Synthesis and Study of Triphenylphosphines Functionalized at the 4-Positions through the Nitrogen Atoms in 1,4,7,10-Tetraoxa-13-azacyclopentadecane and the X-ray Structure of the Oxide of the Molecule Substituted at All Three Positions

Hybrid phosphine crown ether ligands have been obtained from PhP(OMe)₂ and P(OPh)₃ and carbanions generated by low-temperature Li/Br exchange reactions involving 4‘-bromo-N-phenylaza-15-crown-5 and n-butyllithium. The A₁ ν(CO) values for the Ni(CO)₃L complexes of these phosphines have been found to be 2063.7 and 2060.8 cm^-1, for the bis (1b) and tris (1c) crown species, respectively, indicating the significant electron-donating abilities of the nitrogen atoms. Addition of NaSCN salts in dichloromethane causes these frequencies to increase by 2.40 (1b) and 3.70 cm^-1 (1c), indicating that the P(III) centers detect the presence of crown-coordinated ions. The oxide of 1c has been prepared and the X-ray structure obtained. A prominent feature of that structure, R3̄ symmetry, is that the nitrogen atoms are nearly planar and the ring carbon-to-nitrogen distances are 1.375 Å, features that are also consistent with a significant amount of sp² C−N double-bond character. The phenyl rings are arranged in a typical propeller shape with torsion angles of 132.4°.