Konstantinos Mertis

New synthesis of hexamethyltungsten(VI); hexamethylrhenium(VI) and dioxotrimethylrh enium(VII)

Abstract A new synthesis of hexamethyltungsten involves the reaction of WCl 6 and AlMe 3 , while interaction of AlMe 3 and ReOMe 4 gives ReMe 6 ; a dioxorhenium(VII) methyl, ReO 2 Me 3 , is reported.

Trimethylsilylmethyl and methyl compounds of manganese, cobalt and uranium

Abstract Thermally stable alkylmanganese(II) compounds, Mn(CH2R)2 R = SiMe3, CMe3 and CMe2Ph have been isolated; and oxidation with dioxygen shown to give unstable green alkylmanganese(IV) compounds; lithium alkylate anions of manganese(II), cobalt(II) and uranium(IV) have also been isolated as tetrahydrofuran or tetramethylethylenediamine solvates, the uranium compounds, e.g. Li2 [U(CH2SiMe3)6](tmed)7 being the first uranium complexes with more than one metal to carbon σ-bond.

Reactions of potassium carbonyl(π-cyclopentadienyl)nickelate with butenyl and cyclopropylmethyl halides

The reaction of carbonyl(π-cyclopentadienyl)nickel anion with but-3-enyl and cyclopropylmethyl halides has been investigated. In the former case, the only isolated product is 1–3-η-but-2-enyl-π-cyclopentadienylnickel (85 : 15 (trans : cis) whereas in the latter, a cyclopropylmethylnickel complex could be isolated. This was converted by thermolysis, or more effectively by photolysis into a 1-σ : 4–5-η-1-oxopent-4-enylnickel, most probably derived by insertion of a cyclopropane C–C bond into the metal carbonyl system.

Exploring the Reactivity of Na[W2(μ-Cl)3Cl4(THF)2]∙(THF)3 towards the Polymerization of Selected Cycloolefins

The bimetallic compound Na[W2(μ-Cl)3Cl4(THF)2]·(THF)3 (1, {W 3 W}6+, a′2e′4) is a highly efficient room-temperature initiator for ring opening metathesis polymerization (ROMP) of norbornene (NBE) and some of its derivatives. In most cases, addition of phenylacetylene (PA) as co-initiator improves the catalytic activity and retains the high cis-stereoselectivity. On the other hand, 1 can polymerize cyclopentadiene (CPD), not via a metathetic, but rather, via a cationic mechanism. Here, we present a comparison of the reactivity of the two catalytic systems (1 and 1/PA) between themselves and with other systems reported in the literature, the characterization of the polymers formed and mechanistic aspects of the corresponding reactions.

The interaction of hydrogen with tri-µ-chloro-hexakis(trimethylsilylmethyl)-triangulo-trirhenium(III), its adducts with carbon monoxide, triphenylphosphine, and pyridine and with tri-µ-chloro-chloropentakis-(trimethylsilylmethyl)-triangulo-trirhenium(III). The X-ray crystal structures of hydridononakis(trimethylsilylmethyl)bis[tri-µ-chloro-triangulo-trirhenium(III)], tri-µ-chloro-chlorohydridotetrakis(trimethyl-silylmethyl)(triphenylphosphine)-triangulo-trirhenium(III), and syn,syn,-anti-trichloro-tris(µ-trimethylsilylmethyl)-tris(trimethylsilylmethyl)-triangulo-trirhenium(III)

The interaction of tri-µ-chloro-hexakis(trimethylsilylmethyl)-triangulo-trirhenium(III), Re3(µ-Cl)3(CH2SiMe3)6, with dihydrogen in tetrahydrofuran leads to a hexanuclear hydrido-alkyl (Me3SiCH2)5(µ-Cl)3Re3–Re3(µ-Cl)3H-(CH2SiMe3)4,(1), whose structure has been determined by X-ray diffraction. Crystals are triclinic, space group p, with a= 15.950(5), b= 16.351(6), c= 16.386(6)A, α= 62.31(2), β= 94.25(3), γ= 99.77(3)°, and Z= 2. The structure was solved and refined to an R of 0.055 using 6 796 unique observed data (out of 10 203 measured). The two Re3 triangles are linked by a single Re–Re bond of length 2.993(1)A which constitutes, in each case, one of the terminal, out-of-plane bonds on six-co-ordinated Re. The Re–Re distances in the Re3 triangle [2.390–2.420(1)A] are slightly disturbed by the asymmetry of the co-ordinated ligands.Hydrogenation of Re3Cl3(CH2SiMe3)6 in benzene, by contrast, produces a hexanuclear hydrido-alkyl, Re6(µ-Cl)6H6(CH2SiMe3)6, (2), for which a structure with two triangulo-Re3Cl3 units linked by alkyl bridges and with terminal hydrogen atoms is proposed.The interaction of the alkyl Re3(µ- Cl)3Cl(CH2SiMe3)5, which has a terminal Re–Cl group, with hydrogen in the presence of triphenylphosphine gives a green complex, Re3(µ-Cl)3ClH(CH2SiMe3)4(PPh3), (3), whose structure has been determined by X-ray diffraction. These crystals are also triclinic, space group p with a= 17.732(3), b= 13.212(3), c= 11.723(4)A, α= 90.95(3), β= 95.04(3), γ= 83.74(2)°, and Z= 2. The final R value is 0.063 for 3 704 (8 536) observed data. The Re–Re distances in the Re3 triangle [2.382(1)–2.411(2)A] show the expected variation with rhenium co-ordination number. The phosphine is quite weakly bound [Re–P = 2.617(7)A].The interaction of hydrogen with the adducts Re3(µ-Cl)3(CH2SiMe3)6L3, L = CO, PPh3, pyridine (py), and H2O, has been studied. For L = CO and PPh3, reductive cleavage of the cluster occurs to give the rhenium (II) metal–metal bonded dimers Re2Cl2(CH2SiMe3)2(CO)2, (4), and Re2Cl2(CH2SiMe3)2(PPh3)2, (5). For L = py the triangulo-trirhenium cluster is retained in the paramagnetic rhenium(II) alkyl Re3(µ-Cl)3(CH2SiMe3)3(py)3, (6), whose e.s.r. spectrum is discussed. For L = H2O, a polynuclear cluster, probably [Re3(µ-Cl)3(CH2SiMe3)3(OH2)3]6, (7), is obtained.The hydride (2) isomerises alk-1-enes under nitrogen and hydrogenates them under hydrogen, but the catalytic reaction decays due to the formation of a non-hydride hexanuclear species, Re6(µ-Cl)6(CH2SiMe3)6, (8). Thermal decomposition of (2) leads to a dodecameric species, Re12(µ-Cl)12(CH2SiMe3)6, (9).The hydrogenation of the red supernatant from the synthesis of Re3(µ-Cl)3(CH2SiMe3)6 leads to a red isomer of this blue species, which X-ray structural determination shows to have bridging alkyl groups and to be Re3Cl3(µ-CH2SiMe3)3(CH2SiMe3)3, (10), and syn,syn,anti-terminal chlorine atoms. The compound is monoclinic, space group P21/n, with a= 17.939(2), b= 11.280(1), c= 22.933(4)A, β= 109.98(1)°, and Z= 4. The final R value is 0.048 for 5 293 (8 487) observed data. The Re–Re distances here are 2.337–2.359(1)A and are shorter than in the isomeric chloride-bridged species. Small distortions in the Re3C3 cluster are attributed to intramolecular crowding.New aryl triangulo-clusters Re3(µ-Cl)3R6, R = C6H5, (11), and C6H4Me-p, (12), and the bridged methyl Re3(µ-CH3)3(CH2SiMe3)6(13), are described.

Trirhenium(III) cluster alkyls. Synthesis of tertiary phosphine adducts; cleavage to rhenium-(III) and -(II) dimers; reactions with carbon monoxide, nitric oxide, and hydrogen chloride. X-Ray structural determinations of hexamethylbis(diethylphenylphosphine)tri-µ-methyl-triangulo-trirhenium(III) and tri-µ-chloro-(N-nitroso-N-trimethylsilyl-methylhydroxylaminato)pentakis(trimethylsilylmethyl)-triangulo-tri-rhenium(III)

A new cluster benzyl, Re3Cl3(CH2Ph)6, and tertiary phosphine (L) adducts of the corresponding cyclohexyl, Re3Cl3(C6H11)6L3, and of the permethyl, Re3Me3L2,3, have been prepared. The structure of the diethylphenylphosphine derivative Re3Me9(PEt2Ph)2 has been confirmed by a single-crystal X-ray structure determination. Crystals are monoclinic, space group C2/c, with dimensions a= 27.220(4), b= 9.817(1), c= 26.051(5)A, and β= 102.65(2)° and the structure was solved by direct methods and refined by least squares to an R of 0.043 using 4 982 unique observed intensities. The Re3Me9 unit present in the trinuclear molecule is considerably distorted as a result of steric compression from the two strongly bound phosphines. The trinuclear rhenium(III) phosphine adducts undergo cleavage reactions to give dimeric compounds of rhenium(III) or rhenium(II), examples being Re2Me6(PMe2Ph)2 and Re2Cl2(CH2SiMe3)2(PMe3)4. The reactions of the blue trimethylsilylmethyl cluster Re3Cl3(CH2SiMe3)6 with CO, NO, and HCl are described. Nitric oxide is shown to give an insertion product with an N-(trimethylsilylmethyl)-N-nitrosohydroxylaminato-chelate ring, of formula Re3Cl3(CH2SiMe3)5{ON(CH2SiMe3)-NO} whose structure has also been confirmed by X-ray structure determination. Crystals are monoclinic, space group P21/a, with a= 33.33(4), b= 11.733(5), c= 11.947(6)A, and β= 92.93(4)°. The structure was solved by direct methods and refined by least squares to an R of 0.067 using 4 360 observed data. The nitrosohydroxylaminato-ligand chelates symmetrically (Re-O 2.10 A× 2) to one of the metal atoms, using one out-of-plane and the in-plane terminal sites.

Isolation, Characterization, and Computational Studies of the Novel [Mo3(μ3-Br)2(μ-Br)3Br6]2― Cluster Anion

The novel trimolybdenum cluster [Mo(3)(mu(3)-Br)(2)(mu-Br)(3)Br(6)](2-) (1, {Mo(3)}(9+), 9 d-electrons) has been isolated from the reaction of [Mo(CO)(6)] with 1,2-C(2)H(4)Br(2) in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)(4)N(+) (1), Et(4)N(+), Et(3)BzN(+)), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)(4)N(+) salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) A, b = 11.8638(11) A, c = 22.521(2) A, alpha = 90 deg, beta = 109.348(4) deg, gamma = 90 deg, V = 5061.3(9) A(3), Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (mu(eff), 1.55 mu(B), r.t.) is lower than the spin-only value (1.73 mu(B)) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm(-1)). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided.

Theoretical elucidation of a classic reaction: protonation of the quadruple bond of the octachlorodimolybdate(II,II) [Mo2Cl8]4- anion.

The protonation reaction of the unbridged quadruple metal-metal bond of [Mo(2)Cl(8)](4-) anion producing the triply bonded hydride [Mo(2)(μ-H)(μ-Cl)(2)Cl(6)](3-) is studied by accurate Density Functional Theory computations. The reactant, product, stable intermediates, and transition states are located on the potential energy surface. The water solvent is explicitly included in the calculations. Full reaction profiles are calculated and compared to experimental data. The mechanism of the reaction is fully elucidated. This involves two steps. The first is a proton transfer from an oxonium ion to the quadruple bond, being rate determining. The second, involves the internal rearrangement of chlorine atoms and is much faster. Activation energies with a mean value of 19 kcal/mol are calculated, in excellent agreement with experimental values.

Interaction of trirhenium(III) cluster alkyls with carboxylic acids, β-diketones, and diphenyltriazene

The interaction of the triangulo-trirhenium cluster alkyls, Re3Cl3(CH2SiMe3)6 and Re3Me9, With carboxylic acids, β-diketones, and 1,3-diphenyltriazene leads to partial or complete loss of tetramethylsilane or methane from the end alkyl groups, respectively, and the formation of rhenium(III) complexes that may be either monomeric, i.e. triangulo-trirhenium, Re3, or dimeric in which two such units are linked together by carboxylate bridges to give Re6 species.Examples of monomeric complexes are the benzoate, Re3Cl3(CO2Ph)6, β-diketonates, Re3Me6(β-dik)3, and the diphenyltriazenide, Re3Cl3(CH2SiMe3)3(PhN3Ph)3.The dimeric complexes are carboxylates such as Re6(µ-Cl6)(CH2SiMe3)6(µ-CO2Me)6 and Re6(µ-Me6)Me6(µ-CO2Me)6, in which the Cl or Me bridges between rhenium atoms in each Re3 triangle are retained.I.r. and 1H n.m.r. spectra are reported and likely structures for the complexes suggested.

The chemistry of rhenium alkyls. Part III. The synthesis and reactions of hexamethylrhenium(VI), cis-trimethyldioxorhenium(VII), and the octa-methylrhenate(VI) ion

The green, crystalline, paramagnetic (d1) hexamethylrhenium, ReMe6, has been prepared by interaction of tetramethyloxorhenium(VI), ReOMe4, with trimethylaluminium. It is characterised by mass, i.r., and e.s.r. (reported separately) spectra. It reacts with dioxygen to give ReOMe4 and with nitric oxide to give cis-trimethyldioxorhenium(VII), ReO2Me3: the latter is best prepared by the action of NO on ReOMe4. The mechanism of this reaction is discussed and an intermediate of stoicheiometry ReO(CH3)3(CH3NO) is characterised. N.m.r. spectra of the oxo-species are reported.Interaction of hexamethylrhenium with methyl-lithium forms the octamethylrhenate(VI) ion, which can be isolated as the tetramethylethylenediamine (tmed) salt Li2[ReMe8]·tmed.An improved synthesis of ReOMe4 is given.