Poly(dimethylsiloxane)-Derived Phosphine and Phosphinite Ligands:  Synthesis, Characterization, Solubility in Supercritical Carbon Dioxide, and Sequestration on Silica

The synthesis and characterization of eight macromolecular phosphorus-containing ligands are presented (Ph 2 PR ( 1a ), ( 1b ), PhPR 2 ( 1c ); Ph 2 PC(CH 3 ) 2 COR ( 2a ), ( 2b ), PhP{C(CH 3 ) 2 COR} 2 ( 2c ), t-Bu 2 PC(CH 3 ) 2 COR, ( 2d ), Cy 2 PC(CH 3 ) 2 COR ( 2e ); R = OCH 2 CH 2 OCH 2 CH 2 CH 2 [SiMe 2 O] n SiMe 2 Bu, n = 15−20). They contain low-molecular-weight poly(dimethylsiloxane) tags, and their molecular weights have been determined using a number of methods, including GPC and MALDI-TOF mass spectrometry. Solubility studies of 1a, b in supercritical carbon dioxide are described. Reaction of 2a with PdCl 2 (MeCN) 2 yields the air-stable complex trans -Pd( 2a ) 2 Cl 2 ( 3 ) as a yellow oil. Catalytic studies using these ligands in cross-coupling reactions in toluene and supercritical carbon dioxide are reported. The ligands and 3 adsorb reversibly on silica, thus resulting in a method for recycling catalytic species by using a solvent trigger.