Synthesis and properties of crown ether-modified phosphines and their use as ligands in transition metal catalysts

A novel series of crown ether-modified triarylphosphines, 1,2-diphenylphosphino-2,3,5,6,8,9-hexahydro-1,4,7,10-benzotetraoxacyclodecin (IIIa) and its higher homolog (III) (common nomenclature is 3n-diphenylphosphinobenzo-[3n-crown-n]ethers (n = 4, 5, 6, and 7)), is reported. The thermodynamic parameters for the extraction of alkali metal picrates are evaluated. Phosphines III (n = 5 and 6) form 1 : 1 stoichiometric crown-type complexes with na+ and K+. The observed extractability is in good agreement with the cavity size selectivity concept. The thermodynamic parameters ΔH° and TΔS° for the extractive complexation at dgC are −63 to −58 kJ/mol and −41 to −35 kJ/mol, respectively, thus ΔG° is governed by the enthalpy term. These phosphines are applied to reactions in liquid-liquid or liquid-solid phases, as the auxiliary ligands of homogeneous palladium and rhodium catalysis. The catalytic activities correlated well with the extractabilities of the phosphine ligands. The compound [RhCl(cod)]2, combined with IIIc and IIId, shows high activities toward catalytic hydrogenation of potassium and caesium cinnamates, respectively. Replacement of allyl bromide with powdered sodium or potassium iodide in benzene to give allyl iodide are catalyzed by (τ-C3H5PdCl)2 in the presence of phosphines III.