A series of molybdenum complexes bearing new ligands is reported. The study covers a series of molybdenum compounds with the Z 5 -coordinated indenyl ligand substituted with acyl-, ester-and amide-functions. This portfolio was extended by adding one representative with a Z 3 -coordinated estersubstituted indenyl ligand. The functionalized indenes, necessary for the assembly, were prepared by convenient routes starting from inexpensive and readily available materials, enabling their production on a multigram scale. All structural types presented in this experimental study were supported by X-ray crystallographic data.a Distances are given in Å; angles and dihedral angles are given in 1. b O is the envelope fold angle defined for the indenyl ligand as the angle between planes defined by C1, C2 and C3 and that of C1, C3, C8 and C9. 22 c D(M-C) represents the differences in the metal-carbon bonds. It is defined for the indenyl compounds as the difference between the averages of the metal-carbon distances M-C8 and M-C9 and those of M-C1, M-C2, and M-C3. 22 d Data for Ind. e Data for 1-(MeOCO)C 9 H 6 .Scheme 4 Synthesis of a mixed indenyl molybdenum complex. NJCPaper

4 ) was synthesized and characterized by electron paramagnetic resonance. Three structures were determined by X-ray diffraction analysis and revealed the expected bent metallocene structure with two cyclopentadienyl ligands and two chlorides coordinated to niobium in the oxidation state IV. Chlorides and the centroids of the η 5 -bonded cyclopentadienyl rings define a distorted tetrahedron. The cytotoxicity study has demonstrated that substitution with methoxybenzyl groups can lead to highly active species, but the activity strongly varies with the number and positions of the methoxy groups in the benzene ring. The most active species under study -{2,4-(MeO) 2 C 6 H 3 CH 2 C 5 H 4 } 2 NbCl 2 -has a maximal inhibitory concentration value comparable with cisplatin.

A series of new cyclopentadienyl molybdenum compounds bearing substituted phenanthroline ligands [(η5‐C5H4CH2C6H4X‐4)Mo(CO)2(N,NL)][BF4] (X = F, Cl, Br; N,NL = phen, 5‐NH2‐phen, 4,7‐Ph2‐phen) was prepared and characterized using infrared and NMR spectroscopies. Crystal structures of [(η5‐C5H4CH2C6H4F‐4)Mo(CO)2(NCMe)2][BF4], [(η5‐C5H4CH2C6H4X‐4)Mo(CO)2(phen)][BF4] (X = F, Cl, Br) and [(η5‐C5H4CH2C6H4Cl‐4)Mo(CO)2(4,7‐Ph2‐phen)][BF4]⋅(4,7‐Ph2‐phen)⋅HBF4 were determined using X‐ray diffraction analysis. Biological studies revealed a strong cytotoxic effect of the chelating ligands. Although the cytostatic effect of the halogen in the side chain of the cyclopentadienyl ring is negligible, it could be used for future post‐modification of these types of cytotoxic active molybdenum‐based compounds.

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