Sterically Encumbered and Poorly Electron-Donating Oxaphosphaadamantane Ligands for the Pd-Catalyzed Telomerization of Butadiene with Methanol

Oxaphosphaadamantane ligands bearing a variety of aryl and alkyl substituents were synthesized as catalyst promoters in the Pd-catalyzed telomerization of butadiene with methanol. At high methanol concentrations (14 M), ligands with electron-donating substituents on the aryl ring generate catalysts that lead to some of the highest conversions of butadiene and selectivities for 1-methoxy-2,7-octadiene under the conditions tested. Specifically, the ligand 1,3,5,7-tetramethyl-6-(2-methoxyphenyl)-2,4,8-trioxa-6-phosphaada-mantane, when combined with a Pd(II) precursor, forms a catalyst that converts 96% of butadiene with 94% selectivity for 1-methoxy-2,7-octadiene at 70 degrees C and is highly active for telomerization at a low reaction temperature (40 degrees C).