Abstract:
1,3-Xylyl-18-crown-5 functionalized on the 5 position of the benzene ring with diphenylphosphine (5-diphenylphosphino-1,3-xylyl-18-crown-5) was synthesized in a three step reaction scheme yielding 1.82% (1.53 g) of pure product. The first step involved a free radical reaction between bromo-m-xylene and N-bromosuccinimide to produce pure 5-bromo-1,3-bis(bromomethyl)benzene in 28.32% (14.56 g) yield after recrystallization in cyclohexane. The second step involved forming the carbanions by reacting tetraethylene glycol with sodium hydride and reacting this intermediate with 5-bromo-1,3-bis-(bromomethyl)benzene. Following a purification procedure that involved forming the sodium salt of the crown ether, the resulting product was 5bromo-1,3-xylyl-18-crown-5 in 17.98% (2.33 g) yield. Finally, 5-diphenylphosphino-1,3-xylyl-18crown-5 was prepared by first using a bromine-lithium exchange reaction involving n-butyl lithium and 5-bromo-1,3-xylyl-l8-crown-5 which formed an intermediate that was subsequently reacted at low temperatures with chlorodiphenylphosphine. Purification was accomplished using flash quality silica gel with ethyl acetate as the mobile phase. Carbon and hydrogen analysis of the purified compound confirmed the formula C28H4305P with 0.75 H2O complexed with the final product. Infrared spectroscopic studies of the nickel carbonyl complex of this phosphine (Ni(CO)3L) showed a slight decrease (0.2 cm 1) in the vCO frequency as compared to triphenylphosphine. This result indicates that this new phosphine is a slightly better donor than triphenylphosphine towards nickel carbonyl. The addition of alkali metal ions to the Ni(CO)3L complex resulted in increases in the vCO values with lithium ion causing the greatest increase, 0.8 cm-1. This last result indicates that the phosphorus donor ability of this new phosphine can be tuned from approximately the equivalent of, to considerably less than, that of triphenylphosphine.
