Complexes (ER3 = SiMe2Ph, SiPh3, SnMe3): From Linear, Mononuclear Complexes to Polynuclear Complexes with Ultrashort CuI···CuI Distances

Article abstract of DOI:10.1021/acs.inorgchem.6b00210

A series of complexes of the type [(NHC)Cu-ER₃] (NHC = IDipp, IMes, ItBu, Me₂IMe, and ER₃ = SiMe₂Ph, SiPh₃, SnMe₃) and [(NHC)Cu-R′] (NHC = IDipp, Me₂IMe and R′ = Ph, C - CPh) was synthesized in good yields by the reaction of the corresponding [(NHC)Cu-OtBu] complex with the respective silylborane pinB-ER₃ (pin = OCMe₂CMe₂O; ER₃ = SiMe₂Ph, SiPh₃), the stannylborane ((C₂H₄)(iPrN)₂)B-SnMe₃, or a boronic acid ester pinB-R′ (R′ = Ph, C - CPh). Solid structures of all complexes were systematically studied by X-ray diffraction analysis. The solid state structures of the complexes [(NHC)Cu-ER₃] show a dependence of the structural motif from the steric properties of the NHC ligand. The sterically demanding NHC ligands (IDipp, IMes, ItBu) lead to monomeric, linear complexes [(NHC)Cu-ER₃], while with the less demanding Me₂IMe ligand, polynuclear, μ-ER₃-bridged complexes with ultrashort Cu···Cu distances are observed. For the related complexes [(NHC)Cu-R′] no analogous complexes with bridging anionic ligands are realized. Instead, irrespective of the NHC ligand, linear coordinated copper complexes of different types are formed. ²⁹Si heteronuclear solution NMR spectroscopic data on [(NHC)Cu^I-SiR₃] exhibit distinctly different chemical shifts for the (in the solid state) monomeric and dimeric complexes suggesting different structure types also in solution. This agrees well with the observation of a trinuclear complex [(Me₂IMe)Cu-SnMe₃]₃ both in the solid state and in solution. Initial catalytic studies suggest that [(NHC)Cu-OtBu] complexes (NHC = ItBu, Me₂IMe) are, in addition to the established [(IDipp)Cu-OtBu] complex, efficient precatalysts for the silylation of aldehydes and α,β-unsaturated ketones with pinB-SiMe₂Ph.

Full text of DOI:10.1021/acs.inorgchem.6b00210

Article
pubs.acs.org/IC
I
[
(NHC)Cu −ER ] Complexes (ER = SiMe Ph, SiPh , SnMe ): From
3
3
2
3
3
Linear, Mononuclear Complexes to Polynuclear Complexes with
Ultrashort Cu ···Cu Distances
I
I
Jacqueline Plotzitzka and Christian Kleeberg*
Institut fu
Braunschweig, Germany
̈
̈
r Anorganische und Analytische Chemie, Technische Universitat Carolo-Wilhelmina zu Braunschweig, Hagenring 30, 38106
*
S Supporting Information
ABSTRACT: A series of complexes of the type [(NHC)Cu−
ER ] (NHC = IDipp, IMes, ItBu, Me IMe, and ER
=
3
3
2
SiMe Ph, SiPh , SnMe ) and [(NHC)Cu−R′] (NHC = IDipp,
2
3
3
Me IMe and R′ = Ph, CCPh) was synthesized in good
2
yields by the reaction of the corresponding [(NHC)Cu−
OtBu] complex with the respective silylborane pinB−ER (pin
3
=
OCMe CMe O; ER = SiMe Ph, SiPh ), the stannylborane
2 2 3 2 3
(
(
(C H )(iPrN) )B−SnMe , or a boronic acid ester pinB−R′
2
4
2
3
R′ = Ph, CCPh). Solid structures of all complexes were
systematically studied by X-ray diffraction analysis. The solid
state structures of the complexes [(NHC)Cu−ER ] show a
3
dependence of the structural motif from the steric properties
of the NHC ligand. The sterically demanding NHC ligands
(
IDipp, IMes, ItBu) lead to monomeric, linear complexes [(NHC)Cu−ER ], while with the less demanding Me IMe ligand,
3
2
polynuclear, μ-ER -bridged complexes with ultrashort Cu···Cu distances are observed. For the related complexes [(NHC)Cu−
3
R′] no analogous complexes with bridging anionic ligands are realized. Instead, irrespective of the NHC ligand, linear
29
coordinated copper complexes of different types are formed. Si heteronuclear solution NMR spectroscopic data on
I
[
(NHC)Cu −SiR ] exhibit distinctly different chemical shifts for the (in the solid state) monomeric and dimeric complexes
3
suggesting different structure types also in solution. This agrees well with the observation of a trinuclear complex [(Me IMe)Cu−
2
SnMe ] both in the solid state and in solution. Initial catalytic studies suggest that [(NHC)Cu−OtBu] complexes (NHC = ItBu,
3
3
Me IMe) are, in addition to the established [(IDipp)Cu−OtBu] complex, efficient precatalysts for the silylation of aldehydes and
2
α,β-unsaturated ketones with pinB−SiMe Ph.
2
INTRODUCTION
■
I
NHC-Cu complexes are widely used as (pre)catalysts in a
plethora of catalytic transformations, such as conjugate
addition, allylic substitution, and boration reactions of
unsaturated substrates but also in C−H bond activation/
functionalization reactions and the functionalization of carbon−
1
I
heteroatom bonds. NHC−Cu complexes as (pre)catalysts in
silylation reactions of imines, aldehydes, and α,β-unsaturated
carbonyl/carboxyl compounds employing silylboranes have
I
Figure 1. Selected structurally characterized (NHC)Cu complexes
4a,6a,7,8
(dipp =2,6-di-isopropylphenyl).
2
lately been a particularly active field of research. Complexes of
this type have also been studied in detail as models of reactive
intermediates for silylation, borylation, and hydrogenation/
3
,4a−c,5,6
Cu−SiEt(TMS) ] (IMe = 1,3-bis(methyl)imidazol-2-ylidene,
2
reduction processes.
The sterically demanding IDipp
ItBu = 1,3-bis(tert-butyl)imidazol-2-ylidene) have been re-
ligand has been especially successfully employed in order to
8
ported. However, the latter complexes have not been studied
stabilize reactive intermediates such as [(IDipp)Cu−ER ] (SiR
3
3
in the context of silylation reactions and bear silyl groups not
commonly employed in those reactions. Nonetheless, the
=
SiMe Ph (1a), SiPh (1b)), [(IDipp)Cu−H] (Figure 1), and
2
3
2
[
(IDipp)Cu−Bpin] (IDipp = 1,3-bis(2,6-di-isopropylphenyl)-
I
4a,5a,6a,7
structures and reactivity of NHC-Cu silyl complexes have not
imidazol-2-ylidene, pin = pinacolato = OCMe CMe O).
Concerning NHC−Cu silyl complexes in particular besides
1
2
2
I
a,b also the complexes [(IMe)Cu−Si(TMS) ], [(IMe)Cu−
Received: February 5, 2016
3
SiEt(TMS) ] (Figure 1), [(ItBu)Cu−Si(TMS) ], and [(ItBu)-
2
2
3
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.6b00210
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
signal of the solvents (C
D
1H NMR, 7.16 ppm; 13C NMR, 128.06
been systematically studied in dependence of the respective
NHC and silyl ligand.
6
6
1
ppm; CDCl3 H NMR, 7.26 ppm all obtained from Eurisotop with
1
7
31
29
119
I
99.5% deuteration).
P, Si, and Sn chemical shifts are reported
For the mentioned NHC−Cu complexes, generally an
1
3
I
relative to external 85% H
3
PO
4 4 4
, Me Si, and Me Sn, respectively. C,
approximately linear two-coordinated Cu ion may be expected.
3
1
1
29
119
29
P, Si, and Sn NMR spectra were recorded employing ( Si,
However, aggregation with the anionic ligand as bridging
ligands may also be expected. In fact, the combination of the
small hydrido ligand even with a sterically demanding NHC
ligand or of a sterically demanding silyl group but a little
demanding NHC ligand leads to dimeric μ-hydrido/silyl
19
1
Sn: inverse-gated) composite pulse H decoupling. If necessary, 2D
NMR techniques were employed to assign the individual signals
1
1
1
1
1
13
(
H− H NOESY (1 s mixing time), H− H COSY, H− C HSQC,
1 13
and H− C HMBC). Simulations were conducted with the DAISY/
TOPSPIN program package (Bruker). GC/MS measurements were
performed using a Shimadzu GCMS-QP2010SE instrument operating
in positive EI mode (70 eV). Melting points were determined in flame-
sealed capillaries under nitrogen and are not corrected. Elemental
6a,8
bridged structures (Figure 1).
The resulting complexes
[
(IDipp)Cu−H]2 and [(IMe)Cu−SiEt(TMS) ] exhibit, at
2 2
least in the solid state, extraordinarily short Cu···Cu distances
6a,8
analyses were performed at the Institut fu
Analytische Chemie of the Technische Universitat
zu Braunschweig.
(IDipp)Cu−SiMe Ph] (1a).
̈
r Anorganische and
of 2.3 and 2.2854(9) Å, respectivly.
interactions shorter than the sum of the van der Waals radii
2.8 Å) are well-established as cuprophilic interactions, this is
well below the Cu···Cu distances typically found in such cases
Although Cu···Cu
̈
Carolo-Wilhelmina
(
4a 29
1
[
Si{ H} NMR (79.5 MHz, C D , rt):
6 6
2
δ −14.1.
9
,10
(
≥2.35 Å).
[
(IDipp)Cu−SiPh ] (1b). In a nitrogen filled glovebox [(IDipp)Cu−
3
While a bridging coordination mode of the anionic ligands is
OtBu] (100 mg, 0.19 mmol, 1.0 equiv) and pinB−SiPh (74 mg, 0.19
3
not surprising and is well-documented for copper(I) silyl and
related copper(I) boryl, alkynyl, and arenyl complexes, to the
best of our knowledge only the above mentioned complexes
mmol, 1.0 equiv) were combined in dry toluene (3 mL). After 10 min
the turbid mixture was cooled to −40 °C. After a few days, crystals had
separated, and the supernatant solution was decanted. The colorless
crystals (suitable for X-ray diffraction) were washed with n-pentane (2
× 3 mL) and dried in vacuo to give a colorless powder (88 mg, 0.12
3
b,c,11−13
bear NHCs as ancillary ligands.
Considering this and
I
the relevance of (NHC)Cu fragments for silylation reactions, a
deeper insight into the structural chemistry of (NHC)Cu silyl
1
mmol, 65%). H NMR (400 MHz, C D , rt): δ 7.50−7.47 (m 6 H,
I
6
6
3
SiPh ), 7.24 (t, J = 7.8 Hz, 2 H, 4-CH ), 7.19−7.13 (m, 9 H,
3
HH
dipp
complexes, particularly with respect to the influence of the
NHC ligands, appears highly desirable. While sterically little
demanding NHC ligands are frequently used in computational
studies for economic reasons, they have not been widely used
experimentally nor has the impact of the NHC ligand on the
properties of NHC−Cu silyl complexes been studied system-
3
SiPh ), 7.06 (d, J = 7.8 Hz, 4 H, 3,5-CHdipp), 6.21 (s, 2 H, CH ),
3
HH
NHC
3
3
2
.54 (sept, J = 6.9 Hz, 4 H, CH(CH ) ), 1.26 (d, J = 7.0 Hz, 12
HH 3 2 HH
3
13
1
H, CH(CH ) ), 1.05 (d, J = 6.9 Hz, 12 H, CH(CH ) ). C{ H}
3
2
HH
3 2
NMR (100 MHz, C D , rt): 184.7 (C ), 147.4 (C ), 145.9 (2,6-
6
6
NHC
Ph
C
dipp), 137.3 (CHPh), 134.9 (1-Cdipp), 130.6 (4-CHdipp), 127.2 (CHPh),
1
26.5 (CH ), 124.2 (3,5-CH ), 122.1 (CH ), 29.0 (CH(CH ) ),
Ph
dipp
NHC
3 2
29
1
4
a,14,15
25.3 (CH(CH ) ), 23.6 (CH(CH ) ). Si{ H} NMR (79.5 MHz,
3 2 3 2
atically.
Beyond the fundamental relevance of these
C D , rt): δ −0.4. Mp: 202−206 °C. Anal. Calcd for C H CuN Si:
6
6
45 51
2
questions, they are inclined to have a direct impact on
understanding and, hence, the further rational development of
NHC−Cu catalyzed silylation reactions. Furthermore, consid-
C, 75.96; H, 7.22; N, 3.94. Found: C, 76.04; H, 7.23; N, 3.86.
(IDipp)Cu−SnMe ] (1c). In a nitrogen filled glovebox [(IDipp)-
[
3
Cu−OtBu] (100 mg, 0.19 mmol, 1.0 equiv) and ((C H )(iPrN) )B−
2
4
2
I
ering the relevance of NHC−Cu complexes as catalysts in
SnMe (60 mg, 0.19 mmol, 1.0 equiv) were combined in dry toluene
3
general a deeper structural understanding appears even more
crucial.
(4 mL). After 1 h the solvent was evaporated, and the residue was
washed with cold n-pentane (3 × 2 mL) to afford an off-white powder
after drying in vacuo (63 mg, 0.10 mmol, 53%). Crystals suitable for X-
ray diffraction studies were obtained from a PhMe/n-pentane solution
In the present work systematically a number of complexes of
the type [(NHC)Cu−ER ] (NHC = IDipp, IMes (1,3-
3
1
3
at −80 °C. H NMR (400 MHz, C D , rt): δ 7.20 (t, J = 7.7 Hz, 2
6
6
HH
bis(2,4,6-trimethyl-phenyl)imidazol-2-ylidene), ItBu, Me IMe
2
3
H, 4-CH ), 7.05 (d, J = 7.7 Hz, 4 H, 3,5-CH ), 6.21 (s, 2 H,
dipp
HH
dipp
=
1,3,4,5-tetra(methyl)imidazol-2-ylidene; ER3 = SiMe Ph,
3
3
2
CHNHC), 2.56 (sept, J = 6.9 Hz, 4 H, CH(CH ) ), 1.38 (d, J =
HH
3
2
HH
SiPh , SnMe ) are studied regarding their solid state structures’
3
3
3
6
0
.9 Hz; 12 H, CH(CH ) ), 1.07 (d, J = 6.9 Hz, 12 H, CH(CH ) ),
3
2
HH
3 2
dependence on the NHC and the silyl ligand. Moreover, we
2 117/119
13
1
.26 (s sat., J
= 26.6, 27.6 Hz, 9 H, Sn(CH ) ). C{ H}
SnH
3 3
also included other related ligands of the 14th group with a
NMR (75 MHz, C D , rt): 183.4 (CNHC), 145.8 (2,6-Cdipp), 134.8 (1-
6
6
I
known ability to act as bridging ligands in Cu complexes such
Cdipp), 130.7 (4-CHdipp), 124.2 (3,5-CHdipp), 122.1 (CHNHC), 29.0
(CH(CH ), 25.2 (CH(CH ), 23.7 (CH(CH ), −7.4 (s sat.,
= 84.6, 88.3 Hz, Sn(CH ) ). Sn{ H} NMR (149.3 Hz,
11,12
as trimethylstannyl but also phenyl and alkynyl.
3
)
2
3
)
2
)
3 2
1
117/119
119
1
J
SnC
3 3
C D , rt): δ −132.9. Mp: >110 °C dark-brown colorization, melting at
30 45 2
Found: C, 58.54; H, 7.40; N, 4.58.
6
6
EXPERIMENTAL SECTION
■
>150 °C. Anal. Calcd for C H CuN Sn: C, 58.50; H, 7.36; N, 4.55.
1
6a,b
16a,b
16e
General Considerations. pinB−SiMe Ph,
pinB−SiPh ,
3
2
3
1
6a,c
16g
16d
pinB−CC−Ph,
((C H )(iPrN) )B-SnMe ,
ItBu,
[(IMes)Cu−SiMe Ph] (2a). In a nitrogen filled glovebox [(IMes)-
2
4
2
2
16f
16h,i
16h,j
Me IMe, CuOt-Bu, [(IDipp)CuOtBu],
and [(IDipp)Cu−SiMe Ph] (1a) were prepared according to
[(IMes)CuOtBu],
Cu−OtBu] (100 mg, 0.23 mmol, 1.0 equiv) was dissolved in dry THF
2
4a
(1.5 mL), and pinB−SiMe Ph (66 mg, 0.25 mmol, 1.1 equiv) was
2
2
literature procedures. All other compounds were commercially
available and were used as received; their purity and identity were
checked by appropriate methods. All solvents were dried using
MBraun solvent purification systems, deoxygenated using the freeze−
pump−thaw method and stored under purified nitrogen. All
manipulations were performed using standard Schlenk techniques
under an atmosphere of purified nitrogen or in a nitrogen filled
glovebox (MBraun). NMR spectra were recorded on Bruker DPX 200,
Avance 400, or Avance 600 spectrometers. For air sensitive samples
NMR tubes equipped with screw caps (WILMAD) were used, and the
solvents were dried over potassium/benzophenone and degassed.
Chemical shifts (δ) are given in ppm, using the (residual) resonance
added. After 30 min, n-pentane was added to the solution until it was
turbid (ca. 3 mL), and the mixture was stored at −40 °C. After 2 h a
small amount of a brownish oily material had separated. The
supernatant light-brown/yellow solution was decanted into a Schlenk
tube, layered with n-pentane (5 mL), and stored at −40 °C. After 2 d
colorless crystals had separated, and the supernatant solution was
decanted and the residue washed with n-pentane (2 × 2 mL) and dried
1
in vacuo (42 mg, 0.08 mmol, 35%). H NMR (400 MHz, C D , rt): δ
6
6
7.62 (br v dd, JHH = 8.1, 1,4 Hz, 2 H, Ph), 7.31−7.19 (m, 3 H, Ph),
6.72 (s, 4 H, 3,5-CHmes), 5.97 (s, 2 H, CH ), 2.11 (s, 6 H, 4-
NHC
C(CH )mes), 1.94 (s, 12 H, 2,6-C(CH3)mes), 0.51 (s, 6 H, SiMe2).
3
13
1
C{ H} NMR (100 MHz, C D , rt): 183.7 (CNHC), 153.8 (CPh),
6
6
B
DOI: 10.1021/acs.inorgchem.6b00210
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
39.1 (4-Cmes), 135.8 (1-Cmes), 135.2 (CH ), 134.8 (2,6-Cmes), 129.6
UV−vis (PhMe): λ
15 23 2 2
7.15; N, 8.34.
= ∼300, 388 nm. Anal. Calcd for
Ph
max
(
3,5-CHmes), 127.1 (CH ), 125.9 (CH ), 121.1 (CH ), 21.1 (4-
(C H CuN Si) : C, 55.78; H, 7.18; N, 8.67. Found: C, 55.89; H,
Ph
Ph
NHC
2
9
1
C(CH3)mes), 17.9 (2,6-C(CH3)mes), 4.4 (Si(CH ) ). Si{ H} NMR
3
2
(
79.5 MHz, C D , rt): δ −14.4. Mp: >110 °C black colorization,
[(Me IMe)Cu−SiPh ] (4b) . In a nitrogen filled glovebox
2
6
6
2
3 2
2
melting at 130 °C. Anal. Calcd for C H CuN Si: C, 69.21; H, 7.01;
N, 5.57. Found: C, 69.31; H, 6.82; N, 5.29.
[(Me IMe)Cu−OtBu] (50 mg, 0.19 mmol, 1.0 equiv) and pinB−
29
35
2
SiPh (74 mg, 0.19 mmol, 1.0 equiv) were combined in dry toluene (2
3
[
(IMes)Cu−SiPh ] (2b). In a nitrogen filled glovebox [(IMes)Cu−
mL). After 2 h the orange solution was layered with n-pentane and
stored at −40 °C. After a few days, dark orange crystals (suitable for X-
ray diffraction) had separated. The supernatant solution was decanted
and the residue washed with n-pentane (2 × 1 mL) and dried in vacuo
3
OtBu] (60 mg, 0.14 mmol, 1.0 equiv) and pinB−SiPh (53 mg, 0.14
3
mmol, 1.0 equiv) were combined in dry toluene (3 mL). After 1 h at
room temperature the solution was layered with n-pentane and cooled
to −20 °C. After a few days, crystals had separated, and the
supernatant solution was decanted. The colorless crystals (suitable for
X-ray diffraction) were washed with n-pentane (2 × 2 mL) and dried
1
to give a deep orange material (78 mg, 0.09 mmol, 92%). H NMR
3
(
600 MHz, C D , rt): δ 7.97 (br d, 6 H, J = 7.2 Hz, CH ), 7.21 (br
6
6
HH
Ph
3
3
t, J = 7.3 Hz, 6 H, CH ), 7.13 (tt, 3 H, J = 7.3, 1.4 Hz, CH ),
.73 (s, 6 H, N(CH3)NHC), 1.11 (s, 6 H, C(CH3)NHC). C{ H} NMR
HH
Ph
HH
Ph
1
13
1
in vacuo to give a colorless material (48 mg, 0.08 mmol, 57%). H
NMR (400 MHz, C D , rt): δ 7.63−7.58 (m, 6 H, SiPh ), 7.21−7.10
2
6
6
3
(150 MHz, C D , rt): 183.2 (C ), 149.0 (C ), 13713 (CH ),
6
6
NHC
Ph
Ph
(
(
(
1
1
1
m, 9 H, SiPh ), 6.71 (s, 4 H, 3,5-CH ), 5.96 (s, 2 H, CH ), 2.11
s, 6 H, 4−C(CH ) ), 1.94 (s, 12 H, 2,6-C(CH3)mes). C{ H} NMR
100 MHz, C D , rt): 182.8 (C ), 147.5 (C ), 139.2 (4-Cmes),
3 mes NHC
127.3 (CH ), 126.4 (CH ), 123.4 (C(CH )NHC), 34.1 (N-
Ph Ph 3
13
1
29
1
3
mes
(CH3)NHC), 8.1 (C(CH3)NHC). Si{ H} NMR (79.5 MHz, C D ,
6 6
6
6
NHC
Ph
rt): δ −10.1. Mp: 144−147 °C. Anal. Calcd for (C H CuN Si) : C,
25
27
2
2
37.4 (CH ), 135.7 (1-Cmes), 134.8 (2,6-Cmes), 129.6 (3,5-CHmes),
20
Ph
67.15; H, 6.09; N, 6.27. Found: C, 66.62; H, 6.01; N, 6.10.
27.3 (CH ), 126.6 (CH ), 121.6 (CH
), 21.1 (4-C(CH3)mes),
Ph
Ph
NHC
[(Me IMe)Cu−SnMe ] (4c) . In a nitrogen filled glovebox
2
3 3
3
7.9 (2,6-C(CH3) ). Mp: 163−166 °C. Anal. Calcd for
mes
[(Me IMe)Cu−OtBu] (50 mg, 0.19 mmol, 1.0 equiv) was dissolved
2
C H CuN Si: C, 74.66; H, 6.27; N, 4.47. Found: C, 74.26; H,
6
3
9
39
2
in dry toluene (2 mL). Upon addition of ((C H )(iPrN)2)B−SnMe
2
4
3
.33; N, 4.37.
(ItBu)Cu−SiMe Ph] (3a). In a nitrogen filled glovebox [(ItBu)Cu−
(
77 mg, 0.24 mmol, 1.3 equiv) the initially pale solution turned
[
2
immediately dark. After 15 min at room temperature the solution was
layered with n-pentane and stored at −40 °C. After 20 h bronze
crystals had separated, and the supernatant solution was decanted; the
crystals (suitable for X-ray diffraction) were washed with n-pentane (2
OtBu] (100 mg, 0.32 mmol, 1.0 equiv) and pinB−SiMe Ph (83 mg,
0
the solution was layered with n-pentane and stored at −40 °C. After a
few days crystals had separated, and the supernatant solution was
decanted. The colorless crystals (suitable for X-ray diffraction) were
washed with n-pentane (2 × 1 mL) and dried in vacuo to give a
colorless material (80 mg, 0.21 mmol, 66%). H NMR (600 MHz,
C D , rt): δ 8.14−8.10 (m, 2 H, CH ), 7.48−7.43 (m, 2 H, CH ),
7
C(CH ) ), 0.96 (s, 6 H, Si(CH ) ). C{ H} NMR (150 MHz, C D ,
rt): 180.3 (CNHC), 153.9 (C ), 135.0 (CH ), 127.5 (CH ), 126.2
2
.32 mmol, 1.0 equiv) were combined in dry toluene (2 mL). After 2 h
×
1 mL) and dried in vacuo to give a bronze material (56 mg, 0.05
1
mmol, 84%). H NMR (400 MHz, C D , rt): δ 3.55 (s, 6 H,
6
6
2
1
17/119
N(CH3)
NHC
), 1.41 (s, 6 H, C(CH ) ), 0.58 (s sat., J
3
NHC
SnH
= 24.6
1
13
1
Hz, 9 H, Sn(CH ) ). C{ H} NMR (100 MHz, C D , rt): 185.6 (s
3
3
6
6
6
6
Ph
Ph
2
117/119
sat., CNHC
,
JC
= 35 Hz), 123.6 (C(CH )NHC), 35.8 (N-
Sn
3
.31−7.26 (m, 1 H, CH ), 6.26 (s, 2 H, CH ), 1.39 (s, 18 H,
Ph
NHC
117/119
(
CH3)
), 8.6 (C(CH ) ), −0.9 (s sat., J
= 67, 28 Hz,
13 1
NHC
3
NHC
C
Sn
3
3
3
2
6
6
119
1
Sn(CH ) ). Sn{ H} NMR (149.3 MHz, C D , rt): δ −127.1 (s sat.,
3
3
6
6
Ph
Ph
Ph
119 117
Sn Sn
17
J
= 2383 Hz). Mp: 86−93 °C (decomposition). UV−vis
(
(
1
CH ), 115.6 (CH ), 57.7 (C(CH ) ), 31.9 (C(CH ) ), 5.0
Si(CH ) . Si{ H} NMR (79.5 MHz, C D , rt): δ −14.8. Mp: 108−
Ph
NHC
3
3
3 3
29
1
(PhMe): λmax = ∼300, 346, 414 (br shoulder) nm. Anal. Calcd for
3
2
6
6
(
6
C H CuN Sn) : C, 34.17; H, 6.02; N, 7.97. Found: C, 34.28; H,
10 21 2 3
13 °C. Anal. Calcd for C H CuN Si: C, 60.20; H, 8.24; N, 7.39.
19
31
2
.01; N, 8.18.
(Me IMe)Cu−Ph] (4d). In a nitrogen filled glovebox to a solution of
Found: C, 60.11; H, 8.35; N, 7.34.
[
2
[
(ItBu)Cu−SiPh ] (3b). In a nitrogen filled glovebox [(ItBu)Cu−
3
[
(
(Me IMe)Cu−OtBu] (50 mg, 0.19 mmol, 1.0 equiv) in dry toluene
2
OtBu] (100 mg, 0.32 mmol, 1.0 equiv) and pinB−SiPh (123 mg, 0.32
3
1.5 mL) was added a solution of pinB−Ph (39 mg, 0.19 mmol, 1.0
mmol, 1.0 equiv) were combined in dry toluene (2 mL). After 2 h the
solution was layered with n-pentane and stored at −40 °C. After a few
days crystals had separated, and the supernatant solution was
decanted. The colorless crystals (suitable for X-ray diffraction) were
washed with n-pentane (2 × 1 mL) and dried in vacuo to give a
equiv) in dry toluene (1.0 mL). After 3.5 h at room temperature the
mixture was layered with n-pentane and stored at −40 °C. After a few
days, colorless crystals had separated, and the supernatant solution was
decanted; the crystals (suitable for X-ray diffraction) were washed with
cold n-pentane (2 × 2 mL) and dried in vacuo to give a colorless
1
colorless material (121 mg, 0.24 mmol, 75%). H NMR (600 MHz,
C D , rt): δ 8.05−8.01 (m, 6 H, CH ), 7.38−7.33 (m, 6 H, CH ),
7
1
material (40 mg, 0.15 mmol, 79%). H NMR (600 MHz, C D , rt): δ
6
6
6
6
Ph
Ph
7
.85 (v dd, 2 H, JHH = 7.6, 1.4 Hz, CH ), 7.62 (v t, 2 H, J = 7.4 Hz,
.26−7.23 (m, 3 H, CH ), 6.26 (s, 2 H, CH ), 1.38 (s, 18 H,
Ph HH
Ph
NHC
13
1
CH ), 7.45 (tt, 1 H, J = 7.3, 1.5 Hz, CH ), 3.00 (br s, 6 H, Δw
=
C(CH ) ). C{ H} NMR (150 MHz, C D , rt): 179.5 (CNHC), 147.8
Ph
HH
Ph
1/2
3
3
6
6
13
1
1
4.7 Hz, N(CH3)
), 1.20 (s, 6 H, C(CH ) ). C{ H} NMR
(C ), 137.4 (CH ), 127.8 (CH ), 127.0 (CH ), 115.7 (CHNHC),
NHC 3 NHC
Ph
Ph
Ph
Ph
29
1
(150 MHz, C D , rt): 179.4 (C ), 167.2 (C ), 141.3 (CH ), 126.9
5
7.7 (C(CH ) ), 32.2 (C(CH ) ). Si{ H} NMR (79.5 MHz, C D ,
6 6 NHC Ph
Ph
), 34.7 (N(CH3)NHC), 8.1
3
3
3
3
6
6
(
(
5
CH ), 124.8 (CH ), 123.8 (C(CH )
rt): δ −0.7. Mp: 151−155 °C. Anal. Calcd for C H CuN Si: C,
6
Ph
Ph
3
NHC
29
35
2
C(CH3)
NHC
). Mp: 95−100 °C. Anal. Calcd for C H CuN : C,
13 17
2
9.21; H, 7.01; N, 5.57. Found: C, 69.11; H, 7.18; N, 6.03.
(Me IMe)Cu−SiMe Ph] (4a) . In a nitrogen filled glovebox
20
8.96; H, 6.47; N, 10.58. Found: C, 58.44; H, 6.66; N, 10.25.
X-ray Structure Determinations. The crystals were transferred
[
2
2
2
2
[
(Me IMe)Cu−OtBu] (30 mg, 0.12 mmol, 1.0 equiv) was dissolved
2
into inert perfluoroether oil inside a nitrogen filled glovebox and,
in dry toluene (2 mL). Upon addition of pinB−SiMe Ph (31 mg, 0.12
mmol, 1.0 equiv) the initially pale solution turned immediately orange-
2
outside of the glovebox, rapidly mounted on top of a human hair and
21a
placed in the cold nitrogen gas stream on the diffractometer. The
data were either collected on an Oxford Diffraction Xcalibur E
instrument using monochromated Mo Kα radiation or on an Oxford
Diffraction Nova A instrument, using mirror-focused Cu Kα radiation.
The reflections were indexed and integrated, and an empirical
absorption correction was applied as implemented in the CrysAlisPro
red. After 2 h the solution was layered with n-pentane and stored at
−
40 °C. After 48 h, orange crystals (suitable for X-ray diffraction) had
separated. The supernatant solution was decanted and the residue
washed with n-pentane (2 × 1 mL) and dried in vacuo to give an
orange material (32 mg, 0.05 mmol, 83%). H NMR (600 MHz, C D ,
1
6
6
rt): δ 7.85 (dd, 2 H, JHH = 8.1, 1.3 Hz, CH ), 7.30−7.26 (m, 2 H,
Ph
2
1b
CH ), 7.17−7.15 (m, 1 H, CH (overlapping with solvent signal)),
software.
The structures were solved employing the SHELXS,
Ph
Ph
3
.04 (s, 6 H, N(CH )NHC), 1.32 (s, 6 H, C(CH3)NHC), 0.89 (s, 6 H,
SHELXT, or SIR-92 programs and refined anisotropically for all non-
3
13
1
2
Si(CH ) ). C{ H} NMR (150 MHz, C D , rt): 184.9 (CNHC), 156.3
hydrogen atoms by full-matrix least-squares on all F using SHELXL
3
2
6
6
2
1c−e
(
(
C ), 134.3 (CH ), 127.1 (CH ), 125.1 (CH ), 123.2
software.
Generally, hydrogen atoms were refined employing a
Ph
Ph
Ph
Ph
C(CH )NHC), 34.4 (N(CH3)NHC), 8.3 (C(CH3)NHC), 7.1 (Si(CH ) ).
riding model; methyl groups were treated as rigid bodies and were
3
3 2
2
9
1
Si{ H} NMR (79.5 MHz, C D , rt): δ −23.0. Mp: 127−131 °C.
allowed to rotate about the E−CH bond. During refinement and
6
6
3
C
DOI: 10.1021/acs.inorgchem.6b00210
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Inorganic Chemistry
Article
Table 1. Synthesis of [(NHC)Cu−R] by B−R Bond Cleavage
[
(NHC)Cu−OtBu]
[B]
R
[(NHC)Cu−R] (yield)
n
1
a
2
R = dipp , R = H
pinB
SiPh3
1b (65%)
1c (53%)
1
a
2
R = dipp , R = H
((C H )(iPrN) )B
SnMe3
Ph
2
4
2
1
a
2
6b,22
R = dipp , R = H
pinB
1d (86%)
1
a
2
19,23a,b
R = dipp , R = H
pinB
pinB
pinB
pinB
pinB
pinB
pinB
CC−Ph
1e (47%)
1
a
2
R = mes , R = H
SiMe Ph
2a (35%)
2b (57%)
3a (66%)
3b (75%)
2
1
a
2
R = mes , R = H
SiPh3
1
2
R = tBu, R = H
SiMe Ph
2
1
2
R = tBu, R = H
SiPh3
1
2
R = Me, R = Me
SiMe Ph
(4a) (83%)
2
2
1
2
R = Me, R = Me
SiPh3
(4b) (92%)
2
1
2
R = Me, R = Me
((C H )(iPrN) )B
SnMe3
Ph
(4c) (84%)
2
4
2
3
1
2
R = Me, R = Me
pinB
4d (79%)
1
2
b
R = Me, R = Me
pinB
CC−Ph
4e (63%)
a
b
dipp: 2,6-di-isopropyl-phenyl. mes: 2,4,6-trimethyl-phenyl. The actual composition is {[⟨(Me IMe) Cu⟩ ⟨(PhCC) Cu⟩][(PhCC) Cu]-
2
2
2
2
2
[
⟨(Me IMe) Cu⟩⟨(PhCC) Cu⟩]}.
2
2
2
Table 2. Selected Structural Parameters of 1a,b,c, 2a,b, and 3a,b
CNHC−Cu/Å
1.9333(1)
Cu−E [E]/Å
2.2783(4) [Si]
CNHC−Cu−E
170.53(4)°
4
a
a
1
1
1
2
2
3
3
3
a
H−Ct: 3.15 Å
H−Ct: 3.13/3.23 Å
H−Ct: 3.8 Å
1
8
b
b
b
,
ab
b
1.929(2)/1.933(2)
2.2671(5)/2.2738(6) [Si]
171.43(5)°/171.35(5)°
1
8
c
c
c
c a
c
a
1.925
2.474 [Sn]
163.4°
a
a
a
1.943(1)
2.2914(4) [Si]
2.2777(6) [Si]
2.267(2) [Si]
173.57(4)°
171.18(6)°
177.8(2)°
175.2(2)°/174.2(2)°
174.65(4)°
H−Ct: 4.12 Å
H−Ct: 3.48 Å
H−Ct: 4.83 Å ; τ = 79.5(5)°
b
a
1.925(2)
d
1.941(6)
b
b
b
H−Ct: 4.63, 4.02, 4.14 Å ; τ = 71.0(5)/6.3(5)° ,
a
,
b
bd
a(PhMe)1/2
1.938(5)/1.940(5)
1.935(1)
2.260(2)/2.264(2) [Si]
a
b
2.2645(4) [Si]
H−Ct: 3.96 Å
a
18 b
H−Ct: shortest distance for a hydrogen atom on the R group to the centroid of an adjacent aromatic ring (see figures). The values refer to
different independent molecules in the asymmetric unit. Averaged values (see text). τ: N−C −Si−C torsion angle
c
18 d
NHC
ipso
analysis of the crystallographic data, the programs WinGX, PLATON,
Mercury, and Diamond were used.
prone to decomposition. Nonetheless, NMR spectroscopic
characterization in solution was possible for all compounds.
However, it was in our hands restricted to studies at ambient
temperature, as the stability of the (multinuclear) complexes
did not allow (heteronuclear) NMR studies at elevated
temperatures.
21f−i
RESULTS AND DISCUSSION
■
Synthesis. As versatile access to [(NHC)Cu−R] com-
plexes, the reaction of the [(NHC)Cu−OtBu] complex with a
Structural Study. X-ray diffraction structure determina-
suitable boronic acid ester derivative pinB−R (R = SiMe Ph,
2
tions were successfully performed for all synthesized complexes
SiPh , Ph, CC−Ph) or ((C H )(iPrN) )B−SnMe , respec-
3
2
4
2
3
18
(
Tables 2 and 3). The solid state molecular structures of the
tively, has been employed (Table 1). The resulting complexes
complexes 1−3a (R = SiMe Ph), 1−3b (R = SiPh ), and 1c (R
1
a−4e were obtained in good to excellent yields, usually
2
3
=
SnMe ) and the sterically demanding NHCs IDipp (1a−c),
typically directly in crystalline form suitable for crystal structure
determination.
3
IMes (1a,b), and ItBu (1a,b) show the anticipated monomeric
linear structures (Table 2). Similar structures have also been
4a
While this σ-bond metathesis reaction pathway is established
for a range of boronic acid derivatives, its scope is here
significantly extended on the side of the NHC ligand as well as
reported for related complexes with, e.g., R = C H OMe,
6
4
C
H
Me
, boryl, SnPh
, Si(TMS)
, and SiEt(TMS) (vide
6
2
3
3
3
2
3a,b,4a,5a,24a,25
3,5a,7,8,23c,24
with respect to the R substituent.
Moreover, using
supra).
While a comparative discussion of the individual molecular
structures of R = SiMe
3
(1c) appears mandatory, first selected features of the crystal
structures are briefly described.
an adopted procedure the phosphine complex [(Me P) Cu−
3
3
SiMe Ph] was obtained from PMe , CuOtBu, and pinB−
Ph (1−3a), SiPh
2
3
(1−3b), and SnMe
2
3
SiMe Ph extending this reaction to non-NHC copper alkoxido
2
1
8
complexes.
The complexes obtained (1a−4e) are stable in pure form
under an inert atmosphere in the dark at −40 °C as solids for
several months and in solution at least for several days. In
general, the monomeric complexes with sterically more
hindered NHC ligands (vide infra) have been found to be
quite stable while the dimeric complexes appear to be more
Complex 1b crystallizes in space group P1 with two
̅
1
8
molecules in the asymmetric unit (Figure 2). The two
independent molecules adopt virtually identical conformations
differing only slightly in the geometrical parameters (Table
18
2). In contrast, 2a and 2b crystallize with one molecule in the
asymmetric unit in a monoclinic (C2/c) and an orthorhombic
D
DOI: 10.1021/acs.inorgchem.6b00210
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Inorganic Chemistry
Article
Table 3. Selected Structural Parameters of (4a) and (4b)
2
2
a
(
4b) at 100 K
2
(
4a)2
(4b) at 127 K
molecule 1
molecule 2
2
Cu−CNHC (Å)
Cu−Si (Å)
Cu1
Cu2
C1
C8
1.925(2)
1.939(2)
1.937(2)
1.951(5)
1.937(5)
1.936(4)
1.941(4)
Cu1
Cu2
Si1
2.4396(7)
2.5550(7)
2.5041(8)
2.3978(8)
2.4897(7)
2.5602(8)
2.618(2)
2.422(2)
2.385(2)
2.523(2)
2.554(2)
2.398(2)
2.413(2)
2.599(2)
Si1′/2
Si1
Si2
Cu···Cu (Å)
2
.2503(6)
2.2691(4)
2.2879(6)
2.2729(6)
CNHC−Cu−E (deg)
C1
Cu1
Cu2
Si1
126.51(7)
106.99(7)
121.13(8)
119.58(8)
119.79(8)
126.42(8)
125.6(2)
124.8(2)
122.9(2)
123.0(2)
117.0(1)
120.8(1)
118.1(1)
122.1(1)
Si1′/2
Si1
C8
Si2
Si−Cu−Si (deg)
Si1
Cu1
Cu2
Si1′/2
Si2
126.50(2)
119.28(2)
113.77(2)
109.56(5)
114.6(5)
121.93(5)
119.48(5)
Cu−Si−Cu (deg)
Cu1
Si1
Si2
Cu2
Cu2
53.50(2)°
0.0°
54.05(2)
54.35(2)
34.35(3)
54.18(3)
55.07(3)
42.55(4)
54.38(3)
53.93(3)
25.19(6)
b
ϕ
a
b
Two independent molecules in the asymmetric unit. ϕ: interplanar angle included by the two [E,Cu,Cu] planes.
two molecules of 3a and one molecule of PhMe in a monoclinic
18
space group P2 (Figure 3 and Table 2). In the latter, two
1
distinct conformations of 3a differing in the relative orientation
of the silyl group to the NHC ligand are realized [illustrated by
Figure 2. Top: View of the asymmetric unit of 1b approximately
parallel to the [−1 0 −1] vector. Bottom left: Molecular structure of
2
a. Bottom right: Molecular structure of 2b. Only selected hydrogen
26
atoms are shown.
(
Pnma) space group, respectively (Figure 2). While 2a exhibits
no molecular symmetry, the triphenylsilyl complex 2b resides
on a mirror plane perpendicular to the NHC heterocycle and
one of the of the phenyl moieties (through the atoms C1, Cu1,
Si1, C18, and C21).
For the SiMe Ph complex 3a, two pseudopolymorphic
structures were obtained, one containing a single molecule of
a in the asymmetric unit in an orthorhombic space group type
2
Figure 3. Top: View of the asymmetric unit of 3a(PhMe)1/2 parallel to
the b axis (inset shows overlay of the two independent molecules).
Bottom left: Molecular structure of 3a. Bottom right: Molecular
3
26
P2 2 2 and a second one with an asymmetric unit comprising
structure of 3b. Only selected hydrogen atoms are shown.
1
1 1
E
DOI: 10.1021/acs.inorgchem.6b00210
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Inorganic Chemistry
Article
the N−CNHC−Si−Cipso torsion angles, Figure 3 (inset), Table
18
2].
The triphenylsilyl complex of the tert-butyl substituted NHC
3
b crystallizes in a monoclinic space group (P2 /c) with one
1
18
molecule in the asymmetric unit (Figure 3 and Table 2).
The individual molecular structures of 1a,b, 2a,b, and 3a,b
may be best characterized by their respective CNHC−Cu and
Cu−E distances and C −Cu−E angles (Table 2, Figures 2
NHC
and 3). The C −Cu distances are in a small range around
NHC
1
.93 Å for the silyl complexes (1a,b, 2a,b, 3a,b). For related
Figure 4. View of the asymmetric unit of 1c approximately along the
[101] vector. Hydrogen atoms are omitted for clarity.
1
8,26
phenyl and alkynyl complexes (1d,e), shorter CNHC−Cu
distances of around 1.90 Å are found, resembling the reduced
donor properties of the latter ligands (reduced trans
influence). These data are complemented by Cu−Si distances
around 2.27 Å, lying in the range reported for various copper
might be surprising considering the comparably small SnMe3
ligand, it fits into the picture outlined above with the relevance
of not only repulsive but also attractive interactions for the
1
8
1
3
18
silyl complexes.
conformation of these complexes.
A linear angle CNHC−Cu−E may be expected for these
In contrast to the above-discussed linear, mononuclear
complexes, the silyl/stannyl complexes of the sterically little
monomeric (NHC)Cu-SiR complexes; however, especially for
3
the IDipp and IMes ligands (1a,b and 2a,b) bearing aromatic
N-substituents, these angles deviate significantly from 180°
demanding Me IMe adopt more peculiar polynuclear struc-
2
tures. The silyl complexes (4a) and (4b) crystallize as dimers,
2
2
(Table 2). A tentative rationalization on a molecular level may
similar to the reported complexes [(IDipp)Cu−H] and
2
be the subtle interplay between repulsion due to steric bulk and
attractive dispersive π-HC interactions between the aromatic N-
substituent and CH moieties within the anionic ligand. The
latter may be illustrated by the shortest H−Ct distances (with
Ct being the centroid of the aromatic system) found for the
individual complexes (Figure 2 and Table 2). It should be
emphasized that positions of the H atoms were obtained by X-
ray diffraction employing suitable riding models and are not
freely refined. While these distances must be considered with
due caution, the riding models (including refinement of the
orientation of methyl groups) should give reasonably reliable
[
(IMe)Cu−SiEt(TMS) ] , while the stannyl complex (4c)
2
2
3
6a,8
adopts a trimeric strcuture.
In the dimeric silyl complexes
I
a three-coordinated Cu ion is coordinated by one NHC ligand
and two bridging μ-silyl ligands. The structures of the
symmetrical Cu Si core may be described generally as butterfly
2
2
type with a remarkably short Cu···Cu distance. However, a
closer look on the crystal structures requires a more detailed
18
discussion (Table 3 and Figures 5−8).
18
data for this tentative analysis. Moreover, the occurrence of
these short distances corresponds generally reasonably well
with the orientation of the bend CNHC−Cu−E unit.
Nonetheless, into this simplified picture packing effects, and
24d,27
hence intermolecular interactions, certainly have to be included.
The reported complexes [(ItBu)Cu−Si(TMS) ] and
3
[
(ItBu)Cu−SiEt(TMS) ], analogous to 3a,b, but featuring
2
bulkier silyl groups, exhibit geometrical parameters in the same
range: Cu−C 1.937(2) Å, Cu−Si 2.2636(5) Å, CNHC−Cu−
Figure 5. Molecular structure of complex (4a) . Hydrogen atoms are
NHC
2
2
6
Si 178.60(5)°, and Cu−C
NHC
1.948(2) Å, Cu−Si 2.2754(5) Å,
omitted for clarity.
NHC
8
C
−Cu−Si 178.29(5)°, respectively. However, the C
−
NHC
Cu−Si angles are significantly closer to linearity, tentatively an
effect of the increased steric restraints due to the demanding
silyl groups and the lack of π-HC interactions (vide supra).
The heavier homologues of the discussed silyl complexes, the
Complex (4a) crystallizes in a triclinic space group P1
̅
with
2
half of a dimeric molecule (4a) in the asymmetric unit; hence,
2
stannyl complexes [(IDipp)Cu−SnMe ] (1c) and [(IDipp)-
3
7
Cu−SnPh ], also fit into this picture. However, for 1c the
3
crystallographic data have to be considered with some care as
the crystal structure determination is complicated by the
occurrence of a superstructure (three independent molecules
per asymmetric unit) associated with twinning and possibly an
1
8
additional modulation (Table 2 and Figure 4). As a
consequence, only the mean geometrical data of the three
independent molecules are discussed. Nonetheless, in compar-
ison with the reported data for [(IDipp)Cu−SnPh ] (C
−
3
NHC
Cu 1.914(2) Å, Cu−Sn 2.469(5) Å, C −Cu−Sn 169.6(8)°),
NHC
similar Cu−Sn and C −Cu distances are observed, while the
NHC
C
−Cu distance is significantly shorter than that in the silyl
NHC
7
complexes 1a,b, 2a,b, and 3a,b. The coordination geometry at
the Cu atom shows for 1c with 17° the largest deviation from
linearity for all discussed [(NHC)Cu−E] complexes. While this
Figure 6. Molecular structure of (4b) at 127 K. Hydrogen atoms are
2
2
6
omitted for clarity.
F
DOI: 10.1021/acs.inorgchem.6b00210
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Inorganic Chemistry
Article
18
it is located on a center of inversion (Figure 5). This
crystallographic site symmetry requires a planar Cu Si core
2
2
(
interplanar angle ϕ, Table 3) with a planar coordination
environment at the two equivalent copper ions (Σ(Cu) 360°).
However, the two Cu−Si interactions are not equivalent as
shown by the different C −Cu−Si angles and Cu−Si
NHC
distances.
Generally, complex (4b) exhibits the same structural motif
2
as (4a) , a Cu Si core with planar coordinated Cu atoms, but it
2
2
2
is lacking any crystallographic site symmetry. This allows for a
nonplanar Cu Si core with interplanar angles ϕ of 25−43° and
2
2
also a variation in the C −Cu−Si and Si−Cu−Si angles
NHC
(
Table 3, Figures 6 and 7). Moreover, (4b) shows complex
2
structural changes depending on the temperature. At 127 K, a
higher symmetric structure in an orthorhombic space group
with one independent molecule in the asymmetric unit is
realized while at 100 K a lower symmetric monoclinic cell with
two independent molecules in the asymmetric unit is found
18
(
Table 3 and Figure 7). However, this transition is associated
18
with twinning via a C-centered orthorhombic unit cell. Upon
this transition, the geometric parameters of the molecular
structure of (4b)2 change appreciably (Table 3). Most
significantly, the interplanar angle ϕ splits from 34° at 127 K
into 43° and 25° at 100 K for the now two independent
molecules in the asymmetric unit. The Cu···Cu distances for
the two independent molecules are very short throughout and
may, if at all, increase marginally upon cooling (Table 3).
It is illustrative to compare (4a) and (4b) with the closely
Figure 7. View of the asymmetric unit of (4b) at 100 K [inset shows
2
2
2
packing pattern of (4b) at 100 K (only Si (light blue) and Cu (orange
2
related complex [(IMe)Cu−SiEt(TMS) ] (Cu−C
2
2
NHC
and purple) atoms shown; in red, approximate unit cell at 127 K for
1
2
1
.949(4) Å, Cu−Si 2.4232(9)/2.5922(8) Å, Cu···Cu
26
comparison)]. Hydrogen atoms are omitted for clarity.
.2854(9) Å, C −Cu−Si 115.2(1)/123.8(1)°, Si−Cu−Si
NHC
8
20.93(3)°, Cu−Si−Cu 54.09(2)°, ϕ 24.76°) as well as with
the monomeric silyl complexes 1a,b and 3a,b (Table 2). All
these structures reveal a quite narrow range of Cu−C
NHC
distances of 1.93−1.95 Å despite the change in the
coordination number at the Cu ion. However, the Cu−Si
distances increase, as expected, significantly upon dimerization
and, hence, upon increasing the coordination number at the
silicon atom. For all dimeric complexes ((4a) , (4b) ,
2
2
[
(IMe)Cu−SiEt(TMS) ] ) a slightly unsymmetrical coordina-
2
2
tion of the μ-silyl groups is observed as evidenced by
significantly different Cu−Si distances for each silyl group
and differences in the C −Cu−Si angles. The coordination
NHC
environment at each copper atom is within the significance
planar as shown by sums of angles of 360 ± 0.5°. Nonetheless,
the individual angles at each Cu atom vary significantly, as does,
connected with that, the interplanar angle ϕ.
However, the most remarkable feature of these dimers is the
extraordinarily short Cu···Cu distance. In fact, (4a) and (4b)
2
2
are, together with [(IDipp)Cu−H] and [(IMe)Cu−SiEt-
2
(
TMS) ] (vide supra), to the best of our knowledge, the
2 2
only structurally well-characterized Cu complexes featuring a
10
Cu···Cu distance below 2.3 Å. While the distance shows some
variation within (4a) , (4b) , and [(IMe)Cu−SiEt(TMS) ] , it
2
2
2 2
stays always below 2.3 Å and is far shorter than the interatomic
distance in elemental copper (2.56 Å) or the double van der
28
Waals radius (2.8 Å). Complexes featuring the motif of two
Cu ions bridged by a silyl group are well-established, but
typically two Cu ions are bridged by only one silyl ligand,
resulting in Cu···Cu distances in the range 2.36−2.45 Å.
Computational studies on the bonding situation in these and
Figure 8. Molecular structure of complex (4c) and detail of the
3
13
[
Cu Sn (C ) ] subunit with selected distances. Hydrogen atoms are
3
3
NHC 3
26
omitted for clarity.
also related complexes, such as (CuH) , suggest the presence of
2
a three-center−two-electron bond including the two copper
G
DOI: 10.1021/acs.inorgchem.6b00210
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
I
11
+
and the silicon atoms, potentially, but not necessarily,
documented, e.g., for related phosphine Cu complexes.
1
0
10
9,13c
−
accompanied by closed-shell d −d interaction.
However, the ions [(PhCC) Cu] and [(NHC) Cu]
2
2
2
9
The stannyl homologue (4c) realizes in the solid state an
themselves have also been reported independently.
3
unsymmetrical trimeric structure exhibiting similar structural
Finally, it should be mentioned that an attempt to replace the
motifs as discussed above for (4a) and (4b) : Cu···Cu units
NHC ligand in the dimeric complex (4a) by a small phosphine
2
2
2
bridged by a ER moiety. However, the three Cu atoms in
(PMe ) did not lead to the isolation of a polynuclear copper
3
3
(
4c) , occupying the corners of a triangle, are inequivalent. The
complex but the isolation of the mononuclear complex
3
I
18
structure may be formally described as a dimer (as found for
4a) and (4b) ) embodied by the atoms Cu1, Cu3, Sn1, Sn2,
[(Me P) Cu−SiMe Ph] exhibiting a four-coordinate Cu ion.
3
3
2
(
Spectroscopic Characterization. While the molecular
structures of the complexes 1a−4e in the solid state are readily
established by X-ray diffraction, insight into their solution
behavior is not straightforward to obtain. However, hetero-
nuclear NMR spectroscopy may give some indication on the
solution state behavior.
2
2
I
C15, and C1, and additional SnMe (Sn3) and (NHC)Cu
(
Alternatively, (4c) may be described as two μ -stannyl ligands
(
3
Cu2, C8) moieties bridging the Cu1···Cu3 unit (Figure 8).
3
3
Sn1, Sn2) located above the faces of a (Cu) -triangle and one
3
2
μ -stannyl ligand (Sn3) additionally located above one edge of
the (Cu) triangle. The coordination environment of the Cu
For the linear, mononuclear dimethylphenyl silyl complexes,
3
1a, 2a, and 3a 29Si NMR chemical shifts in a narrow range of
atoms is then completed by three NHC ligands each
coordinating one Cu atom. The copper atoms are inequivalent
with respect to their coordination environments exhibiting
coordination numbers of five (Cu2) and six (Cu1, Cu3),
respectively. Although the Cu···Cu distances within the (Cu)3
triangle vary slightly, they are very short (2.3−2.5 Å) but longer
−14.4 ± 0.4 ppm are observed (in C
related triphenylsilyl complexes 1b and 3b show Si NMR
chemical shifts in C of −0.4 and −0.7 ppm, respectively. In
contrast to that, the dimeric complexes (4a) and (4b) give
and at −10.1 ppm (4b) ,
2
D ). In line with that, the
6
6
2
9
D
6
6
2
2
29
Si NMR signals at −23.0 ppm (4a)
respectively (in C D ). Hence, significant shifts of the Si
2
2
9
than those in the silyl complexes (4a) and (4b) . The C
Cu distances are slightly longer than those in the related
−
2
2
NHC
6
6
NMR signals by about 9 ppm compared to the monomeric
complexes are observed. This consistent and systematic
difference in the 29Si NMR data suggests a different electronic
environment, in particular, different coordination numbers, in
solution. This is in agreement with the data of the cuprates
[Cu {Si(TMS) } BrLi(thf) ] and [{Li (OtBu) }{Cu (Si-
mononuclear complexes [(IDipp)Cu−SnPh ] ((C −Cu
3
NHC
1
.914(2) Å, Cu−Sn 2.469(5) Å, C −Cu−Sn 169.6(8)°))
NHC
7
or in 1c (vide supra). The Cu−Sn distances are significantly
increased, and quite varying, as expected for a change to a
2
3
(slightly unsymmetrical) μ /μ coordination mode.
2
3
2
3
7
6
2
2
9
The observation of bridging coordination modes of the ER3
(TMS) ) }], respectively, where similarly distinct Si NMR
3 3
ligands in [(NHC)Cu−ER ] complexes once the formation of
shifts are observed for bridging and terminal silyl groups within
3
13b,c
aggregated species is not sterically prohibited by the sterics of
the NHC ligand provoked the question regarding whether
complexes with other anionic ligands exhibit similar structures.
We synthesized the aryl complexes 1d and 4d as well as the
alkynyl complexes 1e and 4e. For both ligand, the ability to
a single molecule.
In conclusion, in the solid state,
monomeric and dimeric complexes exhibit characteristic and
consistent specific sets of 29Si NMR shifts suggesting different
solution state structures. This may be rationalized by the
solution structures resembling the monomeric and dimeric
molecular structures in the solid state.
I
form bridged Cu complexes (Table 1) is well-documen-
9
e,11,12
ted.
The unique NMR properties of tin comprising two spin 1/2
nuclei (1 Sn and Sn) in virtually equal, relatively high natural
abundances (7.68 and 8.59%) enable a more detailed study of
the solution state structure for (4c)3.
17
119
However, the phenyl complexes [(IDipp)Cu−Ph] 1d and
[
(Me IMe)Cu−Ph] 4d both exhibit similar mononuclear linear
2
structures despite the significantly different steric demand of
1
8
the NHC ligands. The characteristic distances CNHC−Cu and
Especially indicative for the solution state structure of (4c)
3
117/119
Cu−C are similar, while a more linear CNHC−Cu−Ph angle is
are those signals with significant coupling to
Sn nuclei
Ph
(Figure 9). 13C NMR spectroscopy reveals, for the carbene
carbon atom beside the central signal (185.6 ppm), a doublet
arising from coupling to one NMR active Sn nucleus
observed for the sterically less encumbered complex 4d
(
CNHC−Cu: 1.906(3) Å/1.892(3) Å (1d), 1.902(3) Å (4d);
Cu−C : 1.898(3) Å/1.907(3) Å (1d), 1.914(3) Å (4d);
C
The geometrical data also agree well with those of related
Ph
18
13
117/119
119
−Cu−Ph: 174.1(1)°/173.9(1)° (1d), 179.1(1)° (4d)).
(J( C−
Sn) = 35 Hz, averaged coupling constants to
Sn and Sn are used throughout this analysis). In addition,
NHC
1
17
24
[
(NHC)Cu−Ar] complexes.
a second set of signals, a triplet partly overlapping with the
above signals, is recognizable, though just significant. It can
Here, it may be also stated that the complex [(IMe)Cu−
account for a 13C−
117/119
Sn coupling to two
117/119
Sn nuclei.
Si(TMS) ] bearing the sterically demanding tris(trimethylsilyl)-
3
silyl group does not form dimeric complexes as observed in the
The intensity of both satellite signals agrees with the respective
17
related complexes (4a) , (4b) , and [(IMe)Cu−SiEt(TMS) ]
natural abundances. For the stannyl methyl carbon atom
signal (−0.9 ppm) a better s/n ratio is obtained, and three
distinct sets of signals are clearly observable: (a) the main signal
2
2
2 2
8
(
vide supra).
The alkynyl complex [(IDipp)Cu−CC−Ph] (1e) exhibits,
13
117/119
as expected and in agreement with the literature precedent, a
linear, two-coordinated Cu ion.
not experiencing any C−
Sn coupling; (b) a doublet
I
18,19,23
13
117/119
17/119
Surprisingly, the alkynyl
(J( C−
Sn) = 67 Hz) due to coupling with one directly
bound 1
Sn atom; (c) a doublet (J( C−
Hz) due to coupling with one
13
117/119
Sn) = 28
complex with the formal composition [(Me IMe)Cu−CC−
2
117/119
Ph] 4e does not exhibit a similar structure but rather comprises
Sn atom not directly
+
−
[
(Me IMe) Cu] cations and [(PhCC) Cu] anions that are
bound, with doubled intensity with respect to the previous
2
2
2
−
117/119
present in distinct building blocks: [(PhCC) Cu] , [⟨(Me -
satellite signal. Furthermore, two couplings to two
Sn
2
2
+
IMe) Cu⟩ ⟨(PhCC) Cu⟩] , and [⟨(Me IMe) Cu⟩⟨(PhC
atoms have to be included in the simulations for optimal
agreement with the experimental data. These arise from
2
2
2
2
2
1
8
C) Cu⟩]. The occurrence of this structural motif is
2
1
17/119
unexpected as μ-coordinating alkynyl ligands are very well-
coupling to one directly bound and one remote
Sn
H
DOI: 10.1021/acs.inorgchem.6b00210
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 4. Exemplary Catalytic Silylation with
[
Me IMe)CuOtBu] or [ItBu)CuOtBu] as Precatalyst
2
a
b
precatalyst
substrate
t/conv
yield
1
2
4c
R = dipp, R = H
p-tolyl aldehyde
hex-3-en-4-one
p-tolyl aldehyde
hex-3-en-4-one
p-tolyl aldehyde
hex-3-en-4-one
74 h
3 h
75%
13
1
1
2
4b
Figure 9. Selected regions from experimental and simulated C{ H}
R = dipp, R = H
77%
NMR and 1 Sn{ H} NMR spectra of (4c) .
19
1
18
1
2
R = tBu, R = H
<1 h
<1 h
<1 h
<1 h
58%
63%
59%
62%
3
1
2
R = tBu, R = H
1
2
R = Me, R = Me
1
2
R = Me, R = Me
atom and to two remote 117/119Sn atoms, respectively. Again,
the intensities of all satellite signals agree with their respective
a
b
Approximate time required for full conversion (GC/MS). Isolated
yield.
18
119
natural abundances. At last, the Sn NMR signal shows
1
19
117
119
117
satellites arising from Sn− Sn coupling (J( Sn− Sn) =
CONCLUSION
2
383 Hz), again with intensities fitting the expected values for a
trinuclear complex on the basis of the natural abundances.
In summary it can be stated that the C and Sn NMR
■
18
A series of silyl and stannyl [(NHC)Cu−ER ] complexes (ER3
3
1
3
119
= SiMe Ph, SiPh , SnMe ) was synthesized by reaction of
2
3
3
spectroscopic data are in agreement with a trimeric solution
[(NHC)Cu−OtBu] complexes with the respective stannyl- and
silylboranes significantly extending the scope of this versatile
and easy-to-use access to copper silyl/stannyl complexes.
Moreover, this reaction pathway has also been used to
synthesize the related phenyl and alkynyl complexes [(NHC)-
Cu−R] (R = Ph, CCPh) as well as the phosphine complex
state structure of (4c) similar to that present in the solid state;
3
however, unlike in the solid state the spectra indicate the
equivalence of all three tin atoms. This may be explained with a3
rapid interconversion of the two different types of tin atoms (μ
2
(
Sn1, Sn2) and μ (Sn3) coordinating, Figure 8) found in the
[
(Me P) Cu−SiMe Ph].
solid state or by an alternative static symmetrical trimeric
structure. The direct evidence for a trimeric nature of the
3
3
2
Single X-ray structure determinations of the compounds
[
(NHC)Cu−ER ] revealed two major structure types in the
stannyl complex (4c) in solution supports the assumption of
3
3
solid state. For the sterically demanding NHC ligands IDipp,
IMes, and ItBu, monomeric approximately linear CuI
complexes were found for ER = SiMe Ph, SiPh , SnMe as
dimeric solution structures of the silyl complexes (4a) and
2
(4b)2.
3
2
3
3
Catalysis. Copper(I) catalyzed silylation reactions of
well as for Ph and CCPh. However, for the sterically little
aldehydes and α,β-unsaturated carbonyls employing silylbor-
anes have recently been intensely studied. In particular, 1a has
been employed as a model catalyst and enabled the
demanding methyl substituted NHC (Me IMe) dimeric silyl
2
complexes comprising a butterfly shaped Cu Si core with μ-
2
2
4a−c
silyl ligands bridging the two Cu ions were obtained as reported
characterization of a number of relevant intermediates.
It
8
earlier for the related complex [(IMe)Cu−SiEt(TMS) ] .
2
2
has been shown that under the reaction conditions the
precatalyst (NHC)CuOtBu is converted to the catalytically
Similarly a structurally related trimeric complex was obtained
for the trimethylstannyl complex. These complexes feature
ultrashort Cu···Cu distances around 2.3 Å, among the shortest
known today. In contrast, for the phenyl ligands the monomeric
crucial silyl complex upon reaction with pinB−SiMe Ph (vide
2
4
a−c
supra).
To gain a first systematic insight into the impact of
the sterics of the NHC ligand on the catalytic activity the
and linear complex [(Me IMe)Cu−Ph] is obtained while for
2
complexes, [(ItBu)CuOtBu] and [(Me IMe)CuOtBu] were
+
2
the alkynyl ligand the formation of [(Me IMe) Cu ] and
2
2
2
employed as precatalysts in the 1,2-/1,4-silylation of p-
tolylaldehyde and hex-3-en-4-one as exemplary organic
substrates (Table 4).
−
[
(PhCC) Cu] ions was observed in the solid state, despite
2
the well-documented ability of phenyl and alkynyl ligands to
I
realize bridging coordination modes in Cu complexes. The
For both (pre)catalysts efficient conversion to the expected
heteronuclear solution NMR spectroscopic data of the silyl and
stannyl complexes are consistent with different modes of
coordination of the silyl and stannyl ligands with dependence
on the NHC ligand present as observed in the solid state.
A case study of the catalytic properties of sterically less
1
,2- and 1,4-silylation products at ambient temperature was
observed, and the silylated compounds were isolated in good
unoptimized) yields (Table 4). Moreover, in comparison to
(
those of the established (IDipp)Cu system significantly faster
reaction rates were observed. Full conversion was reached after
less than 1 h, while for the IDipp ligand significantly longer
encumbered (NHC)Cu−SiMe Ph complexes for the silylation
2
of aldehydes and α,β-unsaturated ketones with silylboranes was
4b,c
reaction times were reported.
conducted. The complexes (ItBu)CuOtBu and (Me IMe)-
2
I
DOI: 10.1021/acs.inorgchem.6b00210
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
CuOtBu were found to be effective (pre)catalysts for the
silylation of an aldehyde and an α,β-unsaturated ketone,
presumably via the intermediate monomeric ([(ItBu)Cu−
SiMePh ]) and dimeric ([(Me IMe)Cu−SiMePh ] ) com-
4653. (f) Pace, V.; Rae, J. P.; Procter, D. J. Org. Lett. 2014, 16, 476−
4
79.
(3) (a) Semba, K.; Shinomiya, M.; Fujihara, T.; Terao, J.; Tsuji, Y.
Chem. - Eur. J. 2013, 19, 7125−7132. (b) Borner, C.; Kleeberg, C. Eur.
J. Inorg. Chem. 2014, 2014, 2486−2489. (c) Kajiwara, T.; Terabayashi,
T.; Yamashita, M.; Nozaki, K. Angew. Chem., Int. Ed. 2008, 47, 6606−
2
2
2 2
plexes, respectively. Moreover, significantly faster reactions
were observed than those with the established, sterically more
demanding IDipp ligand. However, no significant difference
6
(
610.
4) (a) Kleeberg, C.; Cheung, M. S.; Lin, Z.; Marder, T. B. J. Am.
was observed between the ItBu and Me IMe ligand.
2
Chem. Soc. 2011, 133, 19060−19063. (b) Plotzitzka, J.; Kleeberg, C.
Organometallics 2014, 33, 6915−6926. (c) Kleeberg, C.; Feldmann, E.;
Hartmann, E.; Vyas, D. J.; Oestreich, M. Chem. - Eur. J. 2011, 17,
13538−13543.
The findings are of direct relevance to the growing field of
I
Cu catalyzed silylation reaction, in particular those involving
I
NHC−Cu complexes, where mononuclear complexes are
widely assumed to be the active species. The study suggests
̈
(5) (a) Laitar, D. S.; Muller, P.; Sadighi, J. P. J. Am. Chem. Soc. 2005,
I
1
27, 17196−17197. (b) Laitar, D. S.; Tsui, E. Y.; Sadighi, J. P. J. Am.
that the coordination chemistry of NHC−Cu silyl complexes is
Chem. Soc. 2006, 128, 11036−11037. (c) Laitar, D. S.; Tsui, E. Y.;
Sadighi, J. P. Organometallics 2006, 25, 2405−2408.
more diverse, and aggregation and in particular bridging
coordination of silyl ligands must be considered. Forthcoming
experimental as well as computational studies, regarding the
(6) (a) Mankad, N. P.; Laitar, D. S.; Sadighi, J. P. Organometallics
2
004, 23, 3369−3371. (b) Goj, L. A.; Blue, E. D.; Delp, S. A.; Gunnoe,
I
solution structure of NHC-Cu silyl complexes as well as a
T. B.; Cundari, T. R.; Pierpont, A. W.; Petersen, J. L.; Boyle, P. D.
Inorg. Chem. 2006, 45, 9032−9045. (c) Cox, N.; Dang, H.; Whittaker,
A. M.; Lalic, G. Tetrahedron 2014, 70, 4219−4231. (d) Vergote, T.;
Nahra, F.; Peeters, D.; Riant, O.; Leyssens, T. J. Organomet. Chem.
2013, 730, 95−103. (e) Zhang, L.; Cheng, J.; Hou, Z. Chem. Commun.
2013, 49, 4782−4784. (f) Vergote, T.; Gathy, T.; Nahra, F.; Riant, O.;
Peeters, D.; Leyssens, T. Theor. Chem. Acc. 2012, 131, 1253−1266.
detailed analysis of the ultrashort Cu···Cu distances, will
provide further insight into these intriguing and highly valuable
class of compounds. Moreover, further comparative studies of
the reactivity of monomeric and dimeric/aggregated NHC-CuI
silyl complexes should impact on the further development of
I
Cu catalyzed silylation reactions with silylboranes.
(
2
g) Jurkauskas, V.; Sadighi, J. P.; Buchwald, S. L. Org. Lett. 2003, 5,
417−2420. (h) Vergote, T.; Nahra, F.; Merschaert, A.; Riant, O.;
Peeters, D.; Leyssens, T. Organometallics 2014, 33, 1953−1963.
i) Suess, A. M.; Uehling, M. R.; Kaminsky, W.; Lalic, G. J. Am. Chem.
ASSOCIATED CONTENT
Supporting Information
■
*
S
(
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b00210. The data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/structures.
Soc. 2015, 137, 7747−7753. (j) Mazzacano, T. J.; Mankad, N. P. J. Am.
Chem. Soc. 2013, 135, 17258−17261.
(7) Bhattacharyya, K. X.; Akana, J. A.; Laitar, D. S.; Berlin, J. M.;
Sadighi, J. P. Organometallics 2008, 27, 2682−2684.
(8) Sgro, M. J.; Piers, W. E.; Romero, P. E. Dalton Trans. 2015, 44,
3
(
817−3828.
Additional experimental, analytical, and crystallographic
data (PDF)
Crystallographic data (ZIP)
9) (a) Pyykko, P. Chem. Rev. 1997, 97, 597−636. (b) Davenport, T.
̈
C.; Tilley, T. D. Angew. Chem., Int. Ed. 2011, 50, 12205−12208.
(c) Che, C.-M.; Mao, Z.; Miskowski, V. M.; Tse, M.-C.; Chan, C.-K.;
Cheung, K.-K.; Phillips, D. L.; Leung, K.-H. Angew. Chem., Int. Ed.
2
1
2
̈
000, 39, 4084−4088. (d) Kolmel, C.; Ahlrichs, R. J. Phys. Chem.
AUTHOR INFORMATION
Corresponding Author
E-mail: ch.kleeberg@tu-braunschweig.de. Fax: +49 (0) 531
91 5387.
■
990, 94, 5536−5542. (e) Stollenz, M.; Meyer, F. Organometallics
012, 31, 7708−7727.
*
(10) A search in the CSD database (version 5.37, November 2015)
revealed that [(IDipp)CuH])
only structures comprising a Cu···Cu distance in the range 2.2−2.3 Å,
while for longer distances significantly more structures were found:
3
2
and [(IMe)Cu−SiEt(TMS) ] are the
2 2
Notes
The authors declare no competing financial interest.
2
.3−2.4 Å, 49 structures; 2.4−2.5 Å, 260 structures; 2.5−2.6 Å, 442
structures; 2.6−2.7 Å, 1515 structures. A number of structures
containing polynuclear Cu moieties were found exhibiting very short
Cu···Cu distances; however, these are at least partially the result of
imperfect description of disorder and, hence, are not further
considered.
ACKNOWLEDGMENTS
■
C.K. thanks the Fonds der Chemischen Industrie for the
generous support by a Liebig-Fellowship. J.P. and C.K.
gratefully acknowledge support by a Research Grant (KL
243/4-1) of the Deutsche Forschungsgemeinschaft (DFG).
We thank Dirk Bockfeld and Tim Harig for help with the
laboratory work.
(
11) For selected examples of Cu···Cu bridging alkynyl ligands see:
a) Siu, S.K.-L.; Ko, C.-C.; Au, V.K.-M.; Yam, V. W.-W. J. Cluster Sci.
014, 25, 287−300. (b) Hattori, G.; Sakata, K.; Matsuzawa, H.;
Tanabe, Y.; Miyake, Y.; Nishibayashi, Y. J. Am. Chem. Soc. 2010, 132,
0592−10608. (c) Yam, V. W.-W.; Fung, W. K.-K.; Cheung, K.-K.
2
(
2
1
REFERENCES
Organometallics 1998, 17, 3293−3298. (d) Olbrich, F.; Behrens, U.;
Weiss, E. J. Organomet. Chem. 1994, 472, 365−370. (e) Diez, J.;
Gamasa, M. P.; Gimeno, J.; Aguirre, A.; Garcia-Granda, S. Organo-
metallics 1991, 10, 380−382. (f) Yam, V.W.-W.; Lee, W.-K.; Cheung,
K. K.; Lee, H.-K.; Leung, W.-P. J. Chem. Soc., Dalton Trans. 1996,
2889−2891. (g) Chan, W. H.; Zhang, Z.-Z.; Mak, T. C. W.; Che, C.-
M. J. Organomet. Chem. 1998, 556, 169−172.
(12) For selected examples of Cu−Ar complexes with bridging aryl
ligands see: (a) Schulte, P.; Behrens, U.; Olbrich, F. Z. Anorg. Allg.
Chem. 2000, 626, 1692−1696. (b) Edwards, P. G.; Gellert, R. W.;
Marks, M. W.; Bau, R. J. Am. Chem. Soc. 1982, 104, 2072−2073.
(c) Meyer, E. M.; Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.;
■
(
1) For recent reviews see: (a) Lazreg, F.; Nahra, f.; Cazin, C. S. J.
Coord. Chem. Rev. 2015, 293−294, 48−79. (b) Gaillard, S.; Cazin, C. S.
J.; Nolan, S. P. Acc. Chem. Res. 2012, 45, 778−787. (c) Díez-Gonzal
S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612−3676.
2) For an overview and selected examples see: (a) Oestreich, M.;
Hartmann, E.; Mewald, M. Chem. Rev. 2013, 113, 402−441.
b) Hensel, A.; Nagura, K.; Delvos, L. B.; Oestreich, M. Angew.
Chem., Int. Ed. 2014, 53, 4964−4967. (c) Lee, K-s; Wu, H.; Haeffner,
F.; Hoveyda, A. H. Organometallics 2012, 31, 7823−7826. (d) Lee, K-
s; Hoveyda, A. H. J. Am. Chem. Soc. 2010, 132, 2898−2900. (e) Delvos,
L. B.; Vyas, D. J.; Oestreich, M. Angew. Chem., Int. Ed. 2013, 52, 4650−
́
ez,
(
(
J
DOI: 10.1021/acs.inorgchem.6b00210
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Guastini, C. Organometallics 1989, 8, 1067−1079. (d) Eriksson, H.;
Hakansson, M.; Jagner, S. Inorg. Chim. Acta 1998, 277, 233−236.
2010, 695, 2410−2417. (c) Pouy, M. J.; Delp, S. A.; Uddin, J.;
Ramdeen, V. M.; Cochrane, N. A.; Fortman, G. C.; Gunnoe, T. B.;
Cundari, T. R.; Sabat, M.; Myers, W. H. ACS Catal. 2012, 2, 2182−
2193.
(24) For selected examples of Cu−Ar complexes see: (a) Ohishi, T.;
Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2008, 47, 5792−5795.
(b) Hope, H.; Olmstead, M. M.; Power, P. P.; Sandell, J.; Xu, X. J. Am.
Chem. Soc. 1985, 107, 4337−4338. (c) Haywood, J.; Morey, J. V.;
Wheatley, A. E. H.; Liu, C.-Y; Yasuike, S.; Kurita, J.; Uchiyama, M.;
Raithby, P. R. Organometallics 2009, 28, 38−41. (d) Niemeyer, M. Z.
Anorg. Allg. Chem. 2003, 629, 1535−1540.
(25) (a) Zhao, H.; Lin, Z.; Marder, T. B. J. Am. Chem. Soc. 2006, 128,
15637−15643. (b) Dang, L.; Lin, Z.; Marder, T. B. Organometallics
2010, 29, 917−927.
(26) Thermal ellipsoids are drawn at the 50% probability level.
Disorder and cocrystallized solvent may be omitted for clarity. An
adopted numbering scheme may be used in order to improve
readability. Symmetry equivalent atoms are indicated by a prime.
(
e) Lenders, B.; Grove, D. M.; Smeets, W. J. J.; van der Sluis, P.; Spek,
A. L.; van Koten, G. Organometallics 1991, 10, 786−791. (f) He, X.;
Ruhlandt-Senge, K.; Power, P. P.; Bertz, S. H. J. Am. Chem. Soc. 1994,
1
1
(
16, 6963−6964. (g) Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc.
990, 112, 8008−8014.
13) (a) Klett, J.; Klinkhammer, K. W.; Niemeyer, M. Chem. - Eur. J.
1
999, 5, 2531−2536. (b) Heine, A.; Herbst-Irmer, R.; Stalke, D. J.
Chem. Soc., Chem. Commun. 1993, 1729−1731. (c) Klinkhammer, K.
W. Z. Anorg. Allg. Chem. 2000, 626, 1217−1223. (d) Heine, A.; Stalke,
D. Angew. Chem., Int. Ed. Engl. 1993, 32, 121−123. (e) Klinkhammer,
K. W.; Klett, J.; Xiong, Y.; Yao, S. Eur. J. Inorg. Chem. 2003, 2003,
3
417−3424. (f) Cowley, A. H.; Elkins, T. M.; Jones, R. A.; Nunn, C.
M. Angew. Chem., Int. Ed. Engl. 1988, 27, 1349−1350. (g) Lerner, H.-
W.; Scholz, S.; Bolte, M. Organometallics 2001, 20, 575−577.
(
14) (a) Ariafard, A.; Brookes, N. J.; Stranger, R.; Yates, B. F.
Organometallics 2011, 30, 1340−1349.
(27) For an overview see: (a) Tsuzuki, S.; Fujii, A. Phys. Chem. Chem.
(
15) (a) Dang, L.; Lin, Z.; Marder, T. B. Chem. Commun. 2009,
Phys. 2008, 10, 2584−2594. (b) Nishio, M. CrystEngComm 2004, 6,
3
987−3995. (b) Zhao, H.; Dang, Li; Marder, T. B.; Lin, Z. J. Am.
1
1
30−158. (c) Nishio, M. Phys. Chem. Chem. Phys. 2011, 13, 13873−
Chem. Soc. 2008, 130, 5586−5594. (c) Zhao, H.; Lin, Z.; Marder, T. B.
3900.
J. Am. Chem. Soc. 2006, 128, 15637−15643.
(
28) Wiberg, N. Holleman-Wiberg, Lehrbuch der Anorganischen
Chemie; Walter de Gruyter: Berlin, 2007; p 2002−2006.
29) For selected examples of structurally characterized
(
̈
16) (a) Andersen, M. W.; Hildebrandt, B.; Koster, G.; Hoffmann, R.
W. Chem. Ber. 1989, 122, 1777−1782. (b) Suginome, M.; Matsuda, T.;
Ito, Y. Organometallics 2000, 19, 4647−4649. (c) Nishihara, Y.;
Miyasaka, M.; Okamoto, M.; Takahashi, H.; Inoue, E.; Tanemura, K.;
Takagi, K. J. Am. Chem. Soc. 2007, 129, 12634−12635. (d) Kleeberg,
C.; Grunenberg, J.; Xie, X. Inorg. Chem. 2014, 53, 4400−4410.
(
+
−
[
(NHC) Cu] and [(PhCC) Cu] ions see: (a) Diez-Gonzalez,
2
2
S.; Stevens, E. D.; Scott, N. M.; Petersen, J. L.; Nolan, S. P. Chem. -
Eur. J. 2008, 14, 158−168. (b) Dubinina, G. G.; Ogikubo, J.; Vicic, D.
A. Organometallics 2008, 27, 6233−6235. (c) Diez-Gonzalez, S.; Scott,
N. M.; Nolan, S. P. Organometallics 2006, 25, 2355−2558.
(
e) Haaf, M.; Schmedake, T. A.; Paradise, B. J.; West, R. Can. J. Chem.
2
000, 78, 1526−1533. (f) Kuhn, N.; Kratz, T. Synthesis 1993, 1993,
(
d) Thomson, R. K.; Monreal, M. J.; Masuda, J. D.; Scott, B. L.;
5
61−562. (g) Badiei, Y. M.; Warren, T. H. Inorg. Synth. 2010, 35, 51.
Kiplinger, J. L. J. Organomet. Chem. 2011, 696, 3966−3973.
(h) Hintermann, L. Beilstein J. Org. Chem. 2007, 3, No. 22.
i) Jurkauskas, V.; Sadighi, J. P.; Buchwald, S. L. Org. Lett. 2003, 5,
(
2
417−2420. (j) Fujihara, T.; Xu, T.; Semba, K.; Terao, J.; Tsuji, Y.
Angew. Chem., Int. Ed. 2011, 50, 523−527.
17) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.;
(
Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I.
Organometallics 2010, 29, 2176−2179.
(
(
18) See Supporting Information for further details.
19) Complex 1e has been reported in the literature including a
single-crystal structure determination. However, it was synthesized
differently, and the structure was determined at 150 K. The reported
1
8,23a,b
structure does not differ significantly from the one reported.
20) Repeated elemental analyses for different, independently
(
prepared samples failed to give more satisfactory results; all samples
gave consistent values but are low in carbon. It may be speculated that
this is caused by SiC and/or carbide/carbonate formation. See also:
(
a) Culmo, R. F. Application Note Elemental Analysis; Perkin Elmer,
Inc.: Shelton, CT, 2013. (b) Gawargious, Y. A.; MacDonald, A. M. G.
Anal. Chim. Acta 1962, 27, 300−302.
(
21) (a) Stalke, D. Chem. Soc. Rev. 1998, 27, 171−178.
(
b) CrysAlisPro, Version 1.171.34.44−1.171.36.24; Agilent Technolo-
gies, 2010−2012. (c) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found.
Crystallogr. 2008, A64, 112−122. (d) Sheldrick, G. M. Acta Crystallogr.,
Sect. A: Found. Adv. 2015, A71, 3−8. (e) Altomare, A.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr. 1993, 26, 343−350.
(
f) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838. (g) Spek, A.
L. PLATONA Multipurpose Crystallographic Tool; Utrecht Uni-
versity: Utrecht, The Netherlands, 1998. (h) Macrae, C. F.; Bruno, I.
J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.;
Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A. J. Appl.
Crystallogr. 2008, 41, 466−470. (i) Brandenburg, K. Crystal Impact
GbR, Diamond 3.2i; Bonn, Germany, 1997.
(
22) Complex 1d has been reported in the literature. However, it was
synthesized differently, and no single-crystal X-ray structure was
6b,18
reported.
23) (a) Goj, L. A.; Blue, E. D.; Munro-Leighton, C.; Gunnoe, T. B.;
(
Petersen, J. L. Inorg. Chem. 2005, 44, 8647−8649. (b) Jones, C.; Mills,
D. P.; Rose, R. P.; Stasch, A.; Woodul, W. D. J. Organomet. Chem.
K
DOI: 10.1021/acs.inorgchem.6b00210
Inorg. Chem. XXXX, XXX, XXX−XXX