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 [(κ 3 -Me 3 -tpa)Ir I (ethene) 2 ] + (12 + ) and [(κ 3 -Me 2 -dpaMe)Ir I (ethene) 2 ] + (13 + ) have been prepared {Me 3 -tpa = N,N,N-tris[(6-methyl-2-pyridyl)Complexes 12 + and 13 + lose one ethene fragment in solution, yielding the five-coordinate mono(ethene) complex [(κ 4 -Me 3 -tpa)Ir I (ethene)] + (14 + ) and the four-coordinate mono-(ethene) complex [(κ 3 -Me 2 -dpa-Me)Ir I (ethene)] + (15 + ), respectively. [(κ 4 -Me 3 -tpa)Rh I (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

Transition Metal Peroxides. Synthesis and Role in Oxidation Reactions*Dedicated, on the occasion of his 80th birthday, to our ‘vitae ac studiorum magister in secunda et in adversa fortuna’ Emeritus Professor Giorgio Modena, Padova University, who showed us the way toward Chemistry.

“…Similarly, peroxo Rh(III) and ethene-peroxo Ir(III) have been prepared by reaction of dioxygen and reduced metal precursor 42 .…”

“…Also, Ir(III) and Rh(III) ethene-peroxo complexes belong to the family of species with the bipyramidal pentagonal structure 42 .…”

Functional Models for Rhodium‐Mediated Olefin‐Oxygenation Catalysis

“…125 It is tempting to assume that this reaction as well as the reaction of [(bpa‐R)Rh I (cod)] + with O 2 (Scheme ) proceed via (hydro)peroxides generated in situ 115. 116, 126…”

“…The subsequent reactions are unselective and therefore products could not be identified. However, [(Me 3 tpa)Rh I (ethene)] + is selectively converted into [(Me 3 tpa)Rh III (O 2 )] + upon reaction with O 2 (Scheme ) 126. Apparently, steric shielding of the peroxo fragment by the methyl groups of the Me 3 tpa ligand prevents further reactions.…”

“…In 1973, van der Ent and Onderdelinden proposed (on the basis of spectroscopic studies) the formation of [(PPh 3 ) 2 (Cl)Ir III (O 2 )(ethene)] from [(PPh 3 ) 2 (Cl)Ir I (ethene) 2 ] and O 2 131. 132 In 2002, [(Me 2 bpa‐Me)Ir III (O 2 )(ethene)] + (crystallographically characterized) and [(κ 3 ‐Me 3 tpa)Ir III (O 2 )(ethene)] + were prepared by reaction of tetracoordinate [(Me 2 ‐bpa‐Me)Ir I (ethene)] + and pentacoordinate [(Me 3 tpa)Ir I (ethene)] + , respectively, with O 2 in CH 2 Cl 2 (Scheme ) 126. The yield of these reactions was only 25 %, the remainder being unidentified (EPR‐silent) paramagnetic material.…”