Redox Behaviour of Cymantrene Fischer Carbene Complexes in Designing Organometallic Multi‐tags. Issue 17 (18th March 2014)

• Record Type: Journal Article
• Authors: Bezuidenhout, Daniela I.; van der Westhuizen, Belinda; Swarts, Pieter J.; Chatturgoon, Teshica; Munro, Orde Q.; Fernández, Israel; Swarts, Jannie C.
• Is Part Of: Chemistry. Volume 20:Issue 17(2014)
• Page Start: 4974
• Page End: 4985
• Publication Date: 2014-03-18
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201304711
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>A series of Group 7 Fischer carbene complexes, [Cp(CO)<sub>2</sub>Mn<sup>I</sup>=C(OEt)Ar] (Cp=cyclopentadienyl, Ar=Th=thienyl (<bold>1 a</bold>), Ar=Fu=furyl (<bold>2 a</bold>), Ar=Fc=ferrocenyl (<bold>3 a</bold>)) and biscarbene complexes, [Cp(CO)<sub>2</sub>MnC(OEt)Ar′(OEt)CMn(CO)<sub>2</sub>Cp] (Ar′=Th′=2, 5‐thienylene (<bold>1 b</bold>), Ar′=Fu′=2, 5‐furylene (<bold>2 b</bold>), Ar′=Fc′=1, 1′‐ferrocendiyl (<bold>3 b</bold>)) was synthesized and characterized. Chemical oxidation of [Cp(CO)<sub>2</sub>MnC(OEt)Fc] (<bold>3 a</bold>) and isolation of the oxidised species <bold>[3 a][PF<sub>6</sub>]</bold> possessing a Mn<sup>II</sup> centre proved possible below −30 °C in dichloromethane solution. The ESR spectrum of the transiently stable radical cation, <bold>[3 a][PF<sub>6</sub>]</bold>, confirmed the presence of a low‐spin Mn<sup>II</sup> centre characterized by a rhombic <italic>g</italic> tensor (<italic>g</italic><sub>x</sub>=1.975, <italic>g</italic><sub>y</sub>=2.007 and <italic>g</italic><sub>z</sub>=2.130) in frozen dichloromethane at 77 K with <sup>55</sup> Mn hyperfine coupling constants <italic>A</italic><sub>1</sub>, <italic>A</italic><sub>2</sub> and <italic>A</italic><sub>3</sub> of 115, 33 and 43 G, respectively. Electrochemical studies demonstrated the influence of the Ar substituent on the oxidation potential. All complexes showed that the redox potentials of carbene double bond reduction and Mn<sup>I</sup> oxidation were dependent on the type of Ar group, but only <bold>3 b</bold> showed resolved oxidations for the two Mn<sup>I</sup> centres. Surprisingly, Mn<sup>I</sup> oxidation occurs at lower potentials than ferrocenyl oxidation. Density functional theory (DFT) calculations were carried out to delineate the nature of the species involved in the oxidation and reduction processes and clearly confirm that oxidation of Mn<sup>I</sup> is favoured over that of ferrocene.</p> </abstract>