Synthesis, characterization, X-ray and electronic structures of diethyl ether and 1,2-dimethoxyethane adducts of molybdenum(IV) chloride and tungsten(IV) chloride

The bis(diethyl ether) and 1,2-dimethoxyethane (dme) adducts of molybdenum(IV) chloride and tungsten(IV) chloride are valuable starting materials for a variety of synthetic inorganic and organometallic reactions. Despite the broad utility and extensive use of these 6-coordinate complexes, their syntheses remain unoptimized, and their characterization incomplete after more than three decades. While exploring the ligand exchange behaviour of trans-MoCl₄(OEt₂)₂, we obtained single crystals of this red-orange complex and subsequently compared its structural parameters with those of the recently reported trans-WCl₄(OEt₂)₂. Significantly improved procedures for both MoCl₄(dme) and WCl₄(dme) were developed, and X-ray diffraction data were obtained and analysed. The magnetic properties of the dme adducts were probed, both with Gouy and SQUID magnetometry measurements. The magnetic moment of WCl₄(dme) was smaller than that of MoCl₄(dme), an observation that we attribute to the greater spin-orbit coupling of tungsten. Electronic structure studies were also conducted to probe the preferential trans configuration of the diethyl ether adducts and to assign the UV-Vis spectra of the dme adducts.

Synthesis, properties and structural features of molybdenum(v) oxide trichloride complexes with neutral chalcogenoether ligands

Complexes of oxotrichloromolybdenum(v) with neutral group 16 donor ligands, [MoOCl₃(L-L)] (L-L = RS(CH₂)₂SR, R = ⁱPr, Ph; MeS(CH₂)₃SMe; MeSe(CH₂)₂SeMe; MeSe(CH₂)₃SeMe), [{MoOCl₂(EMe₂)}₂(μ-Cl)₂] (E = S, Se, Te), [(MoOCl₃)₂{o-C₆H₄(EMe)₂}]_n (E = Se or Te) and [(MoOCl₃)₂{MeTe(CH₂)₃TeMe}]_n, have been obtained by reaction of the ligands with [MoOCl₃(thf)₂] or MoOCl₃ in either CH₂Cl₂ or toluene, and characterised by microanalysis, IR and UV-visible spectroscopy and magnetic measurements. The telluroethers are the first examples containing Mo in a positive oxidation state. X-ray crystal structures are reported for the six-coordinate fac-[MoOCl₃{MeS(CH₂)₃SMe}], mer-[MoOCl₃{ⁱPrS(CH₂)₂SⁱPr}] and mer-[MoOCl₃{MeSe(CH₂)₂SeMe}], as well as the six-coordinate chloride-bridged dimers, [{MoOCl₂(SMe₂)}₂(μ-Cl)₂] and [{MoOCl₂(SeMe₂)}₂(μ-Cl)₂]. The structure of the mixed-valence decomposition product, [Mo^IVCl{o-C₆H₄(TeMe)₂}₂(μ-O)Mo^VOCl₄], was also determined. In toluene solution MoOCl₄ is reduced by MeS(CH₂)₃SMe to produce the Mo(v) complex, [MoOCl₃{ MeS(CH₂)₃SMe}]. Crystal structures of the previously unknown diphosphine analogue, [MoOCl₃{Me₂P(CH₂)₂PMe₂}], and the mixed-valence derivative [Mo^IVCl{Me₂P(CH₂)₂PMe₂}₂(μ-O)Mo^VOCl₄] are also reported for comparison and help to clarify earlier contradictory literature reports. In contrast to the dimeric EMe₂ complexes, [{MoOCl₂(EMe₂)}₂(μ-Cl)₂], PMe₃ forms the monomeric complex, fac-[MoOCl₃(PMe₃)₂].

Decarbonylation of phenylacetic acids by high valent transition metal halides

The unusual decarbonylation of α-phenyl carboxylic acids with suitable substituents is a general reaction promoted at room temperature by homoleptic halides of high valent transition metals.

Application of ESI-HRMS for molybdenum speciation in natural waters: An investigation of molybdate-halide reactions

High resolution electrospray ionization mass spectrometry (ESI-HRMS) was used to study the speciation of molybdate in interaction with halides (Cl, F, Br). Desolvation during electrospray ionization induced alteration of aqueous species but method optimization successfully suppressed artefact compounds. At low Mo concentrations, chloro(oxo)molybdate and fluoro(oxo)molybdate species were found and in natural samples, MoO₃Cl was detected for the first time, to the best of our knowledge. Apparent equilibrium constants for Cl substitution on molybdate were calculated for a range of pH values from 4.5 to 8.5. A minor alteration in speciation during the gas phase (conversion of doubly charged MoO₄^2- to HMoO₄^-) did not allow investigation of the molybdate acid-base properties; however this could be determined by speciation modeling. This study provides further evidence that ESI-HRMS is a fast and suitable tool to Deceasedassess the speciation of inorganic compounds such as Mo.

Activation of CN bonds by high-valent group 6 metal chlorides, including the conversion of an α-diimine into a functionalized imidazolium

The direct interactions of WCl₆and MoCl₅with α-diimines (and also a carbodiimide in the case of MoCl₅) have been explored, leading to unusual reaction pathways.

Stable coordination complexes of α-diimines with Nb(v) and Ta(v) halides

Uncommon coordination compounds of high valent transition metal halides with N-aryl α-diimines have been obtained, without the need for reducing agents to quench the activation power of the metal centre.

Synthesis and properties of MoCl4complexes with thio- and seleno-ethers and their use for chemical vapour deposition of MoSe2and MoS2films

A new series of Mo(iv) chloride complexes with thioether and seleneoether ligands is reported; [MoCl₄(ⁿBu₂E)₂] (E = S, Se) function as single source precursors for the CVD of MoE₂thin films.

Synthesis and structural characterization of mixed halide–N,N-diethylcarbamates of group 4 metals, including a case of unusual tetrahydrofuran activation

A straightforward synthesis of dichloride-dicarbamates of group 4 metals consists of the metathesis reaction of the respective tetrahalides with tetracarbamates.

Is bond stretch isomerism in mononuclear transition metal complexes a real issue? The misleading case of the MoCl5/tetrahydropyran reaction system

Distinct batches of orange (1a-e) and green crystals (2a-e) were isolated from the reactions of MoCl5 with tetrahydropyran (thp), respectively at room temperature (in CH2Cl2) and at ca. 80 °C (in ClCH2CH2Cl). Crystals 2a-e are isomorphous to 1a-e and the IR spectra are almost superimposable. 1a-e were identified by X-ray studies as cis-MoCl4(thp)2, in agreement with previous findings. Careful refinement of the X-ray data of 2a-e by modeling one position as disordered between chlorine (minor component) and oxygen (major component) led to the conclusion that 2a-e consisted of a mixture of cis-MoCl4(thp)2 and mer-MoOCl3(thp)2, the latter being largely prevalent.

MoCl5 as an effective chlorinating agent towards α-amino acids: synthesis of α-ammonium-acylchloride salts and α-amino-acylchloride complexes

The reactivity of MoCl5 with α-amino acids was investigated for the first time by choosing CH2Cl2 as the reaction medium. The interaction of MoCl5 with l-proline proceeded with Cl/O interchange and led to the formation of [NH2(CH2)3CHC(O)Cl][MoOCl4], 1, in 63% yield. The reactions of MoCl5 with l-phenylalanine, sarcosine, N,N-dimethylglycine and N,N-dimethyl-l-phenylalanine afforded the α-amino-acylchloride complexes MoOCl3[O[double bond, length as m-dash]C(Cl)CH(R)N(R')(R'')] (R = CH2Ph, R' = R'' = H, 2a; R = R' = H, R'' = Me, 2b; R = H, R' = R'' = Me, 2c R = CH2Ph, R' = R'' = Me, 2d), in ca. 70% yields. According to DFT studies, 2a,d are mononuclear Mo(v) octahedral complexes bearing a N,O-coordinated α-amino-acylchloride ligand. The presumed species formed during the first stages of the MoCl5/l-phenylalanine interaction were DFT-elucidated, thus the calculated Gibbs free energy profile for the multi-step reaction of MoCl5 with l-phenylalanine was traced. [NH3CH(CH2Ph)C(O)Cl][MoOCl4], 3, acting as an intermediate in the course of the formation of 2a, was isolated by combination of [NH3CH(CH2Ph)C(O)Cl][Cl] with MoOCl3.

Synthesis of α-amino acidato derivatives of niobium and tantalum pentahalides and their conversion into iminium salts

Dinuclear complexes of formula Nb2Cl9[O2CCH(R)NR'R″2-κO,κO] (R = CH2CHMe2, R' = R″ = H, 1a; R = CH2Ph, R' = R″ = H, 1b; R = CH2CH2SCH3, R' = R″ = H, 1c; R = R' = H, R″ = Me, 1d; R = CH2Ph, R' = R″ = Me, 1e; Nb2Cl9[O2C⌈CH(CH2)3NH⌉], 1f) were prepared by allowing NbCl5 to react in dichloromethane with the appropriate α-amino acid in 1:2 amino acid/Nb molar ratio. The 1:1 reactions between MX5 (M = Nb, Ta; X = Cl, Br) and a series of α-amino acids resulted in the formation of the iminium salts [(R)CH═NR'R″2][MX6] (R = CH2Ph, R' = R″ = Me: M = Nb, X = Cl, 2a; M = Nb, X = Br, 2b; M = Ta, X = Cl, 2c; M = Ta, X = Br, 2d; R = CH2Ph, R' = R″ = H, M = Nb: X = Cl, 3a; X = Br, 3b; R = CH2CHMe2, R' = R″ = H, M = Nb, X = Cl, 4; R = R' = H, R″ = Me, M = Nb, X = Cl, 5). The formate/amino acidate derivative NbCl3(O2CH)[O2CCH(CH2Ph)NMe2], 6, was isolated and identified as coproduct of the 1:1 reaction between NbCl5 and N,N-dimethyl-l-phenylalanine, leading to 2a. All of the compounds were characterized by analytical and spectroscopic methods and by X-ray diffractometry in the cases of 2a, 2b, and 2d. Moreover, density functional theory studies were carried out to shed light on mechanistic and structural aspects.

Structural characterization of α-amino acid complexes of molybdates: a spectroscopic and DFT study

A joint spectroscopic and computational study has allowed us to determine the dinuclear structural core of the products of the reactions between molybdates and α-amino acids in aqueous medium.

Oxido-molybdenum complexes obtained by Cl/O interchange between MoCl5 and carboxylic acids: a crystallographic, spectroscopic and computational study

The direct interaction of MoCl5 with a series of carboxylic acids has been elucidated for the first time. The reactions proceed with release of hydrogen chloride and Cl/O interchange between the metal centre and one equivalent of organic substrate: this feature is unique in the context of the chemistry generally shown by transition metal halides with carboxylic acids. The dinuclear complexes [MoOCl2(κ(1)-CX3CO2H)(μ-Cl)]2 (X = H, 1a; X = Cl, 1b) and Mo2O2Cl6(μ-CH3CO2H), 2a, were isolated as the prevalent metal products of the 1:2 molar reactions of MoCl5 with CH3COOH and CCl3COOH. Evidence for the formation of Mo2O2Cl6(μ-CCl3CO2H), 2b, was achieved by allowing MoCl5 to react with CCl3COOH in 2:3 ratio. Instead the reactions of MoCl5 with a three-fold molar excess of RCOOH afforded the mononuclear complexes MoOCl3(κ(1)-RCO2H)2 (R = CH3, 3a; CCl3, 3b; CHCl2, 3c; CMe3, 3d) in 50–60% yields. The new compounds were characterized by analytical and spectroscopic techniques, moreover the X-ray molecular structures were ascertained for 1a, 1b and 2a; 1a and 1b display single Mo–Mo bond. DFT calculations were carried out in order to shed light into structural aspects.