Reactions of decaborane(14) with silylated acetylenes. Synthesis of the new monocarbon carborane 9-Me2S-7-(Me3Si)2CH-CB10H 11

Article abstract of DOI:10.1021/om00144a016

The dimethyl sulfide promoted reactions of decaborane(14) with the silylated acetylenes, bis(trimethylsilyl)acetylene and (trimethylsilyl)propyne, have been studied and were not found to yield the expected ortho-carborane derivatives but instead gave either alkenyldecaborane or monocarbon carborane products. Thus, the reaction of decaborane(14) with dimethyl sulfide and bis(trimethylsilyl)acetylene produced 9-(CH₃)₂S-7-[((CH₃)₃Si) ₂CH]-CB₁₀H₁₁ (I) and 5-(CH₃)₂S-6-[((CH₃)₃Si) ₂C=CH]-B₁₀H₁₁ (II) while the analogous reaction with (trimethylsilyl)propyne yielded 5-(CH₃)₂S-6-[(CH₃)₃Si(CH ₃)C=CH]-B₁₀H₁₁ (III). A single-crystal X-ray determination of III demonstrated that compounds II and III result from acetylene hydroboration reactions and have structures based on a decaborane(14) geometry with a dimethyl sulfide bound to the 5-boron and an alkenyl group bound to the 6-boron on the open face. Crystal data for III: space group P1; Z = 4; a = 16.406 (4) ?, b = 16.677 (5) ?, c = 8.627 (2) ?, α = 100.67 (2)°, β = 97.78 (2)°, γ = 118.23 (2)°, V = 1974.9 ?³; R = 0.077 and R_w = 0.103 for the 5208 reflections having F_o² > 3σ(F_o²). The data obtained for compound I indicate that it is an unusual monocarbon carborane resulting from the insertion of only one of the acetylenic carbons of the bis(trimethylsilyl)acetylene into the cage structure. The cluster geometry is based on an icosahedron missing one vertex, with an exopolyhedral bis(trimethylsilyl)methyl group bonded to the cage carbon. The reaction of I with either NaH, LiEt₃BH, Na, or (η⁵-C₅H₅)₂Co results in hydrogen loss, dimethyl sulfide dissociation, and cage closure to yield the 2-((CH₃)₃Si)₂CH-CB₁₀H ₁₀^- anion. A single-crystal X-ray determination of the cobaltocenium salt VI established that the compound has a closo structure based on an octadecahedron, with the cage carbon occupying the four-coordinate 2-position in the structure. Crystal data for VI: space group P2₁/n; Z = 4; a = 12.260 (1) ?, b = 17.252 (3) ?, c = 13.701 (3) ?, β = 107.94 (1)° V = 2757.0 ?³; R = 0.058 and R_w = 0.068 for the 3061 reflections having F_o² > 3σ(F_o²). Thermolysis of I at toluene reflux yielded as the major product 6-(CH₃)₂S-2-[((CH₃)₃Si) ₂CH]-CB₁₀H₉ (VII) while thermolysis of I in the solid phase gave VII and small amounts of 6-(CH₃)₂S-4-OH-2-[((CH₃)₃Si) ₂CH]-CB₁₀H₈ (VIII). Compounds VII and VIII are isoelectronic with VI, and single-crystal X-ray determinations confirmed that VII and VIII have similar octadecahedral structures. Crystal data for VII: space group P1; Z = 2; a = 8.834 (3) ?, b = 19.211 (2) ?, c = 6.998 (1) ?, α = 96.20 (1)°, β= 109.63 (2)°, γ = 91.91 (2)°; V = 1108.9 ?³; R = 0.067 and R_w = 0.081 for the 2864 reflections having F_o² > 3σ(F_o²). Crystal data for VIII: space group P1; Z = 4; a = 13.729 (1) ?, b = 16.345 (2) ?, c = 10.880 (1) ?, α = 96.62 (1)°, β= 93.45 (1)°, γ = 74.47 (1)°; V = 2335.4 ?³; R = 0.065 and R_w = 0.078 for the 5623 reflections having F_o² > 3σ(F_o²).