title: Probing the mer- to fac-isomerization of tris-cyclometallated homo- and heteroleptic (C,N)3 iridium(III) complexes.
abstract: We have developed techniques which allow for covalent tethering, via a "hetero" cyclometallating ligand, of heteroleptic tris-cyclometallated iridium(III) complexes to polymeric supports (for application in light-emitting diode technologies). This involved the selective synthesis and thorough characterization of heteroleptic [Ir(C,N) 2(C',N')] tris-cyclometallated iridium(III) complexes. Furthermore, the synthesis and characterization of heteroleptic [Ir(C,N) 2OR] complexes is presented. Under standard thermal conditions for the synthesis of the facial ( fac) isomer of tris-cyclometallated complexes, it was not possible to synthesize pure heteroleptic complexes of the form [Ir(C,N) 2(C',N')]. Instead, a mixture of homo- and heteroleptic complexes was acquired. It was found that a stepwise procedure involving the synthesis of a pure meridonial ( mer) isomer followed by photochemical isomerization of this mer to the fac isomer was necessary to synthesize pure fac-[Ir(C,N) 2(C',N')] complexes. Under thermal isomerization conditions, the conversion of mer-[Ir(C,N) 2(C',N')] to fac-[Ir(C,N) 2(C',N')] was also not a clean reaction, with again a mixture of homo- and heteroleptic complexes acquired. An investigation into the thermal mer to fac isomerization of both homo- and heteroleptic tris-cyclometallated complexes is presented. It was found that the process is an alcohol-catalyzed reaction with the formation of an iridium alkoxide [Ir(C,N) 2OR] intermediate in the isomerization process. This catalyzed reaction can be carried out between 50 and 100 degrees C, the first such example of low-temperature mer-fac thermal isomerization. We have synthesized analogous complexes and have shown that they do indeed react so as to give fac-tris-cyclometallated products. A detailed explanation of the intermediates (and all of their stereoisomers, in particular when systems of the generic formula [M(a,b) 2(a',b')] are synthesized) formed in the mer to fac isomerization process is presented, including how the formed intermediates react further, and the stereoisomeric products they yield.
authors.affiliation: Chemical Biology & Organic Chemistry, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Aidan R
authors.initials: AR
authors.lastname: McDonald
authors.forename: Martin
authors.initials: M
authors.lastname: Lutz
authors.forename: Lars S
authors.initials: LS
authors.lastname: von Chrzanowski
authors.forename: Gerard P M
authors.initials: GP
authors.lastname: van Klink
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Spek
authors.forename: Gerard
authors.initials: G
authors.lastname: van Koten
mesh_terms: D002244:Carbon / Q000737:chemistry*; D006358:Hot Temperature; D007495:Iridium / Q000737:chemistry*; D007536:Isomerism; D008024:Ligands; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010777:Photochemistry; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D007495:Iridium; D002244:Carbon; D009584:Nitrogen