Instability of Square Planar N₃-Ligand Iridium(I) Ethene Complexes

New, five-coordinate, iridium(I) bis-ethene complexes [fac-(bpa-R)Ir^I(ethene)₂]⁺ (1⁺:  R = H, 2⁺:  R = Me, 3⁺:  R = Bz; bpa-H = N,N-di(2-pyridylmethyl)amine, bpa-Me = N-methyl-N,N-di(2-pyridylmethyl)amine, bpa-Bz = N-benzyl-N,N-di(2-pyridylmethyl)amine) were prepared. In contrast to their previously reported rhodium analogues, these iridium species do not readily lose one of their two ethene fragments to form square planar mono-ethene complexes [mer-(bpa-R)Ir^I(ethene)]⁺. Heating complex 1⁺ results in N−H activation at the bpa-H ligand and formation of the dinuclear iridium(III) species [{(mer-μ₂-bpa^#)Ir^III(ethyl)(MeCN)}₂]²⁺ (4²⁺) with bridging amides (bpa^# = bpa-H deprotonated at NH_amine). Heating bpa-Bz complex 3⁺ results in aromatic C−H activation of the ligand benzyl group to form dinuclear iridium(III) species [{(bpa-Bz^#)Ir^III(μ₂-H)}₂]²⁺ (5²⁺) with unsupported hydride bridges (bpa-Bz^# = bpa-Bz cyclometalated at the benzylic C2-position). The dimeric structure of 5²⁺ easily breaks up in MeCN, giving the mononuclear species [(bpa-Bz^#)Ir^III(H)(MeCN)]⁺ (6⁺). Complex 5²⁺ is also light-sensitive:  glass-filtered daylight converts it to a geometrical isomer, 7²⁺, in which the cyclometalated benzyl functionality of one of the two ligands has switched its position with a pyridyl donor.