Dioxygenation of Sterically Hindered (Ethene)RhI and -IrI Complexes to (Peroxo)RhIII and (Ethene)(peroxo)IrIII Complexes

Abstract

New cationic, five-coordinate bis(ethene)iridium(I) complexes [(κ3-Me3-tpa)IrI(ethene)2]+ (12+) and [(κ3-Me2-dpa-Me)IrI(ethene)2]+ (13+) have been prepared {Me3-tpa = N,N,N-tris[(6-methyl-2-pyridyl)methyl]amine, Me2-dpa-Me = N-methyl-N,N-bis[(6-methyl-2-pyridyl)methyl]amine}. Complexes 12+ and 13+ lose one ethene fragment in solution, yielding the five-coordinate mono(ethene) complex [(κ4-Me3-tpa)IrI(ethene)]+ (14+) and the four-coordinate mono(ethene) complex [(κ3-Me2-dpa-Me)IrI(ethene)]+ (15+), respectively. [(κ4-Me3-tpa)RhI(ethene)]+ (11+), the rhodium analogue of 14+, was also prepared. Whereas rhodium complex 11+ is stable in acetonitrile at room temperature, the iridium analogue 14+ converts to the cyclometallated (acetonitrile)(hydrido) complex 16+ within 72 h by dissociation of the unique 6-methylpyridyl fragment and oxidative addition of the 6-methylpyridyl C3−H bond. The four-coordinate mono(ethene) complex 15+ is even less stable in solution; it converts to a mixture of compounds within 18 h. Reaction of the mono(ethene)RhI complex 11+ with O2 yields the peroxo complex 17+ by ethene displacement. In contrast, the mono(ethene)IrI complexes 14+ and 15+ bind O2 without the loss of ethene, leading to unprecedented (ethene)(peroxo)IrIII complexes 18+ and 19+. At room temperature, peroxo complex 17+ does not react with ethene and, quite remarkably, C−O bond formation does not occur in the (ethene)(peroxo) complexes 18+ and 19+. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)