Indian Journal of Chemistry Vol. 42B, February 2003, pp. 346-352

Polymer supported palladium (II) complexes as hydrogenation catalysts

Debkumar Mukheljee Department of Chemistry, Ramsaday College, Amta, Howrah 711 40 I, India

Received 5 July 2001 .. accepted (revised) 12 April 2002

Dihydrogen reduction of aliphatic and aromatic nitrocompounds, alkenes, aikynes, nitriles and Schiff bases to their cor­responding saturated products is efliciently carried out using the soluble and polymer anchored" palladium (II) complexes. The immobilization of the palladium (II ) complexes in the polymer matrix slight ly decreased the catalytic activities on the basis of metal content but improved the thermal and chemical stabi lities and product selectivities relative to those of the cor­responding homogeneous ones. The soluble catalyst has the propensity to decompose under high pressure, high temperature conditions but the immobilized ones can be used repeatedly and can be stored for long periods without any appreciable loss of catalyt ic activity. XPS study indicates the presence of palladium (II) in the frcsh and used catalyst and a plausible reac­tion mechanism has been suggested on the basis of experimental findings .

The study of the activities of transition metal com­plexes anchored to sol id support has attracted consid­erable attention during the past two decades. A par­ticular emphasis on heterogenizing homogeneous catalysts is due to their high industrial and commer­cial aspects t

-6

. Although a large number of investiga­tions deal with palladium containing systems as cata­lysts for hydrogenation7

-t2

, the study of catalytic ac­tivities of palladium (II) complexes anchored to polymers are relatively rare l3

-t6

. This may be due to poor chemical , thermal and mechanical properties of the selected polymer materials" and tendency of the metal to leave the support on prolonged use I8

-19

• Plclti­tJum and palladium complexes anchored to polyvinyl pyridine20 or polymeric diphenyl benzyl phosphine2l

,

rhodium and palladium complex of anthrani lic acid anchored to polystyrene22 and palladium complex of polyacrylonitrile supported on sil ica23 are among the few successfu l catalysts used for the hydrogenation of organic substrates. The choice of the ligand to be an­chored is usually based on the idea of creating envi­ronments analogous to those in the most active homo­geneous catalysts. With this idea, investigation of the catalytic activity of palladium (II) ani line complex both in homogeneous and heterogeneous phases was carried out.

Materials and Methods The catalytic activity of the homogeneous catalysl

trans-Pd(C6HsNH2)2Cl2 and the heterogeneous cata­lytic systems derived by anchoring palladium (II) spe­cies to p-aminopolystyrene and amino poly-N-

vinylcarbazole were studied in DMF medium both under normal pressure at ambient temperature and under high pressure at elevated temperature. These homogeneous and heterogeneous catalytic systems behave differently to substrates under investigation. For the preparation of all these materials analyt ical grade chemicals including solvents were used lhroughout the work. Palladium was c 'timated by DMG method and chloride by AgN03 method. C, H and N were analysed using semi micro anal ytical tech­niques.

Macroporous polystyrene, crosslinked with divi­nylbenzene (mesh of average pore diameter gOOA) was chosen as polymer backbone for the preparation of the present polymer-bound complexes. The proce­dure fo r the normal and hi gh pressure reduction using the soluble and polymer supported catalysts are simi­lar and have been described elsewhere '2.

24. The high

pressure, high temperature catalytic runs are carried out under complete closed condit ions and after the stipulated time the gas mixture is cooled in an ice-salt bath and then filtered under cold conditions. The products of reactions are then analysed by gas chro­matography using standard samples for authentisa­tion. A Shimadzu GC gas chromatographlflame ioni­zation detector is used in the experiments. Chroma­tograms are plotted with a chart recorder. The column is a 2 meter x 1/8 - in - stainl-ess steel column with a stationary phase of lO% carbo wax on chromosorb W 70-80 mesh support. A helium mobile phase (20-30 mLimin) is ust:d. Hydrogen (30 mLimin) and com­pressed air (240 mLimin) are detector gases. Injector,

MUKHERJEE: PALLADIUM ( II) COMPLEXES AS HYDROGENATION CATALYSTS 347

column and detector temperatures are 175, 80 and 250°C respectively. Analysis is performed by with­drawing and injecting exactly 500 ilL of sample from the vials using a 1 mL Hamilton gas tight syringe. The syringe is flushed with air between runs to prevent cross-contamination.

Preparation of trans-Pd(C6HsNH2hCh. The compound was prepared following a common litera­ture method which involves the addition of aniline (1.5g) to a hydrochloric acid (lOOmL) solution of pal­ladium chloride (l.Og). The solution was warmed gen­tly for 30 min and the yellow crystals of the desired compound separated out on cooling the solution. This was recrystallized from acetone.

The compound can also be prepared by refluxing an alcoholic solution (l50mL) of bis(benzonitrile) palladium (II) chloride (l.Og) and aniline (0.5g) for 30 min. The filtered solution produced the yellow crys­tals of the subject compound on standing overnight. The crystals were purified by recrystallization from acetone. The melting point, chemical analyses, IR and UV spectra and thermal behaviour of the two prepara­tions were almost identical.

The catalytic activities and experimental findings prove beyond doubt the identity of the two com­pounds though majority of the investigation was done using the compound prepared from palladium (II) chloride (method 1). Anal. : Found : C, 40.2%; H, 3.85%; N,7.5%; Pd, 29.08%.

Preparation of polymer bound palladium (II) complexes. For the preparation of polymer bound palladium (II) complexes, the polymers as recei ved were first nitrated and then reduced to amines. The amines were then allowed to react with trans­Pd(C6HsCN)2Cb or PdCb to form the respective polymer aniline complexes.

P HNO) + (CH 3CO)~O P (NO) SnCI 2 + H~I n n 2 CH COOH

3

Pn = polystyrene and poly N-vinyl carbazole back­bone.

The use of trans-Pd(PhCNhCI2 in this case was preferred to PdCh as the former results in better load­ing of Pd(II) in the polymer.

Preparation of p-nitropolystyrene [Pl-(P-C6H4N02)] . The material was prepared following the

method of King and Sweet26. The macroporous poly­

styrene (5g) was added to a mixture of acetic anhy­dride (20mL), nitric acid (70%, 4 mL) and glacial ace­tic acid (6mL). The mixture containing the suspension of polystyrene was stirred for 1 hr at 5°C and 6 hr at 50°C. Further nitration did not occur on continuing the reaction for a longer period. p-Nitropolystyrene thus obtained was successively washed with acetic acid, tetrahydrofuran, water and methanol and finally dried under vacuum. Analysis of the nitro compound (N, 3.02%) indicates 25% nitration at the benzene nng.

Preparation of p-anilinopolystyrene [Pl-(P­C6H 4NH2)]. A mixture containing acetic acid (30mL), stannous chloride dihydrate (8g), concentrated hydro­chloric acid (6mL) and the suspension of p­nitropolystyrene (50g) was stirred for 22 hr at room temperature and filtered . The residue was washed successively with HCI , THF and C2HsOH. Analysi s of the yellow compound (N, 2.96%, CI, 6.83%) corre­sponds to nearly 90% conversion of -N02 to -NH3CI. The product on treatment with dilute NaOH (5 % solu­tion) produces the polymer aniline material which was chloride free.

Preparation of palladium (II) complex with p­anilino polystyrene [P t -(P-C6H4NH2h PdCh] ... (1) . A solution of tralls-Pd(PhCNhCI 2 (0.5g) in methanol (20mL) was added to a suspension of p-anilino poly­styrene (1.0 g) in methanol (20mL) with stirring. The mixture was then refluxed for 5 hr on a water bath . The material slowly changed colour from yellow to brownish yellow. It was then filtered, washed with THF and finally dried under vacuum. Analysis showed nearly 60% complexation of the [Pdp­C6H4NH2) ] group.

Preparation of nitropoly-N-vinyl carbazole [Pr (NC 12H 7N02)27.28. A mixture containing concentrated nitric acid (25mL) and glacial acetic acid (50mL) was added dropwise to the solution of poly-N-vinyl carba­zole (5g) in 1,2 dichloroethane (lOOmL) at room tem­perature with constant stirring. A yellow brown polymer precipitated out with the progress of the reac­tion. Analysis of the compound (N, 11.38%) suggest nearly 90% mononitration per vinylcarbazole unit.

Preparation of aminopoly-N-vinylcarbazole [P2-

(NC12H 7NH2) ] . The solution of stannous chloride dihydrate (lOg) in concentrated hydrochloric acid (20mL) was added to the suspension of the brown polymer in acetic acid (40mL). The mixture was stirred at room temperature for 48 hr when the colour changed from brown to light yellow. It was filtered,

348 INDIAN J. CHEM., SEC B, FEBRUARY 2003

washed in THF and CH30H and then dried in vacuo. Analysis of aniline hydrochloride (N, 1l.29% ; CI, 6.77%) suggests 50% reduction of - N02 to NH3Cl. The product when treated with 5% NaOH solution produced the chloride free material.

Preparation of palladium(II) complex with amino­poly -N -vinylcarbazole[P 2-(N C 12H 7NH2hPd Ch](II) . A suspension of aminopoly-N-vinylcarbazole (lg) in warm methanolic solution of trans-Pd(PhCNhCh (0.8g) was refluxed for 4 hr on a water bath. The col­our of the polymer changed from yellow to brown. This was filtered , washed success ively with THF, CH30H and then dried under vacuum. Analysis of the brown mass showed almost 70% complexation of the anilino groups to palladium (II) (Anal. Found : Cl, 4.37; C, 67.82; N, 10.68; Pd, 6.6%) .

The electronic spectral data of trans-Pd(C6HsNH2)2CIz was taken in DMF and those of the polymer bound complexes were taken in the solid state due to their insolubility in common organic solvents. The nitration of macroporous polystyrene was done in the hetero­geneous phase and this actually explains the cause of very low percentage of nitration on the phenyl ring. The appearance of a new peak at 840 cm" of P,-(p­C6H4N02) suggests paranitration26. In case of poly-N­vinyl carbazole, the product is suggested to be the mononitrated species and the nitration reaction similar to that used to nitrate polystyrene resulted in 90% mononitration on one of the phenyl rings of carbazole. The high yield of mononitrated product was obtained because the reaction was conducted in 1,2-dichloro­ethane solution of carbazole. It is most probable that the mononitrated polymer i insoluble in dichloro­ethane and its precipitation fro m the reaction phase inhibited further reaction. Nitration on one of the phenyl rings of carbazole deactivate the other phenyl ring also and hence further nitration on the second ring of mononitrocarbazole in the solid phase be­comes difficult and does not occur to any appreciable extent. Nitration in both cases was accompanied by the appearance of two new IR peaks at 1520 cm" and 1350 cm" and reaction was conti nued even for some hours till there was no further increase in the intensity of the peaks. During reduction of the nitro groups to amines in both the cases, some amount of unreduced -N02 group was left behind as evidenced from the presence of peaks at 1520 cm" and 1350 cm" in the amine product. The presence of a broad peak in the region 2400-2000 cm" confirms the presence of C6H4NH3Cl. The appearance of IR peaks in the region 3200-3400 cm" also support the presence of

-C6H4NH2 in the reduced materials after washing the polymer amine hydrochloride with dilute NaOH solution.

It was however very difficult to assign the structure of the polymer bound palladium (II) complexes with aminopolystyrene (complex I) and aminopoly-N­vinylcarbazole (complex II) , on the basis of chemical analysis, IR and diffuse reflectance spectra only. Chemical analyses of catalyst I indicates the ratio Pd : N : CI = 1 : 3.7 : 2. The analytical result suggests that there are about 40% uncomplexed -NH2 groups in the polymer matrix. Similar analysis for complex II indi­cates the ratio Pd : N : CI = 1: 1.9: 12.2 and points to nearly 70% complexation of C'2H7NH2 group. IR spectra of all these complexes are very much compa­rable to that of trans-Pd(C6HsNH2h CIz and shows absorption peaks at 450 cm" (vPdN) and 350 cm" (vPdCI) along with weak intensity bands. The com­plexes indicate absorptions at 440, 410 and 360 nm which are also observed as shoulders in the DMF so­lution spectra of trans-Pd(C6HsNH2h Ch. From these physico-chemical studies it was suggested that Pd(JI ) was at least four-coordinated in these complexes with two -NH2 groups bonded to the metal in trans­positions. The presence of palladium (II) complexes with only one coordinated -NH2 group and with chloro bridged dinuclear structure is therefore ruled out.

Results and Discussion Both the simple and polymer bound complexes of

palladium (II) are active as hydrogenation catalysts, but the polymer-anchored complexes appear to be superior to simple ones so far as the number of suc­cessful substrate reductions are concerned. The solu­ble complex trans-Pd(C6HsNH2h CI 2 showed good catalytic activities towards the reduction of aromatic nitro compound, alkenes, alkynes, benzaldehyde and Schiff bases under normal hydrogen pressure and at 20°e. The reaction condition and yield of products are given in Table I. The reduction temperature for nor­mal pressure hydrogenation should invariably be be­low 25C in order to avoid slow decomposition of the complex to Pd(O). Exclusive absence of moisture or air cannot prevent decomposition of the complex in hydrogen above 25°e.

The nature and yield of product, initial hydrogena­tion rate and turn-over number of catalyst (I) and (II) are given in Table II. Nitrobenzene, nitrosobenzene and hydroxylamines are completely reduced to the corresponding amines without the formation of any

MUKHERJEE: PALLADIUM ( II ) COMPLEXES AS HYDROGENATION CATALYSTS 349

Table I-Normal pressure reduction and percentage yie ld ~f products Catalyst = tral1s-Pd(C6HsNH2hCI 2 (4.2x 1O-3M); Temp.=20°C Timc period= a 3hr. b 5hr; Sub.Conc .=0.52M; Total Yol.=20mL

Substrates Initial rate of Initial turnover Product (%) Hrabs.(mLmin-l ) number(min- I)

Nitrobenzene" 5.5 0.98 Aniline (92) Azobenzene (05)

a-Nitrotolueneb 2.4 0.43 a-Toluidine (97) p-Chloronitrobenzeneb 4.0 0.71 p-Chloroaniline (88) p-nitrotolueneb 4.3 0.77 p-Toluidine (92) Styrene" 9.2 4.90 Ethy lbenzene (98) I-Hcxene' 6.1 3.80 Hexane (75)

2-Hexene (22) Phenylacety lenea 8.5 3.02 Ethylbenzene (97) Benzylidineanilineb 3.5 1.87 N-Phenylbenzylamine ( 100) N-Methylbenzaldimineb 4.5 2.40 N-Methylbenzylamine (100)

Table II-Nature of products with the catalyst I = Pol ysty rene complex. 1I = Poly-N-vinylcarbazole complex.

Substrates Catalyst Pd-content Initial H2 -Abs Initial turnover Products (%) with g-atm L-I mLmin -1 number (min-I) I II

Nitrobenzene I 1.69 4.20 2.30 Aniline 97 93 II 1.70 4. 15 2.20

a-Nitrotoluene 1.78 1.20 0.61 a-Toluidine 90 91 (( 1.8 1 1.15 0.50

a-Chloronitrobenzenene 1.78 1.40 0.71 a-Chloroani line 92 93 II 1.81 1.40 0.70

p-Chloron itrobenzenene 1.75 3.00 1.70 p-Chloroaniline 94 94 II 1.81 2.90 1.40

1/1- Dinitrobenzenene 1.82 2.10 1.00 m-Phenylenediamine 92 90 II 1.81 1.90 0.90

p-Nitrotoluene 1.75 3.30 1.30 p-Toluidine 94 93 (( 1.8 1 3.15 1.60

I-Nitronaphthalene I 1.30 1.70 0.80 I-Aminonaphthalene 94 90 (( 1.81 1.60 0.80

Hex- I-ene 1.55 4.40 7.70 Hexane 86 87 (( 1.50 4.10 7.40 Hex-2-ene 12 9

Styrene I 1.35 7.20 14.7 Ethy lbenzene 98 97 II 1.42 6.95 13.3

w-Nitrostyrene 1.67 3.60 5.80 w-Nitroethyl-benzene 95 91 II 1.72 3.40 5.40

Maleic acid 1.72 2. 10 3.30 Succinic acid 93 88 II 1.72 2.10 3.30

Fumaric acid 1.72 1.90 3.00 Succinic acid 92 89 II 1.72 1.80 2.80

Isoprene I 1.35 7.30 14.7 2-Mtlthy I-butane 97 93 II 1.42 7.35 14.1

Diphenyl acetylene I 1.35 3. 10 6.20 cis-Stilbene 92 87 (( 1.70 2.85 4.50

Phenyl- I 1.35 6.50 13.1 Styrene 97 90 acetylene (( 1.42 6.20 11.9

Benzaldehyde 1.69 3.30 5.30 Benzy l-alcohol 98 95 II 1.70 3.05 4.90

Benzylidine-aniline I 1.69 2.70 4.30 N-Phenyl-benzylamine 100 96 (( 1.70 2.50 4.00

N-Methyl-benzaldimine 1.69 3.50 5.60 N-Methyl-benzylamine 100 97 (( 1.70 3.40 5.40

350 INDIAN J. CHEM ., SEC B, FEBRUARY 2003

coupled products at in termediate stages. This is due to non-occurrence of simultaneous cis-coordinate of nitroaromatic derivati ves to the metal atom center. The steric hindrance provided by the polymer framework probably prevented such coordination . The polymer complexes reduced the non-substituted or p-substituted nitroaromatics at much faster rates than the cOITesponding a-subst ituted ones . Nitro­benzene is preferentially reduced almost to 100% when admitted with any artha-substituted derivatives such as a-nitrotoluene and o-chloronitrobenzene (Figure 1). The catalysts are effective for normal pressure hydrogenati on of alkenes, alkynes, aromatic

100

'" c BO

'" c o 0. E 60 o u -o o .. 0

;;--Q,

~ 20 .L

I

2 3 It 6

React ion t ime?, hr

Figure I-Prefercnti al hydrogenation of nitrobenzenc in prescnce of u-nitrotoluenc with PI-(p-C6H4NH 2hPdCI2 as catalyst. Solvent , DM F: Temp., 25°C; Pm , I atm. , [Cat ], 1.69x 10-3 g atom Pd li t"l. I, C6HsN02; 2, C6HSNH 2; 3, Cr,HsN HOH ; 4, o-CH1C6H4N02; 5, o-CH3C6H4NH 2: 6, o-CH3C6H4NHOH .

aldehydes and Schiff bases. Hydrogenation of alk-I­enes occur preferentially over isomerization. Preferential reduction of alk-I-enes to the ex tent of 90% are possible in presence of corresponding cyc lic, internal and branched chain alke nes. Aromatic aldehydes like benzaldehyde is reduced well with the catalysts but the aliphatic aldehydes could not be reduced under normal conditions.

The soluble catalyst Pd(C6HsNH2)2CI2 could not be used for the reduction of nitroa lkanes, aliphatic and aromatic nitriles and aliphati c aldehydes . For these substrates high pressure, high temperature conditions are essentia l. Under high pressure cond ition, the high reduction rate of these substrates at the initial stage slowed down very quickly and become zero with in 30 min s due to ex haustive decomposition of the complex to Pd(O). Details of high pressure reduction conditions with catalyst (I) and (II) are given in Table III. Opti­mum reduction is obtained under PH2 = I 00 atm at 70-80°C. Nitroalkanes were reduced via the formati on of alkylhydroxylamines as these were always detected at intermediate stages. The rate of reduction of nitroal­kanes decreased accord ing to the fo llowing order.

Nitromethane>N itroethane> l-nitropropane>2-nitropro­pane. In general branching greatly retarded the reduc­tion rate due to steric reasons.

The yellow suspension of (I) and (II) in DMF turned deep brown on stirring under hydrogen for 30 min and the addition of substrates at this stage started hydrogen absorption almost with the maximum rate. The change of colour of the catalyst during hydrogen absorption

Table I11--Nature of products under severc conditions

Substrates Catalyst Initi al Hr Abs Initial turnover Temperature Time Products (%) with mLmin-1 number (min-I) °C (hr) I II

Nitromethane I 1.70 11.8 70 6.0 Methylamine 94 92 II 1.75 12.0 70 6.0

Nitroethanc 1.70 11.8 70 6.2 Ethylamine 92 92 II 1.75 12.0 70 6.0

I-Nitropropane I 1.70 11.8 70 6.5 I-Aminopropane 9 1 88 II 1.75 12.0 70 6.4

2-Nitropropanc 1.82 12.2 75 6.8 2-Aminopropane 9 1 88 II 1.80 12.5 80 6.9

I-N itroheptune 1.82 12.2 80 7.5 I-Aminoheptune 89 85 II 1.80 12.5 85 7.7

2-Phenylnitroethane 1.82 12.2 80 7.8 2-Phenylcthylaminc 91 88 II 1.80 12.5 85 8.0

Nitrocyclohexane 1.82 12.2 80 8.5 Aminocyclohexane 70 70 II 1.80 12.5 85 8.8

Benzil I 1.82 10.5 75 3.0 Hydrobenzoin 96 90 11 1.62 10.0 75 3.0

Benzonitrilc 1.90 11.5 75 9.0 Benzy lam ine 85 84 Dibenzylamine 10 13

MUKHERJEE: PALLADIUM ( II ) COMPLEXES AS HYDROGENATION CATALYSTS 35 1

was accompanied by the liberation of HCI as was evi­denced by the increase of conductance and decrease of pH of the medium and the liberation of carbon dioxide from NaHC03. The hydrogen activated brown com­pounds were the actual catalytic species in both cases and the brown compounds left at the end of the cata­lytic run could be used repeatedly for hydrogenation without any loss of catalytic activity.

The deep brown materials obtained from catalyst (I) and (II) after hydrogen activation were identical in catalytic activities and exhibited similar IR spectra to the corresponding ones left at the end of normal and high pressure catalytic run. The IR spectra of the deep brown materi als in both cases exhibit peaks in the re­gion 3300-3400cm-J (vNH2)' 1630-1640 cm-J (vNH), 1970-1980 cm- J (vPd-H) 29, 1670-1680 cm- J (vCO, DMF), 450 cm-J (vPdN)2s and 350 cm-J (vPdCI)2s. The analysis of the brown materials (Pd : CI , 1: 1.2) for cata­lyst (I) and 1 : 1.25 for catalyst (II) and liberation of free HCI during hydrogen activation suggest partial replacement of Pd-CI bond by Pd-H during the activa­tion step. Most of the palladium from the brown mate­rial can be extracted by treating with ethanolic solution of KCN for 24 hr. The residual material was catalyti­cally inactive indicating the activity of the brown mate­rial to be due to Pd(II) complex only.

The above observations suggest that the complexes undergo the following transformation during hydro­gen activation.

H

PhH~ I /DMF "Pd

CI/ "NHi'h

The XPS study of the yellow polymer complexes (I) and (II) and the corresponding brown materials derived from them was taken in the range 330-350 eV. The values show that the oxidation state of palladium (II) remain unchanged after the catalytic run and the signals due to Pd 3d312 and Pd 3ds12 are observed in the range 343-344 and 338.2-338.6 eV respectivel /o. There is no signal due to PdQ in any case. These results definitely prove that the palladium in complexes does not de­compose during the catalytic run . Subsequent use of the catalyst do not show any further decomposition of the materials to the elemental state (Figure 2).

\.Il c: (j)

e

d

~ I ~C

I V~b L~'

350 340 330 Binding energy, eV

Figure 2--Signals due to Pd3dJ/2 and Pd3ds12 obtained from XPS studies. a, Soluble complex Pd(PhNH2h CI2 before catalytic run; b, brown compound left at the end of catalytic run (normal pres­sure reduction of PhN02 at 20°C); c, polysterene anchored com­plex (I) before catalytic run ; d, polyvinyIcarbazole supported palladium complex (II ); e, polystyrene-anchored complex after five catalytic runs (high pressure reduction of 2-nitropropane at 75°C).

It has been observed that trans-Pd(C6HsNH2h CI2

remain indefinitely stable at room temperature and does not show any decomposition when heated in air even to 240°e. The solution of the compound in DMF is quite stable in air and does not show any sign of decomposition even upto lOO°e. High pressure, high temperature study of the solution also indicates the stability of the compound under nitrogen. The com­pound however suffers slow decomposition in pres­ence of hydrogen pressure and the rate of decomposi­tion increased considerably with increasing hydrogen pressure and reaction temperature. The decomposition of trans-Pd(C6HsNH2hCIz during catalytic run, spe­cially under high hydrogen pressure at higher tem­perature must be due to Pd-NH2Ph bond cleavage at the first step. At ambient temperature and normal hy­drogen pressure, the reduction of nitroaromatics with the present group of catalysts probably proceeds in the following way (Scheme I)

Decomposition at high temperature or increased hydrogen pressure may be due to high lability of Pd­ligand bond in the soluble complex. The ligands PhNH2 and DMF interchange position before sub­strate addition (Scheme II).

The greater trans-directing influence of H dissoci ­ates the trans-PhNH2 from the metal and initiates the decomposition process. The decomposition may also

352 [NDIAN J. CHEM., SEC B, FEBRUARY 2003

DMF

... OH

PhN~ 7" NHPh Pd-- "-Cl PhNH:?

H ° (F)

H HO Ph~1 ONPh

'" 2H2 Pd-PhNH2 O~NPh H20 Cl- . P't;NH

"-::Pd/ (G) 2

./' '" Cl PhNH H (E) 2 2

Scheme I

f:.DMF

Scheme II

onglnate from the close proximity interaction of H and Cl in complex C". The polymer supported com­plexes are however stable under the existing reaction conditions. The rigid bond positions in the polymer matrix may be the reason that forbids interchange of ligand positions and formation of C" in these com­plexes have been ruled out.

References I Hartley F R & Vezey P N, Adv orgc/ilomet Chem, 15,1977,1 89. 2 Yermakov Y [, Coral Rev, 13,1976, 77. 3 Brown J M & Molinari H, Tetrahedroll Lett, 20, 1979, 2933. 4 MacDonald R P & Winterbotton J M, J Coral, 57, 1979, 195. 5 Duca D, Leotla L F & Degnell G, J Caull, 154, 1995,69. 6 Parshall G W, Application alld chelllistry of catalyst by soluble

transition metal complexes, Wiley-[nterscience, New York, 1980,227.

7 Bose A & Saha C R , J Mol Caull, 49, 1989, 271. 8 Knifton J F , J Org G em, 41 , 1976,[ 200. 9 Santra P K & Saha C R, J Mol Coral, 39, 1987, 279.

10 Bose A & Saha C R , Indian J G em, 29A, 1990,461 . II Tafesh A M & Beller M, Tetrahedron Lett, 30, 1995,9305. 12 Mukherjee D K, Palil B K & Saha C R , Indian J G em , 31,

1992,243. 13 Holy N L , J Org G em, 44, 1979,239. 14 Barall E & Holy N L , J Org Chem, 49, 1984, 2626. 15 [s lam S M , Bose A, Palil B K & Saha C R, J Carol, 173, 1998,

268. 16 Mukherjee D K , [slam S M, Palit B K & Saha C R, J Mol

Cauti, 124, 1997,5. 17 Hartley F R, Supported Metal Complexes, Reidel, Dordrechet,

1985. 18 Pillmann C U, Wu S K & Jacobson S E, J Catci/ , 44, 1976,

87. 19 Lang W H , Jurewicz A T, Haag W 0 , Whitehursl D D &

Rollmann L D, J Organomet Chem, 134, 1977,85. 20 Saha C R & Bhattacharyya S, J Chem Tecllllol Biotechnol, 37 ,

1987,233. 2 1 Bruner H & Bailer J C,lllorg Chem , 12, 1973, 1465. 22 Holy N L & Baralt E, J Org G em, 37, 1981. 25. 23 Li Y J & Jiang Y Y, J Catal , 2, 1981, 42. 24 Mukherjee D K, Indian J Chelll, 40A, 2001 , 1176 25 During J R, Laylon R, Sink D W & Mitchell B R , Spectrochem

Acta, 21 , 1965, 1367. 26 King R B & Sweet EM, J Org Chelll, 44, 1979, 285 . 27 Biswas M & Mukherjee A, Advances in Polymer Sciellce, 11 5,

1994,9 1. 28 Biswas M & Das S K, J PO/Ylll Sci POIYIIl Lett , 19, 1981 ,235. 29 Brooks E H & Glocking F, J Chelll Soc A, 1966, 124. 30 Holy N L, J Org G em, 43, 1978,4688.