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Intramolecular communication and electrochemical observation of the 17-electron ruthenocenium cation in fluorinated ruthenocene-containing β-diketones; polymorphism of C10H21 and C10F21 derivatives.

Authors :
Erasmus, Elizabeth
Swarts, Jannie C.
Source :
New Journal of Chemistry; Sep2013, Vol. 37 Issue 9, p2862-2873, 12p
Publication Year :
2013

Abstract

Ruthenocene-containing β-diketones, RcCOCH<subscript>2</subscript>COR with Rc = ruthenocenyl and R = C<subscript>10</subscript>F<subscript>21</subscript> (1), CF<subscript>3</subscript> (2), C<subscript>6</subscript>F<subscript>5</subscript> (3), C<subscript>10</subscript>H<subscript>21</subscript> (4), CH<subscript>3</subscript> (5) and C<subscript>6</subscript>H<subscript>5</subscript> (6), were synthesised by Claisen condensation of the appropriate methyl ester with acetylruthenocene, and their spectroscopic, electrochemical and thermal properties were compared. A new synthetic route utilising 1,2,3-benzotriazol-1-ylethanone (9) or 1,2,3-benzotriazol-1-yl(ruthenocenyl)methanone (10) as a reactant, rather than the conventional esters, was found to be more efficient for β-diketone synthesis. The apparent acid dissociation constants, pK<subscript>a</subscript>′, of the new ruthenocene-containing β-diketones are 7.14(4) (1, R = C<subscript>10</subscript>F<subscript>21</subscript>), 9.92(3) (3, R = C<subscript>6</subscript>F<subscript>5</subscript>) and 10.06(2) (4, R = C<subscript>10</subscript>H<subscript>21</subscript>). Peak anodic potentials of the ruthenocenyl group of 1–6, pK<subscript>a</subscript>′ values and the FTIR ν(C=O) stretching frequencies of the precursor esters, RCOOCH<subscript>3</subscript>, correlated linearly with the Gordy scale group electronegativity, χ<subscript>R</subscript>, of the C<subscript>10</subscript>F<subscript>21</subscript> (χ<subscript>C<subscript>10</subscript>F<subscript>21</subscript></subscript> = 3.04), C<subscript>6</subscript>F<subscript>5</subscript> (χ<subscript>C<subscript>6</subscript>F<subscript>5</subscript></subscript> = 2.46), C<subscript>10</subscript>H<subscript>21</subscript> (χ<subscript>C<subscript>10</subscript>H<subscript>21</subscript></subscript> = 2.43) and other R-groups. An electrochemical study in the non-interacting solvent and electrolyte system CH<subscript>2</subscript>Cl<subscript>2</subscript>/0.1 mol dm<superscript>−3</superscript> [N(<superscript>n</superscript>Bu<subscript>4</subscript>)][B(C<subscript>6</subscript>F<subscript>5</subscript>)<subscript>4</subscript>] revealed electrochemically irreversible one-electron transfer Rc/Rc<superscript>+</superscript> couples in the potential range 650 < E<subscript>pa</subscript> < 1110 mV. Strikingly, reduction of the unstable monomeric 17 electron species, [Rc<superscript>+</superscript>(C<subscript>5</subscript>H<subscript>5</subscript>)(C<subscript>5</subscript>H<subscript>4</subscript>COCH<subscript>2</subscript>COR)], was clearly observed for all β-diketones possessing fluorinated R-groups, even at slow (100 mV s<superscript>−1</superscript>) scan rates. The enol isomer of the fluorinated β-diketones had >90% abundance under the conditions of study and the first order rate constant of enol to keto conversion varied between 220 and 50 000 s<superscript>−1</superscript> depending on solvent (CDCl<subscript>3</subscript> or CD<subscript>3</subscript>CN) and R-groups. Thermal analysis (DSC) of 1 and 4 showed no liquid crystalline mesophase behaviour but definite polymorphism was observed. β-diketones 1 and 4 exist as low temperature polymorphs below 42 °C or 12 °C respectively. The high temperature polymorphs converted to isotropic liquids at 83 °C (compound 1) or 52 °C (compound 4). [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
11440546
Volume :
37
Issue :
9
Database :
Complementary Index
Journal :
New Journal of Chemistry
Publication Type :
Academic Journal
Accession number :
100902503
Full Text :
https://doi.org/10.1039/c3nj00354j