Molybdenum Derivatives Research Articles

Tris(Butadiene) Compounds versus Butadiene Oligomerization in Second-Row Transition Metal Chemistry: Effects of Increased Ligand Fields.

The geometries, energetics, and preferred spin states of the second-row transition metal tris(butadiene) complexes (C4H6)3M (M = Zr–Pd) and their isomers, including the experimentally known very stable molybdenum derivative (C4H6)3Mo, have been examined by density functional theory. Such low-energy structures are found to have low-spin singlet and doublet spin states in contrast to the corresponding derivatives of the first-row transition metals. The three butadiene ligands in the lowest-energy (C4H6)3M structures of the late second-row transition metals couple to form a C12H18 ligand that binds to the central metal atom as a hexahapto ligand for M = Pd but as an octahapto ligand for M = Rh and Ru. However, the lowest-energy (C4H6)3M structures of the early transition metals have three separate tetrahapto butadiene ligands for M = Zr, Nb, and Mo or two tetrahapto butadiene ligands and one dihapto butadiene ligand for M = Tc. The low energy of the experimentally known singlet (C4H6)3Mo structure contrasts with the very high energy of its experimentally unknown singlet chromium (C4H6)3Cr analog relative to quintet (C12H18)Cr isomers with an open-chain C12H18 ligand.

Chemical characterization of Cedrus deodara wood extracts using water and molybdenum catalysts

The effect of the presence of some molybdenum catalysts on the amount of extractives in cedar wood has been studied. Autoclave treatment of cedar wood in the presence of some molybdenum catalysts can increase the amount of extracts. While autoclave treatment of cedar wood in water gave 2.85% extractives, the same treatment in the presence of H3PMo12O40 gave 7.51% extractives. In the presence of silica-supported MoO3, the amount of extractives was 5.50%. The extractives obtained using water were partially soluble in chloroform (40.7%). Only 27.6% of the extractives obtained using H3PMo12O40 was soluble in the same organic solvent. When cedar was treated with silica-supported MoO3, 56.4% of the extractives was soluble in chloroform. The extracts can be a source of fatty acids for biodiesel production and simple carbohydrates. The analysis of the chloroform-soluble fraction showed that the autoclave treatment of cedar wood gave 49.7% of a mixture of 2-hydroxy-1-(hydroxymethyl)ethyl hexadecanoate, 2-hydroxy-1-(hydroxymethyl)ethyl octadecanoate, and 2,3-dihydroxypropyl octadecanoate. The extractives obtained in the presence of the polyoxometalate molybdenum derivative gave 95% of the same esters of fatty acids, while those obtained in the presence of silica supported MoO3 showed the presence of 93% of the same esters. Gas chromatography–mass spectrometry (GC-MS) of water-soluble fraction showed the presence of some simple carbohydrates, mainly ribose, xylose, and arabinose.

New Mo(II) complexes in MCM-41 and silica: Synthesis and catalysis

The new complexes [MoI2(CO)3(L1)] (1) and [MoI2(CO)3(L2)] (2) were prepared from reaction of [MoI2(CO)3(NCMe)2] with the ligands 2-(2′-hydroxyphenyl)imidazoline (L1), and 2-(2′-hydroxyphenyl)benzimidazole (L2). These complexes were immobilized in MCM-41 and in silica gel, by grafting (3-chloropropyl)trimethylsilane on the surface of the materials and allowing it to react with [MoI2(CO)3(L1)] (1) or [MoI2(CO)3(L2)] (2). All the molybdenum derivatives were characterized by NMR and FTIR spectroscopies, which showed coordination of L1 and L2 in neutral form. The structure of the MCM materials was analyzed by powder X-ray diffraction and nitrogen adsorption isotherms. The catalytic activity of the complexes and materials was tested in several substrates (cis-cyclooctene, styrene, 1-octene, R-(+)limonene, geraniol, cis-hex-3-en-1-ol and trans-hex-2-en-1-ol), using tert-butylhydroperoxide (TBHP) as oxidant. Complexes 1 and 2 were in general the more active catalysts and 100% selective towards the epoxide of cis-cyclooctene. Complex 1 immobilized in silica (Si-Pr-1) was the best material, showing higher conversion than 1 in the oxidation of R-(+)limonene, with comparable selectivity towards the ring epoxide.

Synthesis and spectroscopic studies of some chromium and molybdenum derivatives of bis-(acetylacetone)ethylenediimine ligand

Interaction of [Cr(CO)6] with bis-(acetylacetone)ethylenediimine Schiff base, H2acacen, under reduced pressure resulted in the formation of [Cr(CO)3(H2acacen)] derivative. The Schiff base acted as a tridentate and coordinated the metal through the nitrogen of the azomethine groups and one hydroxyl group. Reaction of [Mo(CO)6] with H2acacen under sunlight irradiation in presence of air gave the oxo derivative [Mo2O6(H2acacen)2]. The ligand acted as a bidentate and coordinated the metal through the two imine groups. In presence of 2,2′-bipyridine (bpy), the reaction of [Mo(CO)6] with H2acacen gave [Mo2O6(bpy)(H2acacec)]. The structures of the reported complexes were proposed on the basis of spectroscopic studies. The proposed structures were also verified by theoretical calculations based on accurate DFT approximations. Moreover, the relative reactivity was estimated using chemical descriptors analysis.

Synthesis of carboxylate derivatives of molybdenum and tungsten based on joint insertion of CO2 and PhNCS or N, N′-dicyclohexylcarbodiimide into M-Cl bonds

Reactions of the higher molybdenum and tungsten chlorides with phenyl isothiocyanate or with N, N′-dicyclohexylcarbodiimide and carbon dioxide in dichloroethane are the first to demonstrate the possibility of insertion of carbon dioxide in combination with other heterocumulenes into transition metal-halogen bonds. IR spectroscopy and elemental analysis data show that the reactions result in the attachment of the ligands at the same metal-chlorine bond and the formation of heteromolecular insertion products with the compositions $$\left[ {MoOCl_3 \left\{ {N\left( {Ph} \right)C\left( S \right)} \right\}_2 Nc\left( {Me} \right)Cl} \right]$$ and $$MCl_x \left\{ {OC\left( O \right)\left[ {\left( {Hex} \right)NCN\left( {Hex} \right)} \right]_2 } \right\}Cl,$$ where x = 4 and 5 for the Mo and W derivatives, respectively.

The preparation of electrophilic and electroneutral phosphane ligands and their substitution chemistry with Mo(CO)6

The synthesis, characterization and coordination chemistry of electroneutral and electron-poor phosphane ligands is reported. The addition of diaminochlorophosphanes [compounds of the type (R2N)2PCl] to ether solutions of C2F5Li produced the corresponding diaminopentafluoroethylphosphane compounds (R2N)2PC2F5 (R2N=C4H8ON, 1; C5H10N, 2; and C8H8N, 3). Similar treatment of aminodichlorophosphanes with two equivalents of C2F5Li produced compounds of the type (R2N)P(C2F5)2 (R=C4H8ON, 4; C5H10N, 5; C4H8N, 6; and C8H8N, 7). These phosphanes were isolated as high boiling liquids (1, 2, 4–7) or as a solid (3) in moderate yields (44–71%). Substitution reactions of one equivalent of 1–6 with Mo(CO)6 yielded the corresponding pentacarbonyl complexes (L)Mo(CO)5 (1a–6a). Thermolysis of 7 with Mo(CO)6 did not yield the expected pentacarbonyl complex. The phosphane compounds 1–7 and their molybdenum derivatives 1a–6a were characterized by multinuclear NMR; the CF2 region in the 19F NMR for compounds 4–7 and complexes 4a–6a displayed second-order character which complicated their interpretation. Compounds 1a–6a were also characterized by IR spectroscopy; the IR stretching frequencies for these complexes suggest that ligands 1–3 are electroneutral (and approximate the electronic influence of phosphites) while similar stretching frequencies for 4a–6a clearly establish these ligands as electrophilic.

ChemInform Abstract: Stereoselective Addition Reactions of Diphenylphosphine: meso- and rac- 1,2-Diphenyl-1,2-bis(diphenylphosphino)ethane and Their Group 6 Metal Tetracarbonyl Complexes. Crystal Structures of the Molybdenum Derivatives.

The addition of diphenylphosphine, PPh2H, to diphenylethyne in the presence of KOBut has been followed by 31P n.m.r. spectroscopy, and according to the reaction conditions can yield cis, (2) or trans, (3), 1,2-diphenyl(diphenylphosphino)ethene and then meso. (4), or rac, (5), 1,2-diphenyl-1,2-bis(diphenylphosphino)ethane, all of which have been isolated and characterised by elemental analysis and 1H, 13C, and 31P n.m.r. spectroscopy. The M(CO)4(M = Cr, Mo, or W) complexes of (4) and (5) have been prepared, and the structures of the molybdenum derivatives determined by single-crystal X-ray diffraction. In the solid state the chelate rings are puckered with one axial and one equatorial CPh group for the meso diastereomer, and two equatorial for the rac. Carbon-13 n.m.r. data suggest that the latter conformation is not fully maintained in solution.

Synthesis and Spectroscopic Studies of Some New Molybdenum, Tungsten, and Ruthenium Carbonyl Derivatives of 2-Hydroxymethylpyridine

Thermal reactions of 2-hydroxymethylpyridine (HMP) with [M(CO)6] in air resulted in formation of the oxo-complexes [M2O6(HMP)2], where M = Mo, 1, or W, 2. The tricarbonyl complex [Ru(CO)3(HMP)], 3, was obtained from the reaction of [Ru3(CO)12] with HMP. In presence of triphenyl phosphine (PPh3), the reaction of HMP with Ru3(CO)12 gave [Ru(CO)2(HMP)(PPh3)], 4. All the complexes were characterized by elemental analysis, mass spectrometry, IR, and NMR spectroscopy. The thermal properties of the complexes were also investigated by thermogravimetry technique.

Synthesis and characterization of new paramagnetic tetraaryl derivatives of chromium and molybdenum

The low-temperature reaction of [CrCl 3(thf) 3] with LiC 6H 3Cl 2-2,6 yields the organochromium(III) compound [Li(thf) 4][Cr III(C 6H 3Cl 2-2,6) 4] ( 1) in 48% yield. The homoleptic, anionic species [Cr III(C 6H 3Cl 2-2,6) 4] − is electrochemically related to the neutral one [Cr IV(C 6H 3Cl 2-2,6) 4] ( 2) through a reversible one-electron exchange process ( E 1/2 = 0.16 V, Δ E p = 0.09 V, i pa/ i pc = 1.18). Compound 2 was isolated in 74% yield by chemical oxidation of 1 with [N(C 6H 4Br-4) 3][SbCl 6]. Attempts to prepare the salt [NBu 4][Cr III(C 6Cl 5) 4] ( 4) by direct arylation of [CrCl 3(thf) 3] with LiC 6Cl 5 in the presence of [NBu 4]Br gave the organochromium(II) salt [NBu 4] 2[Cr II(C 6Cl 5) 4] ( 3) instead, as the result of a reduction process. The salt [NBu 4][Cr III(C 6Cl 5) 4] ( 4) was cleanly prepared by comproportionation of 3 and [Cr IV(C 6Cl 5) 4]. The reaction of [MoCl 4(dme)] with LiC 6Cl 5 in Et 2O solution proceeded with oxidation of the metal center to give the paramagnetic ( S = 1/2), five-coordinate salt [Li(thf) 4][Mo VO(C 6Cl 5) 4] ( 5). The crystal and molecular structures of 1 and 2 have been established by X-ray diffraction methods. The magnetic properties of 1 and 4 ( S = 3/2) as well as those of 2 ( S = 1) have been established by EPR spectroscopy as well as by ac and dc magnetization measurements.

Synthesis and structural characterization of new mixed-ring indenyl derivatives of molybdenum containing phosphorus ligands

Reaction of NaBH 4 with [IndCpMo(dppe)](BF 4) 2 ( 1) in acetone yields [IndMo(η 4-C 5H 6)(dppe)]BF 4 ( 2) quantitatively. The hydride addition takes place at the external face of the Cp ring. Dissolution of 2 in dichloromethane gives [IndMo(η 4-C 5H 5- exo-CH 2Cl)(dppe)]BF 4, as confirmed by elemental analysis, IR and 1H NMR spectroscopy. The similar dication [IndCpMo{P(OMe) 3} 2](BF 4) 2 ( 4) reacts with NaBH 4, in a solvent dependent manner. In acetonitrile, [IndMo(η 4-C 5H 6){P(OMe) 3} 2]BF 4 ( 5) is obtained and in acetone a P(OMe) 3 ligand is lost resulting in the asymmetric phosphite-hydride, [IndCpMoH{P(OMe) 3}] + ( 6). The molecular structures of [IndMo(η 4-C 5H 6){P(OMe) 3} 2]PF 6 and [IndCpMoH{P(OMe) 3}]PF 6 were characterized by single-crystal X-ray diffraction.

Functional Microporous Materials of Metal Carboxylate: Gas‐Occlusion Properties and Catalytic Activities

AbstractFor Abstract see ChemInform Abstract in Full Text.

Formation of a Superconducting Mixture of β-Mo2C Nanoparticles and Carbon Nanotubes in an Amorphous Matrix of Molybdenum Compounds by the Pyrolysis of a Molybdenum Derivative of a Carboranylenesiloxane

A pyrolytic treatment (to 1000 °C) of the organometallic reaction product of the thermo-oxidatively stable carboranylenesiloxane, 1, and cyclopentadienylmolybdenum tricarbonyl dimer, Cp2Mo2(CO)6, was discovered to yield nanoparticles of Mo2C concomitantly with carbon nanotubes in an amorphous matrix of Mo compounds. X-ray diffraction studies revealed that the Mo2C nanoparticles possess the hexagonal phase. A peak fit analysis using a Gaussian distribution function of the X-ray diffraction data revealed that 80% of the total molybdenum units in the mixture exist as β-Mo2C nanoparticles. The presence of the carbon nanotubes dispersed in the amorphous matrix was determined by both X-ray diffraction and high-resolution TEM analyses. The pyrolytic residue was determined to be superconducting with a critical temperature (Tc) of 8 K. A comparative analysis of Tc value of the residue and the reported individual Tc values of the various components in the residue (β-Mo2C, carbon nanotubes, and some possible Mo comp...

Synthesis, characterisation and molecular structure of stannyl derivatives of molybdenum and iron

In this paper, we have determined the crystal structure of [Mo(CO) 3(Cp)SnCl 3] ( 1) and used [{Fe(CO) 2Cp}SnCl 2] ( 2) to prepare two new Fe–Sn containing compounds [{Fe(CO) 2Cp}Sn(PDC)] ( 3), where PDC=2,6-pyridinedicarboxylate and [{Fe(CO) 2Cp}Sn(SPy) 2] ( 4). All compounds were fully characterised by multinuclear NMR [ 1H, 13C{ 1H} and 119Sn{ 1H}] and 119Sn [( 2)–( 4)] and 57Fe-Mössbauer spectroscopies. In addition, the structure of ( 1) and ( 3) was determined by X-ray crystallographic studies, which can be summarised as follows: ( 1) triclinic, P-1, a=7.66700(10), b=8.6000(2), c=11.3550(2) Å, α=92.8630(10)°, β=106.5030(10)° and γ=109.4020(10)°, V=668.42(2) Å 3 and Z=2. ( 3) Monoclinic, P-21/c, a=7.6586(4) Å, b=14.4866(8) Å, c=20.1209(8) Å; β=101.690(3)°, 2186.05(19) Å 3 and Z=4.

Functional microporous materials of metal carboxylate: Gas-occlusion properties and catalytic activities

Copper(II) terephthalate is the first transition metal complex found capable of adsorbing gases. This complex has opened the new field of adsorbent complex chemistry. It is recognized as the lead complex in the construction of microporous complexes. This specific system has been expanded to a systematic series of derivatives of other isomorphous transition metals, molybdenum(II), ruthenium(II, III), and rhodium(II). These complexes with open frameworks are widely recognized as very useful materials for applications to catalysis, separation at molecular level, and gas storage.

Synthesis and Crystal Structure of N-Heterocyclic Carbene Complexes of Bis(η5-cyclopentadienyl)molybdenum

Abstract The one-pot reaction of [Mo(η5-C5H5)2(H)(OTs)] (1) with 1,3-diisopropylimidazolium chloride (IiPr·HCl, 2a) in the presence of two equivalents of KOtBu in THF gave a bis(η5-cyclopentadienyl)molybdenum derivative bearing the 1,3-diisopropylimidazol-2-ylidene ligand, [Mo(η5-C5H5)2(IiPr)] (3a). 1,3-Dimethyl- and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene coordinated molybdenocene complexes (3b, 3c) were prepared in a similar fashion (Method A). The treatment of [Mo(η5-C5H5)2(H)Li]4 (6-Mo) with the corresponding imidazolium salt in THF under photo-conditions also gave carbene complexes 3a–3c (Method B). X-ray crystal structure analyses of 3a and 3b revealed that the N-heterocyclic carbene ligand is bonded to a bent molybdenocene skeleton. The Mo–C(carbene) bond distances are 2.219(7) Å for 3a and 2.212(6) Å for 3b. The five-membered carbene ligand in both complexes is located on the bisecting plane between two cyclopentadienyl rings.

Mono-indenyl and cyclopentadienyl derivatives of molybdenum(IV) with a 16 valence-electron configuration

Reactions of (ring)MoCl 3 [ring=cyclopentadienyl, η 5-C 5H 5 (Cp) and indenyl η 5-C 9H 7 (Ind)] with salts of the N, N-diethyldithiocarbamate (S 2CNEt 2) −, O, O′-diethyldithiophosphate [S 2P(OEt) 2] −, N, N′-diphenylformamidinate [CH(NPh) 2] −, acetate (O 2CCH 3) − and acetylacetonate [CH 3COCH(O)CH 3] − (acac) − anions yield the molybdenum(IV) complexes of the type (ring)MoCl 2X. Characterisation of new compounds by elemental analysis, IR and 1H-NMR spectroscopy and magnetic susceptibility measurements is discussed.

Synthesis of new half sandwich tetrachloro derivatives of molybdenum(V) and tungsten(V). X-ray structures of (C 5HPr i4)W(CO) 3(CH 3) and (C 5Et 5)WCl 4

The new synthetic intermediates (Ring)MCl 4 [Ring=C 5HPr i 4 or 4Cp, M=Mo, 2; Ring=C 5Et 5 or VCp, M=W, 4, Ring= 4Cp, M=W, 6] containing sterically protecting cyclopentadienyl ligands have been synthesized. Along the synthetic pathway to 2, it was found that the treatment of [ 4CpMo(CO) 3] − with an aqueous ferric solution according to the well established Manning procedure affords the hydride compound 4CpMo(CO) 3H ( 1) by hydrolysis rather than the expected neutral dimer by oxidation. Compound 1 could be converted, however, to 2 upon oxidation with PhICl 2 in good yields. Compound 4 is shown by a single crystal X-ray analysis to adopt a monomeric four-legged piano stool structure. The precursors to compounds 4 and 6, (Ring)W(CO) 3(CH 3) (Ring= VCp, 3; 4Cp, 5) have also been characterized, including an X-ray structure for 5.

Bis-indenyl molybdenum(iv) halide complexes: synthesis and X-ray studies

A stepwise route to bis-indenyl halide derivatives of molybdenum is reported. Treatment of [Ind2Mo(CO)2][BF4]2 with one equivalent of Bu4NBr in CH2Cl2 yielded [Ind2Mo(CO)Br][BF4] (1). When 1 was refluxed in NCMe and irradiated with a 60 W tungsten bulb [Ind2Mo(NCMe)Br][BF4] (2) was isolated. The reaction of [Ind2Mo(CO)Br][BF4] with LiBr afforded Ind2MoBr2 (3). The Ind2MoCl2 (4) analogue has been prepared directly by reaction of [Ind2Mo(CO)2][BF4]2 with LiCl.

The effect of trimethylsilyl substituents on the ring-slippage of bis-indenyl-molybdenocene derivatives

A group of new trimethylsilyl indenyl derivatives of molybdenum is reported, starting from the allyl compound TMSIndMo(η 3-C 3H 5)(CO) 2 [TMSInd=η 3-SiMe 3C 9H 6]. The novel allyl Mo(II) complex, which is synthesized by the reaction of Mo(η 3-C 3H 5)(CO) 2(NCMe) 2Cl with Li(TMSInd) in THF, is the precursor to trimethylsilyl indenyl derivatives. Treatment of TMSIndMo(η 3-C 3H 5)(CO) 2 with HCl and addition of LiInd or LiTMSInd gives the ring-slipped complexes (η 5-TMSInd)Mo(η 3-Ind)(CO) 2 or (η 5-TMSInd)Mo(η 3-TMSInd)(CO) 2 in high yield. The presence of the trimethylsilyl substituent changes substantially the flexibility of the indenyl groups. These new substituted indenyl complexes were characterized by experimental techniques and ab initio calculations, and examined by cyclic voltammetry.

Polymers with a backbone consisting of bimetallic tetracarboxylates and organometallic rhenium(I) complexes: synthesis, characterization, and structural examination

The reaction of [(2,2′-bpy)(CO) 3Re(4,4′-bpy)](CF 3SO 3) with M 2(O 2CR) 4 (M=Mo, R=CF 3; M=Rh, R=CH 3) leads to the tetranuclear complexes [(2,2′-bpy)(CO) 3Re(4,4′-bpy)] 2[LM 2(O 2CR) 4](CF 3SO 3) 2 ( 1, 2). They are characterized by elemental analysis, 1H, 13C and 19F NMR, IR spectroscopy, and examined by UV-spectroscopy, cyclic voltammetry and thermogravimetry (TGA). The molecular structure of the rhodium-complex 2 is additionally determined by X-ray single crystal analysis, revealing comparatively strong axial RhN interactions. The RhRh bond distance (approximately 239.5 pm) is within the expected range. No evidence for intramolecular electronic communication between the Re(I)–ligands via the central metal–metal unit has been found in these tetranuclear systems in CH 3CN solution, probably due to the tilt of the 4,4′-bipyridine ligand which prevents proper orbital overlap. Oligomers 3 and 4 with backbones consisting of M 2(O 2CR) 4 (M=Mo, R=CF 3; M=Rh, R=CH 3) and Re(CO) 3Br(4,4′-bpy) 2 have also been prepared. The elemental analyses are consistent with the stoichiometry M 2(O 2CR) 4–Re(CO) 3Br(4,4′-bpy) 2=1:1. Complexes 3 and 4 are not square with the rhenium(I)-centers at the corners but oligomers with zig-zag chain structures, according to IR-spectroscopy. The rhodium-complex 4 is insoluble in all common solvents, whereas the molybdenum derivative 3 dissolves in the strongly coordinating donor solvent DMF most likely due to the replacement of Re(CO) 3Br(4,4′-bpy) 2 by DMF in the axial positions of Mo 2(O 2CCF 3) 4. TGA studies indicate the strength of the metal–axial ligand interactions both in the tetranuclear complexes and in the oligomers in the solid state.