Janus-Type Bis(maloNHC) and Its Zwitterionic Gold and Silver Metal Complexes

Article abstract of DOI:10.1021/acs.organomet.7b00206

A new Janus-type dianionic bis(maloNHC) (1) was synthesized and characterized by NMR spectroscopy. The utility of this extended biscarbene for the construction of homobimetallic systems has been demonstrated by its coordination to two coinage metals. The resulting zwitterionic metal complexes of the type [(Ph₃P)M(1)M(PPh₃)] (M = Au, Ag) have been fully characterized. The X-ray crystallography shows that the new ligand positions the two metal centers at a distance of 24.2 ?, the longest distance reported to date for any related NHC ligand.

Full text of DOI:10.1021/acs.organomet.7b00206

Article
pubs.acs.org/Organometallics
Janus-Type Bis(maloNHC) and Its Zwitterionic Gold and Silver Metal
Complexes
Ashley Carter,† Alexander Mason,† Michael A. Baker,† Donald G. Bettler,† Angelo Changas,†
Colin D. McMillen,‡ and Daniela Tapu*,†
†Department of Chemistry and Biochemistry, Kennesaw State University, 370 Paulding Avenue NW, Kennesaw, Georgia 30144,
United States
‡Department of Chemistry, Clemson University, 379 Hunter Laboratories, Clemson, South Carolina 29634, United States
S
* Supporting Information
ABSTRACT: A new Janus-type dianionic bis(maloNHC) (1) was
synthesized and characterized by NMR spectroscopy. The utility of this
extended biscarbene for the construction of homobimetallic systems has
been demonstrated by its coordination to two coinage metals. The
resulting zwitterionic metal complexes of the type [(Ph3P)M(1)M-
(PPh3)] (M = Au, Ag) have been fully characterized. The X-ray
crystallography shows that the new ligand positions the two metal centers
at a distance of 24.2 Å, the longest distance reported to date for any
related NHC ligand.
Chart 1
INTRODUCTION
■
Nonchelating multitopic N-heterocyclic carbenes (NHCs) have
been a subject of intense interest recently. While still an
emerging field, these systems have found tremendous utility as
building blocks for a variety of homo- and heterometallic
complexes,1 organic and organometallic polymers,2 and supra-
molecular structures.3 However, despite their versatility,
examples of such systems are still rare. Compounds A−G
(Chart 1) are the only known neutral ditopic NHCs that
display two facially opposed NHC moieties (Janus-type
coordination). Due to their rigidity, carbenes A−G have been
used as bridging ligands for the synthesis of a variety
homobinuclear transition metal complexes (e.g., silver,
rhodium, iridium, palladium, platinum, nickel, ruthenium, and
iron)1d−f,m,2a−c,g,4 or as scaffolds for the preparation of mixed-
valence dimetallic species for use as catalysts in tandem
reactions (e.g., IrIII/IrI, IrIII/RhI, and IrIII/PdII).4d,5 Through the
pioneering work of Bielawski and co-workers, it has been
shown that facially opposed NHCs B and E offer a modular
approach to unsaturated homopolymers, alternating polymers,
and main-chain organometallic polymers (MCOPs).2b,c,g These
NHC-MCOPs exhibit high thermal stability and versatile
electronic properties.2g Triazolediylidenes A have also been
used for the synthesis of polymeric silver complexes.1k,2e In
addition, Hahn and co-workers have recently demonstrated that
supramolecular structures can be obtained from linear dinuclear
metal complexes of benzobiscarbenes B and selected
coligands.1c,3b,c,f,6 Due to the high stability of the M−Ccarbene
bond, it is quite possible that such three-dimensional
architectures could lead to superior hosts for the encapsulation
and catalytic transformation of various substrates with high
selectivity and reactivity. It is now clear that the advancement of
such NHC-based materials would be facilitated if a rich library
Received: March 16, 2017
© XXXX American Chemical Society
A
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a
of bridging scaffolds of various sizes and shapes is available. For
example, the synthesis of new supramolecular hosts of
controlled size and shapes depends on the availability of new
multitopic architectures where each donor moiety functions
independently of one another and where the distance between
the donor moieties can be easily controlled.
Scheme 1. Synthetic Procedure for 6
While early efforts have been made to explore the chemistry
of neutral multitopic nonchelating NHCs, limited progress has
been made in the development of their anionic counterparts.
Our group has recently introduced the first stable dianionic
Janus-type bis(maloNHC) (H) (Dipp = (2,6-diisopropyl)-
phenyl).1h This carbene is composed of two linearly opposed
NHCs connected by a common p-phenylene fragment. In
contrast to carbenes A−G, all of which are neutral ligands,
carbene H contains two remote anionic functionalities
(malonate moieties) within the heterocyclic backbone, which
translates to a 2− overall charge of the ligand. By displacement
of other anionic ligands (e.g., halides) from various transition
metal precursors, this carbene leads to neutral biszwitterionic
species, novel architectures that are not accessible from their
neutral counterparts. Due to their unique electronic makeup, it
is expected that these zwitterionic NHC-metal species would
exhibit potentially valuable advantages such as enhanced
catalytic activity and solubility relative to the classical cationic
metal complexes of the neutral NHCs.
a
Reaction conditions: (a) diethyl malonate, 5 mol % CuI, 10 mol % 2-
picolinic acid, Cs2CO3, dioxane, room temperature; (b) NaOH,
methanol, 0 °C; (c) HCl; (d) PCl5, dichloromethane, room
temperature; (e) N,N′-bis(2,6-diisopropylphenyl)formamidine, di-
chloromethane, 0 °C; (f) Et3N, 0 °C, 3 h; (g) 1,4-benzenediboronic
acid, K3PO4, XPhosPdG3.
Herein we report the synthesis and characterization of a new
bis(maloNHC), 1. This carbene has the two linearly opposed
NHCs bridged by a common p-terphenylene fragment. While
the bis(NHC) ligand H can establish a separation between the
two carbene centers of 11.5 Å, the new bis(NHC) 1 displays a
significantly larger separation of 20.0 Å. To our knowledge, this
nanosized ligand is the longest among all previously reported
biscarbenes. Due to its higher conformational mobility over the
planar, conjugated ligands A−G, this rod-like bis(maloNHC) is
a promising candidate as building block for a large variety of
homo- and heterobimetallic complexes, MCOPs, and supra-
molecular assemblies. Its coordination to two different coinage
metals (gold and silver) is detailed herein.
Figure 1. Solid-state molecular structure of 6 with 50% probability
ellipsoids. Hydrogen atoms and solvent molecules have been omitted
for clarity. Only one of the two unique half-molecules in the
asymmetric unit is depicted. Selected bond lengths (Å) and angles
(deg): C1−N1 1.316(3), C1−N2 1.312(3), N2−C2 1.457(2), N1−C4
1.467(2), C3−C4 1.417(3), C2−C3 1.424(3), C4−O2 1.224(2), C2−
O1 1.225(2), N1−C1−N2 122.19(18).
RESULTS AND DISCUSSION
■
Five steps were necessary to access the zwitterionic salt
precursor 6 (Scheme 1). Initially, diethyl 4-bromophenyl-
malonate (2) was obtained through a copper-catalyzed α-
arylation of diethyl malonate with commercially available 1-
bromo-4-iodobenzene. Hydrolysis of 2 with NaOH in
methanol led to 2-(4-bromophenyl)propanedioic acid in 70%
yield. Conversion of 3 to its corresponding acyl halide 4,
each pyrimidine ring and by 37.61(10)° relative to the central
benzene ring 2. The central benzene ring 2 is nearly in-plane
(8.73(15)°) with the pyrimidine rings. The average N−C1
distance (1.314 Å) and the N1−C1−N2 angle (122.19(18)°)
determined are similar to those reported for the NHC·H+
precursor of carbene H (1.311 Å and 122.0(6)°, respectively).1h
The long C−N amidic bonds (N2−C2 1.457(2) Å and N1−C4
1.467(2) Å) are likely a result of the competitive delocalization
of the negative charge over the C4−C3−C2 fragment and of
the positive charge over the N1−C1−N2 fragment.
Once bisazolium salt 6 was characterized, subsequent efforts
were focused on exploring the synthesis and characterization of
the target carbene 1. In an NMR experiment, 6 was dissolved in
THF-d8 and treated with potassium bis(trimethylsilyl)amide
(KHMDS). The NMR signals of 6 dissapeared, but no signals
for the carbene 1 were observed, an indication of poor
solubility of 1 in THF. The same experiment was then
attempted in DMSO-d6 (Scheme 2). The reaction proceeded
cleanly to afford the free carbene 1, which was sufficiently stable
to be analyzed by NMR spectroscopy. The 13C NMR spectrum
of 1 revealed a characteristic signal at δ 242.5 ppm (DMSO-d6),
followed by coupling of
4 with N,N′-bis(2,6-
diisopropylphenyl)formamidine led to the zwitterionic salt 5
in 97% yield. Salt 5 was then utilized as the starting material in
a palladium-catalyzed Suzuki coupling reaction with benzene-
1,4-diboronic acid to obtain the desired zwitterionic precursor 6
in 83% yield. The 1H and 13C NMR spectra of 6 are consistent
1
with the proposed structure. In the H NMR spectrum, the
azolium proton apears at δ 8.18 ppm in CDCl3, while the 13C
shift of the NCN carbon appears at δ 147.6 ppm.
The molecular structure of 6 was unambigously determined
by single-crystal X-ray diffraction (Figure 1). X-ray quality
crystals were obtained by slow evaporation of a saturated
toluene solution of 6 at room temperature. The asymmetric
unit contains two unique half-molecules. They are closely
related, seemingly differing only by a slight twisting. The
benzene rings 1 (Scheme 1) are twisted by 32.06(9)° relative to
B
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a
Scheme 2. Synthetic Procedures for 1 and 7
Scheme 3. Synthesis of Bimetallic Complexes 8 and 9
a
Reaction conditions: (a) KHMDS, THF, room temperature; (b) for
8: PPh3AuCl, THF, room temperature; for 9: PPh3AgOTf, THF, room
temperature.
exhibits its carbene carbon resonance as a doublet at δ 202.1
ppm (JP−C = 119.8 Hz), comparable to that displayed by the
corresponding gold complex of H (δ 199.8 ppm, JP−C = 120.1
Hz).1h The carbene signal of 9 in the 13C spectrum was not
detected, a result of much lower solubility of 9 and the expected
multiplicity of the resonance arising from coupling with not
only the phosphorus atom of PPh3 but also the two isotopes of
silver (107Ag and 109Ag).
Single crystals of 8 and 9 suitable for X-ray crystallographic
structure determinations were grown by slow evaporation of
saturated solutions of 8 and 9 in a mixture of dichloromethane/
toluene. Both structures are isostructural (Figures 3 and 4), and
a 94.9 ppm downfield shift relative to 6. All attempts to grow X-
ray quality crystals of 1 were not successful.
The corresponding thione 7 was formed by deprotonation of
6 with KHMDS in the presence of excess sulfur (Scheme 2). In
the 13C NMR spectrum of thione 7, the signal for the N2CS
carbon appears at δ 176.5 ppm (DMSO-d6), a chemical shift
typically seen in this class of compounds. A single crystal of 7
suitable for X-ray crystallographic structure determination was
grown by slow diffusion of diethyl ether into a saturated
acetonitrile solution of 7. X-ray crystallographic data revealed
that the potassium atoms bridge the oxygen atoms of
neighboring thione molecules (Figure 2 and the crystal paking
Figure 3. Solid-state molecular structure of 8 with 50% probability
ellipsoids. Hydrogen atoms and solvent molecules have been omitted
for clarity. Selected bond lengths (Å) and angles (deg): Au1−C1
2.057(5), Au1−P1 2.2872(13), C1−N1 1.337(6), C1−N2 1.339(6),
N2−C2 1.453(6), N1−C4 1.450(6), C3−C4 1.408(7), C2−C3
1.404(7), C4−O2 1.232(6), C2−O1 1.220(7), P1−Au1−C1
171.21(13), N1−C1−N2 116.6(4).
Figure 2. Solid-state molecular structure of 7 with 50% probability
ellipsoids. Hydrogen atoms and solvent molecules have been omitted
for clarity. Selected bond lengths (Å) and angles (deg): C1−S1
1.665(2), C1−N1 1.369(3), C1−N2 1.369(3), N2−C2 1.435(3), N1−
C4 1.424(3), C3−C4 1.403(3), C2−C3 1.404(3), C4−O2 1.240(3),
C2−O1 1.240(3), N1−C1−N2 115.68(18).
diagram in the Supporting Information), resulting in relatively
strong K−O bonds (2.6−2.7 Å). Additionally, the benzene
rings 1 are significantly more twisted (54.90(7)° relative to each
pyrimidine ring) in this structure than in its zwitterion
counterpart 6. This likely occurs in order to bring the π-
system of these rings into a bonding arrangement with the
potassium ions (K1−C6 = 3.215(2) Å). Rings 1 and 2 are
inclined at 30.48(11)° to one another, similar to 6, but in the
case of 7 it is an additive twisting that brings ring 2 into a nearly
perpendicular orientation (85.07(8)°) relative to the pyrimi-
dine rings.
Figure 4. Solid-state molecular structure of 9 with 50% probability
ellipsoids. Hydrogen atoms and solvent molecules have been omitted
for clarity. Selected bond lengths (Å) and angles (deg): Ag1−C1
2.124(4), Ag1−P1 2.3577(11), C1−N1 1.335(5), C1−N2 1.336(5),
N2−C2 1.440(5), N1−C4 1.446(5), C3−C4 1.415(6), C2−C3
1.417(6), C4−O2 1.231(5), C2−O1 1.229(6), P1−Ag1−C1
170.03(11), N1−C1−N2 117.2(4).
To investigate the nucleophilic behavior of 1, homobimetallic
complexes of gold and silver were targeted. The in situ
generated carbene 1 was treated with the phosphine-stabilized
precursors (Ph3PAuCl or Ph3PAgOTf) to yield the correspond-
ing complexes 8 and 9 in 71% and 72% yield, respectively
(Scheme 3). The complexes are air stable since they can be
purified by column chromatography on silica gel. The identity
of these complexes was confirmed by 1H and 13C NMR
spectroscopy, as well as elemental analysis. The gold complex 8
they crystallize in the same monoclinic space group C2/c. The
packing diagrams show large voids that are occupied by toluene
molecules. In both cases, only half of each molecule is unique.
The metal centers are coordinated in a linear fashion by the
carbene moieties and PPh3 (C1−Au1−P1 = 171.21(13)° and
C1−Ag1−P1 = 170.03(11)°). As expected, the N1−C1−N2
angles of 8 and 9 (116.6(4)° and 117.2(4)°, respectively) are
smaller than the corresponding angle of the zwitterionic salt 6
C
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65 h. The reaction mixture was allowed to cool, and 25 mL of a
saturated aqueous solution of ammonium chloride was added. The
reaction mixture was extracted with ethyl acetate. The organic layer
was washed with deionized water, dried over sodium sulfate, and
filtered. The solvent was removed in vacuo. The crude product was
purified by column chromatography (silica, 4:7 hexanes/DCM) to
afford 2 as a colorless oil in 70% yield (7.0 g). The NMR spectra are in
accord with the previously published data.8 1H NMR (CDCl3, 300
MHz): δ 7.50 (d, J = 8.4 Hz, 2H, Ar-CH), 7.29 (d, J = 8.4 Hz, 2H,
Ar-CH), 4.56 (s, 1H, CH(CO2Et)2), 4.22 (m, 4H, CH2CH3), 1.26 (t,
3J = 7.1 Hz, 6H, CH3). 13C{1H} NMR (CDCl3, 75.5 MHz): δ 167.7
(C-O), 131.8, 131.7, 131.0, 122.5, 61.9, 57.3, 14.0. Anal. Calcd for
C13H15O4Br: C, 49.54; H, 4.80. Found: C, 49.64; H, 4.88.
(122.19(18)°). The Au−C1 and Ag−C1 bond distances are
2.057(5) and 2.124(4) Å, respectively, and they are comparable
to those reported for the corresponding metal complexes of H
(Au: 2.027(7); Ag: 2.110(6) Å).1h The arrangement of the
central ring structure in 8 and 9 closely resembles that of 6. The
benzene rings 1 are twisted by 35.28(14)° relative to each
pyrimidine ring in 8 and 35.21(12)° in 9. Ring 2 is inclined at
7.67(4)° and 7.59(3)° relative to the pyrimidine rings in 8 and
9, respectively. Furthermore, the new ligand places the two
metal centers at a distance of 24.2 Å, about 8.5 Å longer than its
analogue, carbene H. The longest Janus-type carbene reported
previously in the literature, carbene G, displays an intra-
molecular distance between the two carbene centers of 18.4 Å
and a gold−gold distance of 22.4 Å.1i
3
3
Synthesis of 3. Diethyl 4-bromophenylmalonate (2.16 g, 6.85
mmol) was dissolved in methanol (11.6 mL), and the solution was
cooled to 0 °C. An ice cold solution of sodium hydroxide (0.81 g, 20.3
mmol) in deionized water (11.6 mL) was added dropwise to the
stirring solution of diethyl 4-bromophenylmalonate. The reaction
mixture was stirred for 2 h at room temperature. The solvent was
removed, and the remaining aqueous layer was washed with diethyl
ether and acidified to pH 1 by dropwise addition of concentrated HCl
at 0 °C. The product was extracted with ethyl acetate. The organic
layer was washed with acidified brine and dried over sodium sulfate.
The solvent was removed in vacuo. The resulting white solid was
purified by trituration with dichloromethane (5 times) and pentane (2
times) to afford the title compound 3 as a white solid (1.25 g, 70%
yield). The product contains trace amounts of 4-bromophenylacetic
CONCLUSIONS
■
In summary, this paper describes the synthesis and character-
ization of a new dianionic bis(maloNHC), 1. The correspond-
ing thione was generated by the reaction of 1 with an excess of
sulfur. The utility of this carbene as a bridging ligand in
organometallic chemistry has been demonstrated by its
incorporation in two new dinuclear gold and silver complexes
(8 and 9). These zwitterionic complexes have been fully
characterized by spectroscopic techniques and X-ray crystallog-
raphy. They exhibit a remarkably long metal-to-metal through-
space distance of 24.2 Å, to our knowledge the longest distance
reported so far for a Janus-type bis(NHC) ligand. With its
unique topological properties, this system has the potential to
serve as building blocks for the preparation of novel metal−
organic frameworks such as supramolecular cages and organo-
metallic polymers, systems not accessible with the current
arsenal of neutral Janus-type bis(NHC)s. Further studies aimed
at the construction of such supramolecular systems are under
way in our laboratory.
1
acid, and it decarboxylates slowly in solution. H NMR (DMSO-d6,
300 MHz): δ 13.04 (s, COOH) 7.56 (d, 3J = 8.4 Hz, 2H, Ar-CH), 7.35
3
(d, J = 8.4 Hz, 2H, Ar-CH), 4.71 (s, 1H, CH(CO2H)2).
Synthesis of 5. A mixture of the carboxylic acid 3 (0.050 g, 0.19
mmol) and PCl5 (0.082 g, 0.39 mmol) in anhydrous DCM (1 mL)
was stirred at room temperature for 2 h under argon. The reaction
mixture was then concentrated to dryness under reduced pressure. To
the resulting crude acyl halide 4 were added N,N′-bis(2,6-
diisopropylphenyl)formamidine (0.104 g, 0.285 mmol) and 2 mL of
anhydrous DCM at 0 °C. The reaction mixture was allowed to stir at 0
°C for 30 min. Et3N (0.054 mL, 0.39 mmol) was added gradually over
the course of 10 min. The mixture was stirred for 3 h at 0 °C, and the
volatiles were removed in vacuo. The resulting deep yellow solid was
triturated with water, filtered, and purified by column chromatography
(silica, DCM) to afford the title compound 5 as a bright yellow solid
EXPERIMENTAL SECTION
■
General Methods. All reactions, unless otherwise noted, were
performed using standard Schlenk techniques under an atmosphere of
argon or in a nitrogen-filled gloxebox. Glassware was dried at 180 °C
in an oven for at least 12 h prior to use. Reagents were purchased from
commercial sources and used as supplied. THF was distilled from
sodium/benzophenone. Dry dichloromethane (DCM) was purchased
from Aldrich and used as received. N,N′-Bis(2,6-diisopropylphenyl)-
formamidine was prepared following known methods.7 Column
chromatography was performed using the solvent systems indicated
1
(0.11 g, 97% yield); mp >250 °C. H NMR (CDCl3, 300 MHz): δ
3
3
8.18 (s, 1H, NCHN), 7.93 (d, J = 8.6 Hz, 2H, Ar-CH), 7.48 (d, J =
7.3 Hz, 2H, Ar-CH), 7.44 (t, 3J = 8.6 Hz, 2H, Ar-CH), 7.29 (d, 3J = 7.8
Hz, 4H, Ar-CH), 2.85 (sept, 3J = 6.6 Hz, 4H, CH(CH3)2), 1.31 (d, 3J =
6.7 Hz, 12H, CH3), 1.22 (d, J = 6.8 Hz, 12H, CH3). 13C{1H} NMR
3
(CDCl3, 75.5 MHz): δ 158.5 (C-O), 147.9 (NCHN), 145.8, 133.2,
132.0, 131.9, 131.2, 130.5, 124.6, 119.5, 97.7 (C-CO), 29.4
(CH(CH3)2), 24.3 (CH3). 13C{1H} NMR (THF-d8, 75.5 MHz): δ
159.7 (C-O), 152.4 (NCHN), 147.6, 136.3, 134.5, 133.3, 131.7, 130.9,
125.5, 119.3, 97.0 (C-CO), 30.7 (CH(CH3)2), 24.9 (CH3), 24.8
(CH3). FT-IR (solid ATR): 3051, 2965, 2925, 2870, 1663 (CO),
1598, 1486, 1460, 1322, 1262, 1056, 1005, 932, 807, 763 cm−1. Anal.
Calcd for C34H39O2N2Br: C, 69.50; H, 6.69; N, 4.77. Found: C, 69.29;
H, 6.65; N, 4.75.
1
on silica gel (63−200 μm) or basic alumina (Act.1 50−200 μm). H,
13C, and 31P NMR spectra were recorded using a Bruker DPX 300
MHz spectrometer. Chemical shifts are reported in ppm and are
referenced to internal SiMe4 (1H and 13C) or external H3PO4 (31P).
Solid-state infrared spectra of 5−9 were recorded on a PerkinElmer
Frontier FT-IR/NIR spectrometer. Elemental analyses were per-
formed at Atlantic Microlab (Norcross, GA, USA). Single-crystal X-ray
diffraction measurements were performed using a Bruker D8 Venture
diffractometer with an Incoatec microfocus source and a Photon 100
CMOS detector. Diffraction data for compounds 6−9 were collected
under nitrogen at 100 K using Mo Kα (λ = 0.71073 Å) radiation. The
purity of all new compounds was determined by elemental analysis,
except for compounds 1 and 3, for which the purity was inferred by 1H
and 13C NMR spectroscopy.
Synthesis of 2. In the drybox, a 250 mL oven-dried pressure flask
was charged with 1-bromo-4-iodobenzene (9.00 g, 31.8 mmol), copper
iodide (0.303 g, 1.59 mmol), 2-picolinic acid (0.439 g, 3.56 mmol),
and cesium carbonate (31.24 g, 95.86 mmol). Anhydrous 1,4-dioxane
(31.9 mL) was added to the reaction flask, followed by distilled diethyl
malonate (4.85 mL, 31.8 mmol). The reaction was heated to 94 °C for
Synthesis of 6. Zwitterion 5 (0.50 g, 0.85 mmol), 1,4-
benzenediboronic acid (0.071 g, 0.43 mmol), K3PO4 (0.181 g, 0.853
mmol), and XPhosPdG3 (0.067 g, 0.078 mmol) were added to a
pressure tube under inert conditions. Anhydrous 1,4-dioxane (8 mL)
was added to the reaction flask under argon. Degassed water (1.6 mL)
was added, and the reaction was allowed to stir for 15 h at 60 °C. The
volatiles were removed in vacuo, and the resulting yellow solid was
purified by column chromatography (silica, gradient of 1:3 hexanes/
EtOAc, then 4:3 hexanes/EtOAc) to yield the title compound 6 in
83% yield (0.38 g); mp >250 °C. 1H NMR (CDCl3, 300 MHz): δ 8.18
3
(s, 2H, NCHN), 8.14 (d, J = 8.6 Hz, 4H, Ar-CH), 7.66 (s, 4H, Ar-
3
3
CH), 7.61 (d, J = 8.6 Hz, 4H, Ar-CH), 7.47 (t, J = 7.7 Hz, 4H, Ar-
3
3
CH), 7.30 (d, J = 7.7 Hz, 8H, Ar-CH), 2.90 (sept, J = 6.71 Hz, 8H,
3
3
CH(CH3)2), 1.33 (d, J = 6.7 Hz, 24H, CH3), 1.23 (d, J = 6.8 Hz,
D
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24H, CH3). 1H NMR (DMSO-d6, 300 MHz): δ 9.90 (s, 2H, NCHN),
7.87 (d, 3J = 7.94 Hz, 4H, Ar-CH), 7.75 (s, 4H, Ar-CH), 7.65 (d, 3J =
8.1 Hz, 4H, Ar-CH), 7.51 (t, 3J = 7.5 Hz, 4H, Ar-CH), 7.38 (d, 3J = 7.6
Hz, 8H, Ar-CH), 2.76 (sept, 3J = 6.5 Hz, 8H, CH(CH3)2), 1.21 (d, 3J =
3.2 Hz, 48H, CH3). 13C{1H} NMR (CDCl3, 75.5 MHz): δ 158.7 (C-
O), 147.6 (NCHN), 145.9, 140.3, 138.4, 133.2, 132.2, 131.1, 130.6,
127.5, 126.2, 124.6, 98.5 (C-CO), 29.4 (CH(CH3)2), 24.4 (CH3). FT-
IR (solid ATR): 2960, 2922, 2868, 1667 (CO), 1599, 1466, 1325,
1057, 1033, 1006, 821, 812, 805, 784, 764, 670 cm−1. Anal. Calcd for
C74H82O4N4: C, 81.43; H, 7.57; N, 5.13. Found: C, 81.15; H, 7.63; N,
5.04.
125.9, 124.4, 97.1 (C-CO), 29.4 (CH(CH3)2), 24.6 (CH3), 24.3
(CH3). 31P NMR (CDCl3, 121.49 MHz): δ 39.2. FT-IR (solid ATR):
3448, 3052, 3027, 2959, 2922, 2867, 2162, 1615 (CO), 1481, 1436,
1383, 1328, 1274, 1101, 826, 789, 745, 711, 692 cm−1. Anal. Calcd for
C110H110O4N4Au2P2: C, 65.80; H, 5.52; N, 2.79. Found: C, 65.78; H,
5.71; N, 2.79.
Synthesis of 9. A solution of KHDMS (0.100 g, 0.501 mmol) in
anhydrous THF (2 mL) was slowly added to a stirring suspension of 6
(0.100 g, 0.092 mmol) in anhydrous THF (8 mL). In a separate vial,
PPh3 (0.099 g, 0.38 mmol) and AgOTf (0.098 g, 0.38 mmol) were
stirred in anhydrous THF (2 mL). After 30 min, the latter solution was
added dropwise to the carbene suspension. The reaction mixture was
allowed to stir for 12 h, and the volatiles were removed in vacuo. The
product was dissolved in DCM and precipitated with diethyl ether.
The solid was then triturated with hexane in order to remove the
excess PPh3. The crude product was purified by column chromatog-
raphy (silica, 1:30 MeOH/DCM) to afford the yellow silver complex 9
in 72% yield (0.12 g). 1H NMR (CDCl3, 300 MHz): δ 8.25 (d, 4H, J =
8.5 Hz, Ar-CH), 7.64 (s, 4H, Ar-CH), 7.56 (d, 4H, J = 8.4 Hz, Ar-CH),
7.46 (td, 6H, 3JCC = 7.6 Hz, JCP = 1.8 Hz, Ar-CH), 7.30−7.40 (m, 16H,
CHPPh3 and Ar-CH), 7.22 (d, 3J = 7.7 Hz, 8H, Ar-CH), 6.86 (dd, 12H,
Synthesis of 1. A solution of KHDMS (0.021 g, 0.11 mmol) in
anhydrous THF (2 mL) was slowly added to a stirring suspension of 6
(0.026 g, 0.024 mmol) in anhydrous THF (3 mL). The carbene
precipitated out of solution. The reaction mixture was allowed to stir
for 45 min. The solvent was decanted, and the remaining solid was
washed with THF. The product was dried in vacuo to yield 0.021 g of 1
(76% yield). NMR experiment: In the drybox, precursor 6 (0.026 g,
0.024 mmol) was dissolved in about 1 mL of DMSO-d6, and KHDMS
(0.014 g, 0.070 mmol) was added directly to this NMR tube. The 13C
and 1H NMR spectra were recorded, and they supported the
1
formation of the carbene. H NMR (DMSO-d6, 300 MHz): δ 8.06
3
3JCC = 7.3 Hz, JCP = 12.5 Hz, CHPPh3), 3.11 (sept, J = 6.7 Hz, 8H,
(d, 3J = 8.1 Hz, 4H, Ar-CH), 7.68 (s, 4H, Ar-CH), 7.48 (d, 3J = 8.1 Hz,
3
3
CH(CH3)2), 1.29 (d, J = 6.8 Hz, 24H, CH3), 1.08 (d, J = 6.8 Hz,
24H, CH3). 13C{1H} NMR (CD2Cl2, 75.5 MHz): δ C2 not detected,
161.4 (d, J = 6.26 Hz), 146.9, 140.7 (d, J = 2.3 Hz), 140.4, 137.2,
136.2, 134.1 (d, J = 15.9 Hz), 132.1, 131.5, 129.7 (d, J = 10.8 Hz),
129.2, 128.6, 127.6, 125.9, 124.6, 97.0 (C-CO), 29.3 (CH(CH3)2),
24.7 (CH3), 24.6 (CH3). 31P NMR (CDCl3, 121.49 MHz): δ 18.3 (d +
d, J(31P−109Ag) = 538.8 Hz, J(31P−107Ag) = 466.8 Hz). FT-IR (solid
ATR): 3055, 3030, 2959, 2922, 2867, 1610 (CO), 1480, 1436, 1382,
1327, 1275, 1098, 843, 824, 787, 743, 692 cm−1. Anal. Calcd for
C110H110O4N4Ag2P2: C, 72.21; H, 6.06; N, 3.06. Found: C, 72.09; H,
6.22; N, 2.94.
3
3
4H, Ar-CH), 7.24 (t, J = 6.5 Hz, 4H, Ar-CH), 7.15 (d, J = 7.0 Hz,
8H, Ar-CH), 3.04 (sept. 3J = 6.5 Hz, 8H, CH(CH3)2), 1.15 (d, 3J = 6.5
Hz, 24H, CH3), 1.09 (d, J = 6.5 Hz, 24H, CH3). 13C{1H} NMR
3
(DMSO-d6, 75.5 MHz): δ 242.5 (NCN), 160.8 (C-O), 144.9, 141.6,
138.9, 138.2, 133.6, 130.3, 126.5, 126.4, 124.0, 122.5, 92.9 (C-CO),
27.8 (CH(CH3)2), 23.8 (CH3), 23.3 (CH3).
Synthesis of 7. A solution of KHDMS (0.033 g, 0.17 mmol) in
anhydrous THF (1 mL) was slowly added to a stirring suspension of 6
(0.050 g, 0.046 mmol) in anhydrous THF (4 mL). To the in situ
generated carbene was added excess sulfur (0.027 g, 0.84 mmol). The
reaction mixture was allowed to stir for 12 h at room temperature. The
solvent was removed in vacuo, and the crude product was dissolved in
acetonitrile and filtered through Celite to remove the excess sulfur.
The pale orange residue was purified by trituration with ether, hexanes,
and hot toluene. Thione 7 was obtained as an off-white solid in 69%
X-ray Crystallography. Single-crystal X-ray diffraction data were
collected using a Bruker D8 Venture diffractometer with Mo Kα (λ =
0.710 73 Å) radiation from an Incoatec microfocus source and a
Photon 100 CMOS detector. Data processing and scaling corrections
were performed using the Apex3 software suite (SAINT, SADABS
routines).9 Evaluation of the systematic absences led to unambiguous
space group determinations, and the structures were subsequently
solved by intrinsic phasic (SHELXT) and then refined by full-matrix
least-squares on F2 (SHELXL) using the SHELXTL software suite.10
All non-hydrogen atoms were refined anisotropically. Hydrogen atoms
attached to carbon atoms were placed geometrically using appropriate
riding models. During the structure refinements, the formula units of
compounds 6−9 were found to contain several solvent molecules. In
the case of compound 6, three toluene molecules were modeled
directly from the difference map, and additional toluene molecules
were found to be highly disordered in remaining structural voids. The
latter disordered solvent molecules were modeled using the
SQUEEZE algorithm of PLATON (286 total electrons present in
965 Å3 of voids, corresponding to 1.4 C7H8 per formula unit).11 In 7,
one acetonitrile solvent molecule per formula unit was found to be
coordinated to the potassium ion (half-occupancy based on evaluation
of the ADPs), and an additional two acetonitrile molecules were
disordered over several arrangements in the structural voids and
modeled using SQUEEZE (80 total electrons present in 610 Å3 of
voids). Compounds 8 and 9 both contained one toluene molecule per
formula unit, and these were modeled from the difference map. Data
from the structure refinements are included in the Supporting
Information.
1
3
yield (0.039 g). H NMR (DMSO-d6, 300 MHz): δ 7.97 (d, J = 8.2
3
Hz, 4H, Ar-CH), 7.68 (s, 4H, Ar-CH), 7.49 (d, J = 8.2 Hz, 4H, Ar-
CH), 7.23 (t, J = 7.3 Hz, 4H, Ar-CH), 7.14 (d, J = 7.3 Hz, 8H, Ar-
3
3
3
3
CH), 2.90 (sept, J = 6.5 Hz, 8H, CH(CH3)2), 1.20 (d, J = 6.5 Hz,
24H, CH3), 1.15 (d, 3J = 6.5 Hz, 24H, CH3). 13C{1H} NMR (DMSO-
d6, 75.5 MHz): δ 176.5 (NCN), 161.3 (C-O), 145.1, 138.9, 137.9,
137.7, 133.9, 130.1, 127.2, 126.5, 124.2, 122.9, 90.4 (C-CO), 28.6
(CH(CH3)2), 24.3 (CH3), 23.1 (CH3). FT-IR (solid ATR): 3393,
2963, 2869, 1699, 1579 (CO), 1395, 1302, 1120, 1055, 937, 804, 747,
670 cm−1. Anal. Calcd for C74H80O4N4S2K2·1.5CH2Cl2: C, 66.72; H,
6.15; N, 4.12. Found: C, 66.74; H, 6.43; N, 4.17.
Synthesis of 8. A solution of KHDMS (0.081 g, 0.41 mmol) in
anhydrous THF (1 mL) was slowly added to a stirring suspension of 6
(0.074 g, 0.068 mmol) in anhydrous THF (5 mL). AuCl(SMe2)
(0.086 g, 0.29 mmol), PPh3 (0.079 g, 0.30 mmol), and anhydrous
THF (2 mL) were stirred in a separate vial to ensure the
precoordination of PPh3 to the gold center. After 30 min, the latter
solution was added dropwise to the carbene suspension. The reaction
mixture was allowed to stir for 12 h. THF was removed in vacuo. The
resulting solid was dissolved in DCM and filtered. Hexane was then
added to precipitate the product. The crude product was purified by
column chromatography (silica, 1:30 MeOH/DCM) to afford the gold
1
complex 8 as a yellow solid (0.097 g, 71% yield). H NMR (CDCl3,
300 MHz): δ 8.24 (d, 4H, J = 8.5 Hz, Ar-CH), 7.63 (s, 4H, Ar-CH),
7.55 (d, 4H, J = 8.6 Hz, Ar-CH), 7.46 (td, 6H, 3JCC = 7.4 Hz, JCP = 1.8
3
Hz, Ar-CH), 7.28−7.42 (m, 16H, CHPPh3 and Ar-CH), 7.21 (d, J =
3
ASSOCIATED CONTENT
7.7 Hz, 8H, Ar-CH), 6.86 (dd, 12H, JCC = 6.8 Hz, JCP = 12.9 Hz,
■
CHPPh3), 3.04 (sept. 3J = 6.7 Hz, 8H, CH(CH3)2), 1.27 (d, 3J = 6.8 Hz,
24H, CH3), 1.09 (d, 3J = 6.8 Hz, 24H, CH3). 13C{1H} NMR (CD2Cl2,
75.5 MHz): δ 202.1 (d, J = 119.8 Hz, NCN), 161.3 (d, JCP = 3.7 Hz),
147.1, 140.4, 138.7, 137.4, 135.9, 134.4 (d, JCP = 13.9 Hz), 132.4 (d,
JCP = 11.1 Hz), 131.4, 129.6 (d, JCP = 11.6 Hz), 129.0, 128.3, 127.6,
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00206.
E
DOI: 10.1021/acs.organomet.7b00206
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Dalton Trans. 2009, 7215−7222. (c) Radloff, C.; Weigand, J. J.; Hahn,
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(f) Schmidtendorf, M.; Pape, T.; Hahn, F. E. Angew. Chem., Int. Ed.
NMR spectra of compounds 2, 3, 5−9 and crystallo-
graphic information on 6−9 (PDF)
X-ray crystallographic data for compounds 6−9 (CIF)
Optimized Cartesian coordinates (XYZ)
(XYZ)
(XYZ)
(XYZ)
2012, 51, 2195−2198. (g) Conrady, F. M.; Frohlich, R.; Schulte to
̈
Brinke, C.; Pape, T.; Hahn, F. E. J. Am. Chem. Soc. 2011, 133, 11496−
11499.
(4) (a) Mercs, L.; Neels, A.; Albrecht, M. Dalton Trans. 2008, 5570−
5576. (b) Viciano, M.; Sanau, M.; Peris, E. Organometallics 2007, 26,
́
AUTHOR INFORMATION
Corresponding Author
*E-mail: dtapu@kennesaw.edu.
ORCID
Daniela Tapu: 0000-0003-4432-1976
Notes
The authors declare no competing financial interest.
Crystallographic details were deposited at the Cambridge
Crystallographic Data Centre, Cambridge, UK. The reference
numbers are 1534519 (6·xC7H8), 1534520 (7·3C2H3N),
1534521 (8·C7H8), and 1534522 (9·C7H8).
■
6050−6054. (c) Zanardi, A.; Mata, J. A.; Peris, E. Organometallics
2009, 28, 1480−1483. (d) Zanardi, A.; Mata, J. A.; Peris, E. J. Am.
Chem. Soc. 2009, 131, 14531−14537. (e) Nussbaum, M.; Schuster, O.;
Albrecht, M. Chem. - Eur. J. 2013, 19, 17517−17527. (f) Schuster, O.;
Mercs, L.; Neels, A.; Albrecht, M. Chimia 2010, 64, 184−187.
́
(5) (a) Zanardi, A.; Corberan, R.; Mata, J. A.; Peris, E.
Organometallics 2008, 27, 3570−3576. (b) Mata, J. A.; Hahn, F. E.;
Peris, E. Chem. Sci. 2014, 5, 1723−1732. (c) Peris, E. Chem. Commun.
2016, 52, 5777−5787.
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ACKNOWLEDGMENTS
■
(9) Apex3; Bruker AXS Inc., Madison, WI, 2015. CrystalClear; Rigaku
and Molecular Structure Corporation: The Woodlands, TX, 2006.
(10) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112−122.
This material is based upon work supported by the National
Science Foundation under CHE-1464281 to D.T. C.M.
acknowledges an internal grant from the CU office of the
VPR enabling the purchase of the Bruker diffractometer.
Dedicated to Professor Anthony J. Arduengo, III, on the
occasion of his 65th birthday.
(11) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7−13.
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DOI: 10.1021/acs.organomet.7b00206
Organometallics XXXX, XXX, XXX−XXX