- Title
- Complexation of constrained ligands piperazine, N-substituted piperazines, and thiomorpholine
- Creator
- Clifford, Sarah E.; Tiwow, Vanny; Gendron, Aleasia; Maeder, Marcel; Rossignoli, Monica; Lawrance, Geoffrey A.; Turner, Peter; Blake, Alexander J.; Schröder, Martin
- Relation
- Australian Journal of Chemistry Vol. 62, Issue 10, p. 1196-1206
- Publisher Link
- http://dx.doi.org/10.1071/CH09313
- Publisher
- CSIRO Publishing
- Resource Type
- journal article
- Date
- 2009
- Description
- Complexation of the symmetric cyclic diamine piperazine (1,4-diazacyclohexane) has been examined in dry dimethyl formamide by spectrophotometric titrations (with Cu²⁺, Ni²⁺) to define formation constants, and by stopped-flow kinetics to define the complexation rates and reaction pathway. Initial formation of a rarely observed η¹-piperazine intermediate occurs in a rapid second-order reactions. This intermediate then undergoes two competing reactions: formation of (chelated) η²-piperazine (ML) or the formation of (bridging) μ-piperazine (in M₂L and M₂L₃, speciation depending on relative concentrations). Protonation constants and formation constants for complexation in water of N-ethylpiperazine and thiomorpholine (1-aza-4-thiocyclohexane, tm) have been determined by potentiometric titration; 1:1 complexes with first-row M²⁺ display a log K from ~4 to 6, with speciation that suggests chelation of the heterocycles may be involved. Complexation of thiomorpholine has been further probed by the synthesis of Pd¹¹ complexes. The N-monodentate coordination mode has been confirmed in trans-[Pd(tm)₂Br₂] by an X-ray crystal structure. Complexation of N-(2-aminoethyl)piperazine to Cu¹¹ as a bidentate ligand involving the primary and tertiary amines is also defined by an X-ray crystal structure.
- Subject
- complexation; piperazines; thiomorpholine
- Identifier
- http://hdl.handle.net/1959.13/807306
- Identifier
- uon:7350
- Identifier
- ISSN:0004-9425
- Language
- eng
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