Ligand substitution at 19-electron organometallic centers. Electrocatalytic CO substitution reactions of (methylcyclopentadienyl)Mn(CO)2NO+ and (indenyl)Mn(CO)2NO+

Y. Huang, C. C. Neto, K. A. Pevear, M. M. Banaszak Holl, D. A. Sweigart, Y. K. Chung

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Abstract

(Methylcyclopentadienyl)Mn(CO)NO+ (1+) undergoes a one-electron reduction at an electrode to give a 19-electron neutral radical that rapidly dissociates CO and dimerizes to yield [(MeCp)Mn(CO)2NO]2. In the presence of P-donor nucleophiles (L), the reduction of 1+ initiates a rapid electron transfer catalyzed (ETC) CO substitution to give a quantitative yield of (MeCp)Mn(CO)(L)NO+. The substitution reaction occurs via the 19-electron intermediate 1, which dissociatcs CO in the rate limiting step with the following activation parameters: ΔH=60±6 kJ; δS≠=+ 37 ± 15 J K-1. The 17-electron intermediate (MeCp)Mn(CO)NO is then trapped by the nucleophile to give the electron rich (MeCp)Mn(CO)(L)NO, which spontaneously transfers an electron to 1+ to afford the final product and regenerate 1. A variety of electrochemical techniques, including low temperature voltammetry and steady-state voltammetry with microelectrodes, was employed to quantitatively define the details of the reaction mechanism. The indenyl analogue of 1+, (indenyl)Mn(CO)2NO+ (2+), was found to undergo ETC substitution reactions by the same dissociative mechanism and at approximately the same rate as 1+. The conclusion is that the 'indenyl effect' does not operate in these 19-electron complexes. The rhenium complex CpRe(CO)2NO+ is reduced by orte electron to give a relatively stable neutral radical that does not react with P-donor nucleophiles on the voltammetric time scale of 0.5 V s-1. The conclusion is that CO dissociation from 19-electron complexes follows the reactivity order Mn ≫ Re.

Original languageEnglish
Pages (from-to)53-60
Number of pages8
JournalInorganica Chimica Acta
Volume226
Issue number1-2
DOIs
Publication statusPublished - 1 Jan 1994
Externally publishedYes

Keywords

  • Carbonyl complexes
  • Cyclopentadieny complexes
  • Indenyl complexes
  • Manganese complexes
  • Nitrosyl complexes

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