STUDIES ON NEW RUTHENIUM COMPLEXES AND THEIR REACTIVITIES

Abstract

Coordination chemistry deals with the study of complexes having a central atom (a metal ion) bound to a set of ligand(s). The properties of metal complexes are manifestation of the nature, coordination number as well as oxidation state of metal ion and the donating properties of the bound ligands. Unlike the organic compounds, different ligands bind to metal ion in different coordination modes. Hence, coordination complexes are found to possess different coordination numbers, coordination geometries, and redox properties. On the other hand, a particular coordinated ligand stabilizes the metal ion in a particular oxidation state or may be in more than one oxidation states. The thesis entitled “Studies on new ruthenium complexes and their reactivities” is divided into six chapters. In the present report, we have synthesized different ligands having various groups such as diazo (–N=N–), azomethine (–CH=N–) and carboxamide (–CONH–)groups. These ligands were treated with different precursor ruthenium complexes to afford corresponding ruthenium complexes. These ruthenium complexes were characterized by various spectroscopic techniques like IR, UV-Vis spectroscopy, EPR, 1H as well as 31P NMR spectral studies. Some ruthenium complexes were also treated with in situ generated nitric oxide (NO) from acidified sodium nitrite (NaNO2) solution (pH ~ 2-3) to produce ruthenium nitrosyl complexes. Nitrosyl complexes were characterized by IR, UV-Vis spectroscopy, 1H as well as 31P NMR spectral studies. Molecular structures of complexes were authenticated using X-ray crystallography. The redox properties of the ligand as well as metal center in the ruthenium complexes with non innocent ligands were investigated using cyclic voltammetry. vi Theoretical calculations were also performed on the structure of the complexes to better understand the electronic properties. In chapter one, literature on the redox, photophysical and photochemical properties of several ruthenium complexes along with brief introduction about coordination complexes and general properties of ruthenium will be reviewed. Role of ruthenium complexes as potential catalysts in organic and organometallic syntheses, transfer hydrogenation along with the importance of these complexes in different fields of bioinorganic chemistry will be scrutinized. Along with nitric oxide releasing molecules (photoNORMs), CO releasing molecules (photoCORMs) will also be described in brief. Various chemical methods and equipments used were comprehensively summarized. In chapter two, organometallic ruthenium(III) complexes [Ru(L1)(PPh3)2Cl2] (1) (where L1H2 =(E)-4-chloro-N-(2-(phenyldiazenyl)phenyl)benzamide and H = dissociable proton ) and [Ru(L2)(PPh3)2Cl](2)(where L2H2 = (E)-2-((4-(dimethylamino)phenyl)diazenyl)-N-(ptolyl) benzamide and H = dissociable protons ) were synthesized through C-H bond activation. Complexes 1 and 2 were treated with acidified nitrite solution to afford organometallic ruthenium nitrosyl complexes [Ru(L1)(PPh3)2(NO)Cl](ClO4)(3) and [Ru(L2 NO2)(PPh3)2(NO)Cl](PF6)(4). All the complexes were characterized by UV-vis, IR, ESI-MS, NMR spectroscopic studies. Molecular structures of complexes 3 and 4 were authenticated using X-ray crystallographic studies. Coordinated NO in ruthenium nitrosyls 3 and 4 was found to be photolabile under visible light and photo released NO was transferred to reduced myoglobin. Cytotoxic effects of complexes as well as photo-released NO were investigated. Gene expression studies were performed to understand the different stages of apoptotic cell death. vii In chapter three, novel ruthenium(II) coordinated stable aminyl radical complex [Ru(L5.)(PPh3)2Cl2] (5), was synthesized using ligands L3-5. Cleavage of most stable amide bond and simultaneous production of nitrogen centred radical took place during the reaction course. Complex 5 was characterized by IR, UV-vis and EPR spectroscopic studies. Molecular structure of 5 was authenticated using single crystal X-ray crystallography. Along with spectroscopic characterization, theoretical calculations completely supported the nitrogen centred radical. The interaction of NO with the complex 5 afforded nitrosyl complex [Ru(L5')(PPh3)2(NO)Cl](ClO4) (6). Molecular structure of the resultant nitrosyl complex 6 was authenticated by single crystal X–ray diffraction study. The photolability of coordinated NO was examined by using electronic absorption spectral studies under illumination of UV light. In chapter four, organometallic ruthenium(II) complex [Ru(L6CNN)(PPh3)2(CO)] (7) [where L6H2 is (E)-N-((1H-pyrrol-2-yl)methylene)naphthalen-1-amine] [H represents dissociable proton] was synthesized via C-H bond activation using different synthetic strategies. Ruthenium hydrido carbonyl complexes [Ru(L6NN)(PPh3)2(CO)H] (8) [where L6H2 is (E)-N-((1H-pyrrol-2-yl)methylene)naphthalen-1-amine] and [Ru(L7NN)(PPh3)2(CO)H] (9) [where L7H2 is (E)-N-((1H-pyrrol-2-yl)methylene)-1- phenylmethanamine] were isolated. All the complexes were characterized by UV-Vis, IR and NMR spectral studies. Molecular structures of complexes 7, 8 and 9 were authenticated using X-ray crystallography. Geometry optimization of the complexes 7–9 have been performed using Density Functional Theory (DFT) studies. Time-dependent DFT calculations were performed to better understand the electronic properties of complexes 7–9. Complex 7 was utilized as catalyst in transfer hydrogenation of ketones. On the basis of literature study, the viii plausible mechanisms were proposed for hydride formation and catalytic transfer hydrogenation. Coordinated CO in organometallic ruthenium carbonyl complex 7 was found to be photolabile upon visible light illumination. In chapter five, reaction of (E)-4-((2-nitrophenyl)diazenyl)phenol (L8H, H = dissociable proton) with Ru(PPh3)3Cl2 afforded novel organometallic anion radical complex [Ru(LA 8- .)(Cl)(PPh3)2] (10). During the synthesis of complex 10, nitro group in ligand converted to nitroso group through oxygen atom transfer to labile triphenylphosphine. One electron reduced nitroso group was coordinated to ruthenium in 1(N) mode. Complex 10 was treated with acidified nitrite to afford nitrosyl complex [Ru(LB 8-.)(PPh3)2(NO)](ClO4)(11) and it is a rare example of an organometallic ruthenium complex having azo anion radical as well as two different noninnocent ligands coordinated to one metal. Both the complexes were characterized by UV-vis, IR, NMR spectroscopic studies. Redox properties of complex 10 were investigated using cyclic voltammetry. Molecular structures of complexes 10 and 11 were authenticated using X-ray crystallographic studies. DFT calculations were performed to better understand the electronic properties of complex 10. In chapter six, half sandwich ruthenium complexes [(p-cym)RuII(L9-12)Cl]PF6(12-15) containing NN chelating schiff base ligand were successfully designed and synthesized. All the synthesized complexes were characterized by UV-vis, IR, ESI-MS, NMR spectroscopic studies. Molecular structures of 12 and 15 were authenticated using X-ray crystallography. Complexes 12-15 were utilized to investigate the anti-cancer activity studies on MCF-7, MDA-MB-435s and HEK-293 cell lines. Among all the complexes, complex 15 was found to be more potent against MCF-7 and MDA-MB-435s cancer cells as compared to complexes ix 12-14. However, all the complexes exhibited less cytotoxicity or almost inactivity towards HEK-293 normal cells.