New binucleating ligand with two [P,S] chelation pockets on a single phenyl ring: Syntheses and X-ray structures of 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene and of bimetallic complex (CO)3Fe(μ-[(PPh2)(SMe)C6F2(SMe)(PPh2)])Fe(CO)3

Double deprotonations of 1,4-dibromo-2,5-difluorobenzene with LDA (2 equiv., T < −90 °C) generate a reasonably stable organodilithium intermediate. Quenching this reaction mixture with chlorophosphines ClPR2 produce p-bis(phosphino)benzenes R2P–C6Br2F2–PR2 (R = Ph, 4a; R = iPr, 4b). Facile lithium–bromine exchange occurs upon exposure of 4a to BuLi (2 equiv., −80 °C), leading to the generation of another organodilithium intermediate. Addition of MeS–SMe (2 equiv.) to such reaction mixtures gives 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene (2). Compound 2 is the first example of a neutral binucleating ligand featuring the [P,S] chelating sites on the opposite sides of a single phenyl ring. Compound 4b does not undergo the analogous transformation when subjected to the same conditions (2BuLi/2MeS–SMe). Addition of 2 to Fe(CO)5/2(Me3NO · 2H2O) reaction mixtures led to the isolation of the bimetallic complex {(CO)3Fe[P,S]–C6F2–[P,S]Fe(CO)3} (3), ([P,S] represents the chelating pockets formed by adjacent –PPh2 and –SMe groups). All of the new compounds were characterized by spectroscopic and analytical techniques (multinuclear NMR, mass-spectrometry, and/or elemental analysis). In addition, compounds 2 and 3 were characterized via single crystal X-ray diffraction methods.

Graphical abstractNew binucleating ligand, 1,4-bis(diphenylphosphino)-2,5-difluoro-3,6-bis(methylthio)benzene was obtained via sequential generations of organodilithio reagents from 1,4-dibromo-2,5-difluorobenzene. It contains two phosphine-thioether ([P,S]) chelation pockets positioned on the opposite sides of a single phenyl ring. Bimetallic complex was obtained upon reaction of the ligand with Fe(CO)3 fragments.Figure optionsDownload full-size imageDownload as PowerPoint slide