Xanthene-Bridged Cofacial Bisporphyrins

Chang, Christopher J.; Deng, Yongqi; Heyduk, Alan F.; Chang, C. K.; Nocera, Daniel G.

doi:10.1021/ic990987+

Cited by 107 publications

(95 citation statements)

References 112 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The xanthenebridged cofacial bisporphyrin and the dibenzofuranbridged homologue are furnished from the three-branch approach of Figure 1, 15 which borrows from methods originally developed for the preparation of DPA and DPB Pacman derivatives. The first synthetic branch consists of the regioselective dilithiation of 9,9-dimethylxanthene or dibenzofuran in the presence of dry DMF followed by hydrolysis of the intermediate imidate salt.…”

Section: Xanthene-and Dibenzofuran-bridged Pacman Assembliesmentioning

confidence: 99%

Role of Proton‐Coupled Electron Transfer in O—O Bond Activation

Rosenthal

Nocera

2007

ChemInform

Self Cite

View full text Add to dashboard Cite

The selective reduction of oxygen to water requires four electrons and four protons. The design of catalysts that promote oxygen reduction therefore requires the management of both electron and proton inventories. Pacman and Hangman porphyrins provide a cleft for oxygen binding, a redox shuttle for oxygen reduction, and functionality for tuning the acid-base properties of bound oxygen and its intermediates. With proper control of the proton-coupled electron transfer events, O-O bond breaking of oxygen, and more generally oxygenated substrates, may be achieved with high efficiencies. The rule set developed for oxygen reduction may be applied to a variety of other small molecule activation reactions of consequence to energy conversion.

show abstract

Section: Xanthene-and Dibenzofuran-bridged Pacman Assembliesmentioning

confidence: 99%

Role of Proton‐Coupled Electron Transfer in O—O Bond Activation

Rosenthal

Nocera

2007

ChemInform

Self Cite

View full text Add to dashboard Cite

show abstract

“…Can efficient oxygenactivation chemistry be preserved when this cofacial structural motif exhibits a large range of motion? To address this issue, we have developed methods for the facile assembly of new cofacial bisporphyrins, incorporating dibenzofuran (DPD) 12 or xanthene (DPX) 13 pillars that exhibit variable pocket sizes with minimal lateral displacements. Herein, we report that dicobalt(II) complexes of both DPD and DPX efficiently mediate the direct four-electron reduction of oxygen to water despite a ca.…”

mentioning

confidence: 99%

Electrocatalytic four-electron reduction of oxygen to water by a highly flexible cofacial cobalt bisporphyrin

et al. 2000

Self Cite

View full text Add to dashboard Cite

Dicobalt(II) cofacial bisporphyrins anchored by dibenzofuran (DPD) and xanthene (DPX) are efficient electrocatalysts for the four-electron reduction of oxygen to water despite their ca. 4 Å difference in metal-metal distances, suggesting that the considerable longitudinal 'Pac-Man' flexibility of the pillared platforms is the origin for the similar catalytic reactivity of these structurally disparate systems.Enzymatic systems are remarkable in their ability to accommodate the large range of motion required for the binding and catalysis of small molecules. In many cases, the kinetic steps of the processes involved are ultimately predicated on conformational changes of the active site upon substrate binding, activation, and/or product release. An outstanding example is the binding and biological reduction of dioxygen to water by cytochrome c oxidase (CcO). 1 The critical O-O bond cleavage chemistry is mediated by a flexible, dinuclear iron-heme/ copper (Fe a3 /Cu B ) assembly. 1,2 Nevertheless, the pursuit of structural and functional models for O 2 activation have emphasized, for the most part, bimetallic reaction centers poised within well-defined, rigid pockets. [3][4][5][6][7] For example, pillared cofacial dicobalt bisporphyrins bridged by anthracene (DPA) and biphenylene (DPB) 8-11 impair ring slippage, and as a result, these complexes efficiently electrocatalyze the direct fourelectron reduction of oxygen to water (as opposed to the twoelectron pathway involving peroxide) with little structural reorganization of juxtaposed subunits. Can efficient oxygenactivation chemistry be preserved when this cofacial structural motif exhibits a large range of motion? To address this issue, we have developed methods for the facile assembly of new cofacial bisporphyrins, incorporating dibenzofuran (DPD) 12 or xanthene (DPX) 13 pillars that exhibit variable pocket sizes with minimal lateral displacements. Herein, we report that dicobalt(II) complexes of both DPD and DPX efficiently mediate the direct four-electron reduction of oxygen to water despite a ca. 4 Å difference in their metal-metal distances (as determined from their X-ray crystal structures), suggesting that the longitudinal 'Pac-Man' flexibility of these molecular clefts allows the designed binding pocket to structurally accommodate reaction intermediates during multielectron catalysis.Co 2 (DPD) 1 was obtained in excellent yield (91%) from reaction of the corresponding free base bisporphyrin with CoCl 2 and 2,6-lutidine. † Crystals suitable for X-ray diffraction studies were grown from dichloromethane-methanol solutions. ‡ The structure of 1 (Fig. 1) shows that two methanol solvent molecules are coordinated inside the bisporphyrin pocket to the two cobalt(II) centers. In order to accommodate the two exogeneous ligands, the DPD framework opens its 'bite' considerably. The interplanar angle between the two macrocycles is 56.5°, resulting in metal-metal (8.624 Å) and centerto-center (8.874 Å) distances that are markedly larger than found in Zn 2 (DPD) (d Zn-Zn = ...

show abstract

“…Materials: H 2 P, H 4 DPS, [12] H 4 DPX, [39] H 4 DPB, [61] and their metalated derivatives [12,34,39,41,62] were synthesized by using methods reported in the literature. Unless otherwise stated, all reagents and solvents were used as received.…”

Section: Methodsmentioning

confidence: 99%

“…[17,38] The C meso -C meso (4.32 ) and Ct 1 -Ct 2 (4.01 ) distances determined in this work compare favorably with those of other DPX systems (4.27 < C meso -C meso < 4.47 ; 3.87 < Ct 1 -Ct 2 < 4.70 ; see the Supporting Information). [17,39,40] Absorption spectra: The UV/Vis absorption data are reported in Table 3 and the spectra for (Pd)H 2 DPS, (Pd)H 2 DPX, (Pd)H 2 DPB, (PdZn)DPS, (PdZn)DPX, (Pt)H 2 DPX, and (Pt)H 2 DPB are shown in Figure 3. For the palladium derivatives, the Soret band l max (S 0 -S 2 transition) varies as a function of the spacer in the order DPS > DPX > DPB.…”

Section: Synthesismentioning

confidence: 99%

Triplet–Triplet Energy Transfer Controlled by the Donor–Acceptor Distance in Rigidly Held Palladium‐Containing Cofacial Bisporphyrins

Faure

Stern

Espinosa

et al. 2005

Chemistry A European J

View full text Add to dashboard Cite

Eleven new complexes, including mono-, heterobi-, and homobimetallic cofacial bisporphyrins, (Pd)H2DPS, (M)H2DPX, (M)H2DPB, (PdZn)DPS, (PdZn)DPX, (Pt)2DPX, (M)2DPB (M = Pd, Pt), and (Pt)P (DPS4- = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene tetraanion, DPX(4-) = 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene tetraanion, DPB4- = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene tetraanion, P2- = 5-phenyl-2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrin dianion) have been synthesized and characterized. The photophysical properties of the donor (M)P (M=Pd or Pt, P=porphyrin chromophore) and the acceptor (free base H(2)P or (Zn)P) depend on the C(meso)-C(meso) distance and the presence of a heavy atom such as Pd(II) or Pt(II). The data were compared with those for the known compounds (Pd)2DPS, (Pd)2DPX, H4DPS, H4DPX, H4DPB, (Pd)P, (Zn)P, and H(2)P. The rate constants for triplet-triplet energy transfer (k(ET)) were measured for the heterobimetallic (PdZn) and monometallic [(M)H2] derivatives (M=Pd, Pt). The fluorescence lifetimes (Deltatau(F)) of the acceptors decrease as a result of the heavy-atom effect, and vary as follows: (Pd)H2DPS<<(Pd)H2DPX approximately (Pd)H2DPB. The k(ET) values calculated according to the equation k(ET)=(1/tau(emi)-1/tau(emi) (0)), where tau(emi) (0) is the emission lifetime of the homobimetallic bisporphyrins (no ET occurs), are equal to 0, 247+/-57 and 133+/-52 s(-1) for DPS, DPX, and DPB, respectively, in the (Pd)H(2) series. These measurements allowed the range of distance over which the Dexter mechanism for T(1)-T(1) energy transfer ceases to operate to be determined. This distance is somewhere between 4.3 and 6.3 A, in agreement with our recent findings on singlet-singlet energy transfer. During the course of this study, the X-ray crystal structure for (Pd)H2DPX was obtained; triclinic (P1), a = 11.1016(1), b = 14.9868(2), c = 20.6786(3) A, alpha = 102.091(1), beta = 100.587(1), gamma = 101.817(1) degrees , V = 3199.19(7) A(3), Z = 2.

show abstract

Xanthene-Bridged Cofacial Bisporphyrins

Cited by 107 publications

References 112 publications

Role of Proton‐Coupled Electron Transfer in O—O Bond Activation

Role of Proton‐Coupled Electron Transfer in O—O Bond Activation

Electrocatalytic four-electron reduction of oxygen to water by a highly flexible cofacial cobalt bisporphyrin

Triplet–Triplet Energy Transfer Controlled by the Donor–Acceptor Distance in Rigidly Held Palladium‐Containing Cofacial Bisporphyrins

Contact Info

Product

Resources

About