Diamino- and mixed amino-amido-N-heterocyclic carbenes based on triazine backbones

Article abstract of DOI:10.1021/om201275z

The synthesis of novel hexahydrotriazine-based NHCs from easily available starting materials is described. Tribenzyltriazacyclohexane 1 is converted stepwise to the six-membered diamino carbene 3 with a saturated ring structure. Analogously, the cyclic mixed amino-amido carbene 12 is obtained starting from a cyclic urea derivative. Both carbenes were characterized by trapping reactions with sulfur and selenium as well by the preparation of metal complexes of the type (COD)MX-NHC (M = Rh, Ir; COD = 1,5-cyclooctadiene), which were converted to the respective dicarbonyl complexes (CO)₂MX-NHC. IR spectra of the carbonyl derivatives allowed the Tolman electronic parameter to be determined for carbenes 3 (2052 cm^-1) and 12 (2058 cm^-1) and revealed a shift of 6 cm^-1 due to the presence of one amide function. X-ray structure determinations are reported for an amidinium species, a carbene sulfide, and the (COD)RhBr complex of the amino-amido carbene 12.

Full text of DOI:10.1021/om201275z

Article
pubs.acs.org/Organometallics
Diamino- and Mixed Amino−Amido-N-Heterocyclic Carbenes Based
on Triazine Backbones
Abdelaziz Makhloufi, Walter Frank, and Christian Ganter*
Institut fur Anorganische und Strukturchemie, Heinrich-Heine-Universitat Dusseldorf, Universitatsstrasse 1, D-40225 Dusseldorf,
̈
̈
̈
̈
̈
Germany
S
* Supporting Information
ABSTRACT: The synthesis of novel hexahydrotriazine-based NHCs from easily
available starting materials is described. Tribenzyltriazacyclohexane 1 is converted
stepwise to the six-membered diamino carbene 3 with a saturated ring structure.
Analogously, the cyclic mixed amino−amido carbene 12 is obtained starting from a
cyclic urea derivative. Both carbenes were characterized by trapping reactions with
sulfur and selenium as well by the preparation of metal complexes of the type
(COD)MX-NHC (M = Rh, Ir; COD = 1,5-cyclooctadiene), which were converted
to the respective dicarbonyl complexes (CO)2MX-NHC. IR spectra of the carbonyl derivatives allowed the Tolman electronic
parameter to be determined for carbenes 3 (2052 cm−1) and 12 (2058 cm−1) and revealed a shift of 6 cm−1 due to the presence
of one amide function. X-ray structure determinations are reported for an amidinium species, a carbene sulfide, and the
(COD)RhBr complex of the amino−amido carbene 12.
INTRODUCTION
The chemistry of N-heterocyclic carbenes (NHCs) has a long
tradition based upon preliminary work by Wanzlick and Ofele
RESULTS AND DISCUSSION
Synthesis of NHC Precursors. In order to get access to a
■
■
̈
suitable carbene precursor, our intention was to convert a 1,3,5-
triazacyclohexane derivative to the corresponding amidinium
cation, and two potential routes were found to furnish the
in the 1960s and the synthesis of the first isolable NHC by
Arduengo in 1991. Since then, a tremendous number of
different NHCs have been prepared and examined.1 When
coordinated to metal fragments, they lead to an increased
stability of the NHC metal complexes compared to related
phosphane complexes. As ligands NHCs are strong σ-donors,
while their ability to exhibit additional π-acceptor properties has
been neglected for a long time. The electronic properties can be
modified by substituents attached to the nitrogen atoms or to
the NHC ring,2 which is important for their utilization as
1,3,5-tribenzyltetrahydrotriazinium salts 2X (X = Br−, BF4 )
−
starting from 1,3,5-tribenzylhexahydrotriazine (1), which is
easily obtained10 by condensation of benzylamine with aqueous
formaldehyde under basic conditions in 89% yield (Scheme 1).
In route A the amidinium tetrafluoroborate salt 2BF4 was
obtained from triazine 1 by hydride abstraction using trityl
tetrafluoroborate in dichloromethane in 41% yield following a
slightly modified protocol reported in 1973 by Mohrle.11
̈
According to route B, the amidinium bromide 2Br could be
obtained by treatment of triazine 1 with one equivalent of N-
bromosuccinimide (NBS) in glyme, a procedure that was
successfully applied earlier to related aminals.12 A complete
conversion was observed within only a few minutes, with the
bromide salt 2Br precipitating from the solution. After removal
of the succinimide by washing with glyme, 2Br was isolated in
analytically pure form as a white crystalline solid in virtually
quantitative yield. Given the excellent yield, the short reaction
time, and the high purity of the amidinium salt 2Br, the
reaction with NBS (route B) is the method of choice for
obtaining the cationic carbene precursor. Both salts are stable
toward air and moisture and are soluble in polar organic
solvents such as dichloromethane, acetonitrile, or DMF. They
ligands in catalytic reactions.3 The groups of Ces
́
ar and
Lavigne4 and Bielawski5 reported six-membered diamidocar-
benes derived from malonic acid with reduced σ-donor abilities
and a significant π-acceptor character. The related five-
membered diamidocarbene derived from oxalic acid is an
even poorer σ-donor and shows a higher propensity for π-back-
bonding, as is evident from a Tolman electronic parameter
(TEP) parameter of 2068 cm−1,6 which is the highest value
reported so far for a NHC. In addition, five-membered
monoamidocarbenes were reported independently by Glorius7
and Ces
́
ar.8 NHCs derived from triazine systems have not been
ar,
described yet, apart from a very recent study reported by Ces
́
Lavigne, and co-workers, who prepared a triazine-based
diamidocarbene exhibiting ambidentate behavior.9 In the
present paper we wish to disclose our findings concerning
synthetic routes to and properties of triazine-based NHCs,
including diamino as well as mixed amino−amido derivatives.
These new structures nicely supplement the systems reported
1
were fully characterized by H and 13C NMR spectroscopy,
mass spectrometry, and elemental analysis. The MALDI-TOF
mass spectra are dominated by a base peak centered at m/z 356
Received: December 23, 2011
Published: February 15, 2012
by Ces
́
ar and Lavigne.9
© 2012 American Chemical Society
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Organometallics
Article
Scheme 1. Preparation of Amidinium Salts 2
for the cationic moiety 2+ irrespective of the nature of the
accompanying anion. Crystals of 2Br suitable for an X-ray
diffraction study were obtained from dichloromethane and
hexane, and the molecular structure of the compound is
depicted in Figure 1 together with selected geometrical
of the structure are close to those reported for other amidinium
salts.13 In the H NMR spectra, the chemical shift of the
1
amidinium proton NCHN is significantly affected by the nature
of the counteranion, with the resonance for 2BF4 appearing at
higher field (8.92 ppm) compared to 2Br (10.74 ppm). Singlet
resonances are observed for the CH2 units of the benzyl groups
and the heterocyclic ring, indicating effective C2v symmetry due
to a fast inversion at N2.14 In the 13C NMR spectra the
influence of the anion on the amidinium C resonance is
negligible (153.7 vs 154.4 ppm).
NHC Precusor Deprotonation. The amidinium derivative
2Br could be deprotonated with sodium bis(trimethylsilyl)-
amide (NaHMDS) in THF at −80 °C, leading to the neutral
carbene 3, which could be trapped by addition of elemental
sulfur or selenium to give the thiourea 4 or the analogous
selenide 5 in good yield (Scheme 2). Carbene 3 is not stable at
ambient temperature, as all attempts to isolate the free carbene
resulted in decomposition into unidentified products. The
MALDI mass spectrum of the reaction mixture shows no peaks
attributable to the olefin arising from carbene dimerization.
Like cation 2, derivatives 4 and 5 are C2v-symmetric in
solution according to their NMR spectra, the absence of the
resonance for the amidinium protons (NCHN) being the most
1
notable feature of the H NMR spectra. In the 13C NMR
spectrum of the thiourea 4 the signal for the N2CS carbon atom
is recorded at a typical chemical shift of 180.6 ppm. Compound
4 was crystallized from ether/hexane, and its molecular
structure was determined by X-ray diffraction (Figure 2). The
geometrical data compare well with other thiourea deriva-
tives13a,15 and are also close to those described above for the
cation 2Br with a planar thiourea subunit. The presence of the
sulfur atom leads to a lengthening of the adjacent C1−N bonds
(1.332(7) Å to N1, 1.374(7) Å to N2), the differences for all
other C−N bonds being much smaller.
Figure 1. Molecular structure of the cation 2 in 2Br in the solid state.
Displacement ellipsoids are drawn at the 30% probability level. The
Br− anion and the solvating H2O have been omitted for clarity.
Selected interatomic distances [Å] and bond angles [deg]: N1−C3
1.314(5), N1−C1 1.480(4), N2−C2 1.431(5), N2−C1 1.432(5), N3−
C3 1.297(5), N3−C2 1.482(5); C3−N1−C1 117.8(3), C2−N2−C1
110.5(3), C3−N3−C2 119.8(3), N3−C3−N1 124.2(4), N2−C2−N3
110.9(3), N2−C1−N1 111.7(3).
parameters. As expected, the formamidinium fragment is planar
with angle sums of 360° for N1, N3, and C3, respectively, and
short N−C3 distances around 1.30 Å. In contrast, N2 is in a
pyramidal environment with longer bonds to C1 and C2 (ca.
1.43 Å). The longest C−N bonds are observed for N1−C1 and
N3−C2 (ca. 1.48 Å). The data concerning the amidinium part
After the successful preparation of the carbene adducts 4 and
5 we decided to exploit the intermediate carbene 3 for the
preparation of metal complexes.
Synthesis of Rhodium(I) and Iridium(I) Complexes.
Deprotonation of the amidinium salt 2BF4 with KOtBu at
Scheme 2. Preparation and Reactivity of NHC 3
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Organometallics
Article
= 46.8 Hz), falling in the range previously observed for related
Rh complexes with six-membered NHCs. For the iridium
complex 7 the carbene carbon occurred as a singlet resonance
at 202.2 ppm. The EI mass spectra of both complexes showed
peaks for the molecular ions as well as for the fragments
resulting from the loss of the chlorine atom.
Reaction of Complexes 6 and 7 with CO. In order to
estimate the donor properties of the new carbene ligand 3 by
means of IR spectroscopy, the COD complexes 6 and 7 were
exposed to a slow stream of CO in dichloromethane solution
for a couple of minutes, resulting in a clean conversion to the
corresponding dicarbonyl derivatives 8 and 9 in excellent yield
(Scheme 3). The IR spectrum of complex 8 in CH2Cl2 featured
two strong CO stretching vibrations at 1999.3 and 2079.3 cm−1
(ν(av) = 2039.3 cm−1), from which a TEP of 2052 cm−1 was
calculated.1c,2e,18 Analogously, from the two carbonyl bands at
1983.6 and 2066.8 cm−1 (ν(av) = 2025.2 cm−1) recorded for
the iridium derivative 9 a TEP value of 2053 cm−1 was
calculated, in a good agreement with the Rh-derived value,
indicating that NHC 3 is a similarly powerful donor compared
to other five- and six-membered diamino carbenes. Thus, not
surprisingly, the incorporation of an additional N atom into the
NHC backbone has a negligible effect on the donor properties.
Synthesis of the Mixed Amino−Amido NHC Deriva-
tives. We then turned our attention to modify the electronic
properties of the basic triazine system 3 by converting one N-
CH2-N unit to a N-CO-N motif, i.e., to proceed from the
diamino-NHC 3 to a mixed amino−amido-NHC. Thus, the
cyclic triazinone 10 was prepared from dimethylurea, benzyl-
amine, and formaldehyde solution according to a procedure
reported by Overman19 in 72% yield and subsequently
converted to the corresponding amidinium cation by reaction
with one equivalent of NBS in glyme as outlined above
(Scheme 4). The amidinium bromide 11Br was isolated after
workup in analytically pure form in 89% yield as a white solid
Figure 2. Molecular structure of compound 4 in the solid state.
Displacement ellipsoids are drawn at the 30% probability level.
Selected interatomic distances [Å] and bond angles [deg]: S1−C1
1.694(3), N1−C1 1.332(7), N1−C4 1.427(7), N1−C2 1.504(6), N2−
C1 1.374(7), N2−C3 1.442(6), N3−C2 1.411(6), N3−C3 1.456(7);
C1−N1−C2 120.7(4), C1−N2−C3 121.5(4), C2−N3−C3 107.4(4),
N1−C1−N2 117.2(3), N1−C1−S1 122.0(4), N2−C1−S1 120.7(4),
N3−C2−N1 110.9(4), N2−C3−N3 115.4(4).
−80 °C and subsequent treatment of the intermediate carbene
with [(COD)MCl]2 (M = Rh, Ir) resulted in the formation of
the anticipated carbene metal complexes [(COD)M(3)Cl] 6
(M = Rh) and 7 (M = Ir), respectively, in very good yield
(Scheme 3). The tretrafluoroborate precursor was chosen in
order to prevent a halide exchange at the metal from chloride to
bromide. Both complexes are air and moisture stable and were
purified by chromatography on silica and completely
characterized by analytical and spectroscopic techniques.
1
and fully characterized. The H and 13C resonances for the
amidinium moiety NCHN were detected at 10.64 and 158.4
ppm, respectively. Hydride abstraction from compound 10 with
trityl tetrafluoroborate was not successful in this case.
Analogously to carbene 3, attempts to isolate the amino−
amido carbene 12 after deprotonation of the amidinium cation
11 with either NaHMDS or KOtBu in THF at −80 °C resulted
in decomposition. However, treatment of cation 11 with
NaHMDS at low temperature in the presence of S8 or red
selenium gave the corresponding heteroureas 13 and 14 in 59%
and 63% yield, respectively, which were completely charac-
terized (Scheme 5).
1
In the H NMR spectra of complexes 6 and 7, the CH2
protons of the benzyl groups in positions 1 and 3 appeared to
be diastereotopic, giving rise to AB patterns, as did the
methylene protons of the N-CH2-N units within the triazine
systems. The CH2 protons of the benzyl group at N5 remained
equivalent and were recorded as a singlet. This observation
indicated that there is no rotation around the metal carbene
bond at room temperature. A high-temperature 1H NMR study
in toluene-d8 showed no broadening of the peaks. Similar
results have been reported for five ring NHCs by Crabtree16
17
and Ozdemir. In the 13C NMR spectra of the Rh complex 6
̈
After the successful trapping of the in situ generated carbene
12, the preparation of metal complexes was envisaged. Thus,
the carbene carbon appeared as a doublet at 208.5 ppm (1JC−Rh
Scheme 3. Preparation of Carbene Metal Complexes
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Article
Scheme 4. Preparation of Carbene Precursor 11Br
Scheme 5. Preparation and Trapping of Carbene 12
the rhodium and iridium complexes 15 and 16 were prepared
in ca. 70% yield in an analogous manner by precursor
deprotonation with KOtBu in THF at −80 °C in the presence
of [(COD)MCl]2 (M = Rh, Ir). Both complexes were purified
by column chromatography and fully characterized. Elemental
analyses and an X-ray diffraction study revealed the presence of
the bromo derivatives, arising from a substitution of the initially
metal-bound chloride ligands by the bromide being present as
the counteranion in 11Br. Such halide substitution reactions
have been observed before.20 The methylene protons in the
NHC ring as well as in the benzyl group are diastereotopic and
1
exhibit AB patterns in the H NMR spectra. In the 13C NMR
spectrum of complex 15 the carbene carbon appeared as a
doublet at 222.1 ppm (1JC−Rh = 47.2 Hz).
Crystals of complex 15 were obtained from ether/hexane and
examined by X-ray diffraction (Figure 3). As is usually
observed, the NCN plane of the carbene is in a perpendicular
orientation to the coordination plane around the Rh atom, with
short Rh−C distances to the olefinic COD carbons trans to the
bromide (mean: 2.12 Å) and longer ones trans to the NHC
ligand (mean: 2.22 Å). The heterocyclic ligand is essentially
planar, with the exception of the CH2 carbon C2, which is
located 59 pm above the mean plane defined by the remaining
ring atoms. Within the heterocycle, significantly different bond
lengths are noteworthy. For example, the N1−C1 (1.319(5) Å)
bond is shorter than the N2−C1 bond (1.381(5) Å), whereas
N2−C3 (1.394(6) Å) is shorter than N1−C2 (1.447(5) Å).
The lone pair at N1 obviously donates to the carbene C atom
pz-orbital, leading to a short distance, while the N2 lone pair is
also engaged in the amide resonance involving the carbonyl
group at C3, which makes the C3−N2 bond short and
consequently leads to a longer C1−N2 bond. N3 engages only
in the amide bond with C3 and consequently displays a short
N3−C3 distance (1.356(6) Å). Alternatively, the heterocycle
can also be regarded as a cyclic urea derivative, and,
accordingly, the NHC 12 could be described as an amino-
ureyl carbene. However, given the pronounced difference in the
C3−N bond lengths (see above) and in order to emphasize the
difference from the diamino carbenes, we prefer the description
of 3 as an amino−amido carbene. The Rh−C1 bond length of
2.022(4) Å is at the short edge of the range of values observed
for other NHC-Rh(COD) complexes.21
Figure 3. Molecular structure of complex 15 in the solid state.
Displacement ellipsoids are drawn at the 30% probability level. All H
atoms except those connected to C2 have been omitted for clarity.
Selected interatomic distances [Å] and bond angles [deg]: Rh1−C1
2.022(4), Rh1−C13 2.107(5), Rh1−C14 2.134(5), Rh1−C17
2.208(5), Rh1−C19 2.224(5), Rh1−Br1 2.4884(6), N3−C3
1.356(6), N3−C2 1.458(5), C1−N1 1.319(5), C1−N2 1.381(5),
O1−C3 1.219(5), N2−C3 1.394(6), C2−N1 1.447(5), C13−C14
1.381(8), C19−C17 1.386(8); C1−Rh1−Br1 89.24(12), C3−N3−C2
117.3(4), N1−C1−N2 115.2(4), N1−C1−Rh1 121.8(3), N2−C1−
Rh1 122.9(3), C1−N2−C3 124.0(4), O1−C3−N3 123.1(4), O1−
C3−N2 121.9(4), N3−C3−N2 114.9(4), N1−C2−N3 108.0(3), C1−
N1−C2 120.2(4).
shifted to higher wavenumbers compared to the diamino
carbene complexes 8 and 9 (17: 2008.0 and 2086.1 cm−1; ν(av)
= 2047.1 cm−1; 18: 1992 and 2073 cm−1, ν(av) 2032.5 cm−1).
Additionally, the amide CO group gave rise to an intense band
at 1714 and 1718 cm−1, respectively. From these data, TEP
values of 2058 and 2059 cm−1 were calculated for carbene 12.
Thus, compared to the diamino carbene 3, the introduction of
one amido function into the backbone brings about a shift of 6
cm−1 to higher values, reflecting the diminished donor strength
of the amido−amino carbene 12. It should be noted that the
carbenes 3 and 12 have different steric properties due to their
different substitution patterns at the N atoms (benzyl/benzyl
for 3, %VBur = 32.8; methyl/benzyl for 12, %VBur = 27.6).22 For
comparison, a shift of comparable magnitude (7 cm−1) has
Finally, the COD complexes were converted straightfor-
wardly to the corresponding carbonyl derivatives 17 and 18,
which allowed the electronic nature of the amino−amido
carbene 12 to be inferred from the IR spectra (Scheme 6). As
expected, both complexes exhibited CO vibrations that are
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Organometallics
Article
Scheme 6. Preparation of Metal Complexes 15−18
been observed for the introduction of one keto group to the
saturated N,N′-dimesitylimidazolidin-2-ylidene8b or for the
attachment of one nitro group (6 cm−1) or two chlorine
atoms (4 cm−1) to N,N′-dimethylimidazol-2-ylidene.2a Interest-
ingly, the triazine-based neutral diamido carbene reported
Table 1. Crystal Data and Structure Refinement for
Compounds 2 Br·0.5H2O, 4, and 15
2Br·0.5H2O
859272
4
15
CCDC number
empirical formula
fw
859273
859274
recently by Ces
́
ar and Lavigne9 showed virtually the same TEP
C48H54Br2N6O
890.77
C24H25N3S
387.54
291(2)
trigonal
P31
C20H27BrN3ORh
508.26
as the amino−amido carbene 12, while deprotonation of the
former lead to enhanced donicity and thus a diminished TEP of
2049 cm−1.
temp (K)
291(2)
291(2)
cryst syst
monoclinic
I2/a
monoclinic
P21/c
space group
unit cell dimens
(Å, deg)
a = 19.8620(14) a = 9.2617(4) a = 22.3837(7)
b = 8.3618(2) b = 9.2617(4) b = 7.0530(3)
c = 27.6873(18) c = 20.5439(9) c = 12.7219(4)
CONCLUSION
■
Novel triazine-based NHCs have been straightforwardly
obtained from easily available starting materials. NBS oxidation
of an N-CH2-N fragment to an amidinium functionality allowed
the in situ liberation of the corresponding carbene by
deprotonation at low temperature. The synthetic approach
provided access to both electron-rich diamino (3) and less
donating mixed amino−amido carbenes (12). Evaluation of
their TEP values revealed a pronounced effect exerted by the
additional keto group, leading to a shift of 6 cm−1. Ongoing
work includes attempts to generate bis-carbenes derived from a
triazine system.
β = 95.560(3)
4576.7(5)
4
β = 98.650(3)
1985.59(12)
4
volume (Å3)
1526.14(11)
Z
3
densitycalc (Mg/
1.293
1.265
1.700
m3)
absorp coeff
1.812
0.173
618
2.886
(mm−1
)
F(000)
cryst size (mm3)
1848
1024
0.3 × 0.3 × 0.3 0.35 × 0.3 ×
0.3 × 0.3 × 0.3
0.28
theta range (deg)
reflns collected
indep reflns
2.06 to 25.00
16 455
1.98 to 25.94
21 864
2.76 to 25.00
14 502
EXPERIMENTAL SECTION
■
4024 [R(int) =
0.0730]
3951 [R(int) = 3501 [R(int) =
0.0410] 0.0978]
General Considerations. All reactions were performed with
standard Schlenk techniques in an oxygen-free, dry nitrogen
atmosphere. Solvents were dried and distilled under nitrogen by
using standard procedures. Diethyl ether and THF were distilled over
sodium/benzophenone; dichloromethane was distilled over CaH2, and
n-hexane over sodium. NMR spectra were recorded on a Bruker
Avance DRX 200 and a Bruker Avance DRX 500 spectrometer. 1H and
13C{1H} spectra are referenced to the residual solvent signal. Mass
spectra were recorded on a Thermo Finnigan Trace DSQ 7000 (EI)
and Bruker Ultraflex I TOF (MALDI). Elemental analyses were
recorded on a Perkin CHN 2400 Series II. IR spectra were obtained
with a Shimadzu IR Affinity-1 spectrometer. Reagents such as
potassium tert-butoxide and NaHMDS (2 M in THF) were purchased
from Acros Organics and Sigma Aldrich and used as received.
[RhCl(COD)]2 and [IrCl(COD)]2 were synthesized according to a
literature procedure.
Synthesis of 1,3,5-Tribenzylhexahydrotriazine (1). To a
stirred solution of benzylamine (20.7 g, 193 mmol) at 0 °C was
slowly added a 36.5% aqueous formaldehyde solution (19.4 mL, 200
mmol) so that the temperature remained below 5 °C. Aqueous sodium
hydroxide (1 M) (5 mL) was added to the resulting precipitated gum,
and the mixture was stirred for 1 h at 0 °C. After 1 h 40 mL of diethyl
ether was added, and the aqueous phase was washed with 3 × 15 mL
of diethyl ether. The combined organic fractions were dried over
MgSO4, filtered, and evaporated to dryness in vacuo to yield a colorless
oil, which crystallized upon standing for two weeks (20.45 g, 89%). 1H
NMR (200 MHz, CDCl3): δ 7.41 (m, 15H, Ar-CH), 3.78 (s, 6H, Ph-
CH2), 3.54 (s, 6H, N-CH2-N). 13C NMR (500 MHz, CDCl3): δ 138.9,
129.4, 128.7, 127.5 (all aromatic C), 74.2 (Ph-CH2), 57.5 (N-CH2-N).
MS (MALDI): m/z 356 [M − H]+. Spectral data were consistent with
literature values.10
completeness to
theta = 25.85°
absorption corr
100.0%
99.3% 99.8%
none
none
none
data/restraints/
params
4024/2/261
3951/1/254
3501/0/237
goodness-of-fit on 1.395
1.076
1.093
F2
final R indices [I > R1 = 0.0635, wR2 R1 = 0.0553,
2σ(I)] = 0.0982 wR2 = 0.1378
R1 = 0.0419, wR2 =
0.1139
R indices (all data) R1 = 0.0871, wR2 R1 = 0.0649,
R1 = 0.0461, wR2 =
0.1166
= 0.1026
wR2 = 0.1437
largest diff peak
0.644 and
−0.213
0.498 and
−0.264
0.942 and −1.038
and hole (e·Å−3
)
Synthesis of 1,3,5-Tribenzyl-4,6-tetrahydrotriazinium Tetra-
fluoroborate (2BF4). This compound was synthesized according to a
modified literature procedure.11 To a mixture of trityl tetrafluor-
oborate (1.68 g, 5.1 mmol, 1.1 equiv) in 40 mL of CH2Cl2 was added
1 (1.79 g, 5.0 mmol, 1.0 equiv) in 20 mL of CH2Cl2 over 10 min. The
resulting green solution was stirred at room temperature for 90 min.
Removal of the solvent in vacuo resulted in a yellow compound, which
was treated with 10 mL of water and extracted with CH2Cl2 (3 × 10
mL). The combined organic fractions were dried over MgSO4, filtered,
and evaporated to dryness in vacuo to yield 910 mg (41%) of 2BF4 as a
1
colorless crystalline powder. H NMR (200 MHz, CDCl3): δ 8.92 (s,
1H, NCHN), 7.36 (br s, 10H, Ar-CH), 7.12 (m, 3H, Ar-CH), 6.68 (m,
2H, Ar-CH), 4.64 (s, 4H, N-CH2-N), 4.16 (s, 4H, Ph-CH2), 3.29 (s,
2H, Ph-CH2). 13C NMR (500 MHz, CDCl3): δ 153.7 (NCHN),
135.3, 132.9, 129.5, 129.3, 129.1, 128.91, 128.6, 128.1 (all aromatic C),
62.5 (N-CH2-N), 56.8 (Ph-CH2), 55.6 (Ph-CH2). MS (MALDI): m/z
2005
dx.doi.org/10.1021/om201275z | Organometallics 2012, 31, 2001−2008

Organometallics
Article
355.9 [M − H]+. Anal. Calcd (%) for C24H26BF4N3: C, 65.03; H, 5.91;
N, 9.48. Found: C, 64.97; H, 6.16; N, 9.33.
14.9, Ph-CH2), 5.02 (br s, 2H, CH COD), 3.94 (d, 2H, JHz = 11.7, N-
CH2-N), 3.78 (d, 2H, JHz = 11.7, N-CH2-N), 3.70 (s, 2H, Ph-CH2),
3.61 (br s, 2H, CHCOD), 2.33 (m, 4H, CH2 COD), 1.89 (m, 4H,
CH2 COD). 13C NMR (500 MHz, CDCl3): δ 208.4 (d, 1JRhC = 46.8 Hz,
N2C), 137.4, 136.7, 129.2, 128.8, 128.7, 128.2, 128.0, 127.7 (all
aromatic C), 98.2 (d, JRhC = 6.8 Hz, CHCOD), 69.3 (d, JRhC = 14.8 Hz,
CHCOD), 63.9 (Ph-CH2), 61.2 (N-CH2-N), 54.9 (Ph-CH2), 33.0
(CH2 COD), 29.1 (CH2 COD). MS (EI): m/z 601 [M]+. MS (MALDI):
m/z 566 [M − Cl]+. Anal. Calcd (%) for C32H37ClN3Rh·0.5H2O: C,
62.90; H, 6.27; N, 6.88. Found: C, 62.79; H, 6.58; N, 6.82.
Synthesis of Dicarbonylchlorido-1,3,5-tribenzyl-4,6-tetrahy-
drotriazin-2-ylidenerhodium(I) (8). CO was bubbled into a
solution of 6 (120 mg, 0.2 mmol) in CH2Cl2 (5 mL) for a few
minutes. During this procedure the solution turned from yellow to
bright yellow. After 10 min of stirring, all volatiles were removed in
vacuo. The residue was washed with 5 mL of n-hexane, and 8 was
obtained as a bright yellow solid (106 mg, 96%). 1H NMR (200 MHz,
CDCl3): δ 7.44−7.32 (m, 10H, Ar-CH), 7.22 (m, 3H, Ar-CH), 7.25
(m, 2H, Ar-CH), 5.62 (d, 2H, JHz = 15.1, phenyl-CH2), 4.97 (d, 2H,
JHz = 15.0 phenyl-CH2), 4.02 (d, 2H, JHz = 12.0, N-CH2-N), 3.91 (d,
2H, JHz = 11.9, N-CH2-N), 3.72 (s, 2H, Ph-CH2). 13C NMR (500
MHz. CDCl3): δ 196.3 (d, NCN, 1JRhC = 39.7 Hz), 184.7 (d, CO, JRhC
= 53.5 Hz), 182.3 (d, CO, JRhC = 76.1 Hz), 135.5, 134.2, 128.1, 127.9,
127.6, 127.4, 127.2, 127.1 (all aromatic C), 64.8 (Ph-CH2), 59.8 (N-
CH2-N), 53.9 (Ph-CH2). MS (MALDI): m/z 493 [M − 2CO]+. IR
(CH2Cl2): ν 2079.3, 1999.3 cm−1 (CO). No correct elemental
analysis could be obtained, due to slow decomposition or instability of
the compound.
Synthesis of 1,3,5-Tribenzyl-4,6-tetrahydrotriazinium Bro-
mide (2Br). Compound 1 (1.56 g, 4.35 mmol, 1.0 equiv) was
dissolved in 20 mL of dimethoxyethane and treated with NBS (0.77 g,
4.35 mmol, 1.0 equiv). The resulting yellow solution was stirred at
room temperature. After 2 min a white solid precipitated and was
filtered off, washed with 20 mL of dimethoxyethane and 10 mL of
diethyl ether, and subsequently dried in vacuo to yield 1.87 g (99%) of
2Br as a colorless crystalline powder. Single crystals of 2Br were grown
1
by slow evaporation from methylene chloride/hexane. H NMR (200
MHz, CDCl3): δ 10.74 (s, 1H, NCHN), 7.47−7.37 (m, 10H, Ar-CH),
7.16 (m, 3H, Ar-CH), 6.66 (m, 2H, Ar-CH), 4.87 (s, 4H,N-CH2-N),
4.18 (s, 4H, Ph-CH2), 3.30 (s, 2H, Ph-CH2). 13C NMR (500 MHz,
CDCl3): δ 154.4 (NCHN), 135.1, 133.0, 129.5, 129.4, 129.3, 128.8,
128.7, 128.2 (all aromatic C), 62.6 (N-CH2-N), 56.4 (Ph-CH2), 55.8
(Ph-CH2). MS (MALDI): m/z 355.9 [M − H]+. Anal. Calcd (%) for
C24H26BrN3: C, 66.06; H, 6.01; N, 9.63. Found: C, 66.00; H, 6.20; N,
9.52.
Synthesis of 1,3,5-Tribenzyl-4,6-tetrahydrotriazine-2-thione
(4). A suspension of 2Br (505 mg, 1.16 mmol, 1.0 equiv) and S8 (74
mg, 2.32 mmol, 2.0 equiv) in 20 mL of THF was cooled to −80 °C,
and NaHMDS (2 M in THF, 0.26 mL, 1.28 mmol, 1.1 equiv) was
added dropwise. The resulting orange solution was stirred for 20 min
at −80 °C, the cooling bath was removed, and the solution was
allowed to warm to room temperature within 2 h. After evaporation of
all volatiles, the crude product was purified by flash chromatography
(SiO2, ether) to yield 4 as a bright yellow, crystalline solid (309 mg,
69%). Single crystals of 4 were grown by slow evaporation from ether/
hexane. 1H NMR (200 MHz, CDCl3): δ 7.53−7.36 (m, 10H, Ar-CH),
7.21 (m, 3H, Ar-CH), 6.63 (m, 2H, Ar-CH), 5.26 (s, 4H, N-CH2-N),
4.22 (s, 4H, Ph-CH2), 3.55 (s, 2H, Ph-CH2). 13C NMR (500 MHz,
CDCl3): δ 180.6 (N2CS), 137.3, 136.8, 129.0, 128.8, 128.4, 128.3,
127.8, 127.6 (all aromatic C), 65.7 (N-CH2-N), 55.5 (Ph-CH2), 55.2
(Ph-CH2). MS (EI): m/z 387 [M]+. Anal. Calcd (%) for C24H25N3S:
C, 74.38; H, 6.50; N, 10.84. Found: C, 74.11; H, 6.24; N, 10.97.
Synthesis of 1,3,5-Tribenzyl-4,6-tetrahydrotriazine-2-sele-
nide (5). A mixture of 2Br (435 mg, 1.0 mmol, 1.0 equiv) and red
selenium (157 mg, 2.0 mmol, 2.0 equiv) in 15 mL of THF was cooled
to −80 °C, and NaHMDS (2 M in THF, 0.22 mL, 1.1 mmol, 1.1
equiv) was added dropwise. The resulting dark red suspension was
stirred for 30 min at −80 °C, the cooling bath was removed, and the
suspension was allowed to warm to room temperature over a period of
3 h. All volatiles were removed in vacuo, and the residue was taken up
in 15 mL of CH2Cl2 and filtered through a short pad of Celite. After
washing the solid with CH2Cl2 (5 mL), the combined filtrates were
evaporated, which afforded the desired product as a white crystalline
Synthesis of Chlorido-1,5-cyclooctadiene-1,3,5-tribenzyl-
4,6-tetrahydrotriazin-2-ylideneiridium(I) (7). A 20 mL Schlenk
flask was charged with 2BF4 (332 mg, 0.75 mmol, 1.0 equiv), KOtBu
(101 mg, 0.9 mmol, 1.2 equiv), and [(Ir(COD)Cl)]2 (255 mg, 0.38
mmol, 0.5 equiv). The solid mixture was cooled to −80 °C. After 15
min at −80 °C 15 mL of cold THF was added dropwise with vigorous
stirring. The mixture was stirred for 30 min at −80 °C, the cooling
bath was removed, and the suspension was warmed to room
temperature and stirred overnight. The solvent was removed in
vacuo, and the orange-red crude product was purified by flash
chromatography on silica gel 60 with ether (100%) as mobile phase.
All volatiles were evaporated in vacuo and yielded 7 as a bright yellow
1
solid (409 mg, 79%). H NMR (200 MHz, CDCl3): δ 7.48 (m, 4H,
Ar-CH), 7.34 (m, 6H, Ar-CH), 7.19 (m, 3H, Ar-CH), 7.11 (m, 2H,
Ar-CH), 5.91 (d, 2H, JHz = 14.8, Ph-CH2), 5.29 (d, 2H, JHz = 14.8, Ph-
CH2), 4.52 (br s, 2H, CHCOD), 3.95 (d, 2H, JHz = 11.8, N-CH2-N),
3.78 (d, 2H, JHz = 11.7, N-CH2-N), 3.64 (s, 2H, Ph-CH2), 3.20 (br s,
2H, CHCOD), 2.15 (m, 4H, CH2 COD), 1.58 (m, 4H, CH2 COD). 13C
NMR (500 MHz, CDCl3): δ 201.8 (s, NCN), 137.1, 136.3, 129.1,
128.9, 128.5, 128.5, 127.9, 127.8 (all aromatic C), 83.2 (s, CH COD),
63.9 (s, CH COD), 60.1 (s, Ph-CH2), 54.6 (s, N-CH2-N), 52.9 (s, Ph-
CH2), 33.4 (s,CH2 COD), 29.3 (s, CH2 COD). MS (EI): m/z
691[M]+. MS (MALDI): m/z 691 [M]+, 656 [M − Cl]+. Anal. Calcd
(%) for C32H37ClN3Ir C, 55.59; H, 5.39; N, 6.08. Found: C, 55.65; H,
5.57; N, 6.10.
1
solid (313 mg, 72%). H NMR (200 MHz, CDCl3): δ 7.52−7.29 (m,
10H, Ar-CH), 7.13 (m, 3H, Ar-CH), 6.75 (m, 2H, Ar-CH), 5.34 (s,
4H, N-CH2-N), 4.13 (s, 4H, Ph-CH2), 3.45 (s, 2H, Ph-CH2). 13C
NMR (500 MHz, CDCl3): δ 179.7 (N2CSe), 136.9, 136.7, 129.0,
128.9, 128.5, 128.4, 128.0, 127.7 (all aromatic C), 65.3 (N-CH2-N),
58.7 (Ph-CH2), 55.6 (Ph-CH2). MS (EI): m/z 435 [M]+. Anal. Calcd
(%) for C24H25N3Se: C, 66.35; H, 5.80; N, 9.67. Found: C, 66.10; H,
5.88; N, 9.75.
Synthesis of Dicarbonylchlorido-1,3,5-tribenzyl-4,6-tetrahy-
drotriazin-2-ylideneiridium(I) (9). CO was bubbled into a solution
of 7 (69 mg, 0.1 mmol) in CH2Cl2 (5 mL) for a few minutes. During
this procedure the yellow solution turned bright yellow. After 10 min
of stirring, all volatiles were removed in vacuo. The residue was washed
with 5 mL of n-hexane to give 9 as a bright yellow solid (106 mg,
Synthesis of Chlorido-1,5-cyclooctadiene-1,3,5-tribenzyl-
4,6-tetrahydrotriazin-2-ylidenerhodium(I) (6). A 20 mL Schlenk
flask was charged with 2BF4 (461 mg, 1.04 mmol, 1.0 equiv), KOtBu
(140 mg, 1.25 mmol, 1.2 equiv), and [(Rh(COD)Cl)]2 (256 mg, 0.52
mmol, 0.5 equiv). The solid mixture was cooled to −80 °C. After 10
min at −80 °C, 20 mL of cold THF was added dropwise with vigorous
stirring. The mixture was stirred for 30 min at −80 °C, the cooling
bath was removed, and the suspension was warmed to room
temperature and stirred overnight. The resulting dark red solution
was evaporated to dryness in vacuo, and the crude product was purified
by flash chromatography on silica gel 60 with n-hexane/ether (1:1) as
mobile phase. All volatiles were evaporated in vacuo, yielding 6 as a
yellow solid (513 mg, 82%). 1H NMR (200 MHz, CDCl3): δ 7.54 (m,
3H, Ar-CH), 7.44−7.35 (m, 6H, Ar-CH), 7.25 (m, 4H, Ar-CH), 7.18
1
96%). H NMR (200 MHz, CDCl3): δ 7.26 (m, 10H, Ar-CH), 7.17
(m, 3H, Ar-CH), 7.10 (m, 2H, Ar-CH), 5.61 (d, 2H, JHz = 14.8,
phenyl-CH2), 4.97 (d, 2H, JHz = 14.7, phenyl-CH2), 3.97 (d, 2H, JHz
=
12.16, N-CH2-N), 3.84 (d, 2H, JHz = 11.51, N-CH2-N), 3.73 (s, 2H,
Ph-CH2). 13C NMR (500 MHz. CDCl3): δ 193.8 (s, NCN), 184.3 (s,
CO), 180.5 (s, CO), 134.8, 129.7, 129.3, 129.0, 128.9, 128.7, 128.5,
128.4 (all aromatic C), 63.3 (Ph-CH2), 60.8 (N-CH2-N), 54.9 (Ph-
CH2). MS (MALDI): m/z 576 [M − CO − Cl]+. IR (CH2Cl2): ν
2066.81, 1983.85 cm−1 (CO). No correct elemental analysis could
be obtained, due to slow decomposition or instability of the
compound.
(m, 2H, Ar-CH), 5.97 (d, 2H, JHz= 14.9, Ph-CH2), 5.78 (d, 2H, JHz
=
2006
dx.doi.org/10.1021/om201275z | Organometallics 2012, 31, 2001−2008

Organometallics
Article
Synthesis of 5-Benzyl-1,3-dimethylurea-4-hydrotriazinium
Bromide (11Br). Compound 10 (1.47 g, 6.7 mmol, 1.0 equiv) was
dissolved in 30 mL of dimethoxyethane and treated with NBS (1.19 g,
6.7 mmol). The resulting red solution was stirred at room
temperature. After 45 min a white precipitate formed and the red
solution turned yellow. The white solid was filtered off, washed with
20 mL of dimethoxyethane and 10 mL of diethyl ether, and dried in
vacuo to yield 1.71 g (86%) of 11Br as a colorless crystalline solid. 1H
NMR (200 MHz, CDCl3): δ 10.64 (s, 1H, NCHN), 7.60−7.57 (m,
2H, Ar-CH), 7.56−7.35 (m, 3H, Ar-CH), 5.26 (m, 2H, N-CH2-N),
4.90 (s, 2H, Ph-CH2), 3.49 (s, 3H, CH3), 2.90 (s, 3H, CH3). 13C NMR
(500 MHz, CDCl3): δ 158.4 (NCHN), 147.2 (CO), 130.4, 129.9,
129.6, 129.5 (all aromatic C), 62.6 (N-CH2-N), 57.1 (Ph-CH2), 35.2
(CH3), 33.3 (CH3). MS (MALDI): m/z 217 [M − H]+. Anal. Calcd
(%) for C12H16BrN3O: C, 48.34; H, 5.41; N, 14.09. Found: C, 48.09;
H, 5.69; N, 13.93.
(CH2 COD). MS (MALDI): m/z 428 [M − Br]+. Anal. Calcd (%) for
C20H27BrN3ORh: C, 47.26; H, 5.35; N, 8.28. Found: C, 48.18; H,
5.04; N, 8.34.
Synthesis of Dicarbonylchlorido-1,3-dimethylurea-6-hydro-
triazin-2-ylidenerhodium (17). CO was bubbled into a solution of
15 (76 mg, 0.15 mmol) in CH2Cl2 (5 mL) for a few minutes. During
this procedure the solution turned from yellow to bright yellow. After
10 min of stirring, all volatiles were removed in vacuo. The residue was
washed with 5 mL of n-hexane, resulting in a bright yellow solid (63
mg, 93%). 1H NMR (200 MHz, CDCl3): δ 7.45 (m,5H, Ar-CH), 6.10
(d, 1H, JHz = 15.4, N-CH2-N), 5.85 (d, 1H, JHz = 14.8, N-CH2-N),
4.61 (d, 1H, JHz = 8.9, Ph-CH2), 4.22 (d, 1H, JHz = 8.9, Ph-CH2), 4.37
(s, 3H, CH3), 2.84 (s, 3H, CH3), 13C NMR (500 MHz, CDCl3): δ
1
209.5 (d, NCN, JRhC = 40.32 Hz), 185.9 (d, CO, JRhC = 40.32 Hz),
181.7 (d, CO, JRhC = 76.96 Hz), 148.8 (CO), 132.8, 129.4, 129.2,
128.7, 127.9 (all aromatic C), 61.7 (N-CH2-N), 61.3 (Ph-CH2), 39.8
(CH3), 33.2 (CH3). MS (MALDI): m/z 398 [M − 2CO]+. IR
(CH2Cl2): ν 2086.1, 2008 (CO), 1714 (NCON) cm−1. No correct
elemental analysis could be obtained, due to slow decomposition or
instability of the compound.
Synthesis of 5-Benzyl-1,3-dimethylurea-6-hydrotriazine-4-
thione (13). A suspension of 11Br (320 mg, 1.08 mmol, 1.0 equiv)
and S8 (69 mg, 2.16 mmol, 2.0 equiv) in 20 mL of THF was cooled to
−80 °C, and NaHMDS (2 M in THF, 0.24 mL, 1.19 mmol, 1.1 equiv)
was added dropwise. The yellow solution was stirred for 30 min at
−80 °C, the cooling bath was removed, and the solution was warmed
to room temperature within 3 h. After evaporation of all volatiles, the
crude product was purified by flash chromatography (SiO2, THF
100%) to yield 13 as a bright yellow, crystalline solid (160 mg, 0.64
Synthesis of Bromo-1,5-cyclooctadiene-1,3-dimethylurea-6-
hydrotriazin-2-ylideneiridium (16). A 20 mL Schlenk flask was
charged with 11 (290 mg, 0.98 mmol, 1.0 equiv), KOtBu (132 mg,
1.18 mmol, 1.2 equiv), and [(Ir(COD)Cl)]2 (242 mg, 0.49 mmol, 0.5
equiv). The solid mixture was cooled to −80 °C. After 10 min at −80
°C 20 mL of cold THF was added dropwise with vigorous stirring.
The mixture was stirred for 30 min at −80 °C, the cooling bath was
removed, and the suspension was warmed to room temperature and
stirred overnight. The resulting red solution was removed in vacuo, and
the red crude product was purified by flash chromatography on silica
gel 60 with THF (100%) as mobile phase. All volatiles were
evaporated in vacuo, and 16 was obtained as a dark yellow solid (404
mg, 71%). 1H NMR (200 MHz, CDCl3): δ 7.43 (m, 5H, Ar-CH), 5.84
(d, 1H, JHz = 15.2, Ph-CH2), 5.68 (d, 1H, JHz = 15.1, Ph-CH2), 4.74
(br s, 2H, CHCOD), 4.42 (d, 1H, JHz = 15.2, N-CH2-N), 4.15 (d, 1H,
JHz = 9.8, N-CH2-N), 3.94 (s, 3H, CH3), 3.04 (br s, 2H, CHCOD), 2.81
(s, 3H, CH3), 2.09 (m, 4H, CH2 COD), 1.65 (m, 4H, CH2 COD). 13C
NMR (500 MHz. CDCl3): δ 213.6 (s, NCN), 150.8 (CO), 134.0,
129.35, 128.7, 128.6, 127.9 (all aromatic C), 86.2 (CHCOD), 86.2
(CHCOD), 61.9 (Ph-CH2), 60.0 (N-CH2-N), 54.8 (CHCOD), 54.4
(CHCOD), 38.7 (CH3), 33.3 (CH2 COD), 33.2 (CH2 COD), 32.8 (CH3),
29.6 (CH2 COD), 29.3 (CH2 COD). MS (MALDI): m/z 518 [M − Br]+.
Anal. Calcd (%) for C20H27BrN3OIr: C, 40.20; H, 4.55; N 7.03.
Found: C, 40.17; H, 4.72; N, 6.88.
Synthesis of Dicarbonylchlorido-1,3-dimethylurea-6-hydro-
triazin-2-ylideneiridium(I) (18). CO was bubbled into a solution of
15 (71 mg, 0.12 mmol) in CH2Cl2 (4 mL) for a few minutes. During
this procedure the solution turned from yellow to bright yellow. After
15 min of stirring, all volatiles were removed in vacuo. The residue was
washed with 5 mL of n-hexane, leaving 18 as a bright yellow solid (57
mg, 87%). 1H NMR (200 MHz, CDCl3): δ 7.39 (m, 5H, Ar-CH), 5.77
(d, 1H, JHz = 15.5, N-CH2-N), 5.11 (d, 1H, JHz = 14.8, N-CH2-N),
4.51 (d, 1H, JHz = 9.6, Ph-CH2), 4.37 (d, 1H, JHz = 9.8, Ph-CH2), 3.73
(s, 3H, CH3), 2.84 (s, 3H, CH3). 13C NMR (500 MHz, CDCl3): δ
203.3 (s, NCN), 180.0 (s, CO), 167.3 (s, CO), 149.7 (CO), 132.7,
129.5, 129.2, 128.2, 128.4 (all aromatic C), 62.3 (N-CH2-N), 61.0 (Ph-
CH2), 39.6 (CH3), 33.5 (CH3). MS (MALDI): m/z 438 [M −
2COl]+. IR (CH2Cl2): ν 2073.08, 1999.08 (CO), 1718 (NCON)
cm−1. No correct elemental analysis could be obtained, due to slow
decomposition or instability of the compound.
1
mmol, 59%). H NMR (200 MHz, CDCl3): δ 7.36 (m, 5H, Ar-CH),
5.25 (s, 2H, N-CH2-N), 4.41 (s, 2H, Ph-CH2), 3.56 (s, 3H, CH3), 2.91
(s, 3H, CH3). 13C NMR (500 MHz, CDCl3): δ 181.9 (CS), 151.7
(CO), 135.0, 129.0, 128.3, 127.6, (all aromatic C), 60.9 (N-CH2-
N), 55.4 (Ph-CH2), 35.5 (CH3), 33.3 (CH3). MS (EI): m/z 249 [M]+.
Anal. Calcd (%) for C12H15N3OS: C, 57.81; H, 6.06; N, 16.85. Found:
C, 57.64; H, 6.30; N, 16.94.
Synthesis of 5-Benzyl-1,3-dimethylurea-4-hydrotriazine-6-
selenide (14). A suspension of 11Br (205 mg, 0.69 mmol, 1.0 equiv)
and red selenium (109 mg, 1.38 mmol, 2.0 equiv) in 20 mL of THF
was coolded to −80 °C, and NaHMDS (2 M in THF, 0.16 mL, 0.76
mmol, 1.1 equiv) was added dropwise. The yellow solution was stirred
for 30 min at −80 °C, the cooling bath was removed, and the solution
was warmed to room temperature within 4 h. After evaporation of all
volatiles, the crude product was purified by flash chromatography
(SiO2, THF 100%) to yield 14 as a yellow crystalline solid (129 mg,
63%). 1H NMR (200 MHz, CDCl3): δ 7.32 (m, 5H, Ar-CH), 5.36 (s,
2H, N-CH2-N), 4.36 (s, 2H, Ph-CH2), 3.61 (s, 3H, CH3), 2.83 (s, 3H,
CH3). 13C NMR (500 MHz, CDCl3): δ 184.0 (CS), 150.0 (CO),
134.1, 128.7, 128.1, 127.3 (all aromatic C), 60.8 (N-CH2-N), 58.2 (Ph-
CH2), 38.2 (CH3), 33.0 (CH3). MS (EI): m/z 297 [M]+. Anal. Calcd
(%) for C12H15N3OSe: C, 48.65; H, 5.10; N, 14.19. Found: C, 48.37;
H, 5.26; N, 14.11.
Synthesis of Bromo-1,5-cyclooctadiene-1,3-dimethylurea-6-
hydrotriazin-2-ylidenerhodium (15). A 20 mL Schlenk flask was
charged with 11 (291 mg, 0.98 mmol, 1.0 equiv), KOtBu (132 mg,
1.18 mmol, 1.2 equiv), and [(Ir(COD)Cl)]2 (329 mg, 0.49 mmol, 0.5
equiv). The solid mixture was cooled to −80 °C. After 10 min at −80
°C 20 mL of cold THF was added dropwise with vigorous stirring.
The mixture was stirred for 30 min at −80 °C, the cooling bath was
removed, and the suspension was warmed to room temperature and
stirred overnight. The solvent was removed in vacuo, and the yellow
crude product was purified by flash chromatography on silica gel 60
with THF (100%) as mobile phase. All volatiles were evaporated in
vacuo, giving 15 as a yellow solid (354 mg, 71%). 1H NMR (200 MHz,
CDCl3): δ 7.42 (m, 5H, Ar-CH), 6.06 (d, 1H, JHz = 15.3, Ph-CH2),
5.80 (d, 1H, JHz = 15.8, Ph-CH2), 5.11 (br s, 2H, CHCOD), 4.41 (d, 1H,
JHz = 11.4, N-CH2-N), 4.15 (d, 1H, JHz = 11.6, N-CH2-N), 4.13 (s,
CH3), 3.48 (br s, 1H, CHCOD), 2.80 (s, CH3), 2.26 (m, 4H, CH2 COD),
1.91 (m, 4H, CH2 COD). 13C NMR (500 MHz, CDCl3): δ 222.1 (d,
1JRhC = 47.2 Hz, N2C), 149.6 (N2CO), 134.4, 129.6, 128.9, 128.3,
Crystal Structure Determinations. Crystals of compounds
2Br·0.5H2O, 4, and 15 suitable for X-ray study were selected by
means of a polarization microscope and investigated with a STOE
imaging plate diffraction system and an Oxford Diffraction Xcalibur
diffractometer, respectively, using graphite-monochromatized Mo Kα
radiation (λ = 0.71073 Å). Unit cell parameters were determined by
least-squares refinements on the positions of 13 509, 8000, and 22 305
reflections, respectively. Space group no. 14 was uniquely determined
for 15. For crystals of 2Br·0.5H2O systematic absences were consistent
with reflection conditions of space group types Ia and I2/a. In the
128.1 (all aromatic C), 99.5 (d, JRhC = 6.4 Hz, CHCOD), 99.4 (d, JRhC
=
6.4 Hz, CHCOD), 71.0 (d, JRhC = 14.4 Hz, CHCOD), 70.6 (d, JRhC = 14.5
Hz, CHCOD), 61.9 (N-CH2-N), 60.8 (Ph-CH2), 39.4 (CH3), 33.5
(CH3), 32.7 (CH2 COD), 32.6 (CH2 COD), 29.2 (CH2 COD), 29.2
2007
dx.doi.org/10.1021/om201275z | Organometallics 2012, 31, 2001−2008

Organometallics
Article
course of structure refinement, the latter proved to be the right one.
Taking into account the symmetry of the diffraction pattern, the
systematic absences, and the number of formula units in the unit cell,
the members of the enantiomorphous pair P31 and P32 were identified
as possible space groups for the crystals of the sulfur compound 4. For
the crystal under investigation, P31 proved to be the right one by
inspection of the anomalous dispersion (Flack parameter:23
−0.04(12)). Crystals of 4 suffer from twinning by merohedry, and
the respective twin law (expressed as the matrix that transforms the hkl
indices of one component into the other: 0 1 0 1 0 0 0 0 −1) was
taken into account, assuming additivity of the intensities of the
reflections of the twin components. The fractional contributions of the
twin components for the crystal under investigation were 0.376(3) and
0.624(3). Corrections for Lorentz and polarization effects were applied
in all cases. The structures were solved by direct methods24 and
subsequent ΔF syntheses. Approximate positions of all hydrogen
atoms were found in different stages of converging refinements (max.
shift/s.u. = 0.001, 0.000, and 0.000, respectively) by full-matrix least-
squares calculations on F2.25 Anisotropic displacement parameters
were refined for all atoms heavier than hydrogen. With idealized bond
lengths and angles assumed for all the CH, CH2, and CH3 groups, the
riding model was applied for the corresponding H atoms and their
isotropic displacement parameters were constrained to 120%, 120%,
and 150% of the equivalent isotropic displacement parameters of the
parent carbon atoms, respectively. In addition, the H atoms of the CH3
groups were allowed to rotate around the neighboring C−C bonds.
Selected crystal data and refinement results are compiled in Table 1.
CCDC-859272 (2Br·0.5H2O), CCDC-859273 (4), and CCDC-
859274 (15) contain the supplementary crystallographic data
(excluding structure factors) for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
361. (c) Cesar, V.; Lugan, N.; Lavigne, G. Chem.Eur. J. 2010, 16,
́
11432.
(5) (a) Hudnall, T. W.; Bielawski, C. W. J. Am. Chem. Soc. 2009, 131,
16039. (b) Hudnall, T. W.; Moerdyk, J. P.; Bielawski, C. W. Chem.
Commun. 2010, 46, 4288. (c) Hudnall, T. W.; Moorhead, E. J.; Gusev,
D. G.; Bielawski, C. W. J. Org. Chem. 2010, 75, 2763. (d) Moerdyk, J.
P.; Bielawski, C. W. Organometallics 2011, 30, 2278. (e) For a seven-
membered diamido carbene see: Hudnall, T. W.; Tennyson, A. G.;
Bielawski, C. W. Organometallics 2010, 29, 4569.
(6) Braun, M.; Frank, W.; Reiss, G. J.; Ganter, C. Organometallics
2010, 29, 4418.
(7) (a) Biju, A. T.; Hirano, K.; Frohlich, R.; Glorius, F. Chem. Asian J.
̈
2009, 4, 1786.
(8) (a) Benhamou, L.; Ces
G. Chem. Commun. 2009, 4720. (b) Benhamou, L.; Vujkovic, N.;
Cesar, V.; Gornitzka, H.; Lugan, N.; Lavigne, G. Organometallics 2010,
29, 2616.
́
ar, V.; Gornitzka, H.; Lugan, N.; Lavigne,
́
(9) Vujkovic, N.; Ces
2011, 17, 13151.
́
ar, V.; Lugan, N.; Lavigne, G. Chem.Eur. J.
(10) Lewis, R. T.; Motherwell, W. B. Tetrahedron 1992, 48, 1484.
(11) Mohrle, H.; Scharf, U. Arch. Pharm. (Weinheim, Ger.) 1974, 307,
̈
51.
(12) Mayr, M.; Wurst, K.; Ongania, K.-H.; Buchmeiser, M. R.
Chem.Eur. J. 2004, 10, 1256.
(13) (a) Denk, M. K.; Gupta, S.; Brownie, J.; Tajammul, S.; Lough, A.
J. Chem.Eur. J. 2001, 7, 447. (b) Jazzar, R.; Liang, H.; Donnadieu,
B.; Bertrand, G. J. Organomet. Chem. 2006, 691, 3201.
(14) Nordstrøm, L. U.; Madsen, R. Chem. Commun. 2007, 5034.
(15) For a closely related example see: Giumanini, A. G.; Verardo,
G.; Gorassini, F.; Strazzolini, P.; Benetollo, F.; Bombieri, G. J. Chem.
Soc., Perkin Trans. 1 1994, 1643.
(16) Chianese, A. R.; Li, X.; Janzen, M. C.; Faller, J. W.; Crabtree, R.
H. Organometallics 2003, 22, 1663.
̈
̈
̌
(17) Ozdemir, I.; Yigit, B.; Çetinkaya, B.; Ulku, D.; Tahir, M. N.;
̈
ASSOCIATED CONTENT
■
Arici, C. J. Organomet. Chem. 2001, 633, 27.
S
* Supporting Information
(18) Kelly, R. A. III; Clavier, H.; Giudice, S.; Scott, N. M.; Stevens,
E. D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.; Cavallo, L.; Nolan, S. P.
Organometallics 2008, 27, 202.
(19) Nilsson, B. L.; Overman, L. E. J. Org. Chem. 2006, 71, 7706.
(20) (a) Bortenschlager, M.; Mayr, M.; Nuyken, O.; Buchmeiser, M.
Crystallographic data (CIF files) for compounds 2Br·0.5H2O,
4, and 15. This material is available free of charge via the
Internet at http://pubs.acs.org.
R. J. Mol. Catal. A 2005, 233, 67. (b) Herrmann, W. A.; Schutz, J.;
Frey, G. D.; Herdtweck, E. Organometallics 2006, 25, 2437.
(21) For structures of related NHC-Rh(COD)Br complexes see for
example ref 12 and also: (a) Kim, H. J.; Kim, M.; Chang, S. Org. Lett.
2011, 13, 2368. (b) Herrmann, W. A.; Goossen, L. J.; Spiegler, M. J.
̈
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: christian.ganter@uni-duesseldorf.de.
Notes
Organomet. Chem. 1997, 547, 357. (c) Turkmen, H.; Pape, T.; Hahn,
̈
The authors declare no competing financial interest.
F. E.; Çetinkaya, B. Organometallics 2008, 27, 571. (d) Baker, M. V.;
Brayshaw, S. K.; Skelton, B. W.; White, A. H. Inorg. Chim. Acta 2004,
357, 2841. For structures of related NHC-Rh(COD)Cl complexes
see for example refs 2a, b, 4a, 5e, 8b and also: (e) Hildebrandt, B.;
Frank, W.; Ganter, C. Organometallics 2011, 30, 3483.
(22) %VBur denotes the buried volume, which gives a measure of the
space occupied by the NHC ligand in the first coordination sphere of
the metal center. The given values were calculated using the Web-
based program SambVca provided by Cavallo and co-workers at
http://www.molnac.unisa.it/OMtools.php. For a comprehensive
description of the underlying concept and details concerning the
calculation see: Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.;
Ragone, F.; Scarano, V.; Cavallo, L. Eur. J. Inorg. Chem. 2009, 1759.
(23) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
REFERENCES
■
(1) For current comprehensive reviews see for example:
(a) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem.
Rev. 2000, 100, 39. (b) Jahnke, M. C.; Hahn, F. E. Angew. Chem., Int.
Ed. 2008, 47, 3122. (c) Droge, T.; Glorius, F. Angew. Chem. 2010, 122,
7094. (d) Benhamou, L.; Chardon, E.; Lavigne, G.; Bellemin-
̈
́
Laponnaz, S.; Cesar, V. Chem. Rev. 2011, 111, 2705.
(2) (a) Khramov, D. M.; Lynch, V. M.; Bielawski, C. W.
Organometallics 2007, 26, 6042. (b) Sanderson, M. D.; Kamplain, J.
W.; Bielawski, C. W. J. Am. Chem. Soc. 2006, 128, 16514. (c) Khramov,
D. M.; Rosen, E. L.; Er, J. A. V.; Vu, P. D.; Lynch, V. M.; Bielawski, C.
W. Tetrahedron 2008, 64, 6853. (d) Bittermann, A.; Harter, P.;
̈
(24) Sheldrick, G. M. SHELXS86, Program for the Solution of Crystal
Herdtweck, E.; Hoffmann, S. D.; Hermann, W. A. J. Organomet. Chem.
2008, 693, 2079. (e) Wolf, S.; Plenio, H. J. Organomet. Chem. 2009,
694, 1487. (f) Hobbs, M. G.; Knapp, C. J.; Welsh, P. T.; Borau-Garcia,
J.; Ziegler, T.; Roesler, R. Chem.Eur. J. 2010, 16, 14520.
Structures; University of Gottingen: Germany, 1985.
̈
(25) Sheldrick, G. M. SHELXL97, Program for the Refinement of
Crystal Structures; University of Gottingen: Germany, 1997.
̈
(3) (a) Díez-Gonzal
́
ez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009,
109, 3612. (b) Enders, D.; Niemeier, O.; Henseler, A. Chem. Rev.
2007, 107, 5606.
(4) (a) Ces
11286. (b) Ces
́
ar, V.; Lugan, N.; Lavigne, G. J. Am. Chem. Soc. 2008, 130,
ar, V.; Lugan, N.; Lavigne, G. Eur. J. Inorg. Chem. 2010,
́
2008
dx.doi.org/10.1021/om201275z | Organometallics 2012, 31, 2001−2008