Efficient bulky phosphines for the selective telomerization of 1,3-butadiene with methanol

A series of bulky phosphines containing substituted biphenyl, 2-methylnaphthyl, or 2,7-di-tert-butyl-9,9-dimethylxanthene moiety were prepared. They were used in the preparation of new monophosphine-palladium(0)- dvds complexes, which were employed as catalysts for the selective telomerization of 1,3-butadiene with methanol to obtain 1-methoxyocta-2,7-diene (1-MOD), the key intermediate in the Dow 1-octene process. Several ligands showed improved selectivity and yield compared to that of the benchmark ligand PPh₃. Especially 2,7-di-tert-butyl-9,9-dimethylxanthen-4-yl- diphenylphosphine (4, "mono-xantphos") stands out as an excellent ligand in terms of yield, selectivity, and stability.