Side-on Coordination Mode Research Articles

Unusual coordination mode for 1,3-diphosphete ligands towards a Cr-Cr quintuple bond complex.

The reaction of LCr5̲CrL (L = N2C25H29, 1) with the phosphaalkynes R-C≡P (R = tBu, Me, Ad) yields the neutral dimerisation compounds [L2Cr2(μ,η1:η1:η2:η2-P2C2R2)] (R = tBu (2), Me (3)) and the tetrahedrane complex [L2Cr2(μ,η2:η2-PCAd)] (4). The 1,3-diphosphete ligands in complexes 2 and 3 are the first to possess this structural feature spanned over a metal-metal multiple bond, while the slightly bigger adamantyl phosphaalkyne remains a monomer in 4 with a side-on coordination mode.

Exploring trimetallic clusters containing alkali and alkaline earth metal atoms with high activity for nitrogen activation

Activation of dinitrogen (N2) is the critical step in nitrogen reduction reaction (NRR) in ammonia synthesis. In this paper, reaction mechanisms of N2 activation on trimetallic clusters Mo2M (M = Li, Na, K, Mg, and Ca) and Mo3−xCax (x = 2–3) were systematically studied by density functional theory calculations. Unlike Mo2 which is inert to N2, clusters with alkali or alkaline earth metal atoms have much higher reactivity toward N2 in terms of both thermodynamics and kinetics. Particularly, in one reaction path of N2 with MoCa2, all the intermediates and transition states are well below the energy sum of the reactants, indicating that the dissociation of N2 on MoCa2 can take place spontaneously in gas-phase reactions. N2 transfers on clusters with different coordination modes, and the N−N bond is gradually activated. When N2 is bonded with three metal atoms with end-on: side-on: side-on coordination mode, it is fully activated and easily dissociated into two adsorbed N atoms. These results may serve as a prototype to design single-cluster catalysts with a trimetallic center for nitrogen activation and conversion.

Side-on coordination mode of a pyrazolyl group in the structure of a divalent [Sm{B(3-Mepz)4}2] complex (3-Mepz is 3-methylpyrazol-1-yl).

The discovery of polypyrazolylborate ligands allowed the development of various chemical fields and these ligands are an alternative to cyclopentadienyl, because both ligands have the same charge and donate the same number of electrons, as well as adopting the same facial geometry. Easy control of the bulkiness of polypyrazolylborate ligands is possible by modification of the substituents in the 3- and 5-positions of the pyrazolyl rings. The title complex, bis[tetrakis(3-methyl-1H-pyrazol-1-yl)borato]samarium(II), [Sm(C16H20BN8)2], was synthesized from the reaction of SmI2 with potassium tetrakis(3-methyl-1H-pyrazol-1-yl)borate, denoted K[B(3-Mepz)4], in tetrahydrofuran. The X-ray structure analysis revealed an unusual side-on coordination mode of a 3-methylpyrazolyl group through an N=N group in the B(3-Mepz)4 ligand. The distortion is defined by the B-N-N-Sm torsion angle [85.5 (4)°]. This is in contrast to the structure of the similar divalent samarium complex [Sm(TpMe2 is tris(3,5-dimethylpyrazol-1-yl)borate], which displays normal κ3-bonding modes of the TpMe2 ligands.

Zn···Zn interactions at nickel and palladium centers.

The analogy between ZnR fragments and the hydrogen radical represents a fruitful concept in organometallic synthesis. The organozinc(ii) and -zinc(i) sources ZnMe2 (Me = methyl) and [Zn2Cp*2] (Cp* = pentamethylcyclopentadienyl) provide one-electron fragments ·ZnR (R = Me, Cp*), which can be trapped by transition metal complexes [L a M], yielding [L b (ZnR) n ]. The addition of the dizinc compound [Zn2Cp*2] to coordinatively unsaturated [L a M] by the homolytic cleavage of the Zn-Zn bond can be compared to the classic oxidative addition reaction of H2, forming dihydride complexes [L a M(H)2]. It has also been widely shown that dihydrogen coordinates under preservation of the H-H bond in the case of certain electronic properties of the transition metal fragment. The σ-aromatic triangular clusters [Zn3Cp*3]+ and [Zn2CuCp*3] may be regarded as the first indication of this so far unknown, side-on coordination mode of [Zn2Cp*2]. With this background in mind the question arises if a series of complexes featuring the Zn2M structural motif can be prepared exhibiting a (more or less) intact Zn-Zn interaction, i.e. di-zinc complexes which are analogous to non-classical dihydrogen complexes of the Kubas type. In order to probe this idea, a series of interrelated organozinc nickel and palladium complexes and clusters were synthesized and characterized as model compounds: [Ni(ZnCp*)(ZnMe)(PMe3)3] (1), [Ni(ZnCp*)2(ZnMe)2(PMe3)2] (2), [{Ni(CN t Bu)2(μ2-ZnCp*)(μ2-ZnMe)}2] (3), [Pd(ZnCp*)4(CN t Bu)2] (4) and [Pd3Zn6(PCy3)2(Cp*)4] (5). The dependence of Zn···Zn interactions as a function of the ligand environments and the metal centers was studied. Experimental X-ray crystallographic structural data and DFT calculations support the analogy between dihydrogen and dizinc transition metal complexes.

Homolytic or Heterolytic Dihydrogen Splitting with Ditantalum/Dizirconium Dinitrogen Complexes? A Computational Study

Transition metal complexes play a key role in creating efficient molecular catalysis processes leading to the ammonia production from earth-abundant dinitrogen. It is indispensable to examine the mechanism and influence of transition metal complexes on dinitrogen hydrogenation. In this paper, the mechanism of the dinitrogen hydrogenation triggered by bimetallic complexes [L2M]2(μ-η2:η2-N2) (M = Ta and Zr, L = Sita-type or Chirik-type ligand) is investigated by density functional theory calculation. Our results show that the side-on ditantalum dinitrogen complex with Sita-type ligands favors the pathway of homolytic dihydrogen splitting when hydrogenation products are generated. However, the dihydrogen splitting switches to the heterolytic pathway as the dominant mechanism when Zr is the metal center. The ditantalum dinitrogen complex undergoes hydrogenation much easier from the side-on coordination mode than the side-on-end-on mode with Sita-type or Chirik-type ligands. With these findings from the computational study, this work identifies that different metal centers and coligands (Sita-type or Chirik-type) in different binding modes (side-on-end-on or side-on bridged) dictate the pathway of dihydrogen cleavage triggered by the bimetallic complexes. This work should provide insights on factors impacting the dinitrogen hydrogenation process and shed light on designing new transition metals and ligands for dinitrogen hydrogenation catalysts in the future.

Organocopper(II) Complex of 21-Diphenylphosphoryl-Carbaporpholactone Hybrid: A Side-On Coordination Mode of Copper(II)

The diphenylphosphoryl-carbaporpholactone hybrid is a new aromatic porphyrinoid, which preserves the essential features of the carbaporpholactone frame and provides a suitable environment allowing stabilization of the organocopper(II) complex affording a peculiar side-on coordination of copper(II).

PPh4]3 [W(CN)7(O2)]×4H2O as the Representative of the [M(L)7(LL)] Class for Nine‐Coordinate Complexes.

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PPh4]3[W(CN)7(O2)]·4H2O as the Representative of the [M(L)7(LL)] Class for Nine-Coordinate Complexes

The photoinduced dissociation of a W-CN bond in [W(CN)8]4- in an aqueous solution under ambient conditions, in conjunction with the uptake of molecular oxygen, affords the W(VI) mixed-ligand complex anion [W(CN)(7)(eta2-O2)]3-, conveniently isolable as its [PPh4+] salt. Although research into the chemistry of cyanomolybdates and cyanotungstates has been pursued with great interest and vigor over several decades, there is a paucity of structurally characterized cyano-peroxo complexes of Mo and W. The side-on coordination mode of the peroxo moiety in [W(CN)7(eta2-O2)]3- has been ascertained with X-ray crystal structure determination [d(O-O) = 1.41 A; peroxo bite angle: 41.0 degrees ] and corroborated with vibrational spectroscopy [nu(O-O) = 915 cm(-1)]. The complex ion exhibits trapezoidal tridecahedral geometry and represents the new class of nine-coordinate complexes with one bidentate and seven monodentate ligands. Cyclic voltammetry shows a reversible redox behavior of [W(CN)7(eta2-O2)]3- in CH3CN with its standard reduction potential equal to 1.130 V. Generally, interest in atmospheric oxygen derives from the versatility of this molecule as a ligand and oxidant and extends to the physicochemical features it imparts to transition metals such as copper and iron in biological oxygen carriers.

Comparison of side-on and end-on coordination of E2 ligands in complexes [W(CO)5E2] (E=N, P, As, Sb, Bi, Si-, Ge-, Sn-, Pb-).

Complexes of W(CO)(5) with neutral diatomic pnictogen ligands N(2), P(2), As(2), Sb(2), and Bi(2) and anionic Group 14 ligands Si(2) (2-), Ge(2) (2-), Sn(2) (2-), and Pb(2) (2-) coordinated in both side-on and end-on fashion have been optimized by using density functional theory at the BP86 level with valence sets of TZP quality. The calculated bond energies have been used to compare the preferential binding modes of each respective ligand. The results were interpreted by analyzing the nature of the interaction between the ligands and the metal fragment using an energy partitioning method. This yields quantitative information regarding the strength of covalent and electrostatic interactions between the metal and ligand, as well as the contributions by orbitals of different symmetry to the covalent bonding. Results show that all the ligands studied bind preferentially in a side-on coordination mode, with the exception of N(2), which prefers to coordinate in an end-on mode. The preference of the heavier homologues P(2)-Bi(2) for binding in a side-on mode over the end-on mode in the neutral complexes [(CO)(5)WE(2)] comes mainly from the much stronger electrostatic attraction in the former species. The energy difference between the side-on and end-on isomers of the negatively charged complexes with the ligands Si(2) (2-), Ge(2) (2-), Sn(2) (2-), and Pb(2) (2-) is much less and it cannot be ascribed to a particular bonding component.

CO2 Coordination to Nickel Atoms: Matrix Isolation and Density Functional Studies

The interaction of the CO2 molecule with nickel atoms was studied by using matrix isolation spectroscopy and density functional theory. In argon dilute matrices, no reaction occurs, even after annealing the deposit. In neat CO2 matrices, it is shown that carbon dioxide forms a 1:1 complex with nickel which is characterized by its UV−visible and FTIR absorptions, including isotopically labeled species. Theory predicts the side-on coordination mode to be the most stable. The binding energy of the side-on Ni(CO2) complex is estimated to be 18 kcal/mol. The calculated OCO angle is 145°, which is quite a large value compared to those encountered in other known CO2 complexes. In dinitrogen matrices, the yield of CO2 complexation is considerably enhanced relative to that in argon dilute and neat CO2 matrices, which is attributed to the formation of unsaturated Ni(N2)n complexes prior to CO2 coordination. The CO2 binding energies calculated for the Ni(CO2)(N2)n (n = 1, 2) complexes (respectively 32 and 4 kcal/mol...

Ab initio Density Functional Calculations on Copper(I)–CO2 Coordinations

Abstract Full geometry optimizations have been carried out for the complex formations of Cu+ and Cu(2,2′-bipyridine)+ with CO2 by using the density functional methods. The calculation demonstrated that the end-on coordination mode was mainly favored for all cases, while the binding of 2,2′-bipyridine (bpy) to Cu(CO2)+ largely labilized the end-on coordination mode and stabilized the in-plane side-on coordination mode. The detailed examination of the population analysis indicate that the coordination of bpy to Cu+ weakens the electron donating character of CO2 to Cu+ and promotes the important participation of π-back-donative interaction from the metal ion to CO2.

Bridge bonding of nitrogen to dinuclear transition metal systems

Hb initio quantum chemical calculations have been performed on two different structures of M 2 N 2 for first-and second=row transition metal systems involving titanium, yttrium, and zirconium. In both structures N 2 is bridging the metal atoms, either in a perpendicular side-on coordination mode, or in a parallel end-on coordination mode leading to a linear M-N-N-M. Both types of structures have been observed experimentally for ligated complexes of the type (LnM) 2 N 2 . Comparisons between experiment and theory show that the geometries of the M 2 N 2 unit in the experimentally observed complexes correspond closely to the calculated geometries for different states of the naked M 2 N 2 systems

Formation and fragmentation of gas-phase ion-molecule complexes of transition-metal ions with organic molecules containing two functional groups

A mass spectrometer fast atom bombardment source has been used to synthesize, in the gas phase, the ion-molecule complexes of transition-metal ions (Ni +, Co +, Fe +, and Mn +) with α- or β-unsaturated alkenenitriles, RCHCHCN (RH, CH 3, and C 2H 5) and CH 3CHCHCH 2CN, and 2-methyl glutaronitrile. The metastable ion fragmentations of the complexes are monitored in the first field-free region by B/E linked scans. Surprisingly, an intense HCN loss via an intermediate (C n H 2 n−2 )M +(HCN) is observed for the complexes of the alkenenitriles. The metal ions significantly affect the fragmentation processes. The coexistence of both end-on and side-on coordination modes is suggested to explain the fragmentations.