FULL PAPER Palladium(0) Complexes of a 15-Membered Macrocyclic Triolefin as a Recoverable Catalyst – Monomer- and Polystyrene-Anchored Versions Jordi Corte ´s, [a] Marcial Moreno-Man ˜as,* [a] and Roser Pleixats [a] Keywords: Macrocycles / Palladium / Polymer / Catalysis / Cross-coupling Preparation of the 15-membered cycle (E,E,E)-1,6,11-tris[(2,4,6- reactions and can be recovered. Anchoring to a polystyrene framework affords a solid version of the catalyst, which is triisopropylphenyl)sulfonyl]-1,6,11-triazacyclopentadeca- 3,8,13-triene (8) is reported. This cyclic triolefin forms a recovered by simple filtration and reused without loss of catalytic activity. stable Pd 0 complex 9 which catalyzes several cross-coupling Introduction Results and Discussion Recently we described the formation of (E,E,E)-1,6,11- Palladium has emerged as a versatile transition metal in the tris[(2,4,6-triisopropylphenyl)sulfonyl]-1,6,11-triazacyclo- field of catalysis. [1] [2] However, there is a gap between the pentadeca-3,8,13-triene, (8) and its Pd 0 complex 9 where the enormous potential of palladium in catalysis and the indus- metal is coordinated by the three ring olefinic bonds trial applications found so far. [3] One of the main problems (Scheme 1). [22] Macrocycle 8 and complex 9 were formed to be addressed is the recovery of Pd-containing catalysts. as well as other cyclic and open-chain compounds in a non- In general Pd 0 requires stabilization by phosphanes, which selective reaction which required tedious separation from are readily oxidized. Therefore, the development of phos- the complex mixture. We report in this communication an phane-free Pd catalysts is a topic of enormous importance. independent and selective preparation of 8 and 9, the cata- Several reactions are catalyzed by Pd species not containing lytic properties and recovery of complex 9, and the prep- phosphanes, [4] in particular the olefin complexes Pd(dba) 2 aration, catalytic properties and recovery of functionalized and Pd 2 (dba) 3 ·CHCl 3 have found extensive use. [4] Curiously polystyrene 14 containing the 15-membered macrocycle co- enough, very few Pd-olefin complexes were known until the ordinated to Pd 0 (Scheme 2). recent description of Pd complexes of hepta-1,6-dienes and The preparation of macrocyclic triolefin 8 is shown in related structures. [5] An emerging and highly promising Scheme 1. Alkylation of 2,4,6-triisopropylbenzenesulfona- phosphane-free alternative is based on the coordination mide (1) with (E)-1,4-dibromo-2-butene (2) affords a mix- power of stable heterocyclic carbenes. [6] ture of the dibromo compounds 3 and 4. These compounds Strategies to recover and reutilize organometallic homo- can be separated by column chromatography through silica geneous catalysts have been reviewed. [7-9] Anchoring the gel and each can be used for the preparation of 8. Thus, homogeneous catalyst to an organic [8] [10] or inorganic [8] [11] reaction of 3 with bis-sulfonamide 7, prepared from 2 and polymer (immobilization), or use of biphasic aqueous-or- 5, afforded 8 (44-56%). On the other hand alkylation of 1 ganic [9,12-14] or fluorous-organic [15] solvent systems has with dibromobis-sulfonamide (4) also gave 8 in 79% yield. been proposed for catalyst recovery, and an aqueous-or- Introduction of Pd 0 to obtain complex 9 is achieved by ganic system has become industrially significant. [9] treatment with either Pd(PPh 3 ) 4 in refluxing THF (95%), The use of palladium catalysts anchored to organic poly- Pd 2 (dba) 3 in THF (95%), or PdCl 2 /methanol in the pres- mers in carbon-carbon bond forming reactions has a few ence of NaCl and NaOAc (67%). precedents including Suzuki cross-couplings, [16] Grignard- Since 9 exhibited good catalytic properties and could be based cross-couplings, [17] acetylene couplings, [17] [18] Heck recovered (vide infra) we prepared the macrocycle-contain- reactions, [17] [19] allylation of nucleophiles (Tsuji-Trost reac- ing polystyrenes 13 and 14 as indicated in Scheme 2. Thus, tion), [18] [20] butadiene telomerization, [20e,21] and car- macrocycle 12 was prepared by alkylation of 4-vinylben- bonylation. [20f] Only a few examples of Heck reac- zenesulfonamide (11) with 4 and then copolymerized with tions [19b-19d] and Tsuji-Trost allylations [20c] are based on styrene and divinylbenzene in a molar ratio 10:70:20, with phosphane-free polymers. initiation by AIBN, following a known general method. [23] Polymer 13 was charged with Pd 0 by treatment with Pd(PPh 3 ) 4 in dioxane at 80 °C to afford 14. [24] [a] Department of Chemistry. Universitat Auto ` noma de Barcelona, The model reactions chosen to test catalytic power and Cerdanyola. 08193-Barcelona. Spain recovery of catalysts are the Suzuki-type cross-coupling of Fax: (internat.) + 34-93/581-1265 E-mail: iqorb@cc.uab.es cinnamyl bromide (15) with the arene boronic acids 16ae Eur. J. Org. Chem. 2000, 239-243  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 1434-193X/00/0102-239 $ 17.50+.50/0 239