Synthesis and structures of dilithium (1,2-diphosphido)-benzenes
Abstract
Treatment of the appropriate (1,2-diphosphino)benzenes C6H3(PHR)2-1,2-R′-4 (R′= Me or H; R = H, Ph or SiMe3) with LiBun and tmen [tmen = Me2N(CH2)2NMe2] in hexane afforded the dilithium diphosphides [Li(tmen)]2[C6H3(PR)2-1′,2-R′-4](R′= H, R = Ph 1; R′= H, R = SiMe32; R′= Me, R = Ph 3; R′= H = R 4). Crystal structures of 1 and 2 show that each phosphorus atom is bonded equivalently to the two lithium atoms (and conversely each Li to the two P atoms), the two lithium atoms being on opposite sides of the C6H4P2 plane. Solution multinuclear NMR spectral studies of the parent diphosphines, their dilithio-derivatives 1–3 and the phosphole 10[of which C6H4(PHSiMe3)2-1,2 6 and C6H3(PHPh)2-1,2-Me-4 7, and the phosphole C6H3[{([graphic omitted]Ph]Me-4 10 and 1–3 are new compounds] have been carried out. The diphosphine C6H4(PHPh)25, like 6 and 7, was a ca. 1 : 1 mixture of diastereoisomers, 6 having a much larger (9.2 ppm) chemical shift difference between P and P′ than 5(0.66 ppm). Virtual coupling from both phosphorus atoms was observed for the SiMe31H, 13C and 29Si NMR signals of 6. Variable-temperature 31P-{1H} and 7Li-{1H} NMR spectra for 1 and 2 revealed dynamic behaviour; the low-temperature limiting spectra for each of 1 and 2 showed septets [31P-{1H}] and triplets [7Li-{1H}], consistent with the structures of the crystalline molecules.