Synthesis and characterisation of a semipseudocloso carbaruthenaborane. Molecular structure of [1-(PhCC)-2-Ph-3-(cym)-3,1,2-semipseudocloso-RuC₂B₉H ₉] (cym = p-cymene)

The closo carbaborane 1-(PhCC)-2-Ph-1,2-C₂B₁₀H₁₀ was readily decapitated to afford either [7-(PhCC)-8-Ph-7,8-C₂B₉H₁₀]^- or [7-(PhCC)-S-Ph-7,8-C₂B₉H₉]^2-. Reaction of the thallium(I) salt of the latter with [{RuCl₂(cym)}₂] (cym = p-cymene) yielded the unique semipseudocloso carbaruthenaborane [1-(PhCC)-2-Ph-3-(cym)-3,1,2-RuC₂B₉H₉] characterised by multinuclear NMR spectroscopy (weighted average ¹¹B chemical shift +2.41 ppm) and by single-crystal X-ray diffraction [C(1)-C(2) 2.184(7), Ru(3) ?B(6) 3.166(6) Å]. The semipseudocloso shape thus appears to lie between closo and pseudocloso, although somewhat closer to the latter. Confirmation of the structure strongly supports the idea of a continuum of cluster structures from closo to pseudocloso, the position of a molecule on which may be controlled by steric effects.