Six- and seven-membered ring carbenes: Rational synthesis of amidinium salts, generation of carbenes, synthesis of Ag(I) and Cu(I) complexes

Article abstract of DOI:10.1016/j.jorganchem.2009.03.014

Reactions of neat 1,3- and 1,4-dibromides with N,N′-diarylformamidines in the presence of diisopropylethylamine (DIPEA) afford corresponding amidinium salts in high yields (>80%). Six- and seven-membered ring amidinium salts bearing bulky Mes (2,4,6-Me

Full text of DOI:10.1016/j.jorganchem.2009.03.014

Journal of Organometallic Chemistry 694 (2009) 2454–2462
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Six- and seven-membered ring carbenes: Rational synthesis of amidinium
salts, generation of carbenes, synthesis of Ag(I) and Cu(I) complexes
Eugene L. Kolychev a, Ivan A. Portnyagin a,b, Viacheslav V. Shuntikov c, Victor N. Khrustalev c,
Mikhail S. Nechaev a,b,
*
a Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russian Federation
b A.V. Topchiev Institute of Petrochemical Synthesis, RAS, Leninsky Prosp., 29, Moscow 119991, Russian Federation
c A.N. Nesmeyanov Institute of Organoelement Compounds of RAS, Vavilov Str., 28, Moscow 119991, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Reactions of neat 1,3- and 1,4-dibromides with N,N0-diarylformamidines in the presence of diisopropyl-
ethylamine (DIPEA) afford corresponding amidinium salts in high yields (>80%). Six- and seven-mem-
bered ring amidinium salts bearing bulky Mes (2,4,6-Me3C6H2) and Dipp (2,6-iPr2C6H3) aryl groups
were prepared using this method. Free six-membered ring carbene 6-Dipp was generated from amidini-
um salt using LiHMDS as a base. NHC–Ag(I) complexes were obtained by the reactions of amidinium salts
with Ag2O. NHC complexes of Pd and Rh are not accessible by deprotonation of amidinium salts, nor by
transmetallation of Ag(I) complexes. However NHC–Cu(I) complexes were obtained by transmetallation
of NHC–Ag(I). Thus, transmetallation of six- and seven-membered NHC–Ag(I) complexes was docu-
mented for the first time.
Article history:
Received 24 December 2008
Received in revised form 24 February 2009
Accepted 6 March 2009
Available online 17 March 2009
Keywords:
N-heterocyclic carbene
Amidinium salt
Deprotonation
Silver complex
Copper complex
Transmetallation
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
N-heterocyclic carbenes (NHC) [1] were first proposed by Bre-
slow as intermediates in B1 catalytic cycle as early as in 1957
[2]. A decade later Wanzlick and Schonherr [3] and Öfele [4] pre-
pared complexes of imidazole-2-ylidene with transition metals.
Later, Lappert and coworkers obtained a series of carbene–metal
complexes starting from electron rich olefins (EROs) [5].
Nevertheless, intensive development of NHC chemistry started
in 1991 with Arduengo’s isolation of free imidazole-2-ylidene 1
[6]. In 1995 Arduengo obtained imidazoline-2-ylidene 2, thus
showing that the presence of imidazole aromatic system is not
obligatory for stabilization of a free carbene [7].
N
N
N
N
N
N
N
1
2
3
4
Initially it was supposed that NHCs as ligands are phosphane
mimics [8]. Although a wealth of experimental data show that
NHCs surpass their phosphane counterparts in donor properties,
bonding energies and steric properties [9], many metal NHC com-
plexes have been show to be tolerant to air and moisture. Their
synthetic accessibility [10] and ease of functionalization [11]
opened wide possibilities in utilization of such complexes in catal-
ysis [12].
N
N
N
N
N
5
6
7
Most of NHC–metal complexes known to date are derived from
imidazolylidene 1 and imidazolinyliden 2 type carbenes. There are
two main strategies of enhancing NHC’s donor properties: (i)
decrease of number of nitrogen atoms attached to ylidene center,
* Corresponding author. Address: Department of Chemistry, M.V. Lomonosov
Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russian Federation.
Tel./fax: +7 495 9392677.
E-mail address: nechaev@nmr.chem.msu.ru (M.S. Nechaev).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.03.014

E.L. Kolychev et al. / Journal of Organometallic Chemistry 694 (2009) 2454–2462
2455
Table 1
3 [13,14], 4 [15], 5 [16] and (ii) expansion of heterocycle to six- and
seven-membered rings, 6 [17–23] and 7 [14,24,25].
The yields (%) of cyclic amidinium salts obtained by different methods (Scheme 2).
Method
[(6-Dipp)H][Br]
[(7-Dipp)H][Br]
[(70-Dipp)H][Cl]
[(7-Mes)H][Br]
In this contribution we report on the rational approach to the
synthesis of six- and seven-membered ring amidinium salts, gen-
eration of free carbenes, synthesis of carbene complexes with sil-
ver(I), and synthesis of (NHC)CuX complexes via transmetallation
of silver(I) complexes. During the preparation of this manuscript
a paper by Cavell et al. has appeared which has many intersections
(synthesis and X-ray of amidinium salts, free NHCs and Ag(I) com-
plexes) with this contribution [23].
a
64
88
71
52
82
64
46
–
–
49
92
89
b
ca
a
Ref. [23].
readily recovered. This procedure has been further reproduced on
the tens of gram scale.
2. Results and discussion
Single crystals of six- and seven-membered Dipp derivatives
were obtained from CH2Cl2 or CHCl3. The structures were deter-
mined by X-ray (Fig. 1). [(70-Dipp)H][Cl] is the first amidinium salt
bearing isolated CH@CH moiety in the back-bone. This feature
opens wide possibilities for modification.
2.1. Amidinium salts
There are two main approaches for synthesis of cyclic amidini-
um salts bearing aryl substituents at nitrogen atoms known to
date. First approach is cyclization of arylated diamines (Scheme
1, a [19], b [26], c [20,27]). Such diamines are not readily available.
Moreover, cyclization reactions require harsh conditions and have
low reproducibility.
2.2. Generation of free carbenes
Free carbene 6-Dipp was generated on NMR scale by deproto-
nation of [(6-Dipp)H][Br] with LiHMDS in absolute THF-d8 under
argon (Scheme 3). In 13C NMR spectrum characteristic 245.9 ppm
signal corresponding to ylidene carbon and no signals at
ꢀ160 ppm characteristic to amidinium carbon of the salt were
found.
Deprotonation of the salt [(7-Dipp)H][Br] does not proceed un-
der the same conditions. According to NMR the solution contains
only reactants. Interaction of [(7-Dipp)H][Br] with KOtBu leads to
unidentified mixture of products which does not contain free car-
bene according to 13C NMR (see Scheme 4).
An alternative approach, proposed recently by Bertrand, is
deprotonation of amidine with BuLi and further cyclization with
1,3- or 1,4-dihalide (Scheme 2, a) [14]. Formamidines bearing
bulky aryl substituents are easily prepared from triethyl orthofor-
mate and anilines. This method has been modified by Grubbs [28].
Five-membered imidazolinium salts were obtained by alkylation of
formamidines with dichloroethane in the presence of sterically
hindered diisopropylethylamine (DIPEA; Scheme 2, b). Cavell ob-
tained a row of five, six and seven-membered ring amidinium salts
by alkylation of formamidines by dibromides and diiodides in the
presence of K2CO3 in refluxing acetonitrile (Scheme 2, c) [23].
We obtained four amidinium salts in moderate yields (Scheme
2a, Table 1) using Bertrand’s method. The same salts but [(70-
Dipp)H][Cl] were prepared using modified Grubbs’ method
(Scheme 2, b). DIPEA (1.1 equiv.) was added to a stirred mixture
of formamidine (1 equiv.) and dibromide (3 equiv.) with no sol-
vent. The products are white crystalline substances stable in air
and moisture. All salts were characterized by 1H, 13C NMR, and ele-
mental analysis. This method provides the highest yields of six-
and seven-membered ring N,N0-diarylated amidinium salts (Table
1). Moreover, excess of dibromide and expensive DIPEA may be
We tried to obtain free carbene 7-Dipp by vacuum pyrolysis of
carbene adduct with methanol [29]. Adduct (7-Dipp)(H)(OMe) was
obtained by the reaction of equimolar amounts of the salt [(7-
Dipp)H][Br] and NaOMe in absolute THF. Heating under 0.04 Torr
Ar
Ar
NH
N
N
-
a, b,
c
or
( )n
( )n
X
NH
Ar
Ar
a
c
b
: 1) CH2O, 2) NBS; : CHCl3, OH ;
: HC(OEt)3, NH4X
n= 1,2
Scheme 1.
Fig. 1. X-ray crystal structure of [(70-Dipp)H][Cl] ꢁ 0.5H2O (thermal ellipsoids are
drawn at the 50% level).
Ar
N
Ar
Ar
N
N
a, b, or c
HC(OEt)3
Ar NH2
Y
X
HN
Dipp
Br
Dipp
Dipp
Ar
N
N
N
N
LiN(Si(Me)3)2
6-Dipp
[(
)H][Br], Y = CH2, X = Br, Ar = Dipp
a: n-BuLi, X-CH2YCH2-X
[(7-Dipp)H][Br], Y = CH2-CH2, X = Br, Ar = Dipp
[(7'-Dipp)H][Cl], Y = cis-CH=CH, X = Cl, Ar = Dipp
b
: DIPEA, X-CH2YCH2-X
: K2CO3, X-CH2YCH2-X
Dipp
c
7-Mes
[(
)H][Br], Y = CH2-CH2, X = Br, Ar = Mes
[(6-Dipp)H][Br]
6-Dipp
Scheme 2.
Scheme 3.

2456
E.L. Kolychev et al. / Journal of Organometallic Chemistry 694 (2009) 2454–2462
Dipp
Dipp
O
Dipp
Δ
N
N
N
N
CH3ONa
Br
Dipp
H
Dipp
N
N
Dipp
7-Dipp
7-Dipp
7-Dipp
[(
)H][Br]
(
)(H)(OMe)
Scheme 4.
vacuum has lead only to sublimation of (7-Dipp)(H)(OMe) with no
decomposition (according to 1H and 13C NMR). The structure of (7-
Dipp)(H)(OMe) was unambiguously established by single-crystal
X-ray (Fig. 2).
2.3. NHC–metal complexes via deprotonation
The ultimate goal of our studies is the synthesis of NHC–metal
complexes and testing of their catalytic properties. Unfortunately,
we were unable to obtain free carbenes in quantities sufficient for
further synthesis. Although, the alternative method – transfer of
NHC ligand from Ag(I) complex could be relied upon to produce
sufficient quantities [30].
Fig. 3. X-ray crystal structure of [Ag(7-Mes)2][Cl] ꢁ 2H2O (thermal ellipsoids are
drawn at the 50% level).
Three NHC–Ag(I) complexes were obtained by the reactions of
amidinium salts with silver oxide in dichloromethane at room
temperature for 2 days (Scheme 5). These complexes are white
crystalline solids stable in air and in the presence of moisture,
not sensitive to sun light, melt with decomposition at 280–
300 °C, characterized by 1H, 13C NMR, elemental analysis and X-
ray (Fig. 3).
Both 6-Dipp and 7-Dipp form 1:1 complex with AgBr while 7-
Mes forms ionic 2:1 complex [Ag(7-Mes)2][Cl]. It can be supposed
that bulkier Dipp groups prevent formation of 2:1 complexes.
Interestingly, the counter ion in [Ag(7-Mes)2][Cl] is chloride in-
Fig. 4. X-ray crystal structure of 8 (thermal ellipsoids are drawn at the 50% level).
stead of AgBrꢂ2 [23,30]. We suppose that chloride is abstracted from
methylene chloride under exposure to light.
We were unable to obtain Ag(I) complex from [(70-Dipp)H][Cl]
using the same method. The only product obtained in 80% yield
was 8 (Scheme 7). The structure of 8 was established by 1H, 13C
NMR, X-ray and elemental analysis (Fig. 4). We suppose that 8 is
formed via Hoffman 1,4-elimination under Ag2O action as a base.
It can be also supposed that all attempts by Cavell et al. [23] to ob-
tain free seven-membered ring carbenes bearing xylyl backbone
were unsuccessful due to the analogous elimination (see Scheme
6).
Fig. 2. X-ray crystal structure of (7-Dipp)(H)(OMe) (thermal ellipsoids are drawn at
the 50% level).
Dipp
Dipp
N
N
N
Ag2O
Cl
N
Dipp
[(7'-Dipp)H][Cl]
Dipp
Ar
Ar
Ar
Ar
Ar Ar
Ag
8
X
N
N
N
N
Ag2O, CH2Cl2
48 h
N
N
N
N
(
)
and
(
)
Ag Br
(
)
( )
n
Br
n
n
n
B
H
Ar Ar
n = 1,2
n = 1
n = 1,2
N
N
N
N
N
N
6-Dipp
6-Dipp
7-Dipp
(
)AgBr, 83%
)AgBr, 75%
[(
[(
)H][Br]
)H][Br]
[(7-Mes)2Ag][Cl], 73%
7-Dipp
(
[(7-Mes)H][Br]
Scheme 5.
Scheme 6.

E.L. Kolychev et al. / Journal of Organometallic Chemistry 694 (2009) 2454–2462
2457
Dipp
Dipp
amidinium salt by Cu2O [34], and (3) transmetallation of NHC–
Ag(I) complex with copper salt [30].
CuBr, CH2Cl2
48 h
N
N
(
)
( )n
Ag Br
Cu
Br
n
We attempted to prepare NHC–Cu(I) complexes via deprotona-
tion by Cu2O (route 2). Heating of amidinium salt [(7-Dipp)H][Br]
with Cu2O in the presence of sodium acetate in DMSO at 100 °C for
12 h [34] has lead to formation of a Cu(I) complex in trace amounts
(according to TLC). The attempts to obtain Cu(I) complexes via
transmetallation were more successful. Thus, interaction of equi-
molar amounts of (6-Dipp)AgBr or (7-Dipp)AgBr with copper(I)
bromide in CH2Cl2 have lead to formation of (6-Dipp)CuBr and
(7-Dipp)CuBr, respectively, in high yields (Scheme 7). The products
were isolated in pure form by filtration through Celite and further
concentration of the filtrate to dryness in vacuo. The complexes ob-
tained, were characterized by 1H, 13C NMR, m.p. and elemental
analysis.
N
N
Dipp
n = 1,2
Dipp
n = 1,2
6-Dipp
(
)CuBr, 83%
6-Dipp
(
)AgBr
(7-Dipp)CuBr, 79%
(7-Dipp)AgBr
Scheme 7.
We have also tackled the possibility of preparation of Pd and Rh
complexes via deprotonation of amidinium salts. [(6-Dipp)H][Br]
and [(7-Dipp)H][Br] were treated with different palladium re-
agents: (1) Pd(OAc)2 in DMSO at 120 °C [31], (2) Pd(OAc)2 in the
presence of NaI and t-BuOK in THF [25,32], and (3) PdCl2 in 3-bro-
mopyridine in the presence of K2CO3 [33]. Dark-red materials
which contain amidinium cations (1H NMR) and, probably,
complex palladium anions were obtained. Furthermore, starting
materials only were recovered after refluxing for 15 h of the mix-
ture of [(6-Dipp)H][Br], [RhCl(COD)]2 and t-BuOK in THF [22].
13C NMR spectra of (6-Dipp)CuBr and (7-Dipp)CuBr contain
characteristic ylidene carbon signals at 201.1 and 210.5 ppm,
respectively. As for NHC–silver(I) complexes [23], a downfield shift
of ylidene carbon was observed upon enlargement of carbene het-
erocycle from six- to seven-membered ring.
Single crystals of copper(I) complexes were obtained from
CHCl3, the structures were determined by X-ray (Fig. 5). (6-Dipp)-
CuBr is the first 1:1 complex of N,N0-diarylated six-membered ring
NHC [21] and (7-Dipp)CuBr is the first seven-membered ring NHC
complex of copper(I). Moreover we have shown the possibility of
transmetallation of six- and seven-membered ring NHC–Ag(I)
complexes for the first time.
2.4. Transmetallation of NHC–Ag(I) complexes
The possibility of ligand transfer from silver(I) complexes to
other metals is still arguable for six- and seven-membered NHCs.
Thus, Buchmeiser reported on 6-Mes transfer from silver(I) to pal-
ladium [19]. However, Herrmann et al. [20] has later shown that
the formation of [Ag(6-Mes)2]2[Pd2Cl6] complex salt takes place.
It was also supposed that transmetallation does not take place
due to higher energy of NHC–Ag bond for six-membered ring carb-
enes in respect to five-membered ring counterparts. Moreover, the
formation of Ag(I) from Rh(I) and Pd(II) complexes was docu-
mented [18,25]. Our attempts to obtain Pd and Rh complexes via
transmetallation of (6-Dipp)AgBr and (7-Dipp)AgBr were also
unsuccessful. Prolonged stirring of silver(I) complexes with
PdCl2(PPh3)2, PdCl2(COD), Pd(OAc)2 or [RhCl(COD)]2 at elevated
temperatures in different solvents lead to isolation of starting
materials only.
2.5. X-ray
One six- and three seven-membered amidinium salts were
characterized by X-ray crystallography. The crystal structures of
[(6-Dipp)H][Br] ꢁ 1.5CHCl3, [(7-Dipp)H][Br] ꢁ 3CHCl3, [(7-Dipp)H]-
[Br] ꢁ CH2Cl2 and [(70-Dipp)H][Cl] ꢁ 0.5H2O are shown in Fig. 1,
and S1–S3, and selected geometrical parameters are listed in Table
S1. It should be noted that the structures of [(7-Dipp)H][Br] ꢁ
3CHCl3 and [(7-Dipp)H][Br] ꢁ CH2Cl2 have an important difference:
in the latter, contrary to the former, the proton at the amidinium
carbon atom participates in the hydrogen bonding with the bro-
mide anion. Because of that, in the structures [(6-Dipp)H][Br] ꢁ
1.5CHCl3 and [(70-Dipp)H][Cl] ꢁ 0.5H2O, the amidinium proton also
There are three main routes to NHC–Cu(I) complexes: (1) inter-
action of a free NHC with copper salt [21], (2) deprotonation of
Fig. 5. X-ray crystal structures of (6-Dipp)CuBr ꢁ CHCl3 and (7-Dipp)CuBr ꢁ CHCl3 (thermal ellipsoids are drawn at the 50% level). (6-Dipp)CuBr ꢁ CHCl3 (7-Dipp)CuBr ꢁ CHCl3

2458
E.L. Kolychev et al. / Journal of Organometallic Chemistry 694 (2009) 2454–2462
takes part in the hydrogen bonding with the halogen atom, the
geometrical parameters of [(7-Dipp)H][Br] ꢁ CH2Cl2 are considered
in discussion below.
the sp3-hybridized carbon atoms in the (7-Dipp)AgBr and (7-
Dipp)CuBr range from 111.9(2) to 113.5(2)° and from 111.6(6) to
113.8(6)°, respectively.
The X-ray structure analysis reveals the usual chair conforma-
tion for the saturated six-membered and the unsaturated seven-
membered carbene rings, and the highly twisted conformation
for the saturated seven-membered carbene ring. It is well known
that the larger heterocyclic rings lead to the increased N–Ccarb–N
angles which, in turn, result in the ring strain. The same geometri-
cal peculiarities are also observed when going from six- to seven-
membered carbene rings of the amidinium salts. The N–Ccarb–N an-
gle in the [(6-Dipp)H] cation is 123.7(4)°, whilst in the [(7-Dipp)H]
and [(70-Dipp)H] cations have angles of 125.1(2) and 127.5(1)°,
respectively. The increase of the N–Ccarb–N angle in the seven-
membered amidinium cations gives rise to the substantial distor-
tion of the tetrahedral geometry of the ring carbon atoms in com-
parison with the related six-membered cations. So, in the [(7-
Dipp)H] and [(70-Dipp)H] cations, the endo-angles at the quater-
nary carbon atoms range from 111.8(2) to 114.6(2)° and from
111.1(1) to 111.2(1)°, respectively, whereas the corresponding an-
gle range in the [(6-Dipp)H] cation is 109.5(3)–110.6(4)°. The C–N–
C angle distribution is similar in the six- and seven-membered
A feature of the [Ag(7-Mes)2](+) cation is practically perpendic-
ular arrangement of two seven-membered carbene ligands to
accommodate the bulky mesityl substituents at the nitrogen
atoms. The dihedral angle between the two N–Ccarb–N planes is
84.49(5)°.
No Ag–Ag and Cu–Cu interactions are observed in the crystals.
3. Conclusion
A new effective method of preparation of N,N0-diarylated six-
and seven-membered ring amidinium salts was developed. Se-
ven-membered amidinium salt [(70-Dipp)H][Cl] bearing isolated
C@C double bond in back-bone was prepared for the first time.
Free carbene 6-Dipp was generated upon treatment of amidini-
um salt with LiHMDS. It was also found that vacuum thermolysis of
seven-membered carbene adduct with alcohol (7-Dipp)(H)(OMe)
is not applicable for carbene generation.
A series of NHC–Ag(I) complexes were prepared via interaction
of amidinium salts with Ag2O. It was found that the presence of
isolated C@C double bond in the back-bone prevent the formation
of silver(I) complexes leading to ring opening via 1,4-elimination.
Two new six- and seven-membered ring NHC–Cu(I) complexes
were prepared from corresponding NHC–Ag(I). Thus, transmetalla-
tion of N,N0-diarylated six- and seven-membered NHC–Ag(I) com-
plexes was documented for the first time.
amidinium cations. They change in the order of Cring–N–Ccarb
CAr–N–Ccarb > Cring–N–CAr (Table S1).
>
The two nitrogen atoms have a trigonal planar configuration. Of
interest is the angle between the nitrogen coordination planes (
a
)
which is a useful gauge for the spatial orientation of the aryl sub-
stituents. For the saturated six-membered as well as the unsatu-
rated seven-membered rings having the chair conformation the
angle
a is very close to 0° (2.0(1) and 0.37(5)°, respectively), while
4. Experimental
for the twisted saturated seven-membered ring one is 23.38(5)°.
The twisting effect of the N-substituents in the saturated seven-
membered carbene ring provides an opportunity to design new
chiral ligands.
4.1. General comments
Unless otherwise stated, all manipulations were carried out
using standard Schlenk technique under an argon atmosphere.
All solvents for use in an inert atmosphere were purified by stan-
dard procedures and distilled under argon immediately prior to
use.[35] Other chemicals were obtained from commercial sources
and used without further purification. NMR spectra were obtained
The silver and copper complexes of six- and seven-membered
carbenes were investigated by single-crystal X-ray diffraction
studies. The molecular structures of the (6-Dipp)AgBr ꢁ CH2Cl2,
(6-Dipp)CuBr ꢁ CHCl3, (7-Dipp)AgBr ꢁ CH2Cl2, (7-Dipp)CuBr ꢁ CHCl3,
and [Ag(7-Mes)2][Cl] ꢁ H2O are shown in Figs. 3 and 5, S4 and S5,
selected geometrical parameters are presented in Table S1.
As it can be seen from Table S1, the Ag–Ccarb distances for the
Ag-complexes of six- and seven-membered carbenes are close to
each other and lie in the range of values reported for the related
complexes very recently (2.097(6)–2.122(3) Å). The Ccarb–Ag–X
bond angles are practically linear (177.6(2) and 177.59(5)°). Some-
what larger difference is observed in the Cu–Ccarb distances for the
Cu-complexes of six- and seven-membered carbenes. Interestingly,
in contrast to the Ag-complexes, the Ccarb–Cu–X bond angles
(173.97(6) and 173.5(2)°) in the Cu-complexes indicate more sig-
nificant deviations from linearity.
on
a
Bruker ‘‘Avance 400” spectrometer (400.13 MHz 1H,
100.62 MHz 13C). The chemical shifts are frequency referenced rel-
ative to solvent peaks. Coupling constants J are given in Hertz as
positive values regardless of their real individual signs. The multi-
plicity of the signals is indicated as ‘‘s”, ‘‘d”, or ‘‘m” for singlet, dou-
blet, or multiplet, respectively. The abbreviation ‘‘br” is given for
broadened signals. Elemental analyses were performed on a Carlo
Erba EA1108 CHNS-O elemental analyzer at the Institute of Petro-
chemical Synthesis, Russian Academy of Sciences. Melting points
were measured in an unsealed capillary using a SANYO Gallenk-
amp PLC melting point apparatus without any additional
corrections.
As compared to the amidinium salts, the increase in the N–Ccarb
bond lengths is observed upon complexation with transition met-
als, while the N–Cring and N–CAr bond lengths are kept virtually un-
changed. The coordination geometry of the two nitrogen atoms in
the six- and seven-membered carbenes remains nearly planar
4.2. X-ray structure determination
Data were collected on a Bruker SMART APEX II CCD and a Bru-
upon the complexation, however, the dihedral angle (a) between
ker SMART 1000 CCD diffractometers (k(Mo Ka)-radiation, graph-
the nitrogen coordination planes is slightly decreased (Table S1).
Moreover, the Cring–N–Ccarb bond angles are increased, but the
N–Ccarb–N, CAr–N–Ccarb and Cring–N–CAr bond angles are decreased
upon the complexation. Thus, contrary to the amidinium salts, the
values of the Cring–N–Ccarb bond angles in the transition metal
complexes of six- and seven-membered carbenes exceed the val-
ues of the N–Ccarb–N bond angles, apparently, due to the repulsive
steric interactions between the transition metal and the bulky sub-
stituents at the nitrogen atoms. Furthermore, the complexation of-
fers little relief to the ring strain; for example, the endo-angles at
ite monochromator, and u scan mode) and corrected for
x
absorption using the SADABS program (versions 2.03 [36] and 2.01
[37]). For details, see Table S2. The structures were solved by direct
methods and refined by full-matrix least-squares technique on F2
with anisotropic displacement parameters for non-hydrogen
atoms. One of the three dichloromethane solvate molecules in
[(6-Dipp)H][Br] ꢁ 1.5CHCl3 is disordered over two sites with the
occupancies of 0.5:0.5. The dichloromethane solvate molecule in
[(7-Dipp)H][Br] ꢁ CH2Cl2 is disordered over two sites with the

E.L. Kolychev et al. / Journal of Organometallic Chemistry 694 (2009) 2454–2462
2459
occupancies of 0.7:0.3. The water solvate molecule in [(70-
Dipp)H][Cl] ꢁ 0.5H2O has the position occupancy of 0.5. The methyl
group and hydrogen atom at the carbenoid carbon atom in (7-Dip-
p)(H)(OMe) are disordered over two sites with the occupancies of
0.8:0.2. Two of the four isopropyl groups of one of the two inde-
pendent molecules in the formamidine are disordered over two
sites with the occupancies of 0.5:0.5 and 0.6:0.4. The dichloro-
methane solvate molecule in (6-Dipp)AgBr ꢁ CH2Cl2 is disordered
over two sites with the occupancies of 0.5:0.5. The absolute struc-
tures of (6-Dipp)CuBr ꢁ CHCl3 and (7-Dipp)CuBr ꢁ CHCl3 were
objectively determined by the refinement of Flack parameters
which have become equal to 0.002(5) and 0.01(2), respectively.
The hydrogen atoms of the solvate water molecules in [(70-
Dipp)H][Cl] ꢁ 0.5H2O and [Ag(7-Mes)2][Cl] ꢁ H2O were localized in
the difference-Fourier map and included in the refinement with
fixed positional and isotropic displacement parameters. The other
hydrogen atoms in all compounds were placed in calculated posi-
tions and refined within the riding model with fixed isotropic dis-
placement parameters (Uiso(H) = 1.5Ueq(C) for the CH3-groups and
Uiso(H) = 1.2Ueq(C) for the other groups). All calculations were car-
ried out using the SHELXTL PLUS program (versions 6.12 [38] and 5.10
[39]).
(B) Diisopropylethylamine (33 mmol, 1.1 equiv.) was added to a
stirred solution of formamidine (30 mmol, 1 equiv.) and dihaloge-
nide (90 mmol, 3 equiv.) in a 50 mL round bottomed flack. The
reaction mixture was heated to 125 °C for 2 h. The reaction mix-
ture was then cooled to room temperature, and excess dihaloge-
nide was removed in vacuo. The residue was dissolved in 100 mL
dichloromethane and washed by saturated solution of potassium
carbonate. Organic layer was mixed with 50 mL of toluene and
the solution was evaporated in vacuo to 50 mL, precipitated white
crystals filtered off and dried in vacuo providing pure product.
4.7. [(6-Dipp)H][Br]
Yield: A – 64%, B – 88%, white crystalline powder. M.p.: 269–
270 °C. 1H NMR (CDCl3): d 7.54 (s, 1H, NCHN), 7.42 (t, 2H, J = 7.8,
p-DippH), 7.36 (d, 4H, J = 7.8, m-DippH), 4.24 (t, 4H, J = 5.4,
NCH2), 3.02 (dt, 4H, J = 13.6, 6.8, DippCH), 2.75 (m, 2H, CH2), 1.36
(d, 12H, J = 6.8, DippCH3), 1.21 (d, 12H, J = 6.8, DippCH3). 1H NMR
(DMSO-d6): d 9.03 (s, NCHN), 7.48 (t, J = 7.3, p-DippH), 7.23 (d,
4H, J = 7.8, m-DippH),3.84 (t, 4H, J = 5.5, NCH2), 2.96 (dt, 4H,
J = 13.6, 6.7, DippCH), 2.41 (t, 2H, J = 5.4, CH2), 1.30 (d, 12H,
J = 6.6, DippCH3), 1.19 (d, 12H, J = 6.6, DippCH3). 13C NMR (CDCl3):
d 152.7 (NCHN), 145.6 (o-Dipp), 135.7 (Dipp), 131.2 (p-Dipp), 125.1
(m-Dipp), 48.9 (NCH2), 28.8 (DippCH), 24.8 (DippCH3), 24.7
(DippCH3), 19.4 (CH2). Anal. Calc. for C28H41BrN2: C, 69.26; H,
8.51; N, 5.77. Found: C, 69.24; H, 8.53; N, 5.81%.
4.3. General procedure for the preparation of formamidines
In a distillation apparatus, a mixture of aniline (50 g, 1 equiv.),
triethyl orthoformate (0.5 equiv.) and glacial acetic acid
(0.05 equiv.) was heated under an air atmosphere while tempera-
ture of reaction mixture rise up to 180 °C (approximately 2–3 h),
during which time ethanol distilled off. The crystalline mass ob-
tained upon cooling was recrystallized from toluene or acetone
[40].
4.8. [(7-Dipp)H][Br]
Yield: A – 52%, B – 82%, white crystalline powder, M.p.: 254–
256 °C. 1H NMR (CDCl3): d 7.38 (t, 2H, J = 7.8, p-DippH), 7.25 (s,
1H, NCHN), 7.22 (d, 4H, J = 7.8, m-DippH), 4.67 (br s, 4H, NCH2),
3.20 (dt, 4H, J = 13.6, 6.8, DippCH), 2.61 (dt, 4H, J = 5.5, 2.7,
CH2CH2), 1.37 (d, 12H, J = 6.8, DippCH3), 1.23 (d, 12H, J = 6.8, Dip-
pCH3). 1H NMR (DMSO-d6): d 8.66 (s, 1H, NCHN), 7.45 (t, 2H,
J = 7.8, p-DippH), 7.34 (d, 4H, J = 7.3, m-DippH), 4.27 (br s, 4H,
NCH2), 3.09 (dt, 4H, J = 13.6, 6.8, DippCH), 2.36 (m, 4H, CH2CH2),
1.31 (d, 12H, J = 6.6, DippCH3), 1.21 (d, 12H, J = 6.8, DippCH3). 13C
NMR (CDCl3): d 157.0 (NCHN), 144.8 (o-Dipp), 138.8 (Dipp),
130.9 (p-Dipp), 125.3 (m-Dipp), 56.2 (NCH2), 28.9 (DippCH), 25.0
(DippCH3), 24.8 (CH2), 24.6 (DippCH3). Anal. Calcd for C29H43BrN2:
C, 69.72; H, 8.68; N, 5.61. Found: C, 69.78; H, 8.65; N, 5.62%.
4.4. N,N0-bis(2,6-diisopropylphenyl)formamidine
Yield: 44.59 g, 86%, white fluffy crystalline powder. 1H NMR
(CDCl3): d 7.16 (m, 6H, DippH), 5.54 (br s, 1H, NCHN), 3.28 (m,
4H, DippCH), 1.20 (m, 24H, DippCH3). 13C NMR (CDCl3): d 147.6
(NCHN), 145.8 (o-Dipp), 139.0 (Dipp), 127.8 (p-Dipp), 123.3 (m-
Dipp), 28.1 (DippCH), 24.4 (DippCH3), 23.8 (DippCH3), 23.6
(DippCH3), 22.7 (DippCH3). Anal. Calc. for C25H36N2: C, 82.36; H,
9.95; N, 7.68. Found: C, 82.45; H, 10.04; N, 7.66%.
4.5. N,N0-bis(2,4,6-trimethylphenyl)formamidine
4.9. [(70-Dipp)H][Cl]
Yield: 41.63 g, 82%, colorless crystals. 1H NMR (CDCl3): d 7.30 (s,
0.4H, MesH), 7.19 (s, 0.6H, MesH), 6.92 (s, 1.2H, MesH), 6.87 (s,
2.8H, MesH), 5.52 (br s, 1H, NCHN), 2.24 (m, 12H, MesCH3). 13C
NMR (CDCl3): d 147.1 (NCHN), 142.6 (Mes), 133.9 (Mes), 129.2
(Mes), 128.9 (Mes), 128.8 (Mes), 20.7 (o-MesCH3), 18.6 (p-MesCH3).
Anal. Calc. for C19H24N2: C, 81.38; H, 8.63; N, 9.99. Found: C, 81.24;
H, 8.53; N, 9.91%.
Yield: A – 46%, white crystalline powder, M.p.: 253–255 °C
(with decomp.). 1H NMR (DMSO-d6): d 8.55 (s, 1H, NCHN), 7.44
(m, 2H, p-DippH), 7.32 (d, 4H, J = 7.8, m-DippH), 6.53 (t, 2H,
J = 4.4, CH = CH), 4.93 (d, 4H, J = 5.6, NCH2), 3.20 (dt, 4H, J = 13.5,
6.7, DippCH), 1.29 (d, 12H, J = 6.8, DippCH3), 1.20 (d, 12H, J = 6.6,
DippCH3). 13C NMR (DMSO-d6): d 158.8 (NCHN), 144.2 (o-Dipp),
139.7 (Dipp), 131.2 (CH@CH), 130.1 (p-Dipp), 124.6 (m-Dipp),
50.3 (NCH2), 28.2 (DippCH), 24.4 (DippCH3), 23.7 (DippCH3). Anal.
Calc. for C29H41ClN2: C, 76.87; H, 9.12; N, 6.18. Found: C, 76.76;
H, 9.02; N, 6.14%.
4.6. General procedure for the preparation of amidinium salts
(A) n-BuLi (2.5 M in hexane, 1.05 equiv.) was added at room
temperature to a THF solution (100 mL) of formamidine (30 g,
1 equiv.). The resulting yellow solution was stirred at room tem-
perature for 20 min before dihalogenide (1.5 equiv.) was added
dropwise. The solution was stirred at room temperature overnight.
After evaporation of the solvent under vacuum, the resulting solid
was washed with hexane (100 mL) and Et2O (100 mL). The residue
was dissolved in CH2Cl2 (100 mL), and filtered through short pad of
Celite. After evaporation of the solvent the crude product was
recrystallized from ethyl acetate/CH2Cl2 or ethyl acetate (com-
pound 1) and dried in vacuo at 100 °C.
4.10. [(7-Mes)H][Br]
Yield: A – 47%, B – 92%, white crystalline powder, M.p.: 204–
205 °C. 1H NMR (DMSO-d6): d 8.27 (s, 1H, NCHN), 7.03 (s, 4H, m-
MesH), 4.19 (m, 4H, NCH2), 2.33 (m, 16H, o-MesCH3, CH2CH2),
2.25 (s, 6H, p-MesCH3). 13C NMR (DMSO-d6): d 160.2 (NCHN),
140.0 (Mes), 139.2 (Mes), 134.3 (Mes), 130.9 (Mes), 128.7 (Mes),
54.0 (NCH2), 25.3 (CH2CH2), 20.9 (p-MesCH3); 18.1 (o-MesCH3).
Anal. Calc. for C23H31BrN2: C, 66.50; H, 7.52; N, 6.74. Found: C,
66.53; H, 7.50; N, 6.72%.

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E.L. Kolychev et al. / Journal of Organometallic Chemistry 694 (2009) 2454–2462
4.11. General procedure for the preparation of silver(I) complexes
short pad of Celite, and then the filtrate was concentrated to dry-
ness in vacuo.
Mixture of amidinium salt (2 mmol, 1 equiv.) with silver(I)
oxide (2 mmol, 1 equiv.) was dissolved in absolute dichlorometh-
ane (50 mL). The reaction mixture was stirred for 48 h at room
temperature. The solution was filtered through short pad of silica
gel, and then the filtrate was concentrated to dryness in vacuo.
4.17. (6-Dipp)CuBr
Yield: 83%, white crystalline powder, M.p.: >300 °C (with de-
comp.). 1H NMR (CDCl3): d 7.35 (t, 2H, J = 7.7, p-DippH), 7.20 (d,
4H, J = 7.8, m-DippH), 3.42 (t, 4H, J = 5.9, NCH2), 3.05 (quint, 4H,
J = 6.9, DippCH), 2.36 (t, 4H, J = 5.8, CH2), 1.34 (d, 12H, J = 6.9, Dip-
pCH3), 1.30 (d, 12H, J = 7.1, DippCH3). 13C NMR (CDCl3): d 201.1
(NCHN), 145.5 (o-Dipp), 141.3 (Dipp), 129.4 (p-Dipp), 124.6 (m-
Dipp), 46.2 (NCH2), 28.6 (DippCH), 24.9 (DippCH3), 24.6 (DippCH3),
20.5 (CH2). Anal. Calc. for C28H40CuBrN2: C, 61.36; H, 7.36; N, 5.11.
Found: C, 61.29; H, 7.38; N, 5.10%.
4.12. (6-Dipp)AgBr
Yield: 83%, white crystalline powder, M.p.: 295–296 °C. 1H NMR
(CDCl3): d 7.34 (t, 2H, J = 7.8, p-DippH), 7.19 (d, 4H, J = 7.8, m-
DippH), 3.44 (t, 4H, J = 5.9, NCH2), 3.04 (dt, 4H, J = 13.7, 6.8, Dip-
pCH), 2.36 (dt, 2H, J = 11.7, 6.6, CH2), 1.31 (d, 12H, J = 6.8, DippCH3),
1.28 (d, 12H, J = 6.8, DippCH3). 13C NMR (CDCl3): d 207.4 (dd,
J(107Ag, 13C) = 225.0, J(109Ag, 13C) = 260.4, NCHN), 145.3 (o-Dipp),
142.22 (Dipp), 129.4 (p-Dipp), 124.7 (m-Dipp), 46.0 (NCH2), 28.5
(DippCH), 24.9 (DippCH3), 24.7 (DippCH3), 20.3 (CH2). Anal. Calc.
for C28H40AgBrN2: C, 56.67; H, 6.96; N, 4.72. Found: C, 56.66; H,
6.93; N, 4.77%.
4.18. (7-Dipp)CuBr
Yield: 79%, white crystalline powder, M.p.: >300 °C (with de-
comp.). 1H NMR (CDCl3): d 7.34 (t, 2H, J = 7.8, p-DippH), 7.20 (d,
4H, J = 7.8, m-DippH), 3.98 (br s, 4H, N–CH2), 3.26 (sept, 4H,
J = 6.9, DippCH), 2.35 (br s, 4H, CH2CH2), 1.37 (d, 12H, J = 6.9, Dip-
pCH3), 1.33 (d, 12H, J = 6.9, DippCH3). 13C NMR (CDCl3): d 210.5
(NCHN), 144.8 (o-Dipp), 143.7 (Dipp), 128.9 (p-Dipp), 124.7 (m-
Dipp), 53.8 (NCH2), 28.7 (DippCH), 25.1 (CH2CH2), 24.7 (DippCH3),
24.6 (DippCH3). Anal. Calc. for C29H42CuBrN2: C, 61.96; H, 7.53;
N, 4.98. Found: C, 62.02; H, 7.49; N, 4.95%.
4.13. (7-Dipp)AgBr
Yield: 75%, white crystalline powder, M.p.: 288–291 °C. 1H NMR
(CDCl3): d 7.32 (m, 2H, p-DippH), 7.18 (d, 4H, J = 7.6, m-DippH),
4.01 (m, 4H, NCH2), 3.24 (dt, 4H, J = 13.9, 6.9, DippCH), 2.34 (ddd,
4H, J = 5.8, 2.8, 2.7, CH2CH2), 1.33 (s d, 12H, J = 6.8, DippCH3),
1.31 (d, 12H, J = 6.8, DippCH3). 13C NMR (CDCl3): d 217.3 (dd,
J(107Ag, 13C) = 226.7, J(109Ag, 13C) = 262.9, NCHN), 144.7 (o-Dipp),
144.6 (Dipp), 129.0 (p-Dipp), 124.8 (m-Dipp), 53.8 (NCH2), 53.7
(NCH2), 28.6 (DippCH), 25.0 (CH2), 24.7 (DippCH3), 24.6 (DippCH3),
20.34 (CH2CH2). Anal. Calc. for C29H42AgBrN2: C, 57.34; H, 7.14; N,
4.61. Found: C, 57.32; H, 7.15; N, 4.61%.
4.19. 6-Dipp
Mixture of amidinium salt 1 (0.300 g, 0.62 mmol) and bis(tri-
methylsilyl)lithium (0.103 g, 0.62 mmol) was dissolved in 0.6 mL
absolute THF in NMR tube. Amidinium salt dissolves in 10 min,
during which an almost clear yellow solution formed. 1H NMR
(THF-d8): d 7.20 (m, 6H, DippH), 3.34 (dt, 4H, J = 13.5, 6.7, DippCH),
3.21 (t, 4H, J = 5.6, N–CH2), 2.27 (br s, 2H, CH2), 1.27 (d, J = 6.9, 12H,
DippCH3), 1.17 (d, 12H, J = 6.9, DippCH3). 13C NMR (THF-d8): d
245.9 (NCHN), 146.6 (o-Dipp), 131.1 (Dipp), 127.6 (p-Dipp), 124.2
(m-Dipp), 45.2 (N–CH2), 29.0 (DippCH), 25.2 (DippCH3), 24.6
(DippCH3) 22.8 (CH2).
4.14. [Ag(7-Mes)2][Cl] ꢁ H2O
Yield: 73%, white crystalline powder, M.p.: >300 °C. 1H NMR
(CDCl3): d 6.67 (s, 4H, m-MesH), 3.45 (br s, 4H, NCH2), 2.14 (s,
6H, p-MesCH3), 1.88 (br s, 4H, CH2CH2), 1.62 (s, 12H, o-MesCH3).
13C NMR (CDCl3):
d
214.7 (dd, J(107Ag, 13C) = 175.9, J(109Ag,
13C) = 203.5, NCHN), 144.2 (Mes), 137.0 (Mes), 133.6 (Mes), 129.2
(Mes), 51.9 (NCH2), 51.8 (NCH2), 24.7 (CH2CH2), 20.5 (o-MesCH3),
17.8 (p-MesCH3). Anal. Calc. for C46H62AgClN4O: C, 66.38; H,
7.75; N, 6.73. Found: C, 66.37; H, 7.72; N, 6.74%.
4.20. (7-Dipp)(H)(OMe)
Mixture of amidinium salt 2 (1 g, 2 mmol) with sodium meth-
oxide (0.1 g, 2 mmol) was dissolved in absolute THF (30 mL). The
reaction mixture was stirred for 30 min at room temperature.
The solution was concentrated to dryness in vacuo, dissolved in
10 mL of n-hexane and filtered through short pad of Celite. Evap-
oration of the solvent afforded a pure product. Yield: 0.792 g,
88%, colorless crystals. 1H NMR (toluene-d8): d 7.15 (m, 4H, p-
Dipp), 7.06 (m, 2H, m-Dipp), 5.03 (s, 1H, NCHN), 4.11 (dt, 2H,
J = 13.7, 6.9, DippCH), 3.70 (m, 4H, DippCH, N–CH2) 2.38 (s, 3H,
OCH3), 1.72 (m, 2H, CH2), 1.60 (m, 2H, CH2CH2), 1.31 (m, 24H, Dip-
pCH3). 13C NMR (toluene-d8): d 150.3 (Dipp), 147.4 (Dipp), 144.7
(Dipp), 127.1 (Dipp), 124.8 (Dipp), 124.2 (Dipp), 107.58 (NCHN),
57.9 (OCH3), 52.9 (N–CH2), 31.1 (DippCH), 28.8 (CH2), 28.5
(CH2CH2), 25.5 (DippCH3), 25.4 (DippCH3), 24.5 (DippCH3), 24.4
(DippCH3).
4.15. Formamidine 8
Complex 8 was isolated using the same protocol as for Ag(I)
complexes. Yield 80%, white crystalline powder. 1H NMR (CDCl3):
d 7.47 (t, 1H, J = 7.8, p-DippH), 7.31 (d, 2H, J = 7.8, m-DippH), 7.15
(m, 2H, m-DippH), 7.08 (dd, 1H, J = 8.6, 6.6, p-DippH), 5.33 (br s,
1H, @CH–CH@), 5.17 (m, 1H, @CH–CH@), 4.95 (dd, 1H, J = 16.4,
2.0, CH2@), 4.63 (d, 1H, J = 9.8, CH2@), 3.24 (dt, 4H, J = 13.5, 6.8, Dip-
pCH), 1.26 (m, 24H, DippCH3). 13C NMR (CDCl3): d 149.6 (NCHN),
147.3 (N–CH@), 139.4 (Dipp), 131.1 (Dipp), 129.7 (NCH), 124.5
(Dipp), 123.3 (Dipp), 122.8 (Dipp), 115.4 (CH2@), 109.7
(CH2@CH–CH), 28.4 (DippCH), 27.7 (DippCH), 24.6 (DippCH3),
23.7 (DippCH3). Anal. Calc. for C29H40N2: C, 83.60; H, 9.68; N,
6.72. Found: C, 83.23; H, 9.73; N, 6.70%.
Acknowledgements
4.16. General procedure for the preparation of copper(I) complexes
This work was supported by the Russian Foundation for Basic
Research (04-03-32662-a). The authors are thankful to Prof. Yu.
A. Ustynyuk for the critical discussions during the preparation of
the manuscript.
Mixture of silver(I) complex (1 mmol, 1 equiv.) with copper(I)
bromide (1 mmol, 1 equiv.) was dissolved in absolute dichloro-
methane (30 mL). The reaction mixture was stirred for 48 h at
room temperature in the dark. The solution was filtered through

E.L. Kolychev et al. / Journal of Organometallic Chemistry 694 (2009) 2454–2462
(e) D. Kunz, Angew. Chem., Int. Ed. 46 (2007) 3405;
2461
Appendix A. Supplementary material
(f) S. Gómez-Bujedo, M. Alcarazo, C. Pichon, E. Álvarez, R. Fernández, J.M.
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CCDC 708130, 708131, 708132, 708133, 708134, 708135,
708136, 708137, 708138, 708139 and 708140 contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.jorganchem.2009.03.014.
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