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Oxometalates and Dioxygen in Catalytic Oxidation
G. Centi and F.T r i f i r o ' (Editors), New Developments in Selective Oxidation 0 1990 Elsevier Science Publishers B.V., Amsterdam - Printedin T h e Netherlands
OXOMETALATES AND DIOXYGEN
J.-M.
205
IN CATALYTIC OXIDATION
BRiGEAULTl, B. EL ALI1,
J . M E R C l E R 2 , J . MARTIN1, C . MARTIN' and
0. MOHAMMEDI' ' I E p a r t e i r i e n t de Chiriiie U n i v e r s i t C P . e t M. C u r i e , C a t a l y s e e t C h i i i i i e des S u r f a c e s ; T o u r 44 - Ze ; 4, P l a c e J u s s i e u ; 75252 P a r i s Cedex 05 ( F r a n c e )
n
L
D e p a r t e m e n t de Chiinie U n i v e r s i t e P. e t M. C u r i e , L a b o r a t o i r e de C h i m i e O r g a n i q u e S t r u c t u r a l e , B l t . 74
SUMMARY The a p p l i c a t i o n o f oxovanadium ( I V ) o r ( V ) complexes I VO(acac) 1, I V O i OCH( CH3)21, I a n d h e t e r o p o l y a c i d s IPMo12-nVn0401 "HPA-n", as e a t a l y s t p r e c u r s o r s i s examined f o r t h e o x i d a t i v e cleavage o f ketones. I n t h e presence o f d i o x y g e n , a t room t e m p e r a t u r e o r a t 60"C, t h e y r e a c t w i t h b e n z y l i c k e t o n e s , Ar-CH2-C(0)R, t o p r o d u c e t h e c o r r e s p o n d i n g c a r b o x y l i c a c i d s , R-COOH, a n d benzaldehyde and/or benzoic a c i d i n h i g h y i e l d . S u b s t i t u t e d cycloalkanones, u - k e t o l , u - d i k e t o n e s and 1 - p h e n y l a l k a n o n e s a r e a l s o o x i d a t i v e l y c l e a v e d b y HPA-2 and d i o x y g e n u n d e r v e r y m i l d c o n d i t i o n s . The e x p e r i m e n t s show t h a t t h e e f f i c i e n c y o f HPA-2 i s r e l a t e d t o t h e key r o l e o f Va(V) and t o t h e l a r g e s o l u b i l i t y o f t h i s " a c i d i c c o m p l e x " i n o r g a n i c media. INTRODUCTION As p a r t o f o u r c o n t i n u i n g i n v e s t i g a t i o n i n t o o x i d a t i o n p r o c e s s e s , we h a v e been i n t e r e s t e d i n t h e u s e o f vanadium ( V ) p r e c u r s o r s i n homogenems c a t a l y s i s ( r e f . 1). The o x i d a t i o n o f o r g a n i c compounds by q u i n q u e v a l e n t van3diutii has, b e s i d e s i t s own i n t e r e s t , i m p l i c a t i o n s c o n c e r n i n g t h e b e h a v i o r o f vanadium o x i d e c a t a l y s t s ( r e f . 2 ) . The s u b j e c t was f i r s t examined b y M o r e t t e ct a l . e s s e n t i a l l y f r o m a n a n a l y t i c a l v i e w p o i n t ( r e f . 3 ) and l a t e r b y L i t t l e r e t < X I . ( r e f . 4 ) ; molecular oxtlgen h a s no s i y n ~ f l c a n tc f f e c t o n t h e r a t e s o f o x i d a t i o n and a l l t h e s e o x i d a t i o n p r o c e s s e s a r e s t o i c h i o m e t r i c . I n t h i s c o n t e x t , i t was i n t e r e s t i n g t o t e s t M a t v e e v ' s systems as o x i d i z i n g a g e n t s : p a l l a d i u i i i ( 1 1 ) complexes a n d s a l t s o f h e t e r o p o l y a c i d s a b b r e v i a t e d t o "Pd( I I ) / H P A - n " ( r e f . 5 ) , HPA-n
+
Red
+ iHt
+
H1 I HPA-riI
+
(1)
OX
Thus, HPA-11 i n eqn. 1 i s a h e t e r o p o l y a c i d w i t h t h e K e g g i n s t r u c t u r e :
H3+,,1PM12-nVnOq0(
; M = Mo, W; Red i s a r e d u c i n g a g e n t i n v o l v i n g . [ e l e c t r o n s :
a r e d u c e d f o r m o f a c a t a l y s t o r a s u b s t r a t e . The r e d u c e d fortii, v1 v I V 040) I o r t h e " h e t e r o p o l y - b l u e " c<,n be HI I H P A - n l z H1 IH3+n{ PM12-nVan-l Vl r r o x i d i z e d by dioxygen under v e r y mi I d conditions
:
206
Hi IHPA-n/ + (i/4)02
+
+ (i/2)H20
HPA-n
(2)
S i n c e p o l y o x o i n e t a l a t e s have no s o p h i s t i c a t e d o x i d i z a b l e a n c i l l a r y l i g a n d s , t h e y have c o n s i d e r a b l e p o t e n t i a l as l o n g - l i v e d c a t a l y s t s . A c c o r d i n g t o eqn. ( 1 ) and (2), HPA-II can be used as c o c a t a l y s t s , f o r example, i n a s s o c i a t i o n w i t h p r e c i o u s m e t a l complexes ( r e f . 5-6) o r as d i r e c t c a t a l y s t s ( r e f . 7 ) . While t e s t i n g r e c e n t l y - d e s c r i b e d systems : "Pd( 11) o r Rh( 111) complexes w i t h o r w i t h o u t a c o c a t a l y s t and i n t h e presence o f dioxygen" ( r e f . 5-6,
8)
f o r t h e o x i d a t i o n o f s e v e r a l o l e f i n i c s u b s t r a t e s , we o b t a i n e d c l e a r e v i d e n c e f o r secondary c a t a l y t i c processes; one of t h e s e i s t h e o x i d a t i o n of ketoiies. These r e s u l t s on t h e vanadium(V) c a t a l y t i c o x i d a t i v e cleavage o f ketones w i t h dioxygen a r e discussed. RESULTS AND D I S C U S S I O N
L
O x i d a t i o n o f 1-phenylpropan-2-one,
; evidence f o r a p r e c u r s o r e f f e c t
,
I n o r d e r t o compare s e v e r a l p r e c u r s o r s we t o o k l-phenylpropan-2-one, as a model s u b s t r a t e .
i s o x i d i z e d w i t h o u t an o r g a n i c s o l v e n t . R e s u l t s a r e surnitiarized i n
Ketone Table 1. TABLE 1
O x i d a t i o n o f 1-phenyl-2-propanone,
2
,
by h e t e r o p o l y a c i d s o r vanadium oxo-
complexes and dioxygena ~~
T
Precursors Run
Products
Coriver-
$ionb
)
(0.20 mol 1-l
time
("C)
(h)
. II X
6.5
1.5
x
(% Yieldsc)
5 6.5
X L 1
X i ' -~
1
H31PMo120401. 30 H20
20
6
-
5
2
ti4 IPMollV10401
20
6
70
37
20
62
3.5
9.5
3
H51PMo10V20401. 36 H20
20
6
99
78
10
88
10.5
0.5
4
t i 6 I P M O ~ V ~ O34~ ~H20 ~.
20
6
99
77
10
8R
10.5
20
6
3
20
6
46
. 33 H20
. 29
5
ti3 IPW120401
6
H4 IPWllV1040/.
7
IVO{OCH(Me)213
8
IV0(acac)21
H20
30 H20
I
a Reaction c o n d i t i o n s
. runs
traces
-
traces traces
-
28
7
38
4.5
78
3
66
6
60
24
82
10
Tra
60
24
75
10
56
0.5 traces 7
-
_______
1-6 : s u b s t r a t e = 3 cm3 (22.4 m m o l ) ; runs 7 - 8 : s u b s t r a t e = 1.5
p (02)= l o 5 Pa; w i t h o u t o r g a n i c s o l v e n t ;
% o f s u b s t r a t e consumed;
coupled CC-MS (OV 17 and OV 105 columns);
i n t e r n a l standard anisole.
~ 1 1 1 ~ ;
P r o d u c t s analysed by
I n a l l experiments ( r u n s 1-B), o x i d a t i o n l e a d s t o benzaldehyde,
I Jand a c e t i c
a c i d , X I , as m a j o r p r o d u c t s , and t o b e n z o i c a c i d , J, r e s u l t i n g f r o m benzaldehyde n d
207
c o o x i d a t i o n . Two m i n o r p r o d u c t s , 1-phenylpropan-1.2
dione,
Xc I 1 and
tr;lns-
s t i l b e n e , X I I I , a r e formed. The l a t t e r was i d e n t i f i e d i n a r e a c t i o n between N
benzaldehyde a n d 2 ( r e f . 9 ) . Comparison o f r u n s 1 and 5 w i t h r u n s 2-4,
6-0
shows t h a t vanadium (V) i s a key-element i n t h e c a t a l y t i c s y s t e m . Variadiiiiii
( V ) oxoal k o x i d e ,
IV010CH(Me)213/ o r variadiuiii ( I V ) a c e t y l a c e t o i i a t e can have a l s o
a c a t a l y t i c e f f e c t w i t h dioxygen,
but the substrate/vanadiuin r a t i o , the
c o n v e r s i o n and t h e r e a c t i o n times i n d i c a t e t h a t t h e y a r e l e s s e f f i c i e n t t h a n
HPA-1 w i t h Mo ( r u n 2 ) . These r e s u l t s and t h e easy s y n t h e s i s ( r e f .
.
"H5
10) of t h e a c i d
30-36 H20", o r o f t h e a c i d s a l t s " H 5 ~ x N a x ~ P M o 1 0 V ~ ~,0 4y0 ~H20"
l e d us t o choose these p r e c u r s o r s f o r t h e o x i d a t i v e cleavage of o-ther ketones. O x i d a t i o n o f b e n z y l i c ketones HPA-2 can be used i n t h e o x i d a t i o n o f b e n z y l i c ketones ( r e f . 11). A l l d a t a a r e c o m p a t i b l e w i t h scheme 1 : HPA-2. 0 X-C6H4-CH2-C(0)-R 20°C; MeCN
2X-c
H -CHO t R-COOH
major products ( y i e l d s : 70 90 b)
-
+
X-C6H4-COOH
+ X-C6H4-C(0)-C(0)R
minor products ( y i e l d s 4 10%)
X
:
H
R : Me; E t ; A r o r A r - C H 2
X
:
p-OMe
R : Me
Schenie
1
The o x i d a t i v e c l e a v a g e o f phenylacetones g i v e s h i g h y i e l d s o f a c e t i c a c i d and o f benzaldehyde ( o r o f f u n c t i o n a l i z e d benzaldehyde). The r e a c t i o n can be a p p l i e d t o d i f f e r e n t b e n z y l i c ketones. Oxidation o f a-ketol
,
a - d i ketones and 2-methyl cyclohexanone; e v i d e n c e
f o r a solvent effect I n MeCN t h e c o n v e r s i o n s and t h e s e l e c t i v i t i e s a r e u s u a l l y c l o s e t o t h e values o b t a i n e d w i t h t h e o t h e r p u r e l i q u i d s u b s t r a t e s ( r e f . 1 2 ) . Fladical c h a i n r e a c t i o n s can be i n v o l v e d i n t h e mechanism o f o x i d a t i v e cleavage of ketones ( v i d e i n f r a ) ; t h r s e r e a c t i o n s a r e l e s s s u b j e c t t o i n t e r f e r e n c e frclin p o l a r
e f f e c t s . N e v e r t h e l e s s , f o r some s u b s t r a t e s we observed a d r a m a t i c change on g o i n g f r o m MeCN t o e t h a n o l . For an (1-ketol, 2-hydroxy-2-phenylacetl~phenone,
I,I, t h e
conversion i s low i n a c e t o n i t r i l e ( r u n 9
-
Table 2 ) b u t reaches 95%
i n e t h a n o l ( r u n 1 0 ) even a t room temperature; o t h e r n o n - a l c o h o l i c s o l v e n t s cause i n h i b i t i o n .
208
TABLE 2 O x i d a t i o n o f a k e t o l and t u - d i k e t o n e s b y HPA-2 and 02a
- - -
...icliil'
(11)
(4.8)
0.05
McCN
24
10
2 2
(4.8)
0.05
ELOII
11
ILI
(7.4)
0.03
EtOll
12
IV
(.2 . 4 5 ),
0.05
ECOll
9
-
a R e a c t i o n conditions
p (02;< b,
x
IX
( "6 )
____
0 1
XI
X'
u
__~___.~
. HPA-2
=
25
24
6
95
93
3 24
=loo
-
~
~
91
c
"100
102
52
ti ~ M O , ~ V ~ O ,., 30-36 ~ ~ H20 ; solvent : 6
5
-
211
100
-
cm3 ;
.
T : 20°C ;
Pa
see T a b l e 1
Benzaldehyde,
A ' , are the o n l y i s o l a b l e products. ILI ( o r XJI) and Ph-C(0)-C(0)-Ph, I V ,
Q ,a n d e t h y l b e n z o a t e ,
a - D i k e t o n e s s u c h as Ph-C(0)-C(0)-Me
-
a r e n o t c l e a v e d i n MeCN, w h i l e t h e y r e a c t w i t h h i g h s e l e c t i v i t y i n e t h a n o l a t room t e m p e r a t u r e ( r u n s 1 1 - 1 2 ) . These s u r p r i s i n g r e s u l t s l e d us t o exainirie t h e solvent e f f e c t
on t h e o x i d a t i v e c l e a v a g e o f 2 - m e t h y l c y c l o h e x a n o n e b y HPA-2
( T a b l e 3 ) . Some s o l v e n t s (benzene, d i c h l o r o - 1 , 2
e t h a n e , ...)i n h i b i t t h e r e a c t i o n
o r reduce t h e r a t e o f o x i d a t i o n o f 2-methylcyclohexanone,
1. The
novel c a t a l y s t
s y s t e m s s t u d i e d c a n o p e r a t e i n a l c o h o l i c media ( m e t h a n o l , e t h a n o l , t e r t butanol,
...) b u t
t h e c o n v e r s i o n i s l o w e r t h a n w i t h MeCN o r a c e t i c a c i d a n d
n i t r o m e t h a n e . The m a i n p r o d u c t i s t h e 6 - o x o h e p t a n o i c m e t h y l e s t e r XLV' ( r u n 1 5 ) o r t h e corresponding keto-acid
-
XLV
( r u n 16), w i t h a r i n g - c o n t r a c t i o n product
(cyclopentanone, XV) corresponding t o e t h y l group e l i m i n a t i o n . Nitroinethane f a v o r s t h e f o r m a t i o n o f t h i s minor product, although t h e conversion i s equal t o t h a t o b t a i n e d w i t h MeCN ( r u n 1 4 ) . M i x e d s o l v e n t s ( r u n s 17-18) s u c h as
-
MeCN/MeOH g i v e a l s o X I V ' ,
t h e methyl ester. With ethylene g l y c o l dimethyl
e t h e r ( r u n 19), moderate y i e l d s o f t h e e s t e r s , X I V ' , p a r t ia 1 m e t hy 1a t ion o f t h e ke t oac id
.
a r e o b t a i n e d , due t o t h e
O x i d a t i o n o f c y c l o a l kanones b y HPA-2 a n d O2 The r e s u l t s f o r t h e r e a c t i o n o f some c y c l o a l k a n o n e s a r e p r e s e n t e d i n T a b l e 4. Each k e t o n e was s u b j e c t e d t o n e a r l y i d e n t i c a l o x i d a i o n c o n d i t i o n s w i t h HPA-2. T r e a t m e n t o f 2 - m e t h y l c y c l o p e n t a n o n e , 5 - o x o h e x a n o i c a c i d , XJI, 6-oxoheptanoic acid,
XLV,
c,
f o r 2h
r u n 20) g i v e s
i n h i g h y i e l d (94%). 2-methylcyclohexanone, ( r u n 2 1 ) ; 2,6-dimethylcyclohexanone, VI-I,
m a i n l y 6-0x0-2-methylheptanoic
acid,
Xgl,
1,g i v e s produces
a l s o i n good y i e l d ( 8 9 % ) ( r u n 2 2 ) .
O t h e r c y c l i c k e t o n e s c a n be c l e a v e d , b u t t h e s e l e c t i v i t y depends o n t h e s u b s t r a t e and on t h e c a t a l y t i c system; f o r example, u n d e r t h e s e c o n d i t i o n s ,
209
TABLE 3 O x i d a t i o n o f 2-methylcyclohexanone,
1 , by
HPA-2 and O2 : solvent. effect'
~
Solvent
Convers iomb
(cm3)
($)
Riiii
T iine ( 11
x IV
XIV'
-
-
9
.-u
13
MeCN
(B
Products
xv
98
4
85
2
98
4
81.5
1.5
54
6
0
49
2.5
81
6
69
1
10.5
96
6
4
86
3
96
6
6.5
81.5
5
96
24
16
11
(6) 14
MeN02
14.5
(6) 15
MeOH
(6)
t.iccoon
16
(6) 17
MeCN/McOH
(5) 18
(1)
MeN02/MeOH
(5) 19
(1)
MeO- ( CH2) 20Me
74
.5
(6) a Reaction c o n d i t i o n s
b9
. HPA-2
: 0.075 minol ; s u b s t r a t e : 12.4 nimol ; I : GO'C
; p ( 0 2 ) = 105Pa ;
see Table 1 ; i n t e r n a l standard : l i c p t a n o i c a c i d
TABLE 4
Oxidation o f cycloalkanones by HPA-2 and 02a Substrate
HPA-2
Solvent
Time
Conver-
P r o d u c t s :% Y i e l d s c )
s ionb
Run
20
(nun01 1
(mmol)
0.025
(4.4)
(cm3) MeCN
(h)
(9)
2
96
Xi1
1914)
4
98
XLV
185)
6
91
XZI
189)
24
100
(6) 21
0.075
(12.4)
MeCN
(6) 22
0.075
VLI ( 1 1 . 0 )
MeCN
(6) 23
a Reaction c o n d i t i o n s
b3
0.05
V L I I (4.7)
. HPA-2
MeCN/MeOH (5) ( 1 )
= H5[PlIo10V20,,,-j.
XVLII (40)
30-36 H20 ; T : 60°C ; p ( 0 2 ) Y 105Pa
see Table 1 ; i n t e r n a l s t a n d a r d : h e p t a n o i c a c i d
XLX
____-_____
(17)
210 cyclohexa-1,3 dione, which e x i s t s m a i n l y i n t h e nionoenolic form, can be c l e a v e d w i t h l o s s o f one o r two carbons; i t g i v e s two m a j o r p r o d u c t s i n MeCN-MeOtl :
0
0
COOMe ____)
COOMe
MeCN/MeOH
OH
+
C OCOOMe O M e
X L X
XVLII
The s p e c i e s u n d e r g o i n g cleavage has n o t been i s o l a t e d , b u t i t c o u l d be d i f f e r e n t f r o m t h e t r i k e t o n e formed w i t h t h e sodium p e r i o d a t e system ( r e f . 13) which g i v e s m a i n l y g l u t a r i c a c i d . Mechanism o f o x i d a t i o n and search f o r i n t e r m e d i a t e s
EPR r e s u l t s g i v e c l e a r evidence o n l y of i s o l a t e d V I " s p e c i e s . To d e t e r m i n e whether one mechanism i s more p l a u s i b l e t h a n another, we c a r r i e d o u t a l a b e l i n g experiment u s i n g 1802 b u t w i t h o u t c l e a r - c u t r e s u l t s . C o n s i d e r i n g t h e e x p e r i mental f a c t s , we can propose a p l a u s i b l e mechanism as shown i n scheme 2 f o r c y c l o a l k a n o n e s i n which t h e f o r m a t i o n o f a vanadium e n o l a t e i s a key s t e p ; i t
"O\,+) ,.I/ =0
(>0'
-
-0, b
0 R
Scheme 2
II
~
C
O
O
H
211
c o u l d g e n e r a t e s h o r t - l i v e d r a d i c a l s p e c i e s which c o u l d i n t e r a c t w i t h O2 i n a vanadium-assisted pathway. The i n t e r m e d i a t e p e r o x i d e c o u l d undergo d i r e c t o r vanadium-assisted decomposition t o y i e l d t h e k e t o - a c i d . The most i n t r i g u i n g s t e p i s t h e h o m o l y t i c c l e a v a g e o f V-0 bond t o g i v e t h e s h o r t - l i v c b d r a d i c a l s p e c i e s . A more thorough s t u d y o f t h e system i s now i n p r o g r e s s . CONCLUSION
A new c a t a l y t i c method f o r t h e o x i d a t i v e cleavage o f soiiie open-chain ketones o r o f s u b s t i t u t e d c y c l o a l k a n o n e s has been found. I t emplciys a r a t h e r i n e x p e n s i v e "PMoV" a s s o c i a t i o n as t h e c a t a l y s t i n a homogeneous phase i n c o m b i n a t i o n w i t h dioxygen as t h e p r i m a r y o x i d a n t . Some o f t h e r e a c t i o n s r e p o r t e d h e r e may have s y n t h e t i c p o t e n t i a l : some k e t o - a c i d s have been u t i l i z e d i n t h e s y n t h e s i s o f m a c r o c y c l i c l a c t o n e s . Other a p p l i c a t i o n s i n c l u d e t h e p r e p a r a t i o n o f c a t e c h o l a m i n e c o n j u g a t e s and n a t u r a l - p r o d u c t t o t a l s y n t h e s i s . The r e a c t i o n can be extended t o o t h e r carbon-carbon bond cleavages u s i n g dioxygen; f o r example a - d i o l s have been smoothly c l e a v e d ( r e f . 14) by a c a t a l y t i c amount o f H5 [ P M O ~ ~ V ~ O30-36 ~ ~ ] . H20 o r o f [VO(OCH(CH3)213] under m o l e c u l a r oxygen and v e r y m i l d c o n d i t i o n s .
REFERENCES 1 J.-M. B r e g e a u l t , F. Derdar, J. M a r t i n , C. M a r t i n e t J . M e r c i e r , Proc. 6 t h I n t . Symp. Homogeneous C a t a l y s i s , Vancouver, August 21-26, 1988, p. 34; J.-M. B r e g e a u l t , B. E l A l i , J. M e r c i e r , J. M a r t i n and C. M a r t i n , C.R. Acad. S c i . P a r i s , 307 (1988) s C r i e 1 1 , 2011-2014. 2 G. C e n t i , J. Lopez N i e t o , C. I a p a l u c c i , K. Brickman and E.M. Serwicka, Appl. Catal., 46 (1989) 197-212; J.G. H i g h f i e l d and J.B. M o f f a t , J. C a t a l . , 98 (1986) 245-258; M. Misono, C a t a l . Rev.-Sci. Eng., 29 (1987) 269-321 3 A. M o r e t t e e t G. Gaudefroy, B u l l . SOC. Chim. France, (1954) 956-964. 4 J.S. L i t t l e r , J . Chem. SOC., (1962) 832-837; J.S. L i t t l e r and W.A. Waters, J. Chem. SOC., (1959) 3014-3019. 5 I . V . Kozhevnikov and K . I . Matveev, Russ. Chem. Rev., 51 (1982) 1075-1088; Appl C a t a l . , 5 (1983) 135-150; I . V . Kozhevni kov, Uspeckhi K h i r n i i , 56( 1987) 1417-1443; E.G. Z h i z h i n a , L . I . Kuznetsova and K . I . Matveev, React. K i n e t . C a t a l . L e t t . , 3 1 (1986) 113-120. 6 B. E l A l i , J.-M. B r e g e a u l t and J . M a r t i n , J. Organoinetal. Cheiri., 327 (1987) C9-Cl4. 7 I . V . Kozhevnikov, V . I . Siniagina, G.V. Varnakova and K . I . Matveev, K i n e t . i K a t a l . , 20 (1979) 506-510. 8 0. Mohammedi, Ph. D., U n i v e r s i t e P. e t M. Curie, may 11, 1987. 9 W.V. M i l l e r .and G. Rohde, B e r i c h t e , 23 (1890) 1070-1079. 10 G. Canneri, Gazz. Chim. I t a l . , 56 (1926) 871-889; P. C o u r t i n , Rev. Chim. Min., 8 (1971) 75-85; G.A.T. T s i g d i n o s and C.J. H a l l a d a , I n o r g . Chem., 7 (1968) 437-441; J.-M. B r e g e a u l t e t a i . , u n p u b l i s h e d r e s u l t s . 11 8. E l A l i , J.-M. B r e g e a u l t , J. M a r t i n , C. M a r t i n and J. M e r c i e r , New J . Chem., 13 (1989) 173-175. 12 B. E l A l i , Ph. D., U n i v e r s i t e P. e t M. C u r i e , j u n e 21, 1989. 13 M.L. Wolfrom and J.M. B o b b i t , J . Amer. Chem. SOC., 78 (1956) 2489-2493. 1 4 J.-M. B r e g e a u l t , B. E l A l i , J. M e r c i e r , J . M a r t i n e t C. M a r t i n , C.R. Acad. S c i . P a r i s , 309 (1989) s e r i e 11, 459-462.
.
212 DISCUSSION CONTRIBUTION B.R. JAMES [ U n i v e r s i t y of B r i t i s h Columbia, Vancouver. Canada) : I am confused r e g a r d i n g y o u r i m p l i c a t i o n s f o r t h e mechanism. You n o t e t h a t t h e reduced h e t e r o p o l y - b l u e H.[HPA-nl i s r e o x i d i z e d by O 2 t o g i v e t h e o x i d i z e d f o r m HPA-n, y e t i n Scheme’2 you make a mechanism showing unchanged o x i d a t i o n s t a t e i n t h e HPA m o i e t y ( V 0 2 + ) w i t h 0 a t t a c k i n g t h e c o o r d i n a t e d c y c l o a l k a n o n e t o g i v e a 2 peroxo r a d i c a l . Do you f a v o u r O2 p l a y i n g a r o l e w i t h i n t h e HPA m o i e t y o r w i t h i n t h e organic moiety ? BREGEAULT [ U n i v e r s i t g P . e t M. E u r i e , P a r i s , France) : The e q u a t i o n s o f t h e i n t r o d u c t o r y p a r t a r e n o t t h o s e o f a mechanism [ i . e . elementary processes) b u t o n l y t h o s e of t h e presumed o v e r a l l process. Scheme 2 shows t h e f o r m a t i o n o f i n t e r m e d i a t e vanadium [ I V ) species, b u t o m i t t h e f o r m a t i o n o f an a l k y l p e r o x i d i c complex which would i n v o l v e f r e e radical-dioxygen-vanadium i n t e r a c t i o n . T h i s i n t e r m e d i a t e s p e c i e s c o u l d a s s i s t r e o x i d a t i o n o f vanadium [ I V l . A t p r e s e n t , we have no e x p e r i m e n t a l r e s u l t s which show t h e p r e f e r r e d i n t e r a c t i o n o f d i o x y g e n w i t h t h e o r g a n i c r e s t . so t h e t h i r d and f o u r t h s t e p o f t h e mechanism [Scheme 21 indeed. has t h e c h a r a c t e r o f a p r o p o s a l . J.-M.
R.A. SHELDON [ANDEND, The N e t h e r l a n d s ) : Do any o f t h e oxometalate o r vanadium c a t a l y z e d o x i d a t i v e cleavage o f 3 . 2 - d i o l s a l s o work under n e u t r a l o r b a s i c conditions ? J.-M. BREGEAULT [ U n i v e r s i t b P. e t PI. C u r i e . P a r i s , France) : V i c i n a l d i o l s c a r a l s o be c l e a v e d by some HPA-salts, b u t t h e r a t e o f r e a c t i o n . t h e c o n v e r s i o n and t h e y i e l d s a r e lower t h a n t h o s e o b t a i n e d w i t h HPA-2. I t s h o u l d be m e n t i o ned t h a t r e o x i d a t i o n o f t h e reduced f o r m [ s l i s c o n t r o l l e d by t h e a c i d i t y f u n c t i o n of t h e medium.
H. MIMOUN ( I n s t i t u t FranCais du P e t r o l e , RueiZ-Malmaison, France) : What i s t h e s t a b i l i t y of t h e HPA d u r i n g t h e cleavage r e a c t i o n ? J.-M. BREGEAULT [ U n i v e r s i t Q P. e t M. C u r i e , P a r i s . France] : The s t a b i l i t y o f PPA-n u n d e r our r e a c t i o n c o n d i t i o n s has n o t y e t been s t u d i e d in d e t a i l , b u t t i l l now we have no e x p e r i m e n t a l e v i d e n c e o f i t s i n s t a b i l i t y . Work o n t h i s i s i n progress.
OXOMETALATES AND DIOXYGEN
J.-M.
205
IN CATALYTIC OXIDATION
BRiGEAULTl, B. EL ALI1,
J . M E R C l E R 2 , J . MARTIN1, C . MARTIN' and
0. MOHAMMEDI' ' I E p a r t e i r i e n t de Chiriiie U n i v e r s i t C P . e t M. C u r i e , C a t a l y s e e t C h i i i i i e des S u r f a c e s ; T o u r 44 - Ze ; 4, P l a c e J u s s i e u ; 75252 P a r i s Cedex 05 ( F r a n c e )
n
L
D e p a r t e m e n t de Chiinie U n i v e r s i t e P. e t M. C u r i e , L a b o r a t o i r e de C h i m i e O r g a n i q u e S t r u c t u r a l e , B l t . 74
SUMMARY The a p p l i c a t i o n o f oxovanadium ( I V ) o r ( V ) complexes I VO(acac) 1, I V O i OCH( CH3)21, I a n d h e t e r o p o l y a c i d s IPMo12-nVn0401 "HPA-n", as e a t a l y s t p r e c u r s o r s i s examined f o r t h e o x i d a t i v e cleavage o f ketones. I n t h e presence o f d i o x y g e n , a t room t e m p e r a t u r e o r a t 60"C, t h e y r e a c t w i t h b e n z y l i c k e t o n e s , Ar-CH2-C(0)R, t o p r o d u c e t h e c o r r e s p o n d i n g c a r b o x y l i c a c i d s , R-COOH, a n d benzaldehyde and/or benzoic a c i d i n h i g h y i e l d . S u b s t i t u t e d cycloalkanones, u - k e t o l , u - d i k e t o n e s and 1 - p h e n y l a l k a n o n e s a r e a l s o o x i d a t i v e l y c l e a v e d b y HPA-2 and d i o x y g e n u n d e r v e r y m i l d c o n d i t i o n s . The e x p e r i m e n t s show t h a t t h e e f f i c i e n c y o f HPA-2 i s r e l a t e d t o t h e key r o l e o f Va(V) and t o t h e l a r g e s o l u b i l i t y o f t h i s " a c i d i c c o m p l e x " i n o r g a n i c media. INTRODUCTION As p a r t o f o u r c o n t i n u i n g i n v e s t i g a t i o n i n t o o x i d a t i o n p r o c e s s e s , we h a v e been i n t e r e s t e d i n t h e u s e o f vanadium ( V ) p r e c u r s o r s i n homogenems c a t a l y s i s ( r e f . 1). The o x i d a t i o n o f o r g a n i c compounds by q u i n q u e v a l e n t van3diutii has, b e s i d e s i t s own i n t e r e s t , i m p l i c a t i o n s c o n c e r n i n g t h e b e h a v i o r o f vanadium o x i d e c a t a l y s t s ( r e f . 2 ) . The s u b j e c t was f i r s t examined b y M o r e t t e ct a l . e s s e n t i a l l y f r o m a n a n a l y t i c a l v i e w p o i n t ( r e f . 3 ) and l a t e r b y L i t t l e r e t < X I . ( r e f . 4 ) ; molecular oxtlgen h a s no s i y n ~ f l c a n tc f f e c t o n t h e r a t e s o f o x i d a t i o n and a l l t h e s e o x i d a t i o n p r o c e s s e s a r e s t o i c h i o m e t r i c . I n t h i s c o n t e x t , i t was i n t e r e s t i n g t o t e s t M a t v e e v ' s systems as o x i d i z i n g a g e n t s : p a l l a d i u i i i ( 1 1 ) complexes a n d s a l t s o f h e t e r o p o l y a c i d s a b b r e v i a t e d t o "Pd( I I ) / H P A - n " ( r e f . 5 ) , HPA-n
+
Red
+ iHt
+
H1 I HPA-riI
+
(1)
OX
Thus, HPA-11 i n eqn. 1 i s a h e t e r o p o l y a c i d w i t h t h e K e g g i n s t r u c t u r e :
H3+,,1PM12-nVnOq0(
; M = Mo, W; Red i s a r e d u c i n g a g e n t i n v o l v i n g . [ e l e c t r o n s :
a r e d u c e d f o r m o f a c a t a l y s t o r a s u b s t r a t e . The r e d u c e d fortii, v1 v I V 040) I o r t h e " h e t e r o p o l y - b l u e " c<,n be HI I H P A - n l z H1 IH3+n{ PM12-nVan-l Vl r r o x i d i z e d by dioxygen under v e r y mi I d conditions
:
206
Hi IHPA-n/ + (i/4)02
+
+ (i/2)H20
HPA-n
(2)
S i n c e p o l y o x o i n e t a l a t e s have no s o p h i s t i c a t e d o x i d i z a b l e a n c i l l a r y l i g a n d s , t h e y have c o n s i d e r a b l e p o t e n t i a l as l o n g - l i v e d c a t a l y s t s . A c c o r d i n g t o eqn. ( 1 ) and (2), HPA-II can be used as c o c a t a l y s t s , f o r example, i n a s s o c i a t i o n w i t h p r e c i o u s m e t a l complexes ( r e f . 5-6) o r as d i r e c t c a t a l y s t s ( r e f . 7 ) . While t e s t i n g r e c e n t l y - d e s c r i b e d systems : "Pd( 11) o r Rh( 111) complexes w i t h o r w i t h o u t a c o c a t a l y s t and i n t h e presence o f dioxygen" ( r e f . 5-6,
8)
f o r t h e o x i d a t i o n o f s e v e r a l o l e f i n i c s u b s t r a t e s , we o b t a i n e d c l e a r e v i d e n c e f o r secondary c a t a l y t i c processes; one of t h e s e i s t h e o x i d a t i o n of ketoiies. These r e s u l t s on t h e vanadium(V) c a t a l y t i c o x i d a t i v e cleavage o f ketones w i t h dioxygen a r e discussed. RESULTS AND D I S C U S S I O N
L
O x i d a t i o n o f 1-phenylpropan-2-one,
; evidence f o r a p r e c u r s o r e f f e c t
,
I n o r d e r t o compare s e v e r a l p r e c u r s o r s we t o o k l-phenylpropan-2-one, as a model s u b s t r a t e .
i s o x i d i z e d w i t h o u t an o r g a n i c s o l v e n t . R e s u l t s a r e surnitiarized i n
Ketone Table 1. TABLE 1
O x i d a t i o n o f 1-phenyl-2-propanone,
2
,
by h e t e r o p o l y a c i d s o r vanadium oxo-
complexes and dioxygena ~~
T
Precursors Run
Products
Coriver-
$ionb
)
(0.20 mol 1-l
time
("C)
(h)
. II X
6.5
1.5
x
(% Yieldsc)
5 6.5
X L 1
X i ' -~
1
H31PMo120401. 30 H20
20
6
-
5
2
ti4 IPMollV10401
20
6
70
37
20
62
3.5
9.5
3
H51PMo10V20401. 36 H20
20
6
99
78
10
88
10.5
0.5
4
t i 6 I P M O ~ V ~ O34~ ~H20 ~.
20
6
99
77
10
8R
10.5
20
6
3
20
6
46
. 33 H20
. 29
5
ti3 IPW120401
6
H4 IPWllV1040/.
7
IVO{OCH(Me)213
8
IV0(acac)21
H20
30 H20
I
a Reaction c o n d i t i o n s
. runs
traces
-
traces traces
-
28
7
38
4.5
78
3
66
6
60
24
82
10
Tra
60
24
75
10
56
0.5 traces 7
-
_______
1-6 : s u b s t r a t e = 3 cm3 (22.4 m m o l ) ; runs 7 - 8 : s u b s t r a t e = 1.5
p (02)= l o 5 Pa; w i t h o u t o r g a n i c s o l v e n t ;
% o f s u b s t r a t e consumed;
coupled CC-MS (OV 17 and OV 105 columns);
i n t e r n a l standard anisole.
~ 1 1 1 ~ ;
P r o d u c t s analysed by
I n a l l experiments ( r u n s 1-B), o x i d a t i o n l e a d s t o benzaldehyde,
I Jand a c e t i c
a c i d , X I , as m a j o r p r o d u c t s , and t o b e n z o i c a c i d , J, r e s u l t i n g f r o m benzaldehyde n d
207
c o o x i d a t i o n . Two m i n o r p r o d u c t s , 1-phenylpropan-1.2
dione,
Xc I 1 and
tr;lns-
s t i l b e n e , X I I I , a r e formed. The l a t t e r was i d e n t i f i e d i n a r e a c t i o n between N
benzaldehyde a n d 2 ( r e f . 9 ) . Comparison o f r u n s 1 and 5 w i t h r u n s 2-4,
6-0
shows t h a t vanadium (V) i s a key-element i n t h e c a t a l y t i c s y s t e m . Variadiiiiii
( V ) oxoal k o x i d e ,
IV010CH(Me)213/ o r variadiuiii ( I V ) a c e t y l a c e t o i i a t e can have a l s o
a c a t a l y t i c e f f e c t w i t h dioxygen,
but the substrate/vanadiuin r a t i o , the
c o n v e r s i o n and t h e r e a c t i o n times i n d i c a t e t h a t t h e y a r e l e s s e f f i c i e n t t h a n
HPA-1 w i t h Mo ( r u n 2 ) . These r e s u l t s and t h e easy s y n t h e s i s ( r e f .
.
"H5
10) of t h e a c i d
30-36 H20", o r o f t h e a c i d s a l t s " H 5 ~ x N a x ~ P M o 1 0 V ~ ~,0 4y0 ~H20"
l e d us t o choose these p r e c u r s o r s f o r t h e o x i d a t i v e cleavage of o-ther ketones. O x i d a t i o n o f b e n z y l i c ketones HPA-2 can be used i n t h e o x i d a t i o n o f b e n z y l i c ketones ( r e f . 11). A l l d a t a a r e c o m p a t i b l e w i t h scheme 1 : HPA-2. 0 X-C6H4-CH2-C(0)-R 20°C; MeCN
2X-c
H -CHO t R-COOH
major products ( y i e l d s : 70 90 b)
-
+
X-C6H4-COOH
+ X-C6H4-C(0)-C(0)R
minor products ( y i e l d s 4 10%)
X
:
H
R : Me; E t ; A r o r A r - C H 2
X
:
p-OMe
R : Me
Schenie
1
The o x i d a t i v e c l e a v a g e o f phenylacetones g i v e s h i g h y i e l d s o f a c e t i c a c i d and o f benzaldehyde ( o r o f f u n c t i o n a l i z e d benzaldehyde). The r e a c t i o n can be a p p l i e d t o d i f f e r e n t b e n z y l i c ketones. Oxidation o f a-ketol
,
a - d i ketones and 2-methyl cyclohexanone; e v i d e n c e
f o r a solvent effect I n MeCN t h e c o n v e r s i o n s and t h e s e l e c t i v i t i e s a r e u s u a l l y c l o s e t o t h e values o b t a i n e d w i t h t h e o t h e r p u r e l i q u i d s u b s t r a t e s ( r e f . 1 2 ) . Fladical c h a i n r e a c t i o n s can be i n v o l v e d i n t h e mechanism o f o x i d a t i v e cleavage of ketones ( v i d e i n f r a ) ; t h r s e r e a c t i o n s a r e l e s s s u b j e c t t o i n t e r f e r e n c e frclin p o l a r
e f f e c t s . N e v e r t h e l e s s , f o r some s u b s t r a t e s we observed a d r a m a t i c change on g o i n g f r o m MeCN t o e t h a n o l . For an (1-ketol, 2-hydroxy-2-phenylacetl~phenone,
I,I, t h e
conversion i s low i n a c e t o n i t r i l e ( r u n 9
-
Table 2 ) b u t reaches 95%
i n e t h a n o l ( r u n 1 0 ) even a t room temperature; o t h e r n o n - a l c o h o l i c s o l v e n t s cause i n h i b i t i o n .
208
TABLE 2 O x i d a t i o n o f a k e t o l and t u - d i k e t o n e s b y HPA-2 and 02a
- - -
...icliil'
(11)
(4.8)
0.05
McCN
24
10
2 2
(4.8)
0.05
ELOII
11
ILI
(7.4)
0.03
EtOll
12
IV
(.2 . 4 5 ),
0.05
ECOll
9
-
a R e a c t i o n conditions
p (02;< b,
x
IX
( "6 )
____
0 1
XI
X'
u
__~___.~
. HPA-2
=
25
24
6
95
93
3 24
=loo
-
~
~
91
c
"100
102
52
ti ~ M O , ~ V ~ O ,., 30-36 ~ ~ H20 ; solvent : 6
5
-
211
100
-
cm3 ;
.
T : 20°C ;
Pa
see T a b l e 1
Benzaldehyde,
A ' , are the o n l y i s o l a b l e products. ILI ( o r XJI) and Ph-C(0)-C(0)-Ph, I V ,
Q ,a n d e t h y l b e n z o a t e ,
a - D i k e t o n e s s u c h as Ph-C(0)-C(0)-Me
-
a r e n o t c l e a v e d i n MeCN, w h i l e t h e y r e a c t w i t h h i g h s e l e c t i v i t y i n e t h a n o l a t room t e m p e r a t u r e ( r u n s 1 1 - 1 2 ) . These s u r p r i s i n g r e s u l t s l e d us t o exainirie t h e solvent e f f e c t
on t h e o x i d a t i v e c l e a v a g e o f 2 - m e t h y l c y c l o h e x a n o n e b y HPA-2
( T a b l e 3 ) . Some s o l v e n t s (benzene, d i c h l o r o - 1 , 2
e t h a n e , ...)i n h i b i t t h e r e a c t i o n
o r reduce t h e r a t e o f o x i d a t i o n o f 2-methylcyclohexanone,
1. The
novel c a t a l y s t
s y s t e m s s t u d i e d c a n o p e r a t e i n a l c o h o l i c media ( m e t h a n o l , e t h a n o l , t e r t butanol,
...) b u t
t h e c o n v e r s i o n i s l o w e r t h a n w i t h MeCN o r a c e t i c a c i d a n d
n i t r o m e t h a n e . The m a i n p r o d u c t i s t h e 6 - o x o h e p t a n o i c m e t h y l e s t e r XLV' ( r u n 1 5 ) o r t h e corresponding keto-acid
-
XLV
( r u n 16), w i t h a r i n g - c o n t r a c t i o n product
(cyclopentanone, XV) corresponding t o e t h y l group e l i m i n a t i o n . Nitroinethane f a v o r s t h e f o r m a t i o n o f t h i s minor product, although t h e conversion i s equal t o t h a t o b t a i n e d w i t h MeCN ( r u n 1 4 ) . M i x e d s o l v e n t s ( r u n s 17-18) s u c h as
-
MeCN/MeOH g i v e a l s o X I V ' ,
t h e methyl ester. With ethylene g l y c o l dimethyl
e t h e r ( r u n 19), moderate y i e l d s o f t h e e s t e r s , X I V ' , p a r t ia 1 m e t hy 1a t ion o f t h e ke t oac id
.
a r e o b t a i n e d , due t o t h e
O x i d a t i o n o f c y c l o a l kanones b y HPA-2 a n d O2 The r e s u l t s f o r t h e r e a c t i o n o f some c y c l o a l k a n o n e s a r e p r e s e n t e d i n T a b l e 4. Each k e t o n e was s u b j e c t e d t o n e a r l y i d e n t i c a l o x i d a i o n c o n d i t i o n s w i t h HPA-2. T r e a t m e n t o f 2 - m e t h y l c y c l o p e n t a n o n e , 5 - o x o h e x a n o i c a c i d , XJI, 6-oxoheptanoic acid,
XLV,
c,
f o r 2h
r u n 20) g i v e s
i n h i g h y i e l d (94%). 2-methylcyclohexanone, ( r u n 2 1 ) ; 2,6-dimethylcyclohexanone, VI-I,
m a i n l y 6-0x0-2-methylheptanoic
acid,
Xgl,
1,g i v e s produces
a l s o i n good y i e l d ( 8 9 % ) ( r u n 2 2 ) .
O t h e r c y c l i c k e t o n e s c a n be c l e a v e d , b u t t h e s e l e c t i v i t y depends o n t h e s u b s t r a t e and on t h e c a t a l y t i c system; f o r example, u n d e r t h e s e c o n d i t i o n s ,
209
TABLE 3 O x i d a t i o n o f 2-methylcyclohexanone,
1 , by
HPA-2 and O2 : solvent. effect'
~
Solvent
Convers iomb
(cm3)
($)
Riiii
T iine ( 11
x IV
XIV'
-
-
9
.-u
13
MeCN
(B
Products
xv
98
4
85
2
98
4
81.5
1.5
54
6
0
49
2.5
81
6
69
1
10.5
96
6
4
86
3
96
6
6.5
81.5
5
96
24
16
11
(6) 14
MeN02
14.5
(6) 15
MeOH
(6)
t.iccoon
16
(6) 17
MeCN/McOH
(5) 18
(1)
MeN02/MeOH
(5) 19
(1)
MeO- ( CH2) 20Me
74
.5
(6) a Reaction c o n d i t i o n s
b9
. HPA-2
: 0.075 minol ; s u b s t r a t e : 12.4 nimol ; I : GO'C
; p ( 0 2 ) = 105Pa ;
see Table 1 ; i n t e r n a l standard : l i c p t a n o i c a c i d
TABLE 4
Oxidation o f cycloalkanones by HPA-2 and 02a Substrate
HPA-2
Solvent
Time
Conver-
P r o d u c t s :% Y i e l d s c )
s ionb
Run
20
(nun01 1
(mmol)
0.025
(4.4)
(cm3) MeCN
(h)
(9)
2
96
Xi1
1914)
4
98
XLV
185)
6
91
XZI
189)
24
100
(6) 21
0.075
(12.4)
MeCN
(6) 22
0.075
VLI ( 1 1 . 0 )
MeCN
(6) 23
a Reaction c o n d i t i o n s
b3
0.05
V L I I (4.7)
. HPA-2
MeCN/MeOH (5) ( 1 )
= H5[PlIo10V20,,,-j.
XVLII (40)
30-36 H20 ; T : 60°C ; p ( 0 2 ) Y 105Pa
see Table 1 ; i n t e r n a l s t a n d a r d : h e p t a n o i c a c i d
XLX
____-_____
(17)
210 cyclohexa-1,3 dione, which e x i s t s m a i n l y i n t h e nionoenolic form, can be c l e a v e d w i t h l o s s o f one o r two carbons; i t g i v e s two m a j o r p r o d u c t s i n MeCN-MeOtl :
0
0
COOMe ____)
COOMe
MeCN/MeOH
OH
+
C OCOOMe O M e
X L X
XVLII
The s p e c i e s u n d e r g o i n g cleavage has n o t been i s o l a t e d , b u t i t c o u l d be d i f f e r e n t f r o m t h e t r i k e t o n e formed w i t h t h e sodium p e r i o d a t e system ( r e f . 13) which g i v e s m a i n l y g l u t a r i c a c i d . Mechanism o f o x i d a t i o n and search f o r i n t e r m e d i a t e s
EPR r e s u l t s g i v e c l e a r evidence o n l y of i s o l a t e d V I " s p e c i e s . To d e t e r m i n e whether one mechanism i s more p l a u s i b l e t h a n another, we c a r r i e d o u t a l a b e l i n g experiment u s i n g 1802 b u t w i t h o u t c l e a r - c u t r e s u l t s . C o n s i d e r i n g t h e e x p e r i mental f a c t s , we can propose a p l a u s i b l e mechanism as shown i n scheme 2 f o r c y c l o a l k a n o n e s i n which t h e f o r m a t i o n o f a vanadium e n o l a t e i s a key s t e p ; i t
"O\,+) ,.I/ =0
(>0'
-
-0, b
0 R
Scheme 2
II
~
C
O
O
H
211
c o u l d g e n e r a t e s h o r t - l i v e d r a d i c a l s p e c i e s which c o u l d i n t e r a c t w i t h O2 i n a vanadium-assisted pathway. The i n t e r m e d i a t e p e r o x i d e c o u l d undergo d i r e c t o r vanadium-assisted decomposition t o y i e l d t h e k e t o - a c i d . The most i n t r i g u i n g s t e p i s t h e h o m o l y t i c c l e a v a g e o f V-0 bond t o g i v e t h e s h o r t - l i v c b d r a d i c a l s p e c i e s . A more thorough s t u d y o f t h e system i s now i n p r o g r e s s . CONCLUSION
A new c a t a l y t i c method f o r t h e o x i d a t i v e cleavage o f soiiie open-chain ketones o r o f s u b s t i t u t e d c y c l o a l k a n o n e s has been found. I t emplciys a r a t h e r i n e x p e n s i v e "PMoV" a s s o c i a t i o n as t h e c a t a l y s t i n a homogeneous phase i n c o m b i n a t i o n w i t h dioxygen as t h e p r i m a r y o x i d a n t . Some o f t h e r e a c t i o n s r e p o r t e d h e r e may have s y n t h e t i c p o t e n t i a l : some k e t o - a c i d s have been u t i l i z e d i n t h e s y n t h e s i s o f m a c r o c y c l i c l a c t o n e s . Other a p p l i c a t i o n s i n c l u d e t h e p r e p a r a t i o n o f c a t e c h o l a m i n e c o n j u g a t e s and n a t u r a l - p r o d u c t t o t a l s y n t h e s i s . The r e a c t i o n can be extended t o o t h e r carbon-carbon bond cleavages u s i n g dioxygen; f o r example a - d i o l s have been smoothly c l e a v e d ( r e f . 14) by a c a t a l y t i c amount o f H5 [ P M O ~ ~ V ~ O30-36 ~ ~ ] . H20 o r o f [VO(OCH(CH3)213] under m o l e c u l a r oxygen and v e r y m i l d c o n d i t i o n s .
REFERENCES 1 J.-M. B r e g e a u l t , F. Derdar, J. M a r t i n , C. M a r t i n e t J . M e r c i e r , Proc. 6 t h I n t . Symp. Homogeneous C a t a l y s i s , Vancouver, August 21-26, 1988, p. 34; J.-M. B r e g e a u l t , B. E l A l i , J. M e r c i e r , J. M a r t i n and C. M a r t i n , C.R. Acad. S c i . P a r i s , 307 (1988) s C r i e 1 1 , 2011-2014. 2 G. C e n t i , J. Lopez N i e t o , C. I a p a l u c c i , K. Brickman and E.M. Serwicka, Appl. Catal., 46 (1989) 197-212; J.G. H i g h f i e l d and J.B. M o f f a t , J. C a t a l . , 98 (1986) 245-258; M. Misono, C a t a l . Rev.-Sci. Eng., 29 (1987) 269-321 3 A. M o r e t t e e t G. Gaudefroy, B u l l . SOC. Chim. France, (1954) 956-964. 4 J.S. L i t t l e r , J . Chem. SOC., (1962) 832-837; J.S. L i t t l e r and W.A. Waters, J. Chem. SOC., (1959) 3014-3019. 5 I . V . Kozhevnikov and K . I . Matveev, Russ. Chem. Rev., 51 (1982) 1075-1088; Appl C a t a l . , 5 (1983) 135-150; I . V . Kozhevni kov, Uspeckhi K h i r n i i , 56( 1987) 1417-1443; E.G. Z h i z h i n a , L . I . Kuznetsova and K . I . Matveev, React. K i n e t . C a t a l . L e t t . , 3 1 (1986) 113-120. 6 B. E l A l i , J.-M. B r e g e a u l t and J . M a r t i n , J. Organoinetal. Cheiri., 327 (1987) C9-Cl4. 7 I . V . Kozhevnikov, V . I . Siniagina, G.V. Varnakova and K . I . Matveev, K i n e t . i K a t a l . , 20 (1979) 506-510. 8 0. Mohammedi, Ph. D., U n i v e r s i t e P. e t M. Curie, may 11, 1987. 9 W.V. M i l l e r .and G. Rohde, B e r i c h t e , 23 (1890) 1070-1079. 10 G. Canneri, Gazz. Chim. I t a l . , 56 (1926) 871-889; P. C o u r t i n , Rev. Chim. Min., 8 (1971) 75-85; G.A.T. T s i g d i n o s and C.J. H a l l a d a , I n o r g . Chem., 7 (1968) 437-441; J.-M. B r e g e a u l t e t a i . , u n p u b l i s h e d r e s u l t s . 11 8. E l A l i , J.-M. B r e g e a u l t , J. M a r t i n , C. M a r t i n and J. M e r c i e r , New J . Chem., 13 (1989) 173-175. 12 B. E l A l i , Ph. D., U n i v e r s i t e P. e t M. C u r i e , j u n e 21, 1989. 13 M.L. Wolfrom and J.M. B o b b i t , J . Amer. Chem. SOC., 78 (1956) 2489-2493. 1 4 J.-M. B r e g e a u l t , B. E l A l i , J. M e r c i e r , J . M a r t i n e t C. M a r t i n , C.R. Acad. S c i . P a r i s , 309 (1989) s e r i e 11, 459-462.
.
212 DISCUSSION CONTRIBUTION B.R. JAMES [ U n i v e r s i t y of B r i t i s h Columbia, Vancouver. Canada) : I am confused r e g a r d i n g y o u r i m p l i c a t i o n s f o r t h e mechanism. You n o t e t h a t t h e reduced h e t e r o p o l y - b l u e H.[HPA-nl i s r e o x i d i z e d by O 2 t o g i v e t h e o x i d i z e d f o r m HPA-n, y e t i n Scheme’2 you make a mechanism showing unchanged o x i d a t i o n s t a t e i n t h e HPA m o i e t y ( V 0 2 + ) w i t h 0 a t t a c k i n g t h e c o o r d i n a t e d c y c l o a l k a n o n e t o g i v e a 2 peroxo r a d i c a l . Do you f a v o u r O2 p l a y i n g a r o l e w i t h i n t h e HPA m o i e t y o r w i t h i n t h e organic moiety ? BREGEAULT [ U n i v e r s i t g P . e t M. E u r i e , P a r i s , France) : The e q u a t i o n s o f t h e i n t r o d u c t o r y p a r t a r e n o t t h o s e o f a mechanism [ i . e . elementary processes) b u t o n l y t h o s e of t h e presumed o v e r a l l process. Scheme 2 shows t h e f o r m a t i o n o f i n t e r m e d i a t e vanadium [ I V ) species, b u t o m i t t h e f o r m a t i o n o f an a l k y l p e r o x i d i c complex which would i n v o l v e f r e e radical-dioxygen-vanadium i n t e r a c t i o n . T h i s i n t e r m e d i a t e s p e c i e s c o u l d a s s i s t r e o x i d a t i o n o f vanadium [ I V l . A t p r e s e n t , we have no e x p e r i m e n t a l r e s u l t s which show t h e p r e f e r r e d i n t e r a c t i o n o f d i o x y g e n w i t h t h e o r g a n i c r e s t . so t h e t h i r d and f o u r t h s t e p o f t h e mechanism [Scheme 21 indeed. has t h e c h a r a c t e r o f a p r o p o s a l . J.-M.
R.A. SHELDON [ANDEND, The N e t h e r l a n d s ) : Do any o f t h e oxometalate o r vanadium c a t a l y z e d o x i d a t i v e cleavage o f 3 . 2 - d i o l s a l s o work under n e u t r a l o r b a s i c conditions ? J.-M. BREGEAULT [ U n i v e r s i t b P. e t PI. C u r i e . P a r i s , France) : V i c i n a l d i o l s c a r a l s o be c l e a v e d by some HPA-salts, b u t t h e r a t e o f r e a c t i o n . t h e c o n v e r s i o n and t h e y i e l d s a r e lower t h a n t h o s e o b t a i n e d w i t h HPA-2. I t s h o u l d be m e n t i o ned t h a t r e o x i d a t i o n o f t h e reduced f o r m [ s l i s c o n t r o l l e d by t h e a c i d i t y f u n c t i o n of t h e medium.
H. MIMOUN ( I n s t i t u t FranCais du P e t r o l e , RueiZ-Malmaison, France) : What i s t h e s t a b i l i t y of t h e HPA d u r i n g t h e cleavage r e a c t i o n ? J.-M. BREGEAULT [ U n i v e r s i t Q P. e t M. C u r i e , P a r i s . France] : The s t a b i l i t y o f PPA-n u n d e r our r e a c t i o n c o n d i t i o n s has n o t y e t been s t u d i e d in d e t a i l , b u t t i l l now we have no e x p e r i m e n t a l e v i d e n c e o f i t s i n s t a b i l i t y . Work o n t h i s i s i n progress.