Alkali Metal & Alkaline-Earth Metal Complexes of Various Amidophosphines having P, N, Chalcogen and Borane as Donor atoms/group – Syntheses, Structures and Ring-Opening Polymerization of Caprolactone

During the last decade, heavy alkaline-earth organometallic chemistry has emerged from obscurity to becoming a vibrant area of research, owing to a number of synthetic pathways that provide reliable access to these highly reactive target compounds. The complexes of heavy alkaline-earth metals were employed in various catalytic applications such as ring-opening polymerization of various cyclic esters, polymerization of styrene and dienes, and hydroamination and hydrophosphination reactions of alkenes and alkynes. Particularly, Group 2 metal complexes have been received considerable attention as initiators for the ROP of cyclic esters and some of them have demonstrated impressive results. Aliphatic polyesters are currently considered as alternatives to synthetic petrochemical-based polymers. Their biodegradable and biocompatible nature along with their mechanical and physical properties make them prospective thermoplastics with broad commercial applications such as single-use packaging materials, medical sutures and drug delivery systems. Ring-opening polymerization (ROP) of cyclic esters promoted by alkaline-earth & rare-earth metal initiators proved to be the most efficient way for preparing polyesters with controlled molecular weight and microstructure and narrow molecular-weight distribution. Therefore, the design and synthesis of new well-defined single-site catalysts that exhibits good activity, productivity and selectivity for cyclic ester polymerization is needed

BIOCHEMICAL BASIS AND EMERGING MOLECULAR TARGETS TO TREAT DIABETIC RETINOPATHY

Diabetes being considered as an epidemic, long term untreated complicated diabetes resulting in retinopathy will be a leading cause of blindness worldwide. Many cross-sectional studies reported a strong relationship between chronic hyperglycaemia and development, progression of retinopathy, however the underlying mechanism that cause retinal microvascular damage following prolonged hyperglycaemia, yet to be revealed. Continued research worldwide focuses on understanding the molecular basis with the ultimate goal to prevent diabetic retinopathy by developing newer therapeutic targets. This article reviews multiple biochemical pathways that are implicated in diabetic retinopathy. Recent advancement in the molecular basis of the disease as well as clinical trials undertaken to target these molecules in order to block the signalling cascade prevailing in diabetic retinopathy is also discussed. This review highlights the recent therapeutic targets to prevent the onset as well as the progress of retinopathy in diabetes

BIOCHEMICAL BASIS AND EMERGING MOLECULAR TARGETS TO TREAT DIABETIC RETINOPATHY

Diabetes being considered as an epidemic, long term untreated complicated diabetes resulting in retinopathy will be a leading cause of blindness worldwide. Many cross-sectional studies reported a strong relationship between chronic hyperglycaemia and development, progression of retinopathy, however the underlying mechanism that cause retinal microvascular damage following prolonged hyperglycaemia, yet to be revealed. Continued research worldwide focuses on understanding the molecular basis with the ultimate goal to prevent diabetic retinopathy by developing newer therapeutic targets. This article reviews multiple biochemical pathways that are implicated in diabetic retinopathy. Recent advancement in the molecular basis of the disease as well as clinical trials undertaken to target these molecules in order to block the signalling cascade prevailing in diabetic retinopathy is also discussed. This review highlights the recent therapeutic targets to prevent the onset as well as the progress of retinopathy in diabetes

Amidinate Ligands in Zinc coordination sphere: Synthesis and structural diversity

A one-pot reaction involving neosilyllithium and three different carbodiimides (RN=C=NR, R=cyclohexyl, isopropyl and tert-butyl) in diethyl ether, followed by the addition of anhydrous ZnCl2, afforded, in high yield, corresponding homoleptic zinc amidinate complexes having the molecular formulae [Zn{CyN =C(CH2SiMe3)NCy}2] (1), [Zn{ i PrN =C(CH2SiMe3)N i Pr}2] (2) and [Zn{ t BuN =C(CH2SiMe3) N t Bu}2] (3), respectively, and amidinato moieties in the zinc coordination sphere. Solid state structures of complexes 1-3 are reported thereafter - all the three complexes are isostructural, and each of them consists of two four-membered metallacycles

Zinc-Catalyzed Guanylation Reaction of Amines to Carbodiimides/Isocyanate Leading to of Guanidines/Urea Derivatives Formation

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Syntheses and structures of dimeric sodium and potassium complexes of 2,6-diisopropyl-Anilidophosphine borane ligand

We report here the syntheses and structural studies of dimeric sodium and potassium complexes of composition [Na(THF)2{Ph2P(BH3)N(2,6- i Pr2C6H6)}]2 (2) and [K(THF)2{Ph2P(BH3)N(2,6- i Pr2C6H6)}]2 (3). The sodium complex 2 was readily prepared by the reaction of sodium bis(trimethylsilyl)amide with 2,6-diisopropylanilidophosphine-borane ligand [2,6- i Pr2C6H3NHP(BH3)Ph2] (1-H) at ambient temperature. The potassium complex 3 was prepared by two synthetic routes: in the first method, the ligand 1-H was made to react with potassium hydride at room temperature to afford the corresponding potassium complex. The potassium bis(trimethylsilyl)amides were made to react with protic ligand 1-H in the second method to eliminate the volatile bis(trimethyl)silyl amine. Solid-state structures of both the new complexes were established by single crystal X-ray diffraction analysis. In the molecular structures of complexes 2, the sodium metal is coordinated by the anilido nitrogen (η 1) and borane group (η 1) attached to the phosphorus atom of ligand 1. In contrast, for compound 2, ligand 1 displays η 6 π-arene interaction from 2,6-diisopopylphenyl ring with potassium atom along with η 3 interaction of BH3 group due to larger ionic radius of potassium ion

Imidazol-2-ylidene-N′-phenylureate ligands in alkali and alkaline earth metal coordination spheres - heterocubane core to polymeric structural motif formation

The synthesis and isolation of two potassium, one lithium and two calcium complexes of imidazol-2-ylidene-N′-phenylureate ligands [ImRNCON(H)Ph] [(R = tBu (1a); Mes (1b) and Dipp (1c); Mes = mesityl, Dipp = 2,6-diisopropylphenyl] are described. Potassium complexes, [{κ2-(ImMesNCONPh)K}4] (2b) and [{κ3-(ImDippNCONPh)K}2{KN(SiMe3)2}2]n (2c), were prepared in good yields by the reactions of 1b and 1c, respectively, with potassium bis(trimethyl)silyl amide at ambient temperature in toluene. Lithium complex [{(2,6-tBu2-4-Me-C6H2O)Li(ImtBuNCON(H)Ph)}2{ImtBuNCON(H)Ph}] (3a) was isolated by a one-pot reaction between 1a and LiCH2SiMe3, followed by the addition of 2,6-tBu2-4-Me-C6H2OH in toluene. Calcium complex [{κ2-(ImtBuNCONPh)Ca{N(SiMe3)2}-{KN(SiMe3)2}]n (4a) was isolated by the one-pot reaction of 1a with [KN(SiMe3)2] and calcium diiodide in THF at ambient temperature. The solid-state structures of ligand 1a and complexes 2b, 2c, 3a and 4a were confirmed by single-crystal X-ray diffraction analysis. It was observed that potassium was coordinated to the oxygen atom of urea group and to the nitrogen atom of the imidazolin-2-imine group, in the solid-state structure of 2b. In complex 4a, the calcium ion was ligated to the monoanionic imidazol-2-ylidene-N′-phenylureate ligand in a bi-dentate (κ2) fashion through the oxygen and nitrogen atoms of the isocyanate building block leaving the imidazolin-2-imine fragment uncoordinated. In the solid state of the potassium complex 2c, tri-dentate (κ3) coordination from the imidazol-2-ylidene-N′-phenylureate ligand was observed through the oxygen and nitrogen atoms of the isocyanate building block and of the imidazolin-2-imine fragment. In contrast, in the dimeric lithium complex 3a, the neutral imidazol-2-ylidene-N′-phenylureate ligand was bound to the lithium centre in a mono-dentate fashion (κ1) through an oxygen atom of the isocyanate moiety. It is to be noted that in each complex thus observed, the elongated carbon-nitrogen bond distances indicate substantial electron delocalisation from the imidazole ring to the ureate group present in ligand 1

Nickel(II) complexes having Imidazol-2-ylidene-N′-phenylurea ligand in the coordination sphere - Syntheses and solid state structures

We report the syntheses and structural studies of two nickel(II) complexes of imidazol-2-ylidene- N′-phenylureate ligand of composition [{Im tBuNCON(H)Ph}2Ni(acac)2](1) and [(C6H5NH2)2Ni(acac)2][ImMes NCON(H)Ph] (2). The nickel complex 1 was readily prepared by the reaction of nickel(II) acetylacetonate [Ni(acac)2] with imidazol-2-ylidene-N′-phenylureate ligand [Im tBuNCON(H)Ph] (L1) in THF under reflux condition for 72 h. The nickel complex 2 was obtained by the reaction of [Ni(acac)2], mesityl derivative of imidazol-2-ylidene-N′-phenylureate ligand [Im MesNCON(H)Ph] (L2) in the presence of aniline as base under reflux condition in THF. Both the paramagnetic complexes have been characterized by FT-IR spectroscopy and elemental analyses. Solid-state structures of both the new complexes were established by single crystal X-ray diffraction analysis. In the molecular structures of complexes 1 and 2, each nickel(II) ion is six fold coordinated and form a distorted octahedral geometry. The optical properties of both complexes have been explored. The Hirshfeld surfaces are used to view and analyze the intermolecular contacts in crystalline state for complex 2

Synthesis of monomeric and polymeric alkali and alkaline earth metal complexes using a phosphinoselenoic amide ligand in metal coordination sphere

We report the monomeric complexes of magnesium and calcium of composition [M(THF)n{η 2-Ph2P(Se)N(CMe3)}2] [M = Mg (3), n = 1 and M = Ca (4), n = 2)] and polymeric complexes of potassium and barium of composition [K(THF)2{Ph2P(Se)N(CMe3)}]n (2) and [K(THF)Ba{Ph2P(Se)N(CMe3)}3]n(5) respectively. The potassium complex 2 was readily prepared by the reaction of potassium bis(trimethylsilyl)amide with phosphinoselenoic amide ligand (1) at ambient temperature. The calcium complex 4 was prepared by two synthetic routes: in the first method, commonly known as salt metathesis reaction, the potassium complex 2 was made to react with alkaline earth metal diiodide at room temperature to afford the corresponding calcium complex. The metal bis(trimethylsilyl)amides were made to react with protic ligand 1in the second method to eliminate the volatile bis(trimethyl)silyl amine. The magnesium complex 3and barium complex 5 were prepared only through the first method. Solid-state structures of all the new complexes were established by single crystal X-ray diffraction analysis. The smaller ionic radii of Mg2+ (0.72 Å) and Ca2+ (0.99 Å) ions form the monomeric complex, whereas the larger ions K+ (1.38 Å) and Ba2+ (1.35 Å) were found to form one-dimensional polymeric complexes with monoanionic ligand 1. Compound 2 serves an example of magnesium complex with a Mg-Se direct bond