Ditopic ligands featuring [P,S], [P,P] or [P,B] chelating pockets housed on a protected o-hydroquinone core

1,2-Dibromo-4,5-dimethoxybenzene was explored as a platform for the buildup of ditopic ligands. Low temperature reactions with n-butyllithium followed by quenches with various electrophiles led to the syntheses (2-bromo-4,5-dimethoxyphenyl)diphenylphosphine (1), (4,5-dimethoxy-2-(methylthio)phenyl)diphenylphosphine (2), 1,2-bis(diphenylphosphino)-4,5-dimethoxybenzene (3), and (2-(dicyclohexylboryl)-4,5-dimethoxyphenyl)diphenylphosphine (4). Oxidation of 3 produced 1,2-bis(diphenylphosphoryl)-4,5-dimethoxybenzene (5). All compounds were characterized by multinuclear (1H/13C/31P{1H}) NMR spectroscopy and by high resolution mass spectrometry. In addition, single crystal X-ray diffraction characterizations of 1, 3, 4, and 5 were also carried out. Reactivity of o-phosphinophenylborane 4 toward molecular hydrogen was also probed.

Controlled lithium-halogen exchange in low temperature reactions of 1,2-dibromo-4,5-dimethoxybenzene with n-butyllithium leads to the formation of mono- or dilithio-aryl intermediates. These intermediates are utilized in synthetic sequences allowing for substituting the bromines in the original molecule with two heteroatom-bearing groups.Figure optionsDownload as PowerPoint slideHighlights
► Potentially chelating [P,P], [P,S], and [P,B] ligands were synthesized.
► Four compounds were characterized by single crystal X-ray diffraction methods.
► o-Phosphinophenylborane shows weak interaction between the P and B centers.
► The o-phosphinophenylborane obtained does not react with molecular hydrogen.