Synthesis of an Anthracene-Based Macrocyclic Diphosphine Ligand

The synthesis and coordination chemistry of cis-macrocyclic diphosphine (PhPA)2 (A = C14H10 or anthracene), which features rigid, sterically encumbering groups in its macrocyclic backbone, is reported. Treatment of [EtOP2A2]­AlCl4, obtained in 63% yield from dibenzo-7-phosphanorbornadiene EtOPA and aluminum­(III) chloride, with 2 equiv of phenylmagnesium chloride gives (PhPA)2 in 59% yield. The purple, pseudo-square-planar nickel dichloride complex [(PhPA)2]­NiCl2 was obtained in 89% yield upon combination of (PhPA)2 with (DME)­NiCl2 in dichloromethane. By virtue of the ligand backbone, [(PhPA)2]­NiCl2 exhibits a large percent buried volume of 61.4%, greater than that of other common chelating diphosphines, and the steric bulk is extended into the axial positions of the square-planar complex, as revealed by a single-crystal X-ray diffraction study. Treatment of this nickel dichloride complex with K­[B­(C6F5)4] provided a red dimeric, cationic nickel chloride complex. This dimer was isolated in 43% yield and characterized in a single-crystal X-ray diffraction study.