New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: Structural characterizations of 1,4-(PPh \u3c inf\u3e 2 ) \u3c inf\u3e 2 -2,5-(PR) \u3c inf\u3e 2 ) \u3c inf\u3e 2 -C \u3c inf\u3e 6 F \u3c inf\u3e 2 (R = Ph, \u3c sup\u3e i \u3c/sup\u3e Pr, Et)

Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T \u3c -90 °C) followed by a quench with a slight excess of ClPPh 2 afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1) in good yields. Reacting 1 with two equivalents of BuLi followed by a quench with a slight excess of ClPR 2 yield novel 1,2,4,5-tetrakis(phosphino)-3,6-difluorobenzenes 1,4-(PPh2) 2-2,5-(PR2)2-C6F2 (R = Ph (2a); R = iPr (2b); R = Et (2c)) in moderate yields. Compounds 1 and 2a-c were characterized by multinuclear NMR spectroscopy and elemental analyses. In addition, molecular structures of 2a-c have been determined by single crystal X-ray crystallography. Phosphorus atoms of PPh2/PR2substituents in 2a-c are displaced from the plane of the central phenyl ring due to steric interactions with neighboring groups. © 2004 Elsevier B.V. All rights reserved