Fine-Tunable 3,4-dihydroquinazol-2-ylidene carbenes: Synthesis, rhodium(I) complexes, and reactivity

Article abstract of DOI:10.1021/om300887y

The design and synthesis of various new six-membered cyclic formamidinium salts with a 3,4-dihydroquinazoline core have been reported in this paper. Our synthetic strategy allows access to a kind of tailor-made 3,4- dihydroquinazolinium salts bearing different substituent combinations. A series of novel 3,4-dihydroquinazolin-2-ylidene-based rhodium(I) complexes were prepared by the reaction of [Rh(cod)Cl]₂ with the free carbene obtained in situ from the deprotonation of the corresponding 3,4-dihydroquinazolinium salts with KN(SiMe₃)₂. The NHCs prepared in situ can also react with S₈ or CS₂ to afford the corresponding thiones or NHC-CS₂ adducts, respectively. The rhodium(I) complexes were transformed to the corresponding dicarbonyl complexes, and the ν(CO) values of the corresponding dicarbonyl Rh complexes indicate the 3,4-dihydroquinazol-2-ylidenes are stronger electron donors than normal five-membered NHCs. The Rh complexes are highly active in the arylation of carbonyl compounds, and the 3,4-dihydroquinazolin-2-ylidenes prepared in situ upon deprotonation are powerful in palladium-catalyzed Suzuki cross-coupling reactions at room temperature with a ppm scale catalyst loading with TONs of up to 425 000.

Full text of DOI:10.1021/om300887y

Article
pubs.acs.org/Organometallics
Fine-Tunable 3,4-Dihydroquinazol-2-ylidene Carbenes: Synthesis,
Rhodium(I) Complexes, and Reactivity
Jun Zhang,*,† Xinke Qin,† Jun Fu,† Xiao Wang,† Xiaolong Su,† Fangle Hu,† Jiajun Jiao,† and Min Shi*,‡
†Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry & Molecular Engineering, East China
University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354
Fenglin Road, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: The design and synthesis of various new six-membered cyclic formamidinium salts
with a 3,4-dihydroquinazoline core have been reported in this paper. Our synthetic strategy allows
access to a kind of tailor-made 3,4-dihydroquinazolinium salts bearing different substituent
combinations. A series of novel 3,4-dihydroquinazolin-2-ylidene-based rhodium(I) complexes were
prepared by the reaction of [Rh(cod)Cl]2 with the free carbene obtained in situ from the
deprotonation of the corresponding 3,4-dihydroquinazolinium salts with KN(SiMe3)2. The NHCs
prepared in situ can also react with S8 or CS2 to afford the corresponding thiones or NHC−CS2
adducts, respectively. The rhodium(I) complexes were transformed to the corresponding dicarbonyl
complexes, and the ν(CO) values of the corresponding dicarbonyl Rh complexes indicate the 3,4-dihydroquinazol-2-ylidenes are
stronger electron donors than normal five-membered NHCs. The Rh complexes are highly active in the arylation of carbonyl
compounds, and the 3,4-dihydroquinazolin-2-ylidenes prepared in situ upon deprotonation are powerful in palladium-catalyzed
Suzuki cross-coupling reactions at room temperature with a ppm scale catalyst loading with TONs of up to 425 000.
as for six-membered NHC D, placing the carbene center in the
perimidine-based six-membered ring leaves the divalent carbon
as part of a formally 7π-electron, six-membered heterocyclic
ring, while the more stable unsaturated species A possess the
6π-electron structure expected for aromatic systems.3c,h On the
basis of the ν(CO) values of the corresponding (CO)2RhCl(D)
INTRODUCTION
■
Over the past decade, N-heterocyclic carbenes (NHCs) have
received much attention mainly due to their widespread and
spectacular applications as organocatalysts and as ligands for
organometallic catalysis.1 Because the steric and electronic
properties of NHCs play a prominent role in catalysis, a variety
of NHCs with different N-heterocycle scaffolds have been
developed, among which of special interest are electronic and
steric variations resulting from different backbone structures
and different N-substituents on the NHCs.2
i
(R = Pr) complex, carbene D is an even stronger electron
donor than the imidazolidin-2-ylidene B.3c The NHC D
prepared in situ upon deprotonation of a novel lutidine-bridged
bis-perimidinium dibromide has been reported as a potent
precatalyst in palladium-catalyzed Heck and Suzuki cross-
coupling reactions under aerobic conditions and is efficient in
Suzuki cross-coupling of aryl iodide and phenylboronic acid at
140 °C even with a ppm scale catalyst loading.3i Its stronger σ-
donor character is responsible for its superior catalytic
performance. The palladium complexes based on NHC E
were found highly active in Heck-type reactions, which could
efficiently catalyze the coupling of aliphatic and aromatic vinyl
compounds with aryl bromides and chlorides with high
turnover numbers (TONs) up to 2 000 000.3d Stabilities of
these NHC Pd complexes under Heck-couplings conditions
were correlated with their molecular structure. The NHCs E
are also found to be reactive in other organometallic catalyses,
such as Rh- or Ir-catalyzed arylation of carbonyl compounds
using equimolar amounts of arylboronic acid and carbonyl
compound in the presence of 0.08−1 mol % catalyst,3j Ru-
catalyzed olefin metathesis,3l Pd-catalyzed Suzuki cross-
The vast majority of NHCs are based on five-membered-ring
systems, such as imidazol-2-ylidenes (A), imidazolidin-2-
ylidenes (B), and benzimidazol-2-ylidenes (C) (Figure 1).
Figure 1. Selected five- and six- membered N-heterocyclic carbenes.
Although, compared with five-membered NHCs, six-membered
NHCs such as perimidine-based carbenes (D) and tetrahy-
dropyrimidin-2-ylidenes (E) have rarely been reported, these
ligands afford new possibilities for carbene design.3 This six-
membered NHC scaffold directs the N-bound groups closer to
the carbene atom, which increases the steric impact on both the
carbene and a coordinated metal center, thus providing steric
protection not offered by five-membered NHCs. In particular,
Received: September 19, 2012
Published: November 5, 2012
© 2012 American Chemical Society
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coupling reactions,3m Pt-catalyzed hydrosilylation of alkynes,
alkenes, and ketones,3n and Cu-catalyzed carbonyl hydro-
silylation and cyanosilylation reactions.3o
Carbene D displays a planar molecular geometry, while, in
the scaffold of carbene E, only five atoms, i.e., two N atoms, 4-
and 6-position C atoms, and a carbene C atom, are almost in
one plane, and the middle 5-position C atom is out of the plane
(Figure 2). As part of our studies on the design and synthesis of
Figure 4. Molecular structure of 11c′ with 30% probability ellipsoids.
The anion (I−) has been omitted for clarity. Selected bond distances
(Å) and angles (deg): N(1)−C(1) 1.302(4), N(1)−C(2) 1.459(5),
N(1)−C(9) 1.477(4), N(2)−C(1) 1.331(4), N(2)−C(8) 1.414(4),
N(2)−C(15) 1.501(4), C(2)−C(3) 1.500(5), C(3)−C(8) 1.386(5),
C(1)−N(1)−C(2) 120.7(3), C(1)−N(1)−C(9) 118.9(3), C(2)−
N(1)−C(9) 120.1(3), C(1)−N(2)−C(8) 119.2(3), C(1)−N(2)−
C(15) 117.9(3), C(8)−N(2)−C(15) 121.7(3), N(1)−C(1)−N(2)
124.1(3), N(1)−C(2)−C(3) 110.6(3), C(7)−C(8)−N(2) 122.3(3),
C(3)−C(8)−N(2) 118.2(3).
Figure 2. Six-membered cyclic NHCs D, E, and targeted F.
novel NHC ligands for transition metal-based catalysis,4 we
have undertaken the design of new stable carbenes combining
the scaffolds of the NHCs D and E, and herein we report the
synthesis of various new six-membered cyclic formamidinium
salts with a 3,4-dihydroquinazoline core. A series of novel 3,4-
dihydroquinazolin-2-ylidene-based rhodium(I) complexes were
prepared by the reaction of [Rh(cod)Cl]2 with the free carbene
synthesized in situ. We observed that the 3,4-dihydroquinazo-
lin-2-ylidenes showed high efficiency not only in Rh-cataylzed
arylation of carbonyl compounds using arylboronic acid but
also in palladium-catalyzed Suzuki cross-coupling reactions at
room temperature with a ppm scale catalyst loading with TONs
of up to 425 000.
Scheme 1. Synthesis of 3,4-Dihydroquinazolinium Salt 3
RESULTS AND DISCUSSION
■
We first attempted to synthesize a 3,4-dihydroquinazolinium
salt, with two aryl substitutes on the N1 atom and N3 atom,
respectively (Figure 4). According to a literature method,5 the
Scheme 2. Attempt to Condense 2-Fluorobenzaldehyde with
Alkyl Amine
BnNH2, and CyNH2, respectively, and, after deprotection by p-
toluenesulfonic acid, was converted to the aldehydes 4a−d in
70−74% yields. The condensation reaction of 4a−d with the
corresponding amines and subsequent reduction by LiAlH4
afforded the desired diamines 5a−d in 63−84% yields, which
underwent cyclization to give the corresponding 3,4-dihydro-
quinazolinium salts 6a−d [6a (R1 = Mes, R2 = Bn, X = H), 6b
(R1 3,5-Me2-phenyl, R2 = iPr, X = H), 6c (R1, R2 = Bn, X = H),
and 6d (R1, R2 = Cy, X = OMe)] in 55−92% yields using the
typical method2 (Scheme 3). Following this route, the synthesis
of chiral 3,4-dihydroquinazolinium salts has been also
developed. For example, 2-bromobenzaldehyde diethylacetal
underwent a palladium-catalyzed coupling with (S)-phenyl-
ethylamine and, after deprotection, was converted to the
aldehyde 7 in 84% yield. Further condensation with a second
(S)-phenylethylamine followed by reduction with LiAlH4
afforded the chiral diamine 8 in 90% yield, which then
underwent cyclization to produce the desired chiral 3,4-
dihydroquinazolinium salt 9 in 31% yield using the typical
method2 (Scheme 4).
Figure 3. Targeted substituted 3,4-dihydroquinazolinium salts.
condensation of 2-fluorobenzaldehyde with mesitylaniline
(MesNH2) afforded Schiff base 1, which was treated with
LiNHMes (Mes = mesityl) and subsequently reduced by
LiAlH4 to give diamine 2. Diamine 2 underwent cyclization to
produce the corresponding 3,4-dihydroquinazolinium salt 3 in
44% yield using triethyl orthoformate in the presence of NH4Cl
(Scheme 1).
Next we tried to prepare a 3,4-dihydroquinazolinium salt
with an alkyl substituent on the N3 atom using the
aforementioned method. Unfortunately, the condensation of
2-fluorobenzaldehyde with various aliphatic amines such as
iPrNH2, CyNH2 (Cy = cyclohexyl), and PhCH2NH2 (BnNH2)
failed to give the desired product (Scheme 2). Therefore, we
examined an alternative method starting from 2-bromobenzal-
dehyde diethylacetal,6 which was subjected to a palladium-
catalyzed coupling with mesityl-NH2, 3,5-Me2-phenyl-NH2,
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Scheme 3. Synthesis of 3,4-Dihydroquinazolinium Salts 6a−
d
Scheme 5. Synthesis of 3,4-Dihydroquinazolinium Salts
11a−c
Scheme 6. Synthesis of Chiral 3,4-Dihydroquinazolinium
Salt 13
Scheme 4. Synthesis of Chiral 3,4-Dihydroquinazolinium
Salt 9
81−88% yields. 14a,b underwent cyclization to afford the
expected 3,4-dihydroquinazolinium salt 15a,b in 51−65%
yields.
Scheme 7. Synthesis of 3,4-Dihydroquinazolinium Salts
15a,b
The isopropyl group is often chosen as a sterically
demanding N-substituent in the design of NHCs. Due to low
boiling point of the volatile PrNH2, a 3,4-dihydroquinazoli-
i
The dihydroquinazoline scaffold structure of these 3,4-
dihydroquinazolinium salts was confirmed by the X-ray crystal
structure of 1-isopropyl-3-cyclohexyl-3,4-dihydroquinazolinium
iodide salt (11c′), which was obtained by treatment of 11c with
excess NaI (Figure 4).
nium salt with an isopropyl substituent on the N1 atom was
prepared from the 2-isopropylaminobenzaldehyde, obtained
from 2-aminobenzyl alcohol by a literature method.7 The
condensation of 2-(isopropylamino)benzaldehyde with NH2R
(R = 3,5-Me2-phenyl, Bn, or Cy) and subsequent reduction
afforded the corresponding diamines 10a−c in 66−78% yields,
which underwent cyclization to give 3,4-dihydroquinazolinium
salts 11a−c [11a (R = 3,5-Me2-phenyl), 11b (R = Bn), and 11c
(R = Cy)] in 54−81% yield, respectively (Scheme 5). Chiral
3,4-dihydroquinazolinium salt 13 with an isopropyl substituent
was also prepared in 76% yield by the cyclization of diamine 12,
which was obtained in 61% yield starting from the
condensation of 2-(isopropylamino)benzaldehyde with (S)-
phenylethylamine (Scheme 6).
Our successful synthetic strategy allows access to the
preparation of a novel kind of tailor-made 3,4-dihydroquina-
zolinium salts bearing different substituent combinations, where
the rational changes of different substituent combinations
might be applied to fine-tune the corresponding NHCs,
exhibiting different steric impact and electron-donating ability,
and thus these properties manifest themselves in the behavior
of the NHC−metal complexes. More noticeable is the
formation of chiral 3,4-dihydroquinazolinium salts 9 and 13.
Considering that this six-membered dihydroquinazoline scaf-
fold directs the N-bound groups closer to the carbene atom as
the perimidine scaffold does in E-type NHC complexes,3c,h
which might increase the chiral control on both the carbene
and a coordinated metal, the NHC derived from 9 and 13
could provide potential applications in asymmetric catalysis.
We further synthesized 3,4-dihydroquinazolinium salts with
an n-butyl substituent on the C4 atom. The addition of n-
butyllithium to the corresponding Schiff bases, prepared from
the condensation of 2-(isopropylamino)benzaldehyde with the
corresponding amines (Scheme 7), afforded diamines 14a,b in
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Free NHCs are able to react with S8 and CS2 to form thiones
and NHC−CS2 adducts, which are very useful compounds in
many organic reactions.8,9 For example, imidazolidin-2-thione
could be used as a synthetic precursor for a Liebeskind−Srogl
cross-coupling reaction to prepare the corresponding 2-aryl-2-
imidazoline,8 and a wide range of stable benzimidazolium or
imidazol(in)ium−CS2 adducts have been studied as novel ionic
liquids10 or organocatalysts in the cyanosilylation of alde-
hydes11 and in the Staudinger reaction for the preparation of β-
lactams.12 Furthermore, they can be also used as intermediates
for sulfur heterocycles,13 ligands for gold complexes, surface
units for gold nanoparticles,14 and promising antifungal and
antibacterial agents.15
Scheme 9. Synthesis of Rh Complexes 18a−g Based on 3,4-
Dihydroquinazol-2-ylidene
With these 3,4-dihydroquinazolinium salts in hand, we could
investigate the reactivity of their corresponding NHCs with
elemental sulfur (S8) and carbon disulfide (CS2). In practice,
the representative salt 11c was selected as starting material.
These transformations have been carried out from the reactions
of S8 or CS2 with the free carbene in situ prepared from
deprotonation of 11c by KN(SiMe3)2 (KHMDS). Thereby, the
thione 16 and NHC−CS2 adduct 17 were prepared in
moderate yields (48% for 16, 58% for 17), respectively, and
their structures have been confirmed by NMR and ESI analyses
(Scheme 8). The 13C NMR signals for CS appear at δ =
181.9 ppm for 16, and in 17, the 13C NMR signals for C-2 and
CS2 appear at δ = 162.5 and 232.7 ppm, respectively.
for 18g) in their solid structures. In solution, the interaction is
also apparent in the H NMR spectrum. For example, the
1
chemical shift for the methine septet in NiPr moves from 4.52
ppm in precursor 11c to 7.04 ppm for 18f, and that in NCy
moves from 4.85 ppm in 11c to 6.64 ppm for 18f. The
existence of weak interactions between the Rh atom and H
atom is probably attributed to a direct effect of the six-
membered heterocyclic structure enforcing a close approach of
the N-bonded groups to the metal center, which could bring
additional stabilization to the metal center. Such weak
interactions between the Rh atom and H atom were also
observed in (COD)RhCl(D).3c,h
Scheme 8. Synthesis of the Thione 16 and NHC−CS2
Adduct 17 from 3,4-Dihydroquinazolinium Salt 11c
To evaluate the electron-donating ability of these new
NHCs, 18c−f were treated with excess carbon monoxide,
which afforded the Rh dicarbonyl species 19a−e in 67−83%
yield, respectively (Scheme 10). The average CO vibration
frequency of the Rh carbonyl complexes 19a−e (νav = 2028−
2031) indicates that the corresponding 3,4-dihydroquinazol-2-
ylidenes are stronger electron donors than normal five-
membered NHCs (νav = 2038−2041),17 weaker than the six-
membered NHCs of type E (νav = 2023),3d and similar to the
six-membered NHCs of type D (R = Pr, νav = 2031).3h
i
The catalytic activity of the Rh complexes was studied in
detail. The Rh complexes are highly active in the arylation of
carbonyl compounds using equimolar amounts of arylboronic
acid and carbonyl compound in the presence of 0.1−1 mol %
catalyst (Table S1, see Supporting Information). Moreover the
3,4-dihydroquinazolin-2-ylidenes prepared in situ upon depro-
tonation are proved to be powerful in palladium-catalyzed
Suzuki cross-coupling reactions at room temperature with a
ppm scale catalyst loading with TONs of up to 425 000 (Table
S2, see Supporting Information).
The ability of the new NHCs to ligate a transition metal
fragment was also evaluated. The reaction between the in situ
generated carbene and [(COD)RhCl]2 led to the formation of
the expected NHC complexes 18a−g, which were isolated in
34−65% yield as air-stable yellow solids (Scheme 9). Both mass
and NMR spectra, and in particular the X-ray diffraction
analyses of 18e−g (Figures 5 and 6), confirmed the formation
of these NHC Rh complexes. The Rh−CNHC bond distances of
2.055(3), 2.051(2), and 2.051(3) Å for 18e, 18f, and 18g,
respectively, are shorter than that reported for (COD)RhBr(E)
(R = iPr) (2.0896(18) Å),3d similar to that of (COD)RhCl(D)
(R = Pr) (2.056(11) Å), and longer than that of five-
membered (COD)RhCl(B) (R = Me) (2.023(2) Å) (NHC =
1,3-dimethylimidiazolin-2-ylidene).16
The existence of weak interactions between the Rh atom and
H atom in these Rh complexes is confirmed by the observation
of the short Rh---H distances (Rh(1)---H(16A) 2.4138(2) Å
and Rh(1)---H(9A) 2.4973(2) Å for 18e, Rh(1)---H(5)
2.4757(9) Å and Rh(1)---H(12) 2.4861(6) Å for 18f,
Rh(1)---H(19) 2.4818(9) Å and Rh(1)---H(9) 2.5458(6) Å
CONCLUSION
■
In conclusion, we have described the design and synthesis of
various novel six-membered formamidinium salts with a
substituted 3,4-dihydroquinazoline core. Particularly, by a
successful synthetic strategy, we could make the rational
changes of different substituent combinations in 3,4-dihydro-
quinazolinium salts, which might be applied to fine-tune the
corresponding NHCs exhibiting different steric impact and
electron-donating ability. In the presence of KHMDS as a base,
NHCs prepared in situ from three representative formamidi-
nium salts can react with S8 or CS2 to afford the corresponding
thiones or NHC−CS2 adducts, respectively, and several Rh
3h
i
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Figure 5. Molecular structure of 18e (left) and 18f (right) with 30% probability ellipsoids. Selected bond distances (Å) and angles (deg): 18e:
Rh(1)−C(7) 2.055(3), Rh(1)−Cl(1) 2.3718(7), N(1)−C(7) 1.365(3), N(2)−C(7) 1.329(3), C(1)−C(6) 1.384(4), C(7)−Rh(1)−Cl(1) 87.72(7),
C(7)−N(2)−C(8) 126.0(2), C(7)−N(2)−C(9) 120.7(2), C(6)−C(1)−C(8) 121.2(2), C(1)−C(6)−N(1) 118.8(2), N(2)−C(7)−N(1) 118.4(2),
N(2)−C(7)−Rh(1) 119.81(18), N(1)−C(7)−Rh(1) 121.77(19), N(2)−C(8)−C(1) 112.2(2), Rh(1)---H(16A) 2.4138(2), Rh(1)---H(9A)
2.4973(2); 18f: Rh(1)−C(1) 2.051(2), Rh(1)−Cl(1) 2.3833(10), N(1)−C(1) 1.372(3), N(1)−C(2) 1.416(3), N(2)−C(1) 1.335(3), N(2)−C(4)
1.462(3), C(2)−C(3) 1.394(3), C(3)−C(4) 1.481(3), C(1)−Rh(1)−Cl(1) 89.62(7), C(1)−N(1)−C(2) 121.90(19), C(2)−N(1)−C(5) 120.1(2),
C(1)−N(2)−C(4) 123.51(19), N(2)−C(1)−N(1) 117.1(2), N(2)−C(1)−Rh(1) 120.35(16), N(1)−C(1)−Rh(1) 122.58(16), C(2)−C(3)−C(4)
118.6(2), N(2)−C(4)−C(3) 110.81(18), Rh(1)---H(5) 2.4757(9), Rh(1)---H(12) 2.4861(6).
Scheme 10. Synthesis of Dicarbonyl Rh Complexes 19a−e
2-ylidene a promising NHC ligand for further development in
metal-catalyzed reactions.
Figure 6. Molecular structure of 18g with 30% probability ellipsoids.
Selected bond distances (Å) and angles (deg): Rh(1)−C(1) 2.051(3),
Rh(1)−Cl(1) 2.3772(10), N(1)−C(1) 1.333(3), N(1)−C(2)
1.487(3), N(2)−C(1) 1.368(3) N(2)−C(8) 1.423(3), C(3)−C(8)
1.386(4), C(3)−C(2) 1.489(4), C(1)−Rh(1)−Cl(1) 90.04(8),
C(1)−N(1)−C(2) 121.0(2), C(1)−N(2)−C(8) 120.8(2), C(1)−
N(2)−C(19) 116.7(2), C(1)−N(1)−C(9) 120.1(2), N(1)−C(1)−
N(2) 117.2(2), N(1)−C(1)−Rh(1) 120.72(18), N(2)−C(1)−Rh(1)
122.10(18), Rh(1)---H(19) 2.4818(9), Rh(1)---H(9) 2.5458(6).
EXPERIMENTAL SECTION
■
General Information. Unless otherwise stated, all reactions and
manipulations were performed using standard Schlenk techniques. All
solvents were purified by distillation using standard methods.
Commercially available reagents were used without further purifica-
tion. NMR spectra were recorded by using a Bruker 400 MHz
spectrometer. Chemical shifts are reported in ppm from tetrame-
thylsilane with the solvent resonance as the internal standard (1H
NMR CDCl3: 7.26 ppm; 13C NMR CDCl3: 77.0 ppm). Optical
rotations were determined at 589 nm (sodium D line) by using a
Perkin-Elmer 341 MC digital polarimeter with a 10 cm cell (c given in
g per 100 mL), and [α]D values are given in 10−1 deg cm2 g−1. Mass
spectra were recorded on the HP-5989 instrument by EI/ESI
methods. Infrared spectra were recorded on a Perkin-Elmer PE-983
spectrometer with absorption in cm−1. X-ray diffraction analysis was
performed by using a Bruker Smart-1000 X-ray diffractometer.
2-Fluorobenzaldehyde and KHMDS are commercially available and
were used as received without further purification. The following
compounds have been previously reported, and their spectra were
consistent with that of the published data: 2-(isopropylamino)-
benzaldehyde.12
complexes based on NHC 3,4-dihydroquinazol-2-ylidene were
also prepared by the method. On the basis of the ν(CO) values
of the corresponding dicarbonyl Rh complex, the 3,4-
dihydroquinazol-2-ylidenes are stronger electron donors than
normal five-membered NHCs. The 3,4-dihydroquinazolin-2-
ylidenes showed high efficiency not only in Rh-cataylzed
arylation of carbonyl compounds using arylboronic acid but
also in palladium-catalyzed Suzuki cross-coupling reactions at
room temperature with a ppm scale catalyst loading with TONs
of up to 425 000. These results render the 3,4-dihydroquinazol-
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3-Cyclohexyl-1-isopropyl-3,4-dihydroquinazoline-2-thione (16).
11c (58 mg, 0.2 mmol) was treated with NaI (240 mg, 1.6 mmol)
in acetone (5 mL). After the mixture was stirred for 8 h, the solvent
was removed under vacuum and the residue was extracted with
CH2Cl2 (2 × 20 mL). After removal of solvent, the resulting residue
was suspended in THF (5 mL), and S8 (12.8 mg, 0.4 mmol) and
KHMDS (1.0 M in hexane, 0.22 mL, 0.22 mmol) were added
dropwise at −40 °C. After 1 h, the mixture was warmed to room
temperature and stirred for 1 h. The solvent was evacuated in vacuo,
and the residue was purified by column chromatography on silica gel
(PE/EtOAc = 10:1) to give the product 16 as a white powder (28 mg,
48%): 1H NMR (400 MHz, CDCl3) δ 7.29−7.23 (m, 2H), 7.11−7.05
(m, 2H), 5.54 (sept, J = 7.2 Hz, 1H), 5.27−5.20 (m, 1H), 4.07 (s, 2H),
1.84−1.81 (m, 4H), 1.71−1.68 (m, 1H), 1.62 (d, J = 7.2, 6H), 1.47−
1.40 (m, 4H), 1.18−1.10 (m, 1H); 13C NMR (100 MHz, CDCl3) δ
181.9, 137.4, 127.5, 124.6, 124.5, 123.6, 116.2, 60.0, 53.8, 43.7, 29.8,
25.5, 25.4, 21.3; IR (KBr disk) ν 3121, 2968, 2920, 2851, 1668, 1437,
1400, 1215, 1100, 751 cm−1; HRMS (EI) calcd for C17H24N2S [M +
H]+ 288.1660, found 288.1657.
1-Isopropyl-3-cyclohexyl-3,4-dihydroquinazolinium-2-dithiocar-
boxylate (17). 11c (58 mg, 0.2 mmol) was treated with NaI (240 mg,
1.6 mmol) in acetone (5 mL). After the mixture was stirred for 8 h, the
solvent was removed under vacuum and the residue was extracted with
CH2Cl2 (2 × 20 mL). After removal of solvent, the resulting residue
was suspended in THF (5 mL), and CS2 (30 mg, 0.4 mmol) and
KHMDS (1.0 M in hexane, 0.22 mL, 0.22 mmol) were added
dropwise at −40 °C. After 1 h, the mixture was warmed to room
temperature and stirred for 1 h. The solvent was evacuated in vacuo,
and the residue was purified by column chromatography on silica gel
(PE/EtOAc = 10:1) to give the product 17 as an orange powder (45
mg, 58%): 1H NMR (400 MHz, CDCl3) δ 7.48 (d, J = 8 Hz, 1H), 7.35
(t, J = 8 Hz, 1H), 7.25 (t, J = 6.8 Hz, 1H), 7.15 (d, J = 6.8 Hz, 1H),
5.46 (sept, J = 7.0 Hz,1H), 4.54 (tt, J1 = 11.8 Hz, J2 = 3.8 Hz, 1H),
4.46 (s, 2H), 2.05−2.03 (m, 2H), 1.83−1.79 (m, 2H), 1.70−1.60 (m,
1H), 1.64 (d, J = 7.2 Hz, 6H), 1.55−1.51 (m, 2H), 1.40−1.33 (m,
2H), 1.14−1.05 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 232.7,
162.5, 133.8, 128.6, 126.4, 126.3, 120.4, 118.3, 61.5, 52.9, 43.0, 28.8,
25.0, 24.9, 21.0; IR (KBr disk) ν 3122, 2974, 2920, 1745, 1608, 1551,
1466, 1396, 1365, 1344, 1204, 1088, 1064, 852, 694 cm−1; HRMS (EI)
calcd for C19H24N2S2 [M + H]+ 332.1381, found 332.1386.
14.8 Hz, 1H), 4.99 (m, 2 H), 4.24 (s, 2H), 3.48−3.79 (m, 2H), 2.33−
2.14 (m, 4H), 1.90−1.78 (m, 4H); 13C NMR (100 MHz, CDCl3) δ
1
213.4 (d, JRhC = 47.4 Hz, CcarbRh), 136.9, 135.5, 134.2, 128.9, 128.3,
1
127.9, 127.8, 127.2, 126.8, 125.7, 124.5, 120.5, 114.6, 98.1 (d, JRhC
=
1
1
3.7 Hz, CHcod), 98.0 (d, JRhC = 2.9 Hz, CHcod), 69.8 (d, JRhC = 4.7
1
Hz, CHcod), 69.6 (d, JRhC = 3.7 Hz, CHcod), 61.9, 58.1, 46.6, 32.5,
32.4, 28.7, 28.6; mp 200.4−200.7 °C; HRMS (ESI) m/z [M]+ calcd
for C30H32ClN2Rh 558.1309; found 558.1334.
(1,5-Cyclooctadiene)(1,3-dicyclohexyl-6-methoxy-3,4-dihydro-
quinazolin-2-ylidene)rhodium(I) Chloride (18c). Following the
procedure for the synthesis of 18a, KHMDS (1.0 M in hexane, 0.33
mL, 0.33 mmol), 6d (100 mg, 0.30 mmol), and [(COD)RhCl]2 (74
mg, 0.15 mmol) in THF (5 mL) afforded 18c as an orange powder
(64 mg,39%), which was purified by column chromatography on silica
1
gel (PE/EA = 10:1): H NMR (400 MHz, CDCl3) δ 7.31 (d, J = 9.2
Hz, 1H), 6.71−6.68 (m, 2H), 6.51−6.45 (m, 2H), 4.96−4.90 (m, 2H),
4.21 (d, J = 14.4 Hz, 1H), 4.10 (d, J = 14.4 Hz, 1H), 3.75 (s, 3H),
3.42-.341 (m, 2H), 2.52−2.43 (m, 2H), 2.42−2.32 (m, 5H), 2.21 (m,
1H), 2.07−1.89 (m, 8H), 1.85−1.71 (m, 6H), 1.67−1.60 (m, 2H),
1.50−1.40 (m, 1H), 1.32−1.14 (m, 3H); 13C NMR (100 MHz,
1
CDCl3) δ 209.7 (d, JRhC = 47.0 Hz, CcarbRh), 155.8, 128.6, 122.8,
117.3, 112.7, 110.9, 95.76 (d, 1JRhC = 3.7 Hz, CHcod), 95.69 (d, 1JRhC
=
4.0 Hz, CHcod), 69.2 (d, 1JRhC = 15.4 Hz, CHcod), 67.6 (d, 1JRhC = 13.3
Hz, CHcod), 65.7, 55.4, 43.0, 33.4, 32.1, 30.8, 30.3, 29.3, 28.2, 27.3,
26.8, 26.2, 25.9, 25.7; mp 203.3−203.6 °C; HRMS (ESI) m/z [M]+
calcd for C29H42ClON2Rh 572.2041; found 572.2040.
(1,5-Cyclooctadiene)(3-(3,5-dimethylphenyl)-1-isopropyl-3,4-di-
hydroquinazolin-2-ylidene)rhodium(I) Chloride (18d). Following the
procedure for the synthesis of 18a, KHMDS (1.0 M in hexane, 0.35
mL, 0.35 mmol), 11a (100 mg, 0.32 mmol), and [(COD)RhCl]2 (78
mg, 0.16 mmol) afforded 18d as an orange powder (67 mg, 40%),
which was purified by column chromatography on silica gel (PE/EA =
1
10:1): H NMR (400 MHz, CDCl3) δ 7.64 (s, 2H), 7.36 (d, J = 8.4
Hz, 1H), 7.25 (t, J = 6.4 Hz, 1H), 7.10−7.06 (m, 3H), 6.96 (d, J = 7.6
Hz, 1H), 4.79−4.69 (m, 4H), 3.49 (m, 1H), 2.63 (m, 1H), 2.44 (s,
6H), 2.08−1.93 (m, 3H), 1.83 (d, J = 7.2 Hz, 3H), 1.82 (d, J = 7.2 Hz,
3H), 1.68−1.64 (m, 2H), 1.53−1.44 (m, 1H), 1.30−1.18 (m, 2H); 13C
NMR (100 MHz, CDCl3) δ 212.9 (d, 1JRhC = 46.2 Hz, CcarbRh), 145.5,
1
138.5, 132.9, 128.4, 127.8, 126.1, 124.4, 121.5, 115.9, 96.6 (d, JRhC
=
1
1
6.8 Hz, CHcod), 95.3 (d, JRhC = 7.7 Hz, CHcod), 68.3 (d, JRhC = 14.1
Hz, CHcod), 68.0 (d, JRhC = 5.2 Hz, CHcod), 59.4, 51.1, 34.4, 29.6,
1
(1,5-Cyclooctadiene)(1-(3,5-dimethylphenyl)-3-isopropyl-3,4-di-
hydroquinazolin-2-ylidene)rhodium(I) Chloride (18a). KHMDS (1.0
M in hexane, 0.35 mL, 0.35 mmol) was added dropwise to a solution
of 6b (100 mg, 0.32 mmol) and [(COD)RhCl]2 (78 mg, 0.16 mmol)
in THF (5 mL) at −78 °C. After 30 min, the mixture was warmed to
room temperature and stirred for 2 h. The solvent was evacuated in
vacuo, and the residue was purified by column chromatography on
silica gel (PE/EA = 10:1) to give the product 18a as an orange powder
28.9, 26.7, 22.0, 21.2, 21.0; mp 207.9−208.1 °C; HRMS (ESI) m/z
[M]+ calcd for C27H34ClN2Rh 524.1466; found 524.1459.
(1,5-Cyclooctadiene)(1-isopropyl-3-benzyl-3,4-dihydroquinazo-
lin-2-ylidene)rhodium(I) Chloride (18e). Following the procedure for
the synthesis of 18a, KHMDS (1.0 M in hexane, 0.24 mL, 0.24 mmol),
11b (65 mg, 0.215 mmol), and [(COD)RhCl]2 (36.5 mg, 0.074
mmol) afforded 18e as yellow solids (70 mg, 65%), which was purified
by column chromatography on silica gel (PE/EtOAc = 10:1): 1H
NMR (400 MHz, CDCl3) δ 7.47 (d, J = 6.8 Hz, 2H), 7.37 (t, J = 7.2
Hz, 2H), 7.33−7.18 (m, 4H), 6.99 (t, J = 7.4 Hz, 1H), 6.80 (d, J = 7.6
Hz, 1H), 6.32 (d, J = 14.8, 2H), 6.01 (d, J = 14.8, 2H), 4.96−4.94 (m,
2H), 4.14 (dd, J1 = 19.2, J2 = 14.8 Hz, 2H), 3.55−3.53 (m, 1H), 3.48−
3.44 (m, 1H), 2.42−2.36 (m, 2H), 2.26−2.19 (m, 2H), 1.95−1.90 (m,
2H), 1.91 (d, J = 6.8 Hz, 3H), 1.86−1.80 (m, 2H), 1.70 (d, J = 6.8 Hz,
1
(58 mg, 34%): H NMR (400 MHz, CDCl3) δ 7.52 (s, 1H), 7.15 (s,
1H), 7.06−7.00 (m, 4H), 6.49 (sept, J = 6.8 Hz, 1H), 6.37 (d, J = 7.2
Hz, 1H), 4.73 (t, J = 6.8 Hz, 1H), 4.62 (q, J = 7.6 Hz, 1H), 4.47 (d, J =
14.4 Hz, 1H), 4.24 (d, J = 14.4 Hz, 1H), 3.48−3.44 (m, 1H), 2.64−
2.62 (m, 1H), 2.48−2.46 (m, 1H), 2.44 (s, 6H), 2.04−1.97 (m, 2H),
1.71−1.63 (m, 2H), 1.49 (d, J = 6.4 Hz, 6H), 1.29−1.22 (m, 4H); 13C
NMR (100 MHz, CDCl3) δ 209.5 (d, 1JRhC = 45.7 Hz, CcarbRh), 141.1,
138.8, 137.2, 129.2, 128.1, 125.4, 124.2, 118.6, 115.7, 115.2, 96.4 (d,
1JRhC = 6.2 Hz, CHcod), 95.7 (d, 1JRhC = 7.4 Hz, CHcod), 68.8 (d, 1JRhC
1
3H); 13C NMR (100 MHz, CDCl3) δ 212.6 (d, JRhC = 46.9 Hz,
CcarbRh), 135.6, 133.2, 128.8, 127.7, 126.3, 124.1, 121.5, 115.8, 97.1 (d,
1JRhC = 6.3 Hz, CHcod), 96.7(d, 1JRhC = 6.0 Hz, CHcod), 70.1 (d, 1JRhC
=
1
= 16.4 Hz, CHcod), 66.5 (d, JRhC = 14.7 Hz, CHcod), 58.2, 41.6, 34.9,
1
14.3 Hz, CHcod), 68.5 (d, JRhC = 14.3 Hz, CHcod), 61.9, 58.8, 46.6,
32.7, 32.1, 30.7, 29.3, 28.9, 28.4, 22.6, 20.3; IR (KBr disk) ν = 3551,
3474, 3413, 3131, 1637, 1617, 1528, 1795, 1410, 1284, 1125, 760
cm−1; HRMS (EI) calcd for C26H32ClN2Rh [M]+ 510.1309, found
510.1312.
29.2, 26.4, 22.4, 21.3, 21.2, 20.2, 19.8; mp 207.7−208.0 °C; HRMS
(ESI) m/z [M]+ calcd for C27H34ClN2Rh 524.1466; found 524.1468.
(1,5-Cyclooctadiene)(1,3-dibenzyl-3,4-dihydroquinazolin-2-
ylidene)rhodium(I) Chloride (18b). Following the procedure for the
synthesis of 18a, KHMDS (1.0 M in hexane, 0.32 mL, 0.32 mmol), 6c
(100 mg, 0.29 mmol), and [(COD)RhCl]2 (70 mg, 0.145 mmol)
afforded 18b as an orange powder (95 mg, 59%), which was purified
(1,5-Cyclooctadiene)(1-isopropyl-3-cyclohexyl-3,4-dihydroquina-
zolin-2-ylidene)rhodium(I) Chloride (18f). Following the procedure
for the synthesis of 18a, KHMDS (1.0 M in hexane, 0.37 mL, 0.37
mmol), 11c (100 mg, 0.34 mmol), and [(COD)RhCl]2 (84 mg, 0.17
mmol) afforded 18f as an orange powder (85 mg, 50%), which was
purified by column chromatography on silica gel (PE/EA = 10:1): 1H
NMR (400 MHz, CDCl3) δ 7.24−7.17 (m, 2H), 7.05−7.00 (m, 2H),
1
by column chromatography on silica gel (PE/EA = 10:1): H NMR
(400 MHz, CDCl3) δ 7.53−7.48 (m, 4H), 7.40 (t, J = 8.4 Hz, 2H),
7.35−7.31 (m, 3H), 7.23 (t, J = 7.2 Hz, 2H), 7.08 (t, J = 8.0 Hz, 1H),
6.94 (t, J = 7.4 Hz, 1H), 6.87 (d, J = 8.0 Hz, 1H), 6.80 (d, J = 7.2 Hz,
1H), 6.46 (d, J = 14.2 Hz, 1H), 6.25 (d, J = 14.2 Hz, 1H), 6.13 (d, J =
8280
dx.doi.org/10.1021/om300887y | Organometallics 2012, 31, 8275−8282

Organometallics
Article
6.95 (d, J = 7.2 Hz, 1H), 6.68−6.60 (m, 1H), 5.03−4.98 (m, 1H),
4.91−4.86 (m, 1H), 4.19 (s, 2H), 3.39 (m, 1H), 3.38 (m, 1H), 2.47−
2.30 (m, 5H), 2.01−1.92 (m, 5H), 1.85−1.63 (m, 11H), 1.49−1.43
(m, 2H), 1.24−1.13 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 210.9
(d, 1JRhC = 45.5 Hz, CcarbRh), 134.0, 127.6, 126.1, 123.8, 121.5, 115.4,
96.6 (d, JRhC = 7.2 Hz, CHcod), 95.4 (d, JRhC = 7.6 Hz, CHcod), 68.7
(d, 1JRhC = 14.4 Hz, CHcod), 68.3 (d, 1JRhC = 5.4 Hz, CHcod), 66.0, 58.2,
42.7, 32.9, 32.3, 30.7, 29.3, 28.1, 26.1, 25.9, 22.8, 20.4; mp 202.8−
203.2 °C; HRMS (ESI) m/z [M]+ calcd for C25H36ClN2Rh 502.1622;
found 502.1602.
(3-Cyclohexyl-1-isopropyl-3,4-dihydroquinazolin-2-ylidene)-
rhodium(I) Biscarbonyl Chloride (19d). Following the procedure for
the synthesis of 19a, 18f (50 mg, 0.1 mmol) afforded 19d as an orange
powder (37 mg, 82%), which was purified by column chromatography
1
on silica gel (PE/EA = 12:1): H NMR (400 MHz, CDCl3) δ 7.29−
1
1
7.27 (m, 2H), 7.14−7.10 (m, 1H), 7.04 (d, J = 7.6 Hz, 1H), 6.02 (sept,
J = 7.2 Hz, 1H), 5.52−5.46 (m, 1H), 4.34 (d, J = 14.8 Hz, 1H), 4.25
(d, J = 14.8 Hz, 1H), 2.22−2.19 (m, 1H), 1.92−1.76 (m, 4H), 1.70 (d,
J = 7.2 Hz, 3H), 1.62 (d, J = 7.2 Hz, 3H), 1.52−1.45 (m, 3H), 1.31−
1.25 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 199.3 (d, 1JRhC = 38.4
Hz, CcarbRh), 186.1 (d, 1JRhC = 52.7 Hz, OCRh), 182.9 (d, 1JRhC = 76.6
(1,5-Cyclooctadiene)(1-isopropyl-3-cyclohexyl-4-butyl-3,4-dihy-
droquinazolin-2-ylidene)rhodium(I) Chloride (18g). Following the
procedure for the synthesis of 18a, KHMDS (1.0 M in hexane, 0.32
mL, 0.32 mmol), 15b (100 mg, 0.29 mmol), and [(COD)RhCl]2 (71
mg, 0.145 mmol) afforded 18g as an orange powder (80 mg, 49%),
which was purified by column chromatography on silica gel (PE/EA =
10:1): 1H NMR (400 MHz, CDCl3) δ 7.33 (d, J = 8.4 Hz, 1H), 7.22−
7.15 (m, 2H), 7.03 (t, J = 7.2 Hz, 1H), 6.90 (d, J = 7.2 Hz, 1H), 6.32−
6.27 (m, 1H), 4.99−4.94 (m, 2H), 4.18 (t, J = 6.4 Hz, 1H), 3.36 (m,
1H), 3.23 (m, 1H), 2.51−2.36 (m, 4H), 2.28−2.26 (m, 1H), 2.04−
2.00 (m, 2H), 1.98 (d, J = 7.2 Hz, 3H), 1.92 (m, 1H), 1.76 (m, 2H),
1.66 (d, J = 7.2 Hz, 3H), 1.62 (m, 1H), 1.34−1.24 (m, 3H), 1.23−0.85
(m, 6H), 0.80 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ
Hz, OCRh), 133.8, 127.9, 126.4, 124.8, 121.2, 116.2, 66.8, 58.6, 43.2,
−1
29.6, 28.8, 25.4, 20.9, 19.9; IR (KBr disk) 2070, 1991 cm
.
(4-Butyl-3-cyclohexyl-1-isopropyl-3,4-dihydroquinazolin-2-
ylidene)rhodium(I) Biscarbonyl Chloride (19e). Following the
procedure for the synthesis of 19a, 18g (35 mg, 0.062 mmol)
afforded 19e as an orange powder (21 mg, 67%), which was purified
1
by column chromatography on silica gel (PE/EA = 12:1): H NMR
(400 MHz, CDCl3) δ 7.38−7.30 (m, 2H), 7.17−7.13 (m, 1H), 7.03−
6.97 (m, 1H), 5.89−5.78 (m, 1H), 5.47−5.41 (m, 1H), 4.21 (t, J = 7.0
Hz, 1H), 2.44 (m, 1H), 2.17−2.08 (m, 1H), 1.96−1.89 (m, 2H), 1.78
(d, J = 7.2 Hz, 3H), 1.60−1.54 (m, 5H), 1.51 (d, J = 6.8 Hz, 3H), 1.25
(m, 2H), 1.18−0.81 (m, 5H), 0.79 (t, J = 7.2 Hz, 3H); 13C NMR (100
MHz, CDCl3) δ 197.9 (d, 1JRh1C = 41.1 Hz, CcarbRh), 186.2 (d, 1JRhC
=
1
209.0 (d, JRhC = 47.0 Hz, CcarbRh), 133.6, 127.2, 126.3, 124.9, 123.5,
115.8, 96.9 (d, 1JRhC = 6.4 Hz, CHcod), 96.8 (d, 1JRhC = 7.2 Hz, CHcod),
71.2 (d, 1JRhC = 15.3 Hz, CHcod), 66.1, 57.6, 53.4, 37.0, 32.9, 32.7, 32.4,
32.1, 29.1, 28.6, 26.8, 26.4, 25.7, 22.3, 21.9, 20.0, 13.9; mp: 216.7−
217.0 °C; HRMS (ESI) m/z [M]+ calcd for C29H44ClN2Rh 558.2248;
found 558.2216.
46.3 Hz, OCRh), 183.3 (d, JRhC = 76.4 Hz, OCRh), 133.7, 127.6,
126.1, 124.2, 116.3, 66.7, 57.4, 54.3, 35.1, 31.9, 30.8, 27.3, 25.5, 25.2,
22.3, 22.2, 21.8, 19.3, 13.9; IR (KBr disk) 2071, 1991 cm−1.
ASSOCIATED CONTENT
* Supporting Information
■
(1,3-Dicyclohexyl-6-methoxy-3,4-dihydroquinazolin-2-ylidene)-
rhodium(I) Biscarbonyl Chloride (19a). Rh complex 18c (40 mg, 0.07
mmol) was dissolved in dried CH2Cl2 (3 mL), and carbon monoxide
was bubbled through the solution for 1 h at room temperature. A color
change from yellow to pale yellow was observed during this time. The
solvent was evacuated in vacuo, and the residue was purified by
column chromatography on silica gel (PE/EtOAc = 12:1) to give the
product 19a as an orange powder (25 mg, 68%): 1H NMR (400 MHz,
CDCl3) δ 7.31 (d, J = 8.8 Hz), 6.78 (dd, J1 = 2.8 Hz, J2 = 8.8 Hz, 1H),
6.54 (d, J = 2.8 Hz, 1H), 5.54−5.45 (m, 2H), 4.26 (d, J = 3.2 Hz, 2H),
3.78 (s, 3H, OCH3), 2.26−2.08 (m, 5H), 1.96−1.85 (m, 4H), 1.78−
1.64 (m, 6H), 1.60−1.46 (m, 5H); 13C NMR (100 MHz, CDCl3) δ
198.3 (d, 1JRhC = 38.4 Hz, CcarbRh), 186.3 (d, 1JRhC = 54.4 Hz, OCRh),
S
Text giving experimental procedures for the synthesis of the
ligands and CIF files giving crystal data for the complexes
described herein. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: zhangj@ecust.edu.cn; mshi@mail.sioc.ac.cn.
■
Notes
The authors declare no competing financial interest.
1
183.3 (d, JRhC = 73.4 Hz, OCRh), 156.6, 128.2, 122.8, 117.9, 113.0,
111.2, 67.7, 66.6, 55.5, 43.4, 30.9, 29.9, 29.7, 29.6, 28.8, 26.6, 26.3,
ACKNOWLEDGMENTS
■
−1
25.6, 25.4, 25.2; IR (KBr disk) 2069, 1989 cm
.
Financial support from Shanghai Pujiang Talent Program
(11PJ1402500), the Fundamental Research Funds for the
Central Universities (WK1114014), the Shanghai Municipal
Committee of Science and Technology (11JC1402600),
National Basic Research Program of China (973-
2010CB833302), and the National Natural Science Foundation
of China (21171056, 21072206, 20472096, 20872162,
20672127, 21121062, and 20732008) is greatly acknowledged.
(3-(3,5-Dimethylphenyl)-1-isopropyl-3,4-dihydroquinazolin-2-
ylidene)rhodium(I) Biscarbonyl Chloride (19b). Following the
procedure for the synthesis of 19a, 18d (40 mg, 0.076 mmol)
afforded 19b as an orange powder (30 mg, 83%), which was purified
1
by column chromatography on silica gel (PE/EA = 12:1): H NMR
(400 MHz, CDCl3) δ 7.40 (d, J = 8.0 Hz, 1H), 7.31 (t, J = 8.0 Hz,
1H), 7.18−7.00 (m, 5H), 6.18 (sept, 1H, NCH), 4.80 (d, J1 = 14.8 Hz,
1H), 4.74 (d, J1 = 14.8 Hz, 1H), 2.37 (s, 6H), 1.71 (t, J = 7.8 Hz, 3H);
1
13C NMR (100 MHz, CDCl3) δ 202.0 (d, JRhC = 39.6 Hz, CcarbRh),
186.2 (d, 1JRhC = 53.8 Hz, OCRh), 182.9 (d, 1JRhC = 77.0 Hz, OCRh),
REFERENCES
■
144.9, 139.3, 132.7, 129.8, 128.2, 126.4, 125.4, 125.2, 121.5, 116.7,
−1
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59.8, 51.8, 29.7, 21.3, 20.7, 20.1; IR (KBr disk) 2067, 1989 cm
.
(3-Benzyl-1-isopropyl-3,4-dihydroquinazolin-2-ylidene)rhodium-
(I) Biscarbonyl Chloride (19c). Following the procedure for the
synthesis of 19a, 18e (54 mg, 0.17 mmol) afforded 19c as an orange
powder (35 mg, 72%), which was purified by column chromatography
1
on silica gel (PE/EA = 12:1): H NMR (400 MHz, CDCl3) δ 7.40−
7.32 (m, 1H), 7.24−7.18 (m, 1H, Ar-H), 7.08 (t, J = 7.2 Hz, 1H), 6.88
(d, J = 6.8 Hz, 1H), 6.19 (sept, J = 7.2 Hz, 1H), 6.13 (d, 1H, J = 14.8
Hz), 5.07 (d, J = 15.2 Hz, 1H), 4.34−4.23 (m, 2H, NCH2), 1.75 (d, J
= 7.2 Hz, 3H), 1.67 (d, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3)
(2) For reviews, see: (a) Benhamou, L.; Chardon, E.; Lavigne, G.;
1
1
δ 200.4 (d, JRhC = 39.7 Hz, CcarbRh), 185.7 (d, JRhC = 54.2 Hz,
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