Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/807306

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Title
Complexation of constrained ligands piperazine, N-substituted piperazines, and thiomorpholine
Author/Creator
Clifford, Sarah E.;  Tiwow, Vanny;  Gendron, Aleasia;  Maeder, Marcel;  Rossignoli, Monica;  Lawrance, Geoffrey A.;  Turner, Peter;  Blake, Alexander J.;  Schröder, Martin
Institution
The University of Newcastle. Faculty of Science & Information Technology, School of Environmental and Life Sciences
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.
Relation
Australian Journal of Chemistry Vol. 62, Issue 10, p. 1196-1206
Publisher Link
http://dx.doi.org/10.1071/CH09313
Date
2009
Publisher
CSIRO Publishing
Keyword(s)
complexation;  piperazines;  thiomorpholine
Resource Type
journal article
Identifier
http://hdl.handle.net/1959.13/807306
Identifier
ISSN:0004-9425
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Subject
"Australian Journal of Chemistry"
 
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