Synthesis of tris(1,2-dimethoxyethane-O,O')barium bis(2,2,5,5-tetramethyl-2,5-disilaphospholanide) and the monomer dimer equilibrium in toluene solution

(1,2-Dimethoxyethane-O,O')lithium phosphanide (dme)LiPH2 reacts with 1,2-bis(chloro-dimethylsilyl)ethane to give 2,2,5,5-tetramethyl-2,5-disilaphospholane, 1, as well as 1,1,4,4-tetramethyl-1,4-bis(2,2,5,5-tetramethyl-2,5-disilaphospholanyl)-1 ,4-disilabutane, 2 (P2Si6C18H48, space group <P(1)over bar>, a = 943.3(2) pm, b = 1278.3(3) pm, c = 1413.3(2) pm, alpha = 72.45(1)degrees, beta = 78.13(1)degrees, gamma = 70.83(1)degrees, d = 1.081 g cm(-3), Z = 2, wR2 = 0.1553 at 6548 F-2 values). The reaction of 2,2,5,5-tetramethyl-2,5-disilaphospholane 1 and barium bis [bis(trimethylsilyl)amide] in 1,2-dimethoxyethane yields nearly quantitatively tris(1,2-dimethoxyethane-O,O')barium bis(2,2,5,5-tetramethyl-2,5-disilaphospholanide) , 3A, which crystallizes in the monoclinic space group C2/c (BaP2Si4O6C24H62, a = 2152.3(1) pm, b = 1381.5(1) pm, c = 1459.7(1) pm, beta = 113.73(1)degrees, d(calc) = 1.268 g cm(-3), Z = 4, wR2 = 0.0989 at 5220 F-2 values). Due to the high coordination number of eight of the barium center, rather long Ba-P distances of 333 pm are observed, With loss of the complexating ether solvent this compound forms a dimer 3B of the type R(dme)Ba(mu-R)(3)Ba(dme)(2) in toluene or benzene solution as can be proven by P-31{H-1}-NMR spectroscopy ((2)J(P-P) = 6.7 Hz) and by X-ray structure analysis (Ba2P4Si8O6C48H106, space group P2(1)/n, a = 1256.3(2) pm, b = 2000.0(3) pm, c = 2986.9(2) pm, beta = 98.929(9)degrees, d(calc) = 1.257 g cm(-3), Z = 4, wR2 = 0.1334 at 11580 F-2 values). The Ba-P bond lengths vary between 328 and 338 pm.