Nitrogen donor ligands bearing N–H groups: Effect on catalytic and cytotoxic activity of molybdenum η3-allyldicarbonyl complexes

Reactions of [Mo(η3-C3H5)Br(CO)2(NCMe)2] with the bidentate nitrogen ligands 2-(2′-pyridyl)imidazole (L1), 2-(2′-pyridyl)benzimidazole (L2), N,N′-bis(2′-pyridinecarboxamido)-1,2-ethane (L3), and 2,2′-bisimidazole (L4) led to the new complexes [Mo(η3-C3H5)Br(CO)2(L)] (L = L1, 1; L2, 2; L4, 4) and [{Mo(η3-C3H5)Br(CO)2}2(μ-L3)] (3). The reaction of complexes 2 and 3 with Tl[CF3SO3] afforded [Mo(η3-C3H5)(CF3SO3)(CO)2(L2)] (2T) and [{Mo(η3-C3H5)(CF3SO3)(CO)2}2(μ-L3)] (3T). Complexes 3 and 2T were structurally characterized by single crystal X-ray diffraction, showing the facial allyl/carbonyls arrangement and the formation of the axial isomer. In 2T, two molecules are assembled in a hydrogen bond dimer. The four complexes 1–4 were tested as precursors in the catalytic epoxidation of cyclooctene and styrene, in the presence of t-butylhydroperoxide (TBHP), with moderate conversions and turnover frequencies for complexes 1–3 and very low ones for 4. The increasing number of N–H groups in the complexes seems to be responsible for the loss of catalytic activity, compared with other related systems. The cytotoxic activities of all the complexes were evaluated against HeLa cells. The results showed that compounds 1, 2, 4, and 2T exhibited significant activity, complexes 2 and 2T being particularly promising.