Hydride ion transfer from ruthenium(II) complexes in water: Kinetics and mechanism

Carol Creutz, Mei H. Chou, Hua Hou, James T. Muckerman

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Abstract

Reactions of hydride complexes of ruthenium(II) with hydride acceptors have been examined for Ru(terpy)(bpy)H+, Ru(terpy)(dmb)H+, and Ru(η6-C6Me6)(bpy)(H)+ in aqueous media at 25 °C (terpy = 2,2′6′,2″-terpyridine, bpy = 2,2′-bipyridine, dmb = 4,4′-dimethyl-2,2′-bipyridine). The acceptors include CO2, CO, CH2O, and H3O +. CO reacts with Ru(terpy)(dmb)H+ with a rate constant of 1.2 (0.2) × 101 M-1 s-1, but for Ru(η6-C6Me6)(bpy)(H)+, the reaction was very slow, k ≤ 0.1 M-1 s-1. Ru(terpy)(bpy)H+ and Ru(η6-C6Me 6)(bpy)(H)+ react with CH2O with rate constants of (6 ± 4) × 106 and 1.1 × 103 M -1 s-1, respectively. The reaction of Ru(η 6-C6Me6)(bpy)(H)+ with acid exhibits straightforward, second-order kinetics, with the rate proportional to [Ru(η6-C6Me6)(bpy)(H)+] and [H3O+] and k = 2.2 × 101 M-1 s-1 (μ = 0.1 M, Na2SO4 medium). However, for the case of Ru(terpy)(bpy)H+, the protonation step is very rapid, and only the formation of the product Ru(terpy)(bpy)(H2O) 2+ (presumably via a dihydrogen or dihydride complex) is observed with a kobs of ca. 4 s-1. The hydricities of HCO 2-, HCO-, and H3CO- in water are estimated as +1.48, -0.76, and +1.57 eV/molecule (+34, -17.5, +36 kcal/mol), respectively. Theoretical studies of the reactions with CO 2 reveal a "product-like" transition state with short C-H and long M-H distances. (Reactant) Ru-H stretched 0.68 Å (product) C-H stretched only 0.04 Å. The role of water solvent was explored by including one, two, or three water molecules in the calculation.

Original languageEnglish
Pages (from-to)9809-9822
Number of pages14
JournalInorganic Chemistry
Volume49
Issue number21
DOIs
Publication statusPublished - Nov 1 2010

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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