Oxidatively induced reductive eliminations. Kinetics and mechanism of the elimination of ethane from the 17-electron cation radical of Cp[sup *]Rh(PPh[sub 3])(CH[sub 3])[sub 2]

Journal Article · Fri Jan 01 00:00:00 EST 1993 · Organometallics; (United States)

DOI:https://doi.org/10.1021/om00025a014· OSTI ID:6566679

Pedersen, A; Tilset, M ^[1]

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1. Univ. of Oslo (Norway)

The dimethylrhodium compound Cp[sup *]Rh(PPh[sub 3])(CH[sub 3])[sub 2] (1; Cp[sup *] = [eta][sup 5]-C[sub 5]Me[sub 5]) undergoes an overall 2-electron oxidation at 0.04 V vs the ferrocene/ferrocenium (Fc) couple in 9:1 acetonitrile/dichloromethane, 0.1 M Bu[sub 4]N[sup +]PF[sub 6][sup [minus]]. The oxidation results in the intramolecular reductive elimination of ethane and yields Cp[sup *]Rh(PPh[sub 3])(NCMe)[sub 2][sup 2+] (2) as the Rh-containing product. A mechanistic and kinetic investigation of the reaction by derivative cyclic voltammetry (DCV) showed the reductive elimination to be a first-order reaction with respect to 1[sup [sm bullet]+]. Very small solvent effects (acetonitrile, acetone, THF, dichloromethane) on the reaction rate indicated the nonintervention of 19-electron species in the reductive elimination. The DCV analysis provided kinetic parameters k(20[degrees]C) = 96 [plus minus] 3 s[sup [minus]1], [Delta]H[sup [double dagger]] = 53.1 [plus minus] 0.8 kJ/mol, and [Delta]S[sup [double dagger]] = [minus]25.9 [plus minus] 3.3 J/(K[center dot]mol) in acetonitrile. The data are interpreted in terms of a direct, concerted elimination of ethane from the 17-electron cation radical 1[sup [sm bullet]+]. It is estimated that the rate of reductive elimination has been increased by a factor of at least 3 [times] 10[sup 9] due to the oxidation of 1 to 1[sup [sm bullet]+]. In dichloromethane, the intramolecular elimination of ethane was initiated by an overall 1-electron process. The major product in this case was Cp[sup *]Rh(PPh[sub 3])(CH[sub 3])X[sup +] (X most likely is coordinated dichloromethane or the counterion PF[sub 6][sup [minus]]) as a result of a secondary intermolecular methyl-transfer process. The methyl transfer was mimicked by a quantitative ([sup 1]H NMR) reaction between 1 and 2 which yielded Cp[sup *]Rh(PPh[sub 3])(NCMe)CH[sub 3][sup +] (3). 18 refs., 4 figs., 1 tab.

• OSTI ID: 6566679
• Journal Information: Organometallics; (United States), Vol. 12:1; ISSN 0276-7333
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ETHANE
SYNTHESIS
ORGANOMETALLIC COMPOUNDS
ELECTROCHEMISTRY
RHODIUM COMPOUNDS
CATIONS
CHEMICAL REACTION KINETICS
FERROCENE
NUCLEAR MAGNETIC RESONANCE
OXIDATION
PHOSPHINES
RADICALS
THERMODYNAMIC PROPERTIES
VOLTAMETRY
ALKANES
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DIENES
HYDROCARBONS
IONS
IRON COMPLEXES
KINETICS
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
PHOSPHORUS COMPOUNDS
PHYSICAL PROPERTIES
POLYENES
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
RESONANCE
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
400400* - Electrochemistry