28
compounds. An unstable Mn(IV) species is proposed as active intermediate. Later
on, Lei and co-workers reported that FeCl 3 /Bipy catalytic system could efficiently
promote the oxidative homo-coupling of aryl Grignard reagents using molecular
oxygen as the oxidant to form symmetrical biaryls (Scheme 2.40) [90].
Besides the above transition metal catalysts, other catalysts such as cobalt,
ruthenium, gold/palladium bimetallic alloy, and nickel were also effective in oxidative homo-coupling of organometallic compounds using air or O 2 as oxidant
(Scheme 2.41) [91–94].
RM
[catalyst]/oxidant
R R
catalyst
oxidant
RM
RSnBu 3
a
RSnBu 3
b
RZnI c
Pd(OAc) 2 (5 mol%)
air
PdCl 2 (PPh 3 ) 2 (2 mol%)
Pd(OAc) 2 (5 mol%)
dppp (7.5 mol%)
O 2
RSiMe 2 OH c
O 2
ArB(OH) 2
Pd(OAc) 2 (5 mol%)
PPh 3 (10 mol%)
air
O 2
a: R = Alkenyl, Phenyl, Alkynyl
b: R = Aryl, Alkenyl, Alkynyl
c: R = Aryl, Alkynyl
d: R = Aryl, Alkyl
[PdCl(p-C 3 H 5 )] 2 (1 mol%)
N-(2-diphenylphosphinobenzylidene)aniline (2 mol%)
RB(OH) 2
d
PdCl 2 (5 mol%)
PS-NMe 2 (10 mol%)
scCO 2
O 2
ArB(OH) 2
Pd(OAc) 2 (3 mol%)
a ir
ArB(OH) 2
Pd/C (4.6 mol%)
a ir
ArB(OH) 2
Pd(OAc) 2 (6 mol%)
a ir
Pd np /Te-Dps (0.05 mol%)
air
ArB(OH) 2
or ArBF 3 K
ArB(OH) 2
Pd(OAc) 2 (0.01 mol%)
2-(N methylpiperazinyl-N’-methyl)
-4,6-di-tert-butyl-phenol (0.01 mol%)
air
ArB(OH) 2
Pd(OAc) 2 (1 mol%)
IPM (25 mol%)
air
ArB(OH) 2
Pd[(Phbz)(Aco)(PPh 3 )] (5 mol%)
a ir
Scheme 2.35 Pd-catalyzed oxidative homo-couplings of organometals using air or O 2 as oxidant
H. Zhang