Metall‐π1‐Komplexe von Benzolderivaten, XLI. Bis(η61‐anilin)chrom: Synthese, Redoxverhalten und Brønsted‐Basizität

Abstract

Metal π Complexes of Benzene Derivatives, XLI[1]. — Bis(η61‐aniline)chromium: Synthesis, Redox Properties and Brønsted BasicityBis(η61‐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(η61‐dimethylaniline)chromium (3) is obtained directly from cc. The couples 3+/0 and 6+/0 feature the most negative redox potentials E1/2 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 E1/2 is cast in Nerst‐Clark plots, whose breaks supply the pKs values of the mono‐and diprotonated forms of 3 and 6. η61‐Coordination to CrI increases the basicity of aniline by three pK units, whereas η61‐coordination to Cr1 effects a decrease by more than seven pK units. The first and second dissociation constants of the organometallic bis(ammonium) ions 3(H+)2 and 6(H+)2 differ by 2.7 pK units. This interval reflects the interaction of the two basic centers in 3 and 6 which approaches that of p1‐phenylenediamine. Thus, conjugation across the bis(η61‐arene)chromium unit is virtually uninhibited.