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This work is focused on investigating the interaction of antitumor active metallocene vanadocene dichloride (Cp2VCl2) and amino acids in aqueous solution at physiological pH. Sixteen vanadocene amino acid complexes [Cp2V(aa)][X] (aa = gly, ala, val, leu, ile, phe, his, and trp; X = Cl, PF6) were prepared and characterized on the basis of spectral measurements (EPR, MS, IR, Raman). Amino acids are coordinated to the vanadocene fragment through the oxygen atom of the carboxylic group and the nitrogen of the amino group, resulting in a five-membered chelate ring. Complexes [Cp2V(val)][PF6] and [Cp2V(ile)][PF6] have been characterized by X-ray structure analyses. It was evidenced that all prepared complexes are stable in both aqueous solutions with physiological pH and in therapeutic NaCl solutions. EPR spectra of vanadocene amino acid complexes in Krebs-Ringer solution in human blood plasma and in whole blood showed that these complexes react with the hydrogen carbonate anion present forming complex Cp2V(O2CO).

Binuclear copper(I) complexes [Cu(κ2-P,P-dppf)(CH3CN)2][BF4] (1), [Cu(κ2-P,P-dppf)(bipy)][BF4] (2) containing the chelating dppf ligand (dppf = 1,1‘-bis(diphenylphosphino)ferrocene) have been prepared by substitution reactions of the acetonitrile ligands from the complexes [Cu(CH3CN)4][BF4] and (1) with dppf and bipy, respectively. Similarly, the treatment of the complex [Cu2(μ-dppm)2(CH3CN)2][BF4]2 with dppf in CH2Cl2 at room temperature gives the tetranuclear complex [Cu2(μ-dppm)2(κ2-P,P-dppf)2][BF4]2 (3). The analogous bridging chloride tetranuclear complex [Cu2(μ-Cl)2(κ2-P,P-dppf)2] (4) has been also prepared by the addition of dppf to a solution in THF containing an equimolar mixture of CuCl and tetramethylethylenediamine. Complex 4 has been used as a precursor for μ-η1-alkynyl bridging dicopper(I) complexes containing the framework [Cu2(μ-dppf)2]. Complexes [Cu2(μ-η1-C⋮CR)2(μ-dppf)2] (R = C6H4CH3-4 (5), C6H5 (6), CH2OCH3 (7), CH2CH2CH3 (8), (η5-C5H4)Fe(η5-C5H5) (9)) are obtained by the treatment of complex 4 with an excess of LiC⋮CR in THF. Complexes 5−9 can also be prepared from the reaction of an equimolar mixture of [Cu(C⋮CR)] n and dppf in toluene at room temperature. The crystal structure of complex 5 has been determined by X-ray diffraction. The crystallographic asymmetric unit consists of three molecules of 5, all with related stereochemistries at their centers. The complex consists of two copper atoms linked by two bridging dppf ligands and two bridging alkynyl groups in a μ-η1 bonding arrangement with an almost planar [Cu2(μ-η1-C⋮CR)2] framework. The arylethynyl groups are nearly linear (C⋮C−C angles 174(2)−175(2)°), and the C⋮C distances (1.20(2)−1.21(2) Å) are typical for cases of metal−acetylide σ-bonding. Both bridging dppf ligands are twisted from the eclipsed conformation (mean value 77(2)°) and also show a relatively large value of the angle (mean value 56.8(6)°) formed by the projection of the Cp···Cp axis of dppf onto the Cu···Cu axis. This seems to indicate that the molecular core [Cu2(μ-η1-C⋮CC6H4CH3-4)2] is a sterically demanding system that forces the dppf ligand to adopt a relatively strained conformation.