Two new molybdenum complexes and their structures

"MoCl3(dme)" Revisited: Improved Synthesis, Characterization, and X-ray and Electronic Structures

"MoCl₃(dme)" (dme = 1,2-dimethoxyethane) is an important precursor for midvalent molybdenum chemistry, particularly for triply Mo-Mo bonded compounds of the type Mo₂X₆ (X = bulky anionic ligand). However, its exact structural identity has been obscure for more than 50 years. In search of a convenient, large-scale synthesis, we have found that trans-MoCl₄(Et₂O)₂ dissolved in dme can be cleanly reduced with dimethylphenylsilane, Me₂PhSiH, to provide khaki Mo₂Cl₆(dme)₂ in ∼90% yield. If the reduction is performed on a small scale, single crystals suitable for X-ray crystallography can be obtained. Two different crystal morphologies were identified, each belonging to the P2₁/n space group, but with slightly different unit cell constants. The refined structure of each form is an edge-shared bioctahedron with overall C_i symmetry and metal-metal separations on the order of 2.8 Å. The bulk material is diamagnetic as determined by both the Gouy method and SQUID magnetometry. Density functional theory calculations suggest a σ²π²δ*² ground state for the dimer with the diamagnetism arising from a singlet diradical "broken symmetry" electronic configuration. In addition to a definitive structural assignment for "MoCl₃(dme)", this work highlights the utility of organosilanes as easy to handle, alternative reductants for inorganic synthesis.

Oxygen Atom Transfer Reactivity of Molybdenum(VI) Complexes Employing Pyrimidine- and Pyridine-2-thiolate Ligands

Four dioxidomolybdenum(VI) complexes of the general structure [MoO₂L₂] employing the S,N-bidentate ligands pyrimidine-2-thiolate (PymS, 1), pyridine-2-thiolate (PyS, 2), 4-methylpyridine-2-thiolate (4-MePyS, 3) and 6-methylpyridine-2-thiolate (6-MePyS, 4) were synthesized and characterized by spectroscopic means and single-crystal X-ray diffraction analysis (2-4). Complexes 1-4 were reacted with PPh₃ and PMe₃, respectively, to investigate their oxygen atom transfer (OAT) reactivity and catalytic applicability. Reduction with PPh₃ leads to symmetric molybdenum(V) dimers of the general structure [Mo₂O₃L₄] (6-9). Kinetic studies showed that the OAT from [MoO₂L₂] to PPh₃ is 5 times faster for the PymS system than for the PyS and 4-MePyS systems. The reaction of complexes 1-3 with PMe₃ gives stable molybdenum(IV) complexes of the structure [MoOL₂(PMe₃)₂] (10-12), while reduction of [MoO₂(6-MePyS)₂] (4) yields [MoO(6-MePyS)₂(PMe₃)] (13) with only one PMe₃ coordinated to the metal center. The activity of complexes 1-4 in catalytic OAT reactions involving Me₂SO and Ph₂SO as oxygen donors and PPh₃ as an oxygen acceptor has been investigated to assess the influence of the varied ligand frameworks on the OAT reaction rates. It was found that [MoO₂(PymS)₂] (1) and [MoO₂(6-MePyS)₂] (4) are similarly efficient catalysts, while complexes 2 and 3 are only moderately active. In the catalytic oxidation of PMe₃ with Me₂SO, complex 4 is the only efficient catalyst. Complexes 1-4 were also found to catalytically reduce NO₃^- with PPh₃, although their reactivity is inhibited by further reduced species such as NO, as exemplified by the formation of the nitrosyl complex [Mo(NO)(PymS)₃] (14), which was identified by single-crystal X-ray diffraction analysis. Computed ΔG^⧧ values for the very first step of the OAT were found to be lower for complexes 1 and 4 than for 2 and 3, explaining the difference in catalytic reactivity between the two pairs and revealing the requirement for an electron-deficient ligand system.

6-Methyl-pyridine-2(1H)-thione

There are two unique mol-ecules in the asymmetric unit of the title pyridine-thione derivative, C(6)H(7)NS, each of which adopts the thione rather than the mercaptan form. The rings in both mol-ecules are essentially planar, with maximum deviations from the least-squares planes through all non-H atoms of 0.021 (2) and 0.017 (2) Å. In the crystal structure, the mol-ecules form centrosymmetric cyclic dimers through inter-molecular N-H⋯S hydrogen bonds. Additional C-H(meth-yl)⋯S inter-actions generate a three-dimensional network.

Synthesis and characterization of molybdenum oxo complexes of two tripodal ligands: reactivity studies of a functional model for molybdenum oxotransferases

Reaction of the tetradentate ligand N-(2-hydroxybenzyl)-N,N-bis(2-pyridylmethyl)amine (L-OH) with MoO2Cl2 in methanol in the presence of NaOMe and PF6- results in the formation of [MoO2(L-O)]PF6. Similarly, the reaction of N-(2-mercaptobenzyl)-N,N-bis(2-pyridylmethyl)amine (L-SH) with MoO2(acac)2 leads to the formation of [MoO2(L-S)]+. The dioxo-molybdenum complex [MoO2(L-O)]+ reacts with phosphines in methanol to afford phosphine oxides and an air-sensitive molybdenum complex, tentatively identified as [Mo(IV)O(L-O)(OCH3)]. The latter complex is capable of reducing biological oxygen donors such as DMSO or nitrate, thereby mimicking the activity of DMSO reductase and nitrate reductase. Reaction of [MoO2(L-O)]PF6 with PPh3 in other solvents than methanol leads to the formation of the Mo(V) dimer [(L-O)OMo(micro-O)MoO(L-O)](PF6)2. The crystal structures of [MoO2(L-O)]PF6 and the micro-oxo bridged dimer are presented.

Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 3. Novel Structures with Diethylphosphido-bridges and Terminal Diethylphosphines

The interaction between octachlorodirhenium anions and diethylphosphine has been shown to strongly depend on reaction conditions, mainly the nature of the solvent and the amount of phosphine. As a result, novel dirhenium products with oxidation states ranging from Re(II) to Re(IV) have been obtained. The reaction of [Re(2)Cl(8)](2)(-) with an excess of PEt(2)H in dichloromethane or acetonitrile led to the first example of a face-sharing complex of rhenium(IV) with three phosphido-bridges, namely [Bu(n)(4)N][Re(2)(&mgr;-PEt(2))(3)Cl(6)] (1). The unusual edge-sharing Re(2)(&mgr;-PEt(2))(2)Cl(4)(PEt(2)H)(4) (2) complex of rhenium(III) with C(i)() core symmetry, containing both terminal phosphines and phosphido-bridges, has been obtained by carrying out the reaction with an excess of PEt(2)H in a benzene (or propanol) - HCl mixture at room temperature. A new example of the 1,2,7,8-type of dirhenium(II) complex, Re(2)Cl(4)(PEt(2)H)(4) (3), having diethylphosphine ligands located cis on each Re atom, has been isolated from the reaction of [Re(2)Cl(8)](2)(-) with PEt(2)H in an ethanol-HCl medium. The solid-state structures of complexes 1-3 have been investigated by X-ray crystallography. Complexes 1 and 2 both crystallized in two forms: [Bu(n)(4)N][Re(2)(&mgr;-PEt(2))(3)Cl(6)] 1a, P2(1)/n with a = 10.482(1) Å, b = 16.512(2) Å, c = 23.986(2) Å, beta = 93.637(8) degrees, and Z = 4; [Bu(n)(4)N][Re(2)(&mgr;-PEt(2))(3)Cl(6)].1.5 C(7)H(8) 1b, C2/c with a = 38.746(9) Å, b = 10.322(2) Å, c = 27.277(3) Å, beta = 110.35(1) degrees, and Z = 8; Re(2)(&mgr;-PEt(2))(2)Cl(4)(PEt(2)H)(4) 2a, P2(1)/n with a = 11.081(3) Å, b = 11.029(3) Å, c = 15.627(2) Å, beta = 90.05(1) degrees, and Z = 2; 2b, P2(1)/c with a = 16.094(3) Å, b = 15.193(3) Å, c = 15.548(3) Å, beta = 100.98(3) degrees, and Z = 4. X-ray data for complex Re(2)Cl(4)(PEt(2)H)(4) 3 are as follows: P2(1)/n with a = 10.445(2) Å, b = 10.113(3) Å, c = 13.473(2) Å, beta = 102.17(2) degrees, and Z = 2. Three bridging &mgr;-PEt(2) groups in the face-sharing complex 1 span a short metal-metal distance of 2.4060(6) Å, averaged over 1a and 1b, with a small Re-PEt(2)-Re angle of 61.34(7) degrees. The rhenium-rhenium bond length in the edge-sharing complex 2 is 2.7545(7) Å, averaged over 2a and 2b, while the bridging Re-PEt(2)-Re angle is 72.16(6) degrees, and the P-Re-P angle for the terminal phosphine ligands is 87.11(7) degrees. The Re-Re bond distance in 3, 2.2533(8) Å, is typical for triply bonded dirhenium complexes, and the P-Re-P angle for the cis phosphine groups is 93.12(6) degrees.

Anionic Halomolybdate(III) Chemistry. Tetrahydrofuran Loss from [MoX(3)Y(THF)(2)](-) (X, Y = Cl, Br, I), Preparation and Properties of [Mo(3)X(12)](3)(-) (X = Br, I), and Crystal Structure of the Edge-Sharing Trioctahedral [PPh(4)](3)[Mo(3)I(12)]

By interaction of MoX(3)(THF)(3) with [Cat]X in THF, the salts [Cat][MoX(4)(THF)(2)] have been synthesized [X = I, Cat = PPh(4), NBu(4), NPr(4), (Ph(3)P)(2)N; X = Br, Cat = NBu(4), PPh(4) (Ph(3)P)(2)N]. Mixed-halide species [MoX(3)Y(THF)(2)](-) (X, Y = Cl, Br, I) have also been generated in solution and investigated by (1)H-NMR. When the tetraiodo, tetrabromo, and mixed bromoiodo salts are dissolved in CH(2)Cl(2), clean loss of all coordinated THF is observed by (1)H-NMR. On the other hand, [MoCl(4)(THF)(2)](-) loses only 1.5 THF/Mo. The salts [Cat](3)[Mo(3)X(12)] (X = Br, I) have been isolated from [Cat][MoX(4)(THF)(2)] or by running the reaction between MoX(3)(THF)(3) and [Cat]X directly in CH(2)Cl(2). The crystal structure of [PPh(4)](3)[Mo(3)I(12)] exhibits a linear face-sharing trioctahedron for the trianion: triclinic, space group P&onemacr;; a = 11.385(2), b = 12.697(3), c = 16.849(2) Å; alpha = 76.65(2), beta = 71.967(12), gamma = 84.56(2) degrees; Z = 1; 431 parameters and 3957 data with I > 2sigma(I). The metal-metal distance is 3.258(2) Å. Structural and magnetic data are consistent with the presence of a metal-metal sigma bond order of (1)/(2) and with the remaining 7 electrons being located in 7 substantially nonbonding orbitals. The ground state of the molecule is predicted to be subject to a Jahn-Teller distortion, which is experimentally apparent from the nature of the thermal ellipsoid of the central Mo atom. The [Mo(3)X(12)](3)(-) ions reacts with phosphines (PMe(3), dppe) to form products of lower nuclearity by rupture of the bridging Mo-X bonds.

Coordination Chemistry of 2,2'-Dipyridyl Diselenide: X-ray Crystal Structures of PySeSePy, [Zn(PySeSePy)Cl(2)], [(PySeSePy)Hg(C(6)F(5))(2)], [Mo(SePy)(2)(CO)(3)], [W(SePy)(2)(CO)(3)], and [Fe(SePy)(2)(CO)(2)] (PySeSePy = C(5)H(4)NSeSeC(5)H(4)N; SePy = [C(5)H(4)N(2-Se)-N,Se])

The coordination chemistry of 2,2'-dipyridyl diselenide (PySeSePy) (2) (C(10)H(8)N(2)Se(2)) has been investigated and its crystal structure has been determined (monoclinic, P2(1)/c, a = 10.129(2) Å, b = 5.7332(12) Å, c = 19.173(3) Å, beta = 101.493(8) degrees, Z = 4). In metal complexes the ligand was found to coordinate in three different modes, as also confirmed by X-ray structure determination. N,N'-coordination was found in the zinc complex [Zn(PySeSePy)Cl(2)] (3) (C(10)H(8)Cl(2)N(2)Se(2)Zn, triclinic, P&onemacr;, a = 7.9430(10) Å, b = 8.147(2) Å, c = 11.999(2) Å, alpha = 93.685(10) degrees, beta = 107.763(10) degrees, gamma = 115.440(10) degrees, Z = 2) and Se,Se'-coordination in the adduct of the ligand with bis(pentafluorophenyl)mercury(II) [PySeSePyHg(C(6)F(5))(2)] (5) (C(10)H(8)F(10)HgN(2)Se(2), monoclinic, P2(1)/n, a = 7.7325(10) Å, b = 5.9974(14) Å, c = 25.573, beta = 98.037(10) degrees, Z = 2), which however displays only weak interactions between selenium and mercury. The reaction of the ligand with norbornadiene carbonyl complexes of molybdenum and tungsten leads to reductive cleavage of the selenium-selenium bond with oxidation of the metal center and concomitant addition of the resulting selenolate to the metal carbonyl fragment. Thus the 7-coordinate complexes [Mo(SePy)(2)(CO)(3)] (6) (C(13)H(8)MoN(2)O(3)Se(2), monoclinic, P2(1)/n, a = 9.319(3) Å, b = 12.886(5) Å, c = 13.231(6) Å, beta = 109.23(3) degrees, Z = 4) and [W(SePy)(2)(CO)(3)] (7) (C(13)H(8)N(2)O(3)Se(2)W, monoclinic, P2(1)/n, a = 9.303(2) Å, b = 12.853(2) Å, c = 13.232(2) Å, beta = 109.270(10) degrees, Z = 4) were obtained. The same N,Se-coordination pattern emerges from the reaction of [Fe(2)(CO)(9)] with (2) leading to [Fe(SePy)(2)(CO)(2)] (8) (C(12)H(8)FeN(2)O(2)Se(2), monoclinic, P&onemacr;, a = 8.6691(14) Å, b = 12.443(2) Å, c = 14.085(2) Å, alpha = 105.811(10) degrees, beta = 107.533(8) degrees, gamma = 92.075(10) degrees, Z = 4).