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

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posted on 2005-11-21, 00:00 authored by Simone Thewissen, Maike D. M. Reijnders, Jan M. M. Smits, Bas de Bruin
New, five-coordinate, iridium(I) bis-ethene complexes [fac-(bpa-R)IrI(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)IrI(ethene)]+. Heating complex 1+ results in N−H activation at the bpa-H ligand and formation of the dinuclear iridium(III) species [{(mer2-bpa#)IrIII(ethyl)(MeCN)}2]2+ (42+) with bridging amides (bpa# = bpa-H deprotonated at NHamine). Heating bpa-Bz complex 3+ results in aromatic C−H activation of the ligand benzyl group to form dinuclear iridium(III) species [{(bpa-Bz#)IrIII2-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#)IrIII(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.