Extending the family of N-heterocyclic heavy carbene analogues: Synthesis and crystal and molecular structures of MeN[CH2C(O)N(R)] 2Sn (R = Me2NCH2CH2, PhCH 2, Me3CCH2)

Article abstract of DOI:10.1002/ejic.201300535

We report herein the synthesis of the N-methyl-N′N″- diorganoiminodiacetic acid diamides MeN[CH₂C(O)N(R)H]₂ [3: R = Me₂N(CH₂)₂; 4: R = PhCH₂; 5: R = Me₃CCH₂] and the novel tin(II) derivatives MeN[CH ₂C(O)N(R)]₂Sn [6: R = Me₂N(CH₂) ₂; 7: R = PhCH₂; 8: R = Me₃CCH₂]. The compounds were characterized by elemental analyses, ¹H NMR spectroscopy (3-5), solid-state ¹³C and ¹¹⁹Sn NMR spectroscopy (8), and single-crystal X-ray diffraction analysis (5, 8). Compound 8 shows intramolecular N→Sn and intermolecular O→Sn interactions with distances of 2.370(2) and 2.406(2) A, respectively, the latter indicating that 8 is a coordination polymer. DFT calculations revealed covalent Sn-NC(O) and coordinative N→Sn and C=O→Sn bonds. The wB97Xd functional, which takes into account dispersive interactions, was employed for a correct theoretical description of, in particular, the latter bond. A novel type of intramolecularly coordinated N-heterocyclic diazastannylene is reported that holds great potential for subsequent chemistry due to its high stability in air and the many possibilities to vary the substituents.

Full text of DOI:10.1002/ejic.201300535

FULL PAPER
DOI:10.1002/ejic.201300535
Extending the Family of N-Heterocyclic Heavy Carbene
Analogues: Synthesis and Crystal and Molecular
Structures of MeN[CH2C(O)N(R)]2Sn (R =
Me2NCH2CH2, PhCH2, Me3CCH2)
Ljuba Iovkova-Berends,[a] Miriam Seiger,[a] Thomas Westfeld,[b]
Alexander Hoffmann,[c][‡] Sonja Herres-Pawlis,[c][‡] and
Klaus Jurkschat*[a]
COVER PICTURE
Dedicated to Professor Clemens Mügge on the occasion of his 60th birthday
Keywords: Nitrogen heterocycles / Tin / Density functional calculations / Coordination modes
We report herein the synthesis of the N-methyl-NЈNЈЈ-dior-
ganoiminodiacetic acid diamides MeN[CH2C(O)N(R)H]2 [3:
R = Me2N(CH2)2; 4: R = PhCH2; 5: R = Me3CCH2] and the
8). Compound 8 shows intramolecular NǞSn and intermo-
lecular OǞSn interactions with distances of 2.370(2) and
2.406(2) Å, respectively, the latter indicating that 8 is a coor-
dination polymer. DFT calculations revealed covalent Sn–
NC(O) and coordinative NǞSn and C=OǞSn bonds. The
wB97Xd functional, which takes into account dispersive in-
teractions, was employed for a correct theoretical description
of, in particular, the latter bond.
novel tin(II) derivatives MeN[CH2C(O)N(R)]2Sn [6:
R =
Me2N(CH2)2; 7: R = PhCH2; 8: R = Me3CCH2]. The com-
pounds were characterized by elemental analyses, 1H NMR
spectroscopy (3–5), solid-state 13C and 119Sn NMR spec-
troscopy (8), and single-crystal X-ray diffraction analysis (5,
Introduction
molecular coordination of a built-in donor function that
fills the vacant pz orbital at the tin atom with electron den-
sity.[6–9] Sometimes this is achieved in combination with
steric protection. In the case of tin(II) amides, this has been
demonstrated for the intramolecularly coordinated com-
pounds A,[10] B,[11] C,[12a] and D[12b] (Scheme 1).
Low-valent tin compounds are heavy carbene ana-
logues.[1] Their central feature is their ambivalent reactivity
as both Lewis acid and Lewis base. The tin(II) amide
Sn[N(SiMe3)2]2 and the cyclic diazastannylene Sn[N(tBu)]2-
SiMe2, which were first reported by Harris and Lappert[2]
and by Veith and Grosser,[3] respectively, have been key
compounds in the development of the rather interesting
chemistry of such compounds and have led to intensive and
ongoing research activities in this field.[4] As a result of
steric protection by bulky substituents, these compounds
are monomeric both in solution and in the solid state. This
steric protection proved to be rather useful for the synthesis
of a variety of not only stannylenes, but also other heavy
carbene analogues.[1,5] An alternative approach to the stabi-
lization of molecular low-valent tin compounds is the intra-
[a] Lehrstuhl für Anorganische Chemie II der Technischen
Universität,
44221 Dortmund, Germany
Homepage: http://www.chemie.tu-dortmund.de/fb03/de/
Forschung/AC/Jurkschat/index.html
[b] CURRENTA Analytik, CHEMPARK,
51368 Leverkusen, Germany
[c] Department
München,
Chemie,
Ludwig-Maximilians-Universität
Butenandtstr. 5–13, 81377 München, Germany
[‡] DFT calculations.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300535.
Scheme 1.
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As long ago as 1982 we employed N,NЈ,NЈЈ-trimethyl-
iminodiacetic acid diamide, MeN[CH2C(O)N(Me)H]2, for
the synthesis of intramolecularly coordinated diorgano-
tin(IV) compounds MeN[CH2C(O)N(Me)]2SnR2 (R = Me,
Et, tBu).[13a] Although this chelate ligand can easily be syn-
thesized and offers many possibilities for varying the sub-
stituents at the nitrogen atoms, it has been, to the best of
our knowledge, neglected in main group metal chemistry.
Herein we present the first results of its employment in the
synthesis of tin(II) derivatives of type E (Scheme 1). These
are the first representatives of a novel class of N-heterocy-
clic stannylenes that feature an intramolecular NǞSn inter-
action as well as the possibility of intermolecular OǞSn
coordination.
Results and Discussion
The BF3-catalyzed reaction of the N-methyliminodiacetic
acid, MeN[CH2C(O)OH]2 (1), with methanol gave the cor-
responding methyl ester MeN[CH2C(O)OMe]2 (2) in good
yield. The latter was easily converted into the corresponding
amides MeN[CH2C(O)NRH]2 (3: R = Me2NCH2CH2; 4: R
= PhCH2; 5: R = Me3CCH2) by reaction with N,N-di-
methylethylenediamine, benzylamine, and neo-pentylamine,
respectively, in the presence of a catalytic amount of ammo-
nium chloride (Scheme 2).
Figure 1. ORTEP structure and atom numbering scheme of com-
pound 5 (molecule A). Ellipsoids are drawn at the 30% probability
level. Hydrogen atoms have been omitted for clarity.
N(21)–H(21A)···N(24) hydrogen bonds are structure-direct-
ing.
Compounds 3–5 are colorless crystalline materials solu-
ble in boiling toluene and polar organic solvents such as
CH2Cl2 and CHCl3. All the compounds formed crystals of
poor quality, irrespective of the crystallization conditions,
and only the crystals of the neo-pentyl-substituted acid
amide 5 were suitable for single-crystal X-ray diffraction
studies. The molecular structure of compound 5 is shown
in Figure 1 and selected bond lengths and angles are given
in Table 1.
The N-methyliminodiacetic acid amides 3–5 reacted with
Sn[N(SiMe3)2]2 at room temperature (Scheme 3) to give the
corresponding cyclic tin(II) amides 6–8 as white solids that
show remarkable stability. Thus, no change in the material
was observed after compound 8 had been exposed to air
for 24 h.
The asymmetric unit consists of two crystallographically
independent molecules A and B, each of which forms cen-
trosymmetric head-to-tail dimers through N(17)–H(17A)···
O(12A) (molecule A) and N(27)–H(27A)···O(22A) (mole-
cule B) hydrogen bridges giving rise to 16-membered rings.
Scheme 3. Synthesis of the intramolecularly coordinated tin(II) N-
In addition, the intramolecular N(11)–H(11A)···N(14) and methyliminodiacetic acid amide derivatives 6–8.
Scheme 2. Synthesis of the N-methyl-NЈ,NЈЈ-diorganoiminodiacetic acid diamides 3–5.
Table 1. Intra- and intermolecular hydrogen bonds in compound 5.
D–H···A
d(D–H) [Å]
d(H···A) [Å]
d(D···A) [Å]
Angle DHA [°]
N(11)–H(11A)···N(14)
N(17)–(H17A)···O(12A)
N(21)–H(21A)···N(24)
N(27)–H(27A)···O(22A)
0.83(3)
1.03(3)
0.63(3)
0.91(3)
2.26(3)
1.86(3)
2.34(3)
2.04(3)
2.682(4)
2.879(3)
2.672(4)
2.918(4)
112(3)
170(3)
112(4)
162(3)
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Figure 2. ORTEP structure and atom numbering scheme of the asymmetric unit of compound 8. Ellipsoids are shown at the 30%
probability. Hydrogen atoms have been omitted for clarity.
Table 2. Selected bond lengths [Å] and angles [°] for compound 8 (experimental) and a hypothetical dimer of 8 (determined by DFT
calculations).
Experimental
BP86/def2-TZVP
wB97xD/def2-TZVP
Sn(1)–N(11,amide)
Sn(1)–N(17,amide)
Sn(1)–N(14,amine)
Sn(1)–O(12A)
N(11)–Sn(1)–N(17)
N(14)–Sn(1)–N(17)
N(11)–Sn(1)–N(14)
N(17)–Sn(1)–O(12A)
N(11)–Sn(1)–O(12A)
N(14)–Sn(1)–O(12A)
2.213(2)
2.197(2)
2.370(2)
2.406(2)
97.82(7)
71.14(8)
71.93(7)
87.40(7)
84.26(7)
144.81(6)
2.214
2.180
2.390
2.804
100.7
75.3
72.8
92.8
91.4
157.7
2.173
2.143
2.372
2.515
97.9
75.7
72.8
85.6
88.9
151.5
Compounds 6–8 are almost insoluble in common organic somewhat meaningful comparison can best be made with
solvents such as toluene, dioxane, pyridine, CHCl3, and the Sn–N distances in the intramolecularly coordinated
CH2Cl2. Attempted recrystallization from various solvents eight-membered diazastannylenes Sn[N(Dipp)CH2CH2]2O
to give single crystals of 6–8 failed. However, single crystals [Dipp = 2,6-iPr2C6H3; Sn–N 2.075(2) Å][11] and the N,NЈ-
of compound 8 suitable for X-ray diffraction analysis were disubstituted
benzimidazolin-2-stannylenes
o-C6H4-
obtained by the very slow addition of a solution of the [N(R)]2Sn [R = Me2N(CH2)3; Sn–N(1) 2.111(2), Sn–N(2)
amide 5 in dioxane into a solution of Sn[N(SiMe3)2]2 in 2.149(2) Å].[12] The intramolecular Sn(1)–N(14) interaction
toluene at 0 °C without stirring. The molecular structure of in compound 8 with a distance of 2.370(2) Å is considerably
compound 8 is shown in Figure 2 and selected bond lengths stronger than the intra- and intermolecular Sn–N(4)
and angles are given in Table 2.
[2.612(2) Å] and Sn–N(2*) [2.611(2) Å] interactions, respec-
The Sn(1) atom in compound 8 is four-coordinate and tively, reported for the latter compound.[12] The intramolec-
exhibits a strongly distorted pseudo-trigonal-bipyramidal ular Sn–N distances are also longer in the structurally re-
configuration with O(12A) and N(14) occupying the axial lated 2,8-dioxa-5-aza-1-stanna(II)bicyclo[3.3.0]octane de-
positions and N(11), N(17), and the lone-electron pair at rivatives [MeN(CH2CR2O)2Sn]2 (R = H, Me), ranging be-
Sn(1) the equatorial positions. The distortion from the ideal tween 2.524(2) and 2.413(10) Å. Apparently, the tin(II)
trigonal-bipyramidal geometry is revealed by the O(12A)– atom in 8 has a rather high Lewis acidity.
Sn(1)–N(14) and N(11)–Sn(1)–N(17) angles of 144.81(6)
and 97.82(7)°, respectively, and results from the stereochem- intermolecular O(12A)ǞSn(1) interactions at a distance of
ically active lone-electron pair. 2.406(2) Å to form an infinite chain structure (Figure 3).
In the crystal lattice, molecules of 8 are linked by strong
The Sn(1)–N(11) and Sn(1)–N(17) distances of 2.213(2) This interaction is responsible for the rather poor solubility
and 2.197(2) Å are almost equal. According to a search of of compound 8 even in polar organic solvents.
the Cambridge Crystallographic Database, there is no crys-
This intermolecular O(12A)ǞSn(1) interaction is also re-
tal structure corresponding to a parent tin(II) amide of the flected in the IR spectrum, which shows a rather broad and
type Sn[N(R)C(O)RЈ]2 in the literature.[13b] Consequently, a intense ν(CO) band at 1613 cm–1, a lower value than that of
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Figure 3. ORTEP structure and atom numbering scheme of the coordination polymer of compound 8. Ellipsoids are drawn at the 30%
probability level. tBu substituents have been omitted for clarity.
the N-methyl-NЈ,NЈЈ-diorganoiminodiacetic acid diamide 5 dex of 0.36, whereas the intramolecular NǞSn and inter-
(1654 cm–1). For the monomeric diorganotin derivatives molecular C=OǞSn interactions are estimated to have
MeN[CH2C(O)N(Me)]2SnR2 (R = Me, Et, tBu) showing no Wiberg indices of 0.15 and 0.13, respectively.
intermolecular OǞSn interaction ν(CO), vibrations be-
tween 1630 and 1650 cm–1 were observed.[13]
The 119Sn CP-MAS NMR spectrum displays a broad res-
onance at δ = –332 (ν1/2 = 4400 Hz) and the 13C CP-MAS
NMR spectrum shows broad resonances (ν1/2 = 320–
570 Hz) at δ = 171.2 (CO), 61.8, 52.4 (NCH2), 45.9 (NCH3),
34.3 (CCH3), and 28.7 (CCH3) ppm. The resolution of this
spectrum is not sufficient to distinguish the nonequivalence
of the carbon atoms observed by the X-ray diffraction
analysis.
Conclusions
We have demonstrated that the deprotonated N-methyl-
NЈ,NЈЈ-diorganoiminodiacetic acid diamides are suitable li-
gands for the synthesis of a novel type of N-heterocyclic
intramolecularly coordinated stannylenes. The latter show
remarkable stability towards air. As a result of strong inter-
molecular C=OǞSn interactions giving rise to the forma-
tion of a coordination polymer, the compounds show poor
solubility in common organic solvents. To increase the solu-
bility, more bulky organic substituents at the amide and/or
amine nitrogen atoms are needed, which in turn will allow
further exploration of the chemistry of these tin(II) com-
pounds. The stabilization of other low-valent main-group
elements as well as transition-metal compounds is also en-
visaged. Furthermore, we have learned that for a satisfac-
tory theoretical description by DFT calculations of espe-
cially the coordinative NǞSn and C=OǞSn interactions,
the use of the wB97Xd functional is needed.
To elucidate the bonding situation in the coordination
polymer 8, DFT calculations on a dimeric unit were per-
formed. Gaussian 09[14a] with the pure functional
BP86[14b,14c] and the def2-TZVP basis set[14d] was used for
the geometry optimization because this combination has al-
ready been used on similar compounds.[14e,14f,14g] The re-
sults of the calculations are presented in Table 2.
The data clearly show that BP86 cannot reasonably de-
scribe the bonding situation between the amide oxygen do-
nor atom and the SnII atom. A preliminary NBO analysis
did not show significant dative stabilization by the coordi-
nating oxygen atom. Therefore we performed further calcu-
lations with the wB97Xd functional,[14h] which includes dis-
persive interactions. In this case we found excellent agree-
ment between experimental and calculated data for the
bonding interactions with the tin atom. In a further theoret-
ical investigation, NBO calculations[14i] were performed
Experimental Section
General Methods: All solvents were purified by distillation under
argon from appropriate drying agents. All reactions with air- and
moisture-sensitive compounds were carried out under argon. N-
Methyliminodiacetic acid, MeN[CH2C(O)OH]2,[15] and the tin(II)
amide Sn[N(SiMe3)2]2[16] were prepared according to literature pro-
cedures.
with
the
wB97Xd/def2-TZVP
combination
in
Gaussian 09[14a] to gain an insight into the electronic struc-
ture of the dimer. The Sn–NC(O) bonds involving the
amide nitrogen atoms are shown to be covalent, whereas
the intramolecular NǞSn and intermolecular C=OǞSn in-
teractions involving the amine nitrogen and oxygen donor
atoms are dative bonds with energies of 31 and 33 kcal/
mol, respectively. The Wiberg bond indices show a similar
The NMR experiments were carried out with Bruker DRX 400 and
DPX 300 spectrometers. Chemical shifts δ are given in ppm and
are referenced to the solvent signals with the usual values calibrated
against tetramethylsilane (1H, 13C) and tetramethylstannane
(
119Sn). The 13C and 119Sn CP-MAS NMR spectra were recorded
with a Bruker DPX400 spectrometer operating at a static field of
picture: The Sn–NC(O) amide bonds possess a Wiberg in- 9.4 T. A 4 mm Bruker double-resonance probe was used. The spin-
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ning frequency of the rotor was actively controlled at 15 kHz to
within 5 Hz. All solid-state NMR spectra were recorded under Spi-
nal64 proton decoupling[17] with a RF field strength of 87 kHz. For
the initial cross-polarization step from proton to the heteronucleus,
an adiabatic passage through the Hartmann–Hahn condition was
performed.[18] 13C chemical shifts were calibrated externally to ada-
mantane. 119Sn chemical shifts were calibrated from the 13C scale
by using tabulated conversion factors.[19] The electrospray mass
spectra were recorded with a Thermoquest-Finnigan spectrometer
by using CH3CN or CH2Cl2 as a mobile phase. Samples were intro-
duced as solutions through a syringe pump operating at a rate of
0.5 μL/min. The capillary voltage was 4.5 kV, whereas the cone
skimmer voltage was varied between 50 and 250 kV. The expected
ions were identified by comparison of experimental and calculated
isotopic distribution patterns. Elemental analyses were performed
with a LECO-CHNS-932 analyzer. IR spectra were recorded with
a PerkinElmer Spectrum Two spectrometer equipped with a UATR
accessory.
ference Fourier syntheses. Refinement was performed by full-ma-
trix least-squares methods using SHELXL97.[21] All H atoms were
located in the difference Fourier map and their positions were iso-
tropically refined with Uiso constrained at 1.2 times Ueq of the car-
rier C atom for non-methyl and 1.5 times Ueq of the carrier C atom
for methyl groups. Atomic scattering factors for neutral atoms and
real and imaginary dispersion terms were taken from the Inter-
national Tables for X-ray Crystallography.[22] The figures were cre-
ated by using SHELXTL.[23] Crystallographic data are presented
in Table 3.
CCDC-923354 (for 5) and -923355 (for 8) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computational Details: The calculations were performed with
Gaussian 09[14a] by using the BP86 pure functional[14b,14c] and the
wB97Xd functional, which takes dispersion into account,[14h] in
combination with the Ahlrichs def2-TZVP basis set,[14d] which in-
cludes the effective core potentials on tin. Strict convergence cri-
teria were applied. Stationary points were characterized by fre-
quency analysis and showed the correct number of negative eigen-
values (zero for a local minimum). Based on the geometry obtained
by the wB97Xd/def2-TZVP method, an NBO analysis was per-
formed by using this method with NBO 3.1[14i] as implemented in
Gaussian 09.[14a]
Crystallography: Intensity data for the colorless crystals of 5 and
8 were collected with an Xcalibur2 CCD diffractometer (Oxford
Diffraction) with graphite-monochromated Mo-Kα radiation at
110 K. The data collection covered almost the whole sphere of the
reciprocal space with 8 (5) and 9 (8) sets of data at different κ
angles and 434 (5) and 506 (8) frames by ω rotation (Δ/ω = 1°) at
2ϫ1.5 (5) and 1.5 (8) per frame. The crystal-to-detector distance
was 4.5 cm. Crystal decay was monitored by repeating the initial
frames at the end of data collection. Analysis of the duplicate re-
flections gave no indication of any decay. The structures were
solved by direct methods using SHELXS97[20] and successive dif-
Dimethyl N-Methyliminodiacetate (2): A solution of BF3·MeOH in
MeOH (50%, 38.43 g, 0.38 mol) was added to a suspension of N-
methyliminodiacetic acid (1; 16.18 g, 0.11 mol) in dry methanol
(75 mL).[24] After heating the reaction mixture at reflux for 18 h
and allowing it to cool to room temperature, CHCl3 (300 mL) and
a saturated NaHCO3 solution (150 mL) were added. The pH of the
resulting solution was adjusted to 7–8 by adding solid NaHCO3.
The organic layer was separated, the aqueous phase was extracted
with CHCl3 (2ϫ300 mL), and the combined organic layers were
dried with MgSO4 and filtered. After the solvent of the filtrate had
been removed in vacuo, the resulting slightly yellowish liquid was
distilled (14 mbar, 106 °C) to give compound 2 as a colorless liquid
Table 3. Crystal data and structure refinement for compounds 5
and 8.
5
8
Empirical formula
Formula mass
Temperature [K]
Wavelength [Å]
Crystal system
Space group
Crystal size [mm3]
Unit cell dimensions
a [Å]
C15H31N3O2
285.43
173(2)
0.71073
monoclinic
C2/c
C15H29N3O2Sn
402.12
173(2)
0.71073
tetragonal
I41/a
1
(12.6 g, 70 mmol, 66%). H NMR (400.13 MHz, CDCl3): δ = 3.38
(s, 6 H, CH3), 3.17 (s, 4 H, CH2), 2.19 (s, 3 H, NCH3) ppm.
13C{1H} NMR (100.63 MHz, CDCl3): δ = 171.1 (s, COO), 57.0 (s,
CH2), 51.5 (s, CH3), 42.2 (s, NCH3) ppm. LRMS (ESI): calcd. for
[C7H13NO4 + H]+ 176.1; found 176.1.
0.40ϫ0.30ϫ0.04
0.28ϫ0.24ϫ0.16
16.5617(19)
16.7619(18)
25.417(3)
90
19.9156(12)
19.9156(12)
19.1949(17)
90
b [Å]
c [Å]
α [°]
N-Methyl-NЈ,NЈЈ-bis(2-dimethylaminoethyl)iminodiacetic Acid Di-
amide (3): A mixture of dimethyl N-methyliminodiacetate (2; 3.9 g,
22.2 mmol), N,N-dimethylethylenediamine (3.9 g, 44.5 mmol), and
NH4Cl (1.5 mg, 1.6 mmol) was heated at reflux for 1 h.[23] After
cooling the reaction mixture to room temperature, CH2Cl2 was
added and the organic layer was washed with water. The organic
phase was separated, dried with MgSO4, and filtered. The solvent
of the filtrate was removed in vacuo and compound 3 was obtained
β [°]
γ [°]
94.851(9)
90
7030.6(14)
16
1.079
0.072
90
90
7613.3(9)
16
1.403
Volume [Å3]
Z
Dc [g/cm3]
Abs. coeff. [mm–1]
F(000)
1.350
3296
2528
as
a slightly yellow amorphous solid (m.p. 41 °C, 3.18 g,
θ range for data collection
Index interval
2.29–29.27
–19ՅhՅ22
–22ՅkՅ22
34ՅlՅ32
28256
2.05–25.49
–14ՅhՅ24
–21ՅkՅ24
23ՅlՅ22
15356
11.1 mmol, 50%). 1H NMR (400.13 MHz, CDCl3): δ = 7.32 (br. s,
2 H, NH), 3.36 (t, 4 H, CH2), 3.10 (s, 4 H, CH2), 2.43 (t, 4 H,
CH2), 2.35 (s, 3 H, CH3), 2.24 (s, 12 H, CH3) ppm. 13C{1H} NMR
(100.63 MHz, CDCl3): δ = 170.1 (s, CONH), 62.0 (s, CH2), 58.6 (s,
Reflections collected
Completeness to θ = 25.50° 99.9
99.9
CH ), 45.7 (s, CH ), 44.2 (s, CH ), 36.9 (s, CH ) ppm. IR: ν =
˜
2
3
2
3
Independent reflections/Rint 8408/ 0.2084
3547/0.0433
190
0.812
3375, 3306 (νNH), 1658, 1634 (νCO) cm–1. LRMS (ESI): calcd.
for [C13H29N5O2 + H+]+ 288.2; found 288.2. C13H29N5O2 (287.40):
calcd. C 54.3, H 10.2, N 24.4; found 54.0, H 10.1, N 24.6.
Refined parameters
361
GooF (F2)
0.604
Final R indices [IϾ2σ(I)]
R indices (all data)
Largest diff. peak and hole
[eÅ–3]
0.0465
0.0854
0.171 and –0.171
0.0229
0.0413
0.365 and –0.306
N-Methyl-NЈ,NЈЈ-dibenzyliminodiacetic Acid Diamide (4): A mix-
ture of dimethyl N-methyliminodiacetate (2; 4 g, 22.8 mmol), ben-
zylamine (4.9 g, 45.7 mmol), and NH4Cl (1.5 mg, 1.6 mmol) was
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heated at reflux for 1 h.[23] After cooling the reaction mixture to
room temperature, CH2Cl2 was added and the organic layer was
washed with water. The organic phase was separated, dried with
MgSO4, and filtered. The solvent of the filtrate was removed in
vacuo and compound 4 was obtained as a white amorphous solid
that was recrystallized from toluene (m.p. 116–118 °C, 5.1 g,
1.66 mmol) in dry toluene (15 mL). The reaction mixture was
stirred at room temperature until the intense orange color of
Sn[N(SiMe3)2]2 had disappeared. The formation of a colorless crys-
talline precipitate was observed after a few minutes. The reaction
mixture was kept for 18 h without stirring and the resulting solid
was filtered, washed with n-hexane, and dried in vacuo to give com-
15.7 mmol, 69%). 1H NMR (400.13 MHz, CDCl3): δ = 7.32 (m, pound 8 as a colorless crystalline material that is almost insoluble
10 H, C6H5), 6.97 (br. s, 2 H, CONH), 4.45 (d, 4 H, CH2), 3.16 (s,
in common organic solvents. 119Sn CP-MAS NMR: δ = –332 (ν1/2
4 H, CH2), 2.37 (s, 3 H, CH3) ppm. 13C{1H} NMR (100.63 MHz, = 4400 Hz) ppm. 13C CP-MAS NMR: δ = 171.2 (CO), 61.8, 52.4
CDCl3): δ = 169.9 (s, CONH), 138.5 (s, C6H5), 129.2 (s, C6H5), (NCH ), 45.9 (NCH ), 34.3 (CCH ), 28.7 (CCH ) ppm. IR: ν =
˜
2
3
3
3
128.1 (s, C6H5), 61.9 (s, CH2), 44.4 (s, CH2), 43.6 (s, CH3) ppm. 1613 (νCO) cm–1. C15H29N3O2Sn (402.12): calcd. C 44.8, H 7.3, N
IR: ν = 3351, 3299 (νNH), 1658, 1634 (νCO) cm–1. LRMS (ESI):
10.4; found C 44.4, H 7.3, N 10.1.
˜
calcd. for [C19H23N3O2 + H]+ 326.1; found 326.1. C19H23N3O2
(325.40): calcd. C 70.1, H 7.2, N 12.9; found C 69.9, H 7.1, N 12.9.
Supporting Information (see footnote on the first page of this arti-
cle): Coordinates of the optimized dimer of compound 8 (wB97xd/
N-Methyl-NЈ,NЈЈ-di-neo-pentyliminodiacetic Acid Diamide (5): A def2-TZVP).
mixture of dimethyl N-methyliminodiacetate (2; 4 g, 22.8 mmol),
neo-pentylamine (3.98 g, 45.7 mmol), and NH4Cl (1.5 mg,
[1] For selected reviews, see: a) M. Veith, O. Recktenwald, Top.
1.6 mmol) was heated at reflux for 1 h.[23] After cooling the reaction
mixture to room temperature, CH2Cl2 was added and the organic
layer was washed with water. The organic phase was separated,
dried with MgSO4, and filtered. The solvent of the filtrate was re-
moved in vacuo and compound 5 was obtained as a colorless
amorphous solid that was recrystallized from toluene (m.p. 100–
102 °C, 3.3 g, 10.1 mmol, 50.6%). 1H NMR (400.13 MHz, CDCl3):
δ = 3.77 (br. s, 2 H, NH), 3.17 (s, 4 H, CH2), 3.13 (d, 4 H, CH2),
2.43 (s, 3 H, CH3), 0.93 (s, 18 H, CH3) ppm. 13C{1H} NMR
(100.63 MHz, CDCl3): δ = 169.8 (s, CO), 62.1 (s, CH2), 50.7 (s,
Curr. Chem. 1982, 104, 1–55; b) N. N. Zemlyanskii, I. V. Bo-
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CH ), 44.5 (s, CH ), 32.3 (s, CCH ), 27.7 (s, CH ) ppm. IR: ν =
˜
2
2
3
3
3345, 3304 (νNH), 1682, 1654 (νCO) cm–1. LRMS (ESI): calcd. for
[C15H31N3O2 + H]+ 286.2; found 286.2. C15H31N3O2 (285.24):
calcd. C 63.1, H 11.0, N 14.7; found C 63.4, H 11.4, N 14.7.
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2,8-Bis(dimethylaminoethyl)-5-methyl-2,5,8-triaza-1-stanna(II)bicy-
clo[3.3.0]octane-3,7-dione (6): A solution of N-methyl-NЈ,NЈЈ-bis(2-
dimethylaminoethyl)iminodiacetic
1.13 mmol) in a mixture of dry thf (5 mL) and dry toluene (5 mL)
was added slowly to solution of Sn[N(SiMe3)2]2 (0.5 g,
acid
diamide
(0.33 g,
a
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1.13 mmol) in dry toluene (15 mL). The reaction mixture was
stirred at room temperature until the intense orange color of
Sn[N(SiMe3)2]2 had disappeared. The formation of a white precipi-
tate was observed after several minutes. The reaction mixture was
stirred for a further 18 h and the resulting solid was filtered, washed
with n-hexane, and dried in vacuo to give compound 6 as a white
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powder that is almost insoluble in common organic solvents. IR: ν
˜
= 1616 (νCO) cm–1. C13H27N5O2Sn (404.10): calcd. C 38.6, H 6.7,
N 17.3; found C 38.7, H 6.4, N 17.5.
2,8-Dibenzyl-5-methyl-2,5,8-triaza-1-stanna(II)bicyclo[3.3.0]-
octane-3,7-dione (7): A solution of N-methyl-NЈ,NЈЈ-dibenzyl-
iminodiacetic acid diamide (0.58 g, 1.77 mmol) in dry toluene
(10 mL) was added slowly to a solution of Sn[N(SiMe3)2]2 (0.78 g,
1.77 mmol) in dry toluene (15 mL). The reaction mixture was
stirred at room temperature until the intense orange color of
Sn[N(SiMe3)2]2 had disappeared. The formation of a white precipi-
tate was observed after several minutes. The reaction mixture was
stirred for a further 18 h and the resulting solid was filtered, washed
with n-hexane, and dried in vacuo to give compound 7 as white
powder that is almost insoluble in common organic solvents. IR: ν
˜
= 1604 (νCO) cm–1. C19H21N3O2Sn (442.10): calcd. C 51.6, H 4.8,
N 9.5; found C 51.7, H 4.4, N 9.3.
2,8-Di-neo-pentyl-5-methyl-2,5,8-triaza-1-stanna(II)bicyclo[3.3.0]-
octane-3,7-dione (8): A solution of N-methyl-NЈ,NЈЈ-di-neo-pentyl-
iminodiacetic acid diamide (0.47 g, 1.66 mmol) in dry dioxane
(10 mL) was added slowly to a solution of Sn[N(SiMe3)2]2 (0.73 g,
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Received: March 2, 2013
Revised Version: April 22, 2013
Published Online: July 16, 2013
Eur. J. Inorg. Chem. 2013, 5836–5842
5842
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim