SYNTHESIS AND STRUCTURE OF ALL-TRANS-1,2,3,4-TETRA-TERT-BUTYL-1,2,3,4-TETRACHLOROCYCLOTETRASILANE

The synthesis of all-trans-[(t-Bu)CISi]4 (1) via chlorodephenylation of [(t-Bu)PhSi]4 with HCl/AlCl3 is described. Three isomers of [(t-Bu)PhSi]4 (cis-cis-trans-2, cis-trans-cis-2, and all-trans-2) were separated, and each of them was subjected to chlorodephenylation. The X-ray structures are reported for cis-cis-trans-2 and cis-trans-cis-2. Crystal data for cis-cis-trans-2: monoclinic, P2(1)/c, a = 20.924(10) angstrom, b = 10.813(5) angstrom, c = 19.443(11) angstrom, beta = 117.57(3)-degrees, V = 3900(3) angstrom3, Z = 4, R = 0.047, R(w) = 0.047 for 2572 reflections. Crystal data for cis-trans-cis-2: monoclinic, P2(1)/n, a = 15.407(4) angstrom, b = 23.798(6) angstrom, c = 10.852(2) angstrom, beta = 94.93(2)-degrees, V = 3964(2) angstrom3, Z = 4, R = 0.043, R(w) = 0.046 for 2905 reflections. The chlorodephenylation of cis-cis-trans-2, cis-trans-cis-2, and all-trans-2 gave 1 exclusively. The structure of 1 was established by X-ray crystallography. Crystal data for 1: orthorhombic, Pca2(1), a = 14.848(2) angstrom, b = 13.719(1) angstrom, c = 13.074(4) angstrom, V = 2663(1) angstrom3, Z = 4, R = 0.052, R(w) = 0.077 for 1992 reflections. 1 has a folded structure, the dihedral angle being 26.6-degrees, which accommodates the chlorine atoms in pseudoaxial positions and the tert-butyl groups in less hindered pseudoequatorial positions. The principal average bond distances are Si-Si 2.375 angstrom, Si-C 1.905 angstrom, and Si-Cl 2.086 angstrom. The Si-Cl bond distances are somewhat longer than usual.