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 (Ph2PR (1a), (OCH2CH2O)PR (1b), PhPR2 (1c); Ph2PC(CH3)(2)COR (2a), (OCH2CH2O)PC(CH3)(2)COR (2b), PhP{C(CH3)(2)COR}(2) (2c), t-Bu2PC(CH3)(2)COR, (2d), Cy2PC(CH3)(2)COR (2e); R = OCH2CH2OCH2CH2CH2[SiMe2O](n)SiMe2Bu, 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 PdCl2(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.