Synthesis, Characterization and Reactivity of Chromium(VI) Alkylidenes

Chromium(VI) dialkyls are remarkably acidic, yielding a new set of anionic chromium alkylidenes upon deprotonation with KN(TMS)₂. We describe the characterization of three anionic chromium alkylidenes of the type [(ArN)₂Cr(=CHR)(CH₂R]^- (R = <i>^t</i>Bu, SiMe₃, Ph; Ar = 2,6-diisopropylphenyl). NEt₄[(ArN)₂Cr(=CHSiMe₃)(CH₂SiMe₃)] has been structurally characterized by X-ray diffraction. We have also studied the C-H activation of cyclohexane effected by the transient neopentylidene (ArN)₂Cr(=CHCMe₃). This reaction generated a tri-nuclear chromium(IV) complex, namely ‘[Cr(NAr)₂]₃’, as well as the two organic products cyclohexene and neopentane. A probable intermediate in this reaction could be trapped by PPh₃ to form (ArN)₂Cr(PPh₃)₂. The latter undergoes ligand substitution reactions with ethylene and CO to produce p-acid complexes of tetravalent chromium.

Synthesis, Characterization and Reactivity of Chromium(VI) Alkylidenes

Chromium(VI) dialkyls are remarkably acidic, yielding a new set of anionic chromium alkylidenes upon deprotonation with KN(TMS)₂. We describe the characterization of three anionic chromium alkylidenes of the type [(ArN)₂Cr(=CHR)(CH₂R]^- (R = <i>^t</i>Bu, SiMe₃, Ph; Ar = 2,6-diisopropylphenyl). NEt₄[(ArN)₂Cr(=CHSiMe₃)(CH₂SiMe₃)] has been structurally characterized by X-ray diffraction. We have also studied the C-H activation of cyclohexane effected by the transient neopentylidene (ArN)₂Cr(=CHCMe₃). This reaction generated a tri-nuclear chromium(IV) complex, namely ‘[Cr(NAr)₂]₃’, as well as the two organic products cyclohexene and neopentane. A probable intermediate in this reaction could be trapped by PPh₃ to form (ArN)₂Cr(PPh₃)₂. The latter undergoes ligand substitution reactions with ethylene and CO to produce p-acid complexes of tetravalent chromium.

Physical properties, ligand substitution reactions, and biological activity of Co(iii)-Schiff base complexes

A subset of fluorinated Co(iii) Schiff base complexes was synthesized, and their structural, ligand exchange, and anticancer properties were investigated.

Synthesis and ligand substitution reactions of κ4-B,S,S′,S′′-ruthenaboratranes

Ruthenaboratranes of the form [Ru(CO)L{κ4-B(mt)3}] (mt = N-methimazolyl) arise via substitution of the PPh3 ligand in [Ru(CO)(PPh3){κ4-B(mt)3}] by L (L = PMe2Ph, PMe3, P(OMe)3, P(OEt)3, P(OPh)3) or reactions of [RuCl(R)(CO)Ln] (R = Ph, CHCHPh; n = 2, L = PCy3; n = 3, L = P(OMe)3, PMe2Ph) with Na[HB(mt)3].

Impact of Chloride Concentration on Ligand Substitution Reactions of Zinc(II) Complexes with Biologically Relevant Nitrogen Nucleophiles

The mole-ratio method was used to determine the metal–ligand stoichiometry between [ZnCl2(en)] and [ZnCl2(terpy)] (where en = 1,2-diaminoethane or ethylenediamine and terpy = 2,2′:6′,2″-terpyridine) and imidazole at pH 7.2 in the presence of different chloride concentrations. The results indicated step-wise formation of 1:1 and 1:2 complexes in the presence of 0.010 M NaCl and 1:1 complexes in the presence of 0.001 M NaCl for the [ZnCl2(en)] complex. These results are correlated with additional coordination of chlorides in the first coordination sphere and with changes in coordination geometry. In the presence of 0.001 M NaCl the five-coordinate complex anion [ZnCl3(en)]- is formed initially and then a substitution reaction with imidazole occurs. In the presence of 0.010 M NaCl the octahedral complex anion [ZnCl4(en)]2- is formed. Additional coordination of chloride in the [ZnCl2(terpy)] complex is not found and the metal–ligand stoichiometry is 1:2. The kinetics of ligand substitution reactions of zinc(II) complexes and biologically relevant nitrogen nucleophiles such as imidazole, 1,2,3-triazole and L-histidine were investigated at pH 7.2 as a function of nucleophile concentration in the presence of 0.001 M and 0.010 M NaCl. The reactions were followed under pseudo first-order conditions by UV-Vis spectrophotometry. The substitution reactions included two steps of consecutive displacement of chlorido ligands with changes only in the coordination geometry of the [ZnCl2(en)] complex. The order of reactivity of the investigated nucleophiles for the first reaction step towards both complexes was L-histidine > 1,2,3-triazole > imidazole, while in the presence of 0.010 M NaCl the most reactive ligand was 1,2,3-triazole towards the [ZnCl2(en)] complex.