title: Hydrogenation of two-electron mixed-valence iridium alkyl complexes.
abstract: Two-electron mixed-valence complexes of the general formula (tfepma)(3)Ir(2)(0,II)RBr [tfepma = bis(bis(trifluoroethoxy)phosphino)methylamine, MeN[P(OCH(2)CF(3))(2)](2), and R = CH(3) (2), CH(2)C(CH(3))(3) (3)] have been synthesized and structurally characterized and their reactivity with H(2) investigated. Hydrogenation of 2 and 3 proceeds in a cascade reaction to produce alkane upon initial H(2) addition, followed by the formation of the Ir(2)(I,III) binuclear trihydride-bromide complex (tfepma)(3)Ir(2)(I,III)H(3)Br (4) upon the incorporation of a second molecule of H(2). Hydrogenation of two-electron mixed-valence di-iridium alkyl complexes is examined with nonlocal density-functional calculations. H(2) attacks the Ir(II) metal center prior to alkyl protonation to produce an eta(2)-H(2) complex. Transition states link all intermediates to a complex that has the same regiochemistry as the crystallographically determined final product. Calculated atomic charges suggest that the second H(2) molecule is homolytically cleaved within the di-iridium coordination sphere and that a hydrogen atom migrates across the intact Ir-Ir metal bond. These results are consistent with the emerging trend that two-electron mixed-valence cores manage the two-electron chemistry of substrates with facility when hydrogen is the atom that migrates between metal centers.
authors.affiliation: Department of Chemistry, 6-335, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Veige
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Gray
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Nocera
mesh_terms: D000465:Algorithms; D018360:Crystallography, X-Ray; D006859:Hydrogen / Q000737:chemistry; D006865:Hydrogenation; D007495:Iridium / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D013816:Thermodynamics
chemical_list: D009942:Organometallic Compounds; D007495:Iridium; D006859:Hydrogen