Suzuki water-soluble catalysts

The Suzuki reaction has already found a first industrial application [24], after the catalyst Pd(TPPTS)a n HaO became available [25], In a two-phase procedure, the water-soluble catalyst effects the C-C coupling of arylboronic acis with aryl chlorides to form pharmaceutical intermediates. The Suzuki C-C cross-coupling is on the way to industrial perfection. Since the basic mechanistic features are clear by now, it is desirable that the catalysts are easy to prepare, easy to handle, and cheap, and that they bear cr-donor type ligands of which at least one does not dissociate from the metal throughout the catalytic cycle. Thus the Suzuki coupling will be seen in the syntheses of a growing number of fine chemicals and pharmaceuticals in due course. 

Polymerization via Suzuki coupling in aqueous solution was first reported by Novak et al. [Eq. (11)] [236]. A water-soluble catalyst precursor, [Pd(TPPMS)3] (TPPMS = 3-Ph2PC6H4SO3Na) was employed. The resulting polymer is water soluble, and has a weight average molecular weight on the order of 5 x lO" g mol . ... 

In a modified version of the Suzuki reaction arylboronates or boranes are utilized instead of arylboronic acid. Under the action of phosphine-free palladium catalysts NaBPh4 and tra(l-naphtyl)borane were found suitable phenyl-sources for arylation of haloaromatics in fully or partially aqueous solutions at 20-80 °C with good to excellent yields (Scheme 6.12) [32-34]. Aryl halides can be replaced by water-soluble diaryliodonium salts, At2IX (X = HSO4, BF4, CF3COO) in the presence of a base both Ar groups take part in the coupling [35]. 

The first examples of water-soluble alkylphosphines that were capable of promoting Suzuki couplings of aryl bromides in aqueous solvents at room-temperature were monodentate phosphines 98 and 99 (Scheme 1.64). Catalysts derived from them showed high activity towards aryl bromides, with TONs up to 10 000 at rt, which increased up to 734 000 at 80 °C, while the more sterically demanding ligand 99 gave catalysts with a superior activity towards aryl... 

The cross-coupling reactions of various aryl halides and triflates with vinyl- or arylboronic acids and esters (Suzuki cross-coupling reaction) was also carried out in water in the presence of tetrabutylammonium bromide and a base such as Na2C03, using a phosphine-free palladium catalyst to give biaryl derivatives [Eq. 18)1 [108,109]. More recently, Casalnuovo [101] and Gen t [102,110] have performed this reaction using water-soluble palladium catalysts PdCla (tppms)2 and Pd(OAc)2/tppts in water/acetonitrile. 

The suitability of the homogeneous aqueous catalysts and thus the scope of application in general will be extended in commercial or pilot-plant operation to other central atoms and reactions such as Heck reactions and other carbonylations (with Pd), hydrogenations (Pd, Pt, Rh, Ir), formation of water-soluble polymers (Pd), vinylations, metathesis conversions (Ru), Suzuki couplings, etc. (cf. Section 6.6). 

A highly efficient Pd(OA)2/guanidine aqueous system for the room temperature Suzuki cross coupling reaction was developed. The new water-soluble and air-stable catalyst from Pd(OA)2 and 2-butyl-1,1,3,3-tetramethlyguanidine was synthesized and characterized by X-ray crystallography [86]. The catalyst catalyses reaction of arylboronic acids... 

Shimizu. S. Shirakawa. S. Suzuki, T. Sasaki, Y. Water-soluble calixarenes as new inverse phase-transfer catalysts. Their application to aldol-type condensation and Michael addition reaction in water. Tetrahedron 2001. 57, 6169-6173. 

Kostas, I.D., Coutsolelos, A.G., Charalambidis, G. and Skondra, A. (2007) The first use of porphyrins as catalysts in cross-couphng reactions a water-soluble palladium complex with a porphyrin ligand as an efficient catalyst precursor for the Suzuki-Miyaura reaction in aqueous media under aerobic conditions. Tetrahedron Lett., 48, 6688-91. 

Use of the Suzuki coupling reaction in the synthesis of PPPs has been reported. For example. Wallow and Novak [31] have polymerized 19 and 20 in the presence of palladium(O) catalyst to generate 21, a water-soluble PPP (Scheme 9). We have... 

---