The reactivity of niobium and tantalum pentahalides with imines

The reactivity of NbCl5, NbF5 and TaCl5 with a selection of commercial imines was investigated for the first time by using dichloromethane as reaction medium. NbCl5 reacted with Ph2C=NH, in 1:2 molar ratio, affording [Ph2C=NH2][NbCl5(N=CPh2)], 1, in 55% yield, as result of imine self-protonation. The iminium salt [PhCH=NHtBu][NbCl6], 2, was isolated in 52% yield from NbCl5 and PhCH=NtBu (1:1 molar ratio), while a low yield of [tBu2C=NH2][NbCl6], 3, was identified from NbCl5/tBu2C=NH. The 1:1 reactions of NbF5 with Ph2C=NH and PhCH=NtBu were accompanied by electron interchange and led to the isolation of the salts [Ph2C=NH2][NbF6], 4, and [PhCH=NHtBu][NbF6], 5, respectively, in ca. 50% yields. Few crystals of [Ph2C=NH2]2[Ta2Cl10O], 6, were recovered from TaCl5/Ph2C=NH, the anion being probably generated by the action of adventitious water. Compounds 1-6 were characterized by elemental analysis, IR and NMR spectroscopy. The structures of 1, 4 and 6 were ascertained by X-ray diffraction studies

The reactivity of MoCl5 with molecules containing the alcohol functionality

The 1:1 M reaction of MoCl5 with Cl(CH2)2OH, in dichloromethane at room temperature, proceeded with chlorine–oxygen interchange and HCl release to give MoOCl3 in 65% yield. The analogous reactions involving iPrOH, MeOH, L-menthol and H2O gave impure MoOCl3. MoCl5 reacted with Me2N(CH2)2OH in 1:1 M ratio affording the 2-chloroammonium salt [Me2NH(CH2)2Cl]2[Mo2O2Cl8], 1. The reaction of MoCl5 with MeO(CH2)2OH afforded a mixture of [Mo(O(CH2)2OMe)2Cl2][Mo2O2Cl7], 2a, and [Mo(O(CH2)2OMe)2Cl2][MoOCl4], 2b. The products 1, 2a and 2b were characterized by analytical and spectroscopic techniques, and by X-ray diffractometry. The X-ray structure of 2b shows weak anion–anion interactions, therefore 2b might be alternatively viewed as a [Mo2O2Cl8]2- salt

Gold/Iron Carbonyl Clusters for Tailored Au/FeOx Supported Catalysts

A novel preparation method was developed for the preparation of gold/iron oxide supported catalysts using the bimetallic carbonyl cluster salts [NEt4]4[Au4Fe4(CO)16] and [NEt4][AuFe4(CO)16] as precursors of highly dispersed nanoparticles over different supports. A series of catalysts with different metal loadings were prepared and tested in the complete oxidation of dichlorobenzene, toluene, methanol and in the preferential oxidation of CO in the presence of H2 (PROX) as model reactions. The characterization by BET, XRD, TEM, H2-TPR, ICP-AES and XPS point out the way the nature of the precursors and the thermal treatment conditions affected the dispersion of the active phase and their catalytic activity in the studied reactions

Carbon???Carbon Bond Coupling of Vinyl Molecules with an Allenyl Ligand at a Diruthenium Complex

The room-temperature reactions of the diruthenium μ-allenyl complex [Ru2Cp2(CO)2(NCMe){μ-η1:η2-CH═C═CMe2}]BF4, 3-NCMe, with a series of alkenes, RCH═CH2, afforded the complexes [Ru2Cp2(CO)2{μ-η3:η2-CH(R)CHC(Me)C(Me)CH2}]BF4(R═Ph, 4; 4-C6H4Me, 5; Me, 6; nBu, 7; CO2Me, 8; and H, 9), containing an uncommon pentacarbon alkenyl-allyl ligand. Cross experiments with deuterated reagents, i.e., [Ru2Cp2(CO)2(NCMe){μ-η1:η2-CD═C═CMe2}]BF4(3b-NCMe) and CD2═CD(C6H5) (styrene-d3), revealed that the formation of 4-9 is initiated by an attack of the alkene to the central carbon of the allenyl moiety, triggering two distinct C-H activation processes. Compounds 4-9 were characterized by analytical and spectroscopic methods and by single-crystal X-ray diffraction in the cases of 4, 7, and 8. Reported here is the clean coupling on a metallic scaffold between two C2and C3functions invoked in Fischer-Tropsch mechanistic models

The versatile chemistry of niobium pentachloride with aliphatic amines: Aminolysis, metal reduction and C–H activation

The reactions of NbCl5 with limited amounts (1-2 molar equivalents) of a series of primary, secondary and tertiary amines were investigated in dichloromethane as solvent. The 1:1 reaction of NbCl5 with NHEt2 cleanly afforded an equimolar mixture of [NbCl4(NEt2)]2, 1, and [NH2Et2][NbCl6], 2a; the former product constitutes the first example of structurally characterized Nb(V) chlorido-amido complex. The ammonium salts [NH3nPr][NbCl6], 2b, and [NH2iPr2][NbCl6], 2c, were isolated in 20-30% yields from the 1:1 reactions of NbCl5 with NH2nPr and NHiPr2, respectively. Cα-H bond activation and Nb(V) to Nb(IV) reduction took place in the reactions of NbCl5 with NR3 (R = Bz, Et; Bz = CH2Ph). The iminium salt [(PhCH2)2N=CHPh][NbCl6], 3, and the ammonium ion [NH(CH2Ph)3]+ were identified as the prevalent species generated from the 1:1 NbCl5/NBz3 interaction. [NHEt3][NbCl6], 4, and [NHEt3]2[NbCl6], 5, were isolated in moderate yields from, respectively, the 1:1 and 1:2 molar reactions of NbCl5 with NEt3. The solid state structures of 1, 2a, 3, 4 and 5 were ascertained by single crystal X-ray studies

Ligand-interchange reactions between M(iv) (M = Ti, V) oxide bis-acetylacetonates and halides of high-valent group 4 and 5 metals. A synthetic and electrochemical study

The reactions of M’O(acac)2[M’ = Ti, V; acac = acetylacetonato anion] with equimolar amounts of MF5 (M = Nb, Ta) in CH2Cl2 afforded Ti(acac)2F2, 1a, and [V(acac)3][MF6] (M = Nb,4a;M=Ta,4b), respectively. MOF3 (M = Nb, 2a; M=Ta,2b) were co-produced from MF5/TiO(acac)2. The intermediate species [TaF4{OTi(acac)2}2][TaF6], 3, was intercepted in the course of the formation of 1a from TiO(acac)2/TaF5. NbCl5 reacted with TiO(acac)2 yielding selectively the previously reported [NbO(acac)Cl2]x, 5, and Ti2(acac)2(μ-Cl)2Cl4, 6. Complex 6 was alternatively obtained from the addition of a two-fold excess of TiCl4 to VO(acac)2. The 1 : 1 reactions of TiX4 (X = F, Cl) with TiO(acac)2 in dichloromethane gave Ti(acac)2X2 (X = F,1a; X = Cl, 1b) and TiOX2 (X = F, 7a; X = Cl, 7b). The 1 : 1 combination of TiX4 (X = F, Cl) with VO(acac)2 led to 1a, band VOX2 (X = F, 8a; X = Cl, 8b). The μ-oxido compounds (C6F5)3B–O–M’(acac)2(M’ = Ti, V) underwent fragmentation by [PF6]- in chlorinated solvent, yielding POF3, 9, and [B(C6F5)3F]-, 10, according to NMR studies; 1a and V(acac)3+, respectively, were detected as the metal-containing species. Electrochemical studies were carried out aiming at the full characterization of the products and the observation of possible degradation pathways

Coordination complexes of niobium and tantalum pentahalides with a bulky NHC ligand

The 1 : 1 molar reactions of niobium and tantalum pentahalides with the monodentate NHC ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Ipr), in toluene (or benzene) at ca. 80 °C, afforded the complexes NbX5(Ipr) (X = F, 2; Br, 3) and TaX5(Ipr) (X = F, 4; Cl, 5; Br, 6), in generally good yields. Complexes 2–6 represent uncommon cases of stable NHC adducts of metal halides with the metal in an oxidation state higher than +4, and also rare examples of Nb–NHC and Ta–NHC bonding systems. In particular, the X-ray molecular structure determined for 6 provides the unprecedented crystallographic characterization of a tantalum compound with a monodentate NHC ligand. DFT results indicate that the metal–carbon bond in 2–6 is a purely σ one. According to NMR studies (1H, 13C, 93Nb), the formation of 3, 5, 6, as well as the previously communicated NbCl5(Ipr), 1, proceeded with the intermediacy of [MX6]− salts, presumably due to steric reasons. On the other hand, the intermediate formation of MF6− in the pathways to 2 and 4 was not observed, according to 19F (and 93Nb in the case of 2) NMR. DFT calculations were carried out in order to shed light on structural and mechanistic aspects, and allowed to trace possible reaction routes

Alternative synthetic route for the heterometallic CO-releasing [Sb@Rh12(CO)27]3− icosahedral carbonyl cluster and synthesis of its new unsaturated [Sb@Rh12(CO)24]4− and dimeric [{Sb@Rh12Sb(CO)25}2Rh(CO)2PPh3]7− derivatives

Abstract The hetero-metallic [Sb@Rh12(CO)27]3− cluster has been known as for over three decades thanks to Vidal and co-workers, and represents the first example of an E-centered (E=heteroatom) icosahedral rhodium carbonyl cluster. However, its synthesis required high temperature (140–160 °C) and elevated CO pressure (400 atm). Applying the redox condensation method for cluster preparation, we herein report a new synthetic, high-yield route for preparing [Sb@Rh12(CO)27]3− under much milder conditions of temperature and pressure. Notably, when the same synthesis was carried out under N2 instead of CO atmosphere, the new isostructural but unsaturated derivative [Sb@Rh12(CO)24]4− was obtained, for which we report the full X-ray structural characterization. This species represents one of the few examples of an icosahedral cluster disobeying the electron-counting Wade-Mingos rules, possessing less than the expected 170 cluster valence electrons (CVEs). Judging from IR monitoring, the two species can be obtained one from the other by switching between N2 and CO atmosphere, making [Sb@Rh12(CO)27]3− a spontaneous CO-releasing molecule. Finally, the study of the chemical reactivity of [Sb@Rh12(CO)27]3− with PPh3 allowed us to obtain the new [{Sb@Rh12Sb(CO)25}2Rh(CO)2PPh3]7− dimeric compound, for which we herein report the full X-ray structural and 31P NMR analyses