Synthesis of well-defined N-heterocyclic carbene silver(I) complexes

Article abstract of DOI:10.1021/om050735i

A series of N-heterocyclic carbene (NHC)AgCl complexes [NHC = SIMes (1), IPr (2), SIPr (3), IPrMe (4), IMe (5), ICy (6), lAd (7), IsB (8), IDD (9), and TPh (10)] have been synthesized through reaction of the imidazolium chloride salts with Ag₂O or by direct metalation of the corresponding imidazol-2-ylidene carbene in the presence of AgCl. All silver(I) complexes [(SIMes)AgCl] (11), [(IPr)AgCl] (12), [(SIPr)AgCl] (13), [(IPrMe)AgCl] (14), [(IMe)AgCl] (15), [(ICy)AgCl] (16), [(IAd)AgCl] (17), [(IsB)AgCl] (18), [(IDD)AgCl] (19), and [(TPh)AgCl] (20) have been spectroscopically and structurally characterized. The structure of these silver complexes is dependent on the halide and the solvent used for the synthesis. Adjusting these parameters has led to the previously reported complex, [(IMes) ₂Ag]⁺[AgCl₂]^- (21), and to a new silver complex, [(IMes)₂Ag]₂⁺[Ag ₄I₆]^2- (22).

Full text of DOI:10.1021/om050735i

Organometallics 2005, 24, 6301-6309
6301
Articles
Synthesis of Well-Defined N-Heterocyclic Carbene
Silver(I) Complexes
Pierre de Fre´mont,† Natalie M. Scott,† Edwin D. Stevens,† Taramatee Ramnial,‡
Owen C. Lightbody,‡ Charles L. B. Macdonald,§ Jason A. C. Clyburne,‡
Colin D. Abernethy, and Steven P. Nolan*,†
Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148,
Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, British
Columbia V5A 1S6, Canada, Department of Chemistry and Biochemistry University of
Windsor, 273-1 Essex Hall, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada and
Department of Chemistry, Keene State College, Keene, New Hampshire 03435-2001
Received August 25, 2005
A series of N-heterocyclic carbene (NHC)AgCl complexes [NHC ) SIMes (1), IPr (2), SIPr
(3), IPrMe (4), IMe (5), ICy (6), IAd (7), IsB (8), IDD (9), and TPh (10)] have been synthesized
through reaction of the imidazolium chloride salts with Ag2O or by direct metalation of the
corresponding imidazol-2-ylidene carbene in the presence of AgCl. All silver(I) complexes
[(SIMes)AgCl] (11), [(IPr)AgCl] (12), [(SIPr)AgCl] (13), [(IPrMe)AgCl] (14), [(IMe)AgCl] (15),
[(ICy)AgCl] (16), [(IAd)AgCl] (17), [(IsB)AgCl] (18), [(IDD)AgCl] (19), and [(TPh)AgCl] (20)
have been spectroscopically and structurally characterized. The structure of these silver
complexes is dependent on the halide and the solvent used for the synthesis. Adjusting these
parameters has led to the previously reported complex, [(IMes)2Ag]+[AgCl2]- (21), and to a
new silver complex, [(IMes)2Ag]+ [Ag4I6]2- (22).
2
Introduction
metathesis,7 and hydrogenation8 reactions, among the
most significant. From group 11, copper- and gold-NHCs
are known to catalyze a more limited number of organic
transformations,9,10 but silver-NHC complexes have
been reported recently to behave as efficient catalysts
It is now widely accepted that the saga of N-hetero-
cyclic carbene (NHC) chemistry began in 1968 when
O¨ lefe1 and Wanzlick2 successfully isolated the first
chromium and mercury N-heterocyclic carbene com-
plexes. In 1991, Arduengo’s seminal discovery of a stable
N-heterocyclic carbene3 led to incredible activity and
development in the coordination chemistry of NHCs.
With better sigma donor ability than most phosphines,
NHCs strongly bind and stabilize transition metals,4
leading to a wide variety of well-defined catalytic
systems. NHC complexes of late transition metals
especially those of groups 8, 9, and 10 have been
employed to catalyze Heck reactions,5 cross-coupling
reactions (such as the Suzuki-Miyaura reaction6), olefin
(5) (a) McGuinness, D. S.; Cavell, K. J. Organometallics 2000, 19,
741-748. (b) Andrus, M. B.; Song, C.; Zhang, J. Org. Lett. 2002, 4,
2079-2082. (c) Poyato, M.; Ma´rquez, F.; Peris, E.; Claver, C.; Ferna´n-
dez, E. New J. Chem. 2003, 27, 425-431. (d) Hermann, W. A.; O¨ lefe,
K.; Von Preysing, D.; Schneider, S. K. J. Organomet. Chem. 2003, 687,
229-248. (e) Lee, H. M.; Lu, C. Y.; Chen, C. Y.; Chen, W. L.; Lin, H.
C.; Chiu, P. L.; Cheng, P. Y. Tetrahedron 2004, 60, 5807-5825.
(6) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290-
1309. (b) Hillier, A.; Grasa, G. A.; Viciu, M. S.; Lee, H. M.; Yang, C.;
Nolan, S. P. J. Organomet. Chem. 2002, 653, 69-82. (c) Viciu, M. S.;
Germaneau, R. F.; Navarro-Ferna´ndez, O.; Stevens, E. D.; Nolan, S.
P. Organometallics 2002, 21, 5470-5472.
(7) (a) Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics 2000,
19, 1194-1197. (b) Delaude, L.; Szypa, M.; Demonceau, A.; Noels, A.
F. Adv. Synth. Cat. 2002, 344, 749-756. (c) Courchay, F.; Sworen, J.
C.; Wagener, K. B. Macromolecules 2003, 36, 8231-8239. (d) Choi, T.-
L.; Grubbs, R. H. Angew. Chem., Int. Ed. 2003, 42, 1743-1746. (e)
Yao, Q.; Rodriguez Motta, A. Tetrahedron Lett. 2004, 45, 2447-2451.
(e) Gallivan, J. P.; Jordan, J. P.; Grubbs, R. H. Tetrahedron Lett. 2005,
46, 2577-2580.
(8) (a) Albretch, M.; Miecznikowski, J. R.; Crabtree, R. H. Polyhedron
2004, 23, 2857-2872. (b) Sprengers, J. W.; Wassenaar, J.; Cle´ment,
N. D.; Cavell, K. J.; Elsevier, C. J. Angew. Chem., Int. Ed. 2005, 44,
2026-2029. (c) Dharmasena, U. L.; Foucault, H. M.; Dos Santos, E.
N.; Fogg, D. E.; Nolan, S. P. Organometallics 2005, 24, 1056-1058.
(9) (a) Larsen, A. O.; Leu, W.; Oberhuber, C. N.; Campbell, J. E.;
Hoveyda, A. H. J. Am. Chem. Soc. 2004, 126, 11130-11131. (b) Kaur,
H.; Kauer Zinn, F.; Stevens, E. D.; Nolan, S. P. Organometallics 2004,
23, 1157-1160. (c) D´ıez-Gonza´lez, S.; Kaur, H.; Kauer Zinn, F.;
Stevens, E. D.; Nolan, S. P. J. Org. Chem. 2005, 70, 4787-4796.
(10) (a) Schneider, S. K.; Hermann, W. A.; Herdtwerck, E. Z. Anorg.
Allg. Chem. 2003, 629, 2363-2370. (b) Nieto Oberhuber, C.; Mun˜oz,
M. P.; Bun˜uel, E.; Nevado, C.; Ca´rdenas, D. J.; Echavarren, A. M.
Angew. Chem., Int. Ed. 2004, 43, 2402-2406.
* To whom correspondence should be addressed. E-mail: snolan@
uno.edu.
† University of New Orleans.
‡ Simon Fraser University.
§ University of Windsor.
Keene State College.
(1) O¨ lefe, K. J. Organomet. Chem. 1968, 12, 42-43.
(2) Wanzlick, H.-W.; Scho¨nherr, H.-J. Angew. Chem., Int. Ed. Engl.
1968, 7, 141-142.
(3) Arduengo, A. J. III; Harlow, R. L.; Kline, M. J. Am. Chem. Soc.
1991, 113, 361-363.
(4) (a) Heinemann, W. A.; Mu¨ller, T.; Apeloig, Y.; Schwarz, H. J.
Am. Chem. Soc. 1996, 118, 2023-2038. (b) Hermann, W. A.; Kocher,
C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2162-2187. (c) Gru¨ndemann,
S.; Albrecht, M.; Loch, J. A.; Faller, J. W.; Crabtree, R. H. Organome-
tallics 2001, 20, 5485-5488. (d) McGuiness, D. S.; Cavell, K. J.;
Skelton, B. W.; White, A. H. Organometallics 1999, 18, 1596-1605.
(e) Simms, R. W.; Drewitt, M. J.; Baird, M. C. Organometallics 2002,
21, 2958-2963.
10.1021/om050735i CCC: $30.25 © 2005 American Chemical Society
Publication on Web 11/18/2005

6302 Organometallics, Vol. 24, No. 26, 2005
de Fre´mont et al.
Figure 1. NHC ligands used in this study.
in transesterification reactions.11 While tungsten-NHC
complexes can be used as carbene transfer reagents,12
silver-NHC compounds are the most popular complexes
used for NHC transfer.12,13 Their common use as
transfer agents is due to their straightforward synthe-
sis, usually circumventing the need for free NHC
isolation, and the relative stability of the Ag-NHC
complexes toward air and light.12,15 NHC-silver com-
plexes are known to adopt different architectures de-
pending on the synthetic conditions employed. Most of
the reported complexes are homoleptic with two carbene
units bound to the silver in a linear fashion.11-17 In the
case of argentophilic interactions, some polymeric and
bridged structures have been elucidated.18,19 On the
other hand, mono-carbene silver halides remain rare,
with only a handful of reported examples.20-22 We report
here the synthesis of a series of two-coordinate NHC-
silver(I) chloride complexes of general composition
(NHC)AgCl. The NHC ligands used in the present study
are shown in Figure 1 and are commonly used saturated
and unsaturated ligands: (1,3-bis(2,4,6-trimethylphe-
nyl)imidazolidin-2-ylidene) SIMes (1), (1,3-bis(2,6-diiso-
propylphenyl)imidazol-2-ylidene) IPr (2), (1,3-bis(2,6-
diisopropylphenyl)imidazolidin-2-ylidene) SIPr (3), (1,3-
diisopropyl-4,5-dimethylimidazol-2-ylidene) IPrMe (4),
(1,3,4,5-tetramethylimidazol-2-ylidene) IMe (5), (1,3-bis-
(cyclohexyl)imidazol-2-ylidene) ICy (6), (1,3-bis(adaman-
tyl)imidazol-2-ylidene) IAd (7), (1,3-bis(isobutyl)imidazol-
2-ylidene) IsB (8), and (1,3-bis(dodecyl)imidazol-2-
ylidene) IDD (9), as well as the triazolium ligand
(2,5,6,7-tetrahydro-2-phenyl-3H-pyrrolo[2,1-c]-1,2,4-tria-
zol-3-ylidene) TPh (10). All new Ag(I)-NHC complexes
1
were characterized by H and 13C NMR spectroscopy,
elemental analysis, and X-ray diffraction.
Although the synthesis of the two-coordinate silver-
(I) chloride complex (IMes)AgCl22 has been reported
already, we noticed that the use of a more polar solvent
favors the formation of [(IMes)2Ag]+[AgCl2]- (21). Fi-
nally, by studying the synthesis of (IMes)AgI in a polar
solvent, we have obtained the unusual [(IMes)2Ag]2-
[Ag4I6] (22) complex.
Results and Discussion
Refluxing the imidazolium chloride salts SIMes‚HCl
(1), IPr‚HCl (2), SI‚Pr (3), ICy‚HCl (6), IAd‚HCl (7), IsB‚
HCl (8), and TPh‚HCl (10) in dichloromethane (DCM)
in the presence of a slight excess of Ag2O yields
complexes [(SIMes)AgCl] (11), [(IPr)AgCl] (12), [(SIPr)-
AgCl] (13), [(ICy)AgCl] (16), [(IAd)AgCl] (17), [(IsB)-
AgCl] (18), and [(TPh)AgCl] (20) according to eq 1:
(11) Sentman, A. C.; Szila´rd, C.; Waymouth, R. M.; Hedrick, J. L.
J. Org. Chem. 2005, 70, 2391-2393.
2NHC‚HCl DCM8 2(NHC)AgCl + H2O
(1)
(12) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972-
975.
Ag2O
(13) Lin, I. J. B.; Vasam, C. S. Comm. Inorg. Chem. 2004, 25, 75-
129.
(14) Arduengo, A. J. III.; Dias, H. V. R.; Calabrese, J. C.; Davidson,
F. Organometallics 1993, 12, 3405-3409.
Using the same conditions with the bulky salt IDD‚HCl
(9) leads to a mixture of 55% of the desired complex
[(IDD)AgCl] (19) and 45% of the starting salt 9. To
increase the kinetics of the reaction, a solvent with a
higher boiling point was selected, and after 12 h at
reflux in THF, total conversion to 19 was obtained. It
is noteworthy that contrary to the method described by
Wang and Lin,12 all syntheses can be carried out
without exclusion of light with no deleterious effect on
yields.
In anhydrous THF, under argon and in the dark, the
free carbenes IPrMe (4) and IMe (5) are stirred over-
night at room temperature in the presence of a slight
excess of AgCl to yield complexes [(IPrMe)AgCl] (14) and
(15) Baker, M. V.; Brown, D. H.; Haque, R. A.; Skelton, B. W.; White,
A. H. J. Chem. Soc., Dalton Trans. 2004, 3756-3764.
(16) Garrison, J. C.; Simons, R. S.; Talley, J. M.; Wesdemiotis, C.;
Tessier, C. A.; Youngs, W. J. Organometallics 2001, 20, 1276-1278.
(17) Kascatan-Nebioglu, A.; Panzer, M. J.; Garrison, J. C.; Tessier,
C. A.; Youngs, W. J. Organometallics 2004, 23, 1928-1931.
(18) Catalano, V. J.; Malwitz, M. A. Inorg. Chem. 2003, 5483-5485.
(19) Liu, Q. X.; Xu, F.-B.; Li, Q. S.; Zeng, X.-S.; Leng, X.-B.; Chou,
Y. L.; Zhang, Z.-Z. Organometallics 2003, 22, 309-314.
(20) Chen, W.; Biao, W.; Matsumoto, K. J. Organomet. Chem. 2002,
654, 233-236.
(21) Melaiye, A.; Simons, R. S.; Milsted, A.; Pingitore, F.; Wesde-
miotis, C.; Tessier, C. A.; Youngs, W. J. J. Med. Chem. 2004, 47, 973-
977.
(22) Ramnial, T.; Abernethy, C. D.; Spicer, M. D.; McKenzie, I. D.;
Gay, I. D.; Clyburne, J. A. C. Inorg. Chem. 2003, 42, 1391-1393.

N-Heterocyclic Carbene Silver(I) Complexes
Organometallics, Vol. 24, No. 26, 2005 6303
Table 1. Chemical Shifts of the Carbenic Carbon in NMR for the (NHC)AgCl Complexes
complex
solventa
δ (C-Ag) ppm
appearance of the signal
J1(107-109Ag-13C) Hz
(IMes)AgCl22
CDCl3
CDCl3
CDCl3
CD2Cl2
CD2Cl2
CD2Cl2
CDCl3
CD2Cl2
CDCl3
CDCl3
CDCl3
185.0
207.5
184.6
207.7
172.3
177.6
179.1
173.8
179.8
177.8
176.9
doublet of doublets
doublet of doublets
doublet of doublets
doublet of doublets
broad singlet
270/234
256/222
271/253
253/219
(SIMes)AgCl (11)
(IPr)AgCl (12)
(SIPr)AgCl (13)
(IPrMe)AgCl] (14)
(IMe)AgCl (15)
(ICy)AgCl (16)
(IAd)AgCl (17)
(IsB)AgCl (18)
(IDD)AgCl (19)
(TPh)AgCl (20)
sharp singlet
broad singlet
broad singlet
sharp singlet
broad doublet
unresolved
sharp singlet
a Complexes partially soluble in CDCl3 were fully solubilized in CD2Cl2.
[(IMe)AgCl] (15) and traces of metallic silver according
doublet of doublets with a coupling between silver and
carbon (J1(13C-109Ag) ) 271 Hz and J1(13C-107Ag) )
253 Hz). The similar values in chemical shift for 11 and
13 indicate no significant difference in the electronic
donor properties existing for the saturated carbenes
(SIMes and SIPr) in these silver systems. Nevertheless,
both signals are 20 ppm downfield from that of the
saturated complexes, confirming that saturated com-
plexes exhibit a better electron-donating ability to the
metal in the present system.24 For the unsaturated
NHCs, N,N-bis(alkyl)imidazolylidenes are generally
considered better sigma donors than N,N-bis(aryl)-
imidazolylidenes; however in the present silver(I) com-
plexes, this trend is reversed. Surprisingly, (IPr)AgCl
(12) and (IMes)AgCl22 display the highest downfield
signal for the unsaturated series. This signal appears
at 184.6 ppm as a doublet of doublets with an observable
coupling between carbon and silver of J1(13C-109Ag) )
253 Hz and J1(13C-107Ag) ) 219 Hz. Usually complexes
exhibiting strong coupling are known to exhibit no
exchange or very slow exchange12,24 (on the NMR time
scale) of their carbene moieties with the silver centers
and are poor carbene transfer agents for transmetala-
tion.25 This quasi-static behavior in solution might also
be correlated to the downfield signal of the carbenic
carbon, proving a stronger donation to the silver, and
indicates a stronger Ag-C bond.24 This stronger bond
decreases the lability of the carbene moieties and
inhibits the formation of [(NHC)2Ag]+, preventing the
formation of an equilibrium between (NHC)AgCl and
[(NHC)2Ag]+.24 (IDD)AgCl (19) displays a broad doublet
at 177.8 ppm, due to a weak coupling between carbon
and silver, which is characteristic of a slightly faster
exchange between IDD moieties and the silver centers.
The upper field value of the signal shows that the IDD
carbene does not exhibit strong donating abilities and
the exchange should be faster.24 We believe that this
slow dynamic behavior is not due to electronic consid-
erations but to the steric bulk of the dodecyl groups.
Indeed, we have noticed that the formation of (IDD)-
AgCl (19) was slower and under synthetic conditions
required a higher reaction temperature, possibly due to
the difficulty of the silver center to reach the carbenic
center, which is protected by two large dodecyl groups.
It is clear that having four dodecyl groups around the
same silver center is very unlikely due to the over-
whelming steric hindrance of such a situation. (IPrMe)-
to eq 2:12
AgCl
NHC
8 (NHC)AgCl
(2)
THF
All complexes can be obtained in good yields in this
manner with the notable exception of [(IMe)AgCl] (15).
For this particular complex, and to a lesser extent for
[(SIMes)AgCl] (11), the lower yields are due to the
formation of a side-product. Separation of the desired
com-
plexes and the side-products is easily achieved by crys-
tallization. Interestingly, when we examine the 1H NMR
spectrum of the side-products, we find similarities with
spectra of [(IMe)2Au]Cl and [(IMes)2Au]Cl, two com-
plexes that we have previously encountered while syn-
thesizing a series of NHC gold(I) chloride complexes.23
Usually homoleptic halide silver(I) carbene complexes
have the formulation [Ag(NHC)2]+[AgX2]-,11,12,15 and
we propose the formulation [Ag(IMe)2]+[AgCl2]- and
[Ag(SIMes)2]+[AgCl2]- for both side-products. While
complexes 11, 12, 13, 15, 16, and 20 display high
stability toward light and air, complexes 14, 17, 18,
and 19 slowly decompose within a week to a month
under air and light. Once again, 1H NMR spectra of the
decomposed products indicate a mixture of (NHC)AgCl
and [Ag(NHC)2]+[AgX2]-.
The 1H NMR spectra of complexes [(SIMes)AgCl] (11)
and [(SIPr)AgCl] (13) give a single resonance at 4.00
and 4.07 ppm, respectively, for the saturated imidazole
ring. [(IPrMe)AgCl] (14) and [(IMe)AgCl] (15) give a
single high-field resonance at 2.16 and 2.12 ppm,
respectively, for the methyl group on the unsaturated
imidazole ring and the corresponding signal for the
N-alkyl chains. [(IPr)AgCl] (12), [(ICy)AgCl] (16), [(IAd)-
AgCl] (17), [(IsB)AgCl] (18), and [(IDD)AgCl] (19)
display a single resonance signal at low field between
6.95 and 7.21 ppm for the unsaturated imidazole ring
and the corresponding signals for the N-aryl and N-alkyl
chains. The 13C NMR spectra give a low-field signal,
attributed to the carbenic carbene at 207 ppm for both
saturated complexes 11 and 13, while unsaturated
complexes 12 and 14-20 exhibit a signal between 173
and 185 ppm (Table 1). [(SIMes)AgCl] (11) gives a
carbenic signal at 207.5 ppm as a doublet of doublets
with an observable coupling between carbon and silver
of J1(13C-109Ag) ) 256 Hz and J1(13C-107Ag) ) 222 Hz.
[(SIPr)AgCl] (13) gives a signal at 207.7 ppm as a
(24) Herrmann, W. A.; Schneider, S. K.; O¨ fele, K.; Sakamoto, M.;
Herdtweck, E. J. Organomet. Chem. 2004, 689, 2441-2449.
(25) Lee, K. M.; Wang, H. M. J.; Lin, I. J. B. J. Chem. Soc., Dalton
Trans. 2002, 14, 2852-2856.
(23) De Fre´mont, P.; Scott, N. M.; Stevens, E. D.; Nolan, S. P.
Organometallics 2005, 24, 2411-2418.

6304 Organometallics, Vol. 24, No. 26, 2005
de Fre´mont et al.
C-Ag-Cl (deg)
Table 2. Selected Bond Lengths and Angles for the (NHC)AgCl Complexes
complex
Ag-C (Å)
Ag-Cl (Å)
Ag‚‚‚Ag (Å)
(SIMes)AgCl (11)
(IPr)AgCl (12)
(SIPr)AgCl (13)
(IPrMe)AgCl (14)
(IMe)AgCl (15)
2.0832(19)
2.056(6)
2.081(9)
2.087(3)
2.091(2)
2.077(2)
2.091(5)
2.075(6)
2.096(5)
2.085(5)
2.094(6)
2.073(17)
2.087(17)
2.060(19)
2.067(18)
2.067(4)
2.121(1)
2.105(2)
2.089(2)
2.3358(5)
2.316(17)
2.320(2)
173.70(6)
175.2(2)
173.3(2)
2.3184(8)
2.3608(7)
2.3382(7)
2.3335(14)
2.3290(15)
2.3593(14)
2.3293(14)
21350(16)
2.314(5)
180.00(9)
172.56(7)
168.98(7)
170.06(15)
177.46(16)
166.27(16)
170.91(15)
176.08(14)
175.9(5)
3.0673(3)
3.0650(6)
3.0181(6)
(ICy)AgCl (16)
(IAd)AgCl (17)
(IsB)AgCl (18)
3.108(2)
3.124(2)
2.332(5)
178.7(5)
2.324(5)
178.1(6)
2.359(5)
176.9(5)
(IDD)AgCl (19)
(TPh)AgCl (20)
2.3200(9)
2.4458(6)
2.7978(6)
2.4045(6)
2.3753(6)
2.8685(6)
174.96(11)
150.34(6)
109.61(6)
C-Ag-C (deg)
169.51(9)
Ag-Ag-Ag (deg)
147.295(7)
3.0242(2)
3.0752(2)
Cl-Ag-Cl (deg)
102.177(19)
96.159(18)
AgCl (14), (ICy)AgCl (16), and (IAd)AgCl (17) display
signals at 172.3, 179.1, and 173.8 ppm, respectively, as
broad singlets characteristic of a slow exchange between
the carbene moieties and the silver centers.17,24 This
exchange is nevertheless faster than in the case of
(IDD)AgCl (19). While the signal of (ICy)AgCl (16) is
the most downfield (5 ppm from (IPr)AgCl (12)) and the
IAd carbene leads to strong steric hindrance around the
silver, the absence of coupling shows that these two
parameters provide a small contribution, indicating a
significantly slower exchange for these two complexes.
(IMe)AgCl (15) and (IsB)AgCl (18) exhibit a 13C NMR
signal at 177.6 and 179.8 ppm, respectively, as two
sharp singlets characteristic of a fast exchange of the
carbene moieties17,24 with the silver centers. This rapid
equilibrium must be facilitated by the relatively small
hindrance of both carbene moieties. The triazolium
complex (TPh)AgCl (20) displays a 13C NMR signal at
176.9 ppm, illustrating an average donating ability
similar to the previously discussed unsaturated NHC-
silver complexes. The signal is a sharp singlet, indicat-
ing a fast exchange of the triazolium moieties with
the silver centers. The carbenic carbons of these new
silver(I) complexes display resonances between 172
and 208 ppm, and these are good indicators of the
donating properties of the carbene to silver. While some
silver(I) carbene halide complexes are known to estab-
lish a dynamic equilibrium between (NHC)AgCl and
[(NHC)2Ag]+,12,17,24 a routine 13C NMR can give specific
indications about the rate of the exchange indicated by
the pattern associated with the carbenic signal. For all
complexes we have examined, steric and/or electronic
factors lead to a wide range of exchange rates, as gauged
by NMR signal positions and patterns.
Figure 2. Ball-and-stick representations of complexes
(SIMes)AgCl (11) and (IPr)AgCl (12). Most hydrogen atoms
have been omitted for clarity.
which is in line with other silver bis- or mono-carbene
complexes previously reported.12,14,20,22,24,26 As expected,
the silver-carbon bonds are longer than the gold-
carbene bonds reported for analogous (NHC)Au(I)Cl
complexes (bond lengths between 1.987 and 1.999 Å).23
All Ag-Cl bond distances are between 2.332 and 2.360
Å, which is in the range of other silver(I) chloride
complexes reported.20,22 None of the C-Ag bond lengths
are shortened with a simultaneous elongation of the
Ag-Cl. The absence of a trans-effect for the complexes
does not allow any comparisons of the electron-donating
abilities for different carbene moieties. It is noteworthy
that the shorter length of the Ag-C (2.057 Å) bond
and the more downfield value of the carbenic signal
(184.6 ppm) in (IPr)AgCl (12) hint at the better don-
ating properties of the carbene IPr over other unsatur-
ated carbene ligands. Complexes 11, 12, 13, 14, 17, and
19 are monomeric with no evident argentophilic (Ag-
(I)‚‚‚Ag(I)) interactions (Figures 1, 2, and 3). Indeed, all
distances between silver(I) centers are greater than
3.44 Å, the sum of twice the van der Waals radius of
Ag(I).12 (IMe)AgCl (15) has two molecules in the asym-
While NMR data give specific information about the
complexes and their dynamic properties in solution,
X-ray diffraction was used to unambiguously determine
the structure of NHC-Ag-containing complexes in the
solid state. Selected bond distances and bond angles are
given in Table 2.
All complexes, with the exception of (TPh)AgCl (20),
have a two-coordinate silver(I) atom in a close linear
environment with a C-Ag-Cl bond close to 180°. All
C-Ag bond distances are in the range 2.056-2.094 Å,

N-Heterocyclic Carbene Silver(I) Complexes
Organometallics, Vol. 24, No. 26, 2005 6305
Figure 3. Ball-and-stick representations of complexes (SIPr)AgCl (13), (IPrMe)AgCl (14), (IMe)AgCl (15), and (ICy)AgCl
(16). Most hydrogen atoms have been omitted for clarity.
metric unit and forms a dimer linked by argentophilic
interactions with a Ag(I)‚‚‚Ag(I) distance of 3.067 Å
(Figure 2). (ICy)AgCl (16) and (IsB)AgCl (18) have four
molecules in the asymmetric unit and display a dimeric
structure with Ag(I)‚‚‚Ag(I) distances between dimer
centers longer than 3.44 Å.12 For each dimer, two
molecules of the complex are linked by argentophilic
interactions with two Ag(I)‚‚‚Ag(I) distances of 3.065
and 3.108 Å for (ICy)AgCl (16) and 3.108 and 3.124
Å for (IsB)AgCl (18) (Figure 3). (TPh)AgCl (20) has
a unique structure where (TPh)AgCl coexists with
[(TPh)2Ag]+[AgCl2]- in the asymmetric unit. [(TPh)2Ag]+
is linked to (TPh)AgCl by an argentophilic interaction
with a Ag(I)‚‚‚Ag(I) distance of 3.042 Å to form a trimer.
[(TPh)2Ag]+ is also linked to [AgCl2]- by argentophilic
interactions with a Ag(I)‚‚‚Ag(I) distance of 3.075 Å,
while [AgCl2]- is linked to the silver and the chloride
of (TPh)AgCl to form a bridge. In fact, the structure can
also be envisaged as a polymer with each [(TPh)2Ag]+
unit bound by [(TPh)Ag-(µCl)2-AgCl]- units (Figures
4 and 5). It is interesting to note that in the bridged
[(TPh)Ag-(µCl)2-AgCl]- moiety, even though there is
no direct argentophilic interaction, a Ag(I)‚‚‚Ag(I) dis-
tance of 3.510 Å can induce a preferential orientation
in the packing of the structure.19 For (TPh)AgCl, the
Ag-C distance is slightly longer than others, with a
value of 2.121 Å, but is reasonable if compared with the
2.772 Å of the silver(I) carbene described by Calano et
al.18 The two Ag-Cl bond distances of the bridge have
values of 2.798 and 2.869 Å, which are marginally
longer than the 2.535 Å value found for [AgCl2]-. The
solid-state structure of (TPh)AgCl (20) confirms the
sharp singlet found in 13C NMR for the carbenic carbon,
and it also justifies our expectations of a dynamic
equilibrium between (TPh)AgCl and [(TPh)2Ag]+[AgCl2]-
in solution. For all complexes, no agostic interactions
between silver-hydrogen or even silver-methyl groups
have been observed as described in the silver(I) phos-
phine carborane complexes synthesized by Weller et
al.,27 with Ag-H and Ag-C(H3) distances greater than
2.49 and 3.29 Å, respectively.27
To improve the yields of (NHC)AgCl complexes ob-
tained, especially for (SIMes)AgCl (11) and (IMe)AgCl
(15), the effect of the solvent polarity used in the
synthesis was studied for the already well-defined
(IMes)AgCl complex.22 Three different solvents, chloro-
form, acetonitrile, and dimethyl sulfoxide, with a gradi-
ent of polarity, are used under similar experimental
conditions. When NMR characterization of the crude
reactions is carried out, a side-product is observed and
its NMR spectrum is consistent with the previously
reported bis-NHC [(IMes)2Ag]+[AgCl2]- (21) complex.11
After separation by crystallization, X-ray studies of the
crystals grown confirmed that the side-product was
(26) Bildstein, B.; Malaun, M.; Kopacka, H.; Wurst, K.; Mitterbo¨ck,
M.; Ongania, K.-H.; Opromolla, G.; Zanello, P. Organometallics 1999,
18, 4325-4386.
(27) Clarke, A. J.; Ingleson, M. J.; Kociok-Ko¨hn, G.; Mahon, M. F.;
Patmore, N. J.; Rourke, J. P.; Ruggiero, G. D.; Weller, A. S. J. Am.
Chem. Soc. 2004, 126, 1503-1517.
(28) Lide, D. R. Handbook of Chemistry and Physics, 85th ed.; CRC
Press, Boca Raton, FL, 2004-2005; Section 8, p 141.
(29) Arduengo, A. J. III; Krafczyk, R.; Schmutzler, R.; Craig, H. A.;
Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55,
14523-14534.
(30) Kuhn, N.; Kratz, T. Synthesis 1993, 561-562.

6306 Organometallics, Vol. 24, No. 26, 2005
de Fre´mont et al.
Figure 4. Ball-and-stick representations of complexes (IAd)AgCl (17), (IsB)AgCl (18), (IDD)AgCl (19), and (TPh)AgCl as
a trimer (20a). Hydrogen atoms have been omitted for clarity.
carbene complex formed (Table 3). It is reasonable to
state that polar solvents must stabilize the ionic
[(IMes)2Ag]+ form better than nonpolar solvents and
might shift the equilibrium {(IMes)AgCl/[(IMes)2Ag]+}
toward the bis-NHC-Ag complex.
The 1H NMR spectrum of 21 displays a single
resonance at 7.23 ppm for the unsaturated imidazole
ring and the corresponding signals for the N-mesityl
groups.11 The 13C NMR spectrum does not exhibit any
signal between 160 and 200 ppm, an observation also
made by Hedrick et al.11 Solid-state structural data
showed a two-coordinate silver(I) atom in a linear
environment with a C-Ag-C angle of 180°. The Ag-C
bond distances are 2.066 and 2.084 Å, while both Ag-
Cl bond distances are 2.534 Å (Table 4). All these values
are in good agreement with the other bis-carbene
complexes previously reported.12,14,26 There is one cation
Figure 5. Ball-and-stick representations of complex (TPh)-
[(IMes)2Ag]+ and one anion [AgCl2]- present in the
AgCl as a bridged Ag-(µCl2)-Ag polymer (20b). Hydrogen
asymmetric unit. This complex is monomeric with no
argentophilic interactions and no Ag-(µCl2)-Ag bridg-
ing present, with the minimal Ag(I)‚‚‚Ag(I) distance
being 6.397 Å (Figure 6).
We also attempted to synthesize the complex (IMes)-
AgI in acetonitrile to investigate the effect of the halide
and the solvent polarity on the structure of the complex.
We anticipated a mixture of mono- and bis-carbene. The
atoms have been omitted for clarity.
[(IMes)2Ag]+[AgCl2]- (21) (Figure 6) and confirmed our
hypothesis for the formation of [(SIMes)2Ag]+[AgCl2]-
and [(IMe)2Ag]+[AgCl2]- as side-products from the
syntheses of [(SIMes)AgCl] (11) and [(IMe)AgCl] (15).
The three assays show that increasing the polarity of
the solvent leads to an increase in the amount of bis-

N-Heterocyclic Carbene Silver(I) Complexes
Organometallics, Vol. 24, No. 26, 2005 6307
Figure 6. Ball-and-stick representations of complexes [(IMes)2Ag]+[AgCl2]- (21) and [(IMes)2Ag]+2[Ag4I6]2- (22). Hydrogen
atoms have been omitted for clarity.
Table 3. Product Distribution of
addition, by increasing the solvent polarity, formation
of the bis-NHC complex can be favored. This trend looks
more pronounced with the more easily polarizable iodide
than with the harder chloride, allowing the synthesis
of the first [(NHC)2Ag]+2[Ag4X6]2- (22) complex. Deter-
mination of catalytic activity of this new series of well-
defined silver-NHC complexes in a number of organic
transformations is presently underway.
[(IMes)2Ag]+[AgCl2]- and (IMes)AgCl
solvent
(dielectric constant)28
[Ag(IMes)2]+[AgCl2]- (IMes)AgCl
chloroform (4.2)
acetonitrile (37.5)
dimethyl sulfoxide (46.7)
15%
25%
34%
85%
75%
66%
1H NMR and the 13C NMR spectra of the reaction crude
matched those of [(IMes)2Ag]+[AgCl2]- (21), leading us
to conclude that only the bis-NHC complex 22 is formed
in acetonitrile. The fact that Zhang et al. have reported
a polymeric mono-carbene silver(I) iodide, without any
trace of bis-carbene, in nonpolar dichloromethane19
leads us to believe that polarity of the solvent must be
the dominating factor in directing the structure adopted
by an iodide silver complex between mono- and bis-car-
bene. X-ray studies confirm that the silver(I) atom is
surrounded by two carbon atoms in near linear environ-
ment with a C-Ag-C bond angle of 180°. There are two
[(IMes)2Ag]+ cations and one [Ag4I6]2- anion in the
asymmetric unit, leading to a [(IMes)2Ag]2[Ag4I6] formula-
tion for 22. This complex is monomeric with no argen-
tophilic interactions (Figure 5). The most surprising fea-
ture comes from the massive octahedral anion [Ag4I6]2-
cluster. Inside this cage, the Ag(I)‚‚‚Ag(I) distances are
between 2.0915 and 3.1453 Å with half of the possible
coordination site occupied by the silver anion and the
Ag-I distances are between 2.7052 and 2.8507 Å (Table
4). The structure is centrosymmetric, with an inversion
center located at the origin of the octahedron. This
remarkable structure is the first silver halide complex
Experimental Section
General Considerations. All reactions using an imidazo-
lium salt as starting material were carried out in aerobic
condition. All reactions using a free carbene as starting
material were carried out using standard Schlenk techniques
under an atmosphere of dry argon or in a MBraun glovebox
containing dry argon and less than 1 ppm oxygen. Anhydrous
solvents were either distilled from appropriate drying agents
or purchased from Aldrich and degassed prior to use by
purging with dry argon and kept over molecular sieves.
Solvents for NMR spectroscopy were degassed with argon
and dried over molecular sieves. NMR spectra were collected
on a 400 MHz Varian Gemini spectrometer. Elemental analy-
ses were performed by Robertson Microlit Labs. Carbene
ligands 1-10 were synthesized following literature proce-
dures.29,30
Synthesis of (SIMes)AgCl (11). A 50 mL flask was
charged with SIMes‚HCl (750 mg, 2.19 mmol) and 15 mL of
dichloromethane. To this solution was added silver(I) oxide
(583 mg, 2.52 mmol). The resulting solution was refluxed for
12 h, then filtered over Celite, and the filtrate was reduced to
10 mL. The solution was cooled to 0 °C, and heptane was
slowly added until white crystals appeared. The solid was
filtered, washed with pentane (10 mL), and dried under
vacuum. Yield: 699 mg (71%). 1H NMR (CDCl3): δ (ppm) 6.95
(s, 4H, CH-aromatic), 4.00 (s, 4H, CH2-imidazole), 2.30 (s, 12H,
CH3), 2.29 (s, 6H, CH3). 13C NMR (CD2Cl2): δ (ppm) 207.5 (dd,
J1(109Ag, 13C) ) 256 Hz, J1(107Ag, 13C) ) 222 Hz, C-carbene),
139.0 (s, CH-aromatic), 135.7 (s, CH-aromatic), 135.3 (s, CH-
aromatic), 130.0 (s, CH-aromatic), 51.3 (s, CH2-imidazole), 21.2
(s, CH3), 18.1 (s, CH3). Anal. Calcd for C21H26N2AgCl (450.77):
C, 55.96; H, 5.77; N, 6.21. Found: C, 56.27; H, 5.94; N, 6.08.
Synthesis of (IPr)AgCl (12). A 50 mL flask was charged
with IPr‚HCl (1 g, 2.35 mmol) and 15 mL of dichloromethane.
To this solution was added silver(I) oxide (328 mg, 1.41 mmol).
The resulting solution was stirred at room temperature for
12 h, then filtered over Celite, and the filtrate was reduced to
10 mL. Pentane (30 mL) was added to the solution to
precipitate a white solid. The solid was washed further with
pentane (3 × 10 mL) and dried under vacuum to afford a white
powder. Yield: 2.160 g (88%). 1H NMR (CDCl3): δ (ppm) 7.50
(m, 2H, CH-aromatic), 7.30 (m, 4H, CH-aromatic), 7.21 (s, 2H,
reportedwithageneralformulaof[(NHC)2Ag]+2[Ag4X6]2-
.
Conclusion
We report the synthesis of 10 new silver mono-
carbene complexes. Their straightforward synthesis
can be accomplished by simple reaction of an imidazo-
lium chloride salt with silver oxide or by reaction of a
free NHC with silver chloride. The NMR and crystal-
lographic data do not permit unambiguous determina-
tions of electronic differences between the various
NHC-Ag moieties as a function of NHC. We have
observed a dynamic equilibrium between (NHC)AgCl
and [(NHC)2Ag]+[AgCl2]- species in solution, as gauged
by a simple analysis of the 13C NMR spectrum. It has
also been observed that (TPh)AgCl (20) exhibits both
forms (mono and bis carbene) in the solid state. In

6308 Organometallics, Vol. 24, No. 26, 2005
Table 4. Selected Bond Lengths and Angles for [(IMes)2Ag]+ Complexes
de Fre´mont et al.
2
complex
[(IMes)2Ag]+[AgCl2]- (21)
Ag-C (Å)
Ag-Cl/Ag-I (Å)
2.534(5)
C-Ag-C (deg)
2.066(5)
2.084(5)
2.079(5)
2.082(5)
180.000(1)
[(IMes)2Ag]+2[Ag4I6]2- (22)
2.7556(14)-2.7774(14)
2.8121(14)-2.7212(12)
2.7468(12)-2.7751(13)
2.7157(13)-2.7627(14)
2.8507(14)-2.7025(14)
2.7175(14)-2.8397(14)
2.7052(14)-2.7627(14)
172.5(2)
CH-imidazole), 2.54 (septet, J ) 6.8 Hz, 4H, CH(CH3)2), 1.28
(d, J ) 6.8 Hz, 12H, CH (CH3)2), 1.22 (d, J ) 6.8 Hz, 12H, CH
(CH3)2). 13C NMR (CDCl3): δ (ppm) 184.6 (dd, J1(109Ag, 13C) )
271 Hz, J1(107Ag, 13C) ) 235 Hz, C-carbene), 145.6 (s, CH-
aromatic), 130.8 (s, CH-aromatic), 124.4 (s, CH-aromatic),
123.7 (s, CH-aromatic), 123.6 (s, CH-imidazole), 28.7 (s, CH
(CH3)2), 24.7 (s, CH (CH3)2), 24.0 (s, CH (CH3)2). Anal. Calcd
for C27H36N2AgCl (531.59): C, 61.00; H, 6.77; N, 5.27. Found:
C, 61.20; H, 7.05; N, 5.22.
Synthesis of (SIPr)AgCl (13). A 50 mL flask was charged
with SIPr‚HCl (1 g, 2.60 mmol) and 15 mL of dichloromethane,
to which was added silver(I) oxide (356 mg, 1.61 mmol). The
resulting solution was stirred at room temperature for 12 h,
then filtered over Celite, and the filtrate was reduced to 10
mL. Pentane (30 mL) was added to immediately precipitate a
white solid. The solid was further washed with pentane (3 ×
10 mL) and dried under vacuum to afford a white powder.
Yield: 1.019 g (74%). 1H NMR (CDCl3): δ (ppm) 7.41 (m, 2H,
CH-aromatic), 7.25 (m, 4H, CH-aromatic), 4.07 (s, 4H, CH2-
imidazole), 3.06 (septet, J ) 6.8 Hz, 4H, CH(CH3)2), 1.35 (d, J
) 6.8 Hz, 12H, CH (CH3)2), 1.35 (d, J ) 6.8 Hz, 12H, CH
(CH3)2). 13C NMR (CD2Cl2): δ (ppm) 207.7 (dd, J1(109Ag, 13C)
) 253 Hz, J1(107Ag, 13C ) 219 Hz, C-carbene), 147.0 (s, CH-
aromatic), 134.9 (s, CH-aromatic), 130.1 (s, CH-aromatic),
124.8 (s, CH-aromatic), 54.1 (s, CH2-imidazole), 29.0 (s, CH
(CH3)2), 25.3 (s, CH (CH3)2), 24.0 (s, CH (CH3)2). Anal. Calcd
for C27H38N2AgCl (533.59): C, 60.77; H, 7.12; N, 5.25. Found:
C, 60.64; H, 7.38; N, 5.04.
177.5 (s, C-carbene), 125.8 (s, CH-imidazole), 36.5 (s, CH3),
9.2 (s, CH3). Anal. Calcd for C7H12N2AgCl (267.69): C, 31.43;
H, 4.48; N, 10.46. Found: C, 31.21; H, 4.38; N, 10.19.
Synthesis of (ICy)AgCl (16). A method of preparation
similar to that used for compound (SIMes)AgCl (11) gave a
1
white solid. Yield: 754 mg (72%). H NMR (CDCl3): δ (ppm)
6.98 (s, 2H, CH-imidazole), 4.22 (m, 2H, NCH-cyclohexyl), 2.02
(m, 4H, CH2), 1.87 (m, 4H, CH2), 1.74 (m, 2H, CH2), 1.58 (m,
4H, CH2), 1.43 (m, 4H, CH2), 1.19 (m, 2H, CH). 13C NMR
(CDCl3): δ (ppm) 179.1 (br s, C-carbene), 119.9 (s, CH-
imidazole), 63.9 (s, NCH-cyclohexyl), 36.6 (s, CH2), 27.5 (s,
CH2), 27.2 (s, CH2). Anal. Calcd for C15H24N2AgCl (375.42): C,
47.99; H, 6.39; N, 7.46. Found: C, 48.17; H, 6.56; N, 7.40.
Synthesis of (IAd)AgCl (17). A 50 mL flask was charged
with IAd‚HCl (300 mg, 0.81 mmol) and 10 mL of dichlo-
romethane, to which was added silver(I) oxide (112 mg, 0.48
mmol). The resulting solution was refluxed for 12 h, then
filtered over Celite, and the filtrate was reduced to 5 mL. The
solution was cooled to 0 °C, and pentane was slowly added
until the appearance of white crystals. The solid was filtered
off, washed with pentane (3 × 5 mL), and dried under vacuum
to afford a white powder. Yield: 699 mg (71%). 1H NMR (CD2-
Cl2): δ (ppm) 7.19 (s, 2H, CH-imidazole), 2.35-22 (br m, 20H,
adamantyl), 1.75 (m, 10H, CH2-adamantyl). 13C NMR (CD2-
Cl2): δ (ppm) 173.8 (br s, C-carbene), 116.3 (s, CH-imidazole),
58.2 (s, NCH-adamantyl), 44.9 (s, CH2), 36.0 (s, CH2), 30.2 (s,
CH2). Anal. Calcd for C23H32N2AgCl (478.92): C, 57.68; H, 6.68;
N, 5.85. Found: C, 57.88; H, 6.82; N, 5.59.
Synthesis of (IsB)AgCl (18). A method of preparation
Synthesis of (IPrMe)AgCl (14). In a glovebox, a 50 mL
Schenk flask was charged with 120 mg (0.66 mmol) of IPrMe
and 10 mL of THF, and then 143 mg (0.14 mmol) of silver(I)
chloride was added. The resulting solution was kept in the
dark and stirred at room temperature for 12 h. The remaining
steps were then carried out in air. The solution was filtered
over Celite and the filtrate reduced to 10 mL. Pentane (30 mL)
was added to the solution, resulting in an immediate precipi-
tation of a white solid. The solid was further washed with
pentane (2 × 10 mL) and dried under vacuum, to afford a white
similar to that used for compound (SIMes)AgCl (11) gave a
1
white solid. Yield: 838 mg (75%). H NMR (CDCl3): δ (ppm)
6.95 (s, 2H, CH-imidazole), 3.88 (d, J ) 7.3 Hz, 4H, CH2), 2.12
(m, 2H, CH), 0.91 (d, J ) 6.3 Hz, 12H, CH3). 13C NMR
(CDCl3): δ (ppm) 179.3 (s, C-carbene), 121.6 (s, CH-imidazole),
53.4 (s, CH2), 30.5 (s, CH), 20.0 (s, CH3). Anal. Calcd for
C11H20N2AgCl (323.39): C, 40.85; H, 6.18; N, 8.66. Found: C,
41.12; H, 6.34; N, 8.60.
Synthesis of (IDD)AgCl (19). A 50 mL flask was charged
with IDD‚HCl (500 mg, 1.15 mmol) and 10 mL of THF, to
which was added silver(I) oxide (305 mg, 1.32 mmol). The
resulting solution was stirred at reflux for 16 h, then filtered
over Celite, and the filtrate was reduced to 5 mL. The solution
was cooled to -40 °C, and cold pentane was slowly added until
the appearance of a white precipitate. The solid was filtered
off, washed with cold pentane (10 mL), and dried under
vacuum. Yield: 415 mg (67%). 1H NMR (CDCl3): δ (ppm) 6.96
(s, 2H, CH-imidazole), 4.52 (m, 2H, NCH-cyclododecyl), 2.04
(m, 4H, CH2), 1.69 (m, 4H, CH2), 1.55-1.27 (m, 36H, CH2).
13C NMR (CDCl3): (ppm) δ 177.8 (br d, C-carbene), 118.6 (s,
CH-imidazole), 59.0 (s, NCH-cyclododecyl), 31.7 (s, CH2), 23.8
(s, CH2), 23.7 (s, CH2), 23.6 (s, CH2), 23.5 (s, CH2), 21.8 (s,
CH2). Anal. Calcd for C27H48N2AgCl (543.43): C, 59.67; H, 8.83;
N, 5.15. Found: C, 59.46; H, 8.71; N, 4.94.
1
powder. Yield: 63 mg (71%). H NMR (CDCl3): δ (ppm) 4.55
(septet, J ) 6.9 Hz, 2H, NCH-isopropyl), 2.16 (s, 6H, CH3-
imidazole), 1.56 (d, J ) 6.9 Hz, 12H, CH (CH3)2). 13C NMR
(CD2Cl3): δ (ppm) 172.3 (s, C-carbene), 124.9 (s, CH-imidazole),
51.5 (s, CH (CH3)2), 23.9 (s, CH (CH3)2), 9.5 (s, CH3-imidazole).
Anal. Calcd for C11H20N2AgCl (323.43): C, 40.85; H, 6.18; N,
8.66. Found: C, 40.96; H, 5.92; N, 8.57.
Synthesis of (IMe)AgCl (15). In a glovebox, a 50 mL
Schenk flask was charged with 100 mg (0.81 mmol) of IMe
and 10 mL of THF, and then 230 mg (0.16 mmol) of silver(I)
chloride was added. The resulting solution was kept in the
dark and stirred at room temperature for 12 h. The remaining
steps were then carried out in air. The solution was cooled to
-78 °C and rapidly filtered over Celite. The Celite was rinsed
first with cold THF. The clear green solution obtained was
discarded. Then the Celite was washed with 10 mL of dichlo-
romethane, resulting in a bright yellow solution. Heptane was
slowly added until the appearance of yellow clear crystals. The
solids were filtered off, rinsed with pentane, and dried under
vacuum. Yield: 80 mg (28%). 1H NMR (CDCl3): δ (ppm) 3.65
(s, 6H, NCH3), 2.12 (s, 6H, CH3). 13C NMR (CD2Cl2): δ (ppm)
Synthesis of (TPh)AgCl (20). A method of preparation
similar to that used for compound (IPr)AgCl (12) gave a white
solid. Yield: 590 mg (82%). 1H NMR (CDCl3): δ (ppm) 7.79
(m, 2H, CH-aromatic), 7.41 (m, 3H, CH-aromatic), 4.39 (m,
CH2-pyrrolidine), 3.10 (m, 2H, CH2-pyrrolidine), 2.73 (m, 2H,
CH2-pyrrolidine). 13C NMR (CDCl3): δ (ppm) 176.9 (s, C-

N-Heterocyclic Carbene Silver(I) Complexes
Organometallics, Vol. 24, No. 26, 2005 6309
carbene), 160.7 (s, NCdN), 140.1 (s, NC-aromatic), 129.5 (s,
CH-aromatic), 129.0 (s, CH-aromatic), 122.9 (s, CH-aromatic),
46.6 (s, CCHN-pyrrolidine), 26.1 (s, CH2-pyrrolidine), 21.5 (s,
CH2-pyrrolidine). Anal. Calcd for C11H11N3AgCl (329.43): C,
40.10; H, 3.34; N, 12.75. Found: C, 40.51; H, 3.13; N, 12.51.
Synthesis of [(IMes)2Ag]+[AgCl2]- (21). A 50 mL flask
was charged with IMes‚HCl (340 mg, 0.99 mmol) and 10 mL
of acetonitrile, to which was added silver(I) oxide (120 mg, 0.50
mmol). The resulting solution was refluxed for 24 h, then
filtered over Celite, and the filtrate was reduced to 5 mL. The
solution was left to crystallize, and brown pale crystals were
obtained. Yield: 750 mg (85%). 1H NMR (CD3CN): δ (ppm)
7.23 (s, 2H, CH2-imidazole), 6.97 (s, 4H, CH-aromatic), 2.42
(s, 6H, CH3), 1.71 (s, 12H, CH3). 13C NMR (CD3CN): δ (ppm)
140.2 (s, CH-aromatic), 135.9 (s, CH-aromatic), 135.5 (s, CH-
aromatic), 129.8 (s, CH-aromatic), 123.9 (s, CH-imidazole), 21.1
(s, CH3), 17.3 (s, CH3). Anal. Calcd for C42H48N4Ag2Cl2
(894.96): C, 56.33; H, 5.40; N, 6.26. Found: C, 55.88; H, 5.65;
N, 6.49. HRMS: [(IMes)2Ag] [AgCl2]: Calcd (cation) 717.29304
and experimentally measured 717.3080.
Calcd for C84H96N8Ag6I8 (2625.46): C, 39.41; H, 3.68; N, 4.27.
Found: C, 39.59; H, 3.98; N, 4.56. HRMS: [(IMes)2Ag]2[Ag4I6]:
Calcd (cation) is 717.29304 and measured 717.2941.
Crystallographic information files (CIF) of complexes 11-
22 have been deposited with the CCDC, 12 Union Road,
Cambridge, CB2 1EZ, U.K., and can be obtained on request
free of charge, by quoting the publication citation and deposi-
tion numbers 279034-279044 for complexes 11-21 and
279130 for complex 22.
Acknowledgment. Financial support for this re-
search was provided by the National Science Foundation
(S.P.N.), the donors of the American Chemical Society
Petroleum Research Fund (J.A.C.C.), Simon Fraser
University and the Natural Sciences and Engineering
Research Council of Canada (J.A.C.C.). S.P.N. thanks
Eli Lilly and Co. and Lonza for support in the form of
materials. We thank Professor Tomislav Rovis (Colorado
State University) for the preparation protocol of the
triazolium carbene (ITPh).
Synthesis of [Ag(IMes)2]+2[Ag4I6]2- (22). A method of
preparation similar to that used for compound [(IMes)2Ag]+-
[AgCl2]- (21) gave pale brown crystals. Yield: 299 mg (23%).
1H NMR (CD3CN): δ (ppm) 7.23 (s, 2H, CH2-imidazole), 6.97
(s, 4H, CH-aromatic), 2.42 (s, 6H, CH3), 1.71 (s, 12H, CH3).
13C NMR (CDCl3): δ (ppm) 140.1 (s, CH-aromatic), 135.9 (s,
CH-aromatic), 135.5 (s, CH-aromatic), 129.8 (s, CH-aromatic),
124.0 (s, CH-imidazole), 21.1 (s, CH3), 17.3 (s, CH3). Anal.
Supporting Information Available: Crystallographic
information files (CIF) of complexes 11-22. A discussion of
the disorder associated with the anion [Ag4I6]2-. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM050735I