title: Electrochemical and spectroelectrochemical studies of diphosphorylated metalloporphyrins. Generation of a phlorin anion product.
abstract: Two series of diphosphoryl-substituted porphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The investigated compounds are 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrins (Ph)2(P(O)(OEt)2)2PorM and 5,15-bis(diethoxyphosphoryl)-10,20-di(para-carbomethoxyphenyl)porphyrins (PhCOOMe)2(P(O)(OEt)2)2PorM where M = 2H, Co(II), Ni(II), Cu(II), Zn(II), Cd(II), or Pd(II). The free-base and five metalated porphyrins with nonredox active centers undergo two ring-centered oxidations and two ring-centered reductions, the latter of which is followed by a chemical reaction of the porphyrin dianion to give an anionic phlorin product. The phlorin anion is electroactive and can be reoxidized by two electrons to give back the starting porphyrin, or it can be reversibly reduced by one electron at more negative potentials to give a phlorin dianion. The chemical conversion of the porphyrin dianion to a phlorin anion proceeds at a rate that varies with the nature of the central metal ion and the solvent. This rate is slowest in the basic solvent pyridine as compared to CH2Cl2 and PhCN, giving further evidence for the involvement of protons in the chemical reaction leading to phlorin formation. Calculations of the electronic structure were performed on the Ni(II) porphyrin dianion, and the most favorable atoms for electrophilic attack were determined to be the two phosphorylated carbon atoms. Phlorin formation was not observed after the two-electron reduction of the cobalt porphyrins due to the different oxidation state assignment of the doubly reduced species, a Co(I) π anion radical in one case and an M(II) dianion for all of the other derivatives. Each redox reaction was monitored by thin-layer UV-visible spectroelectrochemistry, and an overall mechanism for each electron transfer is proposed on the basis of these data.
authors: †Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States.
authors: Yuanyuan
authors: Y
authors: Fang
authors: ‡Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Pr. 31,GSP-1, Moscow, 119071, Russia.|§Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Pr. 31, Moscow, 119991, Russia.
authors: Yulia G
authors: YG
authors: Gorbunova
authors: †Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States.
authors: Ping
authors: P
authors: Chen
authors: †Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States.
authors: Xiaoqin
authors: X
authors: Jiang
authors: †Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States.
authors: Machima
authors: M
authors: Manowong
authors: ‡Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Pr. 31,GSP-1, Moscow, 119071, Russia.
authors: Anna A
authors: AA
authors: Sinelshchikova
authors: ‡Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Pr. 31,GSP-1, Moscow, 119071, Russia.
authors: Yulia Yu
authors: YY
authors: Enakieva
authors: ‡Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Pr. 31,GSP-1, Moscow, 119071, Russia.
authors: Alexander G
authors: AG
authors: Martynov
authors: ‡Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Pr. 31,GSP-1, Moscow, 119071, Russia.|§Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Pr. 31, Moscow, 119991, Russia.
authors: Aslan Yu
authors: AY
authors: Tsivadze
authors: ∥Institut de Chimie Moléculaire de l'Université de Bourgogne, Université de Bourgogne, UMR CRNS n° 6302, 9 Avenue Alain Savary BP 47870, Dijon 21078 CEDEX, France.
authors: Alla
authors: A
authors: Bessmertnykh-Lemeune
authors: ∥Institut de Chimie Moléculaire de l'Université de Bourgogne, Université de Bourgogne, UMR CRNS n° 6302, 9 Avenue Alain Savary BP 47870, Dijon 21078 CEDEX, France.
authors: Christine
authors: C
authors: Stern
authors: ∥Institut de Chimie Moléculaire de l'Université de Bourgogne, Université de Bourgogne, UMR CRNS n° 6302, 9 Avenue Alain Savary BP 47870, Dijon 21078 CEDEX, France.
authors: Roger
authors: R
authors: Guilard
authors: †Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States.
authors: Karl M
authors: KM
authors: Kadish