Phosphines Functionalized with Crown Ether Groups: Synthesis and Study of Systems Incorporating 1,3-Xylyl-18-Crown-5 Units

Abstract

Hybrid phosphine crown ether molecules are obtained from Ph2PCl, PhP(OMe)2, or P(OPh)3 and the carbanions generated by a lithium/bromine exchange reaction between n-butyllithium and 5-bromo-1,3-xylyl-18-crown-5 or 5-bromo-2-methoxy-1,3-xylyl-18-crown-5. With these phosphine systems represented as PhxP(crown)3-x, the x = 0−2 and 1−2 members are reported for the former and latter crown ethers, respectively. The A1 υ(CO) stretching frequencies from the Ni(CO)3L (L = PhxP(crown)3-x) complexes are within 0.4 cm-1 of 2068.9 cm-1, the frequency for Ni(CO)3PPh3. For both series of ligands, H or OMe in the 2-position, the υ(CO) stretching frequencies are found to decrease with increasing substitution by the crown ether groups (deceasing x). The addition of Na+−Cs+ (SCN- salts) to the Ni complexes causes the A1 bands to shift to higher frequencies and to broaden. The largest shifts are observed with phosphines substituted with larger numbers of crown ether groups and added Na+ ions. 31P NMR spectral data for the L2PdCl2 complexes of these phosphines are reported. For all ligands, the signals from the trans complexes are observed between 22 and 25 ppm, a range considered consistent with cone angles of ca. 145°. The molecular structure, from X- ray crystallographic studies, of the oxide of the phosphine with x = 2 and H in the 2-position is reported. The crown ether ring is based on regular gauche and anti arrangements of the carbon−carbon and carbon−oxygen bonds, and the planes defined by the benzene ring and the five oxygen atoms form an angle of 38.4°.