1. Synthesis of a Better N-Heterocyclic Carbene Ligand
Yordanos Goshu, Christopher Hansen, Dr. Steven Baldwin, Professor Gregory Hillhouse
University of Chicago Collegiate Scholars Program
Gordon Center for Integrative Science, Department of Chemistry
University of Chicago, Illinois 60637
Synthetic Reaction
BackgroundAbstract
A new bulky N-heterocyclic carbene ligand, ITol*, was prepared
through a 5 step synthesis with 82% overall yield, ending with the
deprotonation of ITol*HCl by potassium t-butoxide. The ITol* ligand
is being investigated on the basis of forming transition metal
complexes by reacting it with PdCl2(SMe2)2 , which may permit its
potential applications as a catalyst.
Representative NMR’s
Synthetic protocols for each step proved to be successful.
The initial goal to improve the NMR spectra and increase
solubility were accomplished, and the NMR spectra has
revealed that ITol* salt has been successfully deprotonated
and used to form a palladium compound , whose
characterization and reactivity evaluation are underway.
N-heterocyclic carbenes (NHC) are
known for acting as ligands for
transition metal catalysts. A
related NHC IPr* has been
successful in stabilizing reactive
low coordinate nickel complexes
such as (IPr*)Ni=N(dmp).
(IPr*)Ni=N(dmp)
(ref 2)
Purpose
IPr* has some undesirable properties including its low
solubility and complicated NMR spectra. The strategy
behind the synthesis of ITol* is to replace the flanking
phenyl groups with flanking p-tolyl groups to increase
solubility and simplify the NMR spectra.
Conclusion
(1) Li, H; Zhu, R; Shi, W; He, K; Shi, Z. Org. Lett. 2012, 14, 4850.
(2) DMP Imido Complex: Laskowski & Hillhouse JACS 2011, 133, 771
Reference
tol
tol
tol
tol
Ar** =
IPr*
ITol*
NH2
OH
2
HCl / ZnCl2
NH2
tol
tol
tol
tol
160 ˚C, 4 hrs
+
N N Ar**Ar**
DCM, 2 hrs
N N
Ar**Ar**
H Cl-
OCl4
NH2
tol
tol
tol
tol
CHCl3, cat HCOOH, 2 days
O O
N N Ar**Ar**
O
H
+
MgBr
thf
0 ˚C rt, 1 day
OH
2
N N
Ar**Ar**
H
Cl-
+ N N
Ar**Ar**
KOtBu
N N
Ar**Ar**
+ thf
thf
78%
96%
94%
104%
ITol*PdCl2(SMe2)PdCl2(SMe2)2
83%
(ref 1)
1 hr
Overnight
ITol*HCl
ITol*