287
Nickel-catalysed photochemical C–H arylation for coupling of benzylic
C(sp
3
)−H bonds with (hetero)aryl bromides using Ir photocatalyst (Scheme 56) has
been demonstrated by Heitz et al. [221]. Mechanistic investigation performed suggested that excitation of nickel and generation of bromine radical are facilitated by
energy transfer in triplet−triplet mode using iridium photocatalyst.
6 W lamp
Ru(dtbbpy)3(PF6)2 (1 mol%)
CH 3CN,
rt, O 2
R
R
N
CO 2 R 1
CO 2 R 1
N
O
O
R 2
N
N R
2
O
O
R 1 O 2 C CO 2 R 1
H
H
H
Scheme 52 Visible-light-assisted synthesis of N-heterocycles via ylide development and cycloaddition reaction
Blue LEDs
Ir(ppy)2(bpy) PF 6 (5 mol%)
MeCN, rt, air
N
R 2
R 1
CN
NC
Ar
R 1
N
NC
CN
Ar
R 2
Scheme 53 Visible-light-catalysed C–H activation reaction of tertiary amine
5 W blue LEDs
Ir(ppy)2(dttbpy)PF6 (1.5 mol%)
K 2 CO 3 (3.0 equiv)
DMSO/CH 3CN, rt, air
R
N
R 1
R 2
N
R 1
O
R
R 2
Scheme 54 Visible-light photoredox synthesis of 3-acylindoles from amines
Blue LEDs
Ru(bpy)3(PF6)2
Co(dmgH)2pyCl
CH 3 CN
N
H
R
COOEt
HN
PMP
N
H
R
H
N
EtOOC
PMP
Scheme 55 Visible light-mediated C−H bond activation of amino acid for construction of indoles
and H 2 evolution
26 W CFLs
Ir dFCF 3 ppy 2(bpy) PF 6 (2 mol%)
Ni(NO3)2 6H 2 O (5 mol%)
dtbbpy (5 mol%)
DMBP (25 mol%)
K 2 HPO 4 (2 equiv)
rt
Ar
R 2
R 1
R 2
R 1
Br Ar
Scheme 56 Photochemical Ni-catalysed C−H arylation of (hetero)aryl bromides
Insights into Sustainable C–H Bond Activation