title: Structural, spectroscopic, and reactivity comparison of xanthene- and dibenzofuran-bridged cofacial bisporphyrins.
abstract: A comparison of the structure, spectroscopy, and oxygen atom-transfer reactivity of cofacial bisporphyrins anchored by xanthene (DPX) and dibenzofuran (DPD) pillars is presented. The synthesis and characterization of dicopper(II) and dinickel(II) complexes of DPD completes a homologous series of homobimetallic zinc(II), copper(II), and nickel(II) complexes for both cofacial platforms. X-ray crystallographic analysis of the parent free-base porphyrins H(4)DPX (1) and H(4)DPD (5) confirms the face-to-face arrangement of the two porphyrin macrocycles with a large available range of vertical pocket sizes: 1 (C(80)H(92)Cl(2)N(8)O), triclinic, space group P1 macro, a = 13.5167(12) A, b = 21.7008(18) A, c = 23.808(2) A, alpha = 80.116(2) degrees, beta = 76.832(2) degrees, gamma = 80.4070(10) degrees, Z = 4; 5 (C(80)H(83)N(8)O(2)), monoclinic, space group C2/c, a = 22.666(2) A, b = 13.6749(14) A, c = 42.084(4) A, beta = 94.554(2) degrees, Z = 8. EPR spectroscopy of dicopper(II) derivatives Cu(2)DPX (3) and Cu(2)DPD (7) complements the crystallographic studies by probing intramolecular metal-metal arrangements in frozen solution. Exciton interactions between the porphyrin subunits in fluid solution are revealed by steady-state and time-resolved electronic absorption and emission spectroscopy. The resulting compilation of structural and spectroscopic data provides a benchmark for the use of these and related platforms for the activation of small-molecule substrates. A structure-function relation is developed for the photoinduced oxygen atom-transfer reactions of bisiron(III) mu-oxo derivatives of DPX and DPD. The efficiency of the photochemical process is markedly dependent (approximately 10(4)-fold) on the vertical flexibility of cofacial architecture provided by the spacer.
authors.affiliation: Department of Chemistry, 6-335, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Chang
authors.forename: Erin A
authors.initials: EA
authors.lastname: Baker
authors.forename: Bradford J
authors.initials: BJ
authors.lastname: Pistorio
authors.forename: Yongqi
authors.initials: Y
authors.lastname: Deng
authors.forename: Zhi-Heng
authors.initials: ZH
authors.lastname: Loh
authors.forename: Scott E
authors.initials: SE
authors.lastname: Miller
authors.forename: Scott D
authors.initials: SD
authors.lastname: Carpenter
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Nocera
mesh_terms: D001572:Benzofurans / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008665:Metalloporphyrins / Q000138:chemical synthesis* / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry; D013329:Structure-Activity Relationship; D014966:Xanthenes / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D001572:Benzofurans; D008665:Metalloporphyrins; D014966:Xanthenes; D003300:Copper; D009532:Nickel; D015032:Zinc