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 P1̄, a = 943.3(2) pm,
b = 1278.3(3) pm, c =
1413.3(2) pm, α = 72.45(1)°, β = 78.13(1)°,
γ = 70.83(1)°, d = 1.081 g
cm-3, Z = 2, wR2 = 0.1553 at
6548
F2 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, β = 113.73(1)°,
dcalc = 1.268 g
cm-3, Z = 4, wR2 = 0.0989
at
5220 F2 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(μ-R)3Ba(dme)2 in
toluene or benzene solution as can be proven by
31P{1H}-NMR spectroscopy
(2J(P−P) = 6.7 Hz) and by X-ray structure
analysis
(Ba2P4Si8O6C48H106,
space group P21/n, a =
1256.3(2) pm,
b = 2000.0(3) pm, c = 2986.9(2) pm,
β = 98.929(9)°, dcalc = 1.257 g
cm-3, Z = 4, wR2 = 0.1334 at
11580 F2
values). The Ba−P bond lengths vary between 318 and 338
pm.