Monomeric and Dimeric Tetrahydrofuran Complexes of Barium Bis[bis(dimethyl-<i>tert</i>-butylsilyl)arsanide]^†

The metathesis reaction of (dme)LiAsH2 with ClSiMe2tBu allows the isolation of bis(dimethyl-tert-butylsilyl)arsane 1 in a rather poor yield. The inversion barrier of 64 kJ·mol-1 for 1 can be deduced from dynamic 1H and 13C{1H} NMR experiments. The metalation of 1 by bis(tetrahydrofuran)barium bis[bis(trimethylsilyl)amide] in tetrahydrofuran leads to the formation of tetrakis(tetrahydrofuran)barium bis[bis(dimethyl-tert-butylsilyl)arsanide] 2. The coordination sphere of the metal center is best described as a pentagonal bipyramid with the arsanide ligands in apical positions; however, one equatorial position remains unoccupied due to the steric shielding by the demanding trialkylsilyl groups. Recrystallization of 1 from toluene leads to the loss of tetrahydrofuran coligands and the formation of dimeric (tetrahydrofuran)barium bis[bis(dimethyl-tert-butylsilyl)arsanide] 3. The barium atom shows the small coordination number of 4, and therefore, extremely short terminal Ba−As bonds of 319 pm are observed. Crystallographic data: 2, monoclinic, C2/c, a = 1981.8(7) pm, b = 1137.4(3) pm, c = 2445.9(7) pm, β = 93.71(4)°, Z = 4, wR2 = 0.1193; 3, monoclinic, P21/c, a = 3077.91(1) pm, b = 1165.53(1) pm, c = 2611.67(1) pm, β = 93.58(1)°, Z = 4, wR2 = 0.1358.