The chemistry of Niobium and Tantalum halides, MX5, with haloacetic acids and their related anhydrides: anhydride C–H bond activation promoted by MF5

Niobium and tantalum pentahalides, MX5 (1), react with acetic acid and halo-substituted acetic acids, in 1:1 ratio, to give the dinuclear complexes [MX4(μ-OOCMe)]2 [M = Nb, X = Cl, 2a; M = Ta, X = Cl, 2b; Br, 2c] and [MCl4(μ-OOCR)]2 [M = Nb, R = CH2Cl, 4a; CHCl2, 4c; CCl3, 4e; CF3, 4g; CHBr2, 4i; CH2I, 4j; M = Ta, R = CH2Cl, 4b; CHCl2, 4d; CCl3, 4f; CF3, 4h]. The solid state structures of 2b and 4e have been ascertained by X-ray diffraction studies. The reactions of 1 with acetic anhydride and halo-substituted acetic anhydrides result in C–O bond activation and afford 2 and 4, respectively, with concomitant formation of acetyl halides. Moreover, the complexes MCl5[OC(Cl)Me] [M = Nb, 3a; M = Ta, 3b] have been detected in significant amounts within the mixtures of the reactions of MCl5 with acetic anhydride. TaI5 is unreactive, at room temperature, towards both MeCOOH and (MeCO)2O. MF5 react with RCOOH (R = Me, CH2Cl) in 1:1 molar ratio, to afford the ionic compounds [MF4(RCOOH)2][MF6], 5a–d, in high yields. The additions of (RCO)2O (R = Me, CH2Cl) to MF5 give 5, suggesting that anhydride C–H and C–O bonds activation is operative during the course of these reactions

Ribosomal RNA Pseudouridylation: Will Newly Available Methods Finally Define the Contribution of This Modification to Human Ribosome Plasticity?

In human rRNA, at least 104 specific uridine residues are modified to pseudouridine. Many of these pseudouridylation sites are located within functionally important ribosomal domains and can influence ribosomal functional features. Until recently, available methods failed to reliably quantify the level of modification at each specific rRNA site. Therefore, information obtained so far only partially explained the degree of regulation of pseudouridylation in different physiological and pathological conditions. In this focused review, we provide a summary of the methods that are now available for the study of rRNA pseudouridylation, discussing the perspectives that newly developed approaches are offering

Reactions of diiron MU-aminocarbyne complexes containing nitrile ligands

The acetonitrile ligand in the mu-aminocarbyne complexes [Fe-2{mu-CN(Me) R}(mu-CO)( CO)(NCMe)(Cp)(2)][SO3CF3] (R = Me, 2a, CH2Ph, 2b, Xyl, 2c) (Xyl = 2,6-Me2C6H3) is readily displaced by halides and cyanide anions affording the corresponding neutral species [Fe-2{mu-CN( Me) R}(mu-CO)(CO)(X)(Cp)(2)] (X = Br, I, CN). Complexes 2 undergo deprotonation and rearrangement of the coordinated MeCN upon treatment with organolithium reagents. Trimethylacetonitrile, that does not contain acidic a hydrogens has been used in place of MeCN to form the complexes [Fe-2{mu-CN(Me)R}(mu-CO)(CO)(NCCMe3)(Cp)(2)][SO3CF3] (7a-c). Attempts to replace the nitrile ligand in 3 with carbon nucleophiles ( by reaction with RLi) failed, resulting in decomposition products. However the reaction of 7c with LiC= CTol (Tol = C6H4Me), followed by treatment with HSO3CF3, yielded the imino complex [Fe-2{mu-CN(Me) Xyl}(mu-CO)(CO) {N(H) C(C= CC6H4Me-4) CMe3}(Cp)(2)][SO3CF3] (8), obtained via acetilyde addition at the coordinated NCCMe3

A Crystallographic and Spectroscopic Study of the Reactions of WCl6 with Carbonyl Compounds

WCl6, 1, reacted with two equivalents of HC(O)NR2 (R = Me, Et) in CH2Cl2 to afford the W(VI) oxo-derivatives WOCl4(OCHNR2) (R = Me, 2a; R = Et, 2b) as main products. The hexachlorotungstate(V) salts [{ }2(-H)][WCl6], 3, and [PhNHC(Me)N(Ph)C(O)Me][WCl6], 4, were isolated in moderate yields from the 1:2 molar reactions of 1 with N-methyl-2-pyrrolidone (in CH2Cl2) and acetanilide (in CDCl3), respectively. The additions of two equivalents of ketones/aldehydes to 1/CH2Cl2 yielded the complexes WOCl4[OC(R)(R’)] (R = Me, R′ = Ph, 5a; R = R’ = Ph, 5b; R = R’ = Me, 5c; R = R’ = Et, 5d; R = H, R’ = 2-Me-C6H4, 5e) and equimolar amounts of C(R)(R’)Cl2. Analogously, WOCl3[2-{1,2-C6H4(O)(CHO)}], 5f, and 1,2-C6H4(OH)(CHCl2) were obtained from 1 and salicylaldehyde. The 1:1 reaction of 1 with acetone in CH2Cl2 resulted in the clean formation of WOCl4 and 2,2-dichloropropane. Compounds 5a,b,f were isolated as crystalline solids, whereas 5c,d,e could be detected by solution NMR only. The interaction of 1/CH2Cl2 with isatin, in 1:1 molar ratio, revealed to be a new, convenient route for the synthesis of 3,3-dichloro-2,3-dihydro-1H-indol-2-one, 6. The 1:1 reactions of 1 with R’OCH(R)CO2Me (R = H, R’ = Me; R = Me, R’ = H) in chlorinated solvent afforded the tungsten(V) adducts WCl4[2-OCH(R)CO2Me] (R = H, 7a; R = Me, 7b). 1/CH2Cl2 reacted sluggishly with equimolar quantities of trans-(CO2Et)CH=CH(CO2Et) and CH2(CO2Me)2 to give, respectively, the W(IV) derivatives WCl4[2-CH2(CO2Me)2], 8a, and [WCl4-2-{trans-(CO2Et)CH=CH (CO2Et)}]n, 8b, in about 70% yields. The molecular structures of 2a, 3, 4, 5a, 5f, 7a and 7b were ascertained by X-ray diffraction studies

Addition of alkynes at bridging vinyliminium ligands in diiron complexes: Unprecedented diene formation by enyne-like metathesis

The zwitterionic bridging vinyliminium complex [Fe(2){mu-eta 1: eta 3-C(Tol)]=C(CS2)C] = N(Me)2}(mu-CO)(CO)( Cp)(2)] (5a) undergoes the addition of two equivalents of MeO(2)C-C C-CO(2)Me affording the bridging bis-alkylidene complex [Fe(2){mu-eta 1: eta 3-C(Me)C{C(CO(2)Me)C(CO(2)Me)CSC(CO(2)Me)C(CO(2)Me)S}CNMe(2)}(mu-CO)( CO)(Cp)(2)] (6). One alkyne unit inserts into a C-CS(2) bond of the bridging ligand, with consequent rearrangement that leads to the formation of a diene. The reaction shows analogies with the enyne metathesis. The second alkyne is incorporated into the bridging frame via cycloaddition at the thiocarboxylate function, affording a 1,3-dithiolene. The complexes [Fe(2){mu-eta(1): eta(3)-C(R')]=C(CS(2))C=N(Me)(R)}(mu-CO)(CO)(Cp)(2)] (R = Xyl, R' = Tol, 5b; R = p-C(6)H(4)OMe, R' = Me, 5c; Xyl = 2,6-Me(2)C(6)H(3)), treated with MeO(2)C-C C-CO(2)Me and then with HBF(4), undergo the cycloaddition of the alkyne with the dithiocarboxylate group and protonation of the dithiocarboxylate carbon, affording the complexes [Fe(2){mu-eta 1: eta 3-C(R')]=C{C(H)SC(CO(2)Me)C(CO(2)Me)S}C]=N(Me)(R)}(mu-CO)(CO)(Cp)(2)][BF(4)] (R = Xyl, R' = Tol, 7a; R= p-C(6)H(4)OMe, R' = Me, 7b), respectively. The X-ray molecular structure of 6 has been determined

Non-precious metal carbamates as catalysts for the aziridine/CO2coupling reaction under mild conditions

The catalytic potential of a large series of easily available metal carbamates (based on thirteen different non-precious metal elements) was explored for the first time in the coupling reaction between 2-aryl-aziridines and carbon dioxide, working under solventless and ambient conditions and using tetraalkylammonium halides as co-catalysts. The straightforward synthesis of novel [NbCl3(O2CNEt2)2],NbCl, and [NbBr3(O2CNEt2)2],NbBr, is reported. The niobium complexNbCl, in combination with NBu4I, emerged as the best catalyst of the overall series to convert aziridines with smallN-alkyl substituents into the corresponding 5-aryl-oxazolidin-2-ones

Addition of protic nucleophiles to alkynyl methoxy carbene ligands in diiron complexes

Different protic nucleophiles (i.e. Ph2C=NH, PhSH, MeCO2H, PhOH) can be added to the C equivalent to C bond of [Fe-2{mu-CN(Me)(Xyl)}-(mu-CO)(CO){C(OMe)C equivalent to CTol}(CP)(2)][SO3CF3] (1), affording new diiron alkenyl methoxy carbene complexes. The additions of Ph2C=NH and MeCO2H are regio and stereoselective, resulting in the formation of the 5-aza-1-metalla-1,3,5-hexatriene [Fe-2{mu-CN(Me)(Xyl)}(mu-CO)(CO){C-alpha(OMe)C beta H=C-gamma(Tol)(N=CPh2)}(CP)(2)][SO3CF3](2), and the 2-(acyloxy)alkenyl methoxy carbene complex [Fe-2{mu-CN(Me)(Xyl)}(mu-CO)(CO){C-alpha(OMe)C beta H=C-gamma(Tol)OC(O)Me)}(CP)(2)][CF3SO3] (5); the E isomer of the former and the Z of the latter are formed exclusively. Conversely, the addition of PhSH is regio but not stereoselective; thus, both the E and Z isomers of [Fe-2{mu-CN(Me)(Xyl)}(mu-CO)(CO){C-alpha(OMe)C beta H=C-gamma(Tol)(SPh)}(CP)(2)][SO3CF3](3) are formed in comparable amounts. Compounds 3 and 5 are demethylated upon chromatography through Al2O3, resulting in the formation of the acyl complexes [Fe-2{mu-CN(Me)(Xyl)}(mu-CO)(CO){C-alpha(O)C beta H=C-gamma(Tol)(SPh)}(Cp)(2)](4) and [Fe-2{mu-CN(Me)(Xyl)}(mu-CO)(CO){C-alpha(O)C beta H=C-gamma(Tol)OC(O)Me}(CP)(2)](6), respectively, both with a Z configured C-beta=C-gamma bond. Finally, the reaction of 1 with PhOH proceeds only in the presence of an excess of Et3N affording the 2-(alkoxy)alkenyl acyl complex [Fe-2{mu-CN(Me)(Xyl)}(mu-CO)(CO){C-alpha(O)C beta H=C-gamma(Tol)(OPh)}(CP)(2)](7). The crystal structures of 4 center dot CH2Cl2 and 7 center dot 0.5CH(2)Cl(2) have been determined by X-ray diffraction experiments

Molecular Fe, CO and Ni carbide carbonyl clusters and Nanoclusters†

The present minireview highlights the work of our group on Fe, Co and Ni carbide carbonyl clusters and nanoclusters, placing it in the context of the recent literature. After a brief introduction, Section 2 gives a short summary on the general features of molecular carbide carbonyl clusters. Then, specific examples of Fe, Co and Ni carbide carbonyl clusters are presented in the following three Sections. Each Section includes both homometallic and heterometallic clusters, as well as discussion of some of their most relevant chemical, electrochemical, structural and physical properties. General conclusions are outlined in Section 6

Diiron-aminocarbyne complexes with amine or imine ligands: C-N coupling between imine and aminocarbyne ligands promoted by tolylacetilyde addition to [Fe2{m-CN(Me)R}(m-CO)(CO)(NH=CPh2)(Cp)2][SO3CF3]

A terminally coordinated CO ligand in the complexes [Fe2{m-CN(Me)R}(m-CO)(CO)2(Cp)2][SO3CF3] (R = Me, 1a; R = Xyl, 1b; Xyl = 2,6-Me2C6H3), is readily displaced by primary and secondary amines (L), in the presence of Me3NO, affording the complexes [Fe2{m-CN(Me)R}(m-CO)(CO)(L)(Cp)2][SO3CF3] (R = Me, L = NH2Et, 4a; R = Xyl, L = NH2Et, 4b; R = Me, L = NH2Pri, 5a; R = Xyl, L = NH2Pri, 5b; R = Xyl, L = NH2C6H11, 6; R = Xyl, L = NH2Ph, 7; R = Xyl, L = NH3, 8; R = Me, L = NHMe2, 9a; R = Xyl, L = NHMe2, 9b; R = Xyl, L= NH(CH2)5, 10). In the absence of Me3NO, NH2Et gives addition at the CO ligand of 1b, yielding [Fe2{CN(Me)(Xyl)}(m-CO)(CO)C(O)NHEt(Cp)2] (11). Carbonyl replacement is also observed in the reaction of 1a-b with pyridine and benzophenone imine, affording [Fe2{m-CN(Me)R}(m-CO)(CO)(L)(Cp)2][SO3CF3] (R= Me, L= Py, 12a; R = Xyl, L= Py, 12b; R= Me, L= HN=CPh2, 13a; R = Xyl, L= HN=CPh2, 13b). The imino complex 13b reacts with p-tolylacetylide leading to the formation of the m-vinylidene-diaminocarbene compound [Fe2-C=C(Tol)C(Ph)2N(H)CN(Me)(Xyl)(m-CO)(CO)(Cp2)] (15) which has been studied by X-ray diffraction

Nitrile ligands activation in dinuclear aminocarbyne complexes

The diiron complexes [Fe(Cp)(CO){μ-η2:η2-C[N(Me)(R)]NC(C6H3R′)CCH(Tol)}Fe(Cp)(CO)] (R = Xyl, R′ = H, 3a; R = Xyl, R′ = Br, 3b; R = Xyl, R′ = OMe, 3c; R = Xyl, R′ = CO2Me, 3d; R = Xyl, R′ = CF3, 3e; R = Me, R′ = H, 3f; R = Me, R′ = CF3, 3g) are obtained in good yields from the reaction of [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)(p-NCC6H4R′)(Cp)2]+ (R = Xyl, R′ = H, 2a; R = Xyl, R′ = Br, 2b; R = Xyl, R′ = OMe, 2c; R = Xyl, R′ = CO2Me, 2d; R = Xyl, R′ = CF3, 2e; R = Me, R′ = H, 2f; R = Me, R′ = CF3, 2g) with TolCCLi. The formation of 3 involves addition of the acetylide at the coordinated nitrile and C–N coupling with the bridging aminocarbyne together with orthometallation of the p-substituted aromatic ring and breaking of the Fe–Fe bond. Complexes3a–e which contain the N(Me)(Xyl) group exist in solution as mixtures of the E-trans and Z-trans isomers, whereas the compounds 3f,g, which posses an exocyclic NMe2 group, exist only in the Z-cis form. The crystal structures of Z-trans-3b, E-trans-3c, Z-trans-3e and Z-cis-3g have been determined by X-ray diffraction experiments