Iridium Complexes with BIAN-Type Ligands: Synthesis, Structure and Redox Chemistry

Abstract

A series of iridium complexes with bis(diisopropylphenyl)iminoacenaphtene (dpp-bian) ligands, [Ir(cod)(dpp-bian)Cl] (<b>1</b>), [Ir(cod)(NO)(dpp-bian)](BF₄)₂ (<b>2</b>) and [Ir(cod)(dpp-bian)](BF₄) (<b>3</b>), were prepared and characterized by spectroscopic techniques, elemental analysis, X-ray diffraction analysis and cyclic voltammetry (CV). The structures of <b>1</b>-<b>3</b> feature a square planar backbone consisting of two C = C π-bonds of 1,5-cyclooctadiene (cod) and two nitrogen atoms of dpp-bian supplemented with a chloride ion (for <b>1</b>) or a NO group (for <b>2</b>) to complete a square-pyramidal geometry. In the nitrosyl complex <b>2</b>, the Ir-N-O group has a bent geometry (the angle is 125°). The CV data for <b>1</b> and <b>3</b> show two reversible waves between 0 and -1.6 V (vs. Ag/AgCl). Reversible oxidation was also found at E_1/2 = 0.60 V for <b>1</b>. Magnetochemical measurements for <b>2</b> in a range from 1.77 to 300 K revealed an increase in the magnetic moment with increasing temperature up to 1.2 μ_B (at 300 K). Nitrosyl complex <b>2</b> is unstable in solution and loses its NO group to yield [Ir(cod)(dpp-bian)](BF₄) (<b>3</b>). A paramagnetic complex, [Ir(cod)(dpp-bian)](BF₄)₂ (<b>4</b>), was also detected in the solution of <b>2</b> as a result of its decomposition. The EPR spectrum of <b>4</b> in CH₂Cl₂ is described by the spin Hamiltonian Ĥ = gβHŜ with S = 1/2 and g_xx = g_yy = 2.393 and g_zz = 1.88, which are characteristic of the low-spin 5d⁷-Ir(II) state. DFT calculations were carried out in order to rationalize the experimental results.