Facile access to mono- and dinuclear heteroleptic N-heterocyclic silylene copper complexes

Article abstract of DOI:10.1021/om4011033

Reaction of the heteroleptic N-heterocyclic chlorosilylene L(Cl)Si: (1; L = PhC(NtBu)₂) with [Cu(tmeda)(CH₃CN)][OTf] (2; tmeda = N,N,N′,N′-tetramethylethylenediamine, OTf = OSO₂CF ₃ (triflate)) affords the Cu(I) complex [L(Cl)Si:→Cu(tmeda)] [OTf] (3) in high yield as the first example of a heteroleptic N-heterocyclic silylene copper complex. Similarly, the reaction of L(OtBu)Si: (4; L = PhC(NtBu)₂) with 2 affords [L(OtBu)Si: → Cu(tmeda)][OTf] (5) and that of L(NMe₂)Si: (6) with 2 leads to [L(NMe₂)Si: →Cu(tmeda)][OTf] (7). Complex 3 shows a rather strong interaction in the solid state between the O atom of the triflate anion and the three-coordinate Cu(I) center with a Cu···O distance of 2.312 A. In contrast, complex 7 features only a weak interaction (ca. 3.28 A), while in complex 5 the cation and anion are fully separated. Strikingly, the reaction of the chelating oxo-bridged silylene:Si(L)(μ₂-O)(L)Si: (8) with the copper source [Cu(CH₃CN)₄][OTf] (9) affords the dinuclear complex salt [Cu₂{η¹:η¹- LSi(μ₂-O)SiL}₂][OTf]₂ (10), featuring a novel metallacyclooctane dication, selectively in a good yield. Complex 10 also exhibits a very strong interaction between the copper centers in the dication and the oxygen atoms of triflate anions in the solid state, evidenced by a Cu···O separation of only 2.141 A. All complexes were fully characterized.

Full text of DOI:10.1021/om4011033

Article
pubs.acs.org/Organometallics
Facile Access to Mono- and Dinuclear Heteroleptic N‑Heterocyclic
Silylene Copper Complexes
Gengwen Tan, Burgert Blom, Daniel Gallego, and Matthias Driess*
Department of Chemistry: Metalorganics and Inorganic Materials, Technische Universitat Berlin, Strasse des 17. Juni 135, Sekr. C2,
̈
D-10623 Berlin, Germany
S
* Supporting Information
ABSTRACT: Reaction of the heteroleptic N-heterocyclic chlorosilylene L(Cl)Si: (1; L =
PhC(NtBu)2) with [Cu(tmeda)(CH3CN)][OTf] (2; tmeda = N,N,N′,N′-tetramethylethy-
lenediamine, OTf = OSO2CF3 (triflate)) affords the Cu(I) complex [L(Cl)Si:→
Cu(tmeda)][OTf] (3) in high yield as the first example of a heteroleptic N-heterocyclic
silylene copper complex. Similarly, the reaction of L(OtBu)Si: (4; L = PhC(NtBu)2) with 2
affords [L(OtBu)Si: → Cu(tmeda)][OTf] (5) and that of L(NMe2)Si: (6) with 2 leads to
[L(NMe2)Si:→Cu(tmeda)][OTf] (7). Complex 3 shows a rather strong interaction in the
solid state between the O atom of the triflate anion and the three-coordinate Cu(I) center
with a Cu···O distance of 2.312 Å. In contrast, complex 7 features only a weak interaction
(ca. 3.28 Å), while in complex 5 the cation and anion are fully separated. Strikingly, the
reaction of the chelating oxo-bridged silylene :Si(L)(μ2-O)(L)Si: (8) with the copper source
[Cu(CH3CN)4][OTf] (9) affords the dinuclear complex salt [Cu2{η1:η1-LSi(μ2-O)SiL}2]-
[OTf]2 (10), featuring a novel metallacyclooctane dication, selectively in a good yield.
Complex 10 also exhibits a very strong interaction between the copper centers in the
dication and the oxygen atoms of triflate anions in the solid state, evidenced by a Cu···O separation of only 2.141 Å. All
complexes were fully characterized.
Chart 1. Recent Examples of Catalytically Active N-
Heterocyclic Silylene (NHSi) Complexes
INTRODUCTION
■
N-heterocyclic silylene (NHSi) transition-metal complexes
have emerged in the past decade as a new class of compounds
which lie at the forefront of contemporary research efforts.1
These efforts have largely been precipitated by the abundance
of silicon in the earth’s crust and the search for new generations
of complexes capable of novel synthetic transformations,
particularly in catalysis.2 To date, they have been implicated
in a relatively small number of catalytic transformations and are
still comparatively scarce in comparison to their carbon
homologues: that is, the N-heterocyclic carbene (NHC)
metal complexes. Recent examples of their use in catalysis
include that of a hydridosilylene iron NHSi complex (I in Chart
1) to perform ketone hydrosilylation,3 catalytic C−C bond
formation by nickel NHSi complexes (II and III in Chart 1),4
catalytic amide reduction effected by NHSi Rh or Ir complexes,
bearing the zwitterionic NHSi (IV in Chart 1),5 and catalytic
borylation of arenes effected by V (Chart 1).6
These examples illustrate the potential locked inside these
complexes and clearly show a need for their fundamental
exploration. Most of the NHSi complexes that exist to date are
of transition metals of groups 5−10, with NHSi group 10 metal
complexes being the most numerous.1 In contrast, group 4
metal NHSi complexes are still rare,7 and reports of NHSi
group 11 or 12 metal complexes are also scant. In fact, other
than a theoretical paper by Frenking studying the stability of
NHSi Cu, Ag, and Au complexes,8 there are only two synthetic
examples, only one of which is isolable. Lappert and co-workers
prepared an isolable tetrahedral copper-based NHSi complex
by reacting a homoleptic NHSi with [CuI(PPh3)3], which
afforded, by elimination of PPh3, the tetrahedral copper NHSi
complex [(PPh3)2Cu(←:Si{N(CH2tBu)}2Ph)I] (VI in Chart
2).9 Apeloig, West, and co-workers have reported the only
other example of a group 11 or 12 metal NHSi complex for Hg,
Received: November 13, 2013
© XXXX American Chemical Society
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reactions of NHSi species 4 and 6 with the copper(I) source 2.
In both cases the reactions proceed, in analogy to the case of
complex 3, to the NHSi Cu(I) complex [L(OtBu)Si:→
Cu(tmeda)][OTf] (5) and [L(NMe2)Si:→Cu(tmeda)][OTf]
(7), in moderate (5) to good (7) yields also as colorless solids
(Scheme 2).
Chart 2. Reported Examples of NHSi Group 11 or 12 Metal
Complexes
Complexes 3, 5, and 7 were all fully characterized by
multinuclear NMR spectroscopy, elemental analyses, and
single-crystal X-ray diffraction analyses. All three complexes
feature singlet resonance signals in the 1H NMR spectra
corresponding to the NtBu signal of the coordinated NHSi
ligand, in CD2Cl2 (Table 1). This suggests either a highly
symmetrical rigid structure or free rotation of the coordinated
NHSi on the NMR time scale in all three cases. Moreover, the
expected two sets of resonance signals (NMe2 and
NCH2CH2N) for the Cu-coordinated tmeda ligands are also
clearly observed in all three complexes. Complex 5 exhibits an
which was found to be highly reactive and could not be
structurally characterized or isolated (VII in Chart 2).10
This early stage of knowledge on NHSi metal complexes
turned our interest to the synthesis of new types of copper-
based NHSi complexes, in an attempt to garner more structural
and spectroscopic data on NHSi group 11 metal complexes,
from a fundamental perspective.
Herein, we report only the second set of isolable examples of
NHSi group 11 or 12 metal complexes, for copper. The facile
reactions of amidinato-stabilized silyenes of the type LSiX (L =
PhC(NtBu)2; X = Cl, OtBu, NMe2)11 with the readily available
Cu(I) precursors [Cu(tmeda)(CH3CN)][OTf] afford the first
examples of heteroleptic NHSi complexes of group 11 metals.
Moreover, the reaction of the chelating oxo-bridged bis-silylene
:SiL(μ2-O)LSi: with the Cu(I) source [Cu(CH3CN)4][OTf] is
also reported and affords the novel dinuclear metallacyclic
complex [Cu2{η1:η1-LSi(μ2-O)SiL}2][OTf]2.
1
additional singlet resonance signal at δ 1.51 ppm in the H
NMR spectrum, corresponding to the OtBu group (9 protons),
while 7 has an additional resonance signal at δ 2.57
corresponding to the NMe2 protons (6 protons), in accordance
with expectations. A key feature in the 13C{1H} NMR spectra
for the complexes is the somewhat deshielded chemical shift
position of the amidinate NCN carbon nucleus, which seems to
be rather invariant on changing the substituent on the Si atom
(Table 1).
Table 1. Summary of Some Key Chemical Shifts (in ppm,
Spectra Recorded in CD2Cl2) Observed in Complexes 3, 5,
and 7
complex
29Si{1H}
1H of tBu
13C{1H} of NCN
RESULTS AND DISCUSSION
3
5
7
32.9
5.4
1.20
1.23
1.11
174.9
172.9
170.9
■
The amidinato-stabilized chlorosilylene 111a by Roesky and co-
workers, L(Cl)Si: (L = PhC(NtBu)2), has been shown to
exhibit remarkable coordination properties to a variety of
transition metals, including for example Ti,7 V,12 Cr, Mo, and
W,13 Mn and Re,14 and Fe.3,15 Inspired by the success of this
ligand in its coordination ability to a range of transition metals,
we decided to explore its coordination chemistry toward Cu(I),
given the lack of reports in this area.
18.3
Most diagnostic is the presence of a sharp singlet resonance
signal observed in the 29Si{1H} NMR spectra of the complexes
(Table 1), where dramatic differences are observed among the
complexes, obviously as a result of changing the substituent
attached to the Si center. In previous cases, for similar NHSi
complexes of Ti and Fe,17 a negative correlation was found to
exist between the chemical shift position in the 29Si{1H} NMR
spectrum and the Hammett constant (σp)18 of the substituent
on the Si center (where the substituents Cl, H, and CH3 were
studied). In contrast, complexes 3, 5, and 7, reveal no such
correlation, and so these substituents do not obey this trend.
However, complex 3 clearly exhibits the most deshielded Si
nucleus in this series. While it is tempting to explain this by the
presence of the electronegative Cl substituent in 3, resulting
from electronic withdrawal from the Si center, in a deshielded
nucleus and concomitant increase in the chemical shift position,
Strikingly, the reaction of 1 with [Cu(tmeda)(CH3CN)]-
[OTf] (2)16 affords the N-heterocyclic chlorosilylene copper
complex salt [L(Cl)Si:→Cu(tmeda)][OTf] (3), with concom-
itant CH3CN elimination, in high yield as a colorless solid in a
straightforward fashion. Complex 3 represents only the second
example of a NHSi copper complex and is the first example of a
heteroleptic NHSi complex for any metal in group 11 or 12
(Scheme 1).
The existence and rather facile synthetic access to other
heteroleptic NHSi species based on 1 featuring substituents
other than Cl at the Si(II) atom, for example: L(OtBu)Si: (4)
and L(NMe2)Si: (6),11b prompted us to explore the analogous
Scheme 1. Facile Access to the Ionic Chlorosilylene Copper(I) Complex 3
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Scheme 2. Facile Access to the Heteroleptic NHSi Cu(I) Ion Pair 5 and 7, Starting from NHSi Species 4 and 6, Respectively
a
Table 2. Summary of Important Metrical Parameters in the Related Heteroleptic NHSi Complexes 3, 5, and 7
b
complex
d(Si−Cu)
d(Si−X)
d(Cu−N3)
d(Cu−N4)
d(Cu−O)
∑(Cu)
3
5
7
2.1716(12)
2.2003(6)
2.1982(12)
2.1198(15)
1.6406(14)
1.710(4)
2.102(3)
2.1058(16)
2.125(4)
2.136(3)
2.0876(17)
2.101(3)
2.312
348.72
359.78
359.84
3.277
a
b
−
All distances are given in Å and sums of the angles in deg. Contact distance to the closest O atom of the counteranion: i.e., Cu···OSO2CF3
(OTf−). For complex 5 this distance is very large (>4 Å) and clearly is separated.
it is more likely that this is due to an increase in the s character
of the Si−Cu bond, which is enhanced in the case of a Cl
substituent on silicon. The higher s character results in a tightly
bound lone pair and hence a shielding effect (vide infra).3,20
Complexes 5 and 7 exhibit more shielded Si nuclei, and for
example in complex 7, this is an indication of electron donation
capacity from the NMe2 substituent to the Si(II) site, for which
our structural studies provide additional support (vide infra),
on the basis of the planarity of the N atom in the NMe2
substituent.
Copper complexes 3, 5, and 7 were also characterized by
single-crystal X-ray diffraction analysis,19 where suitable crystals
were obtained in all three cases from a concentrated toluene
solution upon storage at −30 °C. Table 1s (Supporting
Information) summarizes the relevant crystallographic param-
Figure 1. ORTEP representation of the cation in complex 3. Thermal
ellipsoids are set at the 50% probability level, and H atoms and the
counteranion are omitted for clarity. Selected bond lengths (Å):
Cl(1)−Si(1) 2.1198(15), Si(1)−N(1) 1.828(3), Si(1)−N(2)
1.839(3), Si(1)−Cu(1) 2.1716(12), Cu(1)−N(3) 2.102(3), Cu(1)−
N(4) 2.136(3), Selected bond angles (deg): N(1)−Si(1)−N(2)
71.13(13), N(1)−Si(1)−Cl(1) 101.44(12), N(2)−Si(1)−Cl(1)
101.57(11), N(1)−Si(1)−Cu(1) 125.11(11), N(2)−Si(1)−Cu(1)
128.61(11), Cl(1)−Si(1)−Cu(1) 118.24(6), N(1)−Si(1)−C(7)
35.81(12), N(2)−Si(1)−C(7) 35.51(12), Cl(1)−Si(1)−C(7)
106.92(10), Cu(1)−Si(1)−C(7) 134.77(11). N(3)−Cu(1)−N(4)
85.58(12).
eters for these crystallographic investigations.
All three complexes feature slightly distorted tetrahedral
geometries about the four-coordinate Si(II) atom, in the cation
of the complex salt, as expected. The Si−Cu bond lengths are
similar to each other within narrow limits: 2.1716(12)−
2.2003(6) Å (Table 2 and Figures 1−3). This metrical
parameter is clearly again a reflection of the substituent on
the Si center, where the shortest of the series is observed in
complex 3 with a SiII−Cl moiety. This is readily explained by
the high s character in the lone pair on the silicon atom in 3,
resulting in a relatively short Si→Cu bond. A similar
phenomenon was noted before in a series of iron complexes
of the type [(dmpe)2Fe←:Si(X)L] (X = Cl, H, CH3; dmpe =
1,2-bis(dimethylphosphino)ethane) for X = Cl3 and also for a
series of aluminum and gallium complexes by Fischer, Frenking,
and co-workers; the latter work also featured detailed
theoretical calculations elucidating the effect of s character on
bond length.20 The high s character results in a more “compact”
lone pair and concomitant bond length contraction upon
coordination to a metal.
Of particular interest is the trigonal-planar geometry around
the Cu(I) centers21 in complexes 5 and 7, evidenced by the
sum of angles of Cu approximating 360°. This is notably not
the case for complex 3, which deviates from trigonal planarity at
the copper center, as shown by the sum of bond angles of
348.72°. This deviation is a result of the rather short contact
distance, in the solid state, between the Cu center in the cation
and one of the oxygen atoms of the OTf− anion at d = 2.312 Å.
Hence, complex 3 in the solid state can be considered as a
contact ion pair. This is particularly interesting, as it is likely a
result of the increased Lewis acidity of the Cu(I) center in 3,
effected by the electronegative Cl substituent of the
coordinated NHSi (Figure 4). Complex 5, in contrast to this,
exhibits a very large separation between the copper center and
the O atom of the OTf− anion, while in complex 7 the Cu···O
distance is 3.277 Å. These results further highlight how
changing the substituent at the Si center not only causes
dramatic electronic changes but can also perturb the
organization of the cation and anion in the solid-state structure.
Finally, in complex 7 the nitrogen atom of the NMe2 group is
trigonal planar, as the sum of angles around it approximates
360° (357.52°). The loss of pyramidalization at N suggests a
substantial interaction of the lone pair on the N atom with the
Si center, which also rationalizes the somewhat upfield shifted
signal observed in the 29Si{1H} NMR spectrum (vide supra).
C
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Figure 4. ORTEP representation of complex salt 3, with both the
cation and anion. Thermal ellipsoids are set at the 50% probability
level, and H atoms are omitted for clarity. The contact between the
O(2) atom in the triflate and the Cu(1) center is depicted by a double-
dashed line. The deviation from trigonal-planar coordination at the
copper center is seen clearly.
Figure 2. ORTEP representation of the cation in complex 5. Thermal
ellipsoids are set at the 50% probability level, and H atoms and the
counteranion are omitted for clarity. Selected bond lengths (Å):
Cu(1)−N(4) 2.0876(17), Cu(1)−N(3) 2.1058(16), Cu(1)−Si(1)
2.2003(6), N(1)−Si(1)1.8528(16),N(2)−Si(1) 1.8345(18), O(1)−
Si(1) 1.6406(14). Selected bond angles (deg): N(4)−Cu(1)−N(3)
85.78(7), N(4)−Cu(1)−Si(1) 142.49(5), N(3)−Cu(1)−Si(1)
131.51(5), O(1)−Si(1)−N(2) 102.79(8), O(1)−Si(1)−N(1)
105.69(7), N(2)−Si(1)−N(1) 70.94(7), O(1)−Si(1)−Cu(1)
128.89(6), N(2)−Si(1)−Cu(1) 118.49(6), N(1)−Si(1)−Cu(1)
115.01(5).
the dinuclear metallacyclooctane salt complex 10 (Scheme 3)
selectively in high yield.
Crystals of complex 10 suitable for single-crystal X-ray
diffraction analysis were obtained from a THF/hexane solution
(2:1 v/v) upon standing at room temperature for 2 days, and
the solid-state structure is depicted in Figure 5. The asymmetric
unit possesses one molecule bearing a symmetry operation
rendering half of it metrically invariant to the other (symmetry
element Cs). The compound bears a unique dicationic
metallacyclooctane ring24 with the elements copper, silicon,
and oxygen. This rather unique architecture observed in the
cation of 10 is reminiscent of some copper complexes reported
recently25 and a globular 56-membered copper(I) siloxane.26
The two OTf− counteranions are strongly associated with the
copper centers, evidenced by a rather short Cu−O (O atom of
SO3) bond length of 2.141 Å, rendering 10 a contact ion pair,
akin to what was observed in complex 3 (vide supra: d(Cu−O)
= 2.312 Å).
The multinuclear NMR spectra of complex 10, at ambient
temperature in CD2Cl2, suggest fluxional solution behavior of
the triflate counteranions in addition to a discrete charge-
separated dication coexisting in solution. In the 1H NMR
spectrum, two signals (one broad and one sharp) correspond-
ing to the tBu groups of the amidinato ligand are observed, with
an integral ratio of approximately 1:0.63. The 29Si{1H} NMR
spectrum exhibits two resonance signals, with one sharp (δ
3.26) and one broad (δ 7.73 ppm). Both of these signals are
shifted downfield from the “free” bis-NHSi ligand, which
features a resonance signal at δ −16.1 ppm, clearly signifying
coordination to the metal. Moreover, two signal sets are also
observed in the 13C{1H} NMR spectrum, exemplified inter alia
by the NCN signals, which appear at δ 172.8 and 174.9 ppm,
respectively, the latter also being somewhat broadened.
Collectively, these data clearly show that two species are
present in solution. The sharp signals correspond most likely to
the discrete charge-separated ion pair [Cu2{η1:η1-LSi(μ2-
O)SiL}2]2+, which in itself is highly symmetrical and should
yield only a single resonance signal in the 29Si{1H} spectrum
Figure 3. ORTEP representation of the cation in complex 7. Thermal
ellipsoids are set at the 50% probability level, and H atoms and the
counteranion are omitted for clarity. Selected bond lengths (Å):
Cu(1)−N(4) 2.101(3), Cu(1)−N(3) 2.125(4), Cu(1)−Si(2)
2.1981(12), Si(2)−N(5) 1.710(4), Si(2)−N(1) 1.854(3), Si(2)−
N(2) 1.870(4). Selected bond angles (deg): N(4)−Cu(1)−N(3)
85.59(14), N(4)−Cu(1)−Si(2) 139.03(10), N(3)−Cu(1)−Si(2)
135.23(10), N(5)−Si(2)−N(1) 106.05(16), N(5)−Si(2)−N(2)
107.82(17), N(1)−Si(2)−N(2) 69.85(15), N(5)−Si(2)−Cu(1)
120.21(14), N(1)−Si(2)−Cu(1) 122.34(11), N(2)−Si(2)−Cu(1)
119.77(11).
Having isolated complexes 3, 5, and 7, we became interested
in exploring the reactivity of a bidentate (chelating) NHSi
ligand, targeting the isolation of a chelated Cu(I) bis-NHSi
complex. We employed bis-NHSi :Si(L)(μ2-O)(L)Si: (8)
featuring an oxo bridge between the two Si(II) centers,
previously shown to be a suitable chelating ligand for Ni
complexes.22 On the basis of our observations for complexes 3,
5 ,and 7, we envisaged that reaction of 8 with a Cu(I) source
not bearing a coordinating ligand such as tmeda (for example,
[Cu(CH3CN)4][OTf] (9))23 might enable facile entry to
complex salts of the type [(η2-:Si(L)(μ2-O)(L)Si:)Cu-
(CH3CN)n][OTf] (n = 1, 2), bearing a η2-coordinated bis-
NHSi chelate ligand. Strikingly, the reaction of 8 with 9 affords
1
and one set of signals in the H and 13C spectra, respectively.
The broad components in the spectra are hence attributable to
a dynamic coordination/decoordination of the OTf− to the
dication ([Cu2{η1:η1-LSi(μ2-O)SiL}2]2+···(OTf)− ), n = 1, 2),
n
which is in accord with the structural analysis, where a rather
strong interaction was seen. These findings are akin to those for
D
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a
Scheme 3. Synthesis of Complex Salt 10
a
Here 10 is represented as a charge-separated salt, although OTf− does interact with the Cu centers both in the solid state and in solution.
chemistry of heteroleptic NHSi ligands with coinage metals for
the first time and potentially open up new vistas in group 11
metal NHSi coordination chemistry.
EXPERIMENTAL SECTION
■
General Considerations. All experiments and manipulations were
carried out under a dry and oxygen-free atmosphere of nitrogen or
argon using standard Schlenk techniques or in an MBraun inert-
atmosphere drybox containing an atmosphere of purified nitrogen.
Solvents were dried by standard methods and stored over activated
molecular sieves (4 Å). Prior to use all solvents were degassed at least
once via a freeze−pump−thaw cycle. CD2Cl2 was dried by refluxing
with CaH2 for 48 h, distilled, and stored over activated molecular
sieves (4 Å) for use. The NMR spectra were recorded on a Bruker AV
200 or 400 spectrometer. Concentrated solutions of samples in
CD2Cl2 were sealed off in a Young-type NMR tube for measurements.
1
The H and 13C{1H} spectra were referenced to the residual solvent
Figure 5. ORTEP representation of complex salt 10 in the solid state.
Thermal ellipsoids are set at the 50% probability, and H atoms are
omitted for clarity. Symmetry operation: −x + 1, −y, −z + 1. Selected
bond lengths (Å): Cu(1)−O(2) 2.141(4), Cu(1)−Si(1) 2.2719(13),
Cu(1)−Si(2) 2.2853(14), Si(1)−O(1) 1.642(3), Si(1)−N(2)
1.845(4), Si(1)−N(1) 1.859(4), Si(2)−O(1) 1.639(3), Si(2)−N(3)
1.846(4), Si(2)−N(4) 1.863(4). Selected bond angles (deg): O(2)−
Cu(1)−Si(1) 115.39(12), O(2)−Cu(1)−Si(2) 99.85(12), Si(1)−
Cu(1)−Si(2) 143.90(5), O(1)−Si(1)−N(2) 103.16(17), O(1)−
Si(1)−N(1) 104.91(17), N(2)−Si(1)−N(1) 70.58(17), O(1)−
Si(1)−Cu(1) 119.02(13), N(2)−Si(1)−Cu(1) 127.73(13), N(1)−
Si(1)−Cu(1) 120.78(13).
signals as internal standards (δH 5.32; δc 53.84 ppm for CD2Cl2). The
29Si{1H} NMR spectra were referenced to TMS (tetramethylsilane) as
an external standard. Abbreviations: s, singlet; m, multiplet; br, broad;
quint, quintet. Unambiguous signal assignments were made by
employing a combination of DEPT-45 and 2D NMR H,C-COSY
(HMQC) experiments. For the single-crystal X-ray structure
determinations, crystals were mounted on glass capillaries in
perfluorinated oil and measured under a cold N2 flow. The data
were collected on an Agilent Technologies Xcalibur S Sapphire at 150
K (Mo Kα radiation, λ = 0.71073 Å). The structures were solved by
direct methods and refined on F2 with the SHELX-97 software
package. The positions of the H atoms were calculated and considered
isotropically according to a riding model. N-heterocylic silylenes 1, 4,
611 and the copper precursors [Cu(tmeda)(CH3CN)][OTf]16 and
[Cu(CH3CN)4][OTf]21 were prepared according to the reported
procedures.
recently reported Cu(I) complexes bearing chelating pyrazole
ligands, which also feature similar dynamic behavior of a
coordinating iodide anion.27
Synthesis of [L(Cl)Si:→Cu(tmeda)][OTf] (3). L(Cl)Si (0.147 g,
0.5 mmol) and [Cu(tmeda)(CH3CN)][OTf] (0.185 g, 0.5 mmol)
were placed in a Schlenk flask (100 mL) in the glovebox, and toluene
(30 mL) was transferred to the flask via cannula with stirring at −78
°C. Then the mixture was warmed to room temperature with constant
stirring. After it was stirred for 12 h at room temperature, the obtained
clear colorless solution was concentrated to ca. 5 mL and filtered. The
filtrate was left at 0 °C for 24 h to afford a colorless crystalline product
of 3. The product was collected by decantation of the supernatant, and
the obtained solid was dried in vacuo for several hours. Yield: 0.26 g,
0.4 mmol (80%). 1H NMR (200.1 MHz, CD2Cl2, 298 K, ppm): δ 1.20
(s, 18 H, tBu-H), 2.61 (br, 12 H, N(CH3)2), 2.65 (br, 4 H,
NCH2CH2N), 7.12−7.25 (m, 1 H, Ph-H), 7.40−7.67 (m, 4 H, Ph-H).
13C{1H} NMR (100 MHz, CD2Cl2, 298 K, ppm): δ 31.2 (tBu-CH3),
48.4 (N(CH3)2), 55.0 (tBu-C), 58.3 (NCH2CH2N), 122.9 (CF3, 1JC−F
= 321 Hz) 128.5, 128.8, 129.31, 130.8, 129.9 (Ph-CH), 131.4 (Ph-C),
174.9 (NCN). 19F{1H} NMR (188.3 MHz, CD2Cl2, 298 K, ppm): δ
−78.7. 29Si{1H} NMR (79 MHz, CD2Cl2, 298 K, ppm): δ 32.9. Anal.
SUMMARY AND CONCLUSIONS
■
A series of the first heteroleptic N-heterocyclic silylene (NHSi)
Cu(I) complexes for any coinage metals has been prepared.
Moreover, these complexes represent only the second set of
isolable examples of any NHSi Cu(I) complexes. The
complexes are readily accessible upon straightforward reactions
of the heteroleptic silylenes L(X)Si: (X = Cl, OtBu, NMe2)
with [Cu(tmeda)(CH3CN)][OTf], affording complex salts of
the general formula [L(X)Si:→Cu(tmeda)][OTf]. Reactions of
the chelating oxo-bridged bis-NHSi species :Si(L)(μ2-O)(L)Si:
with [Cu(CH3CN)4][OTf] affords the unusual complex salt
[Cu2{η1:η1-LSi(μ2-O)SiL}2][OTf]2, featuring a metallacyclic
dication. The solid-state structure of the latter reveals a strong
interaction of the triflate anion oxygen atom with the Cu(I)
sites. These complexes reveal the potentially rich coordination
1
Calcd for C29H39ClCuF3N4O3SSi·1/3(toluene) (determined from H
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dx.doi.org/10.1021/om4011033 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
NMR spectroscopy): C, 44.66; H, 6.42; N, 8.56; S, 4.90. Found: C,
43.96; H, 6.49; N, 8.91; S, 4.57.
Synthesis of [L(OtBu)Si:→Cu(tmeda)][OTf] (5). This compound
Notes
The authors declare no competing financial interest.
was synthesized by a procedure similar to that for compound 3. Yield:
0.24 g, 0.36 mmol (72%). H NMR (200.1 MHz, CD2Cl2, 298 K,
ACKNOWLEDGMENTS
1
■
The authors thank the Cluster of Excellence UniCat (financed
by the Deutsche Forschungsgemeinschaft and administered by
the TU Berlin).
ppm): δ 1.23 (s, 18 H, NtBu-H), 1.51 (s, 9 H, OtBu-H), 2.67 (br, 12
H, N(CH3)2), 2.73 (br, 4 H, NCH2CH2N), 7.32−7.36 (m, 1 H, Ph-
H), 7.49−7.66 (m, 4 H, Ph-H). 13C{1H} NMR (50.3 MHz, CD2Cl2,
298 K, ppm): δ 31.3 (NtBu-CH3), 32.2 (OtBu-CH3), 48.1 (N(CH3)2)
53.8 (NtBu-C), 57.9 (NCH2CH2N), 74.5 (OtBu-C), 124.3 (CF3, 1JC−F
= 321 Hz), 127.2, 128.3, 128.4, 128.7, 130.8 (Ph−CH), 131.0 (Ph-C),
172.9 (NCN). 19F{1H} NMR (188.3 MHz, CD2Cl2, 298 K, ppm): δ
−78.8. 29Si{1H} NMR (79 MHz, CD2Cl2, 298 K, ppm): δ 5.4. Anal.
Calcd for [C26H48CuF3N4O4SSi]: C, 47.22; H, 7.32; N, 8.47; S, 4.85.
Found: C, 47.25; H, 7.22; N, 8.33; S, 4.40.
REFERENCES
■
(1) For a comprehensive and recent review on transition-metal NHSi
complexes see: Blom, B.; Stoelzel, M.; Driess, M. Chem. Eur. J. 2012,
19, 40.
(2) The reported use of NHSi complexes in catalysis is in fact very
rare and is limited to less than 10 examples; see: (a) Furstner, A.;
Krause, H.; Lehmann, C. W. Chem. Commun. 2001, 2372. (b) Zhang,
M.; Liu, X.; Shi, C.; Ren, C.; Ding, Y.; Roesky, H. W. Z. Anorg. Allg.
Chem. 2008, 634, 1755. (c) References 3−6.
(3) Blom, B.; Enthaler, S.; Inoue, S.; Irran, E.; Driess, M. J. Am. Chem.
Soc. 2013, 135, 6703.
(4) (a) Someya, C. I.; Haberberger, M.; Wang, W.; Enthaler, S.;
Inoue, S. Chem. Lett. 2013, 42, 286. (b) Gallego, D.; Bruck, A.; Irran,
E.; Meier, F.; Kaupp, M.; Driess, M.; Hartwig, J. F. J. Am. Chem. Soc.
2013, 135, 15617.
(5) Stoelzel, M.; Praesang, C.; Blom, B.; Driess, M. Aust. J. Chem.
2013, 66, 1163.
̈
Synthesis of [L(NMe2)Si:→Cu(tmeda)][OTf] (7). This com-
pound was synthesized by a procedure similar to that for compound 3.
1
Yield: 0.21 g, 0.33 mmol (66%). H NMR (200.1 MHz, CD2Cl2, 298
K, ppm): δ 1.11 (s, 18 H, tBu-H), 2.57 (br, 12 H, N(CH3)2), 2.62 (br,
6 H, NMe2-H), 2.64 (br, 4 H, NCH2CH2N), 7.23−7.30 (m, 1 H, Ph-
H), 7.38−7.56 (m, 4 H, Ph-H). 13C{1H} NMR (50.3 MHz, CD2Cl2,
298 K, ppm): δ 31.0 (tBu-CH3), 47.8 (N(CH3)2), 53.3 (NMe2-C),
57.8 (NCH2CH2N), 124.2 (CF3), 127.0, 128.4, 128.5, 129.1, 130.7
(Ph-CH), 131.2 (Ph-C), 170.9 (NCN). 19F{1H} NMR (188.3 MHz,
CD2Cl2, 298 K, ppm): δ −78.8. 29Si{1H} NMR (79 MHz, CD2Cl2,
298 K, ppm): δ 18.3. Anal. Calcd for [C24H45CuF3N5O3SSi]: C, 45.59;
H, 7.17; N, 11.08; S, 5.07. Found: C, 45.79; H, 6.95; N, 10.49; S, 4.81.
Synthesis of [Cu2{η1:η1-LSi(μ2-O)SiL}2][OTf]2 (10). :Si(L)(μ2-
O)(L)Si: (0.267 g, 0.5 mmol) and [Cu(CH3CN)4][OTf] (0.188 g, 0.5
mmol) were placed in a Schlenk flask in the glovebox (100 mL).
Toluene (40 mL) was transferred to the flask via cannula with stirring
at −78 °C. The mixture was warmed to room temperature gradually
and stirred for another 12 h. Then the solution was filtered, and the
filtrate was concentrated to ca. 5 mL and left at −20 °C for 3 days to
afford a colorless crystalline product of 10. The product was collected
by decantation, and the obtained solid was dried in vacuo for several
hours. Crystals of 10 suitable for X-ray single-crystal diffraction
analysis were obtained by recrystallization in THF and n-hexane (2/1
̈
(6) Bruck, A.; Gallego, D.; Wang, W.; Irran, E.; Driess, M.; Hartwig,
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J. F. Angew. Chem., Int. Ed. Engl. 2012, 51, 11478.
(7) See as the only example: Blom, B.; Driess, M.; Gallego, D.; Inoue,
S. Chem. Eur. J. 2012, 18, 13355.
(8) Boehme, C.; Frenking, G. Organometallics 1998, 17, 5801.
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Maciejewski, H. J. Organomet. Chem. 2003, 686, 321.
(10) (a) Sheberla, D.; Tumanskii, B.; Tomasik, A. C.; Mitra, A.; Hill,
N. J.; West, R.; Apeloig, Y. Chem. Sci. 2010, 1, 234. (b) Cabeza, J. A.;
́
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Fernandez-Colinas, J. M.; Garcıa-Alvarez, P.; Polo, D. Inorg. Chem.
2012, 51, 3896. (c) Zhao, N.; Zhang, J.; Yang, Y.; Zhu, H.; Li, Y.; Fu,
G. Inorg. Chem. 2012, 51, 8710. (d) Zhao, N.; Zhang, J.; Yang, Y.;
Chen, G.; Zhu, H.; Roesky, H. W. Organometallics 2013, 32, 762.
(11) (a) Sen, S. S.; Roesky, H. W.; Stern, D.; Henn, J.; Stalke, D. J.
Am. Chem. Soc. 2010, 132, 1123. (b) Azhakar, R.; Ghadwal, R. S.;
Roesky, H. W.; Wolf, H.; Stalke, D. Organometallics 2012, 31, 4588.
(12) Azhakar, R.; Ghadwal, R. S.; Roesky, H. W.; Hey, J.; Stalke, D.
Chem. Asian J. 2012, 7, 528.
1
v/v) at room temperature. Yield: 0.39 g, 0.26 mmol (52%). H NMR
(200.1 MHz, CD2Cl2, 298 K, ppm): δ 1.24 (s, 36 H, tBu-H,
[Cu2{η1:η1-LSi(μ2-O)SiL}2]2+···(OTf)n), 1.27 (s, 36 H, tBu-H,
[Cu2{η1:η1-LSi(μ2-O)SiL}2]2+), 7.39−7.69 (m, 20 H, Ph-H).
13C{1H} NMR (50.3 MHz, CD2Cl2, 298 K, ppm): δ 31.7 (br s, tBu-
CH3, [Cu2{η1:η1-LSi(μ2-O)SiL}2]2+···(OTf)n), 32.0 (s, tBu-CH3,
[Cu2{η1:η1-LSi(μ2-O)SiL}2]2+), 54.2 (N(CH3)3, [Cu2{η1:η1-LSi(μ2-
O)SiL}2]2+···(OTf)n + [Cu2{η1:η1-LSi(μ2-O)SiL}2]2+), 125.6, 127.0,
128.5, 128.7, 128.8, 128.9, 129.1, 129.3, 129.5, 130.0, 131.3, 131.5 (all
s, Ph-C, [Cu2{η1:η1-LSi(μ2-O)SiL}2]2+···(OTf)n + [Cu2{η1:η1-LSi(μ2-
O)SiL}2]2+) 172.8 (NCN, [Cu2{η1:η1-LSi(μ2-O)SiL}2]2+), 174.9 (br,
NCN, [Cu2{η1:η1-LSi(μ2-O)SiL}2]2+···(OTf)n). The carbon signal for
CF3 is not observed in the 13C NMR spectrum. 19F{1H} NMR (188.3
MHz, CD2Cl2, 298 K, ppm): δ −77.1. 29Si{1H} NMR (79 MHz,
CD2Cl2, 298 K, ppm): δ 3.26 (s, [Cu2{η1:η1-LSi(μ2-O)SiL}2]2+), 7.73
(br, [Cu2{η1:η1-LSi(μ2-O)SiL}2]2+···(OTf)n). Anal. Calcd for
[C62H92Cu2F6N8O8S2Si4]: C, 49.81; H, 6.20; N, 7.50; S, 4.29.
Found: C, 50.11; H, 6.49; N, 7.43; S, 3.97.
(13) Azhahar, R.; Ghadwal, R. S.; Roesky, H. W.; Wolf, H.; Stalke, D.
J. Am. Chem. Soc. 2012, 134, 2423.
(14) Azhakar, R.; Sarish, S. P.; Roesky, H. W.; Hey, J.; Stalke, D.
Inorg. Chem. 2011, 50, 5039.
(15) Yang, W.; Fu, H.; Wang, H.; Chen, M.; Ding, Y.; Roesky, H. W.;
Jana, A. Inorg. Chem. 2009, 48, 5058.
(16) York, J. T.; Brown, E. C.; Tolman, W. B. Angew. Chem., Int. Ed.
2005, 44, 7745.
(17) See ref 3 for a series of Fe complexes featuring coordinated
L(X)Si: (X = Cl, CH3, H) and ref 7 for a series of Ti complexes
featuring coordinated L(X)Si: (X = Cl, CH3, H). In both cases a
negative linear relation is observed when the 29Si{1H} chemical shift
position is plotted against the Hammett (σp) constant for the
substituents on the Si atom.
(18) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165.
(19) See the Supporting Information for more data concerning the
X-ray structures for complexes 3, 5, 7, and 10. In addition, selected
NMR spectra of complex 10 are shown.
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures, tables, and CIF files giving NMR spectra of complex 10
as well as details on X-ray crystal structure analyses and
crystallographic data for 3, 5, 7 and 10. This material is
available free of charge via the Internet at http://pubs.acs.org.
(20) Fischer, R. A.; Schulte, M. M.; Weiss, J.; Zsolnai, L.; Jacobi, I.;
Huttner, G.; Frenking, G.; Boehme, C.; Vyboishchikov, S. F. J. Am.
Chem. Soc. 1998, 120, 1237.
(21) For a recent review on bonding in Cu(I) complexes, see: Pike,
R. D. Organometallics 2012, 31, 7647 and references therein.
(22) Wang, W.; Inoue, S.; Yao, S.; Driess, M. J. Am. Chem. Soc. 2010,
132, 15890.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for M.D.: matthias.driess@tu-berlin.de.
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(23) Kubas, G. J. Inorg. Synth. 1979, 19, 90.
(24) For a general and comprehensive review on metallacycles see:
Blom, B.; Kilkenny, M.; Clayton, H.; Moss, J. R. Adv. Organomet.
Chem. 2006, 54, 149.
(25) Tan, G.; Xiong, Y.; Inoue, S.; Enthaler, S.; Blom, B.; Epping, J.
D.; Driess, M. Chem. Commun. 2013, 49, 5595.
(26) Tan, G.; Yang, Y.; Chu, C.; Zhu, H.; Roesky, H. W. J. Am. Chem.
Soc. 2010, 132, 12231.
(27) Chou, C.-C.; Liu, H.-J.; Chao, L. H.-C.; Syu, H.-B.; Kuo, T-.S.
Polyhedron 2012, 37, 60.
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dx.doi.org/10.1021/om4011033 | Organometallics XXXX, XXX, XXX−XXX