Polyhedral rhenaborane chemistry: crystal and molecular structures of the nido-6-rhenadecaborane cluster compounds [6,6,6,6-(PMe2Ph)3H-nido-6- ReB9H13] and [2-(PMe2Ph)-6,6,6,6-(PMe2Ph)2ClH-nido-6-ReB9H12]; nuclear magnetic resonance parameters of these and other related nido-rhenadecaborane cluster species

Abstract

The compounds [6,6,6,6-(PMe₂Ph)₃H-nido-6-ReB₉H₁₃](1) and [6,6,6,6-(PMe₂Ph)₃H-9-(OEt)-nido-6-ReB₉H₁₂](2) are formed in 40 and 25% yields respectively from the reaction of mer-[ReCl₃(PMe₂Ph)₃] with an excess of [NEt₄][B₉H₁₄] in refluxing ethanol. Also obtained in smaller yields are an isomer of compound (2), [6,6,6,6-(PMe₂Ph)₃H-8-(OEt)-nido-6-ReB₉H₁₂](3; ca. 4%), and a cluster-phosphine-substituted compound, [2-(PMe₂Ph)-6,6,6,6-(PMe₂Ph)₂ClH-nido-6- ReB₉H₁₂](4; < 1%). Compounds (1) and (4) have been structurally characterized by single-crystal X-ray diffraction methods. A chloro-substituted cluster compound, [2-Cl-6,6,6,6-(PMe₂Ph)₃H-nido-6-ReB₉H₁₂](5) can be obtained essentially quantitatively from compound (1) by heating in sym-C₂D₂Cl₄ at ca.+100 °C; it is an isomer of compound (4). All the compounds are air-stable coloured crystalline solids and their formulation as nido-B₁₀H₁₄-like cluster compounds is consistent with their n.m.r. properties. The (PMe₂Ph)₃H groupings in compounds (1), (2), (3), and (5) exhibit a dual pseudo-rotational fluxionality with ΔG^‡ values of 45–60 and of ca. 30 kJ mol^–1 respectively for the two sub-processes. The rhenium atoms in these cluster compounds can be considered to contribute three orbitals to the cluster bonding, and these plus the four ligands associated with the metal centres are in ‘capped octahedral’ type of configurations about the d⁴ metal centres.