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Preparation of the Metal Complex Catalysts Immobilized on Chitosan for Carbonyl Compounds Transfer Hydrogenation
9 1998 Elsevier Science B.V. All rights reserved. Preparation of CatalystsV I I B. Delmonet al., editors.
237
Preparation o f the Metal C o m p l e x Catalysts Immobilized on Chitosan for Carbonyl C o m p o u n d s Transfer Hydrogenation V.Isaeva, V.Sharf, N.Nifant'ev, V.Chernetskii, Zh.Dykh N.D. Zelinsky Institute for Organic Chemistry Russian Academy of Sciences Leninsky Pr.47, Moscow, 117913, Russia
Abstract
Novel catalysts of reduction reactions were prepared by immobilization of binuclear Rh(II) and Ru(II, III) teraaacetate complexes with metal-metal bond on original chitosan and succinamide chitosan derivative. Obtained metal complex systems catalyzed transfer hydrogenation of carbonyl group of cyclohexanone and acetophenone in the liquid phase under mild conditions (82.4~ Ar). 2-Propanol was a hydrogen donor and reaction promoted by KOH in 2-propanol solution. The preparation procedure (solvent, time of the complex deposition, size of chitosan corpuscles) strongly influenced the activity of the prepared catalysts. The metal complex structures formed on the carrier surface were examined by IRand electronic spectroscopy. Introduction.
Metal complexes immobilized on the solid carriers are very attractive for the researchers due to combination of the activity and selectivity of the homogeneous catalysts and the simplicity of the recycling and recovery of heterogeneous ones. Currently, the significantly efforts are focused on the development and design of the fitting materials for the carriers. Presently, various synthetic polymer carriers are successfully applied for the complex immobilization. Simultaneously, the natural carriers have stimulated much interest due to their availability, biodegradability and higher thermal stability in comparison with the most synthetic resins. Generally, the natural carrier application for the metal complexes immobilizaton is restricted by cellulose [ 1]. We suggest that very promising results will be achieved using chitosan as carrier [2]. In contrast with cellulose, monomer of chitosan, deacetylated chitin derivative, contains aminogroup and therefore can be used without preliminary functionalization. It has been shown previously [3,4] that the nature of the ligand environment of immobilized binuclear Rh(II) and Ru(II, III) complexes determines the structure and properties of the catalytic systems being formed. After immobilization on qt-aminopropyl groups containing silica and synthetic polymers modified by heterocyclic amine groups complexes with tetraacetate ligands retaine the binuclear structure with metal-metal bond. Immobilized binuclear Rh(II) and Ru(II,III) complexes differ from mononuclear ones by higher activities in the several reduction reactions [3-5]. To continue the investigations along this line we studied
238 the effect of the structure of Rh and Ru complexes immobilized on original chitosan (Figure 1) and succinamide chitosan derivative (Figure 2) on the activity of the resulting catalysts.
OH
OH
0
0
/0
0
~N
i O~ C--L.coo_Na+
Figure 1. Original chitosan
Figure 2. Succinamide chitosan derivative
Thus the aims of our work were: 1) to investigate the immobilization of Ru and Rh complexes on chitosan and succinamide chitosan derivative; 2) to examine the obtained catalytic systems in the transfer hydrogenation of cyclohexanone and acetophenone; 3) to elucidate the effect of carrier and catalyst preparation conditions on the metal complex structures formed on the carrier surface and by this on the catalytic activity.
Experimental. Purified chitosan and succinamide chitosan derivative were applied for the complex immobilization. [Rh2(O2CCHa)4] and [Ru2(O2CCH3)4] were prepared according to the reported procedures [6,7]. Rh and Ru tetraacetates were deposited from aqueous and 2-propanol solution under Ar. The quantity of Rh/Ru deposited were calculated from the difference between the initial concentration of metal in the solution and the concentration after filtration and washing of the catalyst, as determined by atomic absorption spectroscopy. The experiments were carried out in a reactor equipped with a magnetic stirrer, a water jacket, a reflux condenser, and facility for sampling [3]. 2-propanol was used as hydrogen donor. A catalyst (0.05-0.1 g, 4.96 xl 0.6 moles of Rh/Ru) were placed in reactor, the system was filled with Ar, and 10 ml of 2-propanol was introduced along with a promoter (solution of KOH in 2-propanol). The reaction mixture was stirred and heated to 82.4~ after which a solution of substrate (4.84-9.68)xl 0.4 mole in 5 ml of 2-propanol was added. The composition of the catalysate was determined by GLC using a Biochrom-21 chromatograph with a flame ionization detector at 100-170~ (with N~ as the carrier gas, and a 3mx3mm stainless-steel column filled with Triton on X-545 Celite). The activities of the catalysts were characterized by the initial specific rates of the cyclohexanol (W0~) and 2-phenylethanol (W02) formation determined graphically (mols mo1-1 of M minl). IR-spectra of original and immobilized
239 complexes were recorded on a Specord-M 80 instrument in the form of pressings with KBr. The electronic spectra were taken in a Specord M-40 instrument.
Results and Discussion. Catalytic behavior of immmobilized binuclear tetraacetate Rh(ll) and Ru(ll,lll) complexes Binuclear [Rh2(O2CCH3)4]and [Ru2(O2CCH3)4] were chosen for immobilization due to excellent ability of metals in these complexes to coordinate with N-containing functional groups without leaching [3,4]. Actually, any metal complex remove from carrier surface was observed after immobilization as well as during catalytic process. Transfer hydrogenations of cyclohexanone and acetophenone were examined as model reactions. Reduction of both cyclohexanone and acetophenone proceeded selective without byproduct formation, with yield 99.6%. The reaction of transfer hydrogenation promoted by KOH in 2-propanol solution. It can be seen from Table 1 that activity of Rh catalysts surpassed one of Ru catalytic systems in examined reaction of transfer hydrogenation. Acetophenone was reduced rather slowly then cyclohexanone. It could be explained by more solid coordination of acetophenone with metal in intermediate complex formed during transfer hydrogenation (like in Meerwein-PonndorfVerley reactions). The nature of N-containing group (amino- or succinamide group) of the carrier did not considerably influence in the catalytic activity in this reaction. In contrast, the preparation conditions (solvent, time of the complex deposition, size of chitosan corpuscles) strongly influenced the activity of the prepared catalysts. Effect of the chitosan corpuscle size. The chitosan corpuscle sizes were regulated by subsequent solvation and repricipitation from diluted CH3COOH and NaOH aqueous solutions. The decrease of the chitosan corpuscle size from 3 to 0.1 mm leaded to the significant rise of the initial rate of carbonyl group transfer hydrogenation for both Rh and Ru catalysts (Table 2). Effect of the metal complex deposition conditions The metal complex preparation conditions influenced essentially in the catalyst activity. The data from Table 1 demonstrate that the nature of the solvent from which metal complex deposition carried out considerably effected the catalytic properties of the prepared catalyst. Catalytic activity of immobilized metal complex system on the basis of Rh and Ru complexes deposited from 2-propanol solution surpassed one of these complexes deposited from aqueous solution. It can be seen from Table 1 that decrease of complex deposition time from 72h to 2h leaded to the rise of the initial rates of transfer hydrog~,ation about one order for both Rh and Ru metal complex catalysts (in the case of the deposition from aqueous solution). These catalytic data could be explained by the difference in the structures formed on the carrier surface under different deposition conditions of metal complex. In the case of the deposition from aqueous solution, the hydrolysis of original binuclear metal complex into mononuclear one could be prevented by deposition time shortening. This suggestion was confirmed by IRand electronic spectroscopic examinations.
240 Table 1. Transfer hydrogenation of cyclohexanone and acetophenone in the presence of immobilized Rh and Ru tetracetates (4.9xl 0 .6 moles of Rh/Ru, 4.8x104 moles of substrate, 4.9x104 moles of KOH, 82.4~ 15 ml of 2-propanol Metal complex Carrier Solvent, from Metal W0~, mols W02,mol 1 which metal complex mol ~ of M o f M min ~ complex deposition deposition min ~ was carried out time, h [Rh2(O2CCH3)4] original H20 2 3.7 3.1 chitosan . . . . . . 72 0.3 0.1 . . . . 2-propanol 2 9.5 8.2 . . . . . . 72 9.3 8.1 " succinamide H20 2 3.4 2.1 chitosan derivative . . . . . . 72 0.3 0.1 . . . . 2-propanol 2 10.1 9.6 . . . . . . 72 10.2 9.5 [Ru2(O2CCH3)4] original H20 2 1.6 1.2 chitosan . . . . . . 72 0.2 0.1 . . . . 2-propanol 2 5.1 4.8 . . . . . . 72 4.8 4.4 " succinamide H20 2 1.0 0.8 chitosan derivative . . . . . . 72 0.2 0.1 . . . . 2-propanol 2 5.4 5.1 . . . . . . 72 5.2 4.7
Structure of Immobilized Rh(ll) complexes When the tetraacetate binuclear complexes of rhodium(II) are deposited on chitosan, four different types of surface structures may be formed, as it suggested for immobilization on 7aminopropyl containing silica [3]. One of them is bound to the carrier through the equatorial coordinate (A), two of them through the axial coordinate (B, C). These structures retain their dimeric form. Also possible is the formation of structures with a mononuclear nature (D). The formation of surface structure depends on the deposition conditions of metal complex and the flexibility of the hydrocarbon fragments of the carrier. In the case of Rh teraacetate deposited from 2-propanol solution and from aqueous solution (deposition time 2 h) on original chitosan, the color of the carrier with immobilized complex became lilac. In the case of the Rh teraacetate deposited under the same conditions on succinamide chitosan derivative, the color of carrier changed during the deposition process
241 from lilac to green. A lilac color is observed for the acetate complexes of Rh(II) in the case in which a nitrogen-containing ligand is coordinated through the axial site. The acetate complex takes on a green color when one or two acetate bridge group are split out [8]. In the case of succinamide chitosan derivative, we can assume that the succinamide groups of the Table 2. Influence of the chitosan corpuscle size in the catalytic activity in transfer hydrogenation of cyclohexanone and acetophenone in the presence of immobilized Rh and Ru tetracetates (4.9x10 6 moles of Rla/Ru, 4.8x10 -5 moles of substrate, 4.9x104 moles of KOH, 82.4~ 15 ml of 2-propanol Metal complex Chitosan corpuscle W0~, mols mol l of M W02, mols mol l of M size, mm min ~ min-1 min ~ rain- 1 [Rh2(O2CCH3)4] 0.1 9.5 8.2 " 0.5 5.8 4.9 " 1 1.2 0.8 " 3 0.6 0.3 [Ru2(O2CCH3)4] 0.1 5.2 4.0 " 0.5 2.2 1.7 " 1 0.7 0.5 " 3 0.2 0.1
macroligand are initially coordinated through two axial sites of the complex, and then through equatorial sites, at the expense of splitting out part of the acetate groups. In the electronic reflection spectra of these samples was present a broad absorption band with a maximum in the 16.000 cm ~ region, indicating preservation of the binuclear structure of the complex Rh(II) with an Rh-Rh bond, and also indicating the presence of acetate bridge groups, the number of which varies from 2 to 4 [9]. In the case of original chitosan, we suggested that the binuclear structure (B) was realized on the surface, and in the case of succinamide chitosan derivative, the binuclear structure (A) was realized. In the case of metal complex deposition from aqueous solution with prolonged deposition time (72 h) the color of carrier changed during the deposition process from lilac to grey and the characteristic absorption band was absent in the elrectronic spectra. Thus, possibly, the formation of the mononuclear structure (D) took place on the carrier surface due to hydrolysis of initial binuclear complex. After immobilization of Rh(II) tetraacetates on original chitosan (deposition from 2propanol and from aqueous solution with deposition time 2h), absorption bands (AB) Vas (COO) 1600 cm ~ and v,(COO) 1425 cm ~ were presented in the region of the carboxyl group vibrations (see Figure 3) in IR-spectra. The same AB were presented in initial complex (1585 and 1425 cm~). The frequence 16000 cm ~ was rather higher then in original complex. It could be explained by Rh coordination changing or electronic density. The intensity of these AB as well as the absence of shifts for the COO vibrations (Figure 3), indicated that complexes retaining four acetate bridges were found on the carrier surface (structure B). In the case of deposition from aqueous solution with prolonged deposition time on original chitosan or on
242 succinamide chitosan derivative the characterisic AB of carboxylic group vibrations were absent. It could be explained by the absence of acetates groups or theirs very low concentration. Acetate groups could be replaced by succinamide groups of the carrier or by water during deposition (structure A or D). This agrees with the data obtained by electronic spectroscopy. Thus, our data demonstrated, that when the shorter deposition time during immobilization of metal complex from aqueous solution, the binuclear structure of original complex was preserved. In the case of the deposition time lengthening, binuclear structure degraded to mononuclear one with the substitution of acetate groups of original complex with aminogroups of chitosan.
Figure 3. IR spectra: 1) Chitosan; 2) [Rh2(O2CCH3)4]/original chitosan, deposition from 2-propanol solution; 3) [Rh~(O2CCH3)4]/succinamide chitosan derivative, deposition from 2-propanol solution; 4) [Rh2(O2CCH3)a]/original chitosan, deposition from aqueous solution, deposition time 72 h; 5) [Rh2(O2CCH3)4]/original chitosan, deposition from aqueous solution, deposition time 2 h
Conclusions
1. Original chitosan and succinamide chitosan derivative were applicated for the preparation of the novel transfer hydrogenation catalysts on the basis of immobilized of binuclear Rh and Ru tetraacetates. 2. IR- and electronic spectroscopic examinations demonstrated that type of the metal complex structure formed on the carrier surface depended on the catalyst preparation procedure (mononuclear or binuclear immobilized complex) as well as on the macroligand nature
243 (coordination type of binuclear metal complex with carrier: through equatorial or axial coordination sites). 3. Metal complex immobilized system with binuclear structure possessed more catalytic activity in examined reaction, then mononuclear one.
References.
1. K. Kaneda, H. Yamamoto, T. Imanaka, S. Teranishi, J.Mol.Catal. 29 (1985) 99. 2. V.N. Chemetskii, N.E. Nifant'ev, Mendeleev Chemistry Journal, 41 (1997) 80. 3. Isaeva V.I., SharfV.Z., Zhilyaev A.N., Bull.Acad.Sci. of USSR, Chem. div. 40 (1991) 257. 4. V.I. Isaeva, V.Z. Sharf, Y.V. Smirnova, Zh.L. Dykh, G.N. Baeva, T.A. Fomina, A.N. Zhilyaev, I.B. Baranovskii, Rus. Chem. Bull. 44 (1995) 64. 5. V.I. Isaeva, V.Z. Sharf, Zh.L. Dykh, L.I. Lafer, V.I. Yakerson, Bull. Acad. Sci. of USSR, Chem. div. 41 (1992) 49. 6. B.C.Hui, G.L. Rempel, J. Chem. Sot., Chem. Commun. (1970) 1195. 7. F.A. Cotton, Inorg. Chem. 27 (1988) 43. 8. A.N. Zhiljaev, A.T. Fal'kengof, M.A. Golubnichaya, et al., Koordinats. Khim. 12 (1986) 1862. 9. V.Z. Sharf, V.I. Isaeva, A.N. Zhilyaev, I.B. Baranovskii Bull. Acad. Sci. of USSR, Chem. div. 38. (1990) 1796.
237
Preparation o f the Metal C o m p l e x Catalysts Immobilized on Chitosan for Carbonyl C o m p o u n d s Transfer Hydrogenation V.Isaeva, V.Sharf, N.Nifant'ev, V.Chernetskii, Zh.Dykh N.D. Zelinsky Institute for Organic Chemistry Russian Academy of Sciences Leninsky Pr.47, Moscow, 117913, Russia
Abstract
Novel catalysts of reduction reactions were prepared by immobilization of binuclear Rh(II) and Ru(II, III) teraaacetate complexes with metal-metal bond on original chitosan and succinamide chitosan derivative. Obtained metal complex systems catalyzed transfer hydrogenation of carbonyl group of cyclohexanone and acetophenone in the liquid phase under mild conditions (82.4~ Ar). 2-Propanol was a hydrogen donor and reaction promoted by KOH in 2-propanol solution. The preparation procedure (solvent, time of the complex deposition, size of chitosan corpuscles) strongly influenced the activity of the prepared catalysts. The metal complex structures formed on the carrier surface were examined by IRand electronic spectroscopy. Introduction.
Metal complexes immobilized on the solid carriers are very attractive for the researchers due to combination of the activity and selectivity of the homogeneous catalysts and the simplicity of the recycling and recovery of heterogeneous ones. Currently, the significantly efforts are focused on the development and design of the fitting materials for the carriers. Presently, various synthetic polymer carriers are successfully applied for the complex immobilization. Simultaneously, the natural carriers have stimulated much interest due to their availability, biodegradability and higher thermal stability in comparison with the most synthetic resins. Generally, the natural carrier application for the metal complexes immobilizaton is restricted by cellulose [ 1]. We suggest that very promising results will be achieved using chitosan as carrier [2]. In contrast with cellulose, monomer of chitosan, deacetylated chitin derivative, contains aminogroup and therefore can be used without preliminary functionalization. It has been shown previously [3,4] that the nature of the ligand environment of immobilized binuclear Rh(II) and Ru(II, III) complexes determines the structure and properties of the catalytic systems being formed. After immobilization on qt-aminopropyl groups containing silica and synthetic polymers modified by heterocyclic amine groups complexes with tetraacetate ligands retaine the binuclear structure with metal-metal bond. Immobilized binuclear Rh(II) and Ru(II,III) complexes differ from mononuclear ones by higher activities in the several reduction reactions [3-5]. To continue the investigations along this line we studied
238 the effect of the structure of Rh and Ru complexes immobilized on original chitosan (Figure 1) and succinamide chitosan derivative (Figure 2) on the activity of the resulting catalysts.
OH
OH
0
0
/0
0
~N
i O~ C--L.coo_Na+
Figure 1. Original chitosan
Figure 2. Succinamide chitosan derivative
Thus the aims of our work were: 1) to investigate the immobilization of Ru and Rh complexes on chitosan and succinamide chitosan derivative; 2) to examine the obtained catalytic systems in the transfer hydrogenation of cyclohexanone and acetophenone; 3) to elucidate the effect of carrier and catalyst preparation conditions on the metal complex structures formed on the carrier surface and by this on the catalytic activity.
Experimental. Purified chitosan and succinamide chitosan derivative were applied for the complex immobilization. [Rh2(O2CCHa)4] and [Ru2(O2CCH3)4] were prepared according to the reported procedures [6,7]. Rh and Ru tetraacetates were deposited from aqueous and 2-propanol solution under Ar. The quantity of Rh/Ru deposited were calculated from the difference between the initial concentration of metal in the solution and the concentration after filtration and washing of the catalyst, as determined by atomic absorption spectroscopy. The experiments were carried out in a reactor equipped with a magnetic stirrer, a water jacket, a reflux condenser, and facility for sampling [3]. 2-propanol was used as hydrogen donor. A catalyst (0.05-0.1 g, 4.96 xl 0.6 moles of Rh/Ru) were placed in reactor, the system was filled with Ar, and 10 ml of 2-propanol was introduced along with a promoter (solution of KOH in 2-propanol). The reaction mixture was stirred and heated to 82.4~ after which a solution of substrate (4.84-9.68)xl 0.4 mole in 5 ml of 2-propanol was added. The composition of the catalysate was determined by GLC using a Biochrom-21 chromatograph with a flame ionization detector at 100-170~ (with N~ as the carrier gas, and a 3mx3mm stainless-steel column filled with Triton on X-545 Celite). The activities of the catalysts were characterized by the initial specific rates of the cyclohexanol (W0~) and 2-phenylethanol (W02) formation determined graphically (mols mo1-1 of M minl). IR-spectra of original and immobilized
239 complexes were recorded on a Specord-M 80 instrument in the form of pressings with KBr. The electronic spectra were taken in a Specord M-40 instrument.
Results and Discussion. Catalytic behavior of immmobilized binuclear tetraacetate Rh(ll) and Ru(ll,lll) complexes Binuclear [Rh2(O2CCH3)4]and [Ru2(O2CCH3)4] were chosen for immobilization due to excellent ability of metals in these complexes to coordinate with N-containing functional groups without leaching [3,4]. Actually, any metal complex remove from carrier surface was observed after immobilization as well as during catalytic process. Transfer hydrogenations of cyclohexanone and acetophenone were examined as model reactions. Reduction of both cyclohexanone and acetophenone proceeded selective without byproduct formation, with yield 99.6%. The reaction of transfer hydrogenation promoted by KOH in 2-propanol solution. It can be seen from Table 1 that activity of Rh catalysts surpassed one of Ru catalytic systems in examined reaction of transfer hydrogenation. Acetophenone was reduced rather slowly then cyclohexanone. It could be explained by more solid coordination of acetophenone with metal in intermediate complex formed during transfer hydrogenation (like in Meerwein-PonndorfVerley reactions). The nature of N-containing group (amino- or succinamide group) of the carrier did not considerably influence in the catalytic activity in this reaction. In contrast, the preparation conditions (solvent, time of the complex deposition, size of chitosan corpuscles) strongly influenced the activity of the prepared catalysts. Effect of the chitosan corpuscle size. The chitosan corpuscle sizes were regulated by subsequent solvation and repricipitation from diluted CH3COOH and NaOH aqueous solutions. The decrease of the chitosan corpuscle size from 3 to 0.1 mm leaded to the significant rise of the initial rate of carbonyl group transfer hydrogenation for both Rh and Ru catalysts (Table 2). Effect of the metal complex deposition conditions The metal complex preparation conditions influenced essentially in the catalyst activity. The data from Table 1 demonstrate that the nature of the solvent from which metal complex deposition carried out considerably effected the catalytic properties of the prepared catalyst. Catalytic activity of immobilized metal complex system on the basis of Rh and Ru complexes deposited from 2-propanol solution surpassed one of these complexes deposited from aqueous solution. It can be seen from Table 1 that decrease of complex deposition time from 72h to 2h leaded to the rise of the initial rates of transfer hydrog~,ation about one order for both Rh and Ru metal complex catalysts (in the case of the deposition from aqueous solution). These catalytic data could be explained by the difference in the structures formed on the carrier surface under different deposition conditions of metal complex. In the case of the deposition from aqueous solution, the hydrolysis of original binuclear metal complex into mononuclear one could be prevented by deposition time shortening. This suggestion was confirmed by IRand electronic spectroscopic examinations.
240 Table 1. Transfer hydrogenation of cyclohexanone and acetophenone in the presence of immobilized Rh and Ru tetracetates (4.9xl 0 .6 moles of Rh/Ru, 4.8x104 moles of substrate, 4.9x104 moles of KOH, 82.4~ 15 ml of 2-propanol Metal complex Carrier Solvent, from Metal W0~, mols W02,mol 1 which metal complex mol ~ of M o f M min ~ complex deposition deposition min ~ was carried out time, h [Rh2(O2CCH3)4] original H20 2 3.7 3.1 chitosan . . . . . . 72 0.3 0.1 . . . . 2-propanol 2 9.5 8.2 . . . . . . 72 9.3 8.1 " succinamide H20 2 3.4 2.1 chitosan derivative . . . . . . 72 0.3 0.1 . . . . 2-propanol 2 10.1 9.6 . . . . . . 72 10.2 9.5 [Ru2(O2CCH3)4] original H20 2 1.6 1.2 chitosan . . . . . . 72 0.2 0.1 . . . . 2-propanol 2 5.1 4.8 . . . . . . 72 4.8 4.4 " succinamide H20 2 1.0 0.8 chitosan derivative . . . . . . 72 0.2 0.1 . . . . 2-propanol 2 5.4 5.1 . . . . . . 72 5.2 4.7
Structure of Immobilized Rh(ll) complexes When the tetraacetate binuclear complexes of rhodium(II) are deposited on chitosan, four different types of surface structures may be formed, as it suggested for immobilization on 7aminopropyl containing silica [3]. One of them is bound to the carrier through the equatorial coordinate (A), two of them through the axial coordinate (B, C). These structures retain their dimeric form. Also possible is the formation of structures with a mononuclear nature (D). The formation of surface structure depends on the deposition conditions of metal complex and the flexibility of the hydrocarbon fragments of the carrier. In the case of Rh teraacetate deposited from 2-propanol solution and from aqueous solution (deposition time 2 h) on original chitosan, the color of the carrier with immobilized complex became lilac. In the case of the Rh teraacetate deposited under the same conditions on succinamide chitosan derivative, the color of carrier changed during the deposition process
241 from lilac to green. A lilac color is observed for the acetate complexes of Rh(II) in the case in which a nitrogen-containing ligand is coordinated through the axial site. The acetate complex takes on a green color when one or two acetate bridge group are split out [8]. In the case of succinamide chitosan derivative, we can assume that the succinamide groups of the Table 2. Influence of the chitosan corpuscle size in the catalytic activity in transfer hydrogenation of cyclohexanone and acetophenone in the presence of immobilized Rh and Ru tetracetates (4.9x10 6 moles of Rla/Ru, 4.8x10 -5 moles of substrate, 4.9x104 moles of KOH, 82.4~ 15 ml of 2-propanol Metal complex Chitosan corpuscle W0~, mols mol l of M W02, mols mol l of M size, mm min ~ min-1 min ~ rain- 1 [Rh2(O2CCH3)4] 0.1 9.5 8.2 " 0.5 5.8 4.9 " 1 1.2 0.8 " 3 0.6 0.3 [Ru2(O2CCH3)4] 0.1 5.2 4.0 " 0.5 2.2 1.7 " 1 0.7 0.5 " 3 0.2 0.1
macroligand are initially coordinated through two axial sites of the complex, and then through equatorial sites, at the expense of splitting out part of the acetate groups. In the electronic reflection spectra of these samples was present a broad absorption band with a maximum in the 16.000 cm ~ region, indicating preservation of the binuclear structure of the complex Rh(II) with an Rh-Rh bond, and also indicating the presence of acetate bridge groups, the number of which varies from 2 to 4 [9]. In the case of original chitosan, we suggested that the binuclear structure (B) was realized on the surface, and in the case of succinamide chitosan derivative, the binuclear structure (A) was realized. In the case of metal complex deposition from aqueous solution with prolonged deposition time (72 h) the color of carrier changed during the deposition process from lilac to grey and the characteristic absorption band was absent in the elrectronic spectra. Thus, possibly, the formation of the mononuclear structure (D) took place on the carrier surface due to hydrolysis of initial binuclear complex. After immobilization of Rh(II) tetraacetates on original chitosan (deposition from 2propanol and from aqueous solution with deposition time 2h), absorption bands (AB) Vas (COO) 1600 cm ~ and v,(COO) 1425 cm ~ were presented in the region of the carboxyl group vibrations (see Figure 3) in IR-spectra. The same AB were presented in initial complex (1585 and 1425 cm~). The frequence 16000 cm ~ was rather higher then in original complex. It could be explained by Rh coordination changing or electronic density. The intensity of these AB as well as the absence of shifts for the COO vibrations (Figure 3), indicated that complexes retaining four acetate bridges were found on the carrier surface (structure B). In the case of deposition from aqueous solution with prolonged deposition time on original chitosan or on
242 succinamide chitosan derivative the characterisic AB of carboxylic group vibrations were absent. It could be explained by the absence of acetates groups or theirs very low concentration. Acetate groups could be replaced by succinamide groups of the carrier or by water during deposition (structure A or D). This agrees with the data obtained by electronic spectroscopy. Thus, our data demonstrated, that when the shorter deposition time during immobilization of metal complex from aqueous solution, the binuclear structure of original complex was preserved. In the case of the deposition time lengthening, binuclear structure degraded to mononuclear one with the substitution of acetate groups of original complex with aminogroups of chitosan.
Figure 3. IR spectra: 1) Chitosan; 2) [Rh2(O2CCH3)4]/original chitosan, deposition from 2-propanol solution; 3) [Rh~(O2CCH3)4]/succinamide chitosan derivative, deposition from 2-propanol solution; 4) [Rh2(O2CCH3)a]/original chitosan, deposition from aqueous solution, deposition time 72 h; 5) [Rh2(O2CCH3)4]/original chitosan, deposition from aqueous solution, deposition time 2 h
Conclusions
1. Original chitosan and succinamide chitosan derivative were applicated for the preparation of the novel transfer hydrogenation catalysts on the basis of immobilized of binuclear Rh and Ru tetraacetates. 2. IR- and electronic spectroscopic examinations demonstrated that type of the metal complex structure formed on the carrier surface depended on the catalyst preparation procedure (mononuclear or binuclear immobilized complex) as well as on the macroligand nature
243 (coordination type of binuclear metal complex with carrier: through equatorial or axial coordination sites). 3. Metal complex immobilized system with binuclear structure possessed more catalytic activity in examined reaction, then mononuclear one.
References.
1. K. Kaneda, H. Yamamoto, T. Imanaka, S. Teranishi, J.Mol.Catal. 29 (1985) 99. 2. V.N. Chemetskii, N.E. Nifant'ev, Mendeleev Chemistry Journal, 41 (1997) 80. 3. Isaeva V.I., SharfV.Z., Zhilyaev A.N., Bull.Acad.Sci. of USSR, Chem. div. 40 (1991) 257. 4. V.I. Isaeva, V.Z. Sharf, Y.V. Smirnova, Zh.L. Dykh, G.N. Baeva, T.A. Fomina, A.N. Zhilyaev, I.B. Baranovskii, Rus. Chem. Bull. 44 (1995) 64. 5. V.I. Isaeva, V.Z. Sharf, Zh.L. Dykh, L.I. Lafer, V.I. Yakerson, Bull. Acad. Sci. of USSR, Chem. div. 41 (1992) 49. 6. B.C.Hui, G.L. Rempel, J. Chem. Sot., Chem. Commun. (1970) 1195. 7. F.A. Cotton, Inorg. Chem. 27 (1988) 43. 8. A.N. Zhiljaev, A.T. Fal'kengof, M.A. Golubnichaya, et al., Koordinats. Khim. 12 (1986) 1862. 9. V.Z. Sharf, V.I. Isaeva, A.N. Zhilyaev, I.B. Baranovskii Bull. Acad. Sci. of USSR, Chem. div. 38. (1990) 1796.