Palladium-catalyzed carbonylative synthesis of N-(2-cyanoaryl)benzamides and sequential synthesis of quinazolinones

A convenient procedure for the synthesis of N-(2-cyanoaryl)benzamides has been developed. Using aryl bromides and 2-aminobenzonitriles as the substrates, Mo(CO)₆ as the CO source, the desired amides were produced in good yields. Quinazolinones were produced in good yields in a sequential manner as well.     

Reactions of GeMe2-bridged dicyclopentadienes with molybdenum carbonyl: formation of germylidyne trimolybdenum clusters

In thermal reactions of the doubly bridged dicyclopentadienes (C₅H₃R(SiMe₂))(C₅H₃R(GeMe₂)) (R=H (1), ^tBu (5)) with Mo(CO)₆, the bridging GeMe₂ is cleaved to give the corresponding degermylated products [(η⁵-C₅H₃R)₂(SiMe₂)]Mo₂(CO)₆ (3, rac-7), or both GeMe₂ and SiMe₂ are cleaved to afford the nonbridged products [(η⁵-C₅H₄R)Mo(CO)₃]₂ (2, 6). The reactions also produce germylidyne trimolybdenum clusters [(η⁵-C₅H₃R)₂(SiMe₂)](η⁵-C₅H₄R)[Mo(CO)₂]₃(μ₃-GeMe) (4, rac-/meso-7) containing the Mo₃(μ₃-GeMe) units. Similarly, reaction of the single GeMe₂-bridged dicyclopentadienes (C₅H₅)₂GeMe₂ (9) with Mo(CO)₆ also results in the degermylated 2, as well as the similar trimolybdenum cluster [(η⁵-C₅H₅)Mo(CO)₂]₃(μ₃-GeMe) (10). The molecular structures of 4 and trans-5 were determined by X-ray diffraction.     

A facile and efficient deoxygenation of amine-N-oxides with Mo(CO)6

A variety of amine-N-oxides have been found to be selectively deoxygenated to the corresponding amines in high yields with Mo(CO)₆ in ethanol under mild conditions.     

Metathesis polymerisation of phenylacetylene catalysed by (arene)Mo(CO)3 activated by electron acceptor chloranil

Phenylacetylene (PA) was polymerised by employing (arene)Mo(CO)₃/chloranil mixture as the catalyst. Preliminary kinetic studies of the polymerisation showed the presence of an induction period before commencement of polymerisation, attributable to the activation of the (arene)Mo(CO)₃ by chloranil through charge-transfer. It was shown that better control over polymer molecular weight and polydispersity was achieved with prior mixing of the metal carbonyl complex with the acceptor and by delaying the addition of the monomer. Polymerisation by metathesis route was ascertained by copolymerisation, sequential addition of monomers and also by end-capping reactions.     

Complexation of phthalides and substituted 3-benzylidene phthalides with Cr(CO)6

The acid-catalysed complexation of various substituted phthalides with Cr(CO)₆ has been studied. Complexation of substituted 3-benzylidene phthalides takes place at the phenyl ring in most cases, but with di-halogeno-substituted 3-benzylidene phthalides the complexation took place at the phthalide moiety. An explanation of this difference is based on molecular modelling quantum chemical calculations.     

Synthesis and spectroscopic studies of some new metal carbonyl derivatives of 1-(2-pyridylazo)-2-naphthol

Interaction of 1-(2-pyridylazo)-2-naphthol (PAN) with [Mo(CO)₆] in air resulted in formation of the tricarbonyl oxo-complex [Mo(O)(CO)₃(PAN)], 1. The dicarbonyl complex [Ru(CO)₂(PAN)], 3, was obtained from the reaction of [Ru₃(CO)₁₂] with PAN. In presence of triphenyl phosphine (PPh₃), the reaction of PAN with either Mo(CO)₆ or Ru₃(CO)₁₂ gave [Mo(CO)₃(PAN)(PPh₃)], 2, and [Ru(CO)₂(PAN)(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.     

Thermal characterisation of molybdenum and platinum-molybdenum catalysts

Alumina supported Mo and Pt-Mo catalysts was subject to temperature programmed reduction (TPR) using H₂ and CO. After earlier oxidation step TPR–H₂ profiles shows different surface species, which depends on the composition of the catalysts and reduction temperature. Change in reducing gas from H₂ into CO results in significant changes in catalyst system. Hydrogen causes a decrease in oxidation number of metals, while carbon monoxide reacts with chemisorbed chemicals.     

Comparative Investigation of Mo(CO)6 Adsorption on Clean and Oxidized Si(111) Surfaces

Mo(CO)₆ adsorption on the clean, oxygen-precovered and deeply oxidized Si(111) surfaces was comparatively investigated by high-resolution electron energy loss spectroscopy. The downward vibrational frequency shift of the C-O stretching mode in adsorbed Mo(CO)₆ illustrates that different interactions of adsorbed Mo(CO)₆ occur on clean Si(111) and SiO₂/Si(111) surfaces, weak on the former and strong on the latter. The strong interac-tion on SiO₂/Si(111) might lead to the partial dissociation of Mo(CO)₆, consequently the formation of molybdenum subcarbonyls. Therefore, employing Mo(CO)₆ as the precursor, metallic molybdenum could be successfully deposited on the SiO₂/Si(111) surface but not on the clean Si(111) surface. A portion of the deposited metallic molybdenum is transformed into the MoO₃ on the SiO₂/Si(111) surface upon heating, and the evolved MoO₃ finally desorbs from the substrate upon annealing at elevated temperatures.     

N-Aryl Isoleucine Derivatives as Angiotensin?II AT2 Receptor Ligands

A novel series of ligands for the recombinant human AT₂ receptor has been synthesized utilizing a fast and efficient palladium-catalyzed procedure for aminocarbonylation as the key reaction. Molybdenum hexacarbonyl [Mo(CO)₆] was employed as the carbon monoxide source, and controlled microwave heating was applied. The prepared N-aryl isoleucine derivatives, encompassing a variety of amide groups attached to the aromatic system, exhibit binding affinities at best with K_i values in the low micromolar range versus the recombinant human AT₂ receptor. Some of the new nonpeptidic isoleucine derivatives may serve as starting points for further structural optimization. The presented data emphasize the importance of using human receptors in drug discovery programs.     

Theoretical study on the reaction mechanism of (CH3)3CO+CO

The reaction mechanism of (CH₃)₃CO with CO has been theoretically investigated using density-functional theory (DFT) calculations at B3LYP/6-31G* level. In order to get more reliable energy values the single-point energy is evaluated at CCSD (T)/6-31++G** level. The results show that the reaction is multi-channel and the reaction of (CH₃)₃CO radical with CO mostly produces (CH₃)₃C + CO₂. The reaction could play a role in eliminating air pollution.     

About the Reaction of C(PPh3)2 with [M(CO)6] (M = Cr,Mo): Unusual Formation of μ-Carbonato Complexes of Mo under Participation of THF

Attempts to synthesize complexes of group 6 carbonyl compounds [M(CO)₆] (M = Cr, Mo, W) with the carbone C(PPh₃)₂ ( 1 ) via the photo chemically created adducts [(CO)₅M(THF)] lead to quantitative formation of the salts [HC(PPh₃)₂]₂[M₂(CO)₁₀] ( 2 , Cr; 3 , Mo; 4 , W). Alternatively, a long-time thermal reaction of [Mo(CO)₆] performed with 1 in THF generates a series of products initiated by a Wittig-type reaction. In addition to 3 , minor amounts of [(CO)₅MoCCPPh₃] ( 8 ), [(CO)₅MoO₂CC{PPh₃}₂] ( 5 ), and the carbonate complexes [HC(PPh₃)₂]₂[(CO)₅Mo(CO₃)Mo(CO)₄] ( 6 ) and [HC(PPh₃)₂]₂[(CO)₄Mo(CO₃)Mo(CO)₄] ( 7 ) were found. Compounds 2 , 3 , 5 , 6 , and 7 were characterized by X-ray analyses, ³¹P NMR, and IR spectroscopy. The water, necessary for the formation of the carbonate, stems from decomposition of THF.     

Optisch aktive N.N-bis[phosphinomethylen]-aminosäureester und deren molybdäncarbonyl-komplexe

Aminoacidesters and hydroxymethylphosphines form the title compounds, which react as bidentate ligands with Mo (CO)₆ to give the cyclic Mo (CO)₄ -complexes.     

Multinuclear NMR studies on substituted derivatives of Rh6(CO)16 in solution

Multinuclear NMR data (¹³C, ³¹P, ¹³C–{³¹P}, ¹³C–{¹⁰³Rh} and ³¹P–{¹⁰³Rh}) for a series of mono- and di-substituted derivatives of Rh₆(CO)₁₆ containing neutral two electron donor ligands [Rh₆(CO)₁₅L, (L=NCMe, py, cyclooctene, PPh₃, P(OPh)₃,1/2(μ₂,η¹:η¹-dppe)); Rh₆(CO)₁₄(LL), (LL=cis-CH₂=CMe-CMe=CH₂, dppm, dppe, (P(OPh)₃)₂)] are reported; these data show that the solid state structure is maintained in solution. Detailed assignments of the ¹³CO NMR spectra of Rh₆(CO)₁₅(PPh₃) and Rh₆(CO)₁₄(dppm) clusters have been made on the basis ¹³C–{¹⁰³Rh} double resonance measurements and the specific stereochemical features of the observed long range couplings in these clusters have been studied. The stereochemical dependence of ³J(P–C) for terminal carbonyl ligands is discussed and the values of ³J(P–C) are found to be mainly dependent on the bond angles in the P–Rh–Rh–C fragment; these data enable the fine structure of the complex multiplets in the ¹³C–{¹H} and ³¹P–{¹H} NMR spectra of Rh₆(CO)₁₄ (dppm) to be simulated. Variable temperature ¹³C–{¹H} NMR measurements on Rh₆(CO)₁₅(PPh₃) reveal the carbonyl ligands in this complex to be fluxional. The fluxional process involves exchange of all the CO ligands except the two terminal CO's associated with the rhodium trans to the substituted rhodium and can be explained by a simple oscillation of the PPh₃ on the substituted rhodium atom aided by concomitant exchange of the unique terminal CO on this rhodium with adjacent μ₃-CO's.     

Ultradeep Hydrodesulfurization of Dibenzothiophene (DBT) Derivatives over Mo-Sulfide Catalysts Supported on TiO2-Coated Alumina Composite

The present paper reviews in detail the different studies now being conducted by our research team concerning the ultradeep hydrodesulfurization (HDS) of dibenzothiophene (DBT) derivatives over Mo/TiO₂ and Mo/TiO₂–Al₂O₃ catalysts. First, a detailed characterization of Mo/TiO₂ (P-25 Degussa, 50 m²/g) catalysts prepared by equilibrium adsorption technique shows that Mo- species are highly and uniformly dispersed on the surface of titania up to 6.6 wt% MoO₃ loading. Above this value, some aggregation of Mo occurs, leading to the formation of bulk MoO₃. Below 6.6 wt% MoO₃ loading, the Raman spectroscopy data of the calcined samples show that the supported Mo-species possess a highly distorted octahedral MoO₆ structure. TiO₂–Al₂O₃ composites were prepared by chemical vapor deposition (CVD) using TiCl₄ as a precursor. Using several characterization techniques, we demonstrated that the support composite presents a high dispersion of TiO₂ over -Al₂O₃ without forming precipitates up to ca. 11 wt% loading. Moreover, the textural properties of the composite support are comparable to those of alumina. Under the present sulfidation conditions (673 K, 5%H₂S/95%H₂), Mo-species supported on TiO₂ are better sulfided than on alumina, as demonstrated using XPS. This can be attributed to the relatively lower interaction between Mo-species and titania. The state of sulfide species supported on the composite support can be considered as a transition state between TiO₂ and Al₂O₃. However, at relatively higher TiO₂ loadings (ca. 11 wt%), Mo/TiO₂–Al₂O₃ catalysts exhibit sulfidability similar to that of Mo/TiO₂. The HDS tests conducted in both the laboratory and in industry show that sulfide catalysts supported on TiO₂–Al₂O₃ (ca. 11 wt% TiO₂) are more active than those supported on TiO₂ or Al₂O₃.     

Molybdenum hexacarbonyl supported on functionalized multi-wall carbon nanotubes: Efficient and highly reusable catalysts for epoxidation of alkenes with tert-butyl hydroperoxide

In the present work, highly efficient epoxidation of alkenes catalyzed by Mo(CO)₆ supported on amines modified multi-wall carbon nanotubes, MWCNTs, is reported. The prepared catalysts were characterized by elemental analysis, scanning electron microscopy, FT-IR and diffuse reflectance UV-Vis spectroscopic methods. These new heterogenized catalysts, [Mo(CO)₆@amines-MWCNT], were used as highly efficient catalysts for epoxidation of alkenes with tert-BuOOH. These robust catalysts could be reused several times without loss of their catalytic activities.     

In Situ IR Spectroscopic Studies on Molybdenum Nitride Catalysts: Active Sites and Surface Reactions

Recent IR spectroscopic studies on the surface properties of fresh Mo₂N/-Al₂O₃ catalyst are presented in this paper. The surface sites of fresh Mo₂N/-Al₂O₃, both Mo⁺ (0<<2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm^-1, due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo₂N/-Al₂O₃ behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo₂N/-Al₂O₃ catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo₂N/-Al₂O₃ catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites.     

Palladium-catalyzed carbonylative synthesis of N-cyanobenzamides from aryl iodides/bromides and cyanamide

A novel and convenient protocol for the synthesis of N-cyanobenzamides starting from readily available aryl halides and cyanamide via palladium-catalyzed aminocarbonylation has been developed. The protocol utilizes Mo(CO)₆ as the CO source or CO(gas) and affords the desired N-cyanobenzamides in moderate to good yields.     

Dithiafulvenylphosphine as P- and P,S-ligand towards metal carbonyl fragments

The ability of the dithiafulvenylphosphine (P-DTF) to react as a monodentate (P) or a bidentate (P,S) ligand with metal carbonyl complexes such as Mo(CO)₆ and MnBr(CO)₅ is presented. A series of metal carbonyl complexes are synthesised and characterised by IR, ¹H NMR and ³¹P NMR spectroscopy. X-ray crystallographic analyses on the Mo(CO)₅(P-DTF) and Mo(CO)₄(P,S-DTF) complexes are reported together with the structural investigations on the dithiafulvenes precursors. The electrochemical properties of the various complexes investigated by cyclic voltammetry are discussed.     

Übergangsmetall-substituierte phosphane,arsane und stibane: XXXVI. Diastereomere dreikernkomplexe mit verbrückenden dimethylarsino-, dimethylstibino- oder dimethylbismutino-einheiten

Interaction of the chiral organometallic Lewis bases Cp(CO)(Me₃P)Fe—EMe₂ (E = As, Sb, Bi) (1a–1c) with the norbornadiene metal complex (C₇H₈)Mo(CO)₄ yields the first examples of trinuclear complexes [Cp(CO)(Me₃P)Fe—EMe₂]₂Mo(CO)₄ (2a–2c), bearing two chiral metal atoms separated by a E—Mo—E-linkage. 2a–2c are generated as a mixture of two diastereomers (RS/SR, RR/SS), which gives rise to a resonance doubling in their ¹H and ³¹P NMR spectra. This phenomenon is not observed for the achiral, in part sterically more crowded derivatives [Cp(CO)₂Fe—SbMe₂]₂Mo(CO)₄ (4) and [Cp(CO)₂(Me₃P)Mo—EMe₂]₂Mo(CO)₄ (E = As, Sb (6a, 6b)), which excludes the existence of conformers resulting from restricted rotation about the FeE or MoE bond in the case of 2a–2c.     

Unexpectedly complex structure and dynamic behavior of bis [(η5-cyclopentadienyl)dicarbonyl molybdenum ]-μ-pent-3-yne (MoMo)

The title compound, (η⁵-C₅H₅)₂Mo₂(CO)₄ (μ-EtCCEt) in its crystalline form, has a molecular structure that lacks symmetry. Two (ηs-C₅H₅)Mo groups are connected by an MoMo bond 2.977(1) Å in length with the usual sort of crosswise acetylene bridge. There are two terminal CO groups on Mo(1) and one on Mo(2). The fourth CO group is in a semi-bridging posture with Mo(2)—C = 1.936(6) and Mo(1)—C = 2.826(6). The ¹³CO NMR spectrum at ?126°C has six lines, indicative of the presence of two isomers, in each of which two CO's are either statically or dynamically equivalent. Complex changes occur in the spectrum as the temperature is increased so that at ?40°C there is only a single line. A detailed interpretation of these spectra is not yet available.