Isolation of C1 through C4 derivatives from CO using heteroleptic uranium(iii) metallocene aryloxide complexes

Cross-coupling of CO and an isocyanide mediated by a tetrameric magnesium hydride cluster

Sequential addition of CNXyl (Xyl = 2,6-dimethylphenyl) and CO to a tetrametallic magnesium hydride cluster results in stepwise reduction and cross-coupling of these substrates. Cross-coupling results in the formation of an ethene amidolate ligand [OC1(H1)[double bond, length as m-dash]C2(H2)NAr]2- a previously unknown entity which contains a 1,2-difunctionalised carbon chain reminiscent of those found in aminoalcohols and amino acids. To the best of our knowledge, this is the first example of such reactivity with metal hydride precursors. DFT calculations support a mechanism that parallels that established for coupling of CO to form ethenediolate ligands, with the key carbon-carbon bond step occurring by nucleophilic attack of a putative azamethylene intermediate on CO. The cluster plays a key role in templating the synthesis, providing kinetic control over each of the steps. The ethene amidolate ligand can be transferred to other metals (Al) and semi-metals (B) through onwards metathesis reactions.

Mechanistic investigations of the Fe(ii) mediated synthesis of squaraines

The scission and homologation of CO is a fundamental process in the Fischer-Tropsch reaction. However, given the heterogeneous nature of the catalyst and forcing reaction conditions, it is difficult to determine the intermediates of this reaction. Here we report detailed mechanistic insight into the scission/homologation of CO by two-coordinate iron terphenyl complexes. Mechanistic investigations, conducted using in situ monitoring and reaction sampling techniques (IR, NMR, EPR and Mössbauer spectroscopy) and structural characterisation of isolable species, identify a number of proposed intermediates. Crystallographic and IR spectroscopic data reveal a series of migratory insertion reactions from 1Mes to 4Mes. Further studies past the formation of 4Mes suggest that ketene complexes are formed en route to squaraine 2Mes and iron carboxylate 3Mes, with a number of ketene containing structures being isolated, in addition to the formation of unbound, protonated ketene (8). The synthetic and mechanistic studies are supported by DFT calculations.

Facile Oxidation of Ce(III) to Ce(IV) Using Cu(I) Salts

The synthesis, luminescence, and electrochemical properties of the Ce(III) compound, [(C5Me5)2(2,6-iPr2C6H3O)Ce(THF)], 1, were investigated. Based on the electrochemical data, treatment of 1 with CuX (X = Cl, Br, I) results in the formation of the corresponding Ce(IV) complexes, [(C5Me5)2(2,6-iPr2C6H3O)Ce(X)]. Each complex has been characterized using NMR, IR, and UV-vis spectroscopy as well as structurally determined using X-ray crystallography. Additionally, the treatment of [(C5Me5)2(2,6-iPr2C6H3O)Ce(Br)] with AgF results in the formation of the putative [(C5Me5)2(2,6-iPr2C6H3O)Ce(F)]. The electronic structure of these Ce(IV)-X complexes was investigated by bond analyses and the Ce(IV)-F moiety using quantum chemistry NMR calculations.

Progress in Nonaqueous Molecular Uranium Chemistry: Where to Next?

There is long-standing interest in nonaqueous uranium chemistry because of fundamental questions about uranium's variable chemical bonding and the similarities of this pseudo-Group 6 element to its congener d-block elements molybdenum and tungsten. To provide historical context, with reference to a conference presentation slide presented around 1988 that advanced a defining collection of top targets, and the challenge, for synthetic actinide chemistry to realize in isolable complexes under normal experimental conditions, this Viewpoint surveys progress against those targets, including (i) CO and related π-acid ligand complexes, (ii) alkylidenes, carbynes, and carbidos, (iii) imidos and terminal nitrides, (iv) homoleptic polyalkyls, -alkoxides, and -aryloxides, (v) uranium-uranium bonds, and (vi) examples of topics that can be regarded as branching out in parallel from the leading targets. Having summarized advances from the past four decades, opportunities to build on that progress, and hence possible future directions for the field, are highlighted. The wealth and diversity of uranium chemistry that is described emphasizes the importance of ligand-metal complementarity in developing exciting new chemistry that builds our knowledge and understanding of elements in a relativistic regime.

Spectroscopic and Computational Evidence of Uranium Dihydrogen Complexes

Dihydrogen complexation, a phenomenon with robust precedent in the transition metal series, is spectroscopically detected for a uranium(III) complex and thereby extended for the first time to the 5f series. The vacant coordination site and low valence of (C5H4SiMe3)3U prove to be key to the reversible formation of (C5H4SiMe3)3U-H2 (complex 1), and the paramagnetism of the f3 center facilitates the detection of complex 1 by NMR spectroscopy. Density functional theory calculations reveal that the delocalization of the 5f electron density from (C5H4SiMe3)3U onto the side-on dihydrogen ligand is crucial to complex formation, an unusual bonding situation for an actinide acid-base complex. The spectroscopic and computational results are compared to those reported for lanthanide metallocenes to yield insight into the nature of─and future possibilities for─f-element dihydrogen complexation.

Cooperative dihydrogen activation with unsupported uranium-metal bonds and characterization of a terminal U(iv) hydride

Cooperative chemistry between two or more metal centres can show enhanced reactivity compared to the monometallic fragments. Given the paucity of actinide-metal bonds, especially those with group 13, we targeted uranium(iii)-aluminum(i) and -gallium(i) complexes as we envisioned the low-valent oxidation state of both metals would lead to novel, cooperative reactivity. Herein, we report the molecular structure of [(C5Me5)2(MesO)U-E(C5Me5)], E = Al, Ga, Mes = 2,4,6-Me3C6H2, and their reactivity with dihydrogen. The reaction of H2 with the U(iii)-Al(i) complex affords a trihydroaluminate complex, [(C5Me5)2(MesO)U(μ2-(H)3)-Al(C5Me5)] through a formal three-electron metal-based reduction, with concomitant formation of a terminal U(iv) hydride, [(C5Me5)2(MesO)U(H)]. Noteworthy is that neither U(iii) complexes nor [(C5Me5)Al]4 are capable of reducing dihydrogen on their own. To make the terminal hydride in higher yields, the reaction of [(C5Me5)2(MesO)U(THF)] with half an equivalent of diethylzinc generates [(C5Me5)2(MesO)U(CH2CH3)] or treatment of [(C5Me5)2U(i)(Me)] with KOMes forms [(C5Me5)2(MesO)U(CH3)], which followed by hydrogenation with either complex cleanly affords [(C5Me5)2(MesO)U(H)]. All complexes have been characterized by spectroscopic and structural methods and are rare examples of cooperative chemistry in f element chemistry, dihydrogen activation, and stable, terminal ethyl and hydride compounds with an f element.

Molybdenum carbonyl assisted reductive tetramerization of CO by activated magnesium(i) compounds: squarate dianion vs. metallo-ketene formation

Reactions of a dimagnesium(i) compound, [{(^DipNacnac)Mg}₂] (^DipNacnac = [HC(MeCNDip)₂]^-, Dip = 2,6-diisopropylphenyl), pre-activated by coordination with simple Lewis bases (4-dimethylaminopyridine, DMAP; or TMC, :C(MeNCMe)₂), with 1 atmosphere of CO in the presence of one equivalent of Mo(CO)₆ at room temperature, led to the reductive tetramerisation of the diatomic molecule. When the reactions were carried out at room temperature, there is an apparent competition between the formation of magnesium squarate, [{(^DipNacnac)Mg}{cyclo-(κ⁴-C₄O₄)}{μ-Mg(^DipNacnac)}]₂, and magnesium metallo-ketene products, [{(^DipNacnac)Mg}[μ-O[double bond, length as m-dash]CC{Mo(CO)₅}C(O)CO₂]{Mg(D)(^DipNacnac)}], which are not inter-convertible. Repeating the reactions at 80 °C led to the selective formation of the magnesium squarate, implying that this is the thermodynamic product. In an analogous reaction, in which THF is the Lewis base, only the metallo-ketene complex, [{(^DipNacnac)Mg}[μ-O[double bond, length as m-dash]CC{Mo(CO)₅}C(O)CO₂]{Mg(THF)(^DipNacnac)}] is formed at room temperature, while a complex product mixture is obtained at elevated temperature. In contrast, treatment of a 1 : 1 mixture of the guanidinato magnesium(i) complex, [(Priso)Mg-Mg(Priso)] (Priso = [Prⁱ₂NC(NDip)₂]^-), and Mo(CO)₆, with CO gas in a benzene/THF solution, gave a low yield of the squarate complex, [{(Priso)(THF)Mg}{cyclo-(κ⁴-C₄O₄)}{μ-Mg(THF)(Priso)}]₂, at 80 °C. Computational analyses of the electronic structure of squarate and metallo-ketene product types corroborate the bonding proposed from experimental data, for the C₄O₄ fragments of these systems.