Nine-vertex polyhedral iridamonocarbaborane chemistry. Products of thermolysis of [(CO)(PPh3)2IrCB7H8] and emerging alternative cluster-geometry patterns

Abstract

Thermolysis of [7-(CO)-7,7-(PPh₃)₂-7,1-IrCB₇H₈]1 at 250 °C resulted in isomerisation to give orange air-stable [7-(CO)-7-H-7,9-(PPh₃)₂-7,1-IrCB₇H₇]2 and its 6-(PPh₃) isomer 3 as the major products. The compounds were characterised by NMR spectroscopy and single-crystal X-ray diffraction analysis on 1 and 3. The CH₂Cl₂ disolvate of 1 is monoclinic, space group P2₁/n, with a= 1394.33(10), b= 1276.81 (13), c= 2393.5(2) pm, β= 94.163(9)°, and Z= 4, and the structure was refined to R(R_g)= 0.0351 (0.0384) for 5991 reflections with I > 2.0σ(I). The CH₂Cl₂ monosolvate of 3 is triclinic, space group P, with a= 1150.39(11), b= 1177.08(13), c= 1498.3(2) pm, α= 88.192(9), β= 89.506(8), γ= 80.720(9)°, and Z= 2. and the structure was refined to R(R_g)= 0.0299(0.0311) for 5864 reflections with I > 2.0σ(I). The nine-vertex {IrCB₇} cluster structures of 1 and 3 have quadrilateral open faces (B–B ca. 220 pm) and therefore ‘isonido’ geometries although of formal closo constitution. The cluster opening is briefly discussed in the context of a nine-vertex closo–isonido–isocloso structural continuum, in the context of other contemporaneously recognised structural continua in twelve-, eleven-, ten-, and eight- vertex boron cluster chemistry, and thence in the context of emerging general structural patterns that interrelate the isocloso, isonido and isoarachno cluster geometries.