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N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
The chemistry of organometallic alkaline earth metal complexes closely resembles that of rare-earth elements [35–36]. Therefore, it is not beyond belief that alkaline earth metal complexes are active in the hydroamination/cyclization of aminoalkynes and aminoalkenes, as reported by Hill et al. [37], employing a diketiminato calcium amide complex (Scheme 7). For the synthesis of pyrrolidines, the catalyst activity of calcium amide complex is comparable to rare-earth metal-based catalysts. However, a limiting factor is observed in the form of a facile Schlenk-type ligand redistribution reaction under catalytic conditions, resulting in the formation of diamido and homoleptic bis(diketiminato) species and catalyst deactivation. Initially, asymmetric hydroamination is performed using a chiral bis-oxazolinato calcium complex to afford only low ee (up to 10% ee) as a result of a facile Schlenk equilibrium [38]. Datta et al. [39–40] reported the catalytic activity of aminotroponiminato strontium and calcium complexes applied in catalyst loadings as low as 2 mol%. With increasing ionic radius of the metal, the catalytic activity of alkaline-earth metal catalysts decreases, which contrasts with the trends for rare earth and alkali metal-based catalysts [41].
Organic Small-Molecule Materials for Organic Light-Emitting Diodes
Published in Zhigang Rick Li, Organic Light-Emitting Materials and Devices, 2017
Shijian Su, Norman Herron, Hong Meng
In addition to using pyrazole as the auxiliary ligand to blue shift the emission of phenylpyridine homoleptic iridium complexes, replacing the pyridine ring of phenylpyridine ligands with a pyrazole ring can also widen the HOMO and LUMO band gap of the complexes as a consequence of lowering the HOMO and raising the LUMO energy levels of the complexes, respectively. Thompson’s group synthesized a series of blue homoleptic phenylpyrazolyl iridium complexes (502–506) (Scheme 3.90) [531]. However, these homoleptic complexes showed strong ultrapure blue-to-blue emission (390–440 nm) only at very low temperature (77 K); however, unfortunately, they all showed very weak emission at room temperature, rendering them unsuitable for PHOLED applications. Although heteroleptic phenylpyrazolyl–phenylpyridine complexes showed moderate emission at room temperature, the emission color is bluish–green, and there is no device data reported for these complexes [532].
Nanosensor Laboratory
Published in Vinod Kumar Khanna, Nanosensors, 2021
Let us look closely at some of the methodologies adopted for synthesizing tin oxide nanoparticles of desired morphologies and sizes. Nayral et al. (1999) reported the synthesis of tin-tin oxide nanoparticles of low size-dispersion (the degree of scatter of data, usually about an average value, such as the median) through a mechanism combining the decomposition of an organometallic precursor (homoleptic tin (II) amides; metal compounds with all ligands identical) and controlled surface hydrolysis (decomposition of a chemical compound by reaction with water), as well as their oxidation into tin oxide nanoparticles without coalescence (uniting into a whole) or change in size.
Synthesis, spectroscopic characterization, biological activity, and conducting properties of functionalized Ni(II) dithiocarbamate complexes with solvent extraction studies of the ligands
Published in Journal of Sulfur Chemistry, 2023
Vinay Kumar Maurya, Lal Bahadur Prasad, Anupam Singh, Kunal Shiv, Akhilesh Prasad
The homoleptic complexes of the formula [Ni(L)2] (where L = L1 (1), L2 (2), L3 (3), L4 (4), L5 (5)) were obtained in good yields by the reaction of an aqueous methanolic solution of Ni(OOCCH3)2.4H2O with the potassium salt of ligands, KL1 – KL5 (Schemes 1 and 2) in 1:2 molar ratio. All the complexes are air-stable, non-hygroscopic solids, and soluble in the organic solvents like CHCl3, CH2Cl2, dimethyl sulfoxide, and dimethyl formamide and melt or decompose at temperatures ranging from 181 to 200°C. The complexes have been characterized by elemental analysis, FT-IR, UV-Vis, 1H NMR, and 13C NMR spectroscopy, mass spectrometry (Figures S39 – S48) techniques and their thermal and conducting behaviors are investigated. Diamagnetic nature of all the complexes were determined by Cahn – faraday electro balance using Hg[Co(NCS)4] as a calibrant.
Synthesis and characterization of Ni(0) complexes supported by an unsymmetric C,N ligand
Published in Journal of Coordination Chemistry, 2022
Sarah M. Craig, Kaycie R. Malyk, Elliot S. Silk, Daniel T. Nakamura, William W. Brennessel, C. Rose Kennedy
We have demonstrated that a representative NHC-pyridine C,N ligand can support well-defined, monomeric [Ni]0. Formation of heteroleptic (3) vs. homoleptic (4) complex is governed by ligand:metal ratio, and interconversion between the two species occurs in a dynamic equilibrium. Although 3 can also be generated in situ directly from the imidazolium NHC precursor, material is formed in higher purity following deprotonation to reveal the free carbene prior to metalation. We anticipate the mixed steric and electronic properties of this ligand scaffold will offer an accessible alternative to popular pyridine oxazoline ligands for [Ni] catalysis.