The crystal and molecular structure of [1,1,1,1-(CO)H(PPh3)2-arachno-1-IrB3H7] and some bonding considerations in arachno-type four-vertex metal ‘π-allyl’ and ‘borallyl’ clusters

Abstract

The detailed molecular structure of [(CO)(PPh₃)₂HIrB₃H₇] has been determined by X-ray diffraction analysis. The colourless crystals are monoclinic, space group P2₁/n with a= 1 182.0(3), b= 2 189.4(4), c= 1 355.7(3) pm, β= 104.27(2)°, and Z= 4. The molecular structure (R= 0.032 for 4 119 reflections) features a four-vertex butterfly cluster (IrB₃) with Ir on a ‘hinge’ position. The structure is interpreted in terms of a ‘capped octahedral’ seven-orbital 18-electron d⁴ iridium(V) complex in which the metal–borane bonding occurs predominantly via three two-electron two-centre iridium–boron bonds. The cluster bonding implications are discussed with reference to the ‘π-allyl’ and ‘borallyl’ bonding modes.