Efficient aerobic oxidation of alcohols using CuBr2 and a series of α- pyridyl-imine terminated polydimethylsiloxane ligands Zhenzhong Hu , Fran M.
Download ReportTranscript Efficient aerobic oxidation of alcohols using CuBr2 and a series of α- pyridyl-imine terminated polydimethylsiloxane ligands Zhenzhong Hu , Fran M.
Efficient aerobic oxidation of alcohols using CuBr a series of α-
pyridyl-imine terminated polydimethylsiloxane ligands
2
and
Zhenzhong Hu
Introduction
From the point of view of Green Chemistry, polymer based catalysts are very environmentally friendly. These catalysts can be used and recycled in green solvents such as liquid polymers and supercritical carbon dioxide.
They can also be very selective.
In our recent studies, a series of terminated polydimethylsiloxane α ligands pyridyl-imine have been synthesized and characterized. It is interesting that these carbon dioxide miscible ligands form metallocyclic complexes when coordinated with copper(I) salt.
Meanwhile, they provide perfect binding sites for copper (II) ions which then work as catalysts for more efficient aerobic oxidations of primary and secondary alcohols.
[Cu(CH
3
CN)
4
](PF
6
) +
L
25000 20000 15000 10000 5000 0
Coordination Chemistry
[Cu(
L
)](PF
6
)
/ nm
• L2 titrated with Cu(I) reagent (L1 behaves similarly) • MLCT band max. intensity reached at a ratio C M /C P = 1 • Metallocyclopolymer is characterised by NMR, FT-IR, GPC, CHN, MALDI-TOF MS • • • • •
Summary
α Pyridyl-imine terminated PDMS compounds have been prepared and characterised.
Coordination chemistry with Cu(I) shows the formation of [1+1] metallocycles.
The TEMPO/[CuBr 2 ]/L1 catalytic system is very effective for the aerobic oxidation of alcohols.
Future studies will involve the study of catalytic reaction mechanism and the recycling of the catalyst.
Attempts will also be made to obtain further evidence for the structures of these metallocyclic polymers.
0.2
0.4
0.6
0.8
1.0
L1 Cu
Ligand Synthesis Solubility in Supercritical CO
2
8000 7000 6000 5000 4000 50 70 90 110 Temperature /
o
C
Cloud point data for
L1
( ) and [Cu(
L2
)](PF 6 ) ( ▲ ) in carbon dioxide.
L2
miscible in liquid CO 2 . [Cu(
L1
)](PF 6 ) is insoluble at Ts and Ps studied.
is
Aerobic oxidation of selected alcohols with in situ made TEMPO/[Cu]/L1 system
OH
5 mol% CuBr
2
, 2.5 mol% L1 5 mol% TEMPO, 5 mol%
t
-BuOK
O R 1 R 2
CH
3
CN/H
2
O (2:1), air, 25
º
C
R 1 R 2
Entry Substrate Product t[h] Conversion [%] [a] 1 2
OH OH OMe OH O O OMe O
6 6 100 98 3
O 2 N
6 86
O 2 N OH O
4 5
OH O
8 100 6
HO O H O
6
O
12 93 70
OH O
7 12 88 [b] 8 9
OH OH + O
6 100/0
OH
no product 6 0 [c]
[a]
GC conversion, selectivity > 99%;
[b]
Reaction temperature = 45
o
C, using compressed air;
[c]
Reaction time = 48 h
Acknowledgements; Prof. Christopher M. Kozak; Green Chemistry and Catalysis Group; Dr. Celine Schneider ; C-CART (Brent, Linda & Julie); Chemistry Department, Memorial University