Oxidoperoxidomolybdenum(VI) complexes with acylpyrazolonate ligands: synthesis, structure and catalytic properties

Oxidoperoxido–molybdenum(VI) complexes containing acylpyrazolonate ligands were obtained by reaction of [Mo(O)(O)2(H2O)n] with the corresponding acylpyrazolone compounds HQR. Complexes Ph4P[Mo(O)(O2)2(QR)] (R = neopentyl, 1; perfluoroethyl, 2; hexyl, 3; phenyl, 4; naphthyl, 5; methyl, 6; cyclohexyl, 7; ethylcyclopentyl, 8) were obtained if the reaction was carried out with one equivalent of HQR in the presence of Ph4PCl. Alternatively, neutral complexes [Mo(O)(O2)(QR)2] (R = neopentyl, 9; hexyl, 10; cyclohexyl, 11) were formed when two equivalents of HQR were used in the reaction. These complexes were isolated in good yields as yellow or yellow-orange crystalline solids and were spectroscopically (IR, 1H, 13C{1H} and 31P{1H} NMR), theoretically (DFT) and structurally characterised (X-ray for 1, 2, 9 and 10). Compounds 1 and 9 were selected to investigate their catalytic behaviour in epoxidation of selected alkenes and oxidation of selected sulphides, while 10 and 11 were tested as catalyst precursors in the deoxygenation of selected epoxide substrates to alkenes, using PPh3 as the oxygen-acceptor. Complexes Ph4P[Mo(O)(O2)2(QR)] were shown to be poor catalyst precursors in oxidation reactions, while the activity of [Mo(O)(O2)(QR)2] species is good in all the studied reactions and comparable to related oxidoperoxido–molybdenum(VI) complexes. Complex [Mo(O)2(QC6)2], 12, was obtained by treatment of 10 with one equivalent of PPh3, demonstrating that the first step in the epoxide deoxygenation mechanism was the oxygen atom transfer toward the phosphane.Junta de Andalucía (Proyecto de Excelencia, FQM-7079)Universidad de Sevilla (VI Plan Propio

Koordinationschemie -gebundener Cyclopentadienyl-Chalkogeno-Ether

Coordination Chemistry of rr-Bonded Cyclopentadienyl Chalcogeno Ethers, I. - Chelate Complexes of Pentakis(methylthio)cymantrene with Metal Carbonyls [C5(SMe)5]Mn(CO)3 (1) reacts with W(CO)5(THF), Mo(CO)4(C7H8), Cr(CO)3(NCMe)3, and Re(CO)4(-C3H5)/HBF4 to yield the monochelate complexes [[C5(SMe)5]Mn(C0)3][M(CO)4] (M = W: 2; M = Mo: 3) and the dichelate complexes [[C5(SMe)5]Mn(CO)3][M(C0)4]2 (M = W: 4; M = Cr: 5; M = Re BFF4 : 6). The reaction with Mo(CO)3(p-xylene) in THF leads via unstable intermediates, which contain coordinated THF, to a mixture of 3 and [[C5(SMe)5]Mn(CO)3][Mo(CO)4]2 (7). The structures of 3 and 4 in the crystal have been determined by X-ray diffraction methods

Theoretical investigation of the scope of sequential ligand tuning using a bifunctional scorpionate tris(1,2,4-triazolyl)borate-based architecture

The donor properties of a series of tripodal mixed N-donor/carbene ligands derived through sequential alkylation of hydrotris(1,2,4-triazolyl)borate have been investigated by density functional theory (DFT) methods. The structures of complexes of the form [Mo(L)(CO)3]- were optimized (L = [HB(1,2,4-triazolyl)n(1,2,4-triazol-5-ylidene)3-n]- (n = 0 – 3), hydrotris(pyrazolyl)borate, hydrotris(3,5-dimethylpyrazolyl)borate and hydrotris(imidazol-2-ylidene)borate) and nuCO frequencies for these complexes and partial charges of their Mo(CO)3 fragments were determined. Results show that ligand donation is highly tunable when compared to similar experimentally known ligands with a shift in the symmetric nuCO stretching mode of -39 cm -1 on going from the tris(1,2,4-triazolyl)borate complexes to that of the triscarbene hydrotris(1,2,4-triazol-5-ylidene) and an increase in partial charge (distributed multipole analysis) of the Mo(CO)3 fragment from -0.23 to -0.48

Molybdenum (VI) imido complexes derived from chelating phenols : Synthesis, characterization and ɛ-Caprolactone ROP capability

Reaction of the bulky bi-phenols 2,2′-RCH[4,6-(t-Bu)₂C₆H₂OH]₂ (R = Me L¹ᵐᵉH₂, Ph L¹ᵖʰH₂) with the bis(imido) molybdenum(VI) tert-butoxides [Mo(NR¹)(NR²)(Ot-Bu)₂] (R¹ = R² = 2,6-C₆H₃-i-Pr₂; R¹ = t-Bu, R² = C₆F₅) afforded, following the successive removal of tert-butanol, the complexes [Mo(NC₆H₃ᵢ-Pr₂-2,6)₂L¹ᵐᵉ] (1), [Mo(NC₆H₃i-Pr₂-2,6)₂L¹ᵖʰ] (2) and [Mo(Nt-Bu)(μ-NC₆F₅)(L¹ᵐᵉ)]₂ (3). Similar use of the tri-phenol 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-methylphenol (L²H₃) with [Mo(NC₆H₃ᵢ-Pr₂-2,6)₂(Ot-Bu)₂] afforded the oxo-bridged product [Mo(NC₆H₃i-Pr₂-2,6)(NCMe)(μ-O)L2H]₂ (4), whilst use of the tetra-phenols α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p- or -m-xylene L³ᵖH₄/L³ᵐH₄ led to {[Mo(NC₆H₃ᵢ-Pr₂-2,6)₂]₂(μ-L³ᵖ)} (5) or {[Mo(NC₆H₃ᵢ-Pr₂-2,6)₂]₂(μ-L³ᵐ)} (6), respectively. Similar use of [Mo(NC₆F₅)₂(Ot-Bu)₂] with L³ᵖH₄ afforded, after work-up, the complex {[Mo(NC₆F₅)(Ot-Bu)₂]₂(μ-L³ᵖ)}·6MeCN (7·6MeCN). Molecular structures of 1, 2·CH₂Cl₂, 3, 4·6MeCN, 6·2C₆H₁₄, and 7·6MeCN are reported and these complexes have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; for comparative studies the precursor complex [Mo(NC₆H₃ᵢ-Pr₂-2,6)₂Cl₂(DME)] (DME = 1,2-dimethoxyethane) has also been screened. Results revealed that good activity is only achievable at temperatures of ≥100 °C over periods of 1 h or more. Polymer polydispersities were narrow, but observed molecular weights (Mn) were much lower than calculated values

Surface chemistry of heterobimetallic Ge-M (M = Mo, W) complexes in zeolite Y.

The intrazeolite chemistry of the two germylene complexes Cl2CTHF)GeM(CO)5 (M = Mo, W) was studied with x-ray absorption spectroscopy (Ge, Mo, W edge EXAFS) and in-situ FTIR/TPD-MS techniques. The slightly decarbonylated GeMo complex interacts with the framework of NaY zeolite at room temperature and retains the Ge-Mo bond up to about 100° C. In proton-loaded HY zeolite, framework interactions increase at elevated temperature, and the attached complex retains the Ge-Mo bond up to about 120° C. The Ge-Mo bond is cleaved at higher temperatures. MoClx and Mo-Mo species are formed in NaY and HY zeolite, respectively, while GeClx fragments are anchored to the zeolite framework. The complex Cl2(THF)GeW(CO)5 retains all five CO ligands up to about 100° C in both NaY and the proton form. Detectable anchoring occurs at room temperature in NaY and at about 80° C in the proton form. WC1X species are formed upon cleavage of the Ge-W bond at higher temperatures

Synthesis and reactions of phosphonito polymetallic complexes and halogen oxidation of cyclo-tetraphosphoxane molybdenum cage complexes

Mixed-valent tetrametallic complexes of the type Mo\sb2\lbrackM(CO)\sb4(PhPO\sb2)\sb2\rbrack\sb2\sp{4-} (M = Cr, Mo, W) were synthesized by the nucleophilic attack of the phosphonito metallo-ligand cis-M(CO)\sb4(PhPO\sb2)\sb2\sp{4-} on dimolybdenum tetraacetate. These complexes were characterized by elemental analyses and NMR, IR, and UV-Vis spectroscopy. The x-ray crystal structure for the tetra-molybdenum complex indicates a M-M bondlength of 2.186(2). Only weak interactions were found with potential axial ligands such as amines, phosphines and isonitriles. Oxidation with four equivalents of iodine occurred at the Mo(O) sites yielding Mo\sb2\lbrackMo(CO)\sb3I\sb2(PhPO\sb2)\sb2\rbrack\sb2\sp{4-} with new seven-coordinate Mo(II) sites. The phosphorus-31 NMR spectrum of this complex exhibits temperature-dependent behavior indicating rapid geometric isomerization in solution. Phosphonito metallo-ligands were also used to assemble bimetallic cage complexes of the adamantane type, (CO)\sb4M(RPO\rbrack\sb4M(CO)\sb4. The reactivity of dimolybdenum cages (R = \rm\sp{i}Pr\sb2N, Ph) towards halogen oxidation is dependent on the nature of the phosphorus substituent. In a competitive iodination experiment, the phenyl cage reacted more slowly than the isopropylamino cage. Both cages yield mixed-valent dihalo and tetrahalo complexes upon oxidation. Structural data suggests that the mixed-valent dihalo complexes of the isopropylamino cage are dimers in the solid state but monomers in solution. The tetrahalo complexes, (CO)\sb2X\sb2Mo(RPO\rbrack\sb4Mo(CO)\sb2X\sb2, (X = Cl, Br, I) exhibit solubility behavior consistent with halogen-bridged polymeric units in the solid state. In contrast, halogen oxidations of the phenyl cage yield the less stable, seven-coordinate mixed valent complexes (CO)\sb4Mo(RPO\rbrack\sb4Mo(CO)\sb3X\sb2. These readily lose CO to give unidentified products. Limited data available for the tetrahalo phenyl cage complexes suggest that they exist as seven-coordinate monomers, (CO)\sb3X\sb2Mo(RPO) \sb4Mo(CO)\sb3X\sb2

Imido–hydrido complexes of Mo(IV): catalysis and mechanistic aspects of hydroboration reactions

Imido–hydrido complexes (ArN)Mo(H)(Cl)(PMe3)3 (1) and (ArN)Mo(H)2(PMe3)3 (2) (Ar = 2,6-diisopropylphenyl) catalyse a variety of hydroboration reactions, including the rare examples of addition of HBCat to nitriles to form bis(borylated) amines RCH2N(BCat)2. Stoichiometric reactivity of complexes 1 and 2 with nitriles and HBCat suggest that catalytic reactions proceed via a series of agostic borylamido and borylamino complexes. For complex 1, catalysis starts with addition of nitriles across the Mo–H bond to give (ArN)Mo(Cl)(NvCHR)(PMe3)2; whereas for complex 2 stoichiometric reactions suggest initial addition of HBCat to form the agostic complex Mo(H)2(PMe3)3(η3-NAr-HBcat

Hexaazide octahedral molybdenum cluster complexes: synthesis, properties and the evidence of hydrolysis

This article reports the synthesis, crystal structure of new molybdenum hexaazide cluster complex (ⁿBu₄N)₂[{Mo₆I₈}(N₃)₆] (3) and comparison of its photophysical and electrochemical properties to those of earlier reported analogues (ⁿBu₄N)₂[{M₆X₈}(N₃)₆] (X = Cl, Br). Additionally, the dimerisation of 3 as a result of hydrolysis was revealed by mass spectrometry and single crystal X-Ray diffraction. Indeed, the structurally characterised compound (ⁿBu₄N)₄[{Mo₆I₈}(N₃)₅)₂O] represents the first example of oxo-bridged dimer of octahedral molybdenum clusters complexes

Calculation of transition metal compounds using an extension of the CNDO formalism. II. Metal to metal bonding in binuclear transition metal compounds

A recently developed extension of the CNDO-method (Freund and Hohlneicher, 1979) is used to study the electronic structure of a no. of binuclear transition metal carbonyls and carboxylates with 4-fold or quasi-4-fold symmetry. The results are compared to those available from nonempirical calcns. Special attention is paid to the nature of the metal-metal bond. Connections with qual. MO-considerations allow a fairly general discussion of metal-metal bonding in binuclear transition metal complexes with basic 4-fold symmetry. A few, up to now unknown, but possibly existing, complexes are considered

Mono-oxo molybdenum(VI) and tungsten(VI) complexes bearing chelating aryloxides: synthesis, structure and ring opening polymerization of cyclic esters

The mono-oxo aryloxide complexes [M(O)(L1)2] (M = Mo (1·hexane), W(2·2MeCN)) have been prepared from [Mo(O)(Cl)4] or [W(O)(Ot-Bu)4] and two equivalents of the di-phenol 2,2/-ethylidenebis(4,6-di-tert-butylphenol) L1H2, respectively. Use of in-situ generated [Mo(O)(Ot-Bu)4] with two equivalents of L1H2 also led to the isolation of 1·2MeCN. In the presence of adventitious oxygen, attempts to generate in-situ [Mo(O)(Ot-Bu)4] and reaction with one equivalent of L1H2 afforded the bi-metallic complex [Mo(O)(L1)(-O)Li(THF)(MeCN)]2·2MeCN (3·2MeCN). Use of the tetra-phenol α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xyleneH4 (L2H4) with [Mo(O)(Oi-Pr)4] led to the isolation of {[Mo(O)]L2}2 (4), whilst the analogous tungsten complex {[W(O)]L2}2 (5) was isolated from the reaction of L2H4 with [W(O)(Ot-Bu)4]. Similar reaction of p-tert-butylcalix[4]areneH4 (L3H4) with [Mo(O)(Oi-Pr)4] afforded ([Mo(O)L3(NCMe)]·3MeCN (6·3MeCN). Modification of known routes were employed to access the complexes [W(Cl)2L3]·3.5MeCN (7·3.5MeCN) and ([W(O)L3(NCMe)] (8), whilst use of [WO(Ot-Bu)4] with L3H4 unexpectedly afforded [W(Ot-Bu)2L3]·MeCN (9·MeCN). The molecular crystal structures for 1 – 9 are reported, and the ability of these complexes to act as catalysts for the ring opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL), delta-valerolactone (delta-VL) and gamma-pentadecalactone (gamma-PDL) has been investigated. The molybdenum complexes 1 and 4 were the best performers for epsilon-Cl and delta-VL, but all complexes exhibited poor control and were also inactive toward the ROP of PDL