Browsing by Subject "BOND ACTIVATION"
Now showing items 1-3 of 3
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(2020)Organoboron compounds are essential reagents in modern C-C coupling reactions. Their synthesis via catalytic C-H borylation by main group elements is emerging as a powerful tool alternative to transition metal based catalysis. Herein, a straightforward metal-free synthesis of aryldifluoroboranes from BF(3)and heteroarenes is reported. The reaction is assisted by sterically hindered amines and catalytic amounts of thioureas. According to computational studies the reaction proceeds via frustrated Lewis pair (FLP) mechanism. The obtained aryldifluoroboranes are further stabilized against destructive protodeborylation by converting them to the corresponding air stable tetramethylammonium organotrifluoroborates.
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(2019)Protic NHC iridium complexes, obtained from the corresponding azido-phenylene-isocyanide precursor complexes, were investigated for ligand-based reactivity. Under redox-neutral conditions, acetonitrile inserts into the N-H bonds to provide kappa(2)-NHC-imidoyl ligand-based complexes, while under reductive conditions the complex also expels one N-H proton to provide the corresponding deprotonated analogues. Using zinc as a reductor activates the NHC-iridium complex to form an asymmetric bimetallic iridium hydrido complex, in which two anionic N-deprotonated NHCs bridge the bimetallic core. X-ray crystal structures are reported for the azido-phenylene-isocyanide precursor complex, the protic NHC complex, and the asymmetric bimetallic iridium hydride complex. Density functional computations and a QTAIM analysis of the bimetallic iridium hydrido complex are provided.
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(2020)The reversible reaction of H(2)with a bis-phosphenium complex of chromium provides a rare example of 3d transition metal/phosphenium cooperativity. Photolysis induces the activation of H(2)and yields a spectroscopically detectable phosphenium-stabilized (sigma-H-2)-complex, readily showing exchange with gaseous H(2)and D-2. Further reaction of this complex affords a phosphine-functionalized metal hydride, representing a unique example of reversible H(2)cleavage across a 3d MP bond. The same species is also accessibleviastepwise H+/H(-)transfer to the bis-phosphenium complex, and releases H(2)upon heating or irradiation. Dihydrogen transfer from the H-2-complex to styrene is exploited to demonstrate the first example of promoting hydrogenation with a phosphenium complex.
