Origin of Decomposition in a Family of Molybdenum Precursor Compounds

The bis(tert-butylimido)-molybdenum(VI) framework has been used successfully in the design of vapor-phase precursors for molybdenum-containing thin films, so understanding its thermal behavior is important for such applications. Here, we report the thermal decomposition mechanism for a series of volatile bis(alkylimido)-dichloromolybdenum(VI) adducts with neutral N,N'-chelating ligands, to probe the stability and decomposition pathways for these molecules. The alkyl groups explored were tert-butyl, tert-pentyl, 1-adamantyl, and a cyclic imido (from 2,5-dimethylhexane-2,5-diamine). We also report the synthesis of the new tert-octyl imido adducts, (^tOctN)₂MoCl₂·L (L = N,N,N',N'-tetramethylethylenediamine or 2,2'-bipyridine), which have been fully characterized by spectroscopic techniques as well as single-crystal X-ray diffraction and thermal analysis. We found that the decomposition of all compounds follows the same general pathway, proceeding first by the dissociation of the chelating ligand to give the coordinatively unsaturated species (RN)₂MoCl₂. Subsequent dimerization results in either an imido bridged adduct, [(RN)Mo(μ-NR)Cl₂]₂, or a chloride bridged adduct, [(RN)₂Mo(μ-Cl)Cl]₂, depending on the size of the R group. The dimeric species then likely undergoes an intramolecular γ-hydrogen transfer to yield a nitrido-amido adduct, (RHN)MoNCl₂, and an alkene. Ultimately, the resulting molybdenum species appears to decompose into free tert-alkylamine and Mo₂N or Mo₂C. The thermolysis reactions have been monitored using ¹H NMR spectroscopy, and the volatile decomposition products were analyzed using gas chromatography-mass spectrometry. A key intermediate has also been detected using electron ionization high-resolution mass spectrometry. Finally, a detailed computational investigation supports the mechanism outlined above and helps explain the relative stabilities of different N,N'-chelated bis(alkylimido)-dichloromolybdenum(VI) adducts.

Selective dimerisation of 1-hexene mediated by aluminium alkyl chloride-activated tungsten imido complexes

Tungsten imido complexes, in combination with EtAlCl₂, were found to be efficient pro-catalysts for selective dimerization of 1-hexene to methyl-branched dodecenes, products that can be used for the production of jet and diesel engine fuels.

Additives boosting the performance of tungsten imido-mediated ethylene dimerization systems for industrial application

While activation of tungsten bis(imido) complexes [WCl₂(NAr)₂(dme)] with EtAlCl₂ affords active, and moderately selective ethylene dimerization catalysts, addition of Et₃N or Oct₄NCl leads to a doubling in productivity and activity, along with increased selectivity (e.g., >93% C₄, >99% 1-C₄). The performance of the resulting tungsten-based catalyst package is competitive with that of Axens' commercialised Ti-based AlphaButol process and exemplifies the wide potential of similar additives in selective oligomerization.

Methyl Complexes of the Transition Metals

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH3 compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.

Crystal structure of [N'-(2-hydroxy-4-methoxybenzylidene)-2-hydroxybenzohydrazido]( methanol)dioxomolybdenum(VI) methanol solvate, C16H16MoN2O7·CH3OH, C17H20MoN2O8

C17H20MoN2O8, triclinic, P1̅ (no. 2), a = 6.9004(7) Å, b = 10.225(1) Å, c = 14.332(2) Å, α = 79.346(2)°, β = 82.660(2)°, γ = 77.576(1)°, V = 966.4 Å3, Z = 2, Rgt(F) = 0.0318, wRref(F2) = 0.0813, T = 298 K.

Crystal structure of [N'-(3-bromo-2-hydroxybenzylidene)-2-hydroxybenzohydrazido]( methanol)dioxomolybdenum(VI), C15H13BrMoN2O6

C15H13BrMoN2O6, monoclinic, P21/c (no. 14), a = 7.4143(3) Å, b = 18.7856(7) Å, c = 12.6319(5) Å, β = 104.463(1)°, V = 1703.7 Å3, Z = 4, Rgt(F) = 0.0262, wRref(F2) = 0.0680, T = 298 K.