1
H
‐Imidazole, 2,3‐dihydro‐1,3‐bis[4‐methyl‐2,6‐bis[(1R)‐1‐phenylethyl] phenyl]‐2‐methylidene
Authors: Wang Sijing , Feng Xiaoming , Dong Shunxi 
Published: January 2025

image

R = H [
N
‐heterocyclic olefin (NHO),
NHO‐1
], 1,3‐bis{4‐methyl‐2,6‐bis[(
R
)‐1‐phenylethyl]phenyl}‐2‐methylene‐2,3‐dihydro‐1
H
‐imidazole

[2906177‐25‐9]

C
50
H
50
N
2

(MW 678.96)
CCDC Nr. 2004934

InChI = 
<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="inchi" xlink:href="InChI=1S/C50H50N2/c1-34-30-45(36(3)41-20-12-8-13-21-41)49(46(31-34)37(4)42-22-14-9-15-23-42)51-28-29-52(40(51)7)50-47(38(5)43-24-16-10-17-25-43)32-35(2)33-48(50)39(6)44-26-18-11-19-27-44/h8-33,36-39H,7H2,1-6H3/t36-,37?,38-,39?/m1/s1">1S/C50H50N2/c1‐34‐30‐45(36(3)41‐20‐12‐8‐13‐21‐41)49(46(31‐34)37(4)42‐22‐14‐9‐15‐23‐42)51‐28‐29‐52(40(51)7)50‐47(38(5)43‐24‐16‐10‐17‐25‐43)32‐35(2)33‐48(50)39(6)44‐26‐18‐11‐19‐27‐44/h8‐33,36‐39H,7H2,1‐6H3/t36‐,37?,38‐,39?/m1/s1

InChIKey = 
UQZIGNLWLBDHRV‐ZIBZHWJMSA‐N

R = Et (
NHO‐2
)

[2906177‐31‐7]

C
52
H
54
N
2

(MW 706.43)

InChI = 
<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="inchi" xlink:href="InChI=1S/C52H54N2/c1-8-21-50-53(51-46(38(4)42-22-13-9-14-23-42)32-36(2)33-47(51)39(5)43-24-15-10-16-25-43)30-31-54(50)52-48(40(6)44-26-17-11-18-27-44)34-37(3)35-49(52)41(7)45-28-19-12-20-29-45/h9-35,38-41H,8H2,1-7H3/t38-,39?,40-,41?/m1/s1">1S/C52H54N2/c1‐8‐21‐50‐53(51‐46(38(4)42‐22‐13‐9‐14‐23‐42)32‐36(2)33‐47(51)39(5)43‐24‐15‐10‐16‐25‐43)30‐31‐54(50)52‐48(40(6)44‐26‐17‐11‐18‐27‐44)34‐37(3)35‐49(52)41(7)45‐28‐19‐12‐20‐29‐45/h9‐35,38‐41H,8H2,1‐7H3/t38‐,39?,40‐,41?/m1/s1

InChIKey = 
KRWUFZBDAJFBAG‐JVCMKAOBSA‐N

Alternative Name:
R = H, 1,3‐bis{4‐methyl‐2,6‐bis[(
R
)‐1‐phenylethyl]phenyl}‐2‐methylidene‐2,3‐dihydro‐1
H
‐imidazole.

Physical Data:
yellow crystalline solid.

Solubility:
insoluble in cold
n
‐hexane (−30 °C), slightly soluble in
n
‐hexane (25 °C); soluble in THF, toluene, methyl
tert
‐butyl ether (MTBE).

Form Supplied in:
laboratory preparation.

Purification:
recrystallization with
n
‐hexane and toluene in a glove box.

Handling, Storage, and Precautions:
highly air‐sensitive, stored in N
2
atmosphere; for extended storage, keep refrigerated in a brown bottle.

Preparative Method (eq 1):
inside a glove box,
N
‐heterocyclic carbene (NHC) precursor

1

[
CAS Nr.1325765‐85‐2
] (210.1 mg, 0.3 mmol) and

t

BuOK (80.8 mg, 2.4 equiv) were dissolved in dry THF (0.1 M) in a Schlenk tube. The resulting mixture was stirred at room temperature for 12 h. The reaction mixture was filtered and washed with
n
‐hexane (3 × 10 mL). The solvent was removed in vacuo to afford free NHC
[CAS Nr. 2212005‐78‐0]
as a beige solid. The NHC was dissolved in dry THF (0.1 M) and CH
3
I (51.1 mg, 1.2 equiv) was added dropwise at ambient temperature. The mixture was stirred at room temperature for another 12 h. The reaction mixture was concentrated and the residue was subjected to column chromatography on silica gel (eluent: DCM/MeOH = 9/1, v/v) to afford the desired chiral
N
‐heterocyclic olefin (NHO) salt
NHO‐1·HI
. The chiral NHO salt (83.4 mg, 0.1 mmol) and

t

BuOK (26.9 mg, 2.4 equiv) were dissolved in dry THF (0.1 M) in a Schlenk tube. The resulting mixture was stirred at room temperature for 12 h. The reaction mixture was filtered and washed with
n
‐hexane (3 × 10 mL). The solvent was removed in vacuo, and the desired
NHO‐1
was obtained as yellow crystalline solid (65.3 mg, 82% total yield) by crystallization from the solution of toluene and
n
‐hexane (1/5, v/v).

image

Analysis of Reagent Purity:

1

H NMR
(400 MHz, benzene‐
d
6
)
δ
7.77–7.75 (m, 4
H
), 7.27–7.23 (m, 5
H
), 7.15–7.05 (m, 11
H
), 7.01–6.97 (m, 2
H
), 6.95–6.90 (m, 2
H
), 5.52 (s, 2
H
), 4.78–4.71 (m, 4
H
), 2.92 (s, 2
H
), 1.95 (s, 6
H
), 1.61–1.57 (m, 12
H
).

13

C{

1

H} NMR
(101 MHz, benzene‐
d
6
)
δ
152.0, 148.3, 147.3, 146.0, 145.7, 139.0, 133.1, 128.7, 128.6, 128.54, 128.52, 128.0, 127.1, 126.6, 126.0, 115.1, 44.8, 40.3, 39.3, 22.9, 22.0, 21.5 ppm.

Structure and Properties:
benefiting from the donating property of nitrogen atoms and the effective charge dispersion ability of imidazole ring,
NHO‐1
possesses an electron‐rich and highly polarized exocyclic olefinic double bond. Similar to other NHOs, this unique structure endows the ylidic carbon atom in
NHO‐1
with strong basicity and high nucleophilicity (Figure 1).

2–6

The exact basicity and nucleophilicity of
NHO‐1
are unknown at the current time. However, according to the studies by Mayr, Naumann, Ji and Cheng et al.

7–10

NHOs have comparable or stronger nucleophilicity and basicity than the corresponding NHCs, and these features are closely associated with their structure. Inspired by works from the groups of Kuhn and Beller,

11,12

the utility of NHO in organic synthesis has attracted considerable interest from many groups in the past decade.

2–6

On the one hand, NHOs have been emerging as a new type of organocatalyst for a number of organic transformations.

13–15

On the other hand, NHOs can serve as a σ‐donating type ligands, which have been used in the stabilization of main group elements at low oxidation state and transition metal catalysis.

16,17