Addition of Lappert's stannylenes to carbodiimides, providing a new class of tin(II) guanidinates

Article abstract of DOI:10.1021/om201118m

Reactions of bis[bis(trimethylsilyl)amino]tin and the dimer of [bis(trimethylsilyl)amino]tin chloride with various carbodiimides give pure corresponding tin(II) guanidinates in essentially quantitative yields. Heteroleptic bis(trimethylsilyl)amido ({R-NC[N(SiMe₃) ₂]N-R}SnN(SiMe₃)₂)- and chloro-substituted ({R-NC[N(SiMe₃)₂]N-R}SnCl) tin(II) guanidinates were obtained from reactions of N,N′-diisopropyl-, N,N′-dicyclohexyl-, N,N′-bis(4-methylphenyl)-, and N-[3-(dimethylamino)propyl]-N′- ethylcarbodiimides, respectively. Homoleptic tin(II) guanidinates {R-NC[N(SiMe₃)₂]N-R}₂Sn were obtained from the N,N′-bis(4-methylphenyl)- and N-[3-(dimethylamino)propyl]-N′-ethyl- substituted carbodiimides. Similar reactions of N,N′-bis(2,6- diisopropylphenyl)- and N,N′-bis(trimethylsilyl)carbodiimide, respectively, having the bulkiest substituents of the series, failed to take place under various conditions. The complexes prepared were characterized as monomers in solution by ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy in C₆D₆ and THF-d₈. The solid-state NMR spectra were recorded for structure comparison. X-ray diffraction studies of one homoleptic monomer, two heteroleptic chloro complexes with the structures of two different types of dimers, and the oxidation product of the heteroleptic bis(trimethylsilyl)amido-substituted guanidinate-a centrosymmetric (guanidinato)tin(IV) oxide-were performed on appropriate crystals. Attempts to prepare homoleptic types of isopropyl- and cyclohexyl-substituted tin(II) guanidinate complexes were unsuccessful. The structures were also evaluated by DFT methods.

Full text of DOI:10.1021/om201118m

Article
pubs.acs.org/Organometallics
Addition of Lappert's Stannylenes to Carbodiimides, Providing a
New Class of Tin(II) Guanidinates
Tomas Chlupaty,† Zdenka Padelkova,† Frank DeProft,‡ Rudolph Willem,§ and Ales Ruzicka*,†
́
̌
́
̌
̌
́
̌
̊
̌ ̌
†Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentska
́
573, CZ-532
10, Pardubice, Czech Republic
‡Eenheid Algemene Chemie (ALGC) and Department of Materials and Chemistry (MACH), Vrije Universiteit Brussel (VUB),
§
Pleinlaan 2, B-1050 Brussels, Belgium
S
* Supporting Information
ABSTRACT: Reactions of bis[bis(trimethylsilyl)amino]tin and the
dimer of [bis(trimethylsilyl)amino]tin chloride with various carbodii-
mides give pure corresponding tin(II) guanidinates in essentially
quantitative yields. Heteroleptic bis(trimethylsilyl)amido ({R-NC[N-
(SiMe3)2]N-R}SnN(SiMe3)2)- and chloro-substituted ({R-NC[N-
(SiMe3)2]N-R}SnCl) tin(II) guanidinates were obtained from
reactions of N,N′-diisopropyl-, N,N′-dicyclohexyl-, N,N′-bis(4-methyl-
phenyl)-, and N-[3-(dimethylamino)propyl]-N′-ethylcarbodiimides,
respectively. Homoleptic tin(II) guanidinates {R-NC[N(SiMe3)2]N-
R}2Sn were obtained from the N,N′-bis(4-methylphenyl)- and N-[3-(dimethylamino)propyl]-N′-ethyl-substituted carbodiimides.
Similar reactions of N,N′-bis(2,6-diisopropylphenyl)- and N,N′-bis(trimethylsilyl)carbodiimide, respectively, having the bulkiest
substituents of the series, failed to take place under various conditions. The complexes prepared were characterized as monomers
1
in solution by H, 13C, and 119Sn NMR spectroscopy in C6D6 and THF-d8. The solid-state NMR spectra were recorded for
structure comparison. X-ray diffraction studies of one homoleptic monomer, two heteroleptic chloro complexes with the
structures of two different types of dimers, and the oxidation product of the heteroleptic bis(trimethylsilyl)amido-substituted
guanidinatea centrosymmetric (guanidinato)tin(IV) oxidewere performed on appropriate crystals. Attempts to prepare
homoleptic types of isopropyl- and cyclohexyl-substituted tin(II) guanidinate complexes were unsuccessful. The structures were
also evaluated by DFT methods.
and a single paper on the reactivity of p-block metals with
carbodiimides producing guanidinate, in particular of anti-
mony19 and germanium.20 Two additional papers describe the
reactivity of (β-diketiminato)tin(II) hydride21 and dimeric di-
tert-butyltin(IV) imide22 with carbodiimide producing (β-
diketiminato)tin(II) formamidinate or cyclic di-tert-butyltin-
(IV) imide-guanidinate, respectively.
1. INTRODUCTION
The discovery of steric and electronic stabilization of low-valent
species of group 14 metals by bis(trimethylsilyl)amido ligands,
in particular the preparation of Lappert's stannylenes,1 led to
major developments in this class of chemistry.2 Many reactions
of these compounds, including mainly oxidation,3 oxidative
addition reactions,4 reduction to metal clusters,5 C−H bond or
small molecule activation,6 complexation,7 reactions with
heterocumulenes,8 and others, have been studied mainly in
order to explore analogous reactions of higher congeners of
carbenes.9 The renaissance of this class of chemistry started
with the preparation of very bulky,10 chelating,11 or spectator
ligands, as for example β-diketiminato,12 amidinato,13 and
guanidinato14 complexes, which stabilize the metal center by
their rich π-electron systems, thus forming metallahetero-
cycles.15
The reactivity of tin(II) amides with heterocumulenes (CO2,
RNCO)8 provided mainly products where the tin atom is
bonded to three oxygen atoms, as for example [Me3SiOSn(μ-
OSiMe3)2]2, Me3SiNCO, and carbodiimides. On the other
hand s-block,16 f-block17 and electron deficient d-block18 metal
amides react with carbodiimides to give the corresponding
guanidinates, which are often quite impure or are present in
mixtures with amides and other species. There are two patents
The tin(II or IV) guanidinates,23 which could have
interesting properties similar to those found for related
amidinates to be single-source precursors for thin films of tin
metal or tin(II and IV) compounds,19 are surprisingly a small
group of compounds. Tin(IV) guanidinates were described by
Lappert24 in 1965. Four decades later, the first tin(II)
guanidinates, both the homoleptic and heteroleptic chlorides,
were prepared by salt elimination from lithium guanidinate and
tin dichloride. Jones et al. used their (guanidinato)tin(II)
chlorides for coordination of phosphaheterocycles25 or Ga(I)26
anionic complexes.
In this paper we describe the family of tin(II) guanidinates
with various sterically protecting moieties at the tin center,
Received: November 14, 2011
Published: March 5, 2012
© 2012 American Chemical Society
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prepared with high atom economy by the facile reaction of
Lappert stannylenes with different carbodiimides.
Generally, the successful reactions leading to hetero- and
homoleptic tin(II) guanidinates 5−14 reveal high atom
economy, essentially quantitative yields, high selectivity, and
fast reaction times (less than 1 h) at room temperature.
Except for the oxidation of the ligand in [Pb(CyG)Cl]2 (CyG
= N,N″-bis(2,6-diisopropylphenyl)-N′,N′-dicyclohexylguanidi-
2. RESULTS AND DISCUSSION
2.1. Synthesis. The tin(II) guanidinates prepared are
presented in Figure 1. Heteroleptic bis(trimethylsilyl)amido
nate), thus forming an alcoholate,14a no oxidation product of
group 14 guanidinates is known. The compound {(LpTol
)
-
[(Me3Si)2N]SnO}2 (8a) was obtained as the oxidation product
of 8 (Scheme 1) by slow diffusion of air into the Schlenk tube
Scheme 1
through its insufficiently greased stopcock. The process is fully
reproducible and is described in the Experimental Section. The
oxidation of various tin(II) guanidinates is presently under
further investigation in our laboratory.
2.2. NMR Studies in Solution. Solution-state NMR studies
were performed with all the investigated series of compounds,
not only for solution structure determinations but also in order
to monitor the reactions and further reactivity of the target
Figure 1. Numbering and preparation of target compounds 5−14.
Reagents and conditions: Et2O, room temperature.
1
compounds. All compounds studied reveal resolved H NMR
tin(II) guanidinates 5−8 were prepared by the reaction of the
Lappert's stannylene [(Me3Si)2N]2Sn with N,N′-diisopropyl-,
N,N′-dicyclohexyl-, N,N′-bis(4-methylphenyl)-, and N-[3-
(dimethylamino)propyl]-N′-ethylcarbodiimides, respectively,
in essentially quantitative yield, at room temperature in Et2O
and with a 1:1 stoichiometric ratio of the reagents.
spectral patterns assignable to structures with mutually
symmetric (C2) ligands, except for the cyclohexyl-substituted
compounds, which are usually complex. Complex signals with
usually anisochronous or broad patterns for aliphatic protons
were observed in the spectra of EDC-substituted guanidinates
7, 11, and 13 (see the Experimental Section). This
phenomenon is very likely caused by the presence of a
stereogenic center at the central ipso carbon atom which
induces a diastereotopic character of methylene groups. Two
different signals were found for geometrically nonequivalent
Chlorides 9−12, bearing the same guanidinate units, were
prepared in a similar way from (Me3Si)2NSnCl dimer with the
related carbodiimide under the same reaction conditions.
Reactions of N,N′-bis(2,6-diisopropylphenyl)- and N,N′-bis-
(trimethylsilyl)carbodiimide, respectively, with both stanny-
lenes in the stoichiometric ratio 1:1 failed to provide the
desired guanidinates, most probably due to the higher steric
demand of the carbodiimide substituents. For the reaction of
N,N′-bis(2,6-diisopropylphenyl)carbodiimide with both stanny-
lenes, various reaction conditionschanging the solvents,
raising the reaction temperature up to 90 °C, increasing the
reaction time up to a few days, and adding various species in
catalytic amounts such as acetic acid and hexamethyldisilazane
in order to catalyze the reaction under basic or acidic
conditionsgive virtually no yield of the desired tin(II)
guanidinates. Several attempts to react the (guanidinato)tin(II)
amide 5 or 8 with N,N′-bis(4-methylphenyl)- or N,N′-
bis(propan-2-yl)carbodiimide in order to prepare an unsym-
metrical heteroleptic compound bearing two different guanidi-
nate ligands also failed, only starting compounds being
observed in the NMR spectra.
The homoleptic guanidinate compounds containing N,N′-
bis(4-methylphenyl) and N-[3-(dimethylamino)propyl]-N′-
ethyl substituents were prepared as the only compounds of
this type in quantitative yield at room temperature. The
attempts to prepare the remaining members of this series
containing N,N′-diisopropyl and N,N′-dicyclohexyl substituents
were not successful, even when 5 or 6 was heated with the
respective carbodiimide in various solvents such as THF, Et2O,
and toluene.
1
trimethylsilyl groups of the amido function in the H NMR
spectra of heteroleptic amides 5−8. On the other hand, all
compounds reveal only one signal for the trimethylsilyl group
substituting the guanidinato ligands, which could be explained
1
by a free rotation of the amido group. The H NMR chemical
shifts of the NCH2 group found for compounds where the
EDC ligand fragment is used (7, 11, and 13) are shifted
downfield, in comparison to the chemical shifts found for
starting carbodiimide 4, but it could not be established whether
there is a coordination of the nitrogen atom of this group to the
tin atom.
The 13C NMR spectra are more informative, especially in
cases of the signal of the middle quaternary carbon atom (see
Table 1). Its 13C chemical shift value (160−164 ppm) suggests
that the tin atom is coordinated by the guanidinato and
terminal bis(trimethylsilyl)amido ligands in the cases of amides
5−8, two guanidinato ligands for 13 and 14, and guanidinato
and chloride for 11. The same parameter for chlorides 9−12
was found around 168 ppm in benzene solution, which is
shifted about 4 ppm downfield in comparison to the amides 5−
8 and homoleptic stannylenes 13 and 14. On the other hand,
the chemical shift of the ipso carbon atom in the 13C NMR
spectrum of 11 in THF solution reveals a 5 ppm upfield shift in
comparison to the spectrum measured in benzene, which is
probably caused by a structural change by an interaction with
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Comparison of 119Sn NMR shift values for 9, 10, and 12 in
benzene with literature values for monomeric heteroleptic
guanidinato tin chlorides substituted by bulky aromatic groups
(−55 ppm25) indicate monomeric structures of all three
compounds. The large 119Sn chemical shift decrease for
chloride 11 indicates strong coordination by the pendant
amino group.
Table 1. Selected NMR Spectral Parameters
param (ppm)
compd
solvent
δ(13Cipso
)
δ(119Sn)
LiPrSnN(SiMe3)2 (5)
C6D6
160.4
161.9
160.8
161.5
163.8
163.6
164.0
a
−115.7
−119.5
−126.9
−127.5
−144.6
−87.2
−93.0
−612.8
−30.4
−51.1
−34.9
−51.0
−250.6
−108.2
−220.0
−377.3
−432.0
−427.8
THF-d8
C6D6
LCySnN(SiMe3)2 (6)
THF-d8
C6D6
Differences in 119Sn NMR chemical shift values for all three
types of tin guanidinates are observed. The amidotin
guanidinates 5−8 reveal virtually three subtypes: (i) amidotin
guanidinates with aliphatic substituents 5 and 6, which display
119Sn chemical shifts around −120 ppm, (ii) compound 7 with
possible adjacent coordination from the amino donor group,
with the value at −144.6 ppm, and (iii) the aromatic group
substituted amidotin guanidinate 8 with 119Sn NMR chemical
shift values around −90 ppm.
LEDCSnN(SiMe3)2 (7)
LpTolSnN(SiMe3)2 (8)
C6D6
THF-d8
THF-d8
C6D6
{(LpTol)[(Me3Si)2N]SnO}2 (8a)
LiPrSnCl (9)
167.9
168.0
167.8
168.0
166.9
168.3
163.5
163.2
163.2
163.5
THF-d8
C6D6
LCySnCl (10)
THF-d8
C6D6
LEDCSnCl (11)
LpTolSnCl (12)
The 119Sn chemical shift values around −400 ppm for the
homoleptic compounds 13 and 14 indicate four-coordination
of the tin atoms in coordinating as well as noncoordinating
solvents, resulting in the configuration of the central atom to be
pseudo square pyramidal. The difference in chemical shift
values of 13 and 14 is assigned to the presence of different
types of ligand substituents. There is no literature comparison,
because no 119Sn NMR data were mentioned for the only
existing homoleptic bis(guanidinato)tin(II) complex described
so far.24b Both homo- and heteroleptic (amidinato)tin
complexes display 119Sn chemical shifts13h lower by ca. 80−
200 ppm than for the guanidinates investigated.
C6D6
THF-d8
C6D6
(LEDC)2Sn (13)
(LpTol)2Sn (14)
C6D6
THF-d8
a
Not observed.
THF molecule(s). Almost the same 13C chemical shifts as in
benzene solution were found for the model series of single-
crystal compounds containing the pTol groups 8, 12, and 14
(see the Supporting Information, Figures S1−S3; see below for
structures determined by X-ray diffraction) in the 13C CP/MAS
NMR solid-state spectra. Unfortunately, no literature 13C NMR
data are available for the same type of guanidinates.
The 119Sn NMR spectrum of the oxidation product of 8, 8a,
reveals a 500 ppm shift to lower frequency in comparison to 8,
indicating the presence of five-coordinate tin(IV). Unfortu-
nately, the 13C chemical shift in solution for the ipso carbon as
well as 119Sn NMR shifts in the solid state could not be located,
probably because of very broad resonances collapsing into the
baseline noise. The reasons for that remain unclear but might
be due to large chemical shift anisotropy.
As can be seen in Table 1, the 13C and 119Sn NMR chemical
shifts are nearly solvent independent, which is evidence of the
same structure in noncoordinating as well as in coordinating
solvents as THF. On the other hand, the tin atom in 12 appears
to coordinate the THF molecule(s), resulting in chemical shift
2.3. Crystal Structure Determination by X-ray
Diffraction. To the best of our knowledge the only two
crystal structures determined for heteroleptic (guanidinato)tin-
reduction by ca. 110 ppm and also the in the change of the 13
NMR shift of the ipso carbon (see above).
C
Figure 2. Molecular structure of LCySnCl (10) (ORTEP view, 50% probability level). Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å) and angles (deg), with computed values given in italics: N1−C1 = 1.344(4), 1.344; N1−C2 = 1.455(5), 1.446; N2−C1 = 1.319(5),
1.335; N2−C8 = 1.451(5), 1.447; N3−C1 = 1.411(5), 1.404; N1−Sn1a = 2.198(3), 2.232; N2−Sn1a = 2.211(3), 2.232; Sn1a−Cl1a = 2.4698(11),
2.468; Sn1a−Cl1b = 3.3495(9); C2−C1−C8 = 167.29(19), 167.5; N1−C1−N2 = 111.5(3), 111.9; C1−Sn1a−Cl1a = 97.76(8), 92.5; N1−Sn1a−N2
= 59.90(11), 59.3; Sn1a−Cl1a−Sn1b = 94.92(3).
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(II) chlorides revealed monomeric structural units.25 The
crystal structures of the guanidinatotin chlorides 10 and 12
were determined by X-ray diffraction (Figures 2 and 3). Both
tin(II) as well as (guanidinato)tin(II) chloride complexes. The
main difference between structures of 10 and 12 is the planarity
of the Sn2Cl2 ring in the case of 12 and the orientation of the
guanidinato ligands to the same side of the Sn2Cl2 ring in the
case of 10 and an anti orientation in the case of 12. In 10, the
Sn1b atom deviates from the Sn1a−Cl1a−Cl1b plane by 0.956
Å. On the other hand, the monomeric structures of 10 and 12
were determined using density functional theory calculations,
starting from the crystal structures. Selected computed
equilibrium distances and geometries are also listed in the
caption of Figures 2 and 3. As can be seen, for both 10 and 12,
the computed equilibrium geometries are in very good
agreement with the experimental geometries, confirming,
among others, the π delocalization in the guanidinato unit.
The Sn1 atoms are only slightly above the N3C plane (0.326(3)
Å for 10 and 0.114(4) Å for 12), and the greatest deviation is in
the value of C1−Sn1a−Cl1a angles caused by the short
contacts of C1a with Sn1b in the solid state.
The structure of one of the homoleptic bis(guanidinato)tin-
(II) complexes (14) was also determined by X-ray diffraction
(Figure 4) and turned out to exist as two different solvato
Figure 3. Molecular structure of LpTolSnCl (12) (ORTEP view, 50%
probability level). Hydrogen atoms are omitted for clarity. Selected
interatomic distances (Å) and angles (deg), with computed values
given in italics: N1−C1 = 1.331(2), 1.343; N1−C2 = 1.408(3), 1.410;
N2−C1 = 1.343(2), 1.346; N2−C9 = 1.414(2), 1.406; N3−C1 =
1.395(2), 1.380; N1−Sn1a = 2.2277(16), 2.247; N2−Sn1a =
2.2019(16), 2.253; Sn1a−Cl1a = 2.4732(6), 2.454; Sn1a−Cl1b =
3.1099(7); C2−C1−C9 = 164.99(10), 165.2; N1−C1−N2 =
111.12(15), 111.4; C1−Sn1a−Cl1a = 92.02(4), 89.9; N1−Sn1a−N2
= 59.72(6), 59.1; Sn1a−Cl1a−Sn1b = 100.75(2).
Figure 4. Molecular structure of (LpTol)2Sn (14) (ORTEP view, 50%
probability level, appropriate parameters for 14′ are given in
Supporting Information). Hydrogen atoms are omitted for clarity.
Selected interatomic distances (Å) and angles (deg), with computed
values given in italics: N1−C1 = 1.330(3), 1.333; N1−C2 = 1.415(3),
1.408; N2−C1 = 1.339(3), 1.347; N2−C9 = 1.410(3), 1.409; N3−C1
= 1.403(3), 1.393; N1−Sn1 = 2.399(2), 2.424; N2−Sn1 = 2.164(2),
2.222; N4−Sn1 = 2.201(2), 2.250; N5−Sn1 = 2.358(2), 2.395; N4−
C23 = 1.416(3), 1.408; N4−C22 = 1.346(3), 1.349; N5−C22 =
1.320(3), 1.329; N5−C30 = 1.407(3), 1.401; N6−C22 = 1.400(3),
1.395; C2−C1−C9 = 167.46(14), 166.6; N1−C1−N2 = 112.1(2),
112.4; C23−C22−C30 = 166.58(14), 167.6; N4−C22−N5 =
112.1(2), 112.2; N1−Sn1−N4 = 91.54(7), 89.7; N2−Sn1−N5 =
84.91(8), 84.1; C1−Sn1−C22 = 109.33(7), 105.4.
compounds reveal centrosymmetric dimers with a central
Sn2Cl2 ring generated by interactions of the tin atoms with
chlorine atoms of the second monomeric unit (Sn1a−Cl1b =
3.3495(9) Å for 10 and Sn1a−Cl1b = 3.1099(7) Å for 12). In
both cases these contacts are rather weak in comparison to that
in the dimeric amidotin(II) chloride {Sn[N(C6H3iPr2-2,6)-
(SiMe3)](μ-Cl)}2 (2.765(3) Å5a). On the other hand, other
amidotin(II) (3.149(2) Å27 or 3.425(3) Å28), (β-diketiminato)-
tin (3.900(3) Å29), or (amidinato)tin(II) chlorides30 reveal
similar or even longer distances. The distances Sn1a−Cl1a =
2.4698(11) Å for 10 and 2.4732(6) Å for 12 are slightly longer
by ca. 0.03 Å in comparison to the corresponding distances in
tin(II) chlorides mentioned, with one exception, {Sn[N-
(C6H3iPr2-2,6)(SiMe3)](μ-Cl)}2, at 2.582(3) Å.5a The planar-
ity and distances between the atoms forming the four-
membered heterocyclic rings N1−C1, N2−C1, N1−Sn1, and
N2−Sn1 indicate a high degree of π-electron delocalization
within the guanidinato unit, also reflected in the planar N3C
moiety and short N3−C1 distances. Other distances and angles
are in line with the literature data26 for related (amidinato)-
polymorphs (14 and 14′), one isolated from a diethyl ether and
the second from a hexane solution, where the hexane molecule
is cocrystallized with 14′, having no significant interaction with
the atoms of 14′. Only negligible differences between the
structures of these solvato polymorphs are found as far as
interatomic distances and angles are concerned, but there is a
rather large difference in the mutual orientation of both ligands
(see Figure S5 in the Supporting Information). The mutual
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distortion of both ligands in 14 from the ideal geometry is
probably caused by the strong π−π aromatic stacking
interaction. The tin atom in 14 is four-coordinated with a
distorted pseudo square pyramidal configuration, with the
largest bonding angle value being 127.7(3)°, in contrast to the
C2 symmetry homoleptic bis(guanidinato)tin(II) complex
described by Richeson as distorted pseudo trigonal bipyramidal
with a pseudoaxial vector with an angle of 140.4(3)°.24b In
comparison to the heteroleptic stannylenes (10 and 12)
discussed above, the bonds N1−Sn1 and N5−Sn1 in 14 are
elongated by ca. 0.2 Å, indicating a higher steric demand of
ligands or π-electron delocalization decrease in the N3C system
which is nearly planar with a sum of angles around nitrogen
atoms of 350.62(8)° for N1, 359.83(9)° for N2, 350.67(8)° for
N4, and 358.41(7)° for N5 atoms, respectively. The interplanar
(bite) angle between these rings is 77.1(2)°, which is typical for
metal complexes of guanidinates as well as of amidinates.31
The equilibrium structure of 14 and 14′ were also
determined using DFT calculations, again starting from the
crystal structures; selected optimized bond lengths and angles
are given in the caption of Figure 4 and Figure S6 (Supporting
Information). These computed geometrical parameters are in
good agreement with the experimental data obtained from the
crystal structures. At the level of theory used in the calculations,
14 is only marginally more stable than structure 14′ (about 0.6
kcal mol−1); in view of the possible underestimation of the
strength of the π−π stacking interaction in compound 14 at the
current level of theory, this value probably represents a lower
bound to the energy difference between the two structures 14
and 14′.
Figure 5. Molecular structure of {(LpTol)[(Me3Si)2N]SnO}2·C4H10O
(8a) (ORTEP view, 40% probability level). Hydrogen atoms are
omitted for clarity. Selected interatomic distances (Å) and angles
(deg): N1−C1 = 1.336(7); N1−C2 = 1.431(5); N2−C1 = 1.338(5);
N2−C9 = 1.414(7); N3−C1 = 1.402(6); N1−Sn1 = 2.225(4); N2−
Sn1 = 2.172(4); C1−Sn1 = 2.646(5); N4−Sn1 = 2.033(4); Sn1−O1 =
1.992(3); Sn1−O1a = 1.998(3); Sn1−Sn1a = 3.0039(4); C2−C1−C9
= 166.5(3); N1−C1−N2 = 111.1(4); N1−Sn1−N2 = 60.16(15); C1−
Sn1−Sn1a = 121.77(9); O1−Sn1−O1a = 82.33(14); C1−Sn1−N4 =
115.46(14); Sn1−O1−Sn1a = 97.67(17).
prepared and structurally characterized. Because of the
relatively easy synthesis of the studied compounds they could
be applied in materials chemistry or in the preparation of
various metal guanidinates by transmetalation.
The oxidation product of 8, 8a, crystallizes in the triclinic
crystal system P1. The compound is formed by the central
̅
Sn2O2 ring with a rather short interatomic distance between the
tin atoms of 3.0039(4) Å, which is caused by short interatomic
angles inside the ring (Figure 5). The angle between the plane
defined by this ring and the guanidinato unit is 67.19(9)°. In
contrast with the aforementioned tin(II) guanidinates, the tin
atom in 8a is located out of the guanidinato unit plane
(0.407(3) Å). The angle between the amido and guanidinato
substituents of the tin atom is rather wide (N4−Sn1−C1 =
115.46(9)°), defining the configurations of the tin atoms as
distorted square pyramids, with these atoms located 0.769(3) Å
above the bases of the pyramids each defined by two oxygen
atoms and two nitrogen atoms of the guanidinato ligands. The
mutual orientation of the amido substituents is pseudo trans
with respect to the central ring. The distances between tin and
nitrogen atoms of the amido substituents are quite short,
2.033(4) Å, and thus comparable to those in simple tin
amides.27 Also, the Sn−O distances are within the range found
in the Cambridge Structural Database for tin(IV) compounds
with an Sn2O2 ring. Similar N−C distances within the N3C
guanidinato moiety again indicate a π-electron delocalization
for this system.
4. EXPERIMENTAL SECTION
4.1.1. General Methods. NMR Spectroscopy. NMR spectra
were recorded from solutions in benzene-d6 or THF-d8 on a
Bruker Avance 500 spectrometer (equipped with Z-gradient 5
mm probe) at frequencies for H (500.13 MHz), 13C{1H}
1
(125.76 MHz), and 119Sn{1H} (186.50 MHz) at 295 K. All
deuterated solvents were degassed and then stored over K-
mirror under an argon atmosphere. Solutions were obtained by
dissolving approximately 40 mg of each compound approx-
imately in 0.5 mL of deuterated solvents. Values of 1H chemical
shifts were calibrated to an internal standard, tetramethylsilane
(δ(1H) 0.00), or to residual signals of benzene (δ(1H) = 7.16)
and THF (δ(1H) 3.58 or 1.73). Values of 13C chemical shifts
were calibrated to signals of THF (δ(13C) 67.6) and benzene
(δ(13C) 128.4). The 119Sn chemical shift values are referred to
external neat tetramethylstannane (δ(119Sn) 0.0 ppm). Positive
chemical shift values denote shifts to higher frequencies relative
to standards. 119Sn NMR spectra were measured using the
inverse gated-decoupling mode. All 13C NMR spectra were
measured using standard proton-decoupled experiments, and
CH and CH3 vs C, and CH2 were differentiated with the help
of the APT method.32
The solid-state 13C spectra were recorded under cross-polarization
1
3. CONCLUSION
at 6.5 dB power and BB H decoupling on an Avance 250 Bruker
instrument resonating at 62.5598 MHz for 13C nuclei, under magic
angle spinning at 4 kHz. The sweep width was 300 ppm, the relaxation
delay 4 s, the number of scans 2000, and the CP contact time 1500 μs.
4.1.2. Elemental Analyses. The compositional analyses were
determined under an inert atmosphere of argon on an EA 1108
automatic analyzer by FISONS Instruments.
Eight heteroleptic, both amido- and chloro-substituted, and two
homoleptic monoanionic tin(II) guanidinates were prepared by
reactions of the appropriate carbodiimides with Lappert's
stannylenes with high atom economy and yields under very
mild conditions. The structures of four of them were
determined by X-ray diffraction methods, showing broad
differences. The first oxidation product (oxidizing the metal
from the +II to +IV state) in group 14 metal guanidinates was
4.1.3. Crystallography. The X-ray data (Table 2) obtained from
colorless crystals for all compounds were acquired at 150 K using an
Oxford Cryostream low-temperature device on a Nonius KappaCCD
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Table 2. Crystallographic Data for 10, 12, 14, 14′, and 8a
(LpTol)2Sn·C6H14
(14′)
{(LpTol)[(Me3Si)2N]SnO}2·C4H10O
(8a)
LCySnCl (10)
LpTolSnCl (12)
(LpTol)2Sn (14)
chem formula
C19H40ClN3Si2Sn
520.86
C21H32ClN3Si2Sn
536.82
C42H64N6Si4Sn
884.04
C48H78N6Si4Sn
970.21
C58H110N8O3Si8Sn2
1429.64
formula wt
cryst syst
tetragonal
17.8950(4)
17.8950(19)
16.1841(2)
90
triclinic
monoclinic
24.0972(12)
11.3390(7)
17.7010(8)
90
monoclinic
12.4960(9)
27.177(3)
15.6270(12)
90
triclinic
a/Å
9.9640(5)
11.0551(5)
13.6129(5)
68.420(3)
77.555(3)
68.335(4)
1290.37(11)
150(1)
12.6030(9)
12.7420(7)
14.1991(11)
79.350(5)
64.789(6)
75.427(5)
1988.8(3)
150(1)
b/Å
c/Å
α/deg
β/deg
90
100.487(4)
90
95.929(7)
90
γ/deg
90
unit cell volume/Å3
temp/K
5182.7(7)
150(1)
4755.8(4)
150(1)
P21/c
5278.6(8)
150(1)
P21/c
space group
P42 /c
P1
̅
P1
̅
̅
1
no. of formula units per unit cell, Z
abs coeff, μ/mm−1
no. of rflns measd
no. of indep rflns
8
2
4
4
1
1.190
41 238
5916
1.198
25 206
5902
0.672
0.611
0.789
39 820
8833
35 302
56 294
10 377
12 078
a
Rint
0.0612
0.0322
0.0557
1.177
0.0456
0.0223
0.0504
1.094
0.0470
0.0461
0.0499
0.0545
0.1200
1.181
b
final R1 values (I > 2σ(I))
final wR2(F2) values (I > 2σ(I))
0.0356
0.0423
0.0657
0.0736
c
goodness of fit on F2
1.098
1.126
a
b
2
2
2
Rint = ∑|Fo2 − Fo,mean2|/∑Fo . Weighting scheme: w = [σ2(Fo ) + (w1P)2 + w2P]−1, where P = [max(Fo ) + 2Fc2]. R1(F) = ∑||Fo| − |Fc||/∑|Fo|;
c
wR2(F2) = [∑(w(Fo − Fc2)2)/(∑w(Fo )2)]1/2. S = [∑(w(Fo − Fc2)2)/(Ndiffr − Nparam)]1/2
.
2
2
2
3
diffractometer with Mo Kα radiation (λ = 0.710 73 Å) and a graphite
monochromator, in the ϕ and χ scan mode. Data reductions were
performed with DENZO-SMN.33 The absorption was corrected by
integration methods.34 Structures were solved by direct methods
(Sir92)35 and refined by full-matrix least squares based on F2
(SHELXL97).36 Hydrogen atoms were mostly localized on a
difference Fourier map, but in order to ensure uniformity of the
treatment of the crystal, all hydrogen atoms were recalculated into
idealized positions (riding model) and assigned temperature factors
Uiso(H) = 1.2Ueq(pivot atom) or 1.5Ueq for the methyl moiety with
C−H = 0.96, 0.97, 0.98, and 0.93 Å for methyl, methylene, methine,
and hydrogen atoms in aromatic rings, respectively.
Crystallographic data for structural analysis have been deposited
with the Cambridge Crystallographic Data Centre. Copies of this
information may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EY, U.K. (fax, +44-1223-
336033; e-mail, deposit@ccdc.cam.ac.uk; web, www: http:// www.
ccdc.cam.ac.uk). CCDC deposition numbers are 847157 for 10,
847156 for 12, 847155 for 14, and 847158 for 8a.
4H, ArH); 6.81 (d, J = 8.0 Hz, 4H, ArH); 2.00 (s, 6H, CH3). 13C
NMR (125 MHz, 295 K): δ 136.9 (Ar); 136.7 (NCN); 135.6
(Ar); 130.8 (Ar); 124.7 (Ar); 21.2 (CH3). Data for N-[3-
(dimethylamino)propyl]-N′-ethylcarbodiimide (4, known as EDC)
are as follows. 1H NMR (500 MHz, 295 K): δ 3.11 (t, 3J = 6.7 Hz, 2H,
α-CH2); 2.97 (q, 3J = 7.1 Hz, 2H, δ-CH2); 2.14 (t, 3J = 6.9 Hz, 2H, γ-
3
CH2); 2.00 (s, 6H, (CH3)2N); 1.53 (m, 2H, β-CH2); 0.99 (t, J = 7.2
Hz, 3H, CH3). 13C NMR (C6D6, 125 MHz, 295 K): δ 140.9 (NC
N); 57.1 (α-CH2); 45.8 ((CH3)2N); 44.9 (δ-CH2); 41.7 (γ-CH2); 30.8
(β-CH2); 17.2 (CH3).
General Procedure of Preparation of Heteroleptic Tin(II)
Guanidinates LRSnN(SiMe3)2 (5−8). To a solution of bis[bis-
(trimethylsilyl)amino]tin in Et2O at room temperature was added 1
equiv of starting N,N′-disubstituted carbodiimides 1−4 dissolved in
Et2O. Reaction mixtures were stirred for 2 h, and there was a slight
color fading from orange to pale yellow. Subsequently, the crude
products were filtered and Et2O was evaporated under vacuum to give
pure products of heteroleptic tin(II) guanidinates 5−8 in almost
quantitative yields.
General Procedure of Preparation of Heteroleptic Tin(II)
Guanidinates LRSnCl (9−12). To a yellow suspension of [bis-
(trimethylsilyl)amino]tin chloride in Et2O at room temperature was
added 1 equiv of starting N,N′-disubstituted carbodiimides 1−4 in
Et2O. Reaction mixtures were stirred until complete disappearance of
the initial yellow color. The colorless crude products were filtered, and
then Et2O was evaporated under vacuum. The pure heteroleptic
tin(II) guanidinates 9−12 were obtained.
4.1.4. Computations. All structures were optimized at the MO6-
2X37/cc-pVDZ38 level of theory (cc-pVDZ-PP)39 on Sn, which uses a
cc-pVDZ like basis set for the valence region, together with a small-
core relativistic pseudopotential; the Cartesian coordinates of the
resulting gas-phase optimized geometries can be found in the
Supporting Information. All computations were performed using the
Gaussian 09 program.40
4.2. Synthesis. All syntheses were performed using standard
Schlenk techniques under an inert argon atmosphere. Solvents and
reactants were purchased from commercial sources. Solvents were
distilled over K/Na alloy, degassed, and then stored over a K-mirror
under an argon atmosphere. Single crystals suitable for XRD analyses
were obtained under argon from corresponding saturated solutions of
products in Et2O or hexane cooled to −30 °C. Melting points were
measured in inert perfluoroalkyl ether and were uncorrected. NMR
spectra in benzene-d6 of starting N,N′-disubstituted carbodiimides
were measured for comparison and studies of chemical shifts of
prepared compounds. The parameters for N,N′-diisopropylcarbodii-
mide (1) and N,N′-dicyclohexylcarbodiimide (2) are reported
elsewhere.41 NMR data for N,N′-bis(4-methylphenyl)carbodiimide
(3) are as follows. 1H NMR (500 MHz, 295 K): δ 7.03 (d, 3J = 8.2 Hz,
General Procedure of Preparation of Homoleptic Tin(II)
Guanidinates (LR)2Sn (13 and 14). To a solution of bis[bis-
(trimethylsilyl)amino]tin in Et2O at room temperature was added 2
equiv of starting N,N′-disubstituted carbodiimides 1−4 in Et2O.
1
Reaction mixtures were stirred for
/ h, with complete color
2
disappearance from orange to colorless. Subsequently, the crude
products were filtered and Et2O was evaporated under vacuum to give
colorless pure products of homoleptic tin(II) guanidinates 13 and 14
in almost quantitative yields.
4.2.1. Preparation of Heteroleptic Tin(II) Guanidinate LiPrSnN-
(SiMe3)2 (5). 1.31 g of 1 (10.3 mmol, 0.815 g/cm3, 1.59 mL), 4.53 g of
[(Me3Si)2N]2Sn (10.3 mmol), 40 mL of Et2O. Yield: 5.44 g (93%) of
1
pale yellow oily material of 5. H NMR (C6D6, 500 MHz, 295 K): δ
3
3
3.91 (sep, 2H, CH); 1.23 (d, J = 6.4 Hz, 6H, (CH3)2); 1.20 (d, J =
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6.4 Hz, 6H, (CH3)2); 0.41 (s, 18H, (CH3)3Si); 0.22 (s, 9H, (CH3)3Si);
0.14 (s, 9H, (CH3)3Si). 13C NMR (C6D6, 125 MHz, 295 K): δ 160.4
(NC(N)N); 46.0 (CH); 26.0 ((CH3)2); 25.8 ((CH3)2); 6.0
((CH3)3Si); 2.4 ((CH3)3Si); 2.2 ((CH3)3Si). 119Sn NMR (C6D6, 186
MHz, 295 K): δ −115.7. 1H NMR (THF-d8, 500 MHz, 295 K): δ 4.00
(sep, 2H, CH); 1.25 (d, 3J = 7.2 Hz, 6H, (CH3)2); 1.24 (d, 3J = 6.7 Hz,
6H, (CH3)2); 0.31 (s, 9H, (CH3)3Si); 0.27 (s, 9H, (CH3)3Si); 0.19 (s,
18H, (CH3)3Si). 13C NMR (THF-d8, 125 MHz, 295 K): δ 161.9 (N
C(N)N); 47.2 (CH); 28.4 ((CH3)2); 26.6 ((CH3)2); 6.6 ((CH3)3Si);
3.2 ((CH3)3Si); 2.9 ((CH3)3Si). 119Sn NMR (THF-d8, 186 MHz, 295
K): δ −119.5. Anal. Calcd for C19H50N4Si4Sn: C 40.34; H, 8.91; N,
9.90. Found: C, 40.26; H, 8.80; N, 10.00.
0.05 (s, 36H, (CH3)3Si); −0.23 (s, 18H, (CH3)3Si). 119Sn NMR
(THF-d8, 186 MHz, 295 K): δ −612.8. Anal. Calcd for
C42H64N6O2Si4Sn2: C, 48.75; H, 6.23; N, 8.12. Found: C, 48.62; H,
6.46; N, 8.34.
4.2.6. Preparation of Heteroleptic Tin(II) Guanidinate LiPrSnCl (9).
0.82 g of 1 (6.5 mmol, 0.815 g/cm3, 1.01 mL), 2.05 g of
(Me3Si)2NSnCl (6.5 mmol), 30 mL of Et2O. Yield: 2.55 g (89%) of
colorless oily material of 9. 1H NMR (C6D6, 500 MHz, 295 K): δ 3.88
(sep, 2H, CH); 0.97 (br s, 12H, (CH3)2); 0.16 (s, 18H, (CH3)3Si). 13
C
NMR (C6D6, 125 MHz, 295 K): δ 167.9 (NC(N)N); 45.5 (CH);
26.4 (br signal (CH3)2); 2.5 ((CH3)3Si). 119Sn NMR (C6D6, 186 MHz,
1
295 K): δ −30.4. H NMR (THF-d8, 500 MHz, 295 K): δ 4.02 (sep,
4.2.2. Preparation of Heteroleptic Tin(II) Guanidinate LCySnN-
(SiMe3)2 (6). 1.70 g of 2 (8.3 mmol), 3.63 g of [(Me3Si)2N]2Sn (8.3
mmol), 30 mL of Et2O. Yield: 5.16 g (96%) of pale yellow solid of 6.
Mp: 81−83 °C. 1H NMR (C6D6, 500 MHz, 295 K): δ 3.57−3.53 (m,
2H, CyH); 1.93 (br s, 4H, CyH); 1.73−1.41 (br m, 10H, CyH); 1.23−
1.06 (m, 6H, CyH); 0.48 (s, 18H, (CH3)3Si); 0.25 (s, 9H, (CH3)3Si);
0.17 (s, 9H, (CH3)3Si). 13C NMR (C6D6, 125 MHz, 295 K): δ 160.8
(NC(N)N); 55.2 (Cy); 39.3 (Cy); 37.3 (Cy); 26.9 (Cy); 26.4
(Cy); 26.3 (Cy); 7.0 ((CH3)3Si); 3.2 ((CH3)3Si); 2.9 ((CH3)3Si).
2H, CH); 1.16 (d, 3J = 6.3 Hz, 12H, (CH3)2); 0.11 (s, 18H,
(CH3)3Si). 13C NMR (THF-d8, 125 MHz, 295 K): δ 168.0 (N
C(N)N); 46.1 (CH); 26.4 ((CH3)2); 2.5 ((CH3)3Si). 119Sn NMR
(THF-d8, 186 MHz, 295 K): δ −51.1. Anal. Calcd for
C13H32ClN3Si2Sn: C, 35.43; H, 7.32; N, 9.53. Found: C, 35.73; H,
7.54; N, 9.28.
4.2.7. Preparation of Heteroleptic Tin(II) Guanidinate LCySnCl
(10). 1.26 g of 2 (6.1 mmol), 1.92 g of (Me3Si)2NSnCl (6.1 mmol), 30
mL of Et2O. 3.05 g (96%) of white solid of 10. Mp: 125−127 °C.
Single crystals suitable for XRD analyses were obtained under argon
from a saturated solution of 10 in a mixture of Et2O and hexane (2:1)
1
119Sn NMR (C6D6, 186 MHz, 295 K): δ −126.9. H NMR (THF-d8,
500 MHz, 295 K): δ 3.48−3.43 (m, 2H, CyH); 1.93−1.88 (m, 4H,
CyH); 1.79−1.71 (m, 4H, CyH); 1.65−1.60 (m, 4H, CyH); 1.41−1.17
(br m, 8H, CyH); 0.30 (s, 9H, (CH3)3Si); 0.25 (s, 9H, (CH3)3Si); 0.19
(s, 18H, (CH3)3Si). 13C NMR (THF-d8, 125 MHz, 295 K): δ 161.5
(NC(N)N); 55.5 (Cy); 39.6 (Cy); 37.6 (Cy); 27.2 (Cy); 26.8
(Cy); 26.6 (Cy); 6.7 ((CH3)3Si); 3.2 ((CH3)3Si); 2.8 ((CH3)3Si).
119Sn NMR (THF-d8, 186 MHz, 295 K): δ −127.5. Anal. Calcd for
1
cooled to −30 °C. H NMR (C6D6, 500 MHz, 295 K): δ 3.55−3.51
(m, 2H, CyH); 2.15−1.79 (br m, 4H, CyH); 1.62 (br s, 6H, CyH);
1.45−1.14 (br m, 6H, CyH); 1.06−0.91 (m, 4H, CyH); 0.16 (br s,
18H, (CH3)3Si). 13C NMR (C6D6, 125 MHz, 295 K): δ 167.8 (N
C(N)N); 53.5 (Cy); 37.6 (br signal Cy); 26.2 (Cy); 26.1 (Cy); 2.4 (br
1
signal (CH3)3Si). 119Sn NMR (C6D6, 186 MHz, 295 K): δ −34.9. H
NMR (THF-d8, 500 MHz, 295 K): δ 3.44 (s, 2H, CyH); 1.68 (s, 4H,
CyH); 1.59 (br s, 4H, CyH); 1.44 (br s, 2H, CyH); 1.18−1.05 (br m,
10H, CyH); 0.16 (s, 18H, (CH3)3Si). 13C NMR (THF-d8, 125 MHz,
295 K): δ 168.0 (NC(N)N); 55.0 (Cy); 37.3 (Cy); 26.6 (Cy); 26.5
(Cy); 2.2 ((CH3)3Si). 119Sn NMR (THF-d8, 186 MHz, 295 K): δ
−51.0. Anal. Calcd for C19H40ClN3Si2Sn: C, 43.81; H, 7.74; N, 8.07.
Found: C, 43.92; H, 7.80; N, 8.18.
C25H58N4Si4Sn: C, 46.50; H, 9.05; N, 8.68. Found: C, 46.70; H, 9.30;
N, 8.45.
4.2.3. Preparation of Heteroleptic Tin(II) Guanidinate LEDCSnN-
(SiMe3)2 (7). 2.16 g of 4 (13.9 mmol, 0.877 g/cm3, 2.46 mL), 6.12 g of
[(Me3Si)2N]2Sn (13.9 mmol), 50 mL of Et2O. Yield: 7.52 g (91%) of
1
pale yellow oily material of 7. H NMR (C6D6, 500 MHz, 295 K): δ
3.60−3.56, 3.45−3.41 (m, 2H, α-CH2, anisochronous signals); 3.26 (q,
2H, δ-CH2); 2.28−2.24, 2.18−2.14 (m, 2H, γ-CH2, anisochronous
signals); 2.08 (s, 6H, (CH3)2N); 1.67−1.63, 1.61−1.57 (m, 2H, β-
4.2.8. Preparation of Heteroleptic Tin(II) Guanidinate LEDCSnCl
(11). 1.15 g of 4 (7.4 mmol, 0.877 g/cm3, 1.31 mL), 2.33 g of
(Me3Si)2NSnCl (7.4 mmol), 30 mL of Et2O. Yield: 3.15 g (90%) of
3
CH2, anisochronous signals); 1.19 (t, J = 7.1 Hz, 3H, CH3); 0.40 (s,
1
18H, (CH3)3Si); 0.21 (s, 9H, (CH3)3Si); 0.16 (s, 9H, (CH3)3Si). 13C
NMR (C6D6, 125 MHz, 295 K): δ 163.8 (NC(N)N); 59.7 (α-
CH2); 46.7 ((CH3)2N); 45.9 (δ-CH2); 40.7 (γ-CH2); 30.8 (β-CH2);
18.6 (CH3); 6.4 ((CH3)3Si); 2.7 ((CH3)3Si); 2.5 ((CH3)3Si). 119Sn
NMR (C6D6, 186 MHz, 295 K): δ −144.6. Anal. Calcd for
C20H53N5Si4Sn: C, 40.39; H, 8.98; N, 11.78. Found: C, 40.58; H,
9.05; N, 11.63.
colorless oily material of 11. H NMR (C6D6, 500 MHz, 295 K): δ
3.38, 3.21 (br s, 2H, α-CH2, anisochronous signals); 3.24 (br s, 2H, δ-
CH2); 2.52, 1.97 (br s, 2H, γ-CH2, anisochronous signals); 1.97 (s, 6H,
3
(CH3)2N); 1.30 (br s, 2H, β-CH2); 1.11 (t, J = 7.2 Hz, 3H, CH3);
0.21, 0.13 (br s, 18H, (CH3)3Si). 13C NMR (C6D6, 125 MHz, 295 K):
δ 166.9 (NC(N)N); 60.2 (α-CH2); 46.2 ((CH3)2N); 46.1 (δ-CH2);
40.7 (γ-CH2); 27.5 (β-CH2); 17.3 (CH3); 2.6 (br signal (CH3)3Si); 2.1
(br signal (CH3)3Si). 119Sn NMR (C6D6, 186 MHz, 295 K): δ −250.6.
Anal. Calcd for C14H35ClN4Si2Sn: C, 35.79; H, 7.51; N, 11.93. Found:
C, 35.81; H, 7.26; N, 11.68.
4.2.4. Preparation of Heteroleptic Tin(II) Guanidinate LpTolSnN-
(SiMe3)2 (8). 4.23 g of 3 (19.1 mmol), 8.37 g of [(Me3Si)2N]2Sn (19.1
mmol), 50 mL of Et2O. Yield: 11.80 g (93%) of pale yellow solid of 8.
Mp: 77−78 °C. 1H NMR (C6D6, 500 MHz, 295 K): δ 7.05 (d, 3J = 8.2
Hz, 4H, ArH); 6.95 (d, 3J = 8.1 Hz, 4H, ArH); 2.11 (s, 6H, CH3); 0.27
(s, 18H, (CH3)3Si); 0.03 (s, 9H, (CH3)3Si); −0.12 (s, 9H, (CH3)3Si).
13C NMR (C6D6, 125 MHz, 295 K): δ 163.6 (NC(N)N); 142.4
4.2.9. Preparation of Heteroleptic Tin(II) Guanidinate LpTolSnCl
(12). 5.13 g of 3 (23.1 mmol), 7.27 g of (Me3Si)2NSnCl (23.1 mmol),
60 mL of Et2O. Washed with 10 mL of hexane. Yield: 10.63 g (86%) of
white solid of 12. Mp: 69−73 °C. Single crystals suitable for XRD
analyses were obtained under argon from a saturated solution of 12 in
Et2O cooled to −30 °C. 1H NMR (C6D6, 500 MHz, 295 K): δ 7.02 (d,
(Ar-Cipso); 134.1 (Ar-Cipso); 129.9 (Ar-CH); 127.8 (Ar-CH); 21.3
(CH3); 6.2 ((CH3)3Si); 2.3 ((CH3)3Si); 2.2 ((CH3)3Si). 119Sn NMR
(C6D6, 186 MHz, 295 K): δ −87.2. 1H NMR (THF-d8, 500 MHz, 295
K): δ 7.11 (d, 3J = 8.2 Hz, 4H, ArH); 6.99 (d, 3J = 8.2 Hz, 4H, ArH);
2.30 (s, 6H, CH3); 0.05 (s, 9H, (CH3)3Si); 0.00 (s, 18H, (CH3)3Si);
−0.17 (s, 9H, (CH3)3Si). 13C NMR (THF-d8, 125 MHz, 295 K): δ
164.0 (NC(N)N); 142.7 (Ar-Cipso); 134.6 (Ar-Cipso); 130.1 (Ar-
CH); 128.0 (Ar-CH); 21.1 (CH3); 5.4 ((CH3)3Si); 2.9 ((CH3)3Si); 1.9
((CH3)3Si). 119Sn NMR (THF-d8, 186 MHz, 295 K): δ −93.0. Anal.
Calcd for C27H50N4Si4Sn: C, 49.00; H, 7.62; N, 8.47. Found: C, 48.85;
H, 7.50; N, 8.65.
3
3J = 8.1 Hz, 4H, ArH); 6.95 (d, J = 8.1 Hz, 4H, ArH); 2.10 (s, 6H,
CH3); −0.04 (s, 18H, (CH3)3Si). 13C NMR (C6D6, 125 MHz, 295 K):
δ 168.3 (NC(N)N); 141.6 (Ar-Cipso); 134.3 (Ar-Cipso); 130.2 (Ar-
CH); 126.9 (Ar-CH); 21.3 (CH3); 1.5 ((CH3)3Si). 119Sn NMR (C6D6,
186 MHz, 295 K): δ −108.2. 1H NMR (THF-d8, 500 MHz, 295 K): δ
7.09 (d, 3J = 8.0 Hz, 4H, ArH); 6.99 (d, 3J = 8.1 Hz, 4H, ArH); 2.27 (s,
6H, CH3); −0.03 (s, 18H, (CH3)3Si). 13C NMR (C6D6, 125 MHz, 295
K): δ 163.5 (NC(N)N); 142.6 (Ar-Cipso); 134.0 (Ar-Cipso); 130.3
(Ar-CH); 127.1 (Ar-CH); 21.2 (CH3); 1.6 ((CH3)3Si). 119Sn NMR
(THF-d8, 186 MHz, 295 K): δ −220.0. Anal. Calcd for
C21H32N3Si2Sn: C, 46.98; H, 6.01; N, 7.83. Found: C, 47.03; H,
7.54; N, 8.10.
4.2.5. Preparation of {(LpTol)[(Me3Si)2N]SnO}2 (8a). After standing
of 500 mg of 8 in 20 mL of Et2O in a Schlenk tube with an
insufficiently greased stopcock at −30 °C for 3 weeks, about 50 mg of
1
4.2.10. Preparation of Homoleptic Tin(II) Guanidinate (LEDC)2Sn
(13). 1.47 g of 4 (9.5 mmol, 0.877 g/cm3, 1.67 mL), 2.08 g of
[(Me3Si)2N]2Sn (4.8 mmol), 30 mL of Et2O. Yield: 3.42 g (96%) of
8a has been reproducibly crystallized. Mp: 150−152 °C. H NMR
(THF-d8, 500 MHz, 295 K): δ 7.04 (d, 3J = 8.0 Hz, 8H, ArH); 6.84 (d,
3J = 8.1 Hz, 8H, ArH); 2.26 (s, 12H, CH3); 0.11 (s, 18H, (CH3)3Si);
2209
dx.doi.org/10.1021/om201118m | Organometallics 2012, 31, 2203−2211

Organometallics
Article
1
colorless oily material of 13. H NMR (C6D6, 500 MHz, 295 K): δ
3.47−3.37 (m, 8H, α-CH2 + δ-CH2); 2.35 (t, 3J = 7.0 Hz, 4H, γ-CH2);
2.15 (s, 12H, (CH3)2N); 1.88 (quin, 4H, β-CH2); 1.27 (t, 3J = 7.5 Hz,
6H, CH3); 0.24 (s, 36H, (CH3)3Si). 13C NMR (C6D6, 125 MHz, 295
K): δ 163.2 (NC(N)N); 59.0 (α-CH2); 46.3 ((CH3)2N); 45.9 (δ-
CH2); 41.1 (γ-CH2); 32.3 (β-CH2); 19.0 (CH3); 2.4 ((CH3)3Si). 119Sn
NMR (C6D6, 186 MHz, 295 K): δ −377.2. Anal. Calcd for
C28H70N8Si4Sn: C, 44.84; H, 9.41; N, 14.94. Found: C, 44.88; H,
9.57; N, 14.80.
(f) Veith, M.; Recktenwald, O. Z. Anorg. Allg. Chem. 1979, 459, 208−
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4.2.11. Preparation of Homoleptic Tin(II) Guanidinate (LpTol)2Sn
(14). 4.76 g of 3 (21.4 mmol), 4.71 g of [(Me3Si)2N]2Sn (10.7 mmol),
50 mL of Et2O. Yield: 9.21 g (97%) of white solid of 14. Mp: 83−86
°C. Single crystals suitable for XRD analyses were obtained under
(5) (a) Brynda, M.; Herber, R.; Hitchcock, P. B.; Lappert, M. F.;
Nowik, I.; Power, P. P.; Protchenko, A. V.; Ruzick
a, A.; Steiner, J.
̈
̊
̌
̌
1
argon from a saturated solution of 14 in Et2O cooled to −30 °C. H
Angew. Chem., Int. Ed. 2006, 45, 4333−4337. (b) Schnockel, H. Dalton
NMR (C6D6, 500 MHz, 295 K): δ 6.94 (d, 3J = 7.7 Hz, 8H, ArH); 6.81
(d, 3J = 7.8 Hz, 8H, ArH); 2.19 (s, 12H, CH3); −0.04 (s, 36H,
(CH3)3Si). 13C NMR (C6D6, 125 MHz, 295 K): δ 163.2 (N
C(N)N); 144.1 (Ar-Cipso); 132.7 (Ar-Cipso); 129.6 (Ar-CH); 127.3
(Ar-CH); 21.3 (CH3); 2.1 ((CH3)3Si). 119Sn NMR (C6D6, 186 MHz,
295 K): δ −432.0. 1H NMR (THF-d8, 500 MHz, 295 K): δ 6.93 (d, 3J
Trans. 2005, 3131−3136. (c) Wiberg, N.; Power, P. P. Molecular
Clusters of the Main Group Elements; Wiley-VCH: Weinheim,
Germany, 2004. (d) Schnepf, A.; Koppe, R. Angew. Chem., Int. Ed.
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2003, 42, 911−913.
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(6) (a) Miller, K. A.; Bartolin, J. M.; ONeil, R. M.; Sweeder, R. D.;
Owens, T. M.; Kampf, M. M.; Banaszak Holl, M. M.; Wells, N. J. J. Am.
Chem. Soc. 2003, 125, 8986−8987. (b) Bartolin, J. M.; Kavara, A.;
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4740.
3
= 8.0 Hz, 8H, ArH); 6.63 (d, J = 8.1 Hz, 8H, ArH); 2.28 (s, 12H,
CH3); −0.16 (s, 36H, (CH3)3Si). 13C NMR (THF-d8, 125 MHz, 295
K): δ 163.5 (NC(N)N); 144.3 (Ar-Cipso); 133.0 (Ar-Cipso); 129.7
(Ar-CH); 127.4 (Ar-CH); 21.1 (CH3); 1.94 ((CH3)3Si). 119Sn NMR
(THF-d8, 186 MHz, 295 K): δ −427.8. Anal. Calcd for
C42H64N6Si4Sn: C, 57.06; H, 7.30; N, 9.51. Found: C, 57.28; H,
7.54; N, 9.19.
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ASSOCIATED CONTENT
* Supporting Information
Figures, tables, and CIF files giving NMR spectra, comparisons
of compounds 10 and 12 and of compounds 14 and 14′, the
molecular structure of 14′, computed optimized structures of
10, 12, and 14, and crystallographic data for 8a, 10, 12, 14, and
14′. This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
(8) (a) Sita, L. R.; Babcock, J. R.; Xi, R. J. Am. Chem. Soc. 1996, 118,
10912−10913. (b) Babcock, J. R.; Sita, L. R. J. Am. Chem. Soc. 1998,
120, 5585−5586. (c) Babcock, J. R.; Liable-Sands, L.; Rheingold, A. L.;
Sita, L. R. Organometallics 1999, 18, 4437−4441. (d) Tang, Y. J.; Felix,
A. M.; Manner, V. W.; Zakharov, L. N.; Rheingold, A. L.; Moasser, B.;
Kemp, R. A ACS Symp. Ser. 2006, 917, 410−421. (e) Xi, R. M.; Sita, L.
R. Inorg. Chim. Acta 1998, 270, 118−122. (f) Weinert, C. S.; Guzei, I.
A.; Rheingold, A. L.; Sita, L. R. Organometallics 1998, 17, 498−500.
(9) For selected reviews on NHC’s, see: (a) Bourissou, D.; Guerret,
O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39−91.
(b) Liddle, S. T.; Edworthy, I. S.; Arnold, P. L. Chem. Soc. Rev. 2007,
36, 1732−1744. (c) Cantat, T.; Mezailles, N.; Auffrant, A.; Le Floch, P.
Dalton Trans. 2008, 1957−1972. (d) Hahn, F. E. Angew. Chem., Int. Ed.
2006, 45, 1348−1352. (e) Hahn, F. E.; Jahnke, M. C. Angew. Chem.,
Int. Ed. 2008, 47, 3122−1372. (f) Kaufhold, O.; Hahn, E. E. Angew.
Chem., Int. Ed. 2008, 47, 4057−4061.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: +420-466037068. E-mail: ales.ruzicka@upce.cz.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(10) (a) Power, P. P. Nature 2010, 463, 171−177. (b) Peng, Y.; Guo,
J. D.; Ellis, B. D.; Zhu, Z. L.; Fettinger, J. C.; Nagase, S.; Power, P. P. J.
Am. Chem. Soc. 2009, 131, 16272−16282. (c) Peng, Y.; Ellis, B. D.;
Wang, X.; Power, P. P. Science 2009, 325, 1668−1670. (d) Spikes, G.;
Fettinger, J. C.; Power, P. P. J. Am. Chem. Soc. 2005, 127, 12232−
12233.
■
We thank the Grant Agency of the Czech Republic (Grant Nos.
104/09/0829 and P207/10/P092) and the Ministry of
Education of the Czech Republic (No. VZ 0021627501) for
financial support. F.D.P. wishes to acknowledge the Research
Foundation-Flanders (FWO) and the Vrije Universiteit Brussel
(VUB) for continuous support to this research group.
(11) Van
̌
kat
́
́
ova,
Z.; Ruzick
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H.; Broeckaert, L.; De Proft, F.; Olejník, R.; Turek,
a, A. Inorg. Chem. 2022, 50, 9454−9464.
J.; Padelkova,
̌
̊
̌
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(12) For a review of β-diketiminate complexes, see: (a) Bourget, L.;
Lappert, M. F.; Severn, J. R. Chem. Rev. 2002, 102, 3031−3065. For
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