Syntheses of novel monomeric 1,4,7-trimethyl-1,4,7-triazacyclononane ruthenium complexes. Reactivities and structure of sterically encumbered cationic monoaquaruthenium(II) and monooxoruthenium(IV) complexes
- 1 January 1994
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 1,p. 57-62
- https://doi.org/10.1039/dt9940000057
Abstract
The complexes [RuII(tacn)(bipy)(OH2)]2+1 and [RuIV(tacn)(bipy)O]2+2(tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, bipy = 2,2′-bipyridine) have been synthesised and their crystal structures determined: 1, monoclinic, space group C2/c, a= 34.093(4), b= 10.430(1), c= 17.369(2)Å, β= 118.54(1)° and Z= 8; 2, triclinic, space group , a= 10.795(1), b= 11.076(2), c= 11.248(1)Å, a= 110.41(2), β= 90.66(1), γ= 94.11(1)° and Z= 2. The structures reveal that tacn acts as a facial chelating ligand with bipy nearly perpendicular to the RuO and Ru–OH2 moieties. The RuIV O and Ru–OH2 distances are 1.815(6) and 2.168(3)Å respectively. In aqueous solution both complexes display two reversible proton-coupled one-electron redox couples corresponding to the oxidation of RuII to RuIII and RuIII to RuIV. Complex 2 has been found to be a competent oxidant for alkene epoxidation. Preliminary-kinetic studies revealed the rate law, rate =k2[RuIV][alkene] where k2 at 299 K are (1.30 ± 0.11)× 10–3 and (2.52 ± 0.20)× 10–4 dm3 mol–1 s–1 for the epoxidation of styrene and norbornene respectively. The activation parameters have been measured and are discussed.Keywords
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