Obtaining 1-Heptene from 1-Heptyne Semihydrogenation with an Anchored Rhodium Complex on Different Supports As Catalyst

Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 80:158–163 (2005) DOI: 10.1002/jctb.1168

Obtaining 1-heptene from 1-heptyne semihydrogenation with an anchored rhodium complex on different supports as catalyst Monica´ Quiroga,1 Domingo Liprandi,1 Pablo L’Argentiere,` 1,2∗ and Edgardo Cagnola1 1Quımica´ Inorganica,´ Departamento de Quımica,´ Facultad de Ingenierıa´ Quımica´ (UNL), Argentina 2INCAPE, Instituto de Investigaciones en Catalisis´ y Petroquımica´ (FIQ-UNL, CONICET), Santiago del Estero 2829, 3000 Santa Fe, Argentina

Abstract: The complex [RhCl(NH2(CH2)12CH3)3] was tested for the semihydrogenation of 1-heptyne in homogeneous and heterogeneous conditions. γ -Al2O3 and two different commercial activated carbons (RX-3 EXTRA and GF-45) were used as supports. The results were, then, compared with those previously reported for the [PdCl2(NH2(CH2)12CH3)2] complex supported or unsupported, and with the results obtained with the classic Lindlar catalyst. The complex was characterised by FTIR and elemental analysis. The pure species and the supported one were also characterised by X-ray photoelectron spectroscopy. Results determined by the latter technique suggest that the active species is the complex itself, which is stable under the reaction conditions. The supported rhodium tetra-coordinated complex shows higher activity and selectivity than the same complex unsupported, and also than the classic Lindlar catalyst. Moreover, among the rhodium-supported complexes the one immobilised on RX-3 EXTRA has a better performance than that heterogenised on GF-45, and this one has a better activity and selectivity than the γ - Al2O3 anchored complex. Our results also show that under the same operational conditions (temperature, hydrogen pressure and metal/substrate weight ratio) the rhodium complex, unsupported or supported, has a better performance than the corresponding palladium complex.  2004 Society of Chemical Industry

Keywords: 1-heptyne semihydrogenation; rhodium complex; activated carbons; γ -Al2O3; heterogeneous and homogeneous catalysis

1 INTRODUCTION complexes are widely used because they allow Semihydrogenation of alkynes is important from an higher values of activity and selectivity.10– 12 For any academic and industrial point of view. This is so industrial application, heterogeneous catalysts have because many products obtained from this kind of several advantages compared with their homogeneous reaction are useful in the synthesis of natural products counterparts, for example easy separation and the such as biologically active compounds.1 In these cases, possibility of continuous operation of the reactor.13 avoiding overhydrogenation to single bonds is an Moreover, the most extensively studied reaction in the important requirement. Control over the activity and literature is the semihydrogenation of ethyne, there selectivity of a catalytic reaction can be achieved in being little reported work about semihydrogenation of different ways, eg by varying the active species, the higher chain alkynes.2,14 support, adding a promoter or a poison, or by adding Several investigations revealed that, of all metals a modiﬁer. One of the most studied catalytic systems studied for alkyne semihydrogenation, Pd is the 15 is the Lindlar catalyst (Pd/CaCO3 modiﬁed with most selective catalyst. In previous papers, we have Pb(OAc)2), developed several decades ago. Through studied several aspects related to the use of palladium the years other authors have researched metallic complexes supported on alumina and activated and bimetallic catalysts,2–5 and transition metal carbons as catalysts for selective hydrogenation of complexes in homogeneous6,7 and heterogeneous8,9 double and triple bonds.16– 21 The aims of the conditions, even working under mild conditions present work are, on the one hand, to research the of pressure and temperature.9 Transition metal catalytic behaviour of a previously studied rhodium

∗ Correspondence to: Pablo L’Argentiere,` Quımica´ Inorganica,´ Departamento de Quımica,´ Facultad de Ingenierıa´ Quımica´ (UNL), INCAPE, Instituto de Investigaciones en Catalisis´ y Petroquımica´ (FIQ-UNL, CONICET), Santiago del Estero 2829, 3000 Santa Fe, Argentina E-mail: plargent@fiqus.unl.edu.ar Contract/grant sponsor: UNL Contract/grant sponsor: CONICET Contract/grant sponsor: ANPCYT; contract/grant number: PMT-BID 1201/OC-AR (Received 22 March 2004; revised version received 23 June 2004; accepted 12 August 2004) Published online 12 October 2004  2004 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2004/$30.00 158 Obtaining 1-heptene from 1-heptyne with a rhodium complex on different supports complex,22 anchored on different supports, on the of the samples were dried at 353 K, and they were semihydrogenation of 1-heptyne, a relatively high examined in potassium bromide disks in a concentra- molecular weight alkyne, and on the other hand, tion ranging from 0.5 to 1% to ensure non-saturated to compare the catalytic behaviour of this rhodium spectra.22 complex with those corresponding to the Lindlar catalyst, and with a palladium tetra-coordinated 2.2.3 X-ray photoelectron spectroscopy (XPS) 20,21 complex. The Rh 3d5/2,N1s1/2, and Cl 2p binding energies and the atomic ratios N/Rh and Cl/Rh for the pure and the heterogenised complex, and also the atomic 2 EXPERIMENTAL ratios Rh/Z (where Z refers to Al for Al2O3 support, 2.1 Complex synthesis, purification and or to C for carbon supports) for the supported species, were characterised by XPS. Determinations anchoring were carried out on a Shimadzu ESCA 750 Electron The [RhCl(NH (CH ) CH ) ] complex (here- 2 2 12 3 3 Spectrometer coupled to a Shimadzu ESCAPAC 760 after NH (CH ) CH = TDA) was prepared using 2 2 12 3 Data System. To correct possible deviations caused 35.3 mg of RhCl and 202.3 mg of TDA, giving a 3 by electronic charges of the samples, the C 1s line molar ratio of TDA/Rh = 6, in carbon tetrachloride was taken as an internal standard at 285.0 eV. The as the solvent. The reaction was carried out in glass samples were introduced into the XPS equipment equipment with magnetic stirring and refluxed under sample holder following the operational procedures a purified argon atmosphere at 348 K, for 4.5 h. described by other authors27 in order to ensure that Then, the rhodium complex was purified by column there were no modifications on the electronic states chromatography to eliminate all the aliquots contain- of the species analysed. Exposing the samples to the ing the excess TDA reactant. To do so, silica gel atmosphere for different periods confirmed that there was the stationary phase and a mixture of chloro- were no electronic modifications. Determinations of form/methanol (5/1, v/v) was the running solvent. All the superficial atomic ratios X/Rh (X = N, Cl, Al and of the aliquots were tested to determine the presence C) were made by comparing the areas under the peaks of free TDA using thin-layer chromatography. All of after background subtractions and corrections due to the fractions showing no impurities were gathered differences in escape depths and in photoionisation up and dried in a rotatory evaporator to obtain the cross sections, using Scofield’s results.18 corresponding complex species in the solid state. Heterogenisation of the complex was carried out 2.2.4 Catalytic determinations on a Ketjen CK 300 γ -alumina and two NORIT Catalytic performance was determined for the selective pelletised carbons (RX-3 EXTRA and GF-45), by hydrogenation of 1-heptyne to 1-heptene, using a means of the incipient wetness technique.19 The γ - 2% (v/v) solution of 1-heptyne in toluene with a alumina cylinders of 1.5 mm diameter were previously H pressure of 150 kPa. The reaction was carried calcined in air at 773 K for 3 h, giving a BET surface 2 − − out for 2 h at 303 K, in a batch stainless steel area of 180 m2 g 1, and a pore volume of 0.66 cm3 g 1. stirred tank reactor (V = 100 cm3; stirring velocity = RX-3 EXTRA and GF-45 present respectively BET − 600 rpm). Both the reactor and the stirrer were surface areas of 1411 and 1718 m2 g 1, and pore − poly(tetrafluoroethylene) (PTFE) coated in order to volumes of 1.22 and 1.69 cm3 g 1. A solution of the avoid the possible contamination of the reaction media corresponding metal complex in chloroform/methanol with metal cations. The weight of the supported (5/1, v/v) was used for impregnation in a suitable complex catalyst was 0.075 g in every case. concentration to obtain a catalyst containing 0.3 We have also determined the absence of internal wt% Rh. The procedure was carried out at room and external diffusional limitations in every catalytic temperature (298 K) for 24 h until a constant mass test following the procedures already reported in a equal to the support plus the complex species masses previous work.22 was obtained. Reactants and products were analysed by gas chromatography, using a FID detector and a CP Sill 88 2.2 Complex and catalyst characterisation capillary column. All runs were carried out in triplicate; 2.2.1 Elemental microanalysis the relative experimental error was about 3%. The complex elemental composition for rhodium, chlorine and nitrogen was determined according to 2.2.5 Complex leaching evaluation 23– 26 analytical standard methods. The possibility of complex leaching during the catalytic runs was tested by means of the following procedures: 2.2.2 Fourier transform infrared analysis (FTIR) (a) XPS determinations of the atomic ratios N/Rh, The infrared characteristic peak frequencies of the Cl/Rh and Rh/Z (where Z refers to Al for Al2O3,or pure rhodium complex and the TDA ligand were anal- to C for activated carbons) of the catalysts after each ysed in the 4100–900 cm−1 range in a Shimadzu FTIR catalytic test; (b) spectrophotometric determinations 8101/8101M single beam spectrometer; the equip- to analyse Rh in the remaining solutions after each ment has a Michelson-type optical interferometer. All catalytic run; (c) spectrophotometric determinations

J Chem Technol Biotechnol 80:158–163 (2005) 159 MQuirogaet al to analyse Rh in the remaining solution after doing a blank test performed with the supported complex in pure toluene for 100 h at the same reaction temperature.

3 RESULTS AND DISCUSSION 3.1 Rhodium complex 3.1.1 Minimum complex formula The elemental analyses for the pure complex reveal the following composition (wt%): 57.69%Rh, 19.23%Cl and 23.08%N. These values suggest that the atomic ratios for rhodium, chlorine and nitrogen can be expressed as 1/1/3. Table 1 shows XPS results, the binding energy (BE) values for Rh 3d5/2,Cl2pandN1s1/2,andthe Figure 1. FTIR spectra for pure TDA and pure rhodium complex: A −1 atomic ratios for these elements. The BE values for (NH2 stretching, 3400–3100 cm ), B (NH2 bending, −1 −1 the pure complex are those characteristic for rhodium 1700–1600 cm ) and C (CN stretching, 1200–1000 cm ). as rhodium in the Wilkinson’s catalyst with a +1 oxidation state, nitrogen as nitrogen in an amine the complex spectrum that bands in A, B and C ranges and chlorine in a chloride species, respectively.28 It are present at lower energies. Also, when a primary can be observed that the atomic ratios N/Rh and NH2 is bonded, the stretching absorption peaks are Cl/Rh are around 3 and 1, respectively. On the other considerably different in shape and intensity from the 29 hand, the binding energies in the pure complex and original NH2 bands. This is a fact that can also be in the complex supported on the different surfaces, observed in the same spectrum. All this information before and after each catalytic run, were almost the would confirm that the TDA molecule is part of the same. This permits the assumption that the complex complex coordination sphere. maintains its original ligands after anchoring and The results obtained from compositional analysis, running it. XPS and FTIR techniques suggest that the complex’s Figure 1 shows the spectra for the pure TDA (pur- empirical formula could be [RhCl(NH2(CH2)12 chased at Fluka Chemika catalogue number 91590, CH3)3]. purity > 98%) and the [RhCl(NH2(CH2)12CH3)3] complex. The pure TDA spectrum is in accor- 3.1.2 Absence of complex leaching dance with that reported in the literature.29 Although In Table 1, the atomic ratios Rh/Al or Rh/C (the sixth both curves are quite similar, the one correspond- column) are shown to remain almost the same, before ing to the rhodium complex presents some shifts and after each catalytic test for all the supports used. towards lower energies. Special attention is focused Also, the results of the spectrophotometric tech- on the frequencies related to the nitrogen atom nique show no presence of rhodium in the solutions because they are sensitive to the bond formation analysed after each run, and also in the blank test. during the complex synthesis. This is so because These two facts allow the conclusion that the the amine is attached to the rhodium atom through coordination compound is firmly attached to the the nitrogen lone pair. The zones identified by supports and that there is no leaching of it at all. −1 A(NH2 stretching, 3400–3100 cm ), B (NH2 bending, 1700–1600 cm−1) and C (CN stretching, 3.1.3 Catalytic activity and selectivity 1200–1000 cm−1), are those in which the nitrogen When the conversions to 1-heptene and heptane are surrounding is compromised.30 It can be seen from plotted versus the 1-heptyne total conversion the

Table 1. Rh 3d5/2,N1s1/2, and Cl 2p binding energies and the atomic ratios Rh/Z (where Z refers to Al for Al2O3 support, or to C for carbon supports), N/Rh and Cl/Rh for the unsupported rhodium complex and for the same complex supported on alumina, or supported on activated carbons RX-3 EXTRA and GF-45, before and after catalytic evaluation

Reactant Rh 3d5/2 N1s1/2 Cl 2p Rh/Z N/Rh Cl/Rh Sample solution (eV) (eV) (eV) (at/at) (at/at) (at/at)

[RhCl(TDA)3] Fresh 307.1 402.1 198.1 — 3.00 1.01 [RhCl(TDA)3]/Al2O3 Fresh 307.2 402.2 198.3 0.052 2.99 1.02 1-Heptyne 307.1 402.2 198.2 0.051 2.99 0.99 [RhCl(TDA)3]/GF-45 Fresh 307.2 401.9 198.2 0.042 3.01 1.02 1-Heptyne 307.1 402.09 198.3 0.043 3.00 1.01 [RhCl(TDA)3]/RX-3 Fresh 307.1 401.9 198.0 0.041 3.00 1.02 1-Heptyne 307.2 402.0 198.0 0.042 3.00 1.00

160 J Chem Technol Biotechnol 80:158–163 (2005) Obtaining 1-heptene from 1-heptyne with a rhodium complex on different supports

100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20

20 Selectivity to 1-heptene (%) 10 10 0 0 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Total conversion (%) Conversion to 1- heplene or heptane (%) Total conversion (%) , [RhCl(TDA)3]/RX-3 , [RhCl(TDA)3]/GF-45 , [RhCl (TDA) ]/RX - 3 ; 3 , ; [RhCl (TDA)3]/Al2O3 , [RhCl(TDA)3]/Al2O3 , unsupported [RhCl(TDA)3] , ; [RhCl (TDA)3]/GF - 45 , ; unsupported [RhCl (TDA)3] , Lindlar catalyst , ; Lindlar catalyst Figure 3. Selectivity to 1-heptene (%) as a function of the 1-heptyne Figure 2. Conversion to 1-heptene (%) (filled symbols) and to total conversion (%) for [RhCl(TDA)3]/RX-3, [RhCl(TDA)3]/GF-45, heptane (%) (open symbols) as a function of 1-heptyne total [RhCl(TDA)3]/Al2O3, unsupported [RhCl(TDA)3] and Lindlar catalyst. conversion (%) for [RhCl(TDA)3]/RX-3, [RhCl(TDA)3]/GF-45, [RhCl(TDA) ]/Al O , unsupported [RhCl(TDA) ] and Lindlar catalyst. 3 2 3 3 conversion lower than 45% the selectivity was almost the same for the supported complex on the activated differences in the catalytic behaviour of the selected carbons, the unsupported complex and the Lindlar catalysts are quite evident, as shown in Fig 2. At low catalyst and slightly higher than that for the supported total conversion (<45%) the conversions to 1-heptene, complex on γ -Al2O3. However at higher values and also to heptane, were similar on all five catalysts of the total conversion the differences are quite investigated. Within the range from 45% to 68% the evident. The selectivity for the supported complex same situation is applied for all the rhodium complex on the activated carbon RX-3 EXTRA remained catalysts, supported or not. Differences were observed constant (96%) up to a total conversion of about at higher conversion levels. 91%. For the [RhCl(TDA)3]/GF-45 the selectivity For the Lindlar catalyst the conversion to 1-heptene remained constant (98%) up to a total conversion reached a maximum of 43% at a total conversion of about 78%. For the other two catalytic systems: of about 47% and then decreased sharply as the [RhCl(TDA)3] and [RhCl(TDA)3]/γ -Al2O3,the heptane conversion increased rapidly; at the final total selectivities remained more or less constant (96% and conversion of 58% the conversion to 1-heptene and to 91% each one) up to a total conversion of about 52% heptane were almost the same (approximately 30%). and 84% respectively. The values obtained for the unsupported rhodium complex were higher than that corresponding to 3.2 Rhodium complex vs palladium complex the Lindlar catalyst, as the conversion to 1-heptene 3.2.1 Catalytic activity and selectivity achieved a maximum of 62% at a total conversion of Table 2 shows, in a comparative way, different 69%, and then diminished markedly while the heptane conversions and selectivity values for different catalytic conversion increased; at the final total conversion of chemical species relating to this paper and the ones 78%, the conversion to 1-heptene and to heptane reported in previous works.20,21 They were obtained were almost the same (approximately 40%). Among from Fig 2 and Fig 3 in the sequence shown by the the rhodium complex-supported catalysts, the better column headings in Table 2. The aim of this section performance corresponded to the complex anchored is to compare the catalytic performance of the best on activated carbon RX-3 EXTRA. In this case, rhodium complex catalyst versus that corresponding the conversion to 1-heptene reached a maximum of for the palladium complex. about 90% at a total conversion of approximately As can be seen, from the mentioned values, this is the 94%. Beyond this point the conversion to 1-heptene case for both complex species supported on activated decreased dramatically, meanwhile the conversion to carbon RX-3 EXTRA. The maximum conversion heptane increased impressively; nevertheless at the (%) to 1-heptene for the [RhCl(TDA)3]/RX-3 is final total conversion of about 96% the conversion 89.5, which is obtained for a total conversion (%) to 1-heptene was still 6.5 times higher than the of 1-heptyne of 94.3, giving a selectivity to 1- conversion to heptane (84% versus 13%). heptene (%) of 94.9; meanwhile the same values for The selectivity to 1-heptene values displayed in the [PdCl2(TDA)2]/RX-3 are: 86.4, 92.2 and 93.7 Fig 3 as a function of the 1-heptyne total conversion respectively. From these data it can be said that the also demonstrate the better catalytic behaviour for rhodium catalyst is a better catalytic species than the [RhCl(NH2(CH2)12CH3)3]/RX-3 EXTRA. At a total palladium one. This information suggests that new

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