Ru(II) complexes with bioactive molecules: from 5-(N-heterocycles) to Ruthenacycles

Novel metal Ru(II) complexes were selectively obtained, upon the reaction of [Ru(H)2(CO)(PPh3)3] with bioactive molecules as pyrrole carboxylate ligand, with the purpose to investigate the potential positive alterations added by metal coordination to promote enhanced bioactivity as prodrugs or a diagnostic metallo-tracers . Pyrrole 2−carboxilic acid (A), 2−pyrrolyl imino-phenol (B), 5−hydroxy−L−triptophan (5−HTP) (C) and Lasparagine (D) have been selected to form stable chelate organometallic systems, based on homoleptic O,O− or heteroleptic N,O−bonding fashion mode. Experiments were run by varying the reaction conditions (stoichiometry, temperature, solvent, time duration, and energy source) to selectively drive the reactions towards a single desired isomer. Stereo−electronic features and rotameric behaviour have been studied by spectroscopic techniques (ESI−MS, IR, heteronuclear NMR and VT NMR) and DFT (Density Functional Theory) calculations. The complexes obtained by double coordination through adding two equivalents of pyrrolyl carboxylate form bismonohapto (k1 -O) species, which have been further investigated in MeCN or EtOH/H2O mixture. Longer reaction times are required to afford the mixed species exhibiting simultaneous monohapto−, dihapto [k1 (O), k2 (O,O)−] coordination. Much drastic conditions are required for obtaining conjugated trans−bis-chelate species, which has been calculated to possess a relative higher energy. The B, C and D molecules, exhibiting a preferential N,Ocoordination mode, are reported in the following scheme, likely resulting in stabilized five−membered metallacycle species.