A phototriggered molecular spring for aerobic catalytic oxidation reactions

The first catalytic oxidation reactions with cofacial bisporphyrins using molecular oxygen as the terminal oxidant are presented. The photocatalytic reactions proceed under mild conditions (ambient temperature and pressure) without the need for a co-reductant. A systematic reactivity study of the photooxidation of dimethyl sulfide (DMS) with a homologous series of bisiron(III) mu-oxo porphyrins containing dibenzofuran, xanthene, or no bridge reveals that the facility of these processes is markedly dependent on the vertical flexibility of the catalyst to provide a phototriggered molecular spring.     

Hydrogenation of two-electron mixed-valence iridium alkyl complexes

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.     

Bis(alkylamido)phenylborane complexes of zirconium,hafnium, and vanadium

The coordination chemistry of the bis(tert-butylamido)phenylborane ligand, [(t)BuN-B(Ph)-N(t)Bu](2)(-), is developed. The ligand can be delivered to metals of groups 4 and 5 from its dilithio salt. The reactions of PhB((t)BuNLi)(2), 1, with metal halides of zirconium, hafnium, and vanadium generate complexes of the general formulas ((t)BuN-B(Ph)-N(t)Bu)(2)M(THF) (M = Zr (2), Hf (3)), Li(2)[M((t)BuN-B(Ph)-N(t)Bu)(3)] (M = Zr (4), Hf (5)), and M((t)BuN-B(Ph)-N(t)Bu)(2) (M = V (6)). (1)H and (11)B[(1)H] NMR and single-crystal X-ray analysis show that these amido metal complexes are structurally analogous to amidinates.     

A photocycle for hydrogen production from two-electron mixed-valence complexes

Dihydrides of the formula Rh2(II,II)(tfepma)3H2Cl2 (tfepma = (bis[bis(trifluoroethoxy)phosphino]methylamine, MeN(P[OCH2CF3]2)2), have been prepared by the addition of H2 to the two-electron mixed-valence complex, Rh2(0,II)(tfepma)3Cl2 (1). Three isomeric forms with hydrides in syn (2), anti (3), and cis (4) conformations have been characterized by X-ray diffraction. Photolysis of 2 results in prompt formation of a short-lived blue photoproduct (lambda(max) = 600 nm) and a stoichiometric quantity of H2, as determined by Toepler pump and isotopic labeling experiments. The blue photoproduct was identified as a Rh2(I,I) complex resulting from the reductive elimination of H2, as determined from the examination of bimetallic cores coordinated by tfepm (tfepm = (bis[bis(trifluoroethoxy)phosphino]methane, CH2(P[OCH2CF3]2)2), for which complexes of the formula M2(I,I)(tfepm)3Cl2 (5, M = Rh and 6, M = Ir) have been isolated. The d8...d8 dimer of 5 converts to Rh2(0,II)(tfepm)3Cl2CN(t)Bu (8) upon the addition of 1 equiv of tert-butylisonitrile, a result of halogen migration and disproportionation of the valence symmetric core of 5, which is structurally compared to its two-electron mixed-valence analogue, Rh2(0,II)(dfpma)3Cl2CN(t)Bu (9) (dfpma = bis(difluorophosphino)methylamine, MeN(PF2)2). The halogen migration is captured in Ir2(I,I)(tfepm)3(mu-Cl)Cl (7), which is distinguished by the presence of a chloride that bridges the diiridium centers. Taken together, complexes 1-9 permit the construction of a complete photocycle for the photogeneration of H2 by dirhodium dfpma complexes in homogeneous solutions of hydrohalic acids.     

A model for two-electron mixed valence in metal-metal bonded dirhodium compounds

We propose that two-electron mixed valency in bimetallic complexes possessing three bridging ligands results from a second-order Jahn-Teller instability of the redox-symmetric state.