Iridanonaborane chemistry: preparation and characterization of some arachno-4-iridanonaboranes by nuclear magnetic resonance spectroscopy and single-crystal X-ray diffraction analysis

Abstract

The nido anion [B₉H₁₂]^– reacts rapidly with an equimolar quantity of trans-[Ir(CO)Cl(PMe₃)₂] at room temperature to produce the new, colourless, nine-vertex arachno-iridanonaboranes [HIrB₈H₁₂(CO)-(PMe₃)₂](1; 30% yield) and [(HIrB₈H₁₁Cl)(CO)(PMe₃)₂](2; 7% yield), together with the known yellow ten-vertex nido-[6,6,6-H(PMe₃)₂-6-IrB₉H₁₃]. Similar compounds are formed, although in much smaller yields, when arachno-[B₉H₁₄]^– is used instead of nido-[B₉H₁₂]^–. Single-crystal X-ray diffraction studies show the detailed structure of (2) to be [1-Cl-sym-4,4,4,4-(CO)-endo-H-cis-(PMe₃)₂-arachno-4-IrB₈H₁₁]. Comparative n.m.r. spectroscopy (³¹P, ¹¹B, and ¹H) shows that compound (1) has the configuration [asym-4,4,4,4-(CO)-endo-H-cis-(PMe₃)₂-arachno-4-IrB₈H₁₂]. Minor products of the reaction (⩽1%) include a third new arachno-iridanonaborane [sym-4,4,4,4-endo-H-mer-(PMe₃)₃-4-IrB₈H₁₂](3) and the previously reported five-vertex arachno-iridaborane-[1,1,1-(CO)(PMe₃)₂-arachno-1-IrB₄H₉]. The nine-vertex compounds all have the gross arachno nonaborane structure of iso-B₉H₁₅ similar to that of the platinum analogue [(PtB₈H₁₂)(PMe₂Ph)₂], but there are differences in the detail of the borane-to-metal bonding, which have important wider implications. The arachno-iridanonaboranes may be regarded as octahedral complexes of d⁶ iridium(III).