SYNTHESIS AND STRUCTURES OF DILITHIUM (1,2-DIPHOSPHIDO)BENZENES

Treatment of the appropriate (1,2-diphosphino)benzenes C6H3(PHR)(2)-1,2-R'-4 (R' = Me or H; R = H, Ph or SiMe(3)) with LiBu(n) and tmen [tmen = Me(2)N(CH2)(2)NMe(2)] in hexane afforded the dilithium diphosphides [Li(tmen)](2)[C6H3(PR)(2)-1,2-R'-4] (R' = H, R = Ph 1; R' = H, R = SiMe(3) 2; 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(PHSiMe(3))(2)-1.2 6 and C6H3(PHPh)(2)-1.2-Me-4 7, and the phosphole C6H3[{(PPh)(2)-1,2}PPh]-Me-4 10 and 1-3 are new compounds] have been carried out. The diphosphine C6H4(PHPh)(2) 5, 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 SiMe(3) H-1, C-13 and Si-29 NMR signals of 6. Variable-temperature P-31-{H-1} and Li-7-{H-1} NMR spectra for 1 and 2 revealed dynamic behaviour; the low-temperature limiting spectra for each of 1 and 2 showed septets [P-31-{H-1}] and triplets [7Li-{H-1}], consistent with the structures of the crystalline molecules.