Chemical and Electrochemical Oxidation of mer/fac-Cr(CO)31-L-L)(η2-L-L) Containing a Pendant Donor Atom: ESR Studies of the Cations mer-[Cr(CO)31-L-L)(η2-L-L)]+ and trans-[Cr(CO)22-L-L)2]+ (L-L = Bidentate Group 15 Ligand)

Ramen N. Bagchi, Alan M. Bond, Ray Colton, Ian Creece, Katherine McGregor, Tania Whyte

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Abstract

Reactions between Cr(CO)3(C7H8) and Ph2PCH2CH,AsPh2 (ape) and Ph2AsCH2CH2AsPh2 (dae) give mer-Cr(CO)31-ape)(η2-ape) and fac-Cr(CO)31-dae)(η2-dae), respectively. Phosphorus-31 NMR studies show that the monodentate ape ligand is coordinated through phosphorus. Upon electrochemical oxidation in dichloromethane (0.1 M Bu4NC104) at platinum electrodes, mer-Cr(CO)31-ape)(η2-ape) is reversibly oxidized to mer-[Cr(CO)31-ape)(η2-ape)]+ whilst fac-Cr(CO)31-dae)(η2-dae) gives fac-[Cr(CO)31-dae)(η2-dae)]+, which rapidly isomerizes to mer-[Cr(CO)31-dae)(η2-dae)]+. In addition, for each complex a further irreversible 1-electron process is observed at very positive potentials. ESR studies on several mer-[Cr(CO)31-L-L)(η2-L-L)]+ cations (L-L = bidentate group 15 ligand), electrochemically generated in a sealed tube within the ESR microwave cavity, show that they decompose very slowly to trαns-[Ci-(CO)22-L-L)2]+. The rate of decomposition to trans-[Cr(CO)22-L-L)2]+ is faster in a nonsealed tube with nitrogen purging. The ESR spectra of the tricarbonyl and dicarbonyl 17-electron cations show both phosphorus and arsenic hyperfine structure with very similar values for the coupling constants. Chemical oxidation of mer/fac-Cr(CO)31-L-L)(η2-L-L) with an equimolar (or greater) quantity of AgClO4 also gives mer-[Cr(CO)31-L-L)(η2-L-L)]+. In one case, (L-L = Ph2PCH2PPh2(dpm)), when 0.5 molar equiv of AgCIO4 is used, a diamagnetic intermediate silver complex is identified by phosphorus-31 NMR spectroscopy. In the presence of excess of AgClO4, the rate of decomposition of mer-[Cr(CO)31-L-L)(η2-L-L)]+ to trans-[Cr(CO)22-L-L)2]+ is greatly enhanced, further confirming that the silver ion is a noninnocent oxidant when a pendant donor atom is present.

Original languageEnglish
Pages (from-to)2611-2615
Number of pages5
JournalOrganometallics
Volume10
Issue number8
DOIs
Publication statusPublished - 1 Aug 1991
Externally publishedYes

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