134

M.V. Klyuev and M. L. Khidekel'

andG. Tcrcnghi, Tran~iti,mMct ('hem.. 4. 3tlS(It179).-'2'M. Itidai and Y. Uchida, in 1. Ogata, Y. Ishii and M. Tsutsui (Eds.), Or ganotransition Metal Chemisto,, Plenum Press. New York 1975, p. 265. - t w) S. Otsuka. A. Nakamura. '1". Yoshida. NI. Narutu and K. ,Alaka. Y. Am. ('hem..S)~c., 05, 3lSO 11tl731 ,u \V IIoppc. Acla (,v~t,lh,,,'r.. A25. 67 (1969). -~'~ (i. Shcldrik. System of Computing Programs, University of Cambridge, 1976. - "'~ D. T. Cromer and J. B. Mann, Acta Crystallogr., A24, 321 (1968).- <7~ R. F. Stewart, E. R. Davidson and W. T. Simpson, J. Chem. Phys.. 3175 (1965). - tsl D. T. Cromer, Acta CO,stallogr., 18, 17 (1965). - i,~ L. J. Guggenberg, Inorg. Chem., 12, 499 (1973).- <"'~ J. Ishizu, T. Yamamoto and A. Yamamoto, Bull. Chem. Soc. Japan., 51, 2646 (1978). ill~ p. T. ('hcng. ('. I). ('hook. C. II. Koo. S. ('. Nyburg and M. "1". Shiomi. Acta (Yy.stallo.t~r., B27. 19(14 (1971).- ~,2, A. A. Savlcr.

Transition Met. Chem. 5, 134-139 (1980) H. Beall and ,I. F. Sieckhaus, J. Am. ('hem. Sot., 95. 5790 (1973). cl.;~ D. Brauer and C. Kruger. unpublished results (1972).- {14) j. K. Stulick and J. A. Ibers. J. Am. Chem. So('.. 92, 5333 (1970}. ~ts, (,. Kruger and Yi-Hung Tsay, J. Organomet. Chem,. 34. 387 (1972).- ~l,,J R. Countrwnan and B. R. Pcnfold. J. ('rvst. Mol. Struct., 2, 281 (1972). - ~'~ M. J. S. Dewar, Bull. Soc. ('him. Fr., l& C71 ( 1951 ). J. Chatl arm L. A. Duncanson, J. Chem. Sot., 2939 (1953). ~lm R. Mason and G. B. Robcrtson, J. Che,l. Soc. A, 492 (1969).i i,,~ A. McAdam, J. N. Francis and J. A. Ibers, J. Organomet. Chem., 29. 149 ( 1971 ).

( R e c e i v e d April 4th, 1979)

T M C 244

Reductive Amination of Carbonyl Compounds in the Presence of Cobalt and Rhodium Complexes Mikhail V. Klyuev and Mikhail L. Khidekel'* Tile hlstitute of Chemical Phvsics, U S S R Acadcnlv of Sciences, 142432 C h c r n o g o l o v k a , U S S R

Summary The reductive amination of carbonyl coMpounds in the presence of some cobalt and rhodmnl conlplexes has been studied. The selectivity and efficiency of the process is discussed using tile interaction of c v c l o h e x a n o n c with a n l n l o n i a as ;.In cxanlpie. The possible nlcchanism for the reaction is considered.

and Co( DMG )2(PPh) )2171, H( Rh( DMG )2C12]~''', H Rh( DMG )l,1 P h N H C H 2 R h ( D M G ) 2 ' PhNH2 Iml. C I R h ( D M G ) 2 P P h ) Iltl, [ORh(DMG)2OPPh3]21~21, R h l D S A and RhF11131, RhPy)CI2114~. and HIRh(DBG)2C12] II51. The conditions for carrying out reductive amination <"'~ and tile analytical nlethod for d e t e r m i n i n g the reaction mixtures
Introduction Reductive amination of carbonvl c o m p o u n d s is a pronaising route to various anlines. The h e t e r o g e n e o u s catalysts enlployed in this process It'21 usually hick s e l e c t M t v and

require elevated temperatures and prcssuresi The literature

Results and Discussion Reductive amimttion in tile presence o f c o b a l o x i m e s

data sllow t~ s> that the few nletal complex catalvsts used for reductivc amination still have no adxantages over the h e t e r o g e n e o u s catalysts. H o w e v e r , enzynles whose active centres involve transition metals arc capable of converting ((-

A solution of vitamin B 12r or its sinlplest model, diaquacobaloxinle, has been shown t L7~to catalyze the reaction of f o r m a l d e h y d e with aniline under very mild conditions according to Equation (1):

ketoacMs into <~-anlinoacids with high selectivity and under

Cll20

mild conditioils t"~. t fence, further research in tile field of complex catalysts seems very expedient. This p a p e r deals with reductive amination of carbonyl c o n l p o u n d s in the presence of some cobalt and rhodiunl complexes.

+

PhNH~

+ Co(DMG)2.2H,O+0.5H+ P h N H C H 2 C o ( D M G ) : • PhNH~

(/) ~ + H+ M e N H P h + [Co(DMG)2]

Experimental Tile complexes ...... cnlployed were o b t a i n e d as described earlier: C o ( D M G ) 2 . 2 t120. CICo(DMG)2Py, CICo(DMG)2PPI13

Atuhor to whom all correspondence shoukl bc directed. +* DMG - dimcthylglyoxime: IDSA = ixldigodisulphoacid: FL = Iluorcsccin: DBG = dibcnzylglyoxime. 034(>4285/8010306-01345(12.50/0

(1)

+ H+

Similarly, N-nlethvlaniline and C H , O react to yield N,Ndilnethylaniline, but the product yield was not i e p o r t e d 1~7). Our study of Reaction (1) under similar conditions has shown that ( , , I D M G ) : • 2 H , O forms only the complex (1), which is not ~cduced, even tinder elewlted hydrogen pressure. O t h e r cobah)ximcs used as catalysts tinder similar conditions: C I C o ( D M G ) e P P h 3 , C o ( D M G ) e ( P P h s ) 2 and C I C o ( D M G ) e P y led to the formation of neither reductive amination products

© Verlag Chemie, GmbH, D-6940 Weinheim, 1980

Transition Met. Chem. 5, 129-134 (1980)

Reductive amination of carbonyl compounds

nor any type (1) complexes. Prior activation of the cobaloximes by sodium borohydride, and elevation of the hydrogen pressure during the reaction did not give any positive effect either. Reductive amination of carbonyl compounds by a m m o n i a in the presence of cobaloximes were also unsuccessful. The use of diaquacobaloxime (II) resulted in the formation of products of the reaction between the complex, carbonvl c o m p o u n d , and anmaonia, but it was impossible to assign any particular structure to them such as, for example, that of (1). Thus, only C o ( D M G ) e • 2 HeO is somewhat active in reductive amination, forming stoichiometric amounts of type (1) complexes, Bv contrast, cobaloxime, which contains two other axial ligands (such as, CI, Py or PPh3) proved completely inactive.

was obtained in a study of H R h ( D M G ) 2 by x-ray photoelectron spectroscopy~22L Reduction does not affect the structure of the bis(dimethylglyoximate) ligand. Thus, the t l R h ( D M G ) e structure is ascribed to the product of H[Rh(DMG)2CI2] reduction. The sixth coordination position in the complex appears to be occupied by a water molecule. The H R h ( D M G ) : complex obtained proved to be an efficient catalyst for reductive amination of carbonvl comp o u n d s l m L ' S o m e specific features of the process have been revealed by studying the reaction between cvclohexanone and NH3.

The t{ffect of the NaBHv: H/Rh(DMG)2('I2/ ratio Since H R h ( D M G ) 2 was obtained in situ, we have studied the effect of the NaBH.+ : H/Rh( DMG)eCIe] ratio on the resulting catalytic activity. Figure 1 (Curve 1) and Table 1 show that as the NaBH.+ concentration increases the activity of the catalytic system increases, bringing about greater conversion of cyclohexanone. In all the following experirnents NaBHa was used in threefold excess over (2).

Redttctive atninatiotl in the presence <~1rhodoximes R h o d i u m complexes are known activate tLvdrogen more than their cobalt analogues ~ls' t,H. One might anticipate that this would be true for reductive amination as well. We believed that the most active rhodoxime would be a complex similar in structure to Co(DMG)_~. 2 H 2 0 . Such a complex can be obtained by treating dichlorobis(dimethy, lglyoximato) rhodium (III) (2), with sodium borohvdridel"L Though the reaction has been investigated eather I 2 ( 0 no rigorous evidence regarding the structure of the product was reported. Electrochemical study of the reaction has shown c ~ that reduction of (2) follows Scheme 1. •

Rhm(DMG)_,CI_+ ~

The effect of the catah,st cottcet~ltatioH

t

The parameter chosen to characterize the process was r/5. Figure 2 and Table 2 indicate that both the reaction rate (Curve 1) and the efficiency of the process (Curve 2) increase as the rhodoxime concentration increases. The shape of Curve 1 suggests that the reaction is first order in catalyst.

[RhI(DMG)e] - + 2 C I -

Rhm(DMG)2CI2 + [ R h I ( D M G ) : ] - - - + [RhH(DMG)2]: + 2CI

77ze e/]bet o f tetttperatttre

[ R h t t ( D M G ) : ] : + H, --, 2 H R h m ( D M G ) : Scheme 1

The efficiency of the process grows with telnperature (Figure 3. Curve 1, Table 3). The data in Figure 3 were used to calculate the reaction rate temperatt, re coefficients: from these the effective actiwttion energy of the reaction was calculated as 42 + 0.8 kJ mol ~.

More evidence that rhodium in the product of the reaction of H[RhIII(DMG)2CIe] with NaBHa has the oxidation state + 3

ga ] c

Selectivity of the process

100

~a o

= ca

gO

135

Promotion of amine formation is an important problem. With heterogeneous catalysts, in order to obtain primary amines selectively an excess of ammonia is used or weak acids or salts are added. The effect of cvclohexanone : NI-L ratio and of the presence of acetic acid and ammonium chloride on the selectivity (S), of the process has been studied. S was calculated according to the formula : S = 100 CpA/(CpA + CSA + CSKI), where CpA, CSA, CSKI are concentrations of the primary amine, secondary amine and secondary ketimine, respectively.

// !

ca

0

NaBH~ :H [RhIDMGIzCL2] Figure I. The effect of [NaBHa] on the degree of cyclohcxanone conversion, l - without AcOH, 2 - 11.3 M AcOH. Table I. The el'feet of the NaBHa : H[Rh(DMG):CI_,] ratio"' H[Rh(DMG):CI:] (10 :M)

N IBH.~ {10 :IX/I)

q'emp (o)

Time (rain)

1 1 1 1

1 1.5 3 6

45 45 45 45

61) 60 N) ~l)

2 2 2

3 6 t)

22 22 22

365 2(~5 13{I

AtOll (M)

('atah'sl con/position ('HN i'~ CttA "~

DCHA m

SKI ~

{I.3 11.3 0.3 {I.3

51 _8 ' ' 18 2

48 ~8 711 S t)

1 4 12 t)

-

611 t) S

13 10 5O

17 57 42

8n 24 -

,o PH2 = 1 atm, MeOH. 0.2 M ketone, 0.5 M NHa: h~ (?FIN = cyclohexanone; amine; ':) SKI = secondary ketimine: ~ Plus 2°~ cyclohexanol.

~ CHA = cyclohexylamine;

u~ DCHA = dicyclohexyl-

136

Transition Met. C h e m . 5, 134-139 (1980)

M . V . Klyuev and M. L. Khidekel'

Q/

30

~--

Table 3. The effect of temperature on the reductive amination "~

30

20

::~

E

E

=_

10 10 /

@

o\ I

I

I

0 1 2 3 H[RhIOM6) z CIz] 10-2mo1./-~ Figure 2. W,,(Curve ]) and ~/5 (Curve 2) vs. rhodoximc concentration. For the conditions see Table 2. Table 2. The effect of catalyst concentration "} Catalyst (l(I ~M)

NaBH4 (10 ~M)

5 10 2(1 30

15 30 60 90

Catalyst composition (%) C H N TM CI-IA ~1 19 18 1 2

79 711 89 71

Temp (o)

Time (min)

AcOH (M)

Catalyst composition (%) S C H N '1 C H A cl D C H A d l S K V ~ (%)

9 15 25 35 45 55 15 25 35 45 55

60 60 60 60 60 60 6/) 260 130 6(1 150

0.3 0.3 1).3 0.3 0.3 0.3 -

94 63 60 39 18 19 96 62 17 34

1 10 11 6 12 8 5 8 49 38

1 3 5 3

83.5 73 70 90 85.5 90 100 84.5 72.5 35 38

"~ PH, = 1 atm, M e O H , ketone 0.2 M, NH3 (1.5 M, complex (2) 1 • 10 2 M: "~ C H N = cyclohexanone: "J C H A = cyclohexylamine; ,u D C H A = dicyclohexylamine: "~ SKI = secondary ketimine.

DCHA m 2 12 1fl 27

60

5 27 29 55 70 73 4 32 29 29 25

0 "-"0.---.....~ 0........_.~ 0 ~

/o

60 ct~ /

O

2O

0

"~ Pn: = 1 atm, ketone (I.2 M, NH 3 0.5 M, M c O H , A c O H 0.3 M, T = 45 °, t = 60 min: h~ C H N = cyclohexanone: ~~ C H A = cyclohexylamine; d~ D C H A = dicyclohexylamine.

2 [NH3] [Cyctohexanone]

Figure 4. The effect of [NH3] on the process selectMty. For the conditions see Table 4.

I

e

160

Table 4. Reaction mixture compositions in the experiments on the effect of the cyclohexanone : NH 3 ratio "~

120

~

io

NH 3 : cyclohexanone

Catalyst composition (%) CHNt, I C H A ~1 D C H A m SKI ~1

1 1.5 2.5 3 4 5

30 59 44 27 37 45

80

0

I

0

20

i

40 Temp I°1

i

60

Figure 3. Temperature dependence of r/5. Curve 1 - without A c O H , Curve 2 - with A c O H 0.3 M. For the conditions see Table 3. W i t h a c y c l o h e x a n o n e : N H 3 ratio in t h e 1 : 1 to 1 : 5 r a n g e , s e l e c t i v i t y is m a x i m a l at c a . 1 : 2.5. A t h i g h e r c o n c e n t r a t i o n s o f N H 3, s e l e c t i v i t y d r o p s b e c a u s e o f s e c o n d a r y k e t i m i n e a c c u m u lation in t h e m i x t u r e ( F i g u r e 4). T h u s , by v a r y i n g t h e N H 3 concentration one may attain maximum selectivity (70%). A c e t i c acid c a t a l y z e d c o n d e n s a t i o n o f c a r b o n y l c o m p o u n d s with a m m o n i a a n d with amines(23~; h e n c e it a c c e l e r a t e s r e d u c tive a m i n a t i o n g e n e r a l l y . T h i s fact is c o n f i r m e d by t h e effective rate c o n s t a n t v a l u e s , c a l c u l a t e d at t = 45 ° a n d C T M = 1 - 1 0 - a m o l • 1-I : K d f with A c O H w a s 0.11231 m i n - l : w i t h o u t A c O H 0 . 0 1 4 4 m i n -1. A s s e e n f r o m t h e k i n e t i c c u r v e ( F i g u r e 5), t h e yield o f t h e p r i m a r y a m i n e is a m a x i m u m at ca. o n e h o u r a f t e r t h e b e g i n -

,n P n : = 0.1 M, anone; amine;

20 19 38 48 41 33

45 18 9 12 6 1

3n 4 9 13 16 21

1 atm, c o m p l e x ( 2 ) 5 . 10 3 M ; N a B H 4 15. lfl 3 M , ketone T = 45 ° , t = 60 min, M e O H ; b~ C H N = cyclohexc~ C H A = cyclohexylamine; " D C H A = dicyclohcxyl~ SKI = secondary ketimine: n plus 2% cyclohexanol.

ning of reaction. Therefore, the duration of the experiments dealing with the effect of AcOH on the selectivity was one hour. A s t h e A c O H c o n c e n t r a t i o n i n c r e a s e s f r o m z e r o to 0.2 M , t h e s e l e c t i v i t y g r o w s , to b e c o m e v i r t u a l l y c o n s t a n t at h i g h e r c o n c e n t r a t i o n s ( F i g u r e 6). T a b l e 5 lists t h e c o m p o s i t i o n s o f t h e r e a c t i o n m i x t u r e s o b t a i n e d w h e n s t u d y i n g t h e A c O H effect o n selectivity. A d d i t i o n o f A c O H d o e s n o t affect t h e b a s i c laws g o v e r n i n g t h e r e a c t i o n b e h a v i o u r . F o r e x a m p l e , in t h e p r e s e n c e o f A c O H , t h e c a t a l y s t activity also g r o w s with t e m p e r a t u r e ( F i g u r e 3, C u r v e 2), t h o u g h S in this c a s e is p r a c t i c a l l y c o n s t a n t ( T a b l e 3). A s i m i l a r s i t u a t i o n is o b s e r v e d in e x p e r i m e n t s with d i f f e r e n t N a B H a c o n c e n t r a t i o n s ( F i g u r e 1, C u r v e 2). K i n e t i c

Transition Met. Chem. 5, 129-134 (1980)

Reductive amination of carbonyl compounds

137

100~ 100{

-a 60

\\/...,,/"

80-

ko

~0

/

\

Q

40

20

o

Q '~-'¢'¢~ , "~."

/~..~ °"°'-o "--J

g0

,

,

7

80

120

I%

0

40

120 Time [rain)

Figure 7, Reductive amination of cyelohexanone by NF|~. @ - cvclohcxanonc, ql) - c y c l o h e x y l a m i n c , ~ - dicyclohexylamine, © - secondary ketimine. The conditions arc similar to those in Figure 5 except

Time Iminl Figure 5. Rcductivc anfination of cvclohexanonc bv NH~. ~-~ - cvclohexanone, q[) - cyclohexylaminc. ~ - dicvchdlcxvlamine. Con-

ditions: Pn2 = 1 atm, MeOH, T = 45 °, H[Rh(DMG)2CI2] 0.01 M, NaBH4 0.03 M, ketone 0.2 M, NH~ 0.5 M, AcOH 0.3 M.

for the presence of AcOH.

~° 2 4 I eo _?

100

/o/<'o °----°

o

o 08

-g

i

0.3

200

50

/O

~0

03 Ac0H (rn0l [-11

Figure 6. The effect of AcOH on selectivity of the process. For conditions see Table 5. Table 5. The effect of added AcOH '° AcOH (M)

Catalyst composition ( C,~) CFIA i" CHN ~'

0.05 0.1 0.15 0.2

42 66 60

30 12 23

67

0.3 0.4 0.5 0

70

22 18 19 25 17

71 67 29

i

n

d

160

Figure 8. l,g C c y c l o h . . . . . . . . . as a function of T. qD - without AcOH, (5) with 0.3 M AcOH. For conditions see Figures 5 and 7.

40 01

i

80 120 Time IrninI

DCHA dt

SKV I

28 22 17 I1

trace tracc trace

12 10 8 49

/race trace trace trace 5

~'~ P~ = 1 alto, McOH, ketone 0.2 M, NH~ I).5 IVl, T = 45 °, complexes (2) 0.01 M, NaBH4 0.03 M, t = 60 min; b~ CHA = cyclohexylamine; " ('HN = cyclohexanone; d~ DCHA = dicyclohexylamine; ~ SKI = secondary ketimine.

via f o r m a t i o n of cyclohexylamine and N-cyclohexylcyclohexylimine (secondary ketimine). T h e main product of reductive a m i n a t i o n is dicyclohexylamine, T h e fact that in the presence of A c O H only trace a m o u n t s of secondary k e t i m m e were found is due to acceleration of ketimine hydration to dicyclohexylamine in the presence of AcOt-t ~23~, T h u s , reductive a m i n a t i o n may be regarded conventionally as consisting of two stages. In the first, s p o n t a n e o u s or acidcatalyzed interaction of the carbonyl c o m p o u n d with a m m o n i a or with an a m i n e , lead to the product c o n t a i n e d an imino g r o u p (or Schiff's base) viz : ~ ( ' = O + N H , R ------~ /~" C = N R R = H, alkyl or aryl .

T h e second stage involves h y d r a t i o n of the u n s a t u r a t e d comp o u n d on the catalyst and a p p e a r s to follow the m e c h a n i s m c o m m o n for imines and Schiff's bases i.e. : H R h ( D M G ) 2 + / C = N R ~ "~..(_'-NRH

P

The mechanism o f reductive amination o/ carbonyl compounds in the presence of rhodoximes A c c o r d i n g to the kinetic curves, both in the presence (Figure 5) and absence (Figure 7) of A c O H , the process occurs

(3)

Rh(DMG)e Rh(DMG)2C-NRH

curves (Figures 5 and 7) show that when A c O H added, the reaction retains its first o r d e r in c y c l o h e x a n o n e (Figure 8). T a b l e 6 presents results of e x p e r i m e n t s c o n d u c t e d in tile p r e s e n c e of NH4CI. T h e selectivity sharply increases as [NH4CI] increases, h o w e v e r , the degree of conversion of the c a r b o n y l c o m p o u n d is lower t h a n in reductive a m i n a t i o n without NH4CI.

+ H~O

+ HRh(DMG)2

1

~CHNRH

+ [Rh(DMG)2]2

R = H, alkyl or aryl. H R h ( D M G ) 2 is then r e g e n e r a t e d according to Scheme 1. T h e i n t e r m e d i a t e complex (3) involving a R h - C b o n d , was isolated and identified from the reaction of aniline with formaldehyde ~m. _,21. With stoichiometric a m o u n t s of H R h ( D M G ) > c y c l o h e x a n o n e and NH3, it was impossible to ascribe any definite structure to the product, possibly because in this case t h e r e is no b e n z e n e ring to exert a stabilizing effect, T h e fact that a m i n a t i o n using d i a q u a c o b a l o x i m e ( I I ) stops at the stage of a[kyl complex f o r m a t i o n may be regarded as

138

M . V . Klyuev and M. L. KhidekeF

Transition Met. Chem. 5, 134-139 (1980)

Table 6. The effect of added NH.~(TF'~ NH~('I (M)

('atalysl composition ((4) CHN b~ CHA~

tl.05 O.2

44 68

S {c~ )

DCI iA,h

47

9

27

5

83 93.5

"~ For thc conditions see Table 5 with the cxccption ol t b) CHN = cyclohexanone; o C H A = cyclohexylamine: = di-cyclohexylamine.

ISll rain: m DCHA

f u r t h e r e v i d e n c e that the C o - C b o n d is f a M v s t r o n g . It is n o t e w o r t h y that the C o - C b o n d in c o b a l o x i m e s is s t r o n g e r than the R h - C b o n d in r h o d o x i m e s ~v~) T h e catalytic b e h a v i o u r o f the r h o d o x m a e series d i s p l a y e d an exciting f e a t u r e 124~, n a m e l y , the s t r e n g t h o f the r e s u l t i n g R h - C b o n d a n d , a c c o r d i n g l y , t h e catalytic activity of the c o m plex p r o v e d to be d e p e n d e n t o f the ligand in thc trans-position. T a b l e 7 illustrates the catalytic activity o r d e r o f the HRh(DMG)_~L type c o m p l e x e s for axially p o s i t i o n e d L : HzO > O P P h 3 > PPh~. This o r d e r is the s a m e as that for hydrogenation of C=C and C=O bonds.

Reductive amination in the presence o f other rllodium contph'xes T h e r h o d i u m c o m p l e x e s RhPy3CI3, R h ( f l u o r e s c e i n ) . R h ( i n d i g o d i s u l p h o a c i d ) , and d i c h l o r o b i s ( d i b e n z y l g l y o x i m a t o ) r h o d i u m ( I l l ) (an a n a l o g o f H I R h ( D M G ) ~ C I 2 ] ) have b e e n e v a l u a t e d as catalysts for h y d r o g e n a t i o n o f u n s a t u r a t e d b o n d s . T h e c o m plexes w e r e a c t i v a t e d by a t h r e e - f o l d excess o f s o d i u m b o r o h y d r i d e a n d the results are p r e s e n t e d in T a b l e 8. E x c e p t for H[Rh(DBG)2CI_,] all the c o m p l e x e s d e c o m p o s e in the c o u r s e of r e d u c t i v e a m i n a t i o n , e v i d e n t l y in the p r e s e n c e

Table

o f a m m o n i a . W e can thus infer that a c o m p l e x catalyst for r e d u c t i v e a m i n a t i o n m u s t p o s s e s s , a l o n g with the c a p a c i t y to a c t i v a t e m o l e c u l a r h y d r o g e n , stability t o w a r d s a m m o n i a a n d a m i n e s . T h e s e two r e q u i r e m e n t s are m e t by highly c o n j u g a t e d r h o d i u m c o m p l e x e s with d i m e t h y l - a n d d i b e n z y l g l y o x i m e s . T h e use o f H R h ( D M G ) : a p p l i e d to an a c t i v a t e d coal d e c r e a s e s the r e a c t i o n rate a p p r o x i m a t e l y t w o f o l d . W h e n used r e p e a t e d l y , t h e catalyst b e c o m e s less e f f i c i e n t . T h e r e a c t i o n p r o c e e d s in the s a m e d i r e c t i o n as with the h o t n o g e n e o u s catalyst (with p r e d o m i m m t f o r m a t i o n o f a m i n e s ) . U n d e r similar c o n d i t i o n s 5 % R h : C was inactive as a catalyst.

References

~ljW. S. Emerson, Org. Rea('t. 4. 174 (19481. - ~2~ M. Freifeldcr, Practical Catalytic Hydrogenation. New York, Wiley. 1971L p. 3 3 3 . 131 L. Mark6 and .1. Bakos, J. Organometal. Chenl.. 81, 411 (1974).~'~ M. Murakami, K. Suzuki and ,1. W. Kang, Nippon Kagaku Zasshi, 83, 1226 (1962). - ~5~ M. Murakami, K. Suzuki, J. W. Kang and M. Fujishige, Nippon Kagaku Zasshi, 85, 235 (19641. - " " M. Sund, H. Dieter, R. Koberstein and J. Rasched, J. Mo[. 6)md., 2, 1 (19771.17~ G. N. Schrauser and J. Kohnlc, Chem. Bet-., 97. 31156 (1964). cs) L. A. Chygaycv, Seh,cled Works, vol. 1, Moscmv. Akad. Nauk SSSR, 1954, p. 326. - ~''~ J. H. Weber and G. H. Schrauser, J. Am. Chem. Sot'., 92, 726 (19701. -
7. Reductive amination of cyclohexanonc by Nt-I~ in the presence of rhodoximc catalysts "~

Initial comp lexh~

Tcmp (°)

Time (h)

Catalyst composition (c;-) CHN ° CHA d~

H[Rh(DMG)2CIe] CIRh(DMG),PPh~ [ORh(DMG)2POPh~]e

45 42 42

3 5 3

13 98 58

23 20

D C I t A ~'~

SKI u

CHLi~ trace

59

5

--

--

-

-

2

22

a) Pll2 = 1 atm, complex 0.01 M; NaBH4 0.03 M. ketone 0.2 M, NH~ 0.5 M: b~ after reaction with NaBH 4 the structures are supposedly H R h ( D M G ) , , ' H 2 0 , HRh(DMG)2PPh3 and HRh(DMG)2POPh 3 respectively; ~) CHN = cyclohexanone; J) C H A = cyclohexylamine; ¢) D C H A = dicyclohexylamine; ~) SKI = secondary ketimine; " CHL = cyclohexanol.

Table 8. Reductive amination in the presence of certain rhodium complexes "~ No. Complex

Carbonyl comp. : NH~

Temp (°)

1t" Rh(indigodisulphoacid)

1 :3

50

2 Rh(indigodisulphoacid)

3 1:1.5 1:2.5 1 : 2.5 1 : 2.5 1:2.5

50 20 73 45 45 45

3 Rh(fluorescein) 4 RhPy3Cl 3 5 H[Rh(DBG)2Cle] 6c~ 5% Rh : C 7 d) HRh(DMG)e . H 2 0 : C

1 :

Time (h)

6

10 9 6 2 2 3.5

Solvent

MeOH MeOH MeOH DMF MeOH MeOH MeOH

Catalyst composition (%) carb. primary sec. comp. amine amine 98 100 10 76 4 100 13

-

. 36 20 46 . 51

ketimine

-

.

.

. 47 47 . 36

alcohol

-

2

3 -

4 4 3

-

-

.

.

") P ~ 2 = ~ a t m ~ c ~ m p ~ e x ~ . ~ M ~ N a B H ~ . 0 3 M ~ i n r u n s ~ 3 a n d 5 ~ 7 c v c ~ h e x a n ~ n e ~ . 4 M ~ i n r u n ` 4 M E K ~ . 4 M ~ ~'~ P ~ , = 8 . 4 a t m ; 0.327g catalyst; d) Run 7, AcOH 0.3 M; concentration of Rh in the deposited catalyst is 3wt% which corresponds to0.(ll M.

c) R u n 6 ,

Transition Met. Chem. 5, 139-145 (1980)

Thermoelectric power and electrical conductivity of V2Os-TiO 2 mixtures

776-78.- {tT~ G. N. Schrauser and R. J. Windgassen, Nature, 214, 492 (1967).-IJ"~B.G. Rogachcvand M. L. Khidekel',Izv Akad. Nat& SSSR. ser. khim., 141 (1969).- iv~l V. B. Panov, M. L. Khidckcl" and S. A. Shchepinov, Izv. Akad. Nat& SSSR, ser. khim.. 2397 (1968). lem j. D. Miller and F. D. Oliver, J. Chem. Soc. Dalton Trans., 2469 (i972). ~21~M. V. Klyt.cv, M. L. Khidekel' and V. V. Strelets, 7)'ansition Met. Chem., 3, 380, 11978).- I-~21M. V. Klyuev, B. G. Rogachev, Yu. M.

139

Shulga and M. L. Khidekel', lzv. Akad. Nauk SSSR. ser. khim.. 1869 (1979). - ~2~ Zh. Yungcrs and L. Sagyus, Kinetic .Ah'thod~ ol h;l'cstigating Chemical Processes. Khirniya. Leningrad. 1972. p. 41111(in Russian). - 12..~M. V. Klyuev, B. G. Rogachcv and M. k. Khidckcl'. lzv. Akad. Nauk SSSR, ser. khim., 2621!, (1978).

(Received March 29th, 1979)

T M C 239

Studies on the V2Os-TiO-, System Part 1. Thermoelectric Power and Electrical Conductivity Enrique Pereira* Centro de Investigacidn y Desarrollo en Procesos Catal/ticos C I N D E C A )

Luis A. Gambaro and Horacio J. Thomas Universidad Nacional de La Plata, Consejo National de Investigaciones Cientificas y Tdcnicas and Comisidn de Investigaciones Cientfficas de la Provincia de Buenos Aires, Calle 47 n ° 257, 1900 La Plata, Argentim~

Summary The thermoelectric power and the resistivity of V_~Os-TiO_, mixtures over ranges of composition and temperature from 20 ° to 500 ° in air have been measured. The mixtures were obtained by coprecipitation of aqueous solutions of NHaVO~ and TiCI4, calcined during 90 h at 550 ° and then sintered. Resistances were measured by the four points method. At the VOs/2 35-100% M range, the activation energies for conductivity change from 0.36 to 0.62eV, while for the thermoelectric power they change from 0.18 to 0.24eV. It can be assumed from these values that the conduction mechanism over this concentration range is due to the " h o p p i n g " of small polarons, arising principally, from the presence of V 4+ ions. In the samples with a high TiOe content, the activation energies for conductivity were 0.82 and 0.36eV, for the different samples. From the variation of thermoelectric power with temperature, it can be assumed that the ionization energy of the donors centers lies at 0.83eV under the conducting band. A mechanism for band conduction is inferred from the results, being the V 4+ donating centers and the V 5+ receptive centers.

Introduction The V 2 0 ~ T i O 2 system is largely employed as a catalyst in reactions of industrials importance, such as the naphthalene and o-xylene oxidation to phthalic anhydride. Nevertheless, only a few reports can be found in literature studying catalysis from a structural point of view, in order to find a correlation between physical properties and catalytic activity.

* Author to whom all correspondence should be addressed.

© Verlag Chemie, GmbH, D-6940 Weinheim, 1980

Sterligova el) studied, by e.p.r, spectroscopy, different mixtures of V205 and TiO2 and found the V 4+ signal due to the non-stoichiometry of V205. From x-ray diffraction measurements, it was concluded that both oxides form neither solid solutions nor compounds over the whole concentration range. Vanhove 12~came to the same conclusion from results with sampies of low TiO2 content, although for samples with high content, in which TiOx is found as anatase, a slight contraction in the lattice parameters of the anatase was observed, and was explained starting from the suposition that V 4+ (ionic radius, 0.63 /k), replaces Ti 4+ (ionic radius, 0.68/k) in the anatase lattice. The anatase-rutile phase change is produced with a ca. 35% molar TiO~ content. There is no bibliographic data with regard to the electrical properties of the V2Os-TiO2 system. Kristensen c~l studied the VO2-TiO2 system and measured the thermoelectric power and electric conductivity, and presented evidence for a conduction mechanism involving small thermally activated polarons: he observed that the Seebeck coefficient varied slightly with temperature, while the electrical conductivity increased exponentially with activation energy, 0.24eV. There are several reports on the electrical properties of V205 ('1~10), including some single crystal studies I v ' ' and polycrystalline samples ~7 m~. The activation energies, from conductivity measurements given by the different authors, are approximately equal for the polycrystalline and lhc ones obtained for each of the crystallographic axes of single cr>slals (independently of the measured axis}, and oscillate between 0.19 and 0.23eV. Nevertheless, there are differences concerning the conduction: while some authors ~s s) propose a small polaron conduction mechanism, others ~ 4 ' ' ~'~ discuss a mechanism involving narrow bands. Different authors (l~-131 have studied the thermoelectric power of rutile and obtained activation energies of 0.08eV. 0340-4285/80/0306-0139502.50/0