Boron-Rich Metallaboranes from κ²-N,E-Chelated Ru Complexes (E = S or Se): A Direct Route to Ruthenaboranes

We have established a new route for boron-rich ruthenaborane clusters utilizing [BH₃·THF] and a ruthenium precursor featuring chelating ligands. Salt elimination reactions between [K(C₅H₄NE)], (E = S; Se) and [RuCl₂(PPh₃)₃], <b>1</b> afforded <i>cis</i>-[Ru(κ²-<i>N,E</i>-C₅H₄NE)₂(PPh₃)₂], <i>cis</i>-<b>2a</b>-<b>b</b> (<i>cis</i>-<b>2a</b>: E = S and <i>cis</i>-<b>2b</b>: E = Se). Following the ligand exchange reaction with the 1,2-bis (diphenylphosphino)ethane (dppe) ligand yielded <i>cis</i>-[Ru(κ²-<i>N,E</i>-C₅H₄NE)₂(dppe)] (<i>cis</i>-<b>3a</b>: E = S; <i>cis</i>-<b>3b</b>: E = Se). Reactivity of <i>cis</i>-[Ru(κ²-<i>N,E</i>-C₅H₄NE)₂(dppe)] (<i>cis</i>-<b>3a</b>-<b>b</b>) with [BH₃·THF] under thermolytic conditions led to the formation of two isomeric <i>nido</i>-ruthenadecaboranes [7,7-(PPh₂CH₂)₂-7-E-3-N-<i>nido</i>-7-RuB₉H₁₂] (<b>4a</b>: E = S; <b>4b</b>: E = Se) and [6,6-(PPh₂CH₂)₂-6-E-7-N-<i>nido</i>-6-RuB₉H₁₂] (<b>5a</b>: E = S; <b>5b</b>: E = Se), in which ruthenium occupies the seventh and sixth cluster vertices, respectively. Additionally, 9-vertex <i>nido</i>-ruthenaborane, [2,2,-(PPh₂CH₂)₂-2-E-1-N-<i>nido</i>-2-RuB₈H₁₁] (<b>6a</b>: E = S; <b>6b</b>: E = Se), was also isolated. In contrast, the reactivity of [Ru(κ²-<i>N,E</i>-C₅H₄NE)₂(PPh₃)₂] <i>cis</i>-<b>2a</b>-<b>b</b>, with [BH₃·THF] or [BHCl₂·SMe₂], led to the formation of complexes <i>fac</i>-[Ru{κ³-<i>H,E,E</i>'-(NXHBEBHXN)(EC₅H₄)₂}PPh₃] (<i>fac</i>-<b>7a</b>: X = H, E = S; <i>fac</i>-<b>7b</b>: X = H, E = Se; <i>fac</i>-<b>8a</b>: X = Cl; E = S). All of the synthesized molecules have been thoroughly characterized using NMR spectroscopy, ESI-MS, and single-crystal X-ray diffraction studies for structural elucidation. Additionally, theoretical studies have provided insights into the bonding and electronic structures of these molecules.