Reaction of Na₂[closo-B₁₂H₁₂] with [RuCl₃(PMe₂Ph)₃] gives a 10% yield of the lemon-yellow air-stable covalent complex [(PMe₂Ph)₃RuB₁₂H₁₂], characterized by elemental analysis and multielement nuclear magnetic single- and multiple-resonance spectroscopy. Reaction of [NHEt₃]₂[B₁₂H₁₂] and [RuCl₂(PPh₃)₃] results in the formation of [(PPh₃)₂ClRuB₁₂H₁₁(NEt₃)] as an orange-red air-stable compound (30%), characterized by single-crystal X-ray diffraction analysis as well as n.m.r. spectroscopy. The solvate [(PPh₃)₂ClRuB₁₂H₁₁(NEt₃)]·CH₂Cl₂ forms monoclinic crystals, with a= 2 246.3(2), b= 1 189.2(2), c= 1 972.5(2) pm, β= 111.04(1)°, Z= 4, and space group P2₁/n. The compounds may formally be regarded either as ruthenium(II) complexes of closo-dodecaboranyl ligands which bind in a trihapto tridentate mode to the octahedral metal centres via three two-electron three-centre B–H–Ru bridge bonds, or as 13-vertex pileo 2n-electron metallaborane cluster species which have capped closed deltahedral cluster geometries.