New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: structural characterizations of 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R=Ph, iPr, Et)

1,4-Bis(phosphine)-2,5-difluoro-3,6-dihydroxybenzenes and their P-oxides: Syntheses, structures, ligating and electronic properties

“…Recently we reported on the preparation of several new polydentate phosphine [41,53] and mixed donor [P,S] [54] ligands. The synthetic method utilized in such syntheses relies on the sequential generation of organodilithio intermediates from selected tetrasubstituted benzenes.…”

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

“…Recently, we have shown that organodilithio intermediates can be formed when selected tetrahalobenzenes featuring protons flanked by F/Cl and F/Br atoms are exposed to lithium diisopropylamide (LDA) at low temperatures [9,21]. Quenching such reaction mixtures with chlorophosphines ClPR 2 (R = Ph, i Pr) allowed for the syntheses of 1,4-bis(phosphino)benzenes containing tetrahalogenated central phenyl rings [9,21]. The presence of the heavier halogens (particularly bromine) in the later compounds may be utilized for designing further synthetic steps.…”

“…The presence of the heavier halogens (particularly bromine) in the later compounds may be utilized for designing further synthetic steps. For example, we have shown that 1,4-bis(diphenylphosphino)-2,5-dibromo-3,6-difluorobenzene (4a) undergoes double lithium-bromine exchange upon reactions with BuLi thus generating another organodilithium intermediate, and quenching the reaction mixtures with chlorophosphines ClPR 2 (R = Ph, i Pr, Et) lead to the syntheses of novel tetrakis(phosphino)difluorobenzenes [9]. Such a synthetic approach (sequential generations of organodilithium intermediates from 1,4-dibromo-2,5-difluorobenzene, followed by electrophile quenches) may potentially be developed into a general synthetic strategy for the construction of other binucleating ligands bearing 1,2,4,5-tetrasubstituted benzene structural frames.…”

“…A suitable starting compound, 1,4-bis(diisopropylphosphino)-2,5-dibromo-3,6-difluorobenzene (4b) was obtained in good ($70%) yield via the synthetic sequence used for 4a [9] (dilithiation of 1,4-dibromo-2,5-difluorobenzene followed by ClP i Pr 2 quench). However, substituting 4a by 4b in the reaction sequence depicted in Eq.…”

“…Most of the studies involving such [P,S] ligands have been centered on monometallic complexes, and the number of well-defined binucleating [P,S] ligands and their bimetallic complexes is relatively small [7,8]. Recently, we have reported the new syntheses of potentially binucleating ligands -symmetric and unsymmetric 1,2,4,5-tetrakis(phosphino)benzenes [9], where the sequential generation of organodilithium intermediates from 1,4-dibromo-2,5-difluorobenzene followed by ClPR 2 quenches (R = Ph, Et, i Pr) were utilized. Structurally analogous tetrakis(phosphino)-or tetrakis(thio)benzenes with P-or S-donor ligands at the 1,2,4,5 positions have been successfully used as binucleating ligands for the formation of bimetallic complexes [10][11][12] and of polymetallic aggregates [13][14][15][16][17].…”