Toward molecular rotors: Tetra-N-heterocyclic carbene Ag(i)-halide cubane-type clusters

Article abstract of DOI:10.1039/c3dt32862g

1,3-Bis(3′-butylimidazol-1′-yl)benzene diiodide (2a), 1,3-bis(3′-but-3′′-enyl-imidazolium-3′-yl)benzene diiodide (2b), 1,3-bis(3′-pent-4′′-enyl-imidazolium-3′- yl)benzene diiodide (2c), 1,3-bis(4′-butyl-1′,2′,4′- triazolium-1′-yl)benzene diiodide (2d), or

Full text of DOI:10.1039/c3dt32862g

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Toward molecular rotors: tetra-N-heterocyclic carbene
Ag(I)-halide cubane-type clusters†
Cite this: Dalton Trans., 2013, 42, 7338
Wesley D. Clark,a Ginger E. Tyson,a T. Keith Hollis,*a Henry U. Valle,a
Edward J. Valente,b Allen G. Oliverc and Matthew P. Dukesa
1,3-Bis(3’-butylimidazol-1’-yl)benzene diiodide (2a), 1,3-bis(3’-but-3’’-enyl-imidazolium-3’-yl)benzene
diiodide (2b), 1,3-bis(3’-pent-4’’-enyl-imidazolium-3’-yl)benzene diiodide (2c), 1,3-bis(4’-butyl-1’,2’,4’-tri-
azolium-1’-yl)benzene diiodide (2d), or 1,3-bis(4’-butyl-1’,2’,4’-triazolium-1’-yl)benzene dibromide (2e)
was reacted with Ag2O yielding unprecedented tetra-N-heterocyclic carbene-Ag(I)-X cubane-type clus-
ters. These were characterized by 1H and 13C NMR spectroscopy, ESI-TOF MS, elemental analysis, and
X-ray crystallography. Results from VT 13C NMR spectroscopy and cross-over experiments are consistent
with intramolecular exchange suggesting that the Ag(I) complexes are molecular rotors.
Received 29th November 2012,
Accepted 25th January 2013
DOI: 10.1039/c3dt32862g
www.rsc.org/dalton
synthesis of liquid crystals,9 and as catalytic reagents for the
preparation of 1,2-bis(borate) esters10 and for the ring-opening
Introduction
The first Ag(I)–NHC complex was prepared by deprotonation of polymerization (ROP) of L-lactides.11 Furthermore, they have
the imidazolium salt and reaction with a Ag(I) source.1 The dis- been proven useful in transmetallation to many late transition
closure of the Ag2O synthetic methodology by Lin and Wang metals such as Cu,12,13 Ni,14 Pd,15 Pt,16 Au,17 and Rh.12
led to numerous reports of Ag(I)–NHC complexes.2–4 Ag(I)–
The same properties that gave Ag(I)–NHC complexes unique
NHC complexes are mostly unreactive with air and water which applications in the biomedical field, catalysis and transmetal-
simplifies their synthesis, isolation, and characterization. This lation made them good candidates for incorporation into
persistence in the presence of air and water permits unique supramolecular architectures.18 However, Ag(I)–NHC com-
applications in the biomedical field.4 Ag(I)–NHC complexes of plexes have received little attention in this field.18,19 Only a few
a caffeine derivative were recently shown to be effective against Ag(I) complexes are known to form supramolecular architec-
a variety of respiratory pathogens.5 A recent report illustrated tures, demonstrating coordination polymers in the solid
the use of Ag(I)–NHC complexes against fungi, gram-positive state.18,20,21 Additionally, while organic and inorganic
and gram-negative bacteria.6 Anticancer activity of Ag(I)–NHC examples of molecular rotors are known, to our knowledge no
complexes against ovarian (OVCAR-3) and breast (MB157) molecular rotors with NHC ligands have been reported.22 We
cancers has also been reported.7 They were also reported to be report the synthesis and characterization of the first series of
precursors to Ag nanoparticles, which have been shown to tetra-NHC-Ag(I)-X cubane clusters, which contain a distorted
inhibit HIV-1 replication.8 In addition to their biomedical cubical core in the solid state. VT 13C NMR and cross-over
applications, Ag(I)–NHC complexes have shown promise in the experiments are consistent with intramolecular Ag–C
exchange.
aDepartment of Chemistry and Biochemistry, The University of Mississippi, 407
Coulter Hall, University, MS 38677, USA. E-mail: hollis@olemiss.edu;
Results and discussion
Fax: +1 662 915 7300; Tel: +1 662 915 5337
bDepartment of Chemistry, University of Portland Diffraction Facility, 112A Swindells
Hall, University of Portland, Portland, OR 97203, USA. E-mail: valentee@up.edu;
Tel: +1 503 943 7389
Synthesis and characterization
1,3-Bis(imidazol-1′-yl)benzene (1a)23 and 1,3-bis(1′,2′,4′-triazol-
1′-yl)benzene (1b) were synthesized in good yields using
copper-catalyzed coupling of the desired heterocycle and 1,3-
dibromobenzene. The isolation procedure was improved with
filtration through basic alumina, which eliminated the need
for silica-gel chromatography. Compounds 1a and 1b were
treated with haloalkanes to produce various salts (2a–2e) in
good to excellent yields. The salts were reacted with Ag2O
cDepartment of Chemistry and Biochemistry, University of Notre Dame, 246B
Nieuwland Hall, Notre Dame, IN 46556, USA. E-mail: aoliver2@nd.edu;
Tel: +1 574 631 5935
†Electronic supplementary information (ESI) available: CIF files, tables, VT 13C
NMR spectra, NMR spectra, ESI-TOF MS data, and figures giving crystallographic
data for complexes 3a–3e. CCDC 912930 (3e), 912931 (3d), 921155 (3b), 912933
(3c) and 868624 (3a). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3dt32862g
7338 | Dalton Trans., 2013, 42, 7338–7344
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Scheme 1 Synthesis of Ag(I)-NHC cubane clusters 3a–3e.
yielding free-flowing, white powders (3a–3e, Scheme 1) in good
to excellent yields. The loss of the imidazolium proton signals
at δ 11–12 in the 1H NMR spectra, and the appearance of NHC
signals at δ 180–188 in the 13C NMR spectra were consistent
with the formation of Ag(I)–NHC complexes.
The ESI-TOF MS of the white powders provided more
evidence that a Ag(I)–NHC complex had been formed. The
[M + H]+ ion for compound 2a was observed within 7 ppm of
the calculated value. Many fragments of complexes 3a–3e were
observed, all of which had excellent correlation between the
experimental values and the predicted values. This confirmed
the presence of the Ag(I)–NHC complexes 3a–3e in solution.
Scheme 2 Ions observed in HR ESI-MS.
X-ray crystallography
Crystals suitable for X-ray diffraction were grown for complexes
3a–3e. ORTEP illustrations of the X-ray structures of complexes
3a–3e are illustrated in Fig. 1–5. An alternative perspective on
the “Ag-X-cubane structure” is as a tetra-capped Ag-tetra-
hedron. The ORTEP illustrations in Fig. 1–5 are drawn in this
manner for clarity. The Ag–Ccarbene bond distances vary slightly
(≤0.040 Å). The Ag–I bond lengths are similar to other Ag–I
cubanes.24 The Ag–Ag distances vary significantly. Ag–Ag dis-
tances shorter than the sum of the van der Waals radii (3.44 Å)
are considered evidence for “argentophilic” interactions.25
Complexes 3a, 3d, and 3e may have argentophilic interactions
between Ag1–Ag2 and Ag3–Ag4 as their distances are short
enough for Ag–Ag interactions to occur (Table 1).25 Complex
Supramolecular building blocks
Although the [M + H]+ peak for complex 3a was observed in
ESI-TOF MS it represents only a small fraction of the ions
observed. Other complexes observed in ESI-TOF MS of
complex 3a are shown in Scheme 2. The [M − I]+ fragment for
all complexes was observed with excellent correlation between
the calculated and observed isotopic distributions. The com-
plexes observed included the monomeric complex 4, bis-
carbene complex 5, and the supramolecular complex 6.
Complex 4 was observed via two fragments: [4 − I]+ and
[4 − AgI + H]+. Complex 5 is of the “bis-carbene salt” type and
these types of fragments are found in the MS of most Ag(I)–
NHC complexes.20
Three fragments of complex 5 were observed: [5 + H]+,
[5 − I]+, and [5 − 2I]2+. Five fragments of complex 6 were
observed by losses of AgI and I. This phenomenon is not
limited to complex 3a. Complexes 3b–3d also exhibit this
occurrence. This data confirms that complexes 3a–3d are pre-
cursors to supramolecular building blocks. Supramolecular
complexes, like complex 6, were not observed for AgBr complex
3e. Expansions of each individual fragment along with its
calculated spectra are given in the ESI.†
Fig. 1 ORTEP diagram of imidazolyl-AgI complex 3a with hydrogens omitted
for clarity. Thermal ellipsoids are shown at 50% probability. Selected bond
lengths are given in Table 1. Selected bond angles (°): Ag1–I1–Ag2 61.047(5),
Ag1–I2–Ag2 63.318(5), Ag1–I1–Ag3 81.227(5), Ag1–I2–Ag4 71.522(6), I1–Ag2–
I2 118.866(7).
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Fig. 5 ORTEP diagram of triazolyl-AgBr complex 3e with hydrogens omitted
for clarity. Thermal ellipsoids are shown at 20% probability. Selected bond
lengths are given in Table 1. Selected bond angles (°): Ag1–Br1–Ag2 65.86(4),
Ag1–Br2–Ag2 65.86(4), Ag1–Br1–Ag3 83.35(4), Ag1–Br2–Ag4 87.64(4), Br1–
Ag2–Br2 108.33(4).
Fig. 2 ORTEP diagram of imidazolyl-AgI complex 3b with hydrogens omitted
for clarity. Thermal ellipsoids are shown at 50% probability. Selected bond
lengths are given in Table 1. Selected bond angles (°): Ag1–I1–Ag2 62.769(13),
Ag1–I2–Ag2 58.653(12), I1–Ag2–I2 121.188(15).
3b and 3c may also have argentophilic interactions between
Ag1–Ag2 and Ag1i–Ag2i. The Ag–I–Ag bond angles are acute
whereas the I–Ag–I angles are obtuse, which is in agreement
with other Ag–I cubanes.24
13C NMR studies
Ag has two spin 1/2 NMR active isotopes of roughly equal pro-
portions (107Ag 51.8% and 109Ag 49.2%). Consequently, the
13
predicted
C
carbene
resonance would be two doublets as was
recently reported at low temperatures.26 However, like many
13
other Ag(I)–NHC complexes, the
C
carbene
peaks were singlets
for complexes 3a–3e.20 This phenomenon in the past has been
attributed to the rapid metal exchange at the Ag(I)–NHC
bond.2
Fig. 3 ORTEP diagram of imidazolyl-AgI complex 3c with hydrogens omitted
for clarity. Both occupations of the pentenyl chain are shown. Thermal ellipsoids
are shown at 50% probability. Selected bond lengths are given in Table 1.
Selected bond angles (°): Ag1i–I1–Ag2 79.61(3), Ag1i–I1–Ag1 79.53(3), I1–Ag2–
I2i 93.31(3).
Since the possibility of intermolecular and intramolecular
13C–107/109Ag exchange for complexes 3a–3e exists, several
experiments were performed to examine the 13C–107/109Ag
13
exchange. The concentration dependence of the
C
carbene
signal for imidazolyl complex 3a was found to be negligible in
DMSO-d6. In an attempt to generate the mixed triazolyl/imid-
azolyl cluster in a statistical fashion, the Ag metallation was
carried out with an equimolar mixture of 2a and 2d (see
Experimental section). The spectral data were consistent with
the formation of the homoleptic complexes only. No signals
assignable to the mixed triazolyl/imidazolyl complex were
observed. Additionally crossover experiments were used to test
for intermolecular exchange. Imidazolyl complex 3a and tri-
azolyl complex 3d were combined in DMSO-d6 in varying
13
proportions. The
C
shifts for triazolyl complex 3d were
carbene
13
very small (≤0.14 ppm). The
C
signal for imidazolyl
carbene
complex 3a shifted slightly when exposed to complex 3d. The
largest shift (Δδ = 0.45 ppm) occurred when the two were mixed
Fig. 4 ORTEP diagram of triazolyl-AgI complex 3d with hydrogens omitted for
clarity. Thermal ellipsoids are shown at 25% probability. Selected bond lengths
are given in Table 1. Selected bond angles (°): Ag1–I1–Ag2 63.45(2), Ag1–I2–
Ag2 61.86(2), I1–Ag2–I2 118.95(3).
13
in equal amounts, yet the triazolyl
C
carbene
chemical shift
remained unchanged (see ESI†). These data are not consistent
with intermolecular exchange.
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Table 1 Selected interatomic distances
3a, X = I
3b, X = I
3c, X = I
3d, X = I
3e, X = Br
Ag1–Ag2
3.0566(2)
3.7790(2)
3.4248(2)
3.7978(2)
3.1275(2)
2.9552(2)
2.9259(2)
2.8976(2)
2.8332(2)
2.164(2)
3.0341(6)
3.2985(8)
3.5177(6)
3.5177(6)
3.0341(6)
2.8846(5)
3.1789(5)
3.0084(5)
3.3254(8)
2.185(5)
3.088(2)
3.836(3)
3.724(2)
3.724(2)
3.088(2)
3.073(2)
2.890(2)
2.948(2)
2.926(2)
2.192(8)
3.0882(10)
3.5737(10)
3.5845(10)
3.5352(10)
3.0883(10)
2.9400(9)
3.0575(9)
2.9479(9)
2.9001(9)
2.185(7)
3.1379(12)
3.75674(15)
3.7635(14)
3.7520(13)
3.1564(12)
2.9475(16)
2.6543(15)
2.8697(16)
2.7032(11)
2.122(9)
Ag1–Ag3(Ag1i)
Ag1–Ag4(Ag2i)
Ag2–Ag3(Ag1i)
Ag3(Ag1i)–Ag4(Ag2i)
Ag1–X1
Ag1–X2
Ag2–X2
Ag2–X4(X2i)
C–Ag1
Table 2 VT 13C NMR data
Experimental
k (s−1
)
ΔG‡
General methods
Complex
Coalescence temp (°C)
Molecular sieves, Celite®, K2CO3, and Al2O3 (basic, 50–200 μm)
were stored in an oven at 130 °C prior to use. Ag2O (99%) was
purchased from Sigma-Aldrich and used as received. NMR
spectra were recorded on 300 or 500 MHz Bruker instruments.
Chemical shifts (δ) were expressed in ppm downfield to TMS at
δ = 0 and referenced to the residual solvent peak.27 CD2Cl2,
CH2Cl2, DMSO-d6 and CD3CN were dried by passing through
activated alumina.28 ESI-TOF MS data was collected using a
Synapt G2 HDMS instrument. 1,3-Bis(3′-butylimidazol-1′-yl)-
benzene diiodide (2a) was synthesized and isolated according
to a literature procedure (Scheme 1).29
3aa
3ba
3ca
3db
3eb
−40
−40
−40
−30
−30
478
478
478
362
441
10.7
10.7
10.7
11.3
11.2
a In 2 : 1 DMF : CD2Cl2. b In DMF.
VT 13C NMR studies
13
The
C
carbene
singlet for complexes 3a–3e decoalesced at low
temperature (see ESI†) into two broad signals. The coalescence
temperatures, and subsequently, the ΔG‡ were determined for
each complex (Table 2). The imidazolyl complexes 3a–3c,
which differ only by the alkyl chain-butyl vs. butenyl vs. pente-
nyl, had identical coalescence temperatures and activation bar-
Synthesis and characterization
1,3-Bis(imidazol-1′-yl)benzene
(1a). 1,3-Dibromobenzene
(69.0 mL, 0.571 mol), imidazole (97.2 g, 1.43 mol), K2CO3
riers, thus the side chain did not impact the exchange rate. (235.9 g, 1.43 mol), CuO (11.4 g, 0.143 mol), and DMSO
(540 mL) were combined and heated at 150 °C for 48 h.23 The
The triazolyl complexes 3d and 3e had a slightly higher barrier
than imidazolyl complexes 3a–3c. The halogen had a small
reaction was cooled, CH2Cl2 (2.7 L) was added, and the reaction
effect on the exchange rate of complexes 3d and 3e, and mixture was filtered through a column of basic alumina. The
almost no impact on the ΔG‡. This result is in contrast to
filter was washed with 10 : 1 CH2Cl2 : isopropanol (2 L). The
other reports where the halogen had large impacts on the
resulting filtrate was concentrated under reduced pressure yield-
intermolecular exchange rate.26 The results from crossover and ing a yellow oil that was left overnight in vacuo. The oil became a
VT 13C NMR experiments are consistent with intramolecular
free-flowing, bright yellow solid, which was washed with EtOAc
(30 mL), sonicated for 1 min, cooled in an ice bath and col-
107/109Ag–13C exchange in complexes 3a–3e rather than inter-
molecular exchange. Such an intramolecular process may be lected as an off-white solid (83.4 g, 70%). Spectroscopic data of
1a was identical to previously reported data.23
viewed as
a molecular rotor-type mechanism for Ag–C
interchange.
1,3-Bis(1′,2′,4′-triazol-1′-yl)benzene
(1b). 1,3-Dibromo-
benzene (13.7 mL, 113 mmol), 1,2,4-triazole (19.5 g,
283 mmol), CuO (2.19 g, 28.3 mmol), K2CO3 (39.1 g,
283 mmol), and DMSO (150 mL) were combined and heated at
150 °C for 48 h. After cooling, CH2Cl2 (1.5 L) was added. The
Conclusion
In summary, we report the synthesis and characterization of mixture was filtered through a column of basic alumina, and
five examples of tetra-NHC-Ag(I)-X cubane clusters. The com- the filter was washed with CH2Cl2 (500 mL). The filtrate was
1
plexes were characterized with H and 13C NMR spectroscopy, concentrated, washed with EtOAc (100 mL) and dried to yield
1
ESI-TOF MS, and X-ray crystallography. Complexes 3a–3d are an off-white solid (20 g, 83%). H NMR (DMSO-d6, 300 MHz):
precursors to supramolecular building blocks observed in the δ 9.43 (s, 2H), 8.39 (s, 1H), 8.31 (s, 2H), 7.93 (d, J = 8 Hz, 2H), 7.76
mass spectra. The results from VT 13C NMR, crossover experi- (t, J = 8 Hz, 1H). 13C{1H} NMR (DMSO-d6, 125.8 MHz): δ 153.1,
ments and a mixed synthesis are consistent with intramole- 143.2, 138.2, 131.7, 118.6, 110.7. [M + H]+ found, 212, calc., 212.
cular Ag–C exchange, which can be conceptualized as a
molecular rotor-type mechanism.
1,3-Bis(3′-but-3″-enyl-imidazolium-3′-yl)benzene diiodide
(2b). 1,3-Bis(imidazol-1′-yl)benzene (1a) (0.75 g, 3.57 mmol),
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4-iodo-1-butene (1.96 g, 10.7 mmol) and CH3CN (5 mL) were combined, protected from light and stirred for 12 h under Ar.
combined, protected from light, and heated at 120 °C. After The solution was filtered through celite, concentrated to
1 h, the reaction was allowed to cool yielding yellow needles, dryness, and CH2Cl2 (20 mL) was added. The resulting solu-
which were collected and washed with cold CH3CN (4 mL) and tion was filtered through celite, concentrated under reduced
with Et2O (2 × 4 mL). The resulting white solid (1.22 g, 60%) pressure, and washed with Et2O (3 × 4 mL). The free-flowing,
1
was dried in vacuo. H NMR (CD3OD, 300 MHz): δ 9.99 (s, 2H), white powder was dried overnight under reduced pressure
8.52 (s, 1H), 8.39 (s, 2H), 8.09 (m, 5H), 6.02 (m, 2H), 5.26 (m, yielding 0.37 g, 67%. Crystals suitable for X-ray and elemental
4H), 4.58 (t, J = 7.0 Hz, 4H), 2.89 (m, 4H). 13C{1H} NMR analysis were grown by slow vapor diffusion of Et2O into a
1
(CD3OD, 75.5 MHz): δ 137.6, 137.2, 134.3, 133.7, 125.1, 124.9, saturated solution of complex 3a in CH2Cl2. H NMR (CD2Cl2,
123.1, 119.9, 118.3, 51.0, 35.2. Anal. Calc. for C20H24N4I2: C, 300 MHz): δ 8.38 (t, J = 1.8 Hz, 2H), 7.53 (dd, J = 6.6 Hz, 4H),
41.83; H, 4.21; N, 9.76. Found: C, 41.80; H, 4.08; N, 9.84.
7.43 (t, J = 2.1 Hz, 2H), 7.31 (d, J = 1.7 Hz, 4H), 7.12 (d, J = 1.7
1,3-Bis(3′-pent-4″-enyl-imidazolium-3′-yl)benzene diiodide Hz, 4H), 4.32 (t, J = 7.4 Hz, 8H), 1.89 (m, J = 7.5 Hz, 8H), 1.42
(2c). 1,3-Bis(imidazol-1′-yl)benzene (1a) (1.75 g, 8.30 mmol), (m, J = 7.5 Hz, 8H), 0.96 (t, J = 7.3 Hz, 12H). 13C{1H} NMR
5-iodo-1-pentene (4.88 g, 24.9 mmol), and CH3CN (15 mL) (CD2Cl2, 75.5 MHz): δ 187.0, 141.8, 130.5, 123.4, 122.5, 121.9,
were combined, purged with Ar and heated at 120 °C. After 121.4, 52.5, 34.1, 20.4, 14.2. Anal. Calc. for C40H52N8Ag4I4: C,
1 h, the reaction was cooled and the volatiles were removed 30.33; H, 3.31; N, 7.07. Found: C, 30.46; H, 3.59; N, 6.89.
in vacuo. The resulting pale orange solid was dissolved in a
Bis(μ-1,3-bis(3′-but-3″-enyl-imidazol-2′-ylidene)benzene-κ-C)-
(3b). 1,3-Bis(3′-but-3″-enyl-imid-
minimal amount of CH3CN. Et2O (45 mL) was added to the tetra-μ3-iodotetrasilver(I)
solution producing an off-white precipitate, which was col- azolium-1′-yl)benzene diiodide (2b) (0.40 g, 0.70 mmol), Ag2O
lected yielding 3.87 g, 77%. Crystals for elemental analysis (0.18 g, 0.77 mmol), molecular sieves (0.3 g, 4 Å beads), and
were obtained by slow evaporation of a saturated solution of CH2Cl2 (50 mL) were combined, protected from light and
1
complex 2c in CH2Cl2. H NMR (CD3CN, 500 MHz): δ 10.17 (s, stirred for 12 h under Ar. The solution was filtered through
2H), 8.50 (s, 1H), 8.18 (s, 2H), 7.90 (m, 2H) 7.68 (s, 2H), 5.89 celite, concentrated to dryness, and CH2Cl2 (30 mL) was
(m, 2H), 5.06 (dd, J = 13.7 Hz, 4H), 4.33 (t, J = 7.1 Hz, 4H), 2.16 added. The solution was filtered through celite, concentrated
(m, 9H). 13C{1H} NMR (DMSO-d6, 125.8 MHz): δ 136.9, 135.7, under reduced pressure, and washed onto a filter with Et2O
135.7, 135.6, 131.9, 123.6, 122.6, 121.1, 115.8, 49.1, 29.6, 28.0. (5 mL), and washed with additional Et2O (3 × 4 mL). The free-
Calculated for C22H28N4I2: C, 43.87; H, 4.69; N, 9.30. Found: C, flowing, white powder was dried overnight under reduced
43.90; H, 4.55; N, 9.33.
pressure yielding 0.39 g, 71%. Crystals suitable for X-ray analy-
1,3-Bis(4′-butyl-1′,2′,4′-triazolium-1′-yl)benzene
diiodide sis were grown by slow evaporation of a saturated solution of
1
(2d). 1,3-Bis(1′,2′,4′-triazol-1′-yl)benzene (1b) (2.2 g, 4.7 mmol), complex 3b in CH2Cl2. H NMR (CD2Cl2, 300 MHz): δ 8.48 (s,
1-iodobutane (11 mL, 94 mmol), and CH3CN (40 mL) were 1H), 7.53 (m, 1H), 7.43 (m, 2H), 7.29 (d, J = 1.8 Hz, 2H), 7.12
combined and heated at 140 °C for 18 h. After cooling, the (d, J = 1.8 Hz, 2H), 5.90 (m, 2H), 5.09 (dd, J1 = 17.2 Hz, J2 = 10.3
volatiles were removed under reduced pressure. The crude Hz, 4H), 4.39 (t, J = 7.3 Hz, 4H), 2.70 (m, 4H). 13C{1H} NMR
solid was washed with CH2Cl2 (20 mL) yielding a pale yellow (CD2Cl2, 75.5 MHz): δ 187.8, 141.9, 135.2, 130.5, 123.3, 122.8,
solid (4.9 g, 82%). 1H NMR (DMSO-d6, 500 MHz): δ 11.12 (s, 121.1, 118.0, 52.0, 36.4.
2H), 9.57 (s, 2H), 8.52 (t, J = 2.2 Hz, 1H), 8.21 (dd, J1 = 2.0 Hz,
Bis(μ-1,3-bis(3′-pent-4″-enyl-imidazol-2′-ylidene)benzene-κ-C)-
(3c). 1,3-Bis(3′-pent-4″-enyl-imid-
J2 = 7.5 Hz, 2H), 8.07 (t, J = 8.0 Hz, 1H), 4.36 (t, J = 8.2 Hz, 4H), tetra-μ3-iodotetrasilver(I)
1.95 (m, 4H), 1.42 (m, 4H), 0.96 (t, J = 7.3 Hz, 6H). 13C{1H} azolium-1′-yl)benzene diiodide (2c) (0.51 g, 0.85 mmol), Ag2O
NMR (DMSO-d6, 125.8 MHz): δ 145.0, 142.4, 135.9, 131.9, (0.22 g, 0.93 mmol), molecular sieves (0.3 g, 4 Å beads) and
122.0, 113.0, 47.9, 30.3, 18.7, 13.2.
CH2Cl2 (43 mL) were protected from light and stirred at room
1,3-Bis(4′-butyl-1′,2′,4′-triazolium-1′-yl)benzene
dibromide temperature for 16 h. The reaction mixture was filtered
(2e). 1,3-Bis(1′,2′,4′-triazol-1′-yl)benzene
(1b)
(1.0
g, through celite to produce a pale yellow filtrate, and was con-
4.70 mmol), 1-bromobutane (5.0 mL, 47 mmol), and CH3CN centrated under reduced pressure, yielding a yellow crystalline
(30 mL) were combined and heated at 140 °C for 18 h. After solid. The solid was dissolved in CH2Cl2 (20 mL) and filtered
cooling, the volatiles were removed under reduced pressure. through celite. The volatiles were removed in vacuo, and the
The crude solid was washed with CH2Cl2 (20 mL) yielding a resulting solid was washed with Et2O (3 × 4 mL) to yield an off-
1
light-brown solid (1.6 g, 70%). H NMR (DMSO-d6): δ 11.23 (s, white, free-flowing solid (0.53 g, 39%). Crystals suitable for
2H), 9.59 (s, 2H), 8.56 (s, 1H), 8.22 (d, J = 8.3 Hz, 2H), 8.05 (t, X-ray were obtained through slow vapor diffusion of Et2O into
J = 8.2 Hz, 1H), 4.36 (t, J = 7.2 Hz, 1H), 1.97 (m, 4H), 1.42 (m, a saturated solution of complex 3c in CH2Cl2. 1H NMR
4H), 0.95 (t, J = 7.2 Hz, 6H). 13C{1H} NMR (DMSO-d6, (CD2Cl2, 300 MHz): δ 8.41 (s, 2H), 7.54 (t, J = 7.2 Hz, 2H), 7.42
75.5 MHz): δ 145.2, 142.5, 136.1, 132.0, 122.0, 112.9, 47.9, 30.5, (d, J = 7.2 Hz, 4H), 7.32 (s, 4H), 7.12 (s, 4H), 5.85 (m, 4H), 5.01
18.8, 13.3.
Bis(μ-1,3-bis(3′-butylimidazol-2′-ylidene)benzene-κ-C)tetra-μ3- (m, 8H), 2.02 (m, 8H). 13C{1H} NMR (CD2Cl2, 75.5 MHz):
iodotetrasilver(I) (3a). 1,3-Bis(3′-butylimidazol-1′-yl)benzene δ 187.5, 141.9, 138.3, 130.6, 123.5, 122.0, 121.4, 115.7, 52.1,
(dd, J1 = 17.2 Hz, J2 = 10.2 Hz, 8H), 4.33 (t, J = 7.2 Hz, 8H), 2.16
diiodide (2a) (0.40 g, 0.69 mmol), Ag2O (0.18 g, 0.76 mmol), 31.3, 31.2. Calculated for C44H52Ag4I4N8: C, 32.38; H, 3.21;
molecular sieves (0.3 g, 4 Å beads), and CH2Cl2 (40 mL) were N, 6.87. Found: C, 32.47; H, 3.02; N, 7.13.
7342 | Dalton Trans., 2013, 42, 7338–7344
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Bis(μ-1,3-bis(4′-butyl-1′,2′,4′-triazol-2′-ylidene)benzene-κ-C)-
Acknowledgements
tetra-μ3-iodotetrasilver(I)
(3d). 1,3-Bis(4′-butyl-1′,2′,4′-tri-
azolium-1′-yl)benzene diiodide (2d) (0.51 g, 0.88 mmol), Ag2O We acknowledge the National Science Foundation
(0.19 g, 0.84 mmol), KOH (0.087 g, 1.6 mmol), and CH3CN (EPS0903787, MRI0421319, and MRI0618148) for financial
(40 mL) were combined, protected from light and stirred for support. We thank Professor Amala Dass, Chanaka Ihala, Pra-
18 h, yielding a white precipitate. The solid was collected and neeth Nimmala, and Vijay Jupally for ESI-TOF MS data collec-
the KOH pellets were removed. The solid was washed with tion, and Professor John Rimoldi, Eric Bow and Brian Morgan
CH3CN (10 mL), MeOH (5 mL) and Et2O (2 × 20 mL), and for CHN analysis.
dried under reduced pressure affording an off-white solid
(0.49 g, 73%). Crystals suitable for X-ray and elemental analysis
were grown by slow vapor diffusion of CH3OH into a saturated
Notes and references
solution of complex 3d in DMSO. 1H NMR (DMSO-d6,
300 MHz): δ 9.05 (s, 2H), 8.49 (s, 1H), 7.86 (d, J = 8.3 Hz, 2H),
7.36 (t, J = 8.3 Hz, 1H), 4.34 (s, 4H), 1.76 (m, 4H), 1.22 (m, 4H),
0.82 (t, J = 6.8 Hz, 6H). 13C{1H} NMR (DMSO-d6, 75.5 MHz): δ
186.5, 144.8, 140.0, 130.3, 121.8, 115.9, 48.2, 32.5, 18.9, 13.4.
Anal. Calc. for C36H48Ag4I4N12: C, 27.23; H, 3.05; N, 10.58.
Found: C, 27.22; H, 3.05; N, 10.48.
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Bis(μ-1,3-bis(4′-butyl-1′,2′,4′-triazol-2′-ylidene)benzene-κ-C)-
tetra-μ3-bromotetrasilver(I)
(3e). 1,3-Bis(4′-butyl-1′,2′,4′-tri-
azolium-1′-yl)benzene dibromide (2e) (0.890 g, 1.83 mmol),
Ag2O (0.466 g, 2.01 mmol), and CH3CN (120 mL) were com-
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115.6, 48.6, 32.7, 19.1, 13.5.
Alternate synthesis: 1,3-Bis(4′-butyl-1′,2′,4′-triazolium-1′-yl)-
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7344 | Dalton Trans., 2013, 42, 7338–7344
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