Nickel-Catalyzed Selective Reduction of Carbon Monoxide with Magnesium Alkyl Compounds.

Research on CO activation and homologation is pivotal for promoting sustainable chemistry and the construction of Cn molecular blocks. This work reports the nickel-catalyzed reduction of CO by magnesium alkyl compounds utilizing a bimetallic Mg/Ni synergistic strategy. The exposure of β-diketiminato ligand-supported magnesium monoalkyl compounds LMgR (L = [(DippNCMe)2CH]-, Dipp = 2,6-iPr2C6H3; R = nBu, CH3, C5H9) to 1 bar of CO in the presence of 10 mol% Ni(COD)2 (COD: 1,5-cyclooctadiene) selectively afforded the CO single-insertion product [LMg(CHO)C5H8], the dimerization product [(LMg)2(μ-C2O2)(CH3)2], and the linear trimerization product [(LMg)2(μ-C3O3)(nBu)2], respectively, depending on the R group.

Ligand-Directed Actinide Oxo-Bond Manipulation in Actinyl Thiacalix[4]arene Complexes.

Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO22+ is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An = U, Np, Pu). The thioether calixarene TC4A (4-tert-butyltetrathiacalix[4]arene) binds equatorially to [AnO2]n+ (An = U, Np) forming a conical pocket that differentiates the two trans-oxo groups. The 'ate' complexes, [A]2[UO2(TC4A)] (A = [Li(DME)2], HNEt3) and [HNEt3]2[NpO2(TC4A)], enable selective oxo chemistry.

Nucleophilic and Electrophilic Molybdenum Terminal Oxo Complexes by Coordination-Induced Bond Weakening of Hydroxo O-H Bonds.

The extent of coordination-induced bond weakening in aquo and hydroxo ligands bonded to a molybdenum(III) center complexed by a dianionic, pentadentate ligand system was probed by reacting the known complex (BPzPy)Mo(III)-NTf, , with degassed water or dry lithium hydroxide. The aquo adduct was not observed, but two LiNTf-stabilized hydroxo complexes were fully characterized. Computational and experimental work showed that the O-H bond in these complexes was significantly weakened (to ≈57 kcal mol), such that these compounds could be used to form the diamagnetic, neutral terminal molybdenum oxo complex (BPzPy)Mo(IV)O, , by hydrogen atom abstraction using the aryl oxyl reagent ArO• (Ar = 2,4,6-tri--butylphenyl).

Four-electron reduction of benzene by a samarium(II)-alkyl without the addition of external reducing agents.

Benzene reduction by molecular complexes remains an important synthetic challenge, requiring harsh reaction conditions involving group I metals. Reductions of benzene, to date, typically result in a loss of aromaticity, although the benzene tetra-anion, a 10π-electron system, has been calculated to be stable and aromatic. Due to the lack of sufficiently potent reductants, four-electron reduction of benzene usually requires the use of group I metals.

Multielectron Redox Chemistry of Ytterbium Complexes Reaching the +1 and Zero Formal Oxidation States.

Lanthanide redox reactivity remains limited to one-electron transfer reactions due to their inability to access a broad range of oxidation states. Here, we show that multielectron reductive chemistry is achieved for ytterbium by using the tripodal tris(siloxide)arene redox-active ligand, which can store two electrons in the arene anchor. Reduction of the Yb(III) complex of the tris(siloxide)arene tripodal ligand affords the Yb(II) analogue by metal-centered reduction.

Cerium(III) yldiide complexes with divergent CO reactivity.

Synthesis of cerium yldiide complexes and their reactivity with CO is demonstrated. In the case of the sulphur-tethered yldiide, the ketenyl complex is formed with release of PPh, while PhPCCO is formed along with a sulfinato ligand in the case of the tosyl-substituted yldiide. Computational analysis shows that this diverging reactivity is due to the stability of the two isomers in the first step of each mechanism.

Rare-earth metal complexes bearing electrophilic and nucleophilic carbon centres and their unique reactivity patterns towards pyridine derivatives.

The rare-earth metal dialkyl complexes (κ-L)RE(CHSiMe)·(THF) [RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e)] (L = 1-(2--CHNCHCH)-3-(2,6-PrCHN[double bond, length as m-dash]CH)-CHN) and the rare-earth metal monoalkyl complexes (κ-L)RE(CHSiMe)·(THF) [ = 0, RE = Lu(2a), Yb(2b); = 1, Er(2c), Y(2d), Dy(2e)], (κ-L)RE(CHSiMe)·THF [RE = Yb(3a), Er(3b), Y(3c), Dy(3d), Gd(3e)] (L = 1-(2--CHNCHCH)-3-(AdN[double bond, length as m-dash]CH)-CHN) (Ad = adamantyl, CH) have been synthesized and fully characterized. These complexes feature chelate ligands having a conjugated system (-C[double bond, length as m-dash]C-C[double bond, length as m-dash]N) with an sp carbon, which enables both electrophilic and nucleophilic carbon centres to be directly connected to the highly electrophilic rare-earth metal ions. The reactions of these complexes with different pyridine derivatives have been systematically investigated with the discovery of reactivity patterns distinct from those of previously reported transition metal complexes.

The photo-isomerization of the cyclononatetraenyl ligand and related rare earth complexes.

The cyclononatetraenyl (Cnt) ligand is a large monoanionic ligand. It is easily synthesized by ring expansion after cyclopropanation of the cyclooctatetraenyl (Cot) ligand. The Cnt ligand can be reported as the --- () isomer, where the aromatic ring is flat, and all carbon atoms form a homogenous ring, and as the --- () isomer, where one carbon places itself inside the ring.

Synthesis, Structure, and Bonding of Actinide-Rhenium Polyhydrides.

The synthesis of actinide tetrarhenate complexes completes a series of iridate, osmate, and rhenate polyhydrides, allowing for structural and bonding comparisons to be made. Computational studies examine the bonding interactions, particularly between metals, in these complexes. Several factors─including metal oxidation state, coordination number, and dispersion effects─affect metal-metal distances and covalency in these actinide tetrametallates.

Dinitrogen Reduction and Functionalization by a Siloxide Supported Thulium-Potassium Complex for the Formation of Ammonia or Hydrazine Derivatives.

The dinitrogen (N) chemistry of lanthanides remains less developed compared to the d-block metals and lanthanide-promoted N functionalization chemistry in well-defined lanthanide complexes remains elusive. Here we report the synthesis and characterization (SQUID, EPR, DFT, X-Ray) of the siloxide supported heterobimetallic (Tm/K) complexes [{KTm(OSi(OBu))}(μ-η : η-N)] (1) and [K{Tm(OSi(OBu))}(μ-η : η-N)] (2). Complex 2 provides a rare example of a metal complex of the triply reduced N radical.

Reduction of CS to an ethanetetrathiolate by a hydride-bridged uranium-iridium heterobimetallic complex.

We report the synthesis of a heterobimetallic U(III)-Ir species which reacts with CS to form the novel ethanetetrathiolate fragment hydride insertion and C-C coupling. Computational studies suggest the formation of a radical intermediate, which may couple with another equivalent to form the final product.

Homoleptic Organolanthanum-Catalyzed Carbohalogenation.

Metal-halogen exchange reactions are fundamental processes in chemistry that transform organic halides into organometallic reagents. However, using these reactions to build intricate structures in a cascade manner, especially in a catalytic mode, has been a challenge. In this study, we introduce a homoleptic organolanthanum catalyst to initiate lanthanum-halogen exchange and intramolecular carbohalogenation.

Multi-electron redox reactivity of a samarium(ii) hydrido complex.

Well-defined low-valent molecular rare-earth metal hydrides are rare, and limited to Yb and Eu centers. Here, we report the first example of the divalent samarium(ii) hydrido complex [(Cp)Sm(μ-H)(DABCO)] (4) (Cp = CAr, Ar = 3,5-Pr-CH; DABCO = 1,4-diazabicyclooctane) supported by a super-bulky penta-arylcyclopentadienyl ligand, resulting from the hydrogenolysis of the samarium(ii) alkyl complex [(Cp)Sm{CH(SiMe)}(DABCO)] (3). Complex 4 exhibits multi-electron redox reactivity toward a variety of substrates.

Synthesis, structure and redox properties of single-atom bridged diuranium complexes supported by aryloxides.

Single-atom (group 15 and group 16 anions) bridged dimetallic complexes of low oxidation state uranium provide a convenient route to implement multielectron transfer and promote magnetic communication in uranium chemistry, but remain extremely rare. Here we report the synthesis, redox and magnetic properties of N, O, and S bridged diuranium complexes supported by bulky aryloxide ligands. The U(IV)/U(IV) nitride [Cs(THF)][(U(OAr))(μ-N)], 1 could be prepared and characterized but could not be reduced.

CO cleavage by tantalum/M (M = iridium, osmium) heterobimetallic complexes.

A novel Ta/Os heterobimetallic complex, [Ta(CHBu)(μ-H)OsCp*], 2, is prepared by protonolysis of Ta(CHBu)(CHBu) with Cp*OsH. Treatment of 2 and its iridium analogue [Ta(CHBu)(μ-H)IrCp*], 1, with CO under mild conditions reveal the efficient cleavage of CO, driven by the formation of a tantalum oxo species in conjunction with CO transfer to the osmium or iridium fragments, to form Cp*Ir(CO)H and Cp*Os(CO)H, respectively. This bimetallic reactivity diverges from more classical CO insertion into metal-X (X = metal, hydride, alkyl) bonds.

Reductive Dimerization of Alkenes and Allenes Enabled by Photochemically Activated Zinc-Zinc Bonded Compounds.

Metal radicals have shown versatile reactivity in modern synthetic chemistry. However, the use of zinc radicals for molecular synthesis has been barely explored. Here, we show that a transient zinc radical can be formed through photoactivation of a zinc-zinc bonded compound, which is able to mediate the selective dimerization of alkenes and allenes.

Photolysis-driven bond activation by thorium and uranium tetraosmate polyhydride complexes.

Transition metal multimetallic complexes have seen intense study due to their unique bonding and potential for cooperative reactivity, but actinide-transition metal (An-TM) species are far less understood. We have synthesized uranium- and thorium-osmium heterometallic polyhydride complexes in order to study An-Os bonding and investigate the reactivity of An-Os interactions. Computational studies suggest the presence of a significant bonding interaction between the actinide center and the four coordinated osmium centers supported by bridging hydrides.

π-Bonding of Group 11 Metals to a Tantalum Alkylidyne Alkyl Complex Promotes Unusual Tautomerism to Bis-alkylidene and CO to Ketenyl Transformation.

A salt metathesis synthetic strategy is used to access rare tantalum/coinage metal (Cu, Ag, Au) heterobimetallic complexes. Specifically, complex [Li(THF)][Ta(CBu)(CHBu)], , reacts with (IPr)MCl (M = Cu, Ag, Au, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to afford the alkylidyne-bridged species [Ta(CHBu)(μ-CBu)M(IPr)] . Interestingly, π-bonding of group 11 metals to the Ta─C moiety promotes a rare alkylidyne alkyl to bis-alkylidene tautomerism, in which compounds are in equilibrium with [Ta(CHBu)(CHBu)(μ-CHBu)M(IPr)] .

Panoply of P: An Array of Rhenium-Phosphorus Complexes Generated from a Transition Metal Anion.

We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (, BDI = -bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate) to generate several rhenium-phosphorus complexes. Complex reacts in a metathetical manner with chlorophosphines PhPCl, NHP-Cl, and OHP-Cl to generate XL-type phosphido complexes , , and , respectively (NHP-Cl = 2-chloro-1,3-dimethyl-1,3,2-diazaphospholidine; OHP-Cl = 2-chloro-1,3,2-dioxaphospholane). Crystallographic and computational investigations of phosphido triad , , and reveal that increasing the electronegativity of the phosphorus substituent (C < < O) results in a shortening and strengthening of the rhenium-phosphorus bond.

Hydrogenolysis of Cationic Half-Sandwich Zinc Complexes Containing a Chelating Amine: Facile Cleavage of Zinc-Carbon Bond by Dihydrogen to Give Zinc Hydride Cations.

Cationic half-sandwich zinc complexes containing chelating amines [Cp*Zn(L)][BAr ] (2 a, Cp*=η-CMe, L=N,N,N',N'-tetramethylethylenediamine, TMEDA; 2 b, L=N,N,N',N'-tetraethylethylenediamine, TEEDA; 2 c, Cp*=η-CMe, L=N,N,N',N'',N''-pentamethyldiethylenetriamine, PMDTA; Ar =(3,5-(CF)CH)) reacted with dihydrogen (ca. 2 bar) in THF at 80 °C to give molecular zinc hydride cations [(L)ZnH(thf)][BAr ] (3 a,b, m=1; 3 c, m=0) previously reported along with Cp*H. Pseudo first-order kinetics with respect to the concentration of 2 b suggests heterolytic cleavage of dihydrogen by the Zn-Cp* bond, reminiscent of σ-bond metathesis.

Iron promoted end-on dinitrogen-bridging in heterobimetallic complexes of uranium and lanthanides.

End-on binding of dinitrogen to low valent metal centres is common in transition metal chemistry but remains extremely rare in f-elements chemistry. In particular, heterobimetallic end-on N bridged complexes of lanthanides are unprecedented despite their potential relevance in catalytic reduction of dinitrogen. Here we report the synthesis and characterization of a series of N bridged heterobimetallic complexes of U(iii), Ln(iii) and Ln(ii) which were prepared by reacting the Fe dinitrogen complex [Fe(depe)(N)] (depe = 1,2-bis(diethylphosphino)-ethane), complex A with [M{N(SiMe)}] (M = U, Ce, Sm, Dy, Tm) and [Ln{N(SiMe)}], (Ln = Sm, Yb).