Role of the Meso Substituent in Defining the Reduction of Uranyl Dipyrrin Complexes

The uranyl complex UVIO2Cl(LMes) of the redox-active, acyclic dipyrrin–diimine anion LMes– [HLMes = 1,9-di-tert-butyl-imine-5-(mesityl)dipyrrin] is reported, and its redox property is explored and compared with that of the previously reported UVIO2Cl(LF) [HLF = 1,9-di-tert-butyl-imine-5-(pentafluorophenyl)dipyrrin] to understand the influence of the meso substituent. Cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory studies show that the alteration from an electron-withdrawing meso substituent to an electron-donating meso substituent on the dipyrrin ligand significantly modifies the stability of the products formed after reduction. For UVIO2Cl(LMes), the formation of a diamond-shaped, oxo-bridged uranyl(V) dimer, [UVO2(LMes)]2 is seen, whereas in contrast, for UVIO2Cl(LF), only ligand reduction occurs. Computational modeling of these reactions shows that while ligand reduction followed by chloride dissociation occurs in both cases, ligand-to-metal electron transfer is favorable for UVIO2Cl(LMes) only, which subsequently facilitates uranyl(V) dimerization

From antiferromagnetic to ferromagnetic exchange in a family of oxime-based Mn(III) dimers:a magneto-structural study

The reaction of Mn(ClO4)(2)center dot 6H(2)O, a derivatised phenolic oxime (R-saoH(2)) and the ligand tris(2-pyridylmethyl)amine (tpa) in a basic alcoholic solution leads to the formation of a family of cluster compounds of general formula [(Mn2O)-O-III(R-sao)(tpa)(2)](ClO4)(2) (1, R = H; 2, R = Me; 3, R = Et; 4, R = Ph). The structure is that of a simple, albeit asymmetric, dimer of two Mn-III ions bridged through one mu-O2- ion and the -N-O- moiety of the phenolic oxime. Magnetometry reveals that the exchange interaction between the two MnIII ions in complexes 1, 3 and 4 is antiferromagnetic, but that for complex 2 is ferromagnetic. A theoretically developed magneto-structural correlation reveals that the dominant structural parameter influencing the sign and magnitude of the pairwise interaction is the dihedral Mn-O-N-Mn (torsion) angle. A linear correlation is found, with the magnitude of J varying significantly as the dihedral angle is altered. As the torsion angle increases the AF exchange decreases, matching the experimentally determined data. DFT calculations reveal that the (dyz)vertical bar pi vertical bar d(yz) interaction decreases as the dihedral angle increases leading to ferromagnetic coupling at larger angles

Switching the orientation of Jahn-Teller axes in oxime-based Mn(III) dimers and its effect upon magnetic exchange:a combined experimental and theoretical study

A family of Mn-III dimers of general formula [Mn-2(III)(R-sao)(2)(dpa)(2)](ClO4)(2) (1-5) has been synthesised using derivatised phenolic oximes (R-saoH(2), where R = H, Me, Et, Ph) in combination with di-(2-picolyl)-amine (dpa). Their structures reveal a double-oxime bridged [Mn-III(NO)](2) magnetic core in which the Jahn-Teller axes lie perpendicular to the bridging plane, in contrast to two previously reported family members (6, 7). The switch in the orientation of the Jahn-Teller axes is enforced through the use of the chelating ligand which is present in 1-5 and absent in 6-7. Dc magnetic susceptibility measurements reveal that the exchange interactions between the MnIII metal centres in 1-5 are antiferromagnetic in contrast to that observed for 6 and 7 which are ferromagnetic. DFT calculations performed on complexes 1-6 reproduce both the sign and strength of the J values found experimentally. Molecular orbital analysis unlocks a common mechanism of magnetic coupling based upon the orientation of the Jahn-Teller axis, with the magneto-structural correlation also dependent upon the Mn-N-O-Mn angles - with ferromagnetic interactions at smaller dihedral angles

Reversible Oxidative Addition of Zinc Hydride at a Gallium(I)‐Centre: Labile Mono‐ and Bis(hydridogallyl)zinc Complexes

In the presence of TMEDA (N,N,N',N'-tetramethylethylenediamine), partially deaggregated zinc dihydride as hydrocarbon suspensions react with the gallium(I) compound [(BDI)Ga] (I, BDI={HC(C(CH3)N(2,6-iPr(2)-C6H3))(2)}(-)) by formal oxidative addition of a Zn-H bond to the gallium(I) centre. Dissociation of the labile TMEDA ligand in the resulting complex [(BDI)Ga(H)-(H)Zn(tmeda)] (1) facilitates insertion of a second equiv. of I into the remaining Zn-H to form a thermally sensitive trinuclear species [{(BDI)Ga(H)}(2)Zn] (2). Compound 1 exchanges with polymeric zinc dideuteride [ZnD2](n) in the presence of TMEDA, and with compounds I and 2 via sequential and reversible ligand dissociation and gallium(I) insertion. Spectroscopic and computational studies demonstrate the reversibility of oxidative addition of each Zn-H bond to the gallium(I) centres

CO, CO2 and CS2 activation by divalent ytterbium hydrido complexes

International audienceTreatment of a divalent ytterbium hydride complex [(Tp(Ad,iPr))-Yb(H)(THF)] (Tp(Ad,iPr) = hydrotris(3-adamantyl-5-isopropyl-pyrazolyl)borate) (1) with CO, CO2 and CS2 resulted in the formation of a divalent ytterbium ethenediolate complex [(Tp(Ad,iPr))Yb](2)(cis-OCH=CHO) (2), a formate complex [(Tp(Ad,iPr))Yb(kappa(2)-O2CH)(THF)] (3), and a trivalent ytterbium ethenetetrathiolate complex [(Tp(Ad,iPr))-Yb-III](2)(C2S4) (4), respectively. DFT calculations were carried out to elucidate the reaction profiles of complexes 3 and 4

Reductive activation of N 2 using a calcium/potassium bimetallic system supported by an extremely bulky diamide ligand

An extremely bulky xanthene bridged diamide ligand ((NON)-N-TCHP = 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 [((NON)-N-TCHP)Ca(D)(n)] (D = THF, n = 2, 3; D = toluene, n = 1, 4). Reduction of 4 with 5% w/w K/KI under an N-2 atmosphere gave the first well-defined, hetero-bimetallic s-block complex of activated dinitrogen, [{K((NON)-N-TCHP)Ca}(2)(mu-eta(2):eta(2)-N-2)] 5, presumably via a transient calcium(i) intermediate

Reductive Activation of N2 using a Calcium/Potassium Bimetallic System Supported by an Extremely Bulky Diamide Ligand

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

Synthesis, Characterization, and Reactivity of a Hydrido- and Imido-Bridged Dinuclear Ytterbium(III) Complex

International audienceThe trivalent rare-earth metal hydrido and imido complexes are of versatile reactivity, and many such complexes have been synthesized. However, no example of a rare-earth metal complex bearing both hydrido- and imido-ligands has been reported. Herein, we report the first rare-earth metal complex bearing both hydrido- and imido-ligands, namely a hydrido- and imido-bridged dinuclear ytterbium(III) complex. The complex was synthesized via an unprecedented redox reaction of divalent rare-earth metal hydrido complex with azido compound. DFT calculation indicated that the N-2 release from azido compound in the presence of ytterbium(II) is a kinetically facile process because of the cooperative effects of the two metal centers. The reactivity of the hydrido- and imido-bridged dinuclear ytterbium(III) complex was also explored, which showed the redox, addition and sigma-bond metathesis reactivities

Deciphering the role of anions and secondary coordination sphere in tuning anisotropy in Dy(III) air-stable D5h SIMs

Precise control of the crystal field and symmetry around the paramagnetic spin centre has recently facilitated the engineering of high-temperature single-ion magnets (SIMs), the smallest possible units for future spin-based devices. In the present work, we report a series of air-stable seven coordinate Dy(III) SIMs {[L2Dy(H2O)5][X]3·L2·n(H2O), n = 0, X = Cl (1), n = 1, X = Br (2), I (3)} possessing pseudo-D5h symmetry or pentagonal bipyramidal coordination geometry with high anisotropy energy barrier (Ueff) and blocking temperature (TB). While the strong axial coordination from the sterically encumbered phosphonamide, tBuPO(NHiPr)2 (L), increases the overall anisotropy of the system, the presence of high symmetry significantly quenches quantum tunnelling of magnetization, which is the prominent deactivating factor encountered in SIMs. Although the local coordination geometry and the symmetry around the Dy(III) in all the three complexes are similar and display only slight deviations, the variation of halide anions in the secondary coordination sphere which is hydrogen-bonded to the coordinated equatorial water molecules, show subtle alteration in the magnetic properties. The energy barrier (Ueff) and the blocking temperature (TB) decrease in the order 3 > 2 > 1 with the change of anions from larger iodide to smaller strongly hydrogen-bonded chloride in the secondary coordination sphere. Ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations further provide deeper insights into the dynamics of magnetic relaxation in addition to the role of the secondary coordination sphere in modulating the anisotropy of the D5h systems, using diverse models. Thus, in addition to the importance of the crystal field and the symmetry to obtain high-temperature SIMs, this study also probes the significance of the secondary coordination sphere that can be tailored to accomplish novel SIMs

Solvent‐Dependent Oxidative Addition and Reductive Elimination of H 2 Across a Gallium‐Zinc Bond

H2 adds reversibly across the metal-metal bond of [(BDI)Ga(H)−Zn(tmeda)(thf)][BAr4F] (BDI=[HC{C(CH3)N(2,6-iPr2-C6H3)}2]−, TMEDA=N,N,N′,N′-tetramethylethylenediamine, BAr4F−=[B(C6H3-3,5-(CF3)2)4]−). Due to the stabilising effect of solvent coordination, hydrogenation products [(BDI)GaH2] and [(tmeda)ZnH(thf)][BAr4F] are favoured in THF solution, but THF-free mixtures of [(BDI)GaH2] and [(tmeda)ZnH(OEt2)][BAr4F] are predisposed towards entropically driven dehydrogenation to [(BDI)Ga(H)−Zn(tmeda)][BAr4F] in fluorobenzene solution