4),
N(2)–C(3) 1.327(4), C(1)–C(2) 1.407(4), C(2)–C(3) 1.399(4), Zn(2)–
O(101) 2.000(2), Zn(2)–O(101)#2 1.9447(19), Zn(2)–N(101)
1.990(2), Zn(2)–N(102) 2.002(2), N(101)–C(101) 1.333(3), N(102)–
C(103) 1.330(4), C(101)–C(102) 1.404(4), C(102)–C(103) 1.407(4);
O(1)#1–Zn(1)–N(2) 117.21(9), O(1)#1–Zn(1)–N(1) 128.37(9),
N(2)–Zn(1)–N(1) 95.68(10), O(1)#1–Zn(1)–O(1) 82.77(9), N(2)–
Zn(1)–O(1) 115.72(9), N(1)–Zn(1)–O(1) 118.94(9), O(101)#2–
Zn(2)–N(101) 122.73(9), O(101)#2–Zn(2)–O(101) 81.87(8),
N(101)–Zn(2)–O(101)
118.76(9),
O(101)#2–Zn(2)–N(102)
124.02(9), N(101)–Zn(2)–N(102) 95.90(9), O(101)–Zn(2)–N(102)
115.53(9).
Conclusions
MesnacnacZnH (1) reacts with Lewis bases such as 4-
alkoxides. The endocyclic O–Zn–O bond angles [82.77(9), (dimethylamino)pyridine with the formation of the corre-
81.87(8)°] are smaller than the N–Zn–N bond angles sponding Lewis acid–base adduct. Reactions with hetero-
4
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Reactivity of (β-Diketiminato)zinc Hydride
(100 mg, 0.13 mmol) in THF (20 mL) and stirred at ambient tem-
perature for 1 h. Thereafter, the solvent was evacuated in vacuo.
Yield (isolated crystals) 0.13 g (95%). M.p. 230 °C. C32H48N4Zn
(554.13): calcd. C 69.36, H 8.73, N 10.11; found C 69.21, H 8.65,
cumulenes and with cyclohexene oxide occurred with inser-
tion into the Zn–H bond, whereas the reaction with
Me3SiN3 proceeded with the elimination of trimethylsilane
and subsequent formation of the azido-bridged dimer
[LZnN3]2 (6), in which the azido groups adopt μ-1,1 bridg-
ing positions.
1
N 10.02. H NMR (300 MHz, [D8]THF, 298 K): δ = 0.84 [s, 18 H,
C(CH3)3], 1.67 [s, 6 H, C(CH3)], 2.20 (s, 12 H, o-CH3), 2.21 (s, 6
H, p-CH3), 4.86 (s, 1 H, CH), 6.74 (s, 4 H, ArH), 7.30 (HCN2)
ppm. 13C{1H} NMR (75 MHz, [D8]THF, 298 K): δ = 19.6 (o-CH3),
20.9 (β-CCH3), 23.2 (p-CH3), 32.5 [C(CH3)3], 50.7 [C(CH3)3], 94.6
(γ-C), 129.4 (m-Ar), 132.3 (o-Ar), 133.8 (p-Ar), 168.3 (γ-C) ppm.
Experimental Section
ATR-IR: ν = 2960, 2914, 2858, 2132, 2101, 1546, 1522, 1452, 1397,
˜
General Procedures: All manipulations were performed under Ar.
Solvents were carefully dried with Na/K and degassed prior to use.
tBuNCS, (tBuN)2C, dmap, Me3SiN3 and CHO were commercially
available and used as received. 1H NMR, 13C{1H} NMR and
29Si{1H} NMR spectra were recorded with a Bruker DMX 300
spectrometer and are referenced to internal C6D5H (1H NMR: δ =
7.154 ppm; 13C NMR: δ = 128.0 ppm) and Me4Si (29Si NMR: δ
= 0.0 ppm). IR spectra were recorded with an ALPHA-T FTIR
spectrometer equipped with a single-reflection ATR sampling mod-
ule. Melting points were measured in sealed capillaries. Elemental
analyses were performed at the Elementaranalyse-Labor of the
University of Essen.
1357, 1259, 1200 1148, 1092, 1072, 1016, 857, 798, 752, 631, 598
568, 503, 470 cm–1.
[MesnacnacZn(tBuNC(H)S)] (5): tBuNCS (0.04 g, 0.38 mmol) was
added at ambient temperature by syringe to a solution of 1 (0.15 g,
0.19 mmol) in THF (30 ) and stirred for an additional 2 h. There-
after, the solvent was evaporated in vacuo. Yield (isolated crystals)
0.16 g (84%). M.p. 175 °C. C28H39N3SZn (515.07): calcd. C 65.29,
H 7.63, N 8.16; found C 65.36, H 7.59, N 8.09. 1H NMR
(300 MHz, C6D6, 298 K): δ = 0.60 [s, 9 H, C(CH3)3], 1.65 [s, 6 H,
C(CH3)], 2.12 (s, 6 H, p-CH3), 2.39 (s, 12 H, o-CH3), 4.90 (s, 1 H,
CH), 6.74 (s, 4 H, ArH), 8.40 (s, 1 H, NCSH) ppm. 13C{1H} NMR
(75 MHz, C6D6, 25 °C): δ = 18.2 (o-CH3), 19.2 (β-CCH3), 20.8 (p-
CH3), 23.0 [C(CH3)3], 28.8 [CH(CH3)2], 94.4 (γ-C), 129.0 (m-Ar),
129.4 (o-Ar), 133.7 (p-Ar), 145.2 (ipso-Ar), 167.0 (CNS), 168.3 (γ-
[MesnacnacZn(H)dmap] (2): A solution of dmap (60 mg, 0.5 mmol)
in THF (10 mL) was added to a solution of 1 (200 mg, 0.25 mmol)
in THF (20 mL) and stirred at ambient temperature for 1 h. The
solution was concentrated to 5 mL and stored at ambient tempera-
ture. Colourless crystals of 2 were formed within 24 h and isolated
by filtration. Yield (isolated crystals) 0.24 g (92%). M.p. 205 °C.
C30H40N4Zn (522.03): calcd. C 69.02, H 7.72, N 10.73; found C
69.08, H 7.70, N 10.67. 1H NMR (300 MHz, C6D6, 298 K): δ =
1.60 [s, 6 H, C(CH3)], 1.93 (s, 12 H, o-CH3), 2.17 (s, 6 H, p-CH3),
3.00 [s, 6 H, N(CH3)] 4.50 (s, 1 H, ZnH), 4.72 (s, 1 H, CH), 6.55
C) ppm. ATR-IR: ν = 2963, 2916, 1621, 1549, 1517, 1451, 1394,
˜
1259, 1200, 1085, 856, 793, 567, 503, 388 cm–1.
[MesnacnacZn-μ-N3]2 (6): A solution of 1 (0.25 g, 0.31 mmol) in
THF (30 mL) was treated with Me3SiN3 (0.07 g) and stirred at am-
bient temperature for 12 h. All volatiles were removed under re-
duced pressure, and the resulting solid was dissolved in toluene
(10 mL) and stored at –30 °C. Colourless crystals of 6 were formed
within 24 h and isolated by filtration. Yield (isolated crystals) 0.26 g
(96%). M.p. 180 °C. C46H58N10Zn2 (881.77):calcd. C 62.66, H 6.63,
N 15.88; found C 62.49, H 6.51, N 15.76. 1H NMR (300 MHz,
C6D6, 25 °C): δ = 1.39 [s, 6 H, C(CH3)], 2.01 (s, 12 H, o-CH3), 2.34
(s, 6 H, p-CH3), 4.71 (s, 1 H, CH), 6.74 (s, 4 H, Ar-H) ppm.
13C{1H} NMR (75 MHz, C6D6, 25 °C): δ = 7.6 (o-CH3), 21.4 (β-
CCH3), 22.8 (p-CH3), 129.8 (m-Ar), 131.3 (o-Ar), 133.0 (p-Ar),
144.5 (ipso-Ar), 169.0 (γ-C) ppm. 29Si{1H} NMR (75 MHz, [D8]-
THF, 25 °C): δ = –16.3 (Me3SiH), 16.1 (Me3SiN3) ppm. ATR-IR:
3
4
(dd, JHH = 5.1, JHH = 1.5 Hz, 2 H, m-PyH), 6.74 (s, 4 H, ArH),
8.08 (dd, JHH = 5.1, JHH = 1.5 Hz, 2 H, o-PyH) ppm. 13C{1H}
NMR (75 MHz, C6D6, 25 °C): δ = 19.1 (o-CH3), 20.9 (β-CCH3),
23.2 (p-CH3), 38.1 [N(CH3)2], 93.1 (γ-C), 106.5 (m-Py), 129.8 (m-
Ar), 131.6 (o-Ar), 132.5 (p-Ar), 147.5 (p-Py), 154.7 (ipso-Py), 168.5
3
4
(γ-C) ppm. ATR-IR: ν = 2913, 2853, 2300, 1526, 1455, 1398, 1260,
˜
1203, 1148, 1078, 1014, 856, 767, 632, 568, 502, 435, 394 cm–1.
[MesnacnacZn(Cl)dmap] (3):
A solution of dmap (30 mg,
0.26 mmol) in THF (10 mL) was added to a solution of 1 (100 mg,
0.13 mmol) in THF (20 mL) and stirred at room temperature for
1 h. The solution was concentrated to 5 mL and stored at ambient
temperature. All volatiles were removed under reduced pressure,
and the resulting solid was dissolved in hexane (10 mL) and stored
at 0 °C. Colourless crystals of 3 were formed within 24 h and iso-
lated by filtration. Yield (isolated crystals) 0.11 g (85%). M.p.
245 °C. C30H39ClN4Zn (556.49): calcd. C 64.75, H 7.06, N 11.75;
found C 64.60, H 7.01, N 11.63. 1H NMR (300 MHz, C6D6,
298 K): δ = 1.78 [s, 6 H, C(CH3)], 1.88 (s, 6 H, o-CH3), 1.99 (s, 6
H, o-CH3), 2.15 (s, 6 H, p-CH3), 2.73 [s, 6 H, N(CH3)] 4.96 (s, 1
ν = 2961, 2921, 2858, 2160, 2115, 2059, 1728, 1552, 1522, 1401,
˜
1260, 1204, 1073, 1016, 839, 796, 745 cm–1.
[MesnacnacZn-μ-OCy]2 (7): A solution of 1 (0.30 g, 0.4 mmol) and
CHO (0.15 g, 1.5 mmol) in toluene (20 mL) was stored at 50 °C for
3 d, yielding colourless crystals of 7, which were isolated by fil-
tration. Yield 0.24 g (64%). M.p. 346 °C (dec.). C58H80N4O2Zn2
(996.04): calcd. C 69.94, H 8.09, N 5.62; found C 69.89, H 8.10, N
1
5.58. H NMR (500 MHz, C6D6, 25 °C): δ = 0.90–1.02 [m (br.), 2
H, H(4)], 1.13–1.26 [m (br.), 4 H, H(3/5)], 1.50 (s, 6 H, β-CCH3),
1.72 [d (br.), 4 H, H(3/5)eq], 2.10 (s, 12 H, o-CH3), 2.36 (s, 6 H, p-
CH3), 3.24 [m (br.), 1 H, H(1)], 4.87 (s, 1 H, γ-CH), 7.00 (s, 4 H,
m-H) ppm. Because of the very low solubility of 7 in C6D6 and
[D8]THF, the resonances are rather broad, in particular those of
the Cy (Cy = cyclohexyl) group. As a consequence, it was not pos-
sible to distinguish between the equatorial and axial H atoms of
the Cy group. Moreover, a 13C{1H} NMR spectrum could not be
3
4
H, CH), 5.61 (dd, JHH = 5.0, JHH = 1.5 Hz, 2 H, m-PyH), 6.74
3
4
(s, 2 H, ArH), 6.91 (s, 2 H, Ar-H), 8.12 (dd, JHH = 5.0, JHH
=
1.5 Hz, 2 H, o-PyH) ppm. 13C{1H} NMR (75 MHz, C6D6, 25 °C):
δ = 19.0 (o-CH3), 19.9 (o-CH3), 21.3 (β-CCH3), 23.7 (β-CCH3),
26.2 (p-CH3), 38.3 [N(CH3)2], 93.9 (γ-C), 106.7 (m-Py), 129.2 (m-
Ar), 130.5 (o-Ar), 131.1 (o-Ar), 133.6 (p-Ar), 133.8 (p-Ar), 146.2
recorded. IR: ν = 2916, 2849, 1541, 1519 1477, 1452, 1394, 1365,
˜
(p-Py), 149.2 (p-Py), 155.2 (ipso-Py), 167.9 (γ-C) ppm. ATR-IR: ν
˜
1259, 1228, 1199, 1148, 1076, 1019, 974, 855, 754, 728, 592, 568,
= 2962, 2916, 2857, 1615, 1543, 1518, 1444, 1392, 1261, 1224, 1199,
552, 504, 427 cm–1.
1146, 1067, 1013, 857, 813, 744, 631, 569, 534, 502 cm–1.
[MesnacnacZn(tBuNC(H)NtBu)] (4):
(38 mg, 0.26 mmol) in THF (15 mL) was added to a solution of 1
A
solution of (tBuC)2N Single-Crystal X-ray Analyses: Crystallographic data of 2, 3, 6 and
7, which were collected with a Bruker AXS D8 Kappa dif-
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/KAP1
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Pages: 8
S. Schulz et al.
FULL PAPER
Table 1. Crystallographic data for 2, 3, 6 and 7.
2
3
6
7
Empirical formula
C30H40N4Zn
522.03
monoclinic
P21/n
C30H39ClN4Zn
556.47
C46H58N10Zn2·2C7H8 C58H80N4O2Zn2
Mr [gmol–1]
1066.03
triclinic
996.0
Crystal system
Space group
triclinic
monoclinic
P21/c
¯
¯
P1
P1
a [Å]
b [Å]
c [Å]
α [°]
7.9641(2)
28.7478(7)
12.3878(3)
90
96.1120(10)
90
8.1153(2)
12.4514(4)
16.4631(5)
68.769(2)
80.746(1)
85.334(1)
1529.97(8)
2
9.2569(4)
12.0857(5)
13.4593(5)
101.770(2)
109.520(2)
90.798(2)
1383.88(10)
1
13.0401(4)
19.4242(6)
20.7932(6)
90
94.3590(10)
90
β [°]
γ [°]
V [Å3]
2820.07(12)
4
5251.5(3)
4
Z
T [K]
103(1)
0.71073
0.985
1.230
52.9
100(1)
0.71073
0.913
1.208
61.1
100(1)
0.71073
0.914
1.279
60.0
103(1)
0.71073
0.958
1.260
50.1
λ [Å]
μ [mm–1]
Dcalcd. [gcm–3]
2θmax [°]
Crystal size [mm]
Number of reflections
Number of unique reflections
Rint
0.28ϫ0.23ϫ0.20
33157
5782
0.32ϫ0.23ϫ0.08
64274
9276
0.0257
325/0
0.027
0.0787
1.084
0.35ϫ0.17ϫ0.15
29768
7943
0.0193
325/0
0.0249
0.0682
1.038
0.15ϫ0.13ϫ0.07
56415
9264
0.0366
595/0
0.0407
0.1034
1.029
0.0166
Number of parameters refined/restraints 320/0
[a]
R1
0.0302
0.0760
1.110
[b]
wR2
Gof[c]
Max./min. transmission
0.75/0.67
0.345/–0.290
0.75/0.67
0.515/–0.259
0.75/0.63
0.443/–0.227
0.75/0.67
1.359/–0.598
Final max/min. Δρ [eÅ–3]
2
2 2
2
[a] R1 = Σ(||Fo| – |Fc||)/Σ|Fo| [for IϾ2σ(I)]. [b] wR2 = {Σ[w(Fo2 – Fc ) ]/Σ[w(Fo2)2]}1/2. [c] Goodness of fit = {Σ[w(|Fo2| – |Fc |)2]/(Nobservns
–
Nparams)}1/2. w–1 = σ2(Fo2) + (aP)2 + bP with P = [Fo + 2Fc ]/3, a and b are constants chosen by the program.
2
[2]
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fractometer (Mo-Kα radiation, λ = 0.71073 Å), are summarized in
Table 1. The structures were solved by direct methods (SHELXS-
97)[26] and refined by full-matrix least-squares on F2. Absorption
corrections were performed semiempirically from equivalent reflec-
tions on the basis of multi-scans (Bruker AXS APEX2). All non-
hydrogen atoms were refined anisotropically and hydrogen atoms
by a riding model (SHELXL-97, Program for Crystal Structure
Refinement)[27] on idealized geometries with the 1.2-fold (1.5-fold
for methyl groups) isotropic displacement parameters of the equiv-
alent Uij values of the corresponding carbon atoms. H1 of 2 was
taken from a difference Fourier map and refined freely. In the re-
finement of 3 several peaks of 1.6–2.8 Å3 remained, which were
attributed to hexane molecules highly disorderd over an inversion
centre. Refining the peaks as carbon atoms with reduced SOF
yielded R1 = 0.0344, but no reasonable arrangement of the atoms
could be refined properly. Consequently, the final refinement was
performed with solvent-free reflection data taken from PLATON/
squeeze.[28] CCDC-872730 (2), CCDC-872731 (3), CCDC-872733
(6), CCDC-872732 (7) contain the supplementary crystallo-
graphic 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_request/cif.
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
Acknowledgments
Z. Anorg. Allg. Chem. 2009, 635, 216–220.
S. Schulz, T. Eisenmann, S. Schmidt, D. Bläser, U. Westphal,
R. Boese, Chem. Commun. 2010, 46, 7226–7228.
S. Schulz, J. Spielmann, D. Bläser, C. Wölper, Chem. Commun.
2011, 47, 2676–2678.
a) S. Schulz, T. Eisenmann, U. Westphal, S. Schmidt, U. Flörke,
Z. Anorg. Allg. Chem. 2009, 635, 216–220; b) S. Schulz, T. Ei-
senmann, D. Bläser, R. Boese, Z. Anorg. Allg. Chem. 2009, 635,
995–1000.
S. S. thanks the German Science Foundation (DFG) for financial
support.
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6
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Date: 29-06-12 09:33:00
Pages: 8
Reactivity of (β-Diketiminato)zinc Hydride
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Received: April 17, 2012
Published Online: ᭿
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7

Job/Unit: I20378
/KAP1
Date: 29-06-12 09:33:00
Pages: 8
S. Schulz et al.
FULL PAPER
(β-Diketiminato)zinc Hydride
MesnacnacZnH {Mesnacnac
=
[(2,4,6-
G. Bendt, S. Schulz,* J. Spielmann,
Me3C6H2)NC(Me)]2CH} reacts with 4-(di-
methylamino)pyridine (dmap) upon adduct
formation, whereas reactions with (tBuN)2-
C, tBuNCS and CHO proceed with inser-
tion into the Zn–H bond. In contrast, Me3-
SiN3 was found to react with Mesnac-
nacZnH with the formation of Mesnac-
nacZn(N3), which forms an azido-bridged
dimer in the solid state.
S. Schmidt, D. Bläser, C. Wölper ...... 1–8
Reactivity of (β-Diketiminato)zinc Hydride
toward Lewis Bases, Heterocumulenes and
Cyclohexene Oxide
Keywords: N ligands / Zinc / Insertion /
Cumulenes / Lewis acids
8
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