Contents Polymer-Metal Complexes and Their Catalytic Activity E. ADIHCUST and H. EDIHSIN Strain Energy Density Functions of Rubber Vulcanizates from Biaxial Extension .S ATABAWAK and H. IAWAK 98 ESCA Applied to Polymers D. T. KRALC 521 Polymer Separation and Characterization by Thin-Layer Chromatography H. IKAGANI 981 Author Index Volumes 1-24 239 Polymer-Metal Complexes and TChaetiarl ytic Activity Eishun Tsuchida and Hiroyuki Nishide Department of University, Waseda Chemistry, Polymer Tokyo 160, Japan Table of stnetnoC I. Introduction . . . . . . . . . . . . . . . . . . . . 2 II. Formation and Structure of Pendant.Type Polymer-Metal Complexes 7 A. Pendant-Type Polymer-Co(III) and -Cr(IIIC)o mplexes . . . . . 7 B. Structures of Polymer-Heme Complexes . . . . . . . . . . 14 C. Polymerization of Coordinated Monomer . . . . . . . . . . 21 HI. Formation and Stability of Polymer Chelates . . . . . . . . . 24 A. Formation and Stability of Intra-Polymer Chelates of Cu(II) 24 B. Complexation of Metal Ions on Crosslinked Polymer Ligands 30 C. Resolution of a-Amino Acidsby Chiral Polymer Complexes 36 IV. Reactivity of Polymer-Co(Ill) Complexes . . . . . . . . . . 38 A. Electrostatic Effect of Polymer-Co(III) Complexes . . . . . . . 39 B. Hydrophobic Interaction . . . . . . . . . . . . . . . 43 C. Influence of Conformational Change of Ligand Chain. . . . . . 44 V. Reaction of Polymer-Heine Complexes with Molecular Oxygen. 45 A. Oxygenation of Polymer-Heme Complexes . . . . . . . . . 46 B. Immobilization of Heine on Polymer Matrixes . . . . . . . . 49 C. Pseudo-Allosteric Effect of Poly(L-lysine) Heme Complex . . . . 55 VI. ReactionsC atalyzed by Polymer-Metal Complexes . . . . . . . . 60 A. Oxidative Reactions . . . . . . . . . . . . . . . . . 61 B. Reductive Reactions . . . . . . . . . . . . . . . . . 63 C. Hydrolysis . . . . . . . . . . . . . . . . . . . . 65 VII. Phenol Oxidation Catalyzed by Polymer-Cu Complexes . . . . . . 66 A. Oxidative Polymerization Catalyzed by Polymer.Cu Complexes 67 B. Elementary Reactions of Phenol Oxidation . . . . . . . . . 71 C. Coordination Step of Substrate to Polymer-Cu Catalysts . . . . . 73 D. Effects of Polymer Ligands on the Electron.Transfer Step . . . . 75 VIII. Conclusion and Further Studies . . . . . . . . . . . . . . 82 IX. References . . . . . . . . . . . . . . . . . . . . . 84 2 E. Tsuchida and H. Nishide 1. Introduction A polymer-metal complex is composed of a synthetic polymer and metal ions. Its synthesis represents an attempt to give an organic polymer inorganic functions. Catalytically active polymers can be obtained by inducing a metal complex to cata- lyze a reaction with a polymer backbone, and it is reasonable to assume that the metal complex bound to the polymer will show a specific type of catalytic behav- ior, reflecting the properties of the polymer chain. Indeed, many synthetic polymer- metal complexes have been found to exhibit high catalytic efficiency. On the other hand, it has been shown that in metalloenzymes such as oxidase and hemoglobin, where a metal complex is the active site, the macromolecular protein part plays a significant role, or even controls the reactivity of the metal complex. Thus, research on the catalytic activity of polymer-metal complexes has attracted considerable interest, which has increased in recent years. A wide variety of investigations have been carried out on polymeric metal com- plexes; these include studies of semiconductivity, thermostability, redox reactions, collection of metal ions, biomedical effects, and so on. The polymeric metal com- plexes are classified into the following groups: (A) polymer-metal complexes f I I I I I / ..L L.. L .-L L.. I I 1 I l / ...- -" . L L L L L + M ~ r M "M Schemel ,, "L L" L ""L "L "-- I I I I I I I I I I 1 I I l I L......L L L......"L L L L L L + M ~ M" M Scheme 2 / L ":'L L / L "L 1 i ! I l ............. (B) coordinate polymers i i 1 , , LrL L ¢L\ f-L-,~ rE-,, /-L-N + M ~ L : L :: ...... -- Scheme3 L L L L L L M M"' M" I [ I I I I I 1 [ [ L L L L L L L L L L + ('~ ----"~" ~M~ : Q~.~: : 4 Scheme I I I I i L L L L L L ! = : : : : : Scheme 5 L L ..-L. N fL. .... .--L. N fL. .... --L N fL. .... . 6 Scheme L~---~L + M -''--4~ :..Lfl'------~E.M..~L.~--'~E..M..L.~-~E.M. ' lateM-remyloP sexelpmoC dna Activity Catalytic Their 3 (C) poly(metal-phthalocyanine) type I I I I I I I I --.L L L .......... L -L--L L--L I J l + M or L' + M "'""~:"-~'"i;'" ....""t:'" "M "M"" ""M"' ""t:: "'M"" "" emehcS 7 --'L L ....L .......... L 1 I t I 1 I I I L = coordinating atom or group; M = metal ion Polymer-metal complexes, represented by Schemes 1 to 5, are defined as com- plexes composed of a polymer ligand and metal ions in which the metal ions are attached to the polymer ligand by a coordinate bond. Here a polymer ligand is un- derstood to be a polymeric substance that contains coordinating groups or atoms (mainly N, O, and S), obtained by the polymerization of monomers containing co- ordinating sites, or by the chemical reaction between a polymer and a low-molecu- lar-weight compound having coordinating ability. Typical polymer ligands previously reported are listed in Table I. When a polymer ligand is mixed directly with a metal ion, which generally has four or six coordinate bonding hands, a polymer-metal complex is formed. This may be of the intra-polymer chelate type (Scheme 1) or of the inter-polymer chelate type (Scheme 2). Complex formation proceeds via Scheme 3, where the polymer backbone contains multidentate ligands, such as the iminodiacetic acid group, or acts as a carrier for low-molecular-weight mu!tidentate ligands; many so-called chelating resins fit this scheme. The polymer-metal com- plexes represented by Schemes 1 to 3 have chelating structures in their polymer ligands and are therefore called polymer chelates. The pendant-type polymer-metal complex( Scheme 4) is formed by the reaction of a polymer ligand with a stable metal complex, the central metal ion of which has already been masked with low- molecular-weight ligands except for one coordinate site that remainvsa cant, .g.e metalloporphyrins, or cobaltic chelates. A polymer-metal complex is also obtained by polymerizing a monomeric metal complex (Scheme 5). Scheme 6 represents polymers. coordinate A low.molecular-weight compound with multidentate groups on both ends of the molecule grows into a linear polymer with metal ions, and the polymer chain is composed of coordinate bonds. The par. quetlike polymer complexes, poly(metal-phthalocyanine) and poly(metal-tetracyano- ethylene), are classified into Scheme 7. They are formed by inserting metal ions into planar-network polymerso r by causing a low.molecular-weight ligand derivative to react with a metal salt and a condensation reagent. This article deals with the polymer-metal complexes (Schemes 1-5), because they have the following merits in comparison with other polymeric metal complexes. .)i( Metal ion and ligand site can be chosen for study without restrictions. (ii) It is not difficult to control the molecular weight of a polymer complex and to modify the structure of a polymer ligand(.i ii) The polymerc omplex si soluble in both aqueous and nonaqueous solvent. (iv) It possible is to change the ratio of the organic polymer part to the inorganic metal complex part. This explains why the polymer often af- fects the behavior of the metal complex. 3 ~_~ I (CH2)4 1 NH 2 ~_~ C--C--CH II El -NH-CH-CO- ' N--OH --CH2--CH-- HO--N ~_~ ! CH2 I NR2 CH-- I --cHeerio-- --CHz--CH-- ~ ~_o~:_~ © =CH HO --CH ........... I COOH COOH --CO-- _~_~_ --CH2--CH-- CH2NHCH2CH~NR2 ~ R i C- I COOH ligands --CH~--¢H-- --NH--CHcH2[ ~CH2-- polymer of _~_ HO N units -- 2- NH9 © -°H CH=N OH ligands Repeating --CH2--CH 1 -- NHCH2CH --CH~--CH-- -C~ --CH2--CH-- polymer groups Typical ~NH, ~N of -OH 1. base 2, Table Coordinating Amines -NH Nitrogen heterocyclic compounds Schiff ~C=N- Alcohols carboxylic acids -COOH o o I OH I C--NH II O , C=S I --NH--N-- --NH--N-- --N--CH2--CH2-- CH2COOH --CH2--CH-- I O I C=O ' I SH 2 I SH --CH2--CH-- 2 ' O I CH2--CH--CH2 "N(CH2COOH) II 2 0 N(CH2COOH)2 "~ CH I O-CH2PO(OH) CH2 I --R--C--CH2--C--R-- II O -- CH2 -- CH2~ --CH2--CH-- ~) CH2--SH 3 --CH2--CH-- --CH II O --CH2--C R I I C II O CH2N(CH2COOH)~ I SH © O=P(Ott)2 --CH2--C-- --CH2--CH-- --CH2--CH-- --CH2--CH-- acids 2 amides ~C=O Ketones esters, Aminopoly- carboxylic acids Phosphonic -PO(OH) Thiols -SH 6 .E adihcusT dna .H edihsiN It is the purpose of this article to discuss whether or not there are any differ- ences betweent he chemical reactivity of a polymer-metal complex and that of the corresponding monomeric complex. Although various extensive investigations on polymer-metaclo mplexes have been reported, most of these complexes are too complicated to be discussed quantitatively due to the nonuniformity of their struc- ture. These compounds include not only "complexes of macromolecules" but also the structurally labile "metal complex". Before detailed information can be obtained about the properties of polymer-metal complexes, and especially about the reactivity and catalytic activity of polymer-metal complexes, their structure must be elucidated. A polymer-metal complex having a uniform structure may be defined as follows; (i) the structure within the coordination sphere is uniform, i.e. the species and the composition of the ligand and its configuration are identical in any complex unit existing in the polymer-metal complex; (ii) the primary structure of the polymer ligand is known. If the structure within the coordination sphere is identical in a polymer complex and a monomeric complex, their reactivity ought to be the same even though the complex is bound to a polymer chain. However, it is clear that the reactivity is some- times strongly affected by the polymer ligand that exists outside the coordination sphere and surrounds the metal complex. The effects of polymer ligands will be dis- cussed in the text under the following two terms: (1) the steric effect, which is determined by the conformation and density of the polymer-ligand chain, and (2) the special environment constituted by a polymer-liganddo main. To illustrate these effects, the followinqgu estions will be discussed: (i) When metal complexes attach to a polymer ligand at high concentrations, are the stability and the reactivity of the complexes changed? (ii) In a rigid polymer do the attached metal complexes, at low concentrations, behave virtually as in a solution at infinite dilution? (iii) A polymer ligandi n solution may be extended or densely coiled up, or sometimes helically structured. Does the conformation of the ligand chain influence the reactivity? (iv) Are there any differences between the chelate formation of a polymer-ligand chain and that of the individual monomeric ligand? (v) Because polymer-metal complexes are poly(electrolyte)s, an electrostatic effect is predominant in the reactions of ionic species. (vi) A metal complex in an aqueous solution may be occluded by a hydrophobic polymer matrix, and this hydrophobic microenvironment affects reactivity. These discussions will embrace homogeneous solutions of polymer-metal com- plexes. Of course one of the important advantages offered by the use of a polymer ligand, especially a crosslinked polymer ligand, in catalysis is the insolubilization of the attached complexes; the insolubility of the polymer catalyst makes it verye asy to separate from the other components of the reaction mixture. Several polymer-metal complexes have been used for this purpose, although such applications are not cov- ered in this article. The aim here is (1) to characterize polymer-metal complexes and their behavior in such simple but important elementary reactions as complex formation, ligand substitution, and electron transfer, and (2) to describe their cata- lytic activity. Polymer-Metal Complexes and Their Catalytic Activity 7 II. Formation and Structure of Pendant-Type Polymer-Metal Complexes Examples of the pendant-type polymer-metal complexes represented by Schemes 4 and 5 are shown in Table 2. They are obtained by the reactioni n Scheme 8: a polymer ligand is made to coordinate to a vacant site of a previously prepared, stable, low-molecular-weight metal complex. The structure and hence the functions of the metal complex are hardly changed by attachment to the polymer ligand. The metal complexes attached to the polymer ligands I to 8 are the classic cobaltic E E = Elimination-ligand (weak ligand) chelates 9-13, paramagnetic chromic chelate ,41 metalloporphyrin ,51 which reacts with molecular oxygen, metal-chlorophyllin ,61 which si a derivative of chlorophyll, and so on. In Scheme 8, the degree of coordination (x) means the molar ratio [metal complex]/[repeating unit of polymer tigand]. If all the ligands in the polymer are coordinated to M, the value ofx becomes unity. A. Pendant-type Polymer-Co( I I I) and -Cr( I II) Complexes We prepared a series of pendant-type polymer-metal complexes having a uniform structure by the substitution reaction between a polymer ligand and a Co(Ill) or Cr(III) chelate, the chelate being inert in ligand-substitutiorne actions '1 .)2 A poly- mer-Co(Ill) complex, .g.e 21C]1C)PVP(z)ne(oC[-sic (en=ethylenediamine, PVP= poly(4-vinylpyridine)) 17, was prepared as follows1): CH--CHz X = ;1C Br, or N3 N N : ethylenediamine x 71 An aqueous solution of 21C2)ne(oC[-sic 1C] was added to an ethanolic solution of PVP and the mixture heated. After a few hours the mixture was filtered and dia- 8 .E adihcusT dna .H edihsiN Table .2 complexes polymer-metal Pendant-type HC 2~"" ILC--I """x_-feHC-H ""/ L~ H Polymer dnagil L] lateM complex M__~__/ ,~2._ H2 -HC-2HC- H cx--N~-b- 1C;7 V / ,' Co +2 PVP 1 Hql~F--~/--N~C2H 2. CI- 2 H 2 H HC,c,N2 2 2H -CH2-CH- H c'IN~s 1C;7--~ I 2H /~2 / +2rC / IVNP 2 9 H~/'-~-~I'--"L~-'q/~'C~H 2 2 -1C 21-1 / I 2H HC,c,N2H 2 H _-~N'-'C: F ~:-;f t 2H -CH2-~H- / _Co( , 2HN--r-C~-N.~C2H 2 -1C 14 N IVMP 3 ~ I 1 H k 3HCLNN~I H U,C,N/C,"C2 2 2H 2H H~_~HC- - IVP 4 N~,,NH C3H t /CH3 /C-O-<-t'--;O=C -CH2-CH- HC "> ,'_..Co."-/ .2SH 15 /C=O~__.r~0_C. / SAP 5 C3H HCk 3 NO 2 HN 2 11 2HC=HC .C 3H HC_2HCN_ 2_ H a C ~ sH2C H IEPL 6 C3H ~O--H-O ~HC ~"N~ -~,'~tC/ H ~ C H ~ I .~oC~...', , ~ 3HC /C~lq .... ,L~N~--~- 1-2HC-2HCN-2HC-2HC'N- H C3H ()-H'~'O" 3HC ~H~ ~H 2 COONa 2HC 1C ~ I IEPB 2H COONa 2HC 7 12 I aNOOC 2HN 16 3H C /CH3 ~c-o=---I-->o-c -NH-CH-CO- -~OIC I n c/c=N~ .... ~C=N'~-F (~H2)4 LLP 8 3 H~2HC 2 3HC ! ~HN 2HO 13 Polymer-Metal Complexes and Their Catalytic Activity 9 lyzed in cold water, then, after the water had evaporated, the PVP-Co(III) com- plex was obtained as a transparent, dark-reddish filmy substance. The polymer com- plex, 21C]1C)PVP(2)ne(oC[ 17, had one bivalent cation per complex repeating unit and was water-soluble, regardless of the solubility of the polymer ligand. Co(Ill) and Cr(III) chelates are inert in ligand-substitution reactions, sow e considered that complex formation between a polymer ligand and the Co(III) or Cr(III) chelate would be irreversible under the applied experimental conditions .)2 This assumption was supported by the fact that the degree of coordination (x) did not decrease either during the reaction time or during the purification of the poly- mer complexesa nd that no degradation product from the polymer-Co(Ill) com- plexes could be found. Figure 1 shows the formation curves of the polymer-Co(Ill) @ O O-.-- "O'- .~ 0.5 .-,O,--- 0 0 2 4 6 /f 4~2 Time (h) Fig. 1. Complex formation curves for polymer-Co(III) and -Cr(III) complexes 1-5) o: [Co(acac)2(PVP)(NO2)I, o: [Co(en)2(BPEI)CIlC12, ®: [Cr(en)2(PVP)CIICI2, e: [Co(en)2(PVP)CI]C12, (cid:127): [Co(en)2(QPVP)C1]CI2(-R = -CH3) , m: [Co(en)2(QPVP)C12 (-R = -CH2C6Hs), m: [Co(en)2(PAS)CI]C12, PVP -- poly(4-vinylpyridine), BPEI = branched poly(ethyleneimine), QPVP = partially quaternized PVP, PAS = poly(p-aminostyrene), acac = acetylacetone, en = ethylenediamine, 80 ~C and polymer-Cr(III) complexes, i.e. the variation ofx with time l-s). The initial rates of complexation for [Co(acac)2(PVP)(NO2)] (acac=acetylacetone) 11, for 21C]1C)PVP(z)ne(rC[ 14, and for 21C]1C)IEPB(2)ne(oC[ (BPEI = branched poly(ethyleneimine) = 7), 9 are larger than those for the other complexes under the same conditions. These differences are attributed to the relatively high ligand sub- stitution activity of the acac chelate and the Cr(III) chelate and to the higher basic- ity of BPEI as compared to PVP and PAS(pots(p-aminostyrene) = 5). Complexation of PVP of a lower degree of polymerization proceeds more easily ,)1 and the com- plexation rate for partially alkylated poly(4-vinylpyridine) (QPVP) 18 is -R = -H >3 -CH3 > -CH2C6Hs, as shown in Fig. .1 These findings are interpreted as due to the steric hindrance of the polymer ligands .)3