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.
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.
A novel dinuclear oxygen-bridged chromium(II) complex of [(Ph 3 SiO)Cr 3 (THF)] 2 (μ-OSiPh 3 ) 2 (1) was successfully synthesized and structurally characterized. The crystal structure of complex 1 shows that the chromium centers adopt a tetrahedrally distorted square-planar coordination geometry. Complex 1 was tested for ethylene polymerization upon activation with and without aluminum alkyl cocatalysts. No ethylene polymerization activity was observed in the absence of aluminum alkyl cocatalysts; however, in the presence of methylaluminoxane (MAO), complex 1 demonstrates an unexpected transformation from ethylene polymerization to ethylene oligomerization, with the molar ratio of Al to Cr increasing from 50 to 1000. The activation of complex 1 with MAO was investigated by ESR and 29 Si NMR spectroscopy. It was found that the Ph 3 SiOÀ groups could be transferred from the chromium centers of complex 1 to the aluminum of MAO.
The development of efficient catalysts and processes for synthesizing functionalized (olefinic and/or chiral) primary alcohols and fluoral hemiacetals is currently needed. These are valuable building blocks for pharmaceuticals, agrochemicals, perfumes, and so forth. From an economic standpoint, bench-stable Takasago Int. Corp.’s Ru-PNP, more commonly known as Ru-MACHO, and Gusev’s Ru-SNS complexes are arguably the most appealing molecular catalysts to access primary alcohols from esters and H2 (Waser, M. et al. Org. Proc. Res. Dev. 2018, 22, 862). This work introduces economically competitive Ru-SNP(O) z complexes (z = 0, 1), which combine key structural elements of both of these catalysts. In particular, the incorporation of SNP heteroatoms into the ligand skeleton was found to be crucial for the design of a more product-selective catalyst in the synthesis of fluoral hemiacetals under kinetically controlled conditions. Based on experimental observations and computational analysis, this paper further extends the current state-of-the-art understanding of the accelerative role of KO-t-C4H9 in ester hydrogenation. It attempts to explain why a maximum turnover is seen to occur starting at ∼25 mol % base, in contrast to only ∼10 mol % with ketones as substrates.
We report herein the actinide-mediated insertion of E–H bonds (E = C, N, P, S) into various heterocumulenes including carbodiimides, isocyanates, and isothiocyanates.
A lanthanide series incorporating 2-thiophenecarboxylate and terpyridine is presented. Four structure types are observed with differences in the coordination number and nuclearity of the complexes attributed to the effects of the lanthanide contraction.
A bismuth-organic compound containing 2,2':6'2"-terpyridine (terpy) and 2-thiophenecarboxylate (TC), of the general formula (terpy)Bi(κ -TC) ⋅0.47 H O (BiOM-1), has been synthesized under hydrothermal conditions. Addition of a lanthanide nitrate solution to the reaction mixture led to statistical replacement of the bismuth centers, and yielded isomorphous lanthanide containing compounds Bi Ln OM-1 (Ln=Nd, Sm, Eu, Tb, Dy, Er, and Yb) that showed bismuth and/or ligand sensitized lanthanide-centered emission, and the first example of NIR emission from a lanthanide doped BiOM. The structure was determined by single-crystal X-ray diffraction, and the level and uniformity of lanthanide ion incorporation into the bismuth host was determined by ICP-OES and electron microprobe analysis. For the visible emitters, lifetime data and quantum yields are presented. A high efficiency of sensitization was calculated for the europium analog (50.1 %), showing significant improvement over previously reported europium thiophenecarboxylates. These novel materials may provide strategies to address concerns over the long-term sustainability of the rare earth elements, especially relating to optical devices.
A catalyzed conversion of terminal alkynes into dimers, trimers, and trisubstituted benzenes has been developed using the actinide amides U[N(SiMe 3 ) 2 ] 3 (1) and [(Me 3 Si) 2 N] 2 An[κ 2 -(N,C)-CH 2 Si(CH 3 )N(SiMe 3 )] (An = U (2), Th (3)) as precatalysts. These complexes allow for preferential product formation according to the identity of the metal and the catalyst loading. While these complexes are known as valuable precursors for the preparation of various actinide complexes, this is the first demonstration of their use as catalysts for C−C bond forming reactions. At high uranium catalyst loading, the cycloaddition of the terminal alkyne is generally preferred, whereas at low loadings, linear oligomerization to form enynes is favored. The thorium metallacycle produces only organic enynes, suggesting the importance of the ability of uranium to form stabilizing interactions with arenes and related π-electroncontaining intermediates. Kinetic, spectroscopic, and mechanistic data that inform the nature of the activation and catalytic cycle of these reactions are presented.
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