Metall‐π1‐Komplexe von Benzolderivaten, XLI. Bis(η 6 1‐anilin)chrom: Synthese, Redoxverhalten und Brønsted‐Basizität
1993; Wiley; Volume: 126; Issue: 2 Linguagem: Inglês
10.1002/cber.19931260216
ISSN0009-2940
AutoresChristoph Elschenbroich, Stefan Hoppe, Bernhard Metz,
Tópico(s)Lanthanide and Transition Metal Complexes
ResumoMetal π Complexes of Benzene Derivatives, XLI [1] . — Bis(η 6 1‐aniline)chromium: Synthesis, Redox Properties and Brønsted Basicity Bis(η 6 1‐aniline)chromium ( 6 ) has been prepared by protodesilylation of its N , N , N ′, N ′1‐tetrakis(trimethylsilyl) derivative 5 , which is accessible by metal‐atom ligand‐vapor cocondensation (cc). Bis(η 6 1‐dimethylaniline)chromium ( 3 ) is obtained directly from cc. The couples 3 +/0 and 6 +/0 feature the most negative redox potentials E 1/2 ever reported for bis(arene)1‐metal complexes. According to EPR spectroscopy, applied to the radical cations 3 +· and 6 +· the site of oxidation is largely localized on the metal. The pH dependence of E 1/2 is cast in Nerst‐Clark plots, whose breaks supply the p K s values of the mono‐and diprotonated forms of 3 and 6 . η 6 1‐Coordination to Cr I increases the basicity of aniline by three p K units, whereas η 6 1‐coordination to Cr 1 effects a decrease by more than seven p K units. The first and second dissociation constants of the organometallic bis(ammonium) ions 3 (H + ) 2 and 6 (H + ) 2 differ by 2.7 p K units. This interval reflects the interaction of the two basic centers in 3 and 6 which approaches that of p 1‐phenylenediamine. Thus, conjugation across the bis(η 6 1‐arene)chromium unit is virtually uninhibited.
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