Synthesis and reactivity investigation of iridium maleonitriledithiolate complexes. Redox studies and extended Hückel molecular orbital calculations on Cp∗ IrL(mnt) (where L = PMe3, PPh3, CN-t-Bu)

The reaction between the cyclopentadienyliridium complexes Cp∗ Ir(L)Cl2 (where L = PMe3, PPh3, CN-t-Bu) and disodium maleonitriledithiolate (Na2mnt) yields the corresponding mnt-substituted compounds Cp∗ Ir(PMe3)(mnt) (1), Cp∗ Cp∗ Ir(PPh3)(mnt) (2) and Cp∗ Ir(CN-t-Bu)(mnt) (3). All of these new compounds have been isolated in high yield and characterized in solution by IR and NMR spectroscopy. The solid state structures of 2 and 3 were determined by single-crystal X-ray diffraction analysis. 2 crystallizes in the triclinic space group P 1 with a = 10.4557(8) A , b = 10.630(1) A , c = 14.894(1) A , α = 91.382(8)°, β = 90.141(6)°, γ = 118.182(7)° , V = 1458.5(3) A 3 and Z = 2 . Full-matrix least-squares refinement yielded R = 0.0281 for 3425 (I > σ(I)) reflections. 3 crystallizes in the monoclinic space group P21/n with a = 8.9609(7) A , b = 20.343(1) A , c = 11.9115(9) A , β = 94.168(6)°, V = 2165.(6) A 3 and Z = 4. Full-matrix least-squares refinement yielded R = 0.0245 for 2266 (I> 3 σ (I)) reflections. The redox properties of 1–3 have been explored by cyclic and rotating disc electrode voltammetric techniques in MeCN and CH2Cl2 solvents. Each of these compounds exhibit a well-defined one-electron oxidation wave that is assigned to the 0/ + 1 redox couple, along with a + 1/ + 2 redox wave, the reversibility of which is highly dependent on the nature of the ancillary two-electron donor ligand (L) and the solvent. Extended Huckel calculations have been performed on the model compounds CpIr(PH3)(mnt) and CpIr(CNH)(mnt), with the results used in a discussion of the nature of the HOMO and LUMO levels in 1–3.