Amine Carbonylation Catalyzed by Ruthenium Complexes under Mild

12 Amine Carbonylation Catalyzed by Ruthenium Complexes under Mild Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 24, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0132.ch012

Conditions G. L. REMPEL and W. Κ. TEO University of Waterloo, Waterloo, Ontario, Canada B. R. JAMES and D . V. PLACKETT University of British Columbia, Vancouver, British Columbia, Canada

The ruthenium carbonyl complexes [Ru(CO) (OCOCH )] , Ru (CO) , and a new one, tentatively formulated [HRu(CO) ] , homogeneously catalyze the carbonylation of cyclic secondary amines under mild conditions (1 atm, 75°C) to give exclusively the N-formyl products. The acetate polymer dissolves in amines to give [Ru(CO) (OCOCH )(amine)] dimers. Kinetic studies on piperidine carbonylation cata lyzed by the acetate polymer (in neat amine) and the hydride polymer (in toluene-amine solutions) indicate that a monomeric tricarbonyl species is involved in the mecha nism in each case. 2

3

3

n

12

3 n

2

3

2

' T ' h e carbonylation of amines to give substituted formamides and ureas (Reaction 1) has been reviewed by Rosenthal and Wender ( I ) . Cobalt, nickel, and manganese carbonyls have been used fairly extenR N H + C O —> R N C H O ; 2 R N H + C O 2

2

2

>R NCONR 2

2

+ H

2

(1)

sively as catalysts under severe temperatures and pressures, and the use of rhodium carbonyls under similar conditions has also been noted (2). The mechanisms of these reactions are not well understood. Hieber and Heusinger (3) reported an interesting reaction i n which a liquid ammonia solution of ruthenium carbonyl iodide decomposed above — 30 °C to produce free and coordinated formamide: 166 In Homogeneous Catalysis—II; Forster, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

12.

REMPEL ET AL.

Ru(CO) I 2

NH; 2

Amine Carbonylation

+ Ru(CO) (NH ) I 2

3

2

167

>-30°C

O

2

[Ru(NH ) (H NC-H) _ ]I (2)

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 24, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0132.ch012

3

n

2

4

n

2

Since many ruthenium species, including ammines, are readily carbonylated using carbon monoxide under mild conditions ( 4, 5 ), there seemed a good probability that effective ruthenium catalysts could be found for amine carbonylation under mild conditions. Product selectivity, a prob lem at more severe conditions, should also improve. This paper summarizes our efforts to date and is concerned primarily with kinetic and mechanistic studies on the catalytic carbonylation of piperidirie to N-formyl product using a ruthenium ( I )-bridged acetate dicarbonyl polymer [ R u ( C O ) ( O C O C H ) ] „ (6,7) and a less well-char acterized polymeric hydridocarbonyl [ H R u ( C O ) ] (7). Kealy and Benson (8) noted the formation of N-cyclohexylformamide when carbonylating cyclohexylamine i n the presence of aliène using Ru2(CO)9 [now known (9) to be R u ( C O ) i ] at high temperature and pressure. The use of ruthenium salts to produce isocyanates from amines and C O has been patented by Stern and Spector (10). This likely corresponds to the more well-documented palladium (II) chloride reaction which occurs stoichiometrically under mild conditions according to Reaction 3 (10, 11). 2

3

3

3

RNH

2

+ CO+ PdCl

n

2

2

* R N C O + Pd(0) + 2HC1

(3)

However, Tsuji and Iwamoto (12) reported that a P d C l reaction at more severe conditions gives rise to ureas, formamides, and oxamides via a metal-catalyzed process. Kinetic studies on catalytic amine carbonylation reactions are scarce, although Brackman (13) has reported kinetics on a copper(I)-copper(II) catalyzed production of ureas from cyclic secondary amines using car bon monoxide-oxygen mixtures at ambient conditions. Saegusa and coworkers (14) used cuprous salts and other group IB and IIB metal compounds to carbonylate piperidine to N-formylpiperidine under more severe conditions. W e have published (15) a brief report involving some of the studies described in this paper. 2

Experimental Materials. Ruthenium trichloride was obtained as the soluble drate from Johnson Matthey L t d . Treatment of aqueous acetic acetate solutions of the trichloride with 1 atm C O at 80 °C for 10 hrs gives almost quantitative yields of the tricarbonyl

In Homogeneous Catalysis—II; Forster, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

trihyacidabout dimer

168

HOMOGENEOUS

CATALYSIS

II

[ R u ( C O ) ( O C O C H ) ] (7) which decomposes rapidly in the absence of carbon monoxide into the polymeric acetate dicarbonyl [ R u ( C O ) ( O C O C H ) ] ( l ) . These bridged acetate carbonyl complexes are the same as those synthesized by Crooks and coworkers (6) by treating R u ( C O ) i with glacial acetic acid. Compound 1 dissolves in amines to yield the complexes [ R u ( C O ) ( O C O C H ) ( a m i n e ) ] which are read ily precipitated by addition of water; these compounds analyze satis factorily and show three strong ν ( C O ) IR bands in the 1920-2030 c m region. The following data were obtained, for example, for the piperidine complex 2: C , 35.64; H , 4.60; N , 4.82. C H N 0 R u requires C , 35.90; H , 4.65; N , 4.65; v ( C O ) observed at 2025, 1970, and 1935 c m . A dimeric pyridine complex was made previously in a similar way (6), and by comparison the cyclic secondary amine complexes that we have isolated are formulated also as dimers. Treatment of an aqueous solution of R u C l , 3 H 0 with 1 atm C O at 80 °C for several days leads to pre cipitation of a purple-brown polymeric solid and a clear, colorless filtrate (7). Washing the solid with benzene removes small amounts of R u ( C O ) i and H R u ( C O ) (16). The remaining solid after drying under vacuum contains no chloride and analyzes for a hydridocarbonyl [ H R u ( C O ) ] „ , 3, obtained in about 80% yield. F o u n d : C , 18.97; H , 0.50; R u , 54.97; Ο (by difference) 25.74. C H 0 R u requires C , 19.36; H , 0.54; R u , 54.31; O, 25.79. The IR (Nujol) shows a broad band centered at about 2000 cm" . The polymer is insoluble in organic solvents but dis solves to some extent in liquid amines (see Results) and phosphines. Spectroscopic studies on such solutions have not yet yielded evidence for the presence of a hydride. [High field Ή N M R signals have now been detected in methyldiphenylphosphine solutions.] Amines and the N-formyl derivatives were obtained at 98-99% purity from Aldrich Chemicals and were used without further purifica tion. Carbon monoxide was a Matheson C P . grade product. Kinetics. Kinetic measurements were made by following C O uptake at constant pressure using the apparatus and procedure described earlier (17). The R u catalyst concentration used was in the range (0.6-6.0) X 10" Λί. Total pressures up to 1 atm and C O partial pressures from 55-590 mm were used. The C O solubility in pure piperidine was 6.5 X 10" M atm" at 21 °C and 5.8 X 10" M atm" at 75 °C, Henry's law being obeyed at least up to 1 atm; the solubility in toluene was similar (5.7 X 10" M a t m at both 21° and 7 5 ° C ) . The solubility in a toluene-piperidine mixture ( 1:1 by v o l ) , 5.5 X 10" M atm" at 75°C was only slightly less than those in the pure solvents. The vapor pressures of piperidine and toluene differ by only about 15-20 mm between 5 0 ° - 7 5 ° C , that of piperidine being the greater (18). Vapor pressure measurements on the solvent mixtures showed that Raoult's L a w was obeyed approximately, and the partial C O pressures over toluene-piperidine solutions could be readily estimated. For practical purposes, the partial pressure of piperidine-toluene mixtures, 2.0-10.1M (neat) in piperidine could be taken as that of pure piperidine. Product Analysis. The N-formyl products were identified by G L C using a Hewlett Packard model 5780 Unit fitted with a flame ionization detector and a column of Pennwalt 223 on 80/100 GasChrom R (Applied Science Labs.). 3

3

2

2

3

3

n

2

2

3

2


-1

9

1 4

4

1

3

3

2

2

4

4

1 2

3

3

3

1

2

3

1

3

3

1

1

3

1


12.

REMPFt. E T A L .

169

Amine Carbonylation

Time χ ΊΟ" 2


ι

I

ι

/

1.0

^ —

Α ~ ~

α

0.5

J/ Τ

j^ ^

υ

^

1

£ ί ^ ~ ^

ι

ι

I

15

10

Time χ ΙΟ" , s 4

Figure 1.

Gas uptake plots for the catalytic carbonylation of neat amines at

1 atm A. [Ru(CO)40COCH )] , piperidine, 75°C, 0.03M Ru, B. [HRu(C0) ] , piperidine, 75°C, 0.035M Ru, C. [HRu(C0J ] , piperidine, 71°C, 0.022M Ru, D. [HRu(CO)s] , pyrollidine, 75°C, 0.022M Ru, E. [HRu(C0) ~\n, morpholine, 75°C, 0.022M Ru 3

3 n

n

5

n

n

3

Results The [ R u ( C O ) ( O C O C H ) ] n (1) and [Ru(CO) (OCOCH )(amine)] (2) Catalysts. Compound 1 dissolves in amines to give yellow solutions. These were then subjected to 1 atm C O at about 75 °C, and the reaction was monitored by following the C O absorption. Figure 1 (curve A ) shows an uptake curve for the piperidine system at the con ditions noted. The curve sh,ows an initial autocatalytic region; a maximum rate is reached after about 20 hrs, then the rate slowly decreases after about 30 hrs. The sole product was Af-formylpiperidine (30% after 70 hrs), and the total gas consumption corresponded to this conversion. The maximum rates (see Table I) showed a first-order dependence on C O up to 1 atm total pressure. The R u dependence is not linear and, in fact, analyzes well for a half-order dependence (Figure 2). The morpholine and pyrrolidine systems behaved similarly but showed lower and higher reactivities, respectively (Table I ) . Pyridine and aniline solu2

3

2

2


3

170

HOMOGENEOUS


,M

(Ru)

0.02

0.04

CATALYSIS

II

0.06

0.1

0.2

Figure 2. [Ru\ Hon of piperidx

tions of 1 were essentially unreactive toward C O at 75°C and 1 atm; diethylamine solutions reacted slowly at 40 °C, this being an upper prac tical limit because of the lower boiling point of the amine. Adding small amounts of water to the systems catalyzed by 1 results in an initially faster rate; no autocatalysis is observed, but the catalytic activity falls off as the solutions darken, and conversions to N-formyl products are low ( < 5 % ) after 50 hrs. These systems are more complex chemically than the anhydrous systems. The dimeric [ R u ( C O ) ( O C O C H ) ( p i p ) ] complex (2) may be used at the appropriate ruthenium molarities to reproduce exactly the uptake plots observed with the polymeric catalyst. Solution IR measure ments in regions of maximum activity for both 1- and 2-catalyzed systems showed the presence of the amine dimers which could be readily pre cipitated at any stage of the catalytic carbonylation by adding water. Adding N-formyl product (and other amides such as N,N-dimethylacetamide) decreases the carbonylation rate, and thus accumulation of product slowly poisons the catalyst. The rate for the piperidine system (Table I) after 70 hrs decreased to 0.4 X 10" M sec , and at this stage about 100 moles of amine were carbonylated per mole of ruthenium. Amine solutions of the dimers are quite stable at 75 °C for long periods in vacuo or under argon, and there is no trace of N-formylamine. Although the catalysts are formally R u ( I ) d systems, the dimers are diamagnetic i n the solid state, and this must be accounted for by metal-metal interaction. Following Crooks and coworkers ( 6 ) , we for mulate the complexes as having Structure I. E S R analyses on samples of the reacting solutions i n the region of maximum activity have given no signals at either liquid nitrogen or room temperature. 2

3

2

5

-1

7


12.

REMPEL

Amine Carbonylation

ET AL.

Table I.

Carbonylation of Amines" % Conversion

Catalyst

Amine


171

Maximnn rate X 10 Msec~ 5

b

Primary Amine aniline cyclohexylamine n-octylamine

formylamine

1 or 3 3 3

Secondary Amine diethylamine di-n-butylamine dibenzylamine hexamethyleneimine morpholine

Tertiary Amine pyridine

d

d

e

0.30 J 0.24 0.04 5.80 0.40 1.30 1.0 d

d d

33(45 hrs) 6(20 hrs) 14(48 hrs) 15(30 hrs), 30(70 hrs) 32(55 hrs) 45(65 hrs) 25(200 hrs) 35(35 hrs) 34(48 hrs)

3 4 5 1 3

pyrrolidine

1.57 0.52 >

1(10 hrs)

3 3 3 3 1 3 1 or 2

piperidine

l

10.4 7.2 0.55" 7.4 11.5

1 or 3

At 75°C, 1 atm total pressure, 5 ml amine. [Ru] = 3 X 10~ Af for the bridged ace tate complexes and Ru (CO)i , [Ru] = 2.2 X 10~ M for [HRu(CO) ]n. l [Ru(CO) (OAc)] ; 2 [Ru(CO) (OAc)(pip)] ; 3 [HRu(CO) ]„; 4 Ru (CO) ; 5 [Ru 0(OAc) (H 0) ][OAc]. No carbonylation observed. Catalyst 3 sparingly soluble. Carbonylation ceased after 1000 sec. ' At 50°C. * 10% H 0 added. a

2

3

b

2

3

6

2

2

2

n

2

3

2

3

3

12

3

c

d

e

2

CH

\ Ο

Ru

C I ο

3

.CH„

c ι

(i)

ο

Ο

L=Piperidine

The [ H R u ( C O ) ] „ (3) Catalyst. The systems were investigated in a manner similar to that described for the acetate catalysts. Figure 1 (curves B - E ) shows some representative C O uptake plots by yellow solutions of 3 dissolved i n various amines at the conditions noted. N o autocatalysis is observed; the initial rates, which are readily measured 3



172

HOMOGENEOUS

5.0

(Piperidine), M

CATALYSIS

II

10.0

Figure 3. [HRu(CO) ] -catalyzed carbonylation of piperidine; amine dependence at 75°C, 0.022M Ru in toluene-piperidine solutions. O, 490 mm CO; · , 100 mm CO. 3 u

since they remain constant for at least 1 hr, subsequently decrease grad ually over long times. The only products detected were the N-formylamines which again slowly poisoned the catalyst. The kinetics of the piperidine system were investigated using the initial rates. Compound 3 was also soluble in toluene-piperidine mixtures, and this enabled us to demonstrate that the reaction is first order in amine (Figure 3). The C O dependence was more complex than for the acetate-catalyzed system and was first order at lower concentration, but it approached zero order at partial pressures above 0.5 atm (Figure 4). The R u dependence was first order at least up to 3 X 10" M in conditions of both zero- and firstorder C O dependence (Figure 5). The carbonylation rates were also studied from 5 0 ° - 8 0 ° C at 1 atm total pressure where the reaction is 2

200

CO

400

600

Pressure, mm

Figure 4. [HRufCOj^n-catalyzed carbonylation of piperidine, CO dependence for neat amine solutions. O, 71 °C, 0.022M Ru; #, 75°C, 0.012M Ru.


12.

REMPEL ET AL.

Table IL

Temperature Dependence for [HRu(CO) ] -Catalyzed Carbonylation of Piperidine* 3

Temperature, °C


173

Amine Carbonylation

Max rate Χ 10 Msec 5

50 60 65 71 75 80

w

k' X 10

1

z

1.17 3.52 4.16 7.02 10.4 12.1

M-hec-

1

0.05 0.16 0.19 0.32 0.48 0.55

° [Ru] = 2.2 X 10 M, 1 atm total pressure, neat piperidine (10.1M). _2

0.02 (Ru), M

0.04

Figure 5. [HR^CO^^catalyzed carbonylation of piperidine, Ru dependence at 75°C in neat amine. O, 490 mm CO; · , 100 mm CO. independent of C O pressure (Table I I ) . The initial carbonylation rates and some per cent conversions of a number of amines are summarized in Table I for the conditions noted. W e have not been able to isolate any pure carbonylamine complexes from amine solutions of [ H R u ( C O ) ] although a crude yellow product isolated from piperidine solutions gives an I R spectrum in the C O region (three bands at 2025, 1975, and 1940 cm" ) remarkably similar to that of [ R u ( C O ) ( O C O C H ) ( p i p ) ] . Interestingly, no net gas evolution is ob served on dissolution of the hydridocarbonyl in piperidine under argon at 80°C; but analysis of this system after 12 hrs shows the production of N-formylpiperidine. Two experiments have shown that about 0.7 mole of the carbonylated product is formed per mole of R u . This suggests that one mole of C O is consumed i n a stoichiometric reaction and that the piperidine product is a dicarbonyl. For example, 3

n

1

2

HRu(CO)

3

2

pip 3

> HRu(CO) (pip)* + C H N C H O 2

5

1 0


(4)

174

HOMOGENEOUS

CATALYSIS

II

The IR of the isolated crude complex also indicates some free formylpiperidine, and chemical analyses are consistent with 80% H R u ( C O ) (pip) + 20% C H NCHO. Attempts to locate a hydride ligand in the range τ10-30 by N M R measurements of amine solutions of 3 have been unsuccessful although a limitation is the relatively low solubility ( < 0 . 1 M ) of the complex; exchange with the amine hydrogens could also be occurring. As in the acetate systems, E S R studies have failed to detect any paramagnetic species. Other Ruthenium Catalysts. R u ( C O ) i readily dissolved in piperi dine to give a solution effective for catalytic carbonylation of the amine. The uptake plots resemble those shown in Figure 1 (curves B - E ) , and the maximum rate given in Table I refers to the initial rate. Attempts to characterize the ruthenium complexes formed from reaction of the dodecacarbonyl with amines have been unsuccessful. The oxotriruthenium cluster complex [ R u 0 ( O C O C H ) 6 ( H 0 ) 3 ] [ O C O C H ] which we had used as ruthenium(II) acetate (19), can be used as a catalyst, but small amounts of water are necessary for solubility, and long reaction times are required for reasonable conversions at mild conditions (Table I). 2


5

1 0

3

2

3

3

2

3

Discussion The results show that a number of ruthenium carbonyl complexes are effective for the catalytic carbonylation of secondary cyclic amines at mild conditions. Exclusive formation of N-formylamines occurs, and no isocyanates or coupling products such as ureas or oxamides have been detected. Noncyclic secondary and primary amines and pyridine (a tertiary amine) are not effectively carbonylated. There appears to be a general increase in the reactivity of the amines with increasing basicity (20): pyrrolidine (pK at 25°C = 11.27 > piperidine (11.12) > hexamethyleneimine (11.07) > morpholine (8.39). Brackman (13) has stressed the importance of high basicity and the stereochemistry of the amines showing high reactivity in copper-catalyzed systems. The latter factor manifests itself in the reluctance of the amines to occupy more than two coordination sites on the cupric ion. In some of the hydridocarbonyl systems, low activity must also result in part from the low catalyst solubility (Table I ) . The bridged-acetate catalyst system is reasonably well characterized in that the [ R u ( C O ) ( O C O C H ) ( a m i n e ) ] complexes are present and can be recovered at any stage throughout the reaction. Further, it is clear from the blank reaction that the dimers are precursors to the true catalyst which must be formed via interaction with further carbon monoxide. The a

2

3

2


12.

R E M P E L ET A L .

Amine Carbonylation

175

observations and limited kinetic data may be interpreted in terms of the mechanisms outlined in Reactions 5-8, O A c = O C O C H : 3

[Ru(CO) (OAc)(pip)] + 2(pip) - 2Ru(CO) (OAc)(pip) 2

2

2

2a

2 Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 24, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0132.ch012

(5)

2

k

2

2a + C O Ru(CO) (OAc)(pip) 3

> Ru(CO) (OAc)(pip),

(6)

3

fast

> pip C O + Ru(CO) (OAc)(pip) _i (7)

x

2

x

fast Ru(CO) (OAc)(pip) _i + pip 2

(8)

> 2a

x

The autocatalytic region could be associated with the buildup of a steadystate concentration of an active monomer 2 a from the dimer 2. The spectroscopic evidence indicates that the concentration of 2 a remains low, that is, k_x > ki. Writing Κχ = fci/fc.i yields the rate law shown i n Equation 9 for the region of maximum activity where R u refers to the total ruthenium calculated as monomer. The observed kinetics are conT

= * (IT /2)^[RuT] [pip][CO] 2

(9)

1/2

1

sistent with such a rate law although the piperidine dependence has not been established. The data of Figure 2 using this rate law give a k Ki value of 2.7 X 1 0 " M - sec" at 75°C. Crooks and coworkers ( 6 ) have done molecular weight measurements in solution and noted that ligand dissociation ( L ) is sometimes observed with complexes of the type R u 2 ( C O ) ( R C 0 ) 2 L 2 although details were not reported. A mechanism based on such predissociation of L in neat L (Equation 10) implies a dimer as the active catalyst and w i l l always lead to a first-order dependence on added ruthenium, and thus such a mechanism does not appear to operate, 2

3

3/2

4

2

ki R u ( C 0 ) ( 0 A c ) ( p i p ) - pip + R u ( C 0 ) ( 0 A c ) ( p i p ) fc-i k i CO products 2

4

1/2

1

2

2

2

4

2

(10)

t

[ H R u ( C O ) ] is an interesting complex and has potential for a number of catalytic carbonylation reactions. However, the evidence for the presence of hydrogen is based mainly on chemical analysis which consistently shows the small hydrogen content. The stoichiometric car bonylation according to Reaction 4 and the IR of the crude carbonyl are 3

n


176

HOMOGENEOUS

CATALYSIS

II

consistent with the presence of a tricarbonyl in the starting polymer and, based on analogy with the acetate-bridged-tricarbonyl [ R u ( C O ) ( O C O C H ) ] , -dicarbonyl-polymer [ R u ( C O ) ( O C O C H ) ] , and -dicarbonyl-amine [ R u ( C O ) ( O C O C H ) ( p i p ) ] , we consider that the hy drides probably replace the acetate groups and are present as bridging ligands although we have been unable to detect these by IR. The hydridocarbonyl cluster complex [ H R u ( C O ) ] exists as a tetrahedral arrangement of ruthenium atoms with edge-bridging hydrogen atoms, and weak IR bands assigned to v ( R u - H - R u ) have sometimes been observed for this compound (16, 21, 22, 23). The complex we have isolated is quite different from this and related H R u ( C O ) i complexes (22, 23). Possible isomers for the H R u ( C O ) i and H R u ( C O ) i clusters have been discussed (21, 22, 23). Reaction 4 shows that the ruthenium center with three coordinated carbonyls can transfer one such ligand to the piperidine (presumably coordinated ). The mechanism suggested for the acetate complex includes exactly analogous steps (Reactions 6 and 7). The kinetics for the hydridecatalyzed system, however, are quite different and show a first-order dependence in R u and a more complex dependence on C O (Figure 4). Further, no autocatalysis is evident. The rate law for the hydride-catalyzed system can be written as —dlCOI/dt = Zc'[Ru ] [ p i p ] , where k' is a pseudo-second-order rate constant which includes the C O dependence. A mechanism which in corporates slow steps corresponding to Reactions 5 and 6 w i l l lead to a rate law of the kind shown in Equation 11 which satisfies all the 3

3

2

2

2

3

3

2


3

2

4

n

4

2

4

4

3

2

4

3

T

-d[CO] dt

k\k [dimer][pip][CO] &_i[monomer] + ^ [ C O ] 2

(11)

dependencies at high [ C O ] (when Reaction 5 becomes rate determin ing). However, at low [ C O ] (when Reaction 6 becomes rate deter mining) a less than first order on R u is predicted; this is not observed (Figure 5); alternatively at low [ C O ] a first order in R u can result if Reaction 5 lies well to the right, but then the kinetics should become independent of piperidine, which was not observed (Figure 3). The mechanism suggested for the acetate systems (Reactions 5-8) may be readily modified to account for the observed kinetics if the com plex corresponding to 2 at the conditions of the kinetic study is monomeric in solution, and it seems reasonable that hydride bridges would be cleaved in the piperidine solvent. For example, HRu(CO) (pip)x + pip ^ HRu(CO) (pip)x+i 2

2


(12)

12.

REMPEL ET AL.

Amine Carbonylation

177

k fast (13) HRu(CO) (pip)x+i + C O — > HRu(CO) (pip)x+i • products 2

2

3

This gives a rate law k' [ R u ] [pip] where T

k' = *iA;2[C0]/(fc-i + k [CO])

(14)

2


Rearranging gives k' ~ kMCO]

Wei

K

}

Figure 6 shows a plot of (/c')" vs. [ C O ] " for the two sets of data in Figure 4. Good linear plots result, and the intercept and slope for the data at 75°C give h = 5.3 Χ ΙΟ^Μ" sec" and kjk. = 500. A n alternative mechanism which accounts equally well for the kinetics involves a pre-equilibrium reaction with C O : 1

1

1

1

x

Κ H R u ( C O ) ( p i p ) + C O - HRu(CO) (pip)x 2

x

(CO)" x ίο", M" 05

I

(16)

3

3

]

1

1.0

1

I

I

1

1.0

2.0

3.0

4.0

(CO^xio-f M~

L.

5.0

1

Figure 6. [HRu(CO) ~] -catalyzed carbonylation of piperidine. Analysis of the data of Figure 4 accord ing to Equations 15 or 20. 3

n


178

HOMOGENEOUS

CATALYSIS

II

k HRu(CO) (pip)χ + pip 3

> HRu(CO) (pip)x+i

(17)

3

fast HRu(CO) (pip) 3

> H R u ( C O ) ( p i p ) x + pip C O

x+1

2

(18)


This mechanism gives the rate law - d [ C O ] / d i = ^ [ R u ] [ p i p ] [ C O ] / ( l + K[CO])

(19)

T

i.e., k' = kK[CO]/(l

+ K[CO])

(20)

The same analysis as discussed above (Figure 6) gives the value of 5.3 X 1 0 " M sec" to k and 500 to Κ at 75 °C. W e have no evidence for the existence of Equilibrium 16 although the Κ value implies that the reaction should be observable. Thus we tend to favor the mechanism outlined in Reactions 12 and 13 (followed by Reactions 7 and 8). The mechanisms as presented do not indicate how the N-formyl product is formed although formation of a R u - C O - N moiety at some stage seems essential; metal-assisted hydride shifts are a possibility. A n alternative role of the attacking piperidine in Reaction 12 or 17 could be that of a proton acceptor as discussed by others (J, 13). For example, a plausible scheme would be the follow ing: (writing R for C H ) 4

_1

1

2

r )

1 0

HRu(CO) (R NH) + R N H - HRu(CO) (R N)- + R N H t (cf. Reaction 12) 2

2

HRu(CO) (R N)~ + 2

2

2

2

2

C O —> H R u ( C O ) ( R N ) - -> 3

2

2

HRu(CO) —CONR^ (22) 2

H R u ( C O ) C O N R ^ + R N H + -> H R u ( C O ) + R N C H O + R N H 2

2

2

2

(21)

2

(23)

Reaction 21 for a tricarbonyl species could correspondingly be written instead of Reaction 17. The formation of carbamoyl complexes ( M — C O N R o ) by the reaction of amines with metal carbonyls, especially cationic ones, has been reviewed by Angelici (24). Further studies are in progress. The temperature studies (Table II) were carried out under condi tions approaching a zero-order dependence on CO—i.e., when k' « ki ( or k ) ( Equations 14, 20 ). The k! data give a very good Arrhenius plot and yield the activation parameters ΔΗ* = 17.5 ± 0.7 kcal/mole, AS* = —11 ± 2 eu. In terms of Reactions 12 or 17 the negative entropy of activation seems reasonable for a ligand association reaction; the activa tion energy appears somewhat high but could be related to steric prob-


12.

R E M P E L E T AL.

Amine Carbonylation

179

lems associated with the addition of the bulky piperidine ligand. T h e ΔΗ* value seems compatible with a rate-determining reaction such as Reaction 21 although such ionization reactions commonly have much larger negative entropies of activation (25). The stoichiometric carbonylation observed using [ H R u ( C O ) ] „ and the proposed catalytic schemes all involve tricarbonyl species as the ac tive catalyst; the relatively high activity of R u ( C O ) i is consistent with this. The relative activity of the complexes for piperidine carbonylation is [ H R u ( C O ) L - R u ( C O ) i 2 > [ R u ( C O ) ( O C O M e ) ] . The major cause of the decrease i n carbonylation rates is the accumulation of formyl product although the decrease i n amine concentration is also a contributing factor. This catalyst poisoning is likely attributable to complexation to the ruthenium, presumably via the carbonyl grouping as commonly found for formamide ligands (26). The product could compete with either amine or C O for a metal coordination site. 3


3

3

3

2

2

w

Acknowledgment W e thank Johnson Matthey L t d . for loan of the ruthenium. Literature

Cited

1. Rosenthal, Α., Wender, I., "Organic Synthesis via Metal Carbonyls," I. Wender and P. Pino, Eds., Vol. 1, p. 405, Interscience, New York, 1968. 2. Durand, D., Lassau, C., Tetrahedron Lett. (1969) 2329. 3. Hieber, W., Heusinger, H., J. Inorg. Nucl. Chem. (1957) 4, 179. 4. Allen, A. D., Eliades, T., Harris, R. O., Reinsalu, P., Can. J. Chem. (1969) 47, 1605. 5. James, B. R., Inorg. Chim. Acta Rev. (1970) 4, 73. 6. Crooks, G. R., Johnson, B. F. G., Lewis, J., Williams, I. G., Gamlen, G., J. Chem. Soc. A (1969) 2761. 7. James, B. R., Rempel, G. L., Chem. Ind. (London) (1971) 1036. 8. Kealy, T. J., Benson, R. E., J. Org. Chem. (1961) 26, 3126. 9. Corey, E. R., Dahl, L. F., J. Amer. Chem. Soc. (1961) 83, 2203. 10. Stern, E. W., Spector, M. L., U.S. Patent 3,405,156 (1968). 11. Stern, E. W., Spector, M. L., J. Org. Chem. (1966) 31, 596. 12. Tsuji, J., Iwamoto, N., Chem. Commun. (1966) 380. 13. Brackman, W., Discuss. Faraday Soc. (1968) 46, 122. 14. Saegusa, T., Kobayashi, S., Hirota, K., Ito, Y., Bull. Chem. Soc. Jap. (1969) 42, 2610. 15. Byerley, J. J., Rempel, G. L., Takebe, N., James, B. R., Chem. Commun. (1971) 1482. 16. Kaesz, H. D., Knox, S. A. R., Koepke, J. W., Saillant, R. B., Chem. Commun. (1971) 477. 17. James, B. R., Rempel, G. L., Can. J. Chem. (1966) 44, 233. 18. "Handbook of Chemistry and Physics," 50th ed., pp. D153-155, Chemical Rubber Co., Cleveland, Ohio, 1970. 19. Cotton, F. Α., Norman, J. G., Spencer, Α., Wilkinson, G., Chem. Commun. (1971) 967. In Homogeneous Catalysis—II; Forster, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.


180

HOMOGENEOUS CATALYSIS

II

20. Perrin, D. D., "Dissociation Constants of Organic Bases in Aqueous Solu tion," Butterworths, London, 1965. 21. Knox, S. A. R., Kaesz, H . D., J. Amer. Chem. Soc. (1971) 93, 4594. 22. Johnson, B. F. G., Johnson, R. D., Lewis, J., Robinson, Β. H., Wilkinson, G., J. Chem. Soc. A (1968) 2856. 23. Johnson, B. F. G., Lewis, J., Williams, I. G., J. Chem. Soc. A (1970) 901. 24. Angelici, R. J., Accounts Chem. Res. (1972) 5, 335. 25. Frost, Α. Α., Pearson, R. G., "Kinetics and Mechanism," p. 137, Wiley, New York, 1963. 26. Bull, W. E., Madan, S. K., Willis, J. E., Inorg. Chem. (1963) 2, 303. RECEIVED August 20, 1973. Work was supported by the National Research Council of Canada, the University of Waterloo, and the University of British Columbia.


Amine Carbonylation Catalyzed by Ruthenium Complexes under Mild

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