Low oxidation states ruthenium chemistry VI. Stoichiometric and catalytic oxidation by molecular oxygen of primary amines bound to dichlorobis(triphenylphosphine)ruthenium(II)

Journal

of Molecuiar

Catalysti.

15 (1962)

297

297

- 308

LOW. OXIDATIOPI: STA-I!XSRUTHECHEMISTRY VI+. STCICIZIC~TRIC ANI3 CATALYTIC OXTDATICN BY MOLECULPtR OXYGEN OF PRIMARY AMINES BOUND To DIC~OROBIS(TRlPHENYLPHOSPHINE)R~~(II)

SERGIO CEhllE-,

FRANCESCA

PORTA end MADDALENA

Istiflrto di Cizimico Genenrte and CNR (Received Jazwry

Center,

Viu Venezian

21,

PIZZO’TTI 20133

Milan

({tab)

29.1981)

Under a stict nitrogen atmosphere RQPPh,)sCE, reacts with primary amines to give the complexes, Ru(PPh3)2(RNHZ)2Ci, ER = H (I), CH3(CH2)4 (II), CBH,CH, (III), p-CH3CC6H4 (rV)) _ Chelating ligands such as &methyl1,2-pheny!enediamine, ethylene&amine, benzoylhydraxylamine and henzoylhydrazine give the complexes Ru(PPh,),(cheE)C1,, (V) - (VJII)_ to compounds (I) - (V) react tith moIecL&r oxygen at room kemper2twe give different products depending on the nature of R, while compounds (VI) - (VIII) are stable with respect to oxidation by Oz. Compound {IfI) 2cts as a catalyst in the oxidation of benzylamine to benzonitrile with moIecuku oxygen at 80 “C. The reaction of (III) with molecular oxygen has been followed by ESR spectroscopy, and the intermediate formation of paraaagnetic ruthenium-(III) species has been detected.

Introduction Recently it has been reported that ‘ruthenium trichloride’ is a catalyst for the oxidation of amines by molecular oxygen [I] _ On the other hand it is know-n that Ru(PPh,)&1, readily reacts with molecuiar oxygen, and this complex can act as a catalyst in the oxidation of compounti such &s triphenyIphosphine and cyclohexene [2] _ We have thus synthesized ruthenium(II) complexes having tiphenylphosphine and amines as ligands, and their reaction with molecular oxygen has been investigated. The deprotonation of nitrogen donor ligands by transition meti peroxo complexes in low oxidation state has been previously studied, and it has been shown that two protons of two adjacent atoms of compounds such as *Park V: 5ee ref. 2. **Author TV whom correspondence shouId he addressed. 0 Ekevier Sequoia/Printed in The Nether1aad.s

benzoylhydrazine and benzoylhydroxylamine are displaced by the peroxo group to give hydrogen peroxide and new unsaturated organic ligands [3]. In the present work we have found that aliphatic amines can be catalytically oxidiied to the corresponding nitriles by molecular oxygen in the presence amine)&!, as catalysts. However ESR studies of the complexes Ru(PPh,),( suggest that the action of dioxygen is that of oxidizing =uthenpclm(LT) to ruthenium(III), TNith no evidence for the intermediate formation of ruthenium-peroxo complexes. ’

Experimental Solvents were dry and purified_ The starting complex, Ru(PPh,)3C1,, was prepared by a published procedure 141. Pentyl- and benzylamines were

distilled under nitrogen before use and stored under nitiogen. IR spectra were obtained using Perkin Elmer 457 and Beckman 4210 spectrophotometers. ‘H NMR spectra were recorded on Varian 60 and 100 spectiometers, with Me,Si as internal standard. ESR spectra were taken on a Varian E 109 instrument operating at X-band frequencies. Elemental analyses were carried out in the analytical laboratory of Milan Univ&..ity, except for oxygen analyses which were carried out by Pascher’s Analytical Laboratories. Bonn.

Ammonia was bubbled through benzene (50 ml) for 30 min with magnetic stirring. Solid Ru(PPh,),Cl, (0.6 g) was added. The product precipitated from the initial yellow solution_ After one hour it was filtered off, washed with benzene and dried in uacuo. Ru(PPh.),ICH,(~H~),NH,),CI, (II) To benzene (25 ml) pentylamine (0.146

g) was added under a nitrogen atmosphere. The solution was cooled with dry ice/acetone and evacuated (0.1 mmHg); then the temperature was raised to 20 “C and d:Aitrogen was

admitted. This procedure was repeated three times. Solid Ru(PPhg)&la (0.4 g) was added to the cooled solution, the flask was then evacuated and filled with dinitrogen, while the temperature was allowed to rise to 20 “C. Magnetic stiing was applied. After 5 h the yellow solution was evaporated to a small volume, n-hexane degassed with dinitrogen was added with a syringe through a serum cap, and the precipitate was filtered off under nitrogen and washed with n-hexane degassed with nitrogen. The product was stored under nitrogen_ Rrri~Ph,),(PhCE;r,NN2),CL, (rri) This compound was prepared as described (25 ml), PhCH,NH2 (0.177 g) and Ru(PPh,),Cl, stored under nitrogen.

for (II) by using benzene (0.4 g). The product was

299

Ru(PPh31,~p-CEf,0C6~~NH2)2C11 (IV) This compound was prepared as described for (LI), by using benzene

(30 ml), p-CEE$XsH&Hz (0.206 g), Ru(PPhs)zClz (0.4 g), for 6 h. The product was stored under nitrogen.

CH3

0

NM2

a NH2 (0.05 g), benzene (25 ml) Ru(PPh,)3Clz (0.4 g) and was added under a nitrogen atmosphere. Magnetic stirring was applied. After 20 h the solution was evaporated to a small volume and n-hexane was added. The precipitate was filtered off. It was crystallized from benzene n-hexane under nitrogen, by filtering off a violet material occasionally present and insoluble in benzene. To

To a solution of N;i2(CH2),NH2 (0.028 ml) in benzene (10 ml), Ru(PPh,),CE, (0.2 g) was added. Magnetic stirring was applied. dfter 4 h the initial green solution became a yellow-brown suspension. A dark green by-product was filtered off. The resulting solution was evaporated to a small volume and by addition of n-hexene the ochre-yellow product was obtained. It was filtered off, washed with n-hexene and dried in vacua. The same compound was ob’r;ained by conducting the reaction under a nitrogen atmosphere. Ru(PPh.),CPhC(O)NHOH)CI, (VII) This compound was prepared as described for (If). by using benzene

(15 ml), PhC(O)NHOH (0.057 g) and Ru(PPhs)sC12 (0.2 g). After 5 h the green precipitate was filtered off, washed with ethanol end dried in vacua. The same compound, which is insoluble in the common solvents, was obtained by conducting the reaction under a dioxygen atmosphere. This compound was prepared as described for (II), by using benzene (22 ml), PhC(O)NHNHz (0.085 g) end Ru(PPh,),Clz (0.3 g). After 5 h the yellow-orsnge sok&ion was evaporekd to a small volume; by addition of n-hexane the yenow compound precipitated. It was filtered off, washed with n-hexane and dried in vac~o. The same product was obtained by conducting the reaction under a dioxygen atmosphere.

To Ru(PPhs),Cl, (0.6 g) and p-CHs0Cs&NH2 (Cl.153 g) benzene (40 ml) was added. The blue-violet suspension was left under stirring for 20 h in air. A red-violet compound was filtered off and washed repeatedly with n-hexane. It was refluxed in ethanol under nitrogen with a fivefold

3G0

excess of PPha for 5 h. The product, which is slightly soluble in benzene, was filtered off, washed with n-hexane and dried in uucuo. The crude product can also be purified by crystallization from CHCl,/n-hexane, obtaining a complex which clathrates one mole of chloroform (C&d; C, 57.8; H, 4.4; N, 2.6. Found: C, 58.5; H, 4.3; N, 2.4), and with IR and ‘H NMR spectra identical to those of (IX). [Ru(PhCH,NH,),(PhCN)]

2c2CL- (XI)

To toluene (30 ml) benzylamine (2.2 ml) was added. The so!ution was refluxed while dioxygen was bubbled through. Solid Ru(PPhs)sClz (0.4 g) was added. The initial yellow-brown solution was refluxed for 6 h and then cooled and left under stirring with dioxygen bubbling for 12 h. The orange crystalline product was filtered off, washed with 9 little water, ethanol and dried in uccuo.

Reactions of the complexes with dioxygen (i) (III) ‘and Oa_ D’Ioxygen was bubbled through benzene (30 ml) for 10 min. Compound (III) (0.25 g) was added. A green colour immediately appeared. The g-reel1solution was left stirring with dioxygen bubbling for 2 h. The green solution was evaporated to a small volume and n-hexane was added. The crude, green material was washed repeakdly with ethyl ether and/or crystallized from benzene-n-hexane in order to remove triphenylphosphine oxide [m-p. = 138 - I45 “C; u(NH)(?) = 3300 cm-‘; p(C-N) = 2200 cm-l ; Y (Ru-Cl) = 320 cm-r ; ‘I3 NMR in CDCl, : no signals between 4 and IO r; nonconductor in nitrobenzene. Average elemental analyses: C, 58 - 59; H, 4.7 - 4.8; N, 3.9 - 4.0; Cl, 9.5 - 10.0; 0, 1.9; P, 4.9; m-w., 800 900 in CHCl, and benzene. (ii) (IV) and Oz. When dioxygen was bubbled through a dilute solution of (nr) in benzene, a red-violet colour immediately appeared. _4fter 6 h the sclution was evaporated to a small volume, and by adding n-hexane a redviolet compound with an IR spec&um comparable to that of (IX) was obtained. (iii) (V) and OZ. Dioxygen was bubbled through benzene (25 ml) for 15 min. Compound (V) (0.16 g) was added. The red solution was left stirring with dioxygen bubbling for 24 h. The red precipitate was filtered cff and washed with n-hexane. It was crysklhzed from benzene-n-hexane, washed with hexane and dried in UCCKQ,obtaining the analytically pure compound (X).

Catalytic

reactions

The glass reactor, connectid with a buret, was filled with dioxygen. The solvent and the amine were introduced and the system was thermostatted

at the desired temperature. The solid catalyst was then added and magnetic siiting was applied. Samples of the solutions were periodically removed w-ith a syringe from a serum cap and analysed by gas chromatography. The analyses were carried out on a DAN1 3600 gas chromatograph, using a 2 m column Wed v&h LO% fzikoropropyl silicone on Chromosorb G 60 - 80 mesh (internal standardkation with nitropropane or lcyanotoluene).

Results and discussion Synthesis

of

ruthenium~ll)-amine

complexes

Under a strict nitrogen atmosphere, Ru(PPh3)3CI, reacts with primary amines according to eqn. (1) (Table 1):

TABLE Analytical

1

data= for ruthenium(E)

triphenylphosphine-amine

Campound

Colour

m.p. (%)

(1)

yellow-

Ii5

- 120

brown 98

(11)

@.lOW

WI)

yellow

133

(IV)

dark-

108

- 100

G=Y 165

(VI

216

(VII)

Cl&~yellow green

(VIIi)

@IOFV

146 - 148

(IX)

redviolet

21 % a

orange

220

orange

166 - 170

WI)

(Xl (XI) a Required vaIu= in parenthm. %xygenr 3.8 (3.4). c A(M) = 201 in mekhatol. “Oxygen absent. ePhasphonxs and oxygen absent.

‘G=

174 - Ii6

complexes c

E

N

Cl

w9”1

(4:;’

(3.8) 3.6

10.1 -(9.7)

(63.5) 66.4 (65.9) 63.4 (63.7)

(6.4) 5.2 (5.3) 5.4 (5.1)

(3.2) 3.2 (3.1) 3.0 (2.9)

7.6 (7.8) 7.6 (7.5)

63.8 (63-L) 60.1 (60.3) 62.3 (62.0) 62.1 (62.1) 64.2 (63.9)

4.9

3.3

(;::I (5.0) 4.2 (4.4) 4.7 (4.4) 5.1 (4.7)

%9”) (3.7) 1.6 (1.7)

9.3 (9.4) 8.0 (8.5)

$2) 3.0 (3.0)

(E, 7.3 (7.5)

-4.4 (4-7) (Z)

3.4 (3.4) (10.4) 9.8

68.9

63.5 (63.2) 61.9 (62.2)

4.i

3.7

-

(8.8) 8.4

302

Ru(PPh,),C12

+ 2RNKz

benzene R. ‘I’.

Ru( PPh, )* ( RNHz )sC1z +- PPh,

(I)

These diamagnetic derivatives react with molecular oxygen even in the solid state; however compounds (I) - (ELI) can be left in contact with air for some days without any evident reaction_ A compound analogous to (Iv) has been obtained by using p-CK3C6K4NK2 as ligand; however elementi analyses were not satisfactory_ Compound (IV) reacts with PPh, in refluxing ethanol under a nitrogen atmosphere giving Ru(PPh3),KC1, which was recognized by IR and ‘K NMR spectza. Much more stable compounds have been obtained when chelating diamines or nitrogen donor ligands having an aroyl group available for cdorclination have been used in this reaction (eqn. 2) (Table 1):

TABLE

2

Spectroscopic

data”

For ruthenium(II)triphenylphosphin+~ine

complexes bands

1E NMR

data

v(NH)

v(Ru-Cl)

Other

(1)

3375-3330-3245

325

6 (NH)

= 1605-1225

([I) (111)

3320-3290-3220 3315-324u

320

I -

= 1580

(IV)

3330-3230d

320

v,,(=C-+C) vs_(=C-*c) 6(pCH,)

(V)

3300-3205

-

6(NIi) u(C-N)

(VI)

3340-3300-3240

-

I

(VII)

3240

-

u(N-0)

(VIII)

3310-3240

-

v(C=O) = 1630; &NH) = 1560

-

(IX)

3280

320

u,,(=C-*C) = 1250-1125; sum(=C--O-C) = 1040-1015; &Ha) = 835-826

r(OC&) = 6.3 - 6.5; several signals between 3.5 and 4.37

(X)

3260

-

v(C=N)

= 1360

r(CHz

(XI)

broad bands at 3330 and 3100

-

u(C=N)

= 2200

r(C!Hz) r(NHz)

corn-

significvlt

pound

i(CH*) i(NH2) -

= 6.3b; = 6.gb

= 1550; = 1070

T(CH~) r(NHz)

= 7.8; = 5.4

= 1560; 1040

Complex 7- 7.57

= 1250; = 1035; = 830

= 910

‘IR cm-’ (in nujol); ‘H NMR in CDCl3. bUnder nitrogen atmosphere. =In DMSO. dO’her weak ahsorptions were observed at cu. 3300 cmmL_

sign&

et

-

) = 8.0 = 6.1=; = 5.5=

Ru(PPh,),Cl,

c chel +

[ chel: :H3a+;

Ru(PPh,),(chel)CI, (V). NH&CHzj2N&

+ PPh,

(2)

(VI), PhC(O)NHOH (VII),

T

PhC(O)NHNH,

(VIUj

I

.

With the exception of compound (VIE), these derivatives show the expected sign& in their ER and IH NMR spectra (Table 2). Compound (VII), which is InsoIuble in the common solvents, did not cleearlyshow a band in the IR spectrum attributib2e to the aroyl group, while or_Iy one band was detected in the 3500 - 3200 cm-’ region. The ‘H NMR speckurn of the benzylamine derivative (EE), which is extremely reactive towards molecular oxygen when in solution, has been obtained under a nitrogen atmosphere. En these conditions two distinct signals at&ibutabIe to the CH2 and NE2 groups have been detected. These signals showed a broadening only when the temperature was lowered to -50 “C. Reactions

with

molecutizr oxygen

Compounds (I) - (IV) readily react with molecular oxygen in benzene at room temperature, giving different types of products depending on the nature of R. However only the compound obtained from the oxidation of compound (IV) was a defined product (eqn. 3): Ru(PPha),(p-CH,0CsH;rNHn)2~22 + O2

Ru(PPh3)&12 f p-CH~OC&NK,

(W)

f O2 (3)

Cl, (PPB, j2Ru

m

Cl,(PPh,),Ru

IN\

0CH3

!N’ A

A

When dioxygen is bubbled through a solution of (IV) in benzene, a redviolet colour immediateIy appears and the final product corresponds to the formula Ru(PPh, j2@-CHZ0CsH4NjzCIz (EX). The same compIex can be

304

obtained when the reaction between Ru(PPha)aCla and p-CHsGCsH~NHa is carried out in air. Repeated attempts to obtain the homologous product with p-CHaCsHJ~Hs gave similar results; however the corresponding Ra!rPha)2(P-CH3CsH4N)2C12 could not be obtained in a reproducible, satisfactory way. It is noteworthy that compound (IX) does not react with PPha in boiling e?Lanol, but it is simply purified in this way from small amounts of by-products formed in the reaction. This compound, which shows a single u(NH) in the IR spectrum (Table 2). show? two distinct signals in a one to one ratio in the ‘H NMR spectrum due to the pam substitu.ent of the new aromatic nitrogen donor ligand. Moreover the IR spectrum in the 1600 - 1000 cm-’ region is particularly complex. On the bases of these data the presence in complex (IX) of an orChoquinonediimine chelating ligand, with a possible resonance with the corresponding diamido ligand, is suggested. The proposed formulation should be in agreement with the deep colour of this derivative and with the presence in the ‘Ii NMR spectrum of several bands in the 3.5 - 4.5 ‘; region. The new ligand formed in this metal-assisted reaction corresponds to one of the intermediates proposed in the oxidation of aniline by inorganic oxidants and which leads to a complex mixture of products [5) _ Decomposition of ccmpound (M) with NaBH, did not give p-CH30CsH*NH2, thus supporting the above suggestion. Finally, attempts to oxidize catalytically the aromatic amine with dioxygen at 80 “C in toluene in the presence of Ru(PPh,),Cl, were unsuccessful; this is probably due to the inertness of compound (IX) to a ligand substitution reaction by the amine. The reaction of the ammonia complex (I) with dioxygen simply results in the oxidation of one triphenylphosphine to ‘triphenylphosphine oxide (IR evidence), and in the formation of a green complex having ammonia and PPIQ as ligand, and which was not further investigated. The reactions of the yellow aliphatic amine derivatives (II) and (III) with dioxygen gave green compounds, which showed a band in the IR spectra at co. 2200 cm-l attributable to the vibration of a nitrile group, together with water and OPPh,. Repeated elemental analyses of the derivative of (HI), including phosphorus and oxygen, did not zllow a reasonable formulation of this diamagnetic material, which is non-electrolyte in nitrobenzene and acetonitrile (see Experimental). Unfortunately many attempts to grow crystals of this compound were unsuccessful. However, since we were particularly interested in the interaction of compound (III) with dioxygen (uide infm). we have also followed this reaction by ESR. Compound (HI) is diamagnetic both in the solid state (Guy method or ESR) and in solution, as confirmed by ESR spectra under nitrogen in solvents such as toluene and

THF from -10

“C to +20 “C. When dioxygen

was added to the yellow THF

solution of (III) at -10 “C, a green colour immediately appeared and an isotropic signal was observed (g = 2.15). At this temperature, the signal reached a maWnun_ after 40 min and then decreased, clisappearing com-

305

pletely after 3 h. The same behaviour was observed in toluene. In this solvent however it was possible to freeze the solution at 143 K when the signal was at its maximum, and to obtain a well-resolved spectrum (see Fig. I). At this temperature the signal showed axiaI symmetry and a sfight Z&O~~OPY for the g values (gL = 2.29 ad gri= 1.90). The calculated average value (gay = 2.16) is practic&y coticident with -that observed at --LO “C kii = 2.15). Even in this case, by warming the solution at 20 “C, this signal decreased with time, although more slowly than in the experiments conducted in TKF. By comparison of these g values with those reported in the liteeraturefor Ru(IIIj species [6], it seems likely that even in our case a Ru(III) complex intermediate is formed on oxidation by dioxygen, and

1

DPPH

Fig. 1. ESR spectra of dioxygen at 263

of Ru(PPhs h(PhCH~EiH_t K (a) andat 143 K (6).

)2CI2.

10m2 M in toluene

in the presence

that this species is respon.sible for the deprotonation of the bound aliphatic amine [7]. When a solution of Ru(PPh,),Cl, was refluxed in toluene in the presence of air and of a large excess of benzyknine, a different product was obtained (eqn. 4) (Tsbie 1): Ru(PPhs)sCl,

+ PhCHaNHa (excess)

02

toluene

[Ru(C&IsCHaNHa)s(PhCN)]

reflux

‘+2Cl-

(4)

cw

The orange, crystalline compound (XI) also shows a v(CN) = 2200 cm-l, is insoluble in the reaction medium and is an electrolyte in methanol. Its ‘II NMR spectrum in DMSO shows r(CH,) = 6.1 and r(NII,) = 5.5, with the expected integrated area between aliphatic and aromatic protons. In reaction (a), the formation of free PhCN was also observed_ Of the compounds (V) (VIII), oniy the ortho-phenylenediamine derivative (V) slowly reacts with O2 at room temperature (eqn. 5) (Table 1):

RWPh, 12(~33”““) iv)

‘32

2

RuW’h,

12 (;;a

CH3)

Cl,

(5)

(X)

Compound (X), which shows a single u(NH) in the IR spectrum and which is diamagnetic in the solid state, could be a derivative of the cliimine, rather than of the diamido ligand. This formulation seems to be supported by the absence of peaks near 1600 cm-’ attributable to 6 (NH,). and by the high value of v (C-N). A related ruthenium complex, Ru{(NH),C,H,)(PPhs)s, has been recently reported and even in this case a diimine-type ligand has been proposed [S] . Related deprotonation reactions of orrho-. phenylenediamines by transition metal peroxo complexes have been previously published ]9] _ Catalytic oxidation of benrylamine to berzzextitrile Compounds (III), (XI) and the green material obtained from the oxidation of (IIIj with dioxygen, were tested as catalysts for the oxidation of benzyknine to benzonitrile, a reaction which has been obtained stoichiometrically with cationic ruthenium(II) complexes having 2,2’bipyridine or ammonia as the ancillary ligands of the amine 17, 105. Compound (XI) was practically inactive in the catalytic oxidation conducted in toluene or in ethanol, where it is highly soluble. On the other hand compound (III) ‘and the green derivative arc effective catalysti for the oxidation of benzylamine to benxonitrile by molecular oxygen (Table 3). In some experiments, 2 certain amount of an orange product (compound (XI), IR evidence) precipitated from the toluene green solution, thus explaining why the conversions were not too reproducible_ We have also observed that a slow flux of dioxygen bubbled through the solution. instead

307 TABLE 3 CaMytic otidztiolr of benzylamine (m)=

Cablyst

(mmol)

PhCH2 NH2 (nmol) Toluene (ral) Time (h) Conversion (%)’ PhCN (%)=a Selectivity (%)‘“’

5.21 2.25 15 3.5 77-48 55.57 71.70

to benzonikile

at 80 %. ~(0,)

x lo-’

4.89 2.23 15 15 100 73.89 73.89

Green compoundb

(Wb

ww

x lO-2

3.87 2.18 30 3.5 56.17 37.03 65.92

= 1 atm

x 1O-2

’ 2.02 17 3.5 69-22 40.88 59.06

“Dioxygen was slopcly bubbled through the solution. ‘-ied out under an atmosphere of dioxygen. =By quantitative GLC a~Aysis_ dWith respect to the initial benzylamine. =Mol PhCN produced/mol PhCEizNH2 converted x 100. ’ 37.4 mg.

of conducting the experiments in an oxygen atmosphere, considerably. increases the conversions. We also observed by adding fresh benzylamine at high conversions, that the system was still active, while the addition of hydroquinone before or during the reaction did not significantly change the reaction path. In the best conditions, the selectivity for the formation of benzonitrile was more than 7055, significantly higher than that observed by using ‘RuCla. 3&O’ as catalyst, at 100 “C and with Iow dioxygen pressure [I]. In the mother liquor of the reaction we did not find even small amounts of benzamide (IR evidence), PhCONH,. while other by-products could be dibenzylamine and n-benzylidenebenzylamine, whose formation is promoted by Ru(PPh,),CI, [ll) _ Even CHs(CKz),NH2 can be catalytically oxidized to CHs(CHz),CN with compound (II) as catalyst; however, in this case we have observed lower yields and the reaction appears to be less selective. A secondary amine such as methyl phenyl amine, PhNT5ICRa, was recovered unchanged when treated with dioxygen at 90 “C in toluene and in the presence of 2. On the other hand methyl benzyl amine, PhCH2MHCHs, Ru(PPh,),CI does react with dioxygen in the presence of Ru(PPhs)sCl,; this reaction, and the oxidation of related secondary axnines, is still under investigation.

conckLsions The ESR spectra that we have observed during the oxidation of Ru(PPhs)2(PhCH2NH2)2C1z (lIE) with dioxygen support the view that the oxidation of the bound amine proceeds via the oxidation of mthenium(I1)

308

to ruthenium(III), followed by deprotonation of the amine with concomitant reduction of ruthenium(LII) to ruthenium(I1) [7, IO]. This may explain the selectivity in the oxidation reaction, since in this way no Eree organic radicals are formed in the reaction medium. In fact hydroquinone did not interfere with the reaction intermediates_ The transient formation of a ruthenium(III) species is also supported by the fact that by reaction of Ru(PR,)sX, with primary amines the correspondin& ruthenium(II) cornplexes, Ru(PRs)s(amine)Xs. have ken obtained [IZ]. Finally, the dehydrogenation reaction of aromatic amines bound to rathenium(II) is not catalytic, snd thus only the smines having 2 Cl& group in the Q position can be catalytically oxidized.

Acknowledgements This research was supported Chkmica Fine e Secondaria).

by the Italian CNR (Progetto

Finalizzato

References 1 2 3 4

5 6 7 8 9 10 11 12

R. Tang, S. E. Diamond, N. Neary and F. Mares, J. Ckem. Sot.. Chem. Commun., (1978) 562. S. Cenini, A. Fusi and F. Porta, GazzeCLa. 108 (1978) 109, and references therein. P. L. Bellon, 8. Cenini. F. Demartin, M. Manassero, M. Pizzotti and F. Porta, J. Chem. Sot.. DolLon Tmtzs., (1980) 2060. P. S. Hahnen, T. A. Stephenson and G. Wilkinson, fnog. Syntk.. 12 (1970) 237. M. Hedayatullah, Eull. Sot. Ckim. Fr., (1972) 2957. (a) R_ De Simone and R. S. Drago, J_ Am. Ckem. Sot.. 92 (2970) 2343. (b) D. Gunoni. G_ Mercati, F. Morazzoni, Gazzelfa. 109 (1979) 545. S. E. Diamond, G. M. Tom and H. Taube, J. Am. Ckem. Sot., 97 (1975) 2661. R. 0. Rosere, D. J. Cole-Hamilton and G. Wilkiruon, J. Chem. Sot.. D&OR Truns, (1979) 1618_ M. Pizzotti. S. Cenini and G. La Monica, Inog. Ckim. Ada. 33 (2979) 161. F. R. Keene, D. J. 8alomon and T. J. Meyer, J. Am. Chem_ Sot.. 98 (1976) L884_ Bui-Tne-Khai, C. Concilio and G. Parzi, J. Oganomet. Ckem.. 208 (1981) 249. J. (Shaft, G. J. Leighand and J_ Parke, J. Ckem. Sot. (A), (1969) 854.