Salalens and Salans derived from 3‐Aminopyrrolidine: Aluminium Complexation and Lactide Polymerisation

In this paper a series of 7 salalen ligands based on an aminopyrrolidine backbone have been prepared and characterised. Several systems have been reduced to the salan ONNO type-ligand. All ligands have been complexed to Al III with Al(1–7)Me, Al(2a)(OiPr) and Al(7a)Me being characterised by single-crystal X-ray diffraction. In general the Al III centres are best described as being in a trigonal bipyramidal geometry. The solution and solid-state structures are discussed. All complexes have all been trialled for the production of PLA from rac-lactide, the salalen complexes had a preference for heterotactic PLA (P r = 0.71), whereas the salan had a more isotactic bias (P m = 0.72). In all cases PLA with low dispersities and predictable molecular weights were prepared. The activity of the two classes of ligands is compared with the salan complexes appearing to be significantly more active than the salalen systems. </p

Chemistry of Transition Metal Complexes with O- and/or N- Donor Ligands: Synthesis, Characterization and Study of Reactivity

Chapter 1: In this chapter the scope of the present investigation is delineated briefly along with the aim of the work. Chapter 2: The synthesis of ethoxido bridged divanadium(IV/IV) complexes [(VOL1-3)2(μ˗OEt)][Et3NH] (1‒3) of three azo dyes, 2˗(2′˗carboxy˗5′˗X-phenylazo)˗4˗methylphenol (where X = H (H2L1); X = NO2 (H2L2)) and 2˗(2′˗carboxy˗5′˗Br˗phenylazo)˗2˗naphthol (H2L3), differing in the substituents of the phenyl ring, in order to discern their influence, if any, on their redox potentials, biological activities and magnetochemistry, has been discussed. All the synthesized ligands and the vanadium(IV) complexes were successfully characterized by various physico-chemical techniques, viz. elemental analysis, IR, UV˗vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. Molecular structures of [(VOL1,3)2(μ˗OEt)][Et3NH] (1 and 3) have been determined by X‒ray crystallography. Antiferromagnetic coupling interaction was observed between the vanadium d1˗d1 centers of the complexes and this phenomenon was also established theoretically. The complexes were further screened for their in vitro cytotoxicity against HeLa and HT˗29 cancer cell lines. Chapter 3: Three new monooxidovanadium(IV) [VIVOL1–32] (1–3) and two alkoxido bridged vanadium(IV) trimeric [VIV3O3(μ˗OMe)3(μ3˗OMe)L4,52] (4 and 5), complexes have been reported, which were obtained upon reaction of 2˗{(2˗X)˗diazo)}˗4˗methylphenol (where X = benzo[1,3]dioxol˗5˗yl (HL1), phenyl (HL2) and 4˗methoxyphenyl (HL3)), 1˗(2˗(thiazol˗2˗yl)diazenyl)naphthalene˗2˗ol (HL4) and 2˗(2˗(thiazol˗2˗yl)diazenyl)˗4˗methylphenol (HL5)) with VOSO4.5H2O. The synthesized complexes were successfully characterized by elemental analysis, IR, UV˗vis spectroscopy, ESI˗MS and their redox properties studied by cyclic voltammetry. Molecular structure of 4 has been determined by single crystal X-ray diffraction study. The complexes were probed for their in vitro insulin˗mimetic activity against insulin responsive L6 myoblast cells. The complexes (1−5) have also been screened for their cytotoxicity in human breast adenocarcinoma cell line, MCF-7. The insulin˗mimetic activity of complexes 1−5 was also probed on rat L6 myoblast cells. To further confirm whether these compounds act via insulin signaling pathway, the immunoblot analysis for IRS˗1 was also carried out. Chapter 4: The reaction of 2˗(arylazo)phenols (HL) with [Ru(PPh3)3Cl2] in an ethanolic medium under basic conditions afforded two organometallic Ru(II) complexes, [RuL(PPh3)2(CO)] (1) and [RuL(PPh3)2(CH3CN)] (2). A similar reaction of HL with [Ir(PPh3)3Cl] resulted in the formation of the organometallic Ir(III) complex, [IrL(PPh3)2(H)] (3). The 2˗(arylazo)phenolate ligand is coordinated to the metal center in each complex (1‒3) as a tridentate C, N, O-donor via metal assisted C‒H activation of the ligand. The plausible solvent assisted mechanistic pathway for the unprecedented CO coordination to the Ru(II) center in the case of 1 has been explained. The synthesized complexes have been characterized by various spectroscopic techniques (viz., IR, UV˗vis and NMR spectroscopy), ESI-MS and their electrochemical behavior studied by cyclic voltammetry. Molecular structures of 1‒3 have been determined by X-ray crystallography. Chapter 5: Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes, [MoO2L17] (17) derived from various substituted tetradentate diamino bis(phenolato) “salan” ligands, N,Nʹ˗dimethyl˗N,Nʹ˗bis˗(2˗hydroxy˗3˗X˗5˗Y˗6˗Z˗benzyl)˗1,2˗diaminoethane (H2L1, X = Br, Y = Me, Z = H; H2L2, X = Me, Y = Cl, Z = H; H2L3, X = iPr, Y = Cl, Z = Me) and N,Nʹ˗bis˗(2˗hydroxy˗3˗X˗5˗Y˗6˗Z˗benzyl)˗1,2˗diaminopropane (H2L4, X = Y = tBu, Z = H; H2L5, X = Y = Me, Z = H; H2L6, X = iPr, Y = Cl, Z = Me; H2L7 , X = Y = Br, Z = H) containing ON donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV˗vis and NMR spectroscopy, ESI˗MS and cyclic voltammetry measurements. X-ray crystallography showed the O2N2 donor set to define an octahedral geometry in each case. [MoO2L17] (1‒7) showed moderate DNA binding propensity with binding constants ranging from 104−105 M-1. The experimental results showed that the complexes 1‒7 effectively interact with CT-DNA by both minor and major groove binding mode, while complex 2 additionally interacts by partial intercalative mode of binding. The dioxidomolybdenum(VI) complexes (1‒3) showed moderate photo-induced cleavage of pUC19 supercoiled plasmid DNA. All the complexes (1–7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell lines. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 may be dependent on the substituents in the salan ligand environment coordinated to the metal. Chapter 6: The synthesis and characterization (elemental analysis, UV˗vis spectroscopy, ESI-MS and cyclic voltammetry) of Cu(II) complexes ([CuL1,2] (1 and 2) and [CuL3′,4′]2 (3 and 4)) using salan ligands, N,Nʹ-dimethyl-N,Nʹ-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)˗1,2-diaminoethane (H2L1, X = iPr, Y = Cl, Z = Me; H2L2, X = OCH3, Y = allyl, Z = H) and N,Nʹ-bis-(2-hydroxy-3-X–5-Y-6-Z-benzyl)-1,2-diaminopropane (H2L3, X = iPr, Y= Cl, Z = Me; H2L4, X = Y = CH3, Z = H), have been discussed. Molecular structures of 1 and 3 have been determined by X‒ray crystallography. An unprecedented ligand transformation occurs in the case of 3 and 4, leading to the formation of phenolato bridged Cu(II) dimeric complexes, [CuL3′,4′]2. The organic transformation in the ligand has been mechanistically elucidated to be Cu(II) catalysed. This unusual chemistry of 3 and 4 has been compared with NiII, FeIII and MoVI complexes (5‒7) with similar ligand environment. The anomaly in ligand structure was however not observed in the case of other transition metal complexes (5‒7). The superoxide dismutase (SOD) activity of the Cu(II) complexes (1‒3) has also been investigated; the activity follows the order 3 > 1 > 2. Due to the deliquescent nature of 4, its SOD activity could not be evaluated. Chapter 7: In this chapter a brief resume of the work embodied in the thesis and concluding remarks are stated. The scope for future research work has also been discussed

Manganese Salan Complexes As Catalysts For Hydrosilylation Of Aldehydes And Ketones

New types of manganese(III) complexes containing H2salan ligand have been synthesized and examined as catalysts in the hydrosilylation of carbonyl compounds. Manganese(III) chloride complex (4b) exhibits minimal activity for the hydrosilylation of benzaldehyde at 120 ºC, but can be activated with silver perchlorate. Manganese(III) azide complex (5b) is characterized by the IR spectra, and the stretching frequency for the azide group is 2050 cm-1. This complex shows good activity in the hydrosilylation of benzaldehyde at 120 ºC, generating the corresponding silyl ether in high conversion 99 % within 1 h. Under optimized reaction conditions, phenylsilane as the reductant in C6D6 under nitrogen, the substrate scope has been examined. Several types of aldehydes and ketones can be reduced with tolerance to a variety of functional groups

Bipyrrolidine salan alkoxide complexes of lanthanides: synthesis, characterisation, activity in the polymerisation of lactide and mechanistic investigation by DOSY NMR

Dimeric lanthanide alkoxide and hydroxide complexes with salan ligands have been prepared with Nd, Sm and Yb. Monitoring their activity in the polymerisation of lactide by 1H DOSY NMR reveals a dinuclear catalytic active species.</p

Breaking the symmetry: C1-salans with (N-H) backbones

We disclose a synthetic route that providess an unprecedented library of C1 salan ligands endowed with (N-H) backbones, previously limited to N-methylated backbones. Efforts to identify a generic complexation protocol to yield the corresponding Cu(II)-salan complexes identify the scope and limitations of this approach

EXPLORATION OF CIS-1,2-DIAMINOCYCLOHEXANE-BASED CONFORMATIONALLY LOCKED CHIRAL LIGANDS IN ASYMMETRIC SYNTHESIS

Natural products have been demonstrated to be of great significance to the pharmaceutical industry in the development of new drugs and medicine. Unfortunately, synthetic approaches to obtain these natural products often prove increasingly challenging due to the complexity of synthesizing the target drug in the proper stereochemistry. The availability of enantioselective reactions can play a pivotal role in overcoming this challenge, yielding access to optically pure intermediates and products. Chiral ligands based on a trans-1,2-diaminocyclohexane motif are often employed for this purpose and their complexes with transition metals have been demonstrated to act as efficient chiral catalysts in asymmetric reactions. In contrast, studies involving cis-1,2-diaminocyclohexane derivatives as chiral catalysts are strongly underrepresented. We have designed and performed the synthesis of an axially chiral conformationally locked cis-1,2-diamine scaffold, conveniently designed for further derivatization into more complex structures. A key step in this synthesis was the chiral resolution of a racemic intermediate, realized through both chemical and enzymatic means in a comparative study. Utilizing the newly gained optically pure primary diamine scaffold, a library of chemically diverse secondary diamine ligands has been synthesized and characterized through NMR spectroscopy, mass spectrometry, and chiral HPLC. Assignment of the absolute configuration within the cis-1,2-diamine scaffold was realized through single-crystal X-ray crystallography experiments on one of the synthetic intermediates. The synthesized ligands have been evaluated for their potential to function as chiral catalysts in the asymmetric Henry reaction and asymmetric transfer hydrogenation. As a function of both steric and electronic structural variation, a range of catalytic activities and enantioselectivities in the Henry reaction were observed. The ligands proved to be less suitable for asymmetric transfer hydrogenation with only a select number of ligands catalyzing the reaction, and a single example resulting in a decent enantioselectivity. We additionally explored the possibility of incorporating a chemical switch into the scaffold, responsible for switching the axial chirality of the molecule. As a consequence of inverting the axial chirality, the configuration of the potential reaction product in asymmetric synthesis would also be inverted. To this extent, we performed the synthesis of a novel specifically designed crown ether, dicyclohexeno-18-crown-6, furnished with two π-bonds in the cyclohexane rings, allowing for additional modification into more advanced functionalized structures

Új szulfoszalán ligandumok és átmenetifém komplexeik előállítása és katalitikus sajátságaik: Preparation of new sulfosalan ligands and their transition metal complexes and their catalytic properties

In our research, we have designed and synthetized new water soluble sulfonated salan ligands and their transition metal complexes. Equilibrium investigations (by pH-potentiometry, 1H- and 13C-NMR spectroscopies) on these ligands and their Cu(II)-, Ni(II)-, and Pd(II)-complexes were also carried out. We identified species distributions in these aqueous systems and the results helped to suggest reaction mechanisms of some important catalytic reactions, such as pH-dependent hydrogenation, redox isomerization and C-C couplings. Kivonat Munkánk során új, vízoldható szulfoszalán ligandumok és átmenetifém komplexeik tervezésével és szintézisével foglalkoztunk. Koordinációs kémiai módszerekkel megvizsgáltuk a ligandumok és átmenetifém-komplexeik oldategyensúlyi viszonyait. Elvégeztük a ligandumok Cu(II)-, Ni(II)-, Pd(II)-komplexeinek pH-potenciometriás titrálását, valamint az oldatban jelen lévő részecskék eloszlásának teljes feltérképezését és jellemzését is. Ezen vizsgálatok nagyban elősegítik katalitikus tulajdonságaik megértését, valamint a reakciók mechanizmusának vizsgálatát (pl, pH függő hidrogénezés, redox izomerizáció, C-C keresztkapcsolás)