Voltammetric, specular reflectance infrared, and X-ray electron probe characterization of redox and isomerization processes associated with the [Mn(CO)23-P2P′)Br]+/0 (P2P′ = {Ph2P(CH2)2}2PPh), [Mn(CO)23-P3P′)Br]+/0

Alan M. Bond, Ray Colton, Frank Marken, Jacky N. Walter

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Abstract

Extremely well defined voltammetric responses are obtained for both oxidation of microcrystalline mononuclear trans- and cis,mer-Mn(CO)23-P2P′)Br (P2P′ = {Ph2P(CH2)2}2-PPh) and cis,mer-Mn(CO)23-P3P′)Br (P3P′ = {Ph2PCH2}3P) and binuclear cis,fac-{Mn(CO)2-(η2-dpe)Br}2(μ-dpe) (dpe = Ph2P(CH2)2PPh2) and reduction of cationic trans-[Mn(CO)23-P2P′)Br]BF 4, trans-[Mn(CO)23-P3P′)Br]BF 4, and trans-[{Mn(CO)22-dpe)Br} 2(μ-dpe)](BF4)2 when they are attached to a graphite electrode and placed in water containing either 0.1 M NaCl or KCl as the electrolyte. The combination of access to species in different oxidation states and different isomeric forms, as well as mononuclear and binuclear species, enables the rates of isomerization and the extent of electronic communication between the metal centers to be evaluated in the solid state and compared to data in organic solvent systems previously reported. The voltammetric data, combined with specular reflectance IR and X-ray electron probe data, established that the following processes occur at the graphite electrode-microcrystal-water (electrolyte) interface (subscript "s" denotes solid): trans-Mn(CO)23-P2P′)Brs + Cl- ⇌ trans-[Mn(CO)23-P2P′)Br]Cl s + e-; cis,mer-Mn(CO)23-P2P′)-Br s + Cl- ⇌ cis,mer-[Mn(CO)23-P2P′)Br]Cl s + e- → trans-[Mn(CO)23-P2P′)Br]Cl s; trans-Mn(CO)23-P3P′)Brs + Cl- ⇌ trans-[Mn(CO)23-P3P′)Br]Cl s + e-; cis,mer-Mn(CO)23-P3P′)Br]Cl s + Cl- ⇌ cis,mer-[Mn(CO)23-P3P′)Br]Cl s + e- → trans-[Mn(CO)23-P3P′)Br]Cl s; trans-{Mn-(CO)22-dpe)Br}2(μ-dpe) s + 2Cl- ⇌ trans-[{Mn(CO)22-dpe)Br} 2(μ-dpe)]Cl2s+ 2e-; cis,fac-{Mn(CO)22-dpe)Br}2(μ-dpe) s + 2Cl- ⇌ cis,fac-[{Mn(CO)22-dpe)Br} 2(μ-dpe)]Cl2s + 2e- → irans-[{Mn(CO)22-dpe)Br} 2(μ-dpe)]Cl2 s. The reaction pathways in organic solvents are generally analogous. However, the rates of isomerization are slower in the solid state, and shapes of voltammograms and potentials differ significantly. Interestingly, in the binuclear [{Mn(CO)22-dpe)Br}2(μ-dpe)] 2+/0 system, no intermediate [{Mn(CO)22-dpe)Br}2(μ-dpe)] + species are observed in the solid state, implying that the metal centers are oxidized or reduced at the same potentials, unlike the case in the solution phase, where the [{Mn(CO)22-dpe)-Br}2(μ-dpe)] 2+/+ and [{Mn(CO)22-dpe)Br}2(μ-dpe)] +/0 redox couples are well separated. This result implies that no significant communication occurs between the metal centers in the solid state redox processes.

Original languageEnglish
Pages (from-to)5006-5014
Number of pages9
JournalOrganometallics
Volume16
Issue number23
Publication statusPublished - 11 Nov 1997

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