Rami J. Batrice

Evaluation of donor and steric properties of anionic ligands on high valent transition metals

Synthetic protocols and characterization data for a variety of chromium(VI) nitrido compounds of the general formula NCr(NPr(i)(2))(2)X are reported, where X = NPr(i)(2) (1), I (2), Cl (3), Br (4), OTf (5), 1-adamantoxide (6), OSiPh(3) (7), O(2)CPh (8), OBu(t)(F6) (9), OPh (10), O-p-(OMe)C(6)H(4) (11), O-p-(SMe)C(6)H(4) (12), O-p-(Bu(t))C(6)H(4) (13), O-p-(F)C(6)H(4) (14), O-p-(Cl)C(6)H(4) (15), O-p-(CF(3))C(6)H(4) (16), OC(6)F(5) (17), κ(O)-N-oxy-phthalimide (18), SPh (19), OCH(2)Ph (20), NO(3) (21), pyrrolyl (22), 3-C(6)F(5)-pyrrolyl (23), 3-[3,5-(CF(3))(2)C(6)H(3)]pyrrolyl (24), indolyl (25), carbazolyl (26), N(Me)Ph (27), κ(N)-NCO (28), κ(N)-NCS (29), CN (30), NMe(2) (31), F (33). Several different techniques were employed in the syntheses, including nitrogen-atom transfer for the formation of 1. A cationic chromium complex [NCr(NPr(i)(2))(2)(DMAP)]BF(4) (32) was used as an intermediate for the production of 33, which was produced by tin-catalyzed degredation of the salt. Using spin saturation transfer or line shape analysis, the free energy barriers for diisopropylamido rotation were studied. It is proposed that the estimated enthalpic barriers, Ligand Donor Parameters (LDPs), for amido rotation can be used to parametrize the donor abilities of this diverse set of anionic ligands toward transition metal centers in low d-electron counts. The new LDPs do not correlate well to the pK(a) value of X. Conversely, the LDP values of phenoxide ligands do correlate with Hammett parameters for the para-substituents. Literature data for (13)C NMR chemical shifts for a tungsten-based system with various X ligands plotted versus LDP provided a linear fit. In addition, the angular overlap model derived e(σ) + e(π) values for chromium(III) ammine complexes correlate with LDP values. Also discussed is the correlation with XTiCp*(2) spectroscopic data. X-ray diffraction has been used used to characterize 31 of the compounds. From the X-ray diffraction data, steric parameters for the ligands using the Percent Buried Volume and Solid Angle techniques were found.

Actinide-Catalyzed Intermolecular Addition of Alcohols to Carbodiimides

The unprecedented actinide-catalyzed addition of alcohols to carbodiimides is presented. This represents a rare example of thorium-catalyzed transformations of an alcoholic substrate and the first example of uranium complexes showing catalytic reactivity with alcohols. Using the uranium and thorium amides U[N(SiMe3)2]3 and [(Me3Si)2N]2An[κ(2)-(N,C)-CH2Si(CH3)2N(SiMe3)] (An = Th or U), alcohol additions to unsaturated carbon-nitrogen bonds are achieved in short reaction times with excellent selectivities and high to excellent yields. Computational studies, supported by experimental thermodynamic data, suggest plausible models of the profile of the reaction which allow the system to overcome the high barrier of scission of the actinide-oxygen bond. Accompanied by experimentally determined kinetic parameters, a plausible mechanism is proposed for the catalytic cycle.

Catalytic Aerobic Oxidation of Alcohols using Recoverable IAPNO α-Hydrogen Nitroxyl Radicals

α‐Hydrogen‐substituted nitroxyl radicals are of considerable interest as catalysts for oxidation and polymerization, but are usually inherently unstable. We report herein the catalytic activity of a new family of stable iso‐azaphenalene (IAPNO) α‐hydrogen nitroxyl radicals in the copper/bipyridine/N‐methylimidazole co‐catalyzed aerobic oxidation of alcohols. The nitroxyl radical Mes/TIPSO‐IAPNO (TIPSO=triisopropyloxy, IAPNO=isoazaphenalene N‐oxyl) displays higher activity than TEMPO in the oxidation of benzylic and allylic alcohols. Alkyl, benzyl, allyl, and propargyl alcohols are oxidized with yields up to 96 %. The readily prepared nitroxyl catalysts are recovered in 75–90 % yield after purification of the reaction mixture and are recycled.

Synthesis, structure, and photoluminescent behaviour of molecular lanthanide–2-thiophenecarboxylate–2,2′:6′,2′′-terpyridine materials

The preparation of a lanthanide series, with the exception of promethium, incorporating 2,2′:6′,2′′-terpyridine (terpy) and 2-thiophenecarboxylate (TC) functionality has been achieved via hydrothermal reaction conditions. The structures of the crystalline products were determined using single crystal X-ray diffraction and bulk purity was confirmed via powder X-ray diffraction and elemental analysis. The series is comprised of four structure types wherein the effects of the lanthanide contraction are manifested in changes in the coordination number and nuclearity of the complexes. From lanthanum through holmium an isomorphous series of symmetric dimers of the general formula [Ln2(terpy)2(TC)4(μ-TC)2(H2O)2]·nH2O (Ln-1, Ln = La–Ho, excluding Pm) was isolated. Using holmium oxide resulted in the formation of Ho-1 whereas use of the holmium chloride precursor resulted in the formation of [Ho2(terpy)2(TC)3(μ-TC)2(H2O)2]TC (Ho-2), that consists of an asymmetric dimer. Beyond Ho, Er–Lu were found to form compounds of the general formula [Ln(terpy)(TC)3(H2O)], the structures of which consist of monomeric units. While Er adopts Er-3, Tm–Lu adopt another structure type (Ln-4, where Ln = Tm, Yb, and Lu), the latter arising from differences in intramolecular hydrogen bonding interactions as well as π–π stacking interactions. The luminescent behaviour of the solid samples was examined and showed ligand-sensitized metal-based visible (Sm, Eu Tb, Dy) and NIR (Nd, Sm, and Yb) emission, with lifetimes up to hundreds of microseconds for select samples. Quantum yields of the visible light emitters have been measured and are additionally presented.

Synthesis of Coordinatively Unsaturated Tetravalent Actinide Complexes with η5 Coordination of Pyrrole

The synthesis of new actinide complexes utilizing bridged α-alkyl-pyrrolyl ligands is presented. Lithiation of the ligands followed by treatment with 1 equiv of actinide tetrachloride (uranium or thorium) produces the desired complex in good yield. X-ray diffraction studies reveal unique η(5):η(5) coordination of the pyrrolyl moieties; when the nonsterically demanding methylated ligand is used, rapid addition of the lithiated ligand solution to the metal precursor forms a bis-ligated complex that reveals η(5):η(1) coordination as determined by crystallographic analysis.