Search

Herein we report the first catalytic decarbonylation and decarbonylative hydroamination of formamides without using additives enabled by a redox-neutral rare earth catalyst. The protocol displays complete

Cyclobutadienyl complexes of the f-elements are a relatively new yet poorly understood class of sandwich and half-sandwich organometallic compounds. We now describe cyclobutadienyl transfer reactions of the magnesium reagent [(η4-Cb'''')Mg(THF)3] (1), where Cb'''' is tetrakis(trimethylsilyl)cyclobutadienyl, toward thorium(IV) and uranium(IV) tetrachlorides. The 1:1 stoichiometric reactions between 1 and AnCl4 proceed with intact transfer of Cb'''' to give the half-sandwich complexes [(η4-Cb'''')AnCl(μ-Cl)3Mg(THF)3] (An = Th, 2; An = U, 3). Using a 2:1 reaction stoichiometry produces [Mg2Cl3(THF)6][(η4-Cb'''')An(η3-C4H(SiMe3)3-κ-(CH2SiMe2)(Cl)] (An = Th, [Mg2Cl3(THF)6][4]; An = U [Mg2Cl3(THF)6][5]), in which one Cb'''' ligand has undergone cyclometalation of a trimethylsilyl group, resulting in the formation of an An–C σ-bond, protonation of the four-membered ring, and an η3-allylic interaction with the actinide. Complex solution-phase dynamics are observed with multinuclear nuclear magnetic resonance spectroscopy for both sandwich complexes. A computational analysis of the reaction mechanism leading to the formation of 4 and 5 indicates that the cyclobutadienyl ligands undergo C–H activation across the actinide center.

The activation of dinitrogen (N2) by transition metals is central to the highly energy intensive, heterogenous Haber-Bosch process. Considerable progress has been made towards more sustainable homogeneous activations of N2 with d- and f-block metals, though little success has been had with main group metals. Here we report that the reduction of a bulky magnesium(II) amide [(TCHPNON)Mg] (TCHPNON = 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) with 5% w/w K/KI yields the magnesium-N2 complex [{K(TCHPNON)Mg}2(-N2)]. DFT calculations and experimental data show that the dinitrogen unit in the complex has been reduced to the N22- dianion, via a transient anionic magnesium(I) radical. The compound readily reductively activates CO, H2 and C2H4, in reactions in which it acts as a masked dimagnesium(I) diradical.

The uranyl complexes UO2(OAc)(L) and UO2Cl(L) of the redox-active, acyclic diamido–dipyrrin anion L– are reported and their redox properties explored. Because of the inert nature of the complexes toward hydrolysis and oxidation, synthesis of both the ligands and complexes was conducted under ambient conditions. Voltammetric, electron paramagnetic resonance spectroscopy, and density functional theory studies show that one-electron chemical reduction by the reagent CoCp2 leads to the formation of a dipyrrin radical for both complexes [Cp2Co][UO2(OAc)(L•)] and [Cp2Co][UO2Cl(L•)].

Reduction of a range of amido- and aryloxy-aluminum dihydride complexes, e.g. [AlH2(NR3){N(SiMe3)2}] (NR3 = NMe3 or N-methylpiperidine (NMP)), with -diketiminato dimagnesium(I) reagents, [{(ArNacnac)Mg}2] (ArNacnac = [HC(MeCNAr)2]-, Ar = mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al6H8(NR3)2{Mg(ArNacnac)}4], which have an average Al oxidation state of +0.66, the lowest for any well-defined aluminum hydride compound. In the solid-state, the clusters are shown to have distorted octahedral Al6 cores, having zero-valent Al axial sites and mono-valent AlH2- equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the Mg‒Al bonded magnesio-aluminate complexes, [(ArNacnac)(Me3N)Mg‒Al(-H)3[{Mg(ArNacnac)}2(-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals.

Reduction of a range of amido- and aryloxy-aluminum dihydride complexes, e.g. [AlH2(NR3){N(SiMe3)2}] (NR3 = NMe3 or N-methylpiperidine (NMP)), with -diketiminato dimagnesium(I) reagents, [{(ArNacnac)Mg}2] (ArNacnac = [HC(MeCNAr)2]-, Ar = mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al6H8(NR3)2{Mg(ArNacnac)}4], which have an average Al oxidation state of +0.66, the lowest for any well-defined aluminum hydride compound. In the solid-state, the clusters are shown to have distorted octahedral Al6 cores, having zero-valent Al axial sites and mono-valent AlH2- equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the Mg‒Al bonded magnesio-aluminate complexes, [(ArNacnac)(Me3N)Mg‒Al(-H)3[{Mg(ArNacnac)}2(-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals.

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}(C4O4){-Mg(DipNacnac)}]2, and magnesium metallo-ketene products, [{(DipNacnac)Mg}{-(C4O4)Mo(CO)5}{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}{-(C4O4)Mo(CO)5}{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}(C4O4){-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.

The tetrapyralzolylpyridyl diborate pentadentate ligand B2Pz4Py has been complexed to Ti(III) to form the chloro complex (B2Pz4Py)Ti(III)Cl, which is a convenient starting material for preparing alkyl and hydride derivatives of this ligand. The former (R = CH3 and CH2SiMe3) are highly thermally stable and do not react with dihydrogen to form (B2Pz4Py)Ti(III)H. Rather, treatment of the chloro starting material with NaHBEt3 affords the desired hydrido complex in 85% yield. This Ti(III) hydride was fully characterized and exists in both solution and the solid state as a dimeric species; dissociation into monomers faces a high barrier of over 40 kcal/mol, according to Density Function Theory computations. This is due to stabilization of the dimer by dispersion forces. The computations show that the dimer has an S = 1 ground state, but in solution, partial dissociation into an intermediate dimer which is an open shell singlet is possible, which accounts for the lower than expected magnetic susceptibility of 1.93 per dimer. Full dissociation into reactive monomers does not occur, based on the observed lack of reactivity with carbon dioxide. All of these com-pounds react with water to form a mu-oxo dinuclear species, which reacts further with dioxygen to form oxidized peroxo and oxo Ti(IV) complexes. All three of these compounds were fully characterized.

An extremely bulky xanthene bridged diamide ligand (TCHPNON = 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) has been developed and used to prepare two monomeric diamido-calcium complexes [(TCHPNON)Ca(D)n] (D = THF, n = 2, 3; D = toluene, n = 1, 4). Reduction of 4 with 5% w/w K/KI under an N2 atmosphere gave the first well-defined, anionic s-block complex of activated dinitrogen, [{K(TCHPNON)Ca}2(-2:2-N2)] 5, presumably via a transient calcium(I) intermediate.

International audience; An investigation of the formation of a thorium phosphinidiide reveals that changing from a 2,4,6-(Pr3C6H2)-Pr-i (Tipp)-substituted phosphido ligand to a 2,4,6-Me3C6H2 (Mes) ligand forms a similar product, [(C5Me5)(2)Th](2)(P-2,6-CH2C6H2-4-CH3), but via a different sequence of bond activations. The resulting phosphinidiide was reacted with 1 and 2 equiv of (BuCN)-Bu-t, leading to mono(ketimide), [(C5Me5)(2)Th](2)[mu(2)-P-(2-CH2-6-(N=C(Bu-t)(CH2))-4-Me-C6H2)], and bis(ketimide), [(C5Me5)(2)Th](2)[mu(2)-P-(2-CH2-6-(N=C(Bu-t)(CH2))-4-Me-C6H2)], complexes, respectively, through insertion into the thorium- carbon bonds. An analysis of the Th-P-Th moiety showed a correlation of decreased Th-P-Th bond angle and upheld P-31 NMR chemical shift with decreasing Th-P covalent bond character.

International audience; Calcium is an abundant, biocompatible, and environmentally friendly element. The use of organocalcium complexes as catalysts in organic synthesis has had some breakthroughs recently, but the reported reaction types remain limited. On the other hand, hydrosilanes are highly important reagents in organic and polymer syntheses, and redistribution of hydrosilanes through C-Si and SiH bond cleavage and reformation provides a straightforward strategy to diversify the scope of such compounds. Herein, we report the synthesis and structural characterization of two calcium alkyl complexes supported by beta-diketiminato-based tetradentate ligands. These two calcium alkyl complexes react with PhSiH3 to generate calcium hydrido complexes, and the stability of the hydrido complexes depends on the supporting ligands. One calcium alkyl complex efficiently catalyzes the selective redistribution of ArSiH3 or Ar(alkyl)SiH2 to Ar3SiH and SiH4 or Ar-2(alkyl)SiH and alkylSiH(3), respectively. More significantly, this calcium alkyl complex also catalyzes the cross-coupling between the electron-withdrawing substituted Ar(R)SiH2 and the electron-donating substituted Ar'(R)SiH2, producing ArAr'(alkyl)SiH in good yields. The synthesized ArAr'(alkyl)SiH can be readily transferred to other organosilicon compounds such as ArAr'(alkyl)SiX (where X = OH, OEt, NEt2, and CH2SiMe3). DFT investigations are carried out to shed light on the mechanistic aspects of the redistribution of Ph(Me)SiH2 to Ph-2(Me)SiH and reveal the low activation barriers (17-19 kcal/mol) in the catalytic reaction.

International audience; Treatment of the U(III) complex, [(C5Me5)(2)U(OMes)(THF)], Mes = 2,4,6-Me3C6H2, with Fe(CO)(5) forms [{(C5Me5)(2)(MesO)U}(2)(mu(2)-(OC)(2)Fe(CO)(2))] with the bridging, tetrahedral Fe(CO)(4) moiety. This complex has been studied using H-1 NMR, IR vibrational, UV-vis electronic absorption, and zero-field Fe-57 Mossbauer spectroscopy as well as single-crystal X-ray diffraction analysis, magnetic measurements, and DFT calculations.

International audience; Although a series of complexes with rare earth (RE) metal-metal bonds have been reported, complexes which have multiple RE-Rh bonds are unknown. Here we present the identification of the first example of a molecule containing multiple RE-Rh bonds. The complex with multiple Ce-Rh bonds was synthesized by the reduction of a d-f heterometallic molecular cluster Ce{N[((CH2CH2NPPr2)-Pr-i)RhCl(COD)](3)} with excess potassium-graphite. The oxidation state of Ce in 3a appears to be a mixture of Ce(III) and Ce(IV), which was confirmed by X-ray photoelectron spectroscopy, magnetism, and theoretical investigations (DFT and CASSCF). For comparison, the analogous species with multiple La(III)-Rh and Nd(III)-Rh bonds were also constructed. This study provides a possible route for the construction of complexes with multiple RE metal-metal bonds and an investigation of their potential properties and applications.

International audience; Reactions of the hindered N-heterocyclic carbene, :C{(MesNCH)(2)} (IMes; Mes = mesityl), with a series of beta-diketiminatomagnesium(II) hydride and dimagnesium(I) complexes were carried out at 80 degrees C. The reactions involving the magnesium hydrides, [{((Ar)Nacnac)Mg(mu-H)}(2)] [(Ar)Nacnac = [(ArNCMe)(2)CH](-), where Ar = 2,6-diethylphenyl (Dep) or 2,6-diisopropylphenyl (Dip)], proceeded via activation of an exocyclic C-N bond of IMes, giving magnesium imidazolyl compounds [((Ar)Nacnac)Mg(mu-H)(mu-Imid)Mg((Ar)Nacnac)] (Imid = [NC2H2N-(Mes)C](-)) and mesitylene. A low-yield IMes methyl C-H activation product, [((Dep)Nacnac)Mg(IMes(-H))], was also obtained, via H-2 elimination, from the reaction between IMes and [{((Dep)Nacnac)Mg(mu-H)}(2)]. Reactions between IMes and dimagnesium(I) compounds [{((Ar)Nacnac)Mg}(2)] [Ar = 2,6-dimethylphenyl (Xyl) or Mes] afforded isostructural C-H activation products [((Ar)Nacnac)Mg(IMes(-H))] but in higher yields. Density functional theory calculations suggest that the reactions do not progress via stable adduct complex intermediates, which are sterically inaccessible.

International audience; Since the precise understanding of the underlying mechanism is important for the rational design of catalysts, much attention has been paid for hydroamination reactions catalyzed by organolanthanides during the past three decades. Distinct mechanisms were proposed on the basis of some key experimental features. It is a challenge to distinguish these mechanisms. The present study focuses on this controversial topic by synthesizing an almost entire range of rare-earth metal bisalkyl complexes (Py-CH2-Flu)Ln(CH2SiMe3)(2)(THF)(x) (Ln = Sc (1), Lu (2), Tm (3), Er (4), Ho (5), Y (6), Dy (7), Tb (8), Gd (9), and Pr (10)) stablized by a pyridine methylene fluorenyl ligand to catalyze intramolecular hydroamination (IAHA) of prototypical 1-amino-2,2-diphenyl-4-pentene and intermolecular hydroamination (IEHA) of styrene and pyrrolidine. Among them, thulium-, terbium-, and gadolinium-based catalysts were investigated for the first time. As observed for all the reported catalytic systems, the rate of IAHA increased almost linearly with increasing metal ion radius, whereas the reactivity pattern in IEHA with respect to the ionic radius size follows the opposite trend. Kinetic studies were carried out to obtain the empirical rate law v = k[Ln](1.0)[S](0.0) for IAHA and v = k[Ln](1.0)[St](1.0)[pyrrolidine](0.0) for IEHA. The zero-order dependence on amine was attributed to the population ratio between the rare-earth metal amido adduct and its precursor being larger than 10(4). Density functional theory studies on scandium, yttrium, and praseodymium complex-mediated IAHA and IEHA were investigated using a stepwise sigma-insertive mechanism and a concerted noninsertive mechanism, respectively. The results suggested the prevailing mechanism to be a stepwise sigma-insertive pathway that involves the insertion of C=C into the Ln-N bond and protonolysis of the Ln-C bond. The protonolysis reaction is the turnover-limiting step. The reason behind the influence of the metal ion radius on the catalytic activity was elucidated.

International audience; The first isolation and structural characterization of a rare-earth metal-terminal imido complex were reported in 2010, but a rare-earth metal-terminal phosphinidene complex is still absent, to date. Herein, we report the synthesis and structure of the first example of a rare-earth-terminal phosphinidene complex, namely the scandium boronylphosphinidene complex. Single-crystal X-ray diffraction shows that the complex has a much shorter Sc-P bond length as compared to that in a related scandium boronylphosphido complex, 2.381(1) angstrom vs 2.564(1) angstrom. DFT calculations indicate the presence of a strong Sc-P pi interaction in this complex, which is in striking contrast to the weak interaction found in the phosphido complex. A preliminary reactivity study demonstrates that the scandium-terminal boronylphosphinidene complex behaves as a nucleophilic phosphinidene complex.

The reduction of U(VI) to U(IV) is rare, especially in one step, and not observed electrochemically as a one-wave, two-electron couple. Here, we demonstrate that reduction of the uranium(VI) bis(imido) complex, (C5Me5)2U[═N(4-OiPrC6H4)]2, is readily accomplished with Al(C5Me5), forming the bridging uranium(IV)/aluminum(III) imido complex (C5Me5)2U[μ2-N(4-OiPrC6H4)]2Al(C5Me5). The structure and bonding of the bridging imido complex is examined with electrochemical measurements in tandem with density functional theory calculations.

A study of the comparative reactivity of CO, CO2, tBuCN, and tBuNC with (C5Me5)2An[P(H)Mes]2 (An = Th, U) has been undertaken. While CO2 and tBuNC form identical products with both metals, namely (...

Out of the 14 lanthanide (Ln) ions, molecular complexes of Ln(IV) were known only for cerium and more recently terbium. Here we demonstrate that the +IV oxidation state is also accessible for the large praseodymium (Pr) cation. The oxidation of the tetrakis(triphenysiloxide) Pr(III) ate complex, [KPr(OSiPh3)(4)(THF)(3)], 1-Pr-Ph, with [N(C6H4Br)(3)][SbCl6], affords the Pr(IV) complex [Pr(OSiPh3)(4)(MeCN)(2)], 2-Pr-Ph, which is stable once isolated. The solid state structure, UV-visible spectroscopy, magnetometry, and cyclic voltammetry data along with the DFT computations of the 2-Pr-Ph complex unambiguously confirm the presence of Pr(IV).

Ammonia oxidation catalyzed by molecular compounds is of current interest as a carbon free source of dihydrogen. Activation of N-H bonds through coordination to transition metal centers is a key reaction in this process. We report the substantial activation of ammonia through via reaction with low valent Mo complexes of a diborate pentadentate ligand system. Spontaneous loss of hydrogen atoms from (B2Pz4Py)Mo(II)-NH3 at room temperature to produce H2 and the dinuclear -nitrido compound (B2Pz4Py)Mo-N-Mo(B2Pz4Py) is observed due to substantial N-H bond weakening upon coordination to Mo. Mechanistic details are supported through the experimental observation characterization of terminal amido, imido and nitrido complexes and density functional theory computations. The generally under-appreciated role of bridging nitrido intermediates is revealed and discussed, providing guidance for further catalyst development for this process.

International audience; An alternative synthesis for M(κ2-bipy)4 (M = La, Ce) and [Li(thf)4][M(κ2-bipy)4] (M = Tb, Dy) and the crystal structures for M = La, Ce, and Tb are described. The isomorphous and isostructural neutral molecules, M = La and Ce, are polymeric in the solid-state, as are those of M = Sm and Eu, which were reported in earlier work. The polymeric network is built from eight coordinate units whose geometry in all four cases is that of a square prism. The known molecules, M = Yb and Lu, are also polymeric, but the eight coordinate units have dodecahedral geometries. The structure of the anions in the separated ion pair, [Li(thf)4][M(κ2-bipy)4], in which Tb is reported in this work and Lu is known, are monomeric with geometries that are between that of a square antiprism and a dodecahdron. The electronic structure, from CASSCF multireference quantum mechanical calculations, shows that the electronic ground states for M = La and Lu are multiconfigurational spin doublets and those for the M = Ce and Yb are multiconfigurational spin triplets. This is confirmed by magnetic susceptibility studies as a function of temperature that are consistent with the metals (La, Ce, Sm, Tb, Dy, Yb, and Lu) being trivalent, as are the LIII-edge XANES spectra (Ce, Yb), and divalent for Eu. The multiconfigurational nature of the ground states, developed from CASSCF molecular orbital calculations, renders a single Lewis structure and a single reference molecular orbital representation misleading. The results from the multireference calculations are extended to the other lanthanide molecules and are the genesis of a new model for understanding the magnetic properties of these molecules.

International audience; A series of Ln(II) and Ca(II) bis(alkyl) complexes with bulky benzhydryl ligands, [(p-tBu-C6H4)(2)-CH](2)M(L-n) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI2(THF)(n) (n = 0-2) and [(p-tBu-C6H4)(2)CH]Na--(+). In complex 1, the benzhydryl ligands are bound to the metal center in eta(2)-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in eta(3)-fashion. In complex 2, one ligand is eta(3)-coordinated while the second one is eta(4)-coordinated to the Sm(II) ion. Complexes 2-4 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C6D6 at 100 degrees C during 72 h. Complex 1 behaves differently: thermolysis in C6D6 solution at 75 degrees C results in total decomposition in 8 h. Addition of DME promotes decomposition of 2-4 and makes it feasible at 40 degrees C. Complexes 1-4 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C-C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH2 toward the internal C=C bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph2PH and PhPH2 was realized due to the application of Yb(II) complex as a catalyst.

A new monoanionic pentadentate ligand is designed to accommodate Sc=E bonds (E = N, P). The imido complex is stable enough to isolate and characterize, and reacts rapidly with CO2. The phosphinidene, on the other hand, is highly reactive and induces C-C bond cleavage to yield a phosphido-pyridyl complex which also undergoes rapid reacton with CO2.

Reactions of two magnesium(I) compounds, [{(Ar Nacnac)Mg}2 ] (Ar Nacnac=[HC(MeCNAr)2 ]- ; Ar=mesityl (Mes) or o-xylyl (Xyl)), with CO in the presence of [Mo(CO)6 ] lead to the reductive hexamerization of CO, and formation of magnesium benzenehexolate complexes, [{(Ar Nacnac)Mg}6 (C6 O6 )]. [Mo(CO)6 ] is not consumed in these reactions, but is apparently required to initiate (or catalyze) the CO hexamerizations. A range of studies were used to probe the mechanism of formation of the benzenehexolate complexes. The magnesium(I) reductive hexamerizations of CO are closely related to Liebig's reduction of CO with molten potassium (to give K6 C6 O6 , amongst other products), originally reported in 1834. As the mechanism of that reaction is still unknown, it seems reasonable that magnesium(I) reductions of CO could prove useful homogeneous models for its elucidation, and for the study of other C-C bond forming reactions that use CO as a C1 feedstock (e.g. the Fischer-Tropsch process).

International audience; We report the results of Born-Oppenheimer molecular dynamics (BOMD) simulations on the aqueous solvation of the SmI3 molecule and of the bare Sm3+ cation at room temperature using the cluster microsolvation approach including 37 and 29 water molecules, respectively. The electronic structure calculations were done using the M062X hybrid exchange-correlation functional in conjunction with the 6-31G** basis sets for oxygen and hydrogen. For the iodine and samarium atoms, the Stuttgart-Koln relativistic effective-core potentials were utilized with their associated valence basis sets. When SmI3 is embedded in the microsolvation environment, we find that substitution of the iodine ions by water molecules around Sm(III) cannot be achieved due to an insufficient number of explicit water molecules to fully solvate the four separate metal and halogen ions. Therefore, we studied the solvation dynamics of the bare Sm3+ cation with a 29-water molecule model cluster. Through the Sm-O radial distribution function and the evolution of the Sm-O distances, the present study yields a very tightly bound first rigid Sm(III) solvation shell from 2.3 to 2.9 angstrom whose integration leads to a coordination number of 9 water molecules and a second softer solvation sphere from 3.9 to 5 angstrom with 12 water molecules. No water exchange processes were found. The theoretical EXAFS spectrum is in excellent agreement with the experimental spectrum for Sm(III) in liquid water. The strong differences between the solvation patterns of Sm(III) vs Sm(II) are discussed in detail.

The base-free divalent samarium complex Cptt2Sm (1; Cptt = 1,3-(tBu)2(C5H3)) has been synthesized in diethyl ether by salt metathesis of SmI2. Crystals of 1 suitable for X-ray study have been obtained by sublimation at 116 °C under reduced pressure. The dissolution of 1 in thf and pyridine solution leads to the solvent adducts Cptt2Sm(thf)2 (3) and Cptt2Sm(py) (4), respectively, while drying 3 under reduced pressure yields CpttSm(thf) (5). The reaction of CO2 with the base-free divalent samarium complexes Cptt2Sm (1) and Cpttt2Sm (2; Cpttt =1,2,4-(tBu)3(C5H2)) leads to the clean formation of bridged carbonate samarium dimers [Cpttt2Sm]2(μ-CO3) (7) and [Cptt2Sm]2(μ-CO3) (8). This is indicative of the reductive disproportionation of CO2 in both cases with release of CO. This contrasts with the formation of the oxalate-bridged samarium dimer reported from the reaction of CO2 with the Cp*2Sm(thf)2 complex. Otherwise, the reaction with CO does not proceed with the bulky complexes, while traces of O2 have led t...

Reaction of the trivalent uranium complex [((Ad,MeArO)3N)U(DME)] with [Na(OCP)(dioxane)2.5] and 2.2.2-crypt yields the μ-oxo-bridged, diuranium complex [Na(2.2.2-crypt)][{((Ad,MeArO)3N)U(DME)}(μ-O){((Ad,MeArO)3N)U(CP)}] (1). Complex 1 features an asymmetric, dinuclear UIV–O–UIV core structure with a cyaphide (CP–) anion η1-CP bound to one of the U ions, and a κ2-O DME coordinated to the other. The CP– ligand is unprecedented in uranium chemistry and is formed through reductive C–O bond cleavage of the phosphaethynolate anion (OCP–). An analogous reaction was performed starting from the tetravalent uranium halide complex [((Ad,MeArO)3N)U(DME)(Cl)]. This salt metathesis approach with [Na(OCP)(dioxane)2.5] results in formation of the mononuclear complex [((Ad,MeArO)3N)U(DME)(OCP)] (2) with an OCP– anion bound to the uranium(IV) center via the oxygen atom in an η1-OCP fashion.

A new type of synthesis, referred to as oxidative methylation, is developed for [Cp*2Yb]2(μ-X) and [Cp*2Yb]2(μ-X)(X), where X = Me, using MeCu or Cp*2VMe as the methyl transfer reagent and Cp*2Yb. The synthetic methodology is extended to other X derivatives such as the halides and BH4. Reaction of [Cp*2Yb]2(μ-Me)(Me) and H2 yields the mixed-valent hydride [Cp*2Yb]2(μ-H), which eliminates H2 on gentle heating, forming Cp*2Yb. When Cp*2VX is replaced by Cp*2TiX, 1:1 adducts based upon Ti(III,d1) are isolated. The X-ray crystal structure of [Cp*2Yb](μ-Me)[TiCp*2] shows that the methyl group bridges the two different decamethylmetallocene fragments in a near-linear fashion, a geometry that is likely to resemble the transition state of the single-electron-transfer precursor complex. A CASSCF computational study on the mixed-valent hydride [Cp*2Yb]2(μ-H) shows that the ground state is a spin doublet in which the hydride forms a symmetric bridge to both Yb atoms. The three spins forming the ground-state doublet ...

bibtex: ISI:000398986700049 bibtex\location:'1155 16TH ST, NW, WASHINGTON, DC 20036 USA',publisher:'AMER CHEMICAL SOC',type:'Article',affiliation:'Martin-Vaca, B; Bourissou, D (Reprint Author), Univ Toulouse, CNRS, UMR 5069, UPS,LHFA, 118 Route Narbonne, F-31062 Toulouse, France. Brunel, Paul; Monot, Julien; Martin-Vaca, Blanca; Bourissou, Didier, Univ Toulouse, CNRS, UMR 5069, UPS,LHFA, 118 Route Narbonne, F-31062 Toulouse, France. Kefalidis, Christos E.; Maron, Laurent, Univ Toulouse, CNRS, UMR 5215, INSA,UPS,LPCNO, 135 Ave Rangueil, F-31400 Toulouse, France.','author-email':'bmv@chimie.ups-tlse.fr dbouriss@chimie.ups-tlse.fr',da:'2018-12-05','doc-delivery-number':'ER7IS','funding-acknowledgement':'Centre National de la Recherche Scientifique; Universite de Toulouse; Agence Nationale de la Recherche [ANR CE6-CYCLOOP]; COST Action [CM1205 CARISMA]','funding-text':'This manuscript is in memory of Prof. Jose Barluenga. This work was supported financially by the Centre National de la Recherche Scientifique, the Universite de Toulouse, the Agence Nationale de la Recherche (ANR CE6-CYCLOOP), and the COST Action CM1205 CARISMA (Catalytic Routines for Small Molecule Activation). The authors are grateful to CalMip (CNRS, Toulouse, France) for calculation facilities. L.M. thanks the Institut Universitaire de France. Dr. J. Babinot is acknowledged for the preparation of substrates 1j,k.','journal-iso':'ACS Catal.','keywords-plus':'PALLADIUM PINCER COMPLEXES; CARBON-DIOXIDE INCORPORATION; N BOND FORMATION; CARBOXYLATIVE CYCLIZATION; EFFICIENT SYNTHESIS; PROPARGYLIC AMINES; ACETYLENIC AMINES; ATMOSPHERIC CO2; C-N; IONIC LIQUIDS','number-of-cited-references':'73',oa:'Bronze','orcid-numbers':'Kefalidis, Christos/0000-0002-1380-4337 Bourissou, Didier/0000-0002-0249-1769','research-areas':'Chemistry','researcherid-numbers':'Kefalidis, Christos/G-1067-2012','times-cited':'19','unique-id':'ISI:000398986700049','usage-count-last-180-days':'10','usage-count-since-2013':'32','web-of-science-categories':'Chemistry, Physical'\; International audience; The capture and utilization of CO, to prepare high value compounds is very attractive chemically and highly desirable socially. Indenediide-based Pd SCS pincer complexes are shown here to promote the carboxylative cyclization of propargylamines leading to 2-oxazolidinones under mild conditions (0.5-1 bar of CO2, DMSO, 40-80 degrees C, mol % Pd loading). The indenediide Pd complex is competitive with known catalysts. It proved successful for a wide range of propargylamines, including hitherto challenging substrates such as secondary propargylamines bearing tertiary alkyl groups at nitrogen, primary propargylamines, and propargylanilines. Thorough experimental (NMR) and computational (DFT) investigations were undertaken to gain mechanistic insights. Accordingly, (i) the resting state of the catalytic cycle is a Pd DMSO complex; (ii) the indenediide backbone and Pd center act in concert to activate the carbamic acid intermediate and promote its cyclization; (iii) proton shuttling is essential to lower the activation barriers of the initial amine carboxylation as well as of the proton transfers between the ligand backbone and the organic fragments at Pd.

Reaction of trivalent [((Ad,tBuArO)3tacn)U] (1) with 2,2′-bipyridine (bipy) yields [((Ad,tBuArO)3tacn)U(bipy)] (2) and subsequent reduction of 2 with KC8 in the presence of Kryptofix222 furnishes [K(2.2.2-crypt)][((Ad,tBuArO)3tacn)U(bipy)] (3). Alternatively, complex 3 can be synthesized from 1 by addition of [K(bipy)] in the presence of the cryptand. New complexes 2 and 3 are characterized by a variety of spectroscopic, electrochemical, and magnetochemical methods, single-crystal X-ray diffraction, computational methods, and CHN elemental analysis. Structural analyses reveal a bipyridine radical (bipy•–) ligand in 2 and a dianionic (bipy2–) species in 3. Complex 3 represents a rare example of an isolated and unambiguously characterized bipy2– ligand coordinated to a uranium ion. The electronic structure assignments are supported by UV/vis/NIR and EPR spectroscopy, as well as SQUID magnetometry. The results of CASSCF calculations indicate multiconfigurational ground states for complexes 2 and 3. The elect...

The first scandium phosphinoalkylidene complex was synthesized and structurally characterized. The complex has the shortest Sc–C bond lengths reported to date (2.089(3) A). DFT calculations reveal the presence of a three center π interaction in the complex. This scandium phosphinoalkylidene complex undergoes intermolecular C–H bond activation of pyridine, 4-dimethylamino pyridine and 1,3-dimethylpyrazole at room temperature. Furthermore, the complex rapidly activates H2 under mild conditions. DFT calculations also demonstrate that the C–H activation of 1,3-dimethylpyrazole is selective for thermodynamic reasons and the relatively slow reaction is due to the need of fully breaking the chelating effect of the phosphino group to undergo the reaction whereas this is not the case for H2.

Two synthetic approaches to the new three-decker Yb(II) complex [CpBn5Yb(DME)]2[μ-C10H8] (1) were successfully employed: the reaction of [CpBn5Yb(DME)(μ-I)]2 (2) with 2 molar equiv of [C10H8]−·K in DME and the reaction of [YbI(DME)2]2[μ-C10H8] (3) with CpBn5K in a 1:2 molar ratio in DME. Complex 1 was proved to be a Yb(II) binuclear triple-decker complex containing a dianionic naphthalene ligand bridging two CpBn5Yb(DME) fragments in a μ-η4:η4 fashion. An oxidative substitution of (C10H8)2– by trans-(1E,3E)-1,4-diphenylbuta-1,3-diene afforded the three-decker Yb(II) complex [CpBn5Yb(DME)]2(μ-η4:η4 -PhCHCHCHCHPh) (4) with a dianionic μ-η4:η4-bridging diphenylbutadiene ligand and naphthalene. The reaction of 1 with excess P4 also occurs with oxidation of (C10H8)2–, whereas Yb remains divalent. The reaction results in the formation of the trinuclear Yb(II) complex with a μ-bridging P73– ligand [CpBn5Yb(DME)]3(P7) (5). Protonation of the Yb–C10H8 bond in 1 with PhPH2 (1:2 molar ratio) afforded the dimeric pho...

International audience; Lu[CH(SiMe3)2]3 reacts with [SiO2-700] to give [(≡SiO)Lu[CH(SiMe3)2]2] and CH2(SiMe3)2. [(≡SiO)Lu[CH(SiMe3)2]2] is characterized by solid-state NMR and EXAFS spectroscopy, which show that secondary Lu···C and Lu···O interactions, involving a γ-CH3 and a siloxane bridge, are present. From X-ray crystallographic analysis, the molecular analogues Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 0-2) also have secondary Lu···C interactions. The (1)H NMR spectrum of Lu[CH(SiMe3)2]3 shows that the -SiMe3 groups are equivalent to -125 °C and inequivalent below that temperature, ΔG(⧧)(Tc = 148 K) = 7.1 kcal mol(-1). Both -SiMe3 groups in Lu[CH(SiMe3)2]3 have (1)JCH = 117 ± 1 Hz at -140 °C. The solid-state (13)C CPMAS NMR spectrum at 20 °C shows three chemically inequivalent resonances in the area ratio of 4:1:1 (12:3:3); the J-resolved spectra for each resonance give (1)JCH = 117 ± 2 Hz. The (29)Si CPMAS NMR spectrum shows two chemically inequivalent resonances with different values of chemical shift anisotropy. Similar observations are obtained for Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 1 and 2). The spectroscopic data point to short Lu···Cγ contacts corresponding to 3c-2e Lu···Cγ-Siβ interactions, which are supported by DFT calculations. Calculated natural bond orbital (NBO) charges show that Cγ carries a negative charge, while Lu, Hγ, and Siβ carry positive charges; as the number of O-based ligands increases so does the positive charge at Lu, which in turns shortens the Lu···Cγ distance. The change in NBO charges and the resulting changes in the spectroscopic and crystallographic properties show how ligands and surface-support sites rearrange to accommodate these changes, consistent with Pauling's electroneutrality concept.

bibtex: ISI:000414820100007 bibtex\location:'1155 16TH ST, NW, WASHINGTON, DC 20036 USA',publisher:'AMER CHEMICAL SOC',type:'Article',affiliation:'Albrecht-Schmitt, TE (Reprint Author), Florida State Univ, Dept Chem & Biochem, Tallahassee, FL 32306 USA. Galley, Shane S.; Van Alstine, Cayla E.; Albrecht-Schmitt, Thomas E., Florida State Univ, Dept Chem & Biochem, Tallahassee, FL 32306 USA. Maron, Laurent, Inst Natl Sci Appl, Lab Phys & Chim Nanoobjets, F-31077 Toulouse 4, France.','author-email':'albrecht-schmitt@chem.fsu.edu',da:'2018-12-05','doc-delivery-number':'FM2MY',eissn:'1520-510X','funding-acknowledgement':'Center for Actinide Science and Technology, an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0016568]','funding-text':'This work was supported as part of the Center for Actinide Science and Technology, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award DE-SC0016568.','journal-iso':'Inorg. Chem.','keywords-plus':'MOLECULAR-ORBITAL METHODS; VALENCE BASIS-SETS; ENERGY; PSEUDOPOTENTIALS; ACTINIDES; EXCHANGE; ELEMENTS; IR','number-of-cited-references':'26','orcid-numbers':'Albrecht-Schmitt, Thomas/0000-0002-2989-3311','research-areas':'Chemistry','times-cited':'2','unique-id':'ISI:000414820100007','usage-count-last-180-days':'2','usage-count-since-2013':'14','web-of-science-categories':'Chemistry, Inorganic & Nuclear'\; International audience; The reaction of Th(NO3)(4)center dot 5H(2)O with 3 equiv of 2,2',6',2\''\-terpyridine (terpy) in a mixture of acetonitrile and methanol results in formation of the trinuclear thorium peroxide cluster \[\Th(O-2)(terpy)-(NO3)(2)](3). This cluster is assembled via bridging by mu eta(2):eta(2) peroxide anions between thorium centers. It decomposes upon removal from the mother liquor to yield Th(terpy)(NO3)(4) and Th(terpy)(NO3)(4)(EtOH). The peroxide formation appears to be radiolytic in origin and is, most likely, generated from radiolysis of water by short-lived daughters generated from Th-232 decay. This cluster does not form when freshly recrystallized Th(NO3)(4)center dot 5H(2)O is used as the starting material and requires an aged source of thorium. Analysis of the bonding in these clusters shows that, unlike uranium(VI) peroxide interactions, thorium(IV) complexation by peroxide is quite weak and largely ionic. This explains its much lower stability, which is more comparable to that observed in similar zirconium(IV) peroxide clusters.

Diprotonation of a remarkably stable, toluene soluble cobalt peroxo complex supported by a neutral, dianionic pentadentate ligand leads to facile O-O bond cleavage and production of a highly reactive Co(IV) oxyl cation intermediate that dimerizes and releases O2. These processes are relevant to both O2 reduction and O2 evolution and the mechanism was probed in detail both experimentally and computationally.

Alkyl and hydrido scandium complexes of the dianionic pentatdentate ligand B2Pz4Py are reported. The key starting material (B2Pz4Py)ScCl is readily prepared and alkylated with organolithium reagents RLi (R = CH3, CH2SiMe3, CH2SiMe2Ph, CH2CH2CH3 and CH2CHMe2) to form alkyl derivatives in 61-93% yields. These compounds are very thermally stable and do not undergo sigma bond metathesis reactions with dihydrogen. The hydrido complex was prepared from (B2Pz4Py)ScCl and NaHBEt3 in 80% yield and was found to be more stable by 28 kcal mol-1 as a dimer, rather than a monomeric hydrido complex. However, the monomer is accessible through dissociation of the dimer at 80˚C. All of the compounds (B2Pz4Py)ScR react with water to form the bridging oxo dimer (B2Pz4Py)ScOSc(B2Pz4Py). The reactivity of the hydrido and methyl complexes towards carbon dioxide was explored; heating to 80˚C results in the formation of k2 formato and acetate complexes, respectively. The mechanisms were studied via density function theory and distinct transition states for insertion of CO2 into the Sc-R (R = H, CH3) were found, with the insertion into the Sc-CH3 being more enthalpically difficult (by 18 kcal mol-1) than insertion into Sc-H. The slow rate of reaction between [(B2Pz4Py)ScH]2 and CO2 is attributed to the barrier associated with dimer dissociation. In both insertion reactions, the kinetic products are k1 formato or acetate complexes that are only slightly less stable than the observed k2 derivatives. The k1 compounds can therefore be trapped by treating the k2 isomers with tris-pentafluorophenyl borane.

The synthesis and structural determination of the first thorium phosphinidene complex are reported. The reaction of 2 equiv of (C5Me5)2Th(CH3)2 with H2P(2,4,6-(i)Pr3C6H2) at 95 °C produces [(C5Me5)2Th]2(μ2-P[(2,6-CH2CHCH3)2-4-(i)PrC6H2] as well as 4 equiv of methane, 2 equiv from deprotonation of the phosphine and 2 equiv from C-H bond activation of one methyl group of each of the isopropyl groups at the 2- and 6-positions. Transition state calculations indicate that the steps in the mechanism are P-H, C-H, C-H, and then P-H bond activation to form the phosphinidene.

Molecules containing actinide–nitrogen multiple bonds are of current interest as simple models for new actinide nitride nuclear fuels, and for their potential for the catalytic activation of inert hydrocarbon C–H bonds. Complexes with up to three uranium–nitrogen double bonds are now being widely studied, yet those with one thorium–nitrogen double bond are rare, and those with two are unknown. A new, simple mono(imido) thorium complex and the first bis(imido) thorium complex, K[Th(═NAr)N″3] and K2[Th(═NAr)2N″2], are readily made from insertion reactions (Ar = aryl, N″ = N(SiMe3)2) into the Th–C bond of the cyclometalated thorium amides [ThN″2(N(SiMe3)(SiMe2CH2))] and K[ThN″(N(SiMe3)(SiMe2CH2))2]. X-ray and computational structural analyses show a “transition-metal-like” cis-bis(imido) geometry and polarized Th═N bonds with twice the Wiberg bond order of the formally single Th–N bond in the same molecule.

Monocationic bis(hydrocarbyl)yttrium complexes [YR2(THF)2][A] (R = CH2SiMe3, CH2C6H4-o-NMe2; A = weakly coordinating anion) underwent hydrogenolysis using dihydrogen or phenylsilane to give a mixture of polynuclear solvent-stabilized dihydride cations [YH2(THF)2]n[A]n. The mixture composition as well as the nuclearity n depended on the starting material, solvent, and reaction conditions. NMR spectroscopic data in solution and X-ray diffraction data suggested that the main product was tetranuclear, although conclusive structural data were not obtained. DFT calculations supported a closo-type tetrahedral [YH2(THF)2]44+ core. The hydridic character of these cations was revealed by their reaction with benzophenone to give the bis(diphenylmethoxy) cation [Y(OCHPh2)2(THF)4][AlR4]. The reaction of this cluster with the (NNNN)-type macrocycle Me4TACD under dihydrogen gave the dinuclear tetrahydride dication with quadruply bridging hydride ligands, [Y2(μ-H)4(Me4TACD)2][A]2, analogous to the previously characterized lutetium derivative. NH-acidic (Me3TACD)H gave the dinuclear dihydride dication [Y2(μ-H)2(Me3TACD)2(THF)2][A]2.

International audience; This study details the formal hydrogenation of two magnesium(I) dimers {(Nacnac)Mg}2 (Nacnac = [{(C6H3R2-2,6)NCMe}2CH]−; R = Pri (DipNacnac), Et (DepNacnac)) using 1,3-cyclohexadiene. These reactions afford the magnesium(II) hydride complexes, {(Nacnac)Mg(μ-H)}2. Their reactions with excess CO are sterically controlled and lead cleanly to different C–C coupled products, viz. the ethenediolate complex, (DipNacnac)Mg{κ1-O-[(DipNacnac)Mg(κ2-O,O-O2C2H2)]}, and the first cyclopropanetriolate complex of any metal, cis-{(DepNacnac)Mg}3{μ-C3(H3)O3}. Computational studies imply the CO activation processes proceed via very similar mechanisms to those previously reported for related reactions involving f-block metal hydride compounds. This work highlights the potential magnesium compounds hold for use in the “Fischer–Tropsch-like” transformation of CO/H2 mixtures to value added oxygenate products.

Coordination of the triphosphine–fluorosilane [o-(iPr2P)C6H4]3SiF to AuCl results in the formation of a trigonal pyramidal cationic complex. Though cationic, the gold center acts as a Lewis base and is engaged in significant Au→Si interaction, as substantiated by X-ray diffraction and NMR spectroscopy. In solution, the P,P,P,Si tetracoordinate cationic complex coexists with a neutral P,P,Cl tricoordinate form, with a pendant phosphine buttress and without Au→Si interaction. The bonding situation in the two isomeric forms has been assessed by DFT calculations. Coordination of the third phosphine arm is shown to induce cationization and to play a key role in the presence of the Au→Si interaction.

Ambiphilic phosphine–borane derivatives 1-B(OR)2-2-PR′2–C6H4 (R′ = Ph (1), iPr (2); (OR)2 = (OMe)2 (1a, 2a); catechol (1b, 2b) pinacol (1c, 2c), −OCH2C(CH3)2CH2O– (1d)) were tested as catalysts for the hydroboration of CO2 using HBcat or BH3·SMe2 to generate methoxyboranes. It was shown that the most active species were the catechol derivatives 1b and 2b. In the presence of HBcat, without CO2, ambiphilic species 1a, 1c, and 1d were shown to transform to 1b, whereas 2a and 2c were shown to transform to 2b. The formaldehyde adducts 1b·CH2O and 2b·CH2O are postulated to be the active catalysts in the reduction of CO2 rather than being simple resting states. Isotope labeling experiments and density functional theory (DFT) studies show that once the formaldehyde adduct is generated, the CH2O moiety remains on the ambiphilic system through catalysis. Species 2b·CH2O was shown to exhibit turnover frequencies for the CO2 reduction using BH3·SMe2 up to 228 h–1 at ambient temperature and up to 873 h–1 at 70 °C, mir...

Introduction of four tBu groups into a carbazol-yl framework leads to switching of the metal–ligand bonding in the Ln(II) and Ca complexes from σ to π. Complexes [(tBu4Carb)2Ln] (Ln = Sm, Eu, Yb, Ca) are amido analogues of metallocenes, which adopt the sandwich structures with parallel disposition of the aromatic ligands and strong contribution of η3-mode into η5 metal–ligand bonding. The DFT calculations demonstrated that the geometry is due to steric effects (presence of the bulky tBu groups) as well as the maximization of the overlap between the Sm 4f orbital and the π-type nitrogen lone pair of the carbazol-yl ligand. Coordination of DME to the metal centers in [(tBu4Carb)2M] (M = Sm, Yb) results in the heterolytic dissociation of the metal–ligand π-bond and the formation of ionic complexes [tBu4Carb–]2[Ln2+(DME)n].

International audience; The scandium complex bearing both methylidene and phosphinidene ligands, [(LSc) 2 (μ 2-CH 2)(μ 2-PDIPP)] (L = [MeC(NDIPP)CHC(NDIPP)Me] − , DIPP = 2,6-(i Pr) 2 C 6 H 3) (2), has been synthesized, and its reactivity has been investigated. Reaction of scandium methyl phosphide [LSc(Me){P(H)DIPP}] with 1 equiv of scandium dimethyl complex [LScMe 2 ] in toluene at 60 °C provided complex 2 in good yield, and the structure of complex 2 was determined by single-crystal X-ray diffraction. Complex 2 easily undergoes nucleophilic addition reactions with CO 2 , CS 2 , benzonitrile, and tert-butyl isocyanide. In the above reactions, the unsaturated substrates insert into the Sc−C(methylidene) bond to give some interesting dianionic ligands while the Sc−P(phosphinidene) bond remains untouched. The bonding situation of complex 2 was analyzed using DFT methods, indicating a more covalent bond between the scandium ion and the phosphinidene ligand than between the scandium ion and the methylidene ligand. ■ INTRODUCTION Alkylidene (or carbene) and phosphinidene complexes of transition metals have attracted intense interest and been extensively studied in the past decades. 1,2 The research on such complexes has revealed rich reactivity and applications in group-transfer and catalytic reactions. One exception is those complexes with rare-earth metal (Sc, Y, and lanthanide metal) ions. Rare-earth metal ions are among the hardest Lewis acids, whereas alkylidene and phosphinidene ligands are soft Lewis bases; thus, the rare-earth metal−alkylidene (or phosphini-dene) coordination is mismatched based on the Pearson's HSAB principle. 3 Up to now, the rare-earth metal alkylidene and phosphinidene complexes remain limited. 4−6 The reactivity study showed that most of the rare-earth metal alkylidene and phosphinidene complexes can react as the alkylidene or phosphinidene transfer agents with ketones to give alkenes or phosphaalkenes. 4 It was also found that some of the rare-earth metal alkylidene and phosphinidene complexes undergo nucleophilic addition reactions with unsaturated substrates, such as CO, isocyanate, carbodiimide, and isocyanide. 5k,l,6f,g We have developed a type of β-diketiminato based tridentate ligands, which can stabilize a series of rare-earth metal dialkyl complexes, 7 and a scandium terminal imido complex. 8 Recently, we obtained a scandium bridged phosphinidene complex [{MeC(NDIPP)CHC(Me)NCH 2 CH 2 N(i Pr) 2 }Sc{μ-PC 6 H 3-(2,6-Me 2)}] 2 (DIPP = 2,6-(i Pr) 2 C 6 H 3)), in which the pendant arm of the tridentate ligand is not coordinated to the scandium ion due to the phosphinidene ligand having a strong tendency to bridge two or more rare-earth metal centers. 6f Thus, we carried out a study to synthesize a scandium phosphinidene complex supported by the bulky β-diketiminato ligand, [MeC(NDIPP)CHC(NDIPP)Me] − (DIPP = 2,6-(i Pr) 2 C 6 H 3). 9 During this study, we obtained an unprecedented scandium complex which bears both phosphinidene and methylidene ligands. This scandium methylidene phosphini-dene complex reacts with a variety of unsaturated small molecules, and favoring reaction with the methylidene ligand over the phoshinidene ligand. ■ RESULTS AND DISCUSSION A salt elimination reaction of scandium methyl chloride [LSc(Me)Cl] (L = [MeC(NDIPP)CHC(NDIPP)Me] − , DIPP = 2,6-(i Pr) 2 C 6 H 3) 10 with 1 equiv of K[P(H)DIPP] in toluene at room temperature yielded a scandium methyl phosphide [LSc(Me){P(H)DIPP}] (1) in 85% yield. Complex 1 was

A series of uranium tritylimido complexes with structural continuity across complexes in different oxidation states, namely U(IV), U(V), and U(VI), is reported. This series was successfully synthesized by employing the trivalent uranium precursor, [(((nP,Me)ArO)3tacn)U(III)] (1) (where ((nP,Me)ArO)3tacn(3-) = trianion of 1,4,7-tris(2-hydroxy-5-methyl-3-neopentylbenzyl)-1,4,7-triazacyclononane), with the organic azides Me3SiN3, Me3SnN3, and Ph3CN3 (tritylazide). While the reaction with Me3SiN3 yields an inseparable mixture of both the azido and imido uranium complexes, applying the heavier Sn homologue yields the bis-μ-azido complex [{(((nP,Me)ArO)3tacn)U(IV)}2(μ-N3)2] (2) exclusively. In contrast to this one-electron redox chemistry, the reaction of precursor 1 with tritylazide solely leads to the two-electron oxidized U(V) imido [(((nP,Me)ArO)3tacn)U(V)(N-CPh3)] (3). Oxidation and reduction of 3 yield the corresponding U(VI) and U(IV) complexes [(((nP,Me)ArO)3tacn)U(VI)(N-CPh3)][B(C6F5)4] (4) and K[(((nP,Me)ArO)3tacn)U(IV)(N-CPh3)] (5), respectively. In addition, the U(V) imido 3 engages in a H atom abstraction reaction with toluene to yield the closely related amido complex [(((nP,Me)ArO)3tacn)U(IV)(N(H)-CPh3)] (6). Complex 6 and the three tritylimido complexes 3, 4, and 5, with oxidation states ranging from +IV to +VI and homologous core structures, were investigated by X-ray diffraction analyses and magnetochemical and spectroscopic studies as well as density functional theory (DFT) computational analysis. The series of structurally very similar imido complexes provides a unique opportunity to study electronic properties and to probe the uranium imido reactivity solely as a function of electron count of the metal-imido entity. Evidence for the U-N bond covalency and f-orbital participation in complexes 3-6 was drawn from the in-depth and comparative DFT study. The reactivity of the imido and amido complexes with CO2 was probed, and conclusions about the influence of the formal oxidation state are reported.