ca01 only detailed ToC 1..24

72 Science of Synthesis 1.1 Organometallic Complexes of Nickel
1.1.4.5 Method 5:
Alkene Hydrocyanation
The hydrocyanation of alkenes is a well-studied and synthetically useful process. [33,161,162]
A significant amount of the attention that this reaction has received is derived from its
utility in the preparation of adiponitrile from butadiene (Section 1.1.1.6). A complete catalytic
cycle for the hydrocyanation of alkenes is shown in Scheme 71. Steric effects in the
Lewis acid promoter have been shown to affect critically the reaction selectivities. [163]
Scheme 71 Mechanism of Alkene Hydrocyanation [33]
EtCN
L C2H4 L
NC
Ni Et
L
L
Ni
L
L Ni Et L Ni H
CN
CN
H2C CH2 HCN
L2 Ni
CN
H
The asymmetric hydrocyanation of alkenes has also received considerable attention.
[164,165] In a representative example by RajanBabu, the glucose-derived phosphine ligand
94 allows useful enantioselectivities to be obtained in the hydrocyanation of arylsubstituted
alkenes (Scheme 72).
Scheme 72 Asymmetric Hydrocyanation of Alkenes [164,165]
1 Ar + HCN
L = Ph O
O
O
O
O
Ar2 Ar
2P
2 2P
94
OPh
NiL
Ar 1
CN
up to 90% ee
Asymmetric Hydrocyanation; General Procedure: [164]
CAUTION: Hydrogen cyanide is highly toxic! Appropriate safety precautions and procedures
should be adopted during all stages of the handling and disposal of this reagent.
Catalyst scouting reactions were carried out by the dropwise addition of a toluene soln of
HCN (typically 0.05–1.0 equiv of HCN per equiv of alkene) to a hexane soln of the alkene
(0.1–0.2 M), [Ni(cod) 2](2; 0.01–0.5 equiv), and the chiral ligand (0.01–0.05 equiv). Ligands
that were insoluble in hexane were stirred separately with [Ni(cod) 2] in benzene. The resulting
catalyst solns were evaporated to dryness and then the residue dissolved or slurried
with hexane and the substrate. Hydrocyanation reactions were usually stirred at rt
(~ 258C) overnight. The product nitriles were isolated by flash chromatography (typically
silica gel, hexane/Et 2O 90:10).
L