Diiron μ-aminocarbyne compounds, 1a-e, are prepared in two steps from Fe 2 Cp 2 (CO) 4 , negating the need for difficult purification procedures of intermediate species; they are efficiently isolated by alumina chromatography. Minor amounts of μ-aminocarbyne aryl isocyanide compounds, 2a-c, are obtained as side products. The structures of the cations in 1a,c,e are calculated using DFT; the carbyne carbon is generally predicted to be the thermodynamic site of hydride addition, in agreement with a previous experimental finding concerning 1a. Accordingly, the reaction of 1e with NaBH 4 affords a bridging aminocarbene complex, 4, in 85 % yield. Otherwise, the reaction of 1c with NaBH 4 yields the aminocarbyne-cyclopentadiene derivative 3 (70 %), presumably as a consequence of the [a] Scheme 1. Regioselective additions of nucleophiles to the diiron aminocarbyne complex 1a.
Results and DiscussionThe commercial compound [Fe 2 Cp 2 (CO) 4 ] was reacted with the appropriate isocyanide, in a ca. 3:2 molar ratio, in acetonitrile solution. [16] The reactions with alkyl isocyanides were conducted under reflux conditions, whereas the reactions with aryl isocyanides proceeded at room temperature. The resulting mixtures were dried under vacuum and the residues were dissolved in dichloromethane and then treated with methyl triflate, thus affording the μ-aminocarbyne complexes 1a-e (Scheme 2). The difficult isolation of the monoisocyanide intermediates (see the Introduction) was unnecessary. The final products 1a-e were efficiently purified by alumina chromatography and were then isolated as microcrystalline, air-stable compounds in 65-92 % yields. The synthesis of 1c-e was accompanied by the side formation of minor products derived from di-isocyanide species, 2a-c. Compounds 2a-c were recovered by the chromatography in 3-12 % yields, although 2a was formerly reported as being Scheme 2. Synthesis of diiron μ-aminocarbyne complexes.Eur. J. Inorg. Chem. 2018, 960-971 www.eurjic.org
α-Diimines are among the most robust and versatile ligands available in synthetic coordination chemistry, possessing finely tunable steric and electronic properties. A series of novel cationic ruthenium(II) p-cymene complexes bearing simple α-diimine ligands, [(η- p-cymene)RuCl{κ N-(HCNR)}]NO (R = Cy, [1]NO; R = 4-CHOH, [2]NO; R = 4-CHOH, [3]NO), were prepared in near-quantitative yields as their nitrate salts. [2]NO displays high water solubility. The potential of the α-diimine ligand in [3]NO as a carrier of bioactive molecules was investigated via esterification reactions with the hydroxyl groups. Thus, the double-functionalized derivatives [(η- p-cymene)RuCl{κ N-(HCN(4-CHOCO-R))}]NO (R = aspirinate, [5]NO; valproate, [6]NO) and also [4]Cl (R = Me) were obtained in good-to-high yields. UV-vis and multinuclear NMR spectroscopy and cyclic voltammetric studies in aqueous solution revealed only minor ruthenium chloride hydrolytic cleavage, biologically accessible reduction potentials, and pH-dependent behavior of [3]NO. Density functional theory analysis was performed in order to compare the Ru-Cl bond strength in [1] with the analogous ethylenediamine complex, showing that the higher stability observed in the former is related to the electron-withdrawing properties of the α-diimine ligand. In vitro cytotoxicity studies were performed against tumorigenic (A2780 and A2780cisR) and nontumorigenic (HEK-293) cell lines, with the complexes bearing simple α-diimine ligands ranging from inactive to IC values in the low micromolar range. The complexes functionalized with bioactive components, i.e., [5]NO and [6]NO, exhibited a marked increase in the cytotoxicity with respect to the precursor [3]NO.
a b s t r a c tThe Beckmann rearrangement of cyclohexanone oxime to e-caprolactam catalyzed by trifluoroacetic acid in aprotic solvents such as toluene, 1,2-dichloroethane, acetonitrile, benzonitrile, nitromethane and their mixtures is described. High yield and selectivity in e-caprolactam have been observed. Data relative to cyclohexanone oxime protonation equilibrium, interaction of e-caprolactam with the acid, solvent effect on reaction kinetics and apparent activation energy are given together with some thoughts on the reaction mechanism.
Triangular clusters [{MFe(CO)4}3]3– (M = Cu, 4; Ag, 5; Au, 6) were selectively obtained
by heating Fe(CO)4(MIMes)2 (M = Cu, 1; Ag, 2; Au, 3; IMes = C3N2H2(C6H2Me3)2). 1–3 were synthesized by
reacting Na2[Fe(CO)4]·2thf
with 2 equiv of M(IMes)Cl. As previously described, the direct reactions
of Na2[Fe(CO)4]·2thf with
one equivalent of M(I) salts resulted in the triangular cluster [{CuFe(CO)4}3]3– for Cu, whereas the square
clusters [{MFe(CO)4}4]4– were
formed for Ag and Au. Thus, depending on the synthetic protocol adopted,
both the triangular [{MFe(CO)4}3]3– and square [{MFe(CO)4}4]4– polymerization isomers can be selectively obtained, at least for
Ag and Au. Polymerization isomerism, that is two compounds having
the same elemental compositions but different molecular weights, was
investigated in [{MFe(CO)4}
n
]
n− (n = 3, 4;
M = Cu, Ag, Au) by means of structural and theoretical methods and
the role of metallophilic interactions was computationally studied
by means of the atoms-in-molecules (AIM) approach.
The selective reactions of niobium pentachloride with two bulky NHC carbenes afforded NbCl5(NHC) complexes, bearing the highest oxidation state ever found for a metal centre in a transition metal halide-NHC adduct. The X-ray structure of 2a is the first one reported for a monodentate NHC-niobium species, and exhibits an abnormally long Nb-C bond.
Tin trihydride Os(SnH3)(Tp)L(PPh3) [L = P(OMe)3, P(OEt)3] complexes were prepared by allowing chloro OsCl(Tp)L(PPh3) complexes to react first with SnCl2 and then with NaBH4 in
ethanol. The complexes were characterized spectroscopically and by the X-ray crystal structure determination of the Os(SnH3)(Tp){P(OMe)3}(PPh3) derivative. Reaction of tin trihydride complexes with CO2 led to formate Os[SnH{OC(H)=O}2](Tp)L(PPh3) derivatives
In recent studies regarding acid-catalysed Beckmann rearrangement of cyclohexanone oxime in aprotic solvents it has been observed that a quite surprising hydrolysis of the starting material, i.e., cyclohexanone oxime, occurs even if the experimental conditions and the water concentration in the reaction mixture can not justify such a side-reaction. Being this apparent hydrolysis critical for catalyst selectivity and poisoning, a computational DFT study on a possible secondary reaction pathway, involving a bi-molecular reaction between two cyclohexanone oxime molecules in acid media as the primary step, is here reported to explain the experimental results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.