A formal E-selective hydrophophination of terminal and internal alkynes catalyzed by well-defined [Co(PMe3)4] (A) complex is achieved under mild conditions in good-toexcellent yield. The reaction does not require any additives and/or external base for an efficient hydrophosphination reaction. The reaction provided excellent scope and good functional tolerance. Detailed spectroscopic analysis (NMR, EPR, and UV-Vis) revealed that the low valent cobalt(0) complex undergoes oxidative addition with diphenylphosphine followed by hydrometallation with alkyne and subsequent reductive elimination led to the expected product. The detailed spectroscopic analyses along with the isotopic labelled experiments facilitate to intercept the active intermediates that are involved in the catalytic cycle, which are detailed. It was revealed that the suprafacial (vide infra) delivery of H and phosphorus to π-alkynes in synfashion lead to formal E-vinyl phosphine.

The reaction of [Ni(COD)2] (COD; cyclooctadiene) in THF with the NNN-pincer ligand bis(imino)pyridyl (L1) reveals a susceptibility to oxidation in an inert atmosphere ([O2] level <0.5 ppm), results in a transient Ni:dioxygen adduct. This reactive intermediate abstracts a hydrogen atom from THF and stabilizes an uncommon Ni(III) complex. The complex is crystallographically characterized by a molecular formula of [Ni III (L1 •• ) 2-(OH)] (1). Various isotopically labelled experiments ( 16 O/ 18 O) assertively endorses that the origin of terminal oxygen based ligand in 1 due to the activation of molecular dioxygen. The presence of proton bound to the terminal oxygen in 1 is well supported by NMR, IR spectroscopy, DFT calculations and hydrogen atom transfer (HAT) reactions promoted by 1. The observation of shake-up satellite peaks for the primary photoelectron lines of Ni(2p) in the X-ray photoelectron spectroscopy (XPS) spectrum unambiguously confirms the paramagnetic signature associated with the distorted square planar nickel ion, which is consistent with the trivalent oxidation state assigned for the nickel ion in 1. The variable temperature magnetic susceptibility data of 1 show dominant antiferromagnetic interactions exist among the paramagnetic centres, results in an overall S = ½ ground state. Variable temperature X-band EPR studies performed on 1 show evidence for S = ½ ground state, which is consistent with magnetic data. The unusual g-tensor extracted for a ground state, S = ½ is analyzed under a strong exchange limit of spin-coupled centres. The electronic structure predicted for 1 is in good agreement with theoretical calculations.

Three structurally analogous hexanuclear ruthenium­(III) complexes were isolated with the general molecular formula of [Ru6 III(O)2(μ4-η2-η2-CH2O2)­(t-BuCO2)12(L)2] where L = pyridine (1) or 4-dimethylamino pyridine (DMAP; 2) or 4-cyanopyridine (3). Complexes 1 and 3 were solved in the tetragonal I4̅c2 and P4 1212 space group, respectively, while 2 crystallized in the monoclinic system with P2 1 /c space group. In all three complexes, two oxo-centered Ru­(III) triangles were bridged by a unique and a rare methylenediolate (CH2O2)2–) ligand. This (CH2O2)2– group is reported to be an intermediate, which is not isolated in its metal-free form, to date, as it is unstable. Control experiments performed evidently reveal that the unique reaction condition followed is mandatory to isolate 1–3 and the origin of (CH2O2)2– is unknown at the moment, as no precursor was used to form this intermediate. The presence of (CH2O2)2– identified through X-ray diffraction was further unambiguously confirmed by various 1D (1H and 13C) and 2D-NMR (HSQC, TOCSY, NOESY, and DEPT) spectroscopies. Direct current (dc) magnetic susceptibility measurements performed on 1 and 2 reveal the predominant antiferromagnetic exchange interaction between the Ru­(III) centers result in a diamagnetic ground state at 2.0 K. The paramagnetic influence of 1–3 at room temperature evidently felt by the 1H nuclei of the (CH2O2)2– unit predominates compared to other NMR active nuclei in the complexes. The presence of an electron donating or withdrawing substituent on the terminal pyridine results in significant change in the dihedral angle of two oxo-centered triangular (Ru3O−) planes. The change in the structural parameters of 1–3 due to the substituents markedly reflected on the absorption profile and redox behavior, which are systematically investigated. Preliminary galvanostatic charge/discharge cycling experiments performed on a representative complex (3) suggest that 3 can be a promising candidate to employ as an effective multiple electron charge carrier in a nonaqueous redox flow battery.

The homometallic hexameric ruthenium cluster of the formula [Ru(III)6(μ3-O)2(μ-OH)2((CH3)3CCO2)12(py)2] (1) (py = pyridine) is solved by single-crystal X-ray diffraction. Magnetic susceptibility measurements performed on 1 suggest that the antiferromagnetic interaction between the Ru(III) centers is dominant, and this is supported by theoretical studies. Theoretical calculations based on density functional methods yield eight different exchange interaction values for 1: J1 = -737.6, J2 = +63.4, J3 = -187.6, J4 = +124.4, J5 = -376.4, J6 = -601.2, J7 = -657.0, and J8 = -800.6 cm(-1). Among all the computed J values, six are found to be antiferromagnetic. Four exchange values (J1, J6, J7 and J8) are computed to be extremely strong, with J8, mediated through one μ-hydroxo and a carboxylate bridge, being by far the largest exchange obtained for any transition-metal cluster. The origin of these strong interactions is the orientation of the magnetic orbitals in the Ru(III) centers, and the computed J values are rationalized by using molecular orbital and natural bond order analysis. Detailed NMR studies ((1)H, (13)C, HSQC, NOESY, and TOCSY) of 1 (in CDCl3) confirm the existence of the solid-state structure in solution. The observation of sharp NMR peaks and spin-lattice time relaxation (T1 relaxation) experiments support the existence of strong intramolecular antiferromagnetic exchange interactions between the metal centers. A broad absorption peak around 600-1000 nm in the visible to near-IR region is a characteristic signature of an intracluster charge-transfer transition. Cyclic voltammetry experiments show that there are three reversible one-electron redox couples at -0.865, +0.186, and +1.159 V with respect to the Ag/AgCl reference electrode, which corresponds to two metal-based one-electron oxidations and one reduction process.

The coordination chemistry and the activities in the ring‐opening polymerization catalysis of racemic lactide (LA) of magnesium complexes of a series of {ONNN}‐type sequential monoanionic ligands are described. All ligands include pyridyl and substituted‐phenolate as peripheral groups. The ligands bearing either chiral or meso‐bipyrrolidine cores led to single diastereomeric complexes, whereas the ligands bearing a diaminoethane core led to diastereomer mixtures. All {ONNN}Mg‐X complexes [X=Cl, HMDS (hexamethyldisilazide)] led to highly active and isoselective catalysts. The complexes bearing the chiral bipyrrolidine core exhibited the highest activities (full consumption of 5000 equiv. of rac‐LA at RT within 5 min) and highest isoselectivities (Pm=0.91), as well as a living character. The complexes of the meso‐bipyrrolidine based ligands were almost as active and slightly less stereoselective, while those of the diaminoethane based ligands exhibited reduced activities and isoselectivities.