The Suzuki-Miyaura coupling of aryl chlorides and PhB(OH)(2) under biphasic conditions (DMSO/heptane) can be performed in almost quantitative yields over several cycles by means of polymeric Pd catalysts with soluble polyethylene glycol phase tags. Three sterically demanding and electron-rich phosphines 1-CH(2)Br,4-CH(2)P(1-Ad)(2)-C(6)H(4), and 2-PCy(2),2'-OH-biphenyl, and 2-PtBu(2),2'-OH-biphenyl were covalently bonded to 2000 Dalton MeOPEG-OH. The catalysts, which were formed in situ from Na(2)[PdCl(4)], the respective polymeric phosphine, KF/K(3)PO(4), and PhB(OH)(2), efficiently couple aryl chlorides at 80 degrees C at 0.5 mol % loading, resulting in a >90 % yield of the respective biphenyl derivatives. The use of polar phase tags allows the efficient recovery of palladium-phosphine catalysts by simple phase separation of the catalyst-containing DMSO solution and the product-containing n-heptane phase. The high activity (TOF) of the catalyst remains almost constant over more than five reaction cycles, which involve the catalytic reaction, separation of the product phase from the catalyst phase, and addition of new reactants to initiate the next cycle. The Buchwald type biphenyl phosphines form the most active Pd catalysts, which are 1.3-2.8 times more active than catalysts derived from diadamantyl-benzylphosphine, but appear to be less robust in the recycling experiments. There is no apparent leaching of the catalyst into the heptane solution (<0.05 %), as evidenced by spectrophotometric measurements, and contamination of the product with Pd is avoided.

The rates of Sonogashira coupling reactions using [Pd-PR(3)] complexes depend on a combination of the steric bulk of phosphines and substrates; however, below a critical cone angle of ca. 170 degrees the catalytic activity drops drastically.

The difficulties associated with the recovery of catalysts after product formation and catalyst metal contamination of products pose a serious drawback for large-scale applications of homogeneous catalysis. An interesting approach to solve these problems is to covalently link a catalyst to a phase tag in order to define its phase preference in a liquid/liquid biphasic solvent system composed of two room temperature immiscible liquids. Consequently, the separation of a polar product and a catalyst can be achieved by simple phase separation of the two solutions.We have attached either a polar and soluble polymer (polyethylene glycol) or a low polarity, soluble polymer (polymethylstyrene) to sterically demanding and electron-rich phosphines or N-heterocyclic carbenes. The complexes of the polymer-supported ligands with palladium and ruthenium are high activity catalysts for different carbon-carbon