Syntheses of cofacial dimetallodiporphyrins and their applications to dihydrogen activation or proton reduction catalysis: Models for hydrogen electrode catalysts
Dihydrogen may be a future fuel source which could help relieve our present, heavy dependence on coal and oil. Electrochemical methods are the most efficient ways of producing H[sub 2]. It is necessary to catalyze this process. In the present work, activation of dihydrogen and proton reduction to dihydrogen have been studied with new cofacial dimetalloporphyrin complexes. A cofacial dirhodium diporphyrin, Rh[sub 2]DPB, was prepared and used to activate dihydrogen in the presence of ancillary ligands. The reaction of Rh[sub 2]DPB with H[sub 2] and CO resulted in the dirhodium diporphyrin dihydride, Rh(H)Rh(H)DPB. When phosphines or phosphites were employed in the reaction between Rh[sub 2]DPB and H[sub 2], a different type of hydride complex was produced. Three-center two-electron bonded hydride structures have been suggested, based on the upfield M-H chemical shifts, large T[sub 1] values, the absence of [sup 1]J[sub HD], and small [sup 2]J[sub P-H] coupling constants. Catalytic dihydrogen evolution via proton reduction has been achieved using a series of cofacial bisorganometallic diporphyrins. These compounds were synthesized by addition of the corresponding Grignard reagent to the dication of the dimetallodiporphyrins. Chemical two-electron reduction of M[sub 2][sup III/III]R[sub 2]DPB, protonation with a suitable acid, and subsequent H[sub 2] elimination with concurrent re-oxidation of the complexes were investigated. Reduction potentials of M[sub 2]R[sub 2]DPB were measured, and the pK[sub a] values of the catalysts estimated. By changing the central metal and modifying axial ligation, more efficient proton reduction and/or dihydrogen oxidation can be realized. Dinuclear centers in close proximity provide methods for activating molecules and/or performing redox reactions with substrates. Complexes derived from these dinuclear systems constitute additional models for understanding reactivity observed at metal surfaces, in homogeneous catalysis, and in clusters.
- Research Organization:
- Stanford Univ., CA (United States)
- OSTI ID:
- 5534281
- Country of Publication:
- United States
- Language:
- English
Similar Records
Unprecedented, bridged dihydrogen complex of a cofacial metallodiporphyrin and its relevance to the bimolecular reductive elimination of hydrogen
Coordination chemistry of dihydrogen
Related Subjects
080101* -- Hydrogen-- Production-- Electrolysis
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400400 -- Electrochemistry
CARBOXYLIC ACIDS
CATALYSIS
CATALYTIC EFFECTS
CHEMICAL PREPARATION
CHEMICAL REACTIONS
CHEMISTRY
ELECTROCHEMISTRY
ELECTRODES
ELECTRON TRANSFER
ELEMENTS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HOMOGENEOUS CATALYSIS
HYDROGEN
NONMETALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOMETALLIC COMPOUNDS
PORPHYRINS
REDOX REACTIONS
REDUCTION
REFRACTORY METAL COMPOUNDS
RHODIUM COMPOUNDS
SUBSTRATES
SYNTHESIS
TRANSITION ELEMENT COMPOUNDS