Polyhedral metallacarbaborane chemistry: preparation, molecular structure, and nuclear magnetic resonance investigation of [3-(η5-C5Me5)-closo-3,1,2-MC2B9H11] (M = Rh or Ir)

Abstract

Reaction between Cs[nido-7,8-C₂B₉H₁₁] and [{M(η⁵-C₅Me₅)Cl₂}₂] (M = Rh or Ir) yielded orange-yellow, air-stable crystals of [3-(η⁵-C₅Me₅)-closo-3,1,2-RhC₂B₉H₁₁] [compound (2), 34%] or [3-(η⁵-C₅Me₅)-closo-3,1,2-IrC₂B₉H₁₁] [compound (3), 96%] both of which were characterized by their assigned ¹¹B and ¹H n.m.r. spectra and by single-crystal X-ray diffraction analyses. Crystals of (2) were orthorhombic, space group P2₁2₁2₁, with a = 1 081.0(2), b = 1 278.2(1), c = 1 278.4(2) pm, and Z = 4; R = 0.0197, R′ = 0.0204 for 1 756 observed reflections [I > 2.0σ(I)]. Crystals of (3) were also orthorhombic, space group P2₁2₁2₁, with a = 1 076.3(1), b = 1 282.9(1), c = 1 292.8(2) pm, and Z = 4; R = 0.0286, R′ = 0.0307, for 1 712 observed reflections [I > 2.0σ(I)]. The n.m.r. properties of the C₂B₉H₁₁ fragments of (2) and (3) are compared with the ¹¹B and hitherto unreported ¹H n.m.r. characteristics of the corresponding fragments of [3-(η⁵-C₅H₅)-closo-3,1,2-CoC₂B₉H₁₁] (4), closo-1,2-C₂B₁₀H₁₂, nido-7,8-C₂B₉H₁₃, and [nido-7,8-C₂B₉H₁₂]⁻, in order to assess any n.m.r. shielding patterns that might reveal bonding trends. The unique endo/bridging open-face hydrogen atom in [nido-7,8-C₂B₉H₁₂]⁻ is discussed in the light of its n.m.r. properties.