Constantinos G. Screttas

Bio: Constantinos G. Screttas is an academic researcher from Fudan University. The author has contributed to research in topics: Tetrahydrofuran & Metalation. The author has an hindex of 17, co-authored 101 publications receiving 1193 citations. Previous affiliations of Constantinos G. Screttas include University of Oxford & Moscow State University.

Electronic and magnetic metal–metal interactions in dinuclear oxomolybdenum(V) complexes across bis-phenolate bridging ligands with different spacers between the phenolate termini: ligand-centred vs. metal-centred redox activity

Abstract: A series of dinuclear complexes has been prepared in which two {MoV(TpMe,Me)(O)Cl} fragments (abbreviated as Mo; TpMe,Me = tris(3,5-dimethylpyrazol-1-yl)hydroborate) are attached to either end of a bis-p-phenolate bridging ligand [(4,4′-OC6H4)–X–(4,4′-C6H4O)]2−. The complexes are Mo2(CC) (X = CHCH), Mo2(CC)2 (X = CHCH–CHCH), Mo2(CC)3 (X = CHCH–CHCH–CHCH), Mo2(th) (X = 2,5-thiophenediyl), Mo2(th)2 (X = 2,5:2′,5′-bithiophenediyl), Mo2(th)3 (X = 2,5:2′,5′:2″,5″-terthiophenediyl), Mo2(CC) (X = CC), Mo2(NN) (X = NN), Mo2(CO) [X = C(O)] and Mo2(C2ΦC2) [X = CHCH(1,4-C6H4)CHCH]. Electrochemical, UV/VIS/NIR spectroelectrochemical and magnetic measurements have been carried out in order to see how effectively the different spacer groups X mediate electronic and magnetic interactions between the two redox-active, paramagnetic, Mo centres. The electronic interactions were determined from the redox separation between the two successive one-electron oxidations which are formally Mo(VI)–Mo(V) couples; it was found that thienyl units in the bridging ligand are much more effective at maintaining electronic communication over long distances than p-phenylene or ethenyl spacers of comparable lengths. The azo (NN) linkage afforded a much weaker electronic interaction than the ethenyl or ethynyl spacers. UV/VIS/NIR spectroelectrochemical studies showed that whereas the first oxidation is metal-centred to give Mo(VI)–Mo(V) species with characteristic intense phenolate→Mo(VI) LMCT transitions in the near-IR region, the spectra of the doubly oxidised complexes are characteristic of quinones: thus, the sequence of species formed on oxidation is [Mo(V)(μ-diolate)Mo(V)]0 → [Mo(V)(μ-diolate)Mo(VI)]+ → [Mo(V)(μ-quinone)Mo(V)]2+, with an internal charge redistribution associated with the second oxidation. Semi-empirical ZINDO calculations provide some support for this. Magnetic susceptibility measurements on Mo2(CC), Mo2(th), Mo2(NN) and Mo2(CC) show that all are weakly antiferromagnetically coupled, as expected on the basis of a spin-polarisation picture, with the order of strength of the magnetic interaction being the reverse of the order for electronic coupling, such that Mo2(th) affords the strongest electronic interaction but the weakest magnetic interaction.

Chemical Redox Agents for Organometallic Chemistry

Abstract: 1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

On the Nature of the Active Species in Palladium Catalyzed Mizoroki–Heck and Suzuki–Miyaura Couplings – Homogeneous or Heterogeneous Catalysis, A Critical Review

Abstract: A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true “catalysts” in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano- and macroparticles, soluble palladium nanoparticles, soluble ligand-free palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.

Conjugated oligomers with terminal donor-acceptor substitution.

Abstract: Conjugated oligomers represent a prominent class of compounds from a viewpoint of their theory, synthesis, and applications in materials science. Push-pull substitution with an electron donor D at one end of the conjugation and an electron acceptor A at the other end results in them having outstanding optical and electronical properties. This Review highlights fundamental synthetic strategies for the preparation of such oligomers with n repeat units (n=1, 2, 3, 4, ..) and the rules that govern their linear and nonlinear optical properties (absorption, frequency doubling and tripling). The unification of chemical, physical, and theoretical aspects with an interdisciplinary image of this class of compounds is attempted herein.