Organoruthenaborane chemistry. Part 7. Preparation, molecular structure, and nuclear magnetic resonance properties of eleven-vertex closo-type clusters: [2,4-Me2-1 -(pcym)-1,2,4-RuC2B8H8], [2,3-Me2-1 -(pcym)-1,2,3-RuC2B8H8], [1-(pcym)-1-RuB10H10] and some related species

Abstract

Reaction of [{Ru(pcym)Cl₂}₂] or [{Ru(hmb)Cl₂}₂](pcym =p-cymene, 1-Me-4-PrⁱC₆H₄, hmb = hexamethylbenzene, C₆Me₆) with the nido-dicarbaborane 5,6-Me₂-5,6-C₂B₈H₁₀ in the presence of N,N,N′, N′-tetramethylnaphthalene-1,8-diamine gave, respectively, the orange-yellow air-stable metalladicarbaborane [2,4-Me₂-1-(pcym)-1,2,4-RuC₂B₈H₈](1a) or the corresponding yellow hmb derivative [2,4-Me₂-1 -(hmb)-1,2,4-RuC₂B₈H₈](1b), both of which were characterized by elemental analysis, mass spectrometry, and n.m.r. spectroscopy. A single-crystal X-ray diffraction analysis of (1a) revealed considerable distortion from idealized C_2v cluster symmetry due to the presence of a quadrilateral open face Ru(1)C(2)C(4)B(7) with an essentially non-bonding Ru(1)–C(4) distance of 268.3(7) pm. Crystals of (1a) are orthorhombic, space group P2₁2₁2₁, with a= 827.5(1), b= 1 066.0(1 ), and c= 2 154.4(2) pm, and Z= 4. Possible interpretations of the distortion are discussed. Thermal isomerization of (1a) at 400 °C gave a quantitative yield of the yellow symmetrical isomer [2,3-Me₂-1-(pcym)-closo-1,2,3-RuC₂B₈H₈](2a) in which the ‘distortion’ as revealed by a single-crystal X-ray study, manifests itself as a substantial lengthening of the distances from Ru(1) to each of the six directly bonded atoms in the η⁶-dicarbaborane ligand. Crystals of (2a) are monoclinic, space group P2₁/n, with a= 879.7(1), b= 1 527.7(2), and c= 1 414.3(1) pm, β= 92.90(1)°, and Z= 4. N.m.r. data on (2a) are also reported. Further insight into the structure and bonding relations of eleven-vertex metalladicarbaborane clusters was obtained by the synthesis and characterization of the non-carbon-containing analogue [1-(pcym)-1-RuB₁₀H₁₀](3a) and its (known) hmb congener [1 -(hmb)-1 -RuB₁₀H₁₀](3b). Crystals of (3a) are orthorhombic, space group Pbca, with a= 787.8(1), b= 1 417.0(2), and c= 3 019.9(4) pm, and Z= 4. The {RuB₁₀} cluster is significantly more compact than its symmetrical dicarba analogue {RuC₂B₈}. Further compounds studied include the monomethylated dicarba derivatives [4-Me-1-(hmb)-1,2,4-RuC₂B₈H₉](4), [3-Cl-4-Me-1-(hmb)-1,2,4-RuC₂B₈H₈](7) and [2-Me-1-(hmb)-closo-1,2,3-RuC₂B₈H₉](8).