Reprogramming of a malonic N-heterocyclic carbene: A simple backbone modification with dramatic consequences on the ligand's donor properties

Article abstract of DOI:10.1002/ejic.200901113

Reaction of N,N′-dimesitylformamidine with dimethylmalonyl dichloride in dichloromethane in the presence of an excess of Methylamine gives the 2-chloro-4,5-dioxohexahydropyrimidine 1. The corresponding diamidocarbene 3 is generated in situ by further deprotonation with. KHMDS at -40 °C and identified by trapping with S₈ to give the fully characterized (including X-ray structure) sulfur adduct: 4. It also reacts with [RhCl(Cod)]₂ to yield the NHC complex [RhCl(3)-(cod)] (5) (characterized, also by X-ray structure). The donor properties of 3 were evaluated against the established. IR [v(CO)] scale from [RhCl(3)(CO) ₂] (6). The average value of v(CO) = 2045 cm^-1 indicates that the diamidocarbene 3 is much less nucleophilic than structurally relevant six-membered NHCs including the anionic diaminocarbenes previously reported, in our group.

Full text of DOI:10.1002/ejic.200901113

SHORT COMMUNICATION
DOI: 10.1002/ejic.200901113
Reprogramming of a Malonic N-Heterocyclic Carbene: A Simple Backbone
Modification with Dramatic Consequences on the Ligand’s Donor Properties
Vincent César,*[a,b] Noël Lugan,[a,b] and Guy Lavigne*[a,b]
Keywords: Heterocyclic carbenes / Diamidocarbene / Organometallic chemistry / Electronic properties / Rhodium
Reaction of N,NЈ-dimesitylformamidine with dimethylmal-
onyl dichloride in dichloromethane in the presence of an ex-
cess of triethylamine gives the 2-chloro-4,5-dioxohexahydro-
(cod)] (5) (characterized also by X-ray structure). The donor
properties of 3 were evaluated against the established IR
[ν(CO)] scale from [RhCl(3)(CO)2] (6). The average value of
pyrimidine 1. The corresponding diamidocarbene 3 is gener- ν(CO) = 2045 cm–1 indicates that the diamidocarbene 3 is
ated in situ by further deprotonation with KHMDS at –40 °C
and identified by trapping with S8 to give the fully charac-
much less nucleophilic than structurally relevant six-mem-
bered NHCs including the anionic diaminocarbenes pre-
terized (including X-ray structure) sulfur adduct 4. It also re- viously reported in our group.
acts with [RhCl(cod)]2 to yield the NHC complex [RhCl(3)-
Introduction
N-Heterocyclic carbenes (NHCs)[1,2] have gained valu-
able significance over the past fifteen years, both as organ-
ocatalysts[3] and as “universal” ligands for organometallic
catalysis.[4] Due to the presence of at least one amino-type
nitrogen atom (two nitrogen atoms directly connected to
Figure 1. Anionic N-heterocyclic carbene and diamidocarbene
the carbene atom for the most studied cyclic diaminocarb-
enes) in the vicinity of the carbene centre, they are typically
classified as nucleophilic carbenes and, by consequence, be-
have as strong electron-donor ligands, particularly in com-
parison with phosphanes.[5] So, whereas the successful de-
sign of highly nucleophilic NHCs has received considerable
attention,[6] the alternate possibility of reducing their donor
properties has been only reported in a few cases.[7]
Our recent disclosure of a modulable synthetic strategy[8]
leading to the six-membered anionic NHC A incorporating
a malonate backbone (Figure 1) offered further possibilities
to devise structurally related derivatives exhibiting different
donor properties.[8] Indeed, we reasoned that a slightly
modified approach based on dimethylmalonyl chloride as a
coupling partner (vide infra) would allow the introduction
of a second substituent at the position 5 of the heterocycle,
thereby blocking the electronic delocalisation through the
malonate skeleton, ultimately producing the neutral car-
bene of type B, being much less nucleophilic due to the
incorporation of nitrogen atoms as amide groups.
based on the same six-membered skeleton.
During the course of this work, we became aware of the
very recent independent publication by Bielawski and co-
workers of a slightly different synthetic approach leading to
the first diamidocarbene of type B.[9] This prompted us to
disclose our parallel results giving additional insight into
the chemistry of this fascinating new type of N-heterocyclic
carbene incorporating amide-type nitrogen atoms.[10]
Results and Discussion
In a logical transposition of our synthesis of A,[8] the
precursor of B was prepared by coupling N,NЈ-dimesityl-
formamidine with dimethylmalonyl dichloride in dichloro-
methane in the presence of an excess of triethylamine as a
base (Scheme 1). Surprisingly, the product did not display
any salt-like character but behaved as a neutral compound,
with a relative good solubility in aromatic solvents (toluene
or benzene) as well as in nonpolar mixtures usually unable
to dissolve chloride salts. Such properties facilitated the iso-
lation of the product by simple selective extraction from a
CH2Cl2/Et2O mixture (1:2, v/v). Considering that the
attachment of two electron-withdrawing carbonyl func-
tionalities on the nitrogen atoms renders the formamid-
[a] CNRS, LCC (Laboratoire de Chimie de Coordination),
205 route de Narbonne, 31077 Toulouse Cedex 4, France
[b] Université de Toulouse, UPS, INPT,
31077 Toulouse Cedex 4, France
E-mail: vincent.cesar@lcc-toulouse.fr
guy.lavigne@lcc-toulouse.fr
Eur. J. Inorg. Chem. 2010, 361–365
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V. C ésar, N. Lugan, G. Lavigne
SHORT COMMUNICATION
inium unit sufficiently electrophilic to undergo a nucleo-
philic attack by the chloride counteranion, a formulation of
the compound as a 2-chloro-4,5-dioxohexahydropyrimidine
1 – a “masked” form for a formamidinium – was reasonably
1
anticipated.[11] Such a structure was confirmed by H and
13C NMR spectra, where the proton and carbon resonances
at the position 2 of the heterocycle appeared at δ =
6.93 ppm (singlet) and δ = 90.5 ppm, respectively. Such sig-
nals are in agreement with the chemical shifts reported for
4,6-dioxo-1,3-diazine with an sp3-hybridized carbon atom
at the position 2.[12]
Scheme 2. Generation of diamidocarbene 3, its trapping with S8
and complexation with a rhodium(I) center.
Scheme 1. Synthesis of compound 1 and its subsequent meth-
anolysis.
The chloride adduct 1 proved to be extremely moisture-
sensitive, thus requiring manipulation under an inert gas.
Typically, the chlorine atom in position 2 of the heterocycle
could be readily replaced by better nucleophiles, as exem-
plified by the reaction of 1 with methanol to produce the
air-stable, methoxy-substituted heterocycle 2 (Scheme 1),
1
exhibiting a shift of the H NMR signal at position 2 to δ
= 5.28 ppm, consistent with a reduced electrophilicity.
The free N,NЈ-diamidocarbene 3 could be generated by
treatment of 1 with potassium bis(trimethylsilyl)amide
(KHMDS) in thf at low temperature (–40 °C) (Scheme 2).
Whereas 3 appears to be viable only at low temperature,
its formulation as a carbene was established by its trapping
Figure 2. Perspective view of 4. Anisotropic displacement param-
eter ellipsoids are shown at the 50% probability level, whereas hy-
drogen atoms were omitted for clarity. Selected bond lengths [Å]:
C1–S1 1.640(2), C1–N1 1.397(3), C1–N2 1.391(3), C2–O1 1.210(3),
C6–02 1.205(3), C2–C3 1.514(3), C3–C6 1.516(3).
with S8 to form the thiourea 4. The architecture of the new its reduced nucleophilicity. The latter characteristics can be
heterocycle was confirmed by the crystal structure of 4, de- illustrated by the carbene’s 13C NMR resonance appearing
picted in Figure 2. Very characteristically, the cycle exhibits at δ = 245.2 ppm (d, JRhC = 49 Hz), which is significantly
boat conformation, with the sp3-hydridized carbon atom C3 downfield-shifted compared to those observed in related
lying out of the plane of the cycle in contrast to the pre- (NHC)rhodium complexes reported in the literature (δ =
viously reported case of a planar pyrimidinium betaine.[8] 175–225 ppm),[13] and in particular the (4-oxoimidazolin-2-
This clearly reflects the disappearance of the electron-de- ylidene)rhodium complex reported by us (δ
=
localisation along the malonate unit, as also corroborated 229.7 ppm).[10a] Such a high chemical shift can be attributed
by a concomitant lengthening of interatomic distances C2– to a decrease of the electron density on the carbene centre
C3 and C3–C6, now appearing as C–C single bonds due to the electron-withdrawing effect of the two carbonyl
[1.514(3) Å and 1.516(3) Å, respectively].
groups.
A perspective view of the molecular structure of complex
The reaction between the in situ generated carbene 3 and
[RhCl(cod)]2 (cod = 1,5-cyclooctadiene) led to the forma- 5 established by X-ray diffraction is depicted in Figure 3
tion of the expected NHC complex [RhCl(3)(cod)] (5) in along with the principal interatomic distances and bond
good yield (68%), confirming Bielawski’s original observa- angles. The complex exhibits a square-planar arrangement
tion (in the case of iridium) that the carbene 3 is still a of ligands around the rhodium centre, with the carbene ring
suitable ligand for transition metal complexes in spite of being orthogonal to the mean coordination plane [torsion
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Eur. J. Inorg. Chem. 2010, 361–365

Reprogramming of a Malonic N-Heterocyclic Carbene
angle: N1–C1–Rh1–Cl1 83.9(2)°]. Again, the heterocycle is the two CO ligands, respectively. The average value of νav
=
not planar and exhibits a half-chair conformation in which 2045.4 cm–1 is much higher than those reported for other
the sp3-hybridized carbon atom C3 is pointing towards the six-membered NHCs, which typically are in the range 2029
chloride atom, C3 being off the mean plane defined by C2– Ͻ νav Ͻ 2038 cm–1. This result points out the critical role
N1–C1–N2–C4 (average deviation from mean plane of the two carbonyl groups on the electronic structure of
0.004 Å) by 0.486(2) Å. Most importantly, the Rh1–C1 the carbene, which renders carbene ligand 3 much less of an
bond [2.0107(19) Å] is considerably shorter than those re- electron donor than typical NHCs. Moreover, the Tolman
ported for six-membered (NHC)RhCl(cod) complexes electronic parameter (TEP) of the carbene 3 could be calcu-
[2.036(2) Å Ͻ Rh–Ccarbene Ͻ 2.090(3) Å].[14] This reflects a lated by the two linear regressions developed by Plenio and
stronger interaction between the carbene and the rhodium Nolan,[17] and was found to be equal to 2055 cm–1. Con-
center, probably due to a greater level of π-backdonation sidering the approximations due to the linear regressions,
from the metal centre to the carbene ligand. Further studies this value confirms that of 2057 cm–1 obtained by Bielawski
are currently carried out in order to completely understand et al.
the real nature of the metal–carbene bonding.
Conclusions
It is hoped that this and earlier reports from several
groups cited above will draw growing attention on the rich
chemistry of functional six-membered N-heterocyclic carb-
enes. Indeed, with one more skeletal atom than for five-
membered NHCs, they offer not only different steric prop-
erties, but also a broader variability in the number and na-
ture of the functionalities that can be introduced as integral
parts of their heterocyclic backbone. This is particularly im-
portant, since we see growing evidence that such remote
functionalities can very significantly modify the intrinsic
properties of the carbene ligand.
Experimental Section
General: All manipulations were performed under dry nitrogen by
using standard vacuum-line and Schlenk-tube techniques. Glass-
ware was dried at 120 °C in an oven for at least 3 h. Solvents were
dried and distilled by classical methods. NMR spectra were re-
Figure 3. Perspective view of complex 5. Anisotropic displacement
corded with Bruker ARX250 or AV300 spectrometers. Chemical
parameter ellipsoids are shown at 50% probability level, whereas
shifts are reported in ppm (δ) compared to TMS (1H and 13C) by
hydrogen atoms were omitted for clarity. Selected bond lengths [Å]:
using the residual peak of the deuterated solvent as internal stan-
Rh1–C1 2.0107(19), C1–N1 1.374(2), C1–N2 1.380(3), N1–C2
dard. IR spectra were obtained with a Perkin–Elmer Spectrum 100
1.410(3), N2–C4 1.416(3), C2–O1 1.201(3), C4–O2 1.204(3). Se-
FT-IR spectrometer. Microanalyses were performed by the Labora-
lected bond angles [°]: Rh1–C1–N1 117.71(13), Rh1–C1–N2
toire de Chimie de Coordination Microanalytical Service, and mass
spectra were obtained from the Mass Spectrometry Service of the
Paul Sabatier University. N,NЈ-dimesitylformamidine[18] was syn-
thesized according to a literature procedure.
125.77(14), N1–C1–N2 115.49(16).
Due to the adjunction of the two carbonyl groups in its
core, the electron-donating properties of the carbene 3 were
also expected to be significantly reduced. In order to quan-
tify this, complex 5 was converted into its dicarbonyl ana-
logue [RhCl(3)(CO)2] by bubbling CO gas into a solution
2-Chloro-1,3-dimesityl-5,5-dimethyl-4,6-dioxohexahydropyrimidine
(1): Dimethylmalonyl dichloride (0.75 mL, 5.6 mmol, 1.05 equiv.)
was added dropwise to a well-stirred solution of N,NЈ-dimesitylfor-
mamidine (1.5 g, 5.35 mmol) and Et3N (1.1 mL, 8.0 mmol,
of 5 in CH2Cl2. The outcome of the reaction was observable 1.5 equiv.) in CH2Cl2 (15 mL) at 0 °C. After stirring at this tem-
perature for 1 h, all volatiles were removed in vacuo, and the resi-
due was taken up in CH2Cl2/Et2O (1:2, v/v; 18 mL) and filtered
through a pad of Celite to remove triethylammonium chloride. Af-
ter washing the solid a second time with CH2Cl2/Et2O (1:2, v/v;
6 mL), the solvents were evaporated, which afforded the desired
product as a white, fluffy solid (1.6 g, 73%); m.p. 212–214 °C (dec.).
1H NMR (300 MHz, CDCl3): δ = 6.96 (s, 4 H, CHMes), 6.93 (s, 1
H, N2CHCl), 2.30 (s, 12 H, CH3 ortho), 2.29 (s, 6 H, CH3 para), 1.79
[s, 6 H, C(CH3)2] ppm. 13C{1H} NMR (75.4 MHz, CDCl3): δ =
170.8 (C=O), 139.0 (CMes), 136.0 (CMes), 132.2 (CMes), 130.2
by a colour change of the solution from dark red to pale
yellow. Complex 6 was obtained in excellent yields (99%)
and was fully characterized.[15] As for complex 5, the 13C
NMR carbene signal at δ = 230.8 ppm is found at much
higher field than those reported for known
[RhCl(NHC)(CO)2] complexes (δ Ͻ 219.6 ppm).[16] The
electron deficiency of the carbene 3 was confirmed by the
IR spectra of complex 6 in CH2Cl2. Two strong bands at
2005.3 and 2086.1 cm–1 were indeed observed, correspond-
ing to the asymmetric and symmetric normal vibrations of (CHMes), 90.5 (N2CHCl), 48.2 [C(CH3)2], 23.6 [C(CH3)2], 20.9
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363

V. C ésar, N. Lugan, G. Lavigne
SHORT COMMUNICATION
(CH3 para), 19.2 (CH3 ortho) ppm. IR (ATR): ν = 2975, 2925, 1713,
3.23 (br., 2 H, CHcod), 2.54 (s, 6 H, CH3 Mes), 2.39 (s, 6 H, CH3 Mes),
1.99 [s, 3 H, C(CH3)2], 1.98 (s, 6 H, CH3 Mes), 1.58–1.44 (m, 8 H,
CH2 cod), 1.55 [s, 3 H, C(CH3)2] ppm. 13C{1H} NMR (75.4 MHz,
˜
1682, 1665, 1608, 1459, 1401, 1356, 1261, 1249, 1189, 1167, 1103,
1034, 974, 910, 856, 763, 739, 720 cm–1. MS (ESI): m/z (%) = 412
(100) [M]+, 395 (98) [M – Cl + H2O]+.
1
3
CDCl3): δ = 245.2 (d, JRhC = 49.1 Hz, N2C), 169.1 (d, JRhC
2.2 Hz, C=O), 139.0, 137.4, 135.8, 135.1 (CMes), 130.5 (CHMes),
128.4 (CHMes), 101.3 (d, JRhC = 6.3 Hz, CHcod), 72.7 (d, JRhC
=
1,3-Dimesityl-2-methoxy-5,5-dimethyl-4,6-dioxohexahydropyrimid-
ine (2): To a solution of N,NЈ-dimesitylformamidine (373 mg,
1.33 mmol) and Et3N (0.28 mL, 2.0 mmol, 1.5 equiv.) in CH2Cl2
(5 mL) was added dimethylmalonyl dichloride (186 µL, 1.39 mmol,
1.05 equiv.) at 0 °C. The resulting solution was then stirred for 1 h,
before MeOH (1 mL) was added. After 5 min, all volatiles were
removed in vacuo, and the residue was purified by flash chromatog-
raphy (SiO2; CH2Cl2/MeOH, 95:5) to afford the expected product
=
13.9 Hz, CHcod), 50.8 [C(CH3)2], 31.8 (CH2 cod), 29.8 [C(CH3)2],
27.2 (CH2 cod), 21.0 (CH3 Mes), 20.1 (CH3 Mes), 19.6 (CH3 Mes), 18.8
[C(CH ) ] ppm. IR (ATR): ν = 2919, 2877, 1738, 1711, 1697, 1668,
˜
3 2
1460, 1429, 1384, 1365, 1351, 1322, 1306, 1226, 1104, 1071, 1053,
1037, 1016, 957, 941, 848, 783, 767 cm–1. MS (ESI): m/z (%) = 769
(39), 683 (69), 624 (22) [M + H]+, 587 (100) [M – Cl]+, 566 (30),
413 (18), 286 (28). C32H40ClN2O2Rh (623.03): calcd. C 61.69, H
6.47, N 4.50; found C 61.78, H 6.57, N 4.44.
1
as a white solid (540 mg, 99%); m.p. 185 °C. H NMR (300 MHz,
CDCl3): δ = 6.94 (s, 4 H, CHMes), 5.28 [s, 1 H, N2CH(OMe)], 2.83
(s, 3 H, OCH3), 2.28 (s, 12 H, CH3 ortho), 2.27 (s, 6 H, CH3 para),
1.83 [s, 3 H, C(CH3)2], 1.58 [s, 3 H, C(CH3)2] ppm. 13C{1H} NMR
(75.4 MHz, CDCl3): δ = 170.8 (C=O), 138.3, 138.0, 134.5, 133.4
(CMes), 129.9, 129.5 (CHMes), 98.5 [N2CH(OMe)], 59.6 (OCH3),
47.0 [C(CH3)2], 28.1 [C(CH3)2], 21.2 [C(CH3)2], 20.9 (CH3 para),
Dicarbonyl(chlorido)(1,3-dimesityl-5,5-dimethyl-4,6-dioxotetrahy-
dropyrimidin-2-ylidene)rhodium(I) (6): CO was bubbled into a solu-
tion of 5 (43 mg, 69 mmol) in CH2Cl2 (3 mL) for 10 min. From
dark red, the solution gradually turned pale yellow. After 1 h of
stirring, all volatiles were removed in vacuo. In order to thoroughly
remove the liberated cyclooctadiene, pentane (2ϫ3 mL) was added
to the crude product, the mixture was sonicated and concentrated
again. This procedure gave pure 6 as a pale yellow powder (39 mg,
18.5 (CH3 ortho), 18.3 (CH3 ortho) ppm. IR (ATR): ν = 2984, 2918,
˜
2859, 1696 (C=O), 1666, 1606, 1484, 1456, 1422, 1366, 1353, 1238,
1167, 1108, 1059, 957, 862, 776, 725, 684 cm–1. MS (ESI): m/z (%)
= 431 (100) [M + Na]+, 281 (26) [HC(NHMes)2]+. C25H32N2O3
(408.53): calcd. C 73.50, H 7.90, N 6.86; found C 73.39, H 8.00, N
6.79.
1
98%); m.p. 235 °C (dec.). H NMR (250 MHz, CDCl3): δ = 7.00
(s, 4 H, CHMes), 2.36 (s, 6 H, CH3 Mes), 2.34 (s, 6 H, CH3 Mes), 2.20
(s, 6 H, CH3 Mes), 1.92 [s, 3 H, C(CH3)2], 1.69 [s, 3 H, C(CH3)2]
1
ppm. 13C{1H} NMR (63 MHz, CDCl3): δ = 230.8 (d, JRhC
=
=
1,3-Dimesityl-5,5-dimethylhexahydropyrimidin-4,6-dione-2-thione
(4): A solution of 1 (856 mg, 2.07 mmol) in thf (15 mL) was cooled
to –80 °C, and KHMDS (0.5  in toluene, 4.6 mL, 1.1 equiv.) was
added dropwise. The very pale yellow solution was stirred for
30 min, and S8 (139 mg, 4.35 mmol) was added as a solid all at
once. After 1 h of stirring at –80 °C, the cooling bath was removed,
and the solution was warmed to room temperature. After evapora-
tion of all volatiles, the crude product was purified by flash
chromatography (SiO2; hexane/CH2Cl2, 1:1 then 1:2) to yield 4 as
a bright orange crystalline solid (573 mg, 68%); m.p. 282 °C (dec.).
1H NMR (300 MHz, CDCl3): δ = 6.97 (s, 4 H, CHMes), 2.32 (s, 6
H, CH3 para), 2.13 (s, 12 H, CH3 ortho), 1.79 [s, 6 H, C(CH3)2] ppm.
13C{1H} NMR (75.4 MHz, CDCl3): δ = 177.4 (C=S), 170.3 (C=O),
138.7, 134.4, 134.3 (CMes), 129.6 (CHMes), 48.6 [C(CH3)2], 25.0
43.4 Hz, N2C), 184.6 (d, JRhC = 53.9 Hz, RhCO), 182.4 (d, JRhC
75.7 Hz, RhCO), 169.9 (C=O), 139.8, 136.1, 134.9, 134.1 (CMes),
130.4 (CHMes), 129.4 (CHMes), 51.5 [C(CH3)2], 28.7 [C(CH3)2], 21.1
(CH3 Mes), 20.4 (CH3 Mes), 19.5 (CH3 Mes), 18.5 [C(CH3)2] ppm. IR
(ATR): ν = 2923, 2077, 1994, 1768, 1736, 1697, 1667, 1469, 1411,
˜
1389, 1315, 1289, 1243, 1172, 1096, 1036, 1008, 870, 848, 782, 767,
678 cm–1. IR (CH Cl ): ν = 2086.1 (CO), 2005.3 (CO), 1764.5,
˜
2
2
1735.2 cm–1. MS (ESI): m/z (%) = 611 (43) [M – 2 CO + 2 CH3CN
+ H]+, 507 (65) [M – Cl – CO]+, 415 (100) [M – Cl – Mes]+.
C26H28ClN2O4Rh (570.87): calcd. C 54.70, H 4.94, N 4.91; found
C 55.13, H 4.99, N 4.75.
X-ray Diffraction Studies: Crystals of 4 and 5, suitable for X-ray
diffraction, were obtained through crystallization from CH2Cl2/
pentane and thf/pentane, respectively. Data were collected at 180 K
with a Bruker D8 Apex II diffractomer and an Oxford Diffraction
Xcalibur diffractometer, respectiveley. All calculations were per-
formed with a PC-compatible computer by using the WinGX sys-
tem.[19] The structures were solved by using the SIR92 program,[20]
which revealed in each instance the position of most of the non-
hydrogen atoms. All remaining non-hydrogen atoms were located
by the usual combination of full-matrix least-squares refinement
and difference electron-density syntheses by using the SHELXL97
program.[21] Atomic scattering factors were taken from the usual
tabulations. Anomalous dispersion terms for Rh, S, and Cl atoms
[C(CH3)2], 21.2 (CH3 para), 17.5 (CH3 ortho) ppm. IR (ATR): ν =
˜
2971, 2916, 1855, 1731, 1701, 1671, 1658, 1608, 1480, 1459, 1382,
1330, 1305, 1263, 1222, 1144, 1121, 1034, 1011, 963, 856, 818,
762 cm–1. MS (ESI): m/z (%) = 431 (100) [M + Na]+, 409 (18) [M
+ H]+. C24H28N2O2S (408.56): calcd. C 70.55, H 6.91, N 6.86;
found C 70.53, H 6.96, N 6.78.
Chlorido(1,5-cyclooctadiene)(1,3-dimesityl-5,5-dimethyl-4,6-dioxo-
tetrahydropyrimidin-2-ylidene)rhodium(I) (5): Compound 1
(143 mg, 0.346 mmol) was dissolved in thf (6 mL), and the solution
was cooled to –40 °C. A solution of KHMDS in toluene (0.5 ,
0.73 mL, 0.36 mmol, 1.05 equiv.) was then added dropwise, and,
after stirring for 30 min, [RhCl(cod)]2 (85 mg, 0.17 mmol, were included in Fc. All non-hydrogen atoms were allowed to vi-
0.5 equiv.) was added as a solid all at once. After 15 min at that
temperature, the cooling bath was removed and the reaction mix-
ture warmed up to room temperature, during which time the solu-
tion gradually turned from yellow to dark red. After 30 min at
room temperature, all volatiles were evaporated in vacuo, and the
crude product was directly purified by flash chromatography (neu-
tral Al2O3 type III; CH2Cl2) to leave the desired complex as a red
powder (147 mg, 68%). Single crystals suitable for an X-ray diffrac-
brate anisotropically. All the hydrogen atoms – except for olefinic
H atoms of the cod ligand in 5 – were set in idealized positions
[R3CH: C–H = 0.96 Å; R2CH2: C–H = 0.97 Å; RCH3: C–H =
0.98 Å; C(sp2)–H = 0.93 Å; Uiso = 1.2 or 1.5 times that of the Ueq
of the carbon atom to which the hydrogen atom is attached], and
their position were refined as “riding” atoms. The olefinic H atoms
of the cod ligand in 5 were located from a difference electron-den-
sity synthesis; their positions and isotropic thermal parameters (ar-
bitrarily set to 0.05 Å2) were kept fixed during the final refinement.
tion experiment were obtained by slow diffusion of pentane into a
1
solution of 5 in thf; m.p. 197 °C. H NMR (300 MHz, CDCl3): δ CCDC-755193 (4) and CCDC-755194 (5) contain the supplemen-
= 7.11 (s, 2 H, CHMes), 6.98 (s, 2 H, CHMes), 4.71 (br., 2 H, CHcod),
tary crystallographic data for this paper. These data can be ob-
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Reprogramming of a Malonic N-Heterocyclic Carbene
R. Fernández, E. Alvarez, J. M. Lassaletta, J. Organomet.
Chem. 2005, 690, 5979–5988; e) M. Viciano, E. Mas-Marza,
M. Sanau, E. Peris, Organometallics 2006, 25, 3063–3069.
[8] V. C ésar, N. Lugan, G. Lavigne, J. Am. Chem. Soc. 2008, 130,
11286–11287.
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
[9] T. W. Hudnall, C. W. Bielawski, J. Am. Chem. Soc. 2009, 131,
16039–16041.
Support from the Centre National de la Recherche Scientifique
(CNRS) and from the Agence Nationale de la Recherche (ANR)
(programme blanc, ANR-08-BLAN-0137-01) is gratefully ac-
knowledged.
[10] We and others have also disclosed very recently a mixed amino/
amidocarbene, see: a) L. Benhamou, V. César, H. Gornitzka,
N. Lugan, G. Lavigne, Chem. Commun. 2009, 4720–4722; b)
A. T. Biju, K. Hirano, R. Fröhlich, F. Glorius, Chem. Asian J.
2009, 4, 1786–1789.
[11] Such an attack was already reported leading to a similar struc-
ture, see: E. A. Barsa, R. Richter, J. Org. Chem. 1986, 51, 4483–
4485.
[12] a) K.-U. Fulda, E. Maassen, H. Ritter, R. Sperber, B. Tieke,
Langmuir 1996, 12, 854–856; b) H. Gotthardt, M. Riegels,
Chem. Ber. 1987, 120, 445–447; c) H. Gotthardt, J. Blum,
Chem. Ber. 1987, 120, 109–114.
[1] For monographs, see: a) N-Heterocyclic Carbenes in Transition
Metal Catalysis (Ed.: F. Glorius), Top. Organomet. Chem. 2007,
21; b) N-Heterocyclic Carbenes in Synthesis (Ed.: S. P. Nolan),
Wiley-VCH, Weinheim, 2006.
[2] For general reviews, see: a) O. Schuster, L. Yang, H. G. Raub-
enheimer, M. Albrecht, Chem. Rev. 2009, 109, 3445–3478; b)
F. E. Hahn, M. C. Jahnke, Angew. Chem. Int. Ed. 2008, 47,
3122–3172; c) D. Bourissou, O. Guerret, F. Gabbaï, G. Ber-
trand, Chem. Rev. 2000, 100, 39–91.
[13]
For a compilation, see: a) D. Tapu, D. A. Dixon, C. Roe, Chem.
Rev. 2009, 109, 3385–3407.
a) Ref.[8]; b) M. Mayr, K. Wurst, K.-H. Ongania, M. R. Buch-
meiser, Chem. Eur. J. 2004, 10, 1256–1266; c) C. Präsang, B.
Donnadieu, G. Bertrand, J. Am. Chem. Soc. 2005, 127, 10182–
10183; d) P. Bazinet, T.-G. Ong, J. S. O’Brien, N. Lavoie, E.
Bell, G. P. A. Yap, I. Korobkov, D. S. Richeson, Organometal-
lics 2007, 26, 2885–2895; e) H. Arslan, D. VanDerveer, I. Ozde-
mir, S. Demir, B. Cetinkaya, Acta Crystallogr., Sect. E 2007,
63, m770–m771.
[14]
[3] a) D. Enders, O. Niemeier, A. Henseler, Chem. Rev. 2007, 107,
5606–5655; b) N. Marion, S. Díez-González, S. P. Nolan, An-
gew. Chem. Int. Ed. 2007, 46, 2–15.
[4] a) S. Díez-González, N. Marion, S. P. Nolan, Chem. Rev. 2009,
109, 3612–3676; b) C. Samojlowicz, M. Bieniek, K. Grela,
Chem. Rev. 2009, 109, 3708–3742; c) M. Poyatos, J. A. Mata,
E. Peris, Chem. Rev. 2009, 109, 3677–3707; d) E. A. B.
Kantchev, C. J. O’Brien, M. G. Organ, Angew. Chem. Int. Ed.
2007, 46, 2768–2813; e) V. César, S. Bellemin-Laponnaz, L. H.
Gade, Chem. Soc. Rev. 2004, 33, 619–636; f) C. M. Crudden,
D. P. Allen, Coord. Chem. Rev. 2004, 248, 2247–2273; g) W. A.
Herrmann, Angew. Chem. Int. Ed. 2002, 41, 1290–1309.
[5] a) S. Díez-González, S. P. Nolan, Coord. Chem. Rev. 2007, 251,
874–883; b) A. Fürstner, M. Alcarazo, H. Krause, C. W.
Lehmann, J. Am. Chem. Soc. 2007, 129, 12676–12678.
[6] a) A. Fürstner, M. Alcarazo, K. Radkowski, C. W. Lehmann,
Angew. Chem. Int. Ed. 2008, 47, 8302–8306; b) S. Nakafuji, J.
Kobayashi, T. Kawashima, Angew. Chem. Int. Ed. 2008, 47,
1141–1144; c) V. Lavallo, Y. Canac, C. Präsang, B. Donnadieu,
G. Bertrand, Angew. Chem. Int. Ed. 2005, 44, 5705–5709; d)
[15] In particular, no decomposition and no loss of carbon mon-
oxide were observed during the workup of the reaction mixture,
contrary to other reports dealing with poor-donating NHC
systems, see: a) M. D. Sanderson, J. W. Kamplain, C. W. Biel-
awski, J. Am. Chem. Soc. 2007, 128, 16514–16515; b) S. Wolf,
H. Plenio, J. Organomet. Chem. 2009, 694, 1487–1492.
[16] The most downfield carbene 13C chemical shift in
[RhCl(NHC)(CO)2] was found in ref.[14c]
[17] For Plenio’s linear regression, see ref.[15b]; for Nolan’s method,
see: R. A. I. Kelly, H. Clavier, S. Giudice, N. M. Scott, E. D.
Stevens, J. Bordner, I. Samardjiev, C. D. Hoff, L. Cavallo, S. P.
Nolan, Organometallics 2008, 27, 202–210.
M. Mayr, K. Wurst, K.-H. Ongania, M. R. Buchmeiser, Chem. [18] K. E. Krahulic, G. D. Enright, M. Parvez, R. Roesler, J. Am.
Eur. J. 2004, 10, 1256–1266; e) P. Bazinet, G. P. A. Yap, D. S.
Chem. Soc. 2005, 127, 4142–4143.
Richeson, J. Am. Chem. Soc. 2003, 125, 13314–13315.
[19] L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837–838.
[20] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J.
Appl. Crystallogr. 1993, 26, 343–350.
[7] a) U. Siemeling, C. Färber, C. Bruhn, Chem. Commun. 2009,
98–100; b) D. M. Khramov, E. L. Rosen, V. M. Lynch, C. W.
Bielawski, Angew. Chem. Int. Ed. 2008, 47, 2267–2270; c) D. M.
Khramov, E. L. Rosen, J. A. V. Er, P. D. Vu, V. M. Lynch, C. W.
Bielawski, Tetrahedron 2008, 64, 6853–6862; d) M. Alcarazo,
[21] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
Received: November 17, 2009
Published Online: December 17, 2009
Eur. J. Inorg. Chem. 2010, 361–365
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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