Hydration of Nitriles to Amides by Thiolate-Bridged Diiron Complexes

Green and efficient synthesis of dibenzyl cyanamides and ureas with cyanamide as a block

A method for the two-step synthesis of dibenzyl cyanamide and dibenzyl urea via cyanamide is presented. This approach is both efficient and environmentally friendly. Various N,N-dibenzyl ureas could be obtained by reactions of N,N-dibenzyl cyanamides and N,N-dibenzyl cyanamides as intermediates formed from cyanamide. In the absence of metal, ligand and hydrogen peroxide as the oxidant, products with moderate yields have been obtained under mild conditions. Key features include the use of widely available and easily handled cyanamide sources as starting materials.

Formation of thiolate-bridged diiron complexes featuring anionic isocyanide originating from the activation of counterions in the outer sphere

Transition metal isocyanide complexes have attracted increasing attention owing to their versatile applications in catalytic organic transformations. Compared with metal complexes with neutral isocyanide ligands, those featuring anionic isocyanide groups are relatively rare and poorly understood. So far, there has been no report on structurally characterized metal anionic isocyanopentafluorophosphate complexes that may have potential for the development of some unique polymerization reactions. In this paper, we adopt a dicationic thiolate-bridged diiron complex as the reaction platform for the coordination activation and functionalization of cyanide. When treating with KCN, a facile salt metathesis with hexafluorophosphate anions occurred to generate monocyanide or dicyanide species. However, using trimethylsilyl cyanide as the substrate, an unsymmetrical diiron complex bearing a terminal [CNSiMe₃] ligand and an anionic [NCPF₅]^- group derived from the activation of one non-coordinating anion PF₆^- was obtained in a high yield. Interestingly, due to the lability of the N-Si bond in the [CNSiMe₃] ligand, it can play the role of an active site for the interaction with counter anions in the outer sphere. On one hand, this labile ligand can facilitate the activation of the P-F bond in PF₆^- and the C-B bond in BPh₄^- to afford structurally characterized thiolate-bridged diiron anionic isocyanopentafluorophosphate and isocyanotriphenylborate complexes, respectively. On the other hand, it can also interact with Lut·HCl to convert into a cyanide ligand stabilized by a hydrogen bonding interaction. This work represents a new synthetic pathway to furnish metal anionic isocyanide complexes.

Tetrasubstituted Selenophenes from the Stepwise Assembly of Molecular Fragments on a Diiron Frame and Final Cleavage of a Bridging Alkylidene

A series of 2,3-dicarboxylato-5-acetyl-4-aminoselenophenes, 5a–j, was obtained via the uncommon assembly of building blocks on a diiron platform, starting from commercial [Fe₂Cp₂(CO)₄] through the stepwise formation of diiron complexes [2a–d]CF₃SO₃, 3a–d, and 4a–j. The selenophene-substituted bridging alkylidene ligand in 4a–j is removed from coordination upon treatment with water in air under mild conditions (ambient temperature in most cases), affording 5a–j in good to excellent yields. This process is highly selective and is accompanied by the disruption of the organometallic scaffold: cyclopentadiene (CpH) and lepidocrocite (γ-FeO(OH)) were identified by NMR and Raman analyses at the end of one representative reaction. The straightforward cleavage of the linkage between a bridging Fischer alkylidene and two (or more) metal centers, as observed here, is an unprecedented reaction in organometallic chemistry: in the present case, the carbene function is converted to a ketone which is incorporated into the organic product. DFT calculations and electrochemical experiments were carried out to give insight into the release of the selenophene-alkylidene ligand. Compounds 5a–j were fully characterized by elemental analysis, mass spectrometry, IR, and multinuclear NMR spectroscopy and by X-ray diffraction and cyclic voltammetry in one case.

Metal−metal cooperativity in action! Different fragments are combined on the {Fe₂Cp₂(CO)₂} skeleton to give highly functionalized selenophene ligands, linked to the iron centers through a bridging alkylidene, which is easily removed from coordination by exposure to air/water in ethereal solution.

Facile C-N coupling of coordinated ammonia and labile carbonyl or acetonitrile promoted by a thiolate-bridged dicobalt reaction scaffold

At low temperature, interaction of the thiolate-bridged dicobalt carbonyl complex [Cp*Co(i)(μ-SEt)₂(CO)CoCp*][I] (Cp* = η⁵-C₅Me₅) (1) with NH₃ resulted in the C-N coupling of the coordinated CO and amido group that originate from ammonia activation to afford a dicobalt formylamino complex [Cp*Co(μ-SEt)₂(μ-η¹:η¹-O[double bond, length as m-dash]CNH₂)CoCp*][I] (2). Interestingly, at relatively high temperatures, the labile CO ligand was replaced by NH₃ to give a thiolate-bridged dicobalt ammonia complex [Cp*Co(i)(μ-SEt)₂(NH₃)CoCp*][I] (3). Subsequently, in the presence of the dehalogenation reagent AgPF₆, the Co₂S₂ scaffold can simultaneously activate NH₃ and MeCN to produce the complex [Cp*Co(MeCN)(μ-SEt)₂(NH₃)CoCp*][PF₆]₂ (4). Furthermore, in the presence of NaOEt, the facile occurrence of the intramolecular cyclization led to the formation of acetamidino-bridged dicobalt complex [Cp*Co(μ-SEt)₂(μ-η¹:η¹-NH(CCH₃)NH)CoCp*][PF₆] (5), which may proceed through the nucleophilic attack of amido from NH₃ to coordinated MeCN followed by the hydrogen atom transfer process. In the presence of MeCN, treatment of 5 with HBF₄ released the corresponding [MeC(NH₂)NH₂]BF₄; meanwhile, the [Co₂S₂] core structural scaffold remained. In this Co₂S₂ reaction system, the cooperative activation effect between the two cobalt centers plays an important role for NH₃ activation and functionalization.

Catalytic hydration of cyanamides with phosphinous acid-based ruthenium(ii) and osmium(ii) complexes: scope and mechanistic insights

The catalytic hydration of cyanamides to ureas has been accomplished employing, for the first time, homogeneous catalysts, i.e. the phosphinous acid complexes [MCl₂(η⁶-p-cymene)(PMe₂OH)] (M = Ru, Os).

Anticancer Potential of Diiron Vinyliminium Complexes

Although ferrocene derivatives have attracted considerable attention as possible anticancer agents, the medicinal potential of diiron complexes has remained largely unexplored. Herein, we describe the straightforward multigram-scale synthesis and the antiproliferative activity of a series of diiron cyclopentadienyl complexes containing bridging vinyliminium ligands. IC₅₀ values in the low-to-mid micromolar range were determined against cisplatin sensitive and resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines. Notable selectivity towards the cancerous cells lines compared to the non-tumoral human embryonic kidney (HEK-293) cell line was observed for selected compounds. The activity seems to be multimodal, involving reactive oxygen species (ROS) generation and, in some cases, a fragmentation process to afford monoiron derivatives. The large structural variability, amphiphilic character and good stability in aqueous media of the diiron vinyliminium complexes provide favorable properties compared to other widely studied classes of iron-based anticancer candidates.

CO2 fixation and transformation on a thiolate-bridged dicobalt scaffold under oxidising conditions

CO2 fixation and conversion promoted by a thiolate-bridged dicobalt complex in the presence of an oxidant.

Monomeric nickel hydroxide stabilized by a sterically demanding phosphorus–nitrogen PN3P-pincer ligand: synthesis, reactivity and catalysis

Various new nickel complexes and amides are synthesized using monomeric nickel hydroxide (PN³P)Ni(OH) (3) as the precursor or catalyst.

Synthesis and reactivity of thiolate-bridged multi-iron complexes supported by cyclic (alkyl)(amino)carbene

The combined utilization of Me₂-cAAC (Me₂-cAAC = :C(CH₂)(CMe₂)₂N-2,6-ⁱPr₂C₆H₃) and thiolates as supporting ligands enables the access of unprecedented carbene coordinated thiolate-bridged diiron(ii) complexes [(Me₂-cAAC)Fe(μ-SR)(Br)]₂ (R = Me, 3; R = Et, 4). The coordination environment of each tetrahedral iron(ii) center in complexes 3 and 4 is composed of one terminal bromide atom, one carbene carbon atom and two thiolate sulfur atoms, which is similar to the carbide-containing sulfur-rich environment of iron centers in the belt region of the FeMo-cofactor. Interestingly, when NaSCPh₃ was chosen as the thiolate ligand, C-S bond homolysis occurred to form a rare [3 : 1] site-differentiated cubane-type cluster [(Me₂-cAAC)Fe₄S₄(Br)₃][Me₂-cAACH] (5). Furthermore, complexes 3 and 4 exhibit good exchange reactivity toward the azide anion to give novel thiolate-bridged diiron complexes with two azido ligands in a trans arrangement.

Migratory insertion and hydrogenation of a bridging azide in a thiolate-bridged dicobalt reaction platform

A novel well-defined thiolate-bridged dicobalt azido complex is converted to a rare sulfilimide-bridged dicobalt complex via nitrogen atom migratory insertion into the Co-S bond upon thermolysis. Intriguingly, the homolytic cleavage of hydrogen is achieved by this azide under mild conditions to furnish a partially hydrogenated azido complex.

Hemilability-Driven Water Activation: A NiII Catalyst for Base-Free Hydration of Nitriles to Amides

The Ni^II complex 1 containing pyridyl- and hydroxy-functionalized N-heterocyclic carbenes (NHCs) is synthesized and its catalytic utility for the selective nitrile hydration to the corresponding amide under base-free conditions is evaluated. The title compound exploits a hemilabile pyridyl unit to interact with a catalytically relevant water molecule through hydrogen-bonding and promotes a nucleophilic water attack to the nitrile. A wide variety of nitriles is hydrated to the corresponding amides including the pharmaceutical drugs rufinamide, Rifater, and piracetam. Synthetically challenging α-hydroxyamides are accessed from cyanohydrins under neutral conditions. Related catalysts that lack the pyridyl unit (i.e., compounds 2 and 4) are not active whereas those containing both the pyridyl and the hydroxy or only the pyridyl pendant (i.e., compounds 1 and 3) show substantial activity. The linkage isomer 1' where the hydroxy group is bound to the metal instead of the pyridyl group was isolated under different crystallization conditions insinuating a ligand hemilabile behavior. Additional pK_a measurements reveal an accessible pyridyl unit under the catalytic conditions. Kinetic studies support a ligand-promoted nucleophilic water addition to a metal-bound nitrile group. This work reports a Ni-based catalyst that exhibits functional hemilability for hydration chemistry.

Synthesis, structural characterization and conversion of dinuclear iron-sulfur clusters containing the disulfide ligand: [Cp*Fe(μ-η2:η2-bdt)(cis-μ-η1:η1-S2)FeCp*], [Cp*Fe(μ-S(C6H4S2))(cis-μ-η1:η1-S2)FeCp*], and [{Cp*Fe(bdt)}2(trans-μ-η1:η1-S2)]

The treatment of [Cp*Fe(μ-η²:η⁴-bdt)FeCp*] (1, Cp* = η⁵-C₅Me₅, bdt = benzene-1,2-dithiolate) with 1/4 equiv. of elemental sulfur (S₈) gave a dinuclear iron-sulfur cluster [Cp*Fe(μ-η²:η²-bdt)(cis-μ-η¹:η¹-S₂)FeCp*] (2), which contains a cis-1,2-disulfide ligand. When complex 2 further interacted with 1/8 equiv. of S₈, another sulfur atom inserted into an Fe-S bond to give a rare product [Cp*Fe(μ-S(C₆H₄S₂))(cis-μ-η¹:η¹-S₂)FeCp*] (3). Unexpectedly, a trans-1,2 disulfide-bridged diiron complex [{Cp*Fe(bdt)}₂(trans-μ-η¹:η¹-S₂)] (4) was isolated from the reaction of complex 1 with 1/2 equiv. of S₈, which represents a structural isomer of [2Fe-2S] ferredoxin-type clusters. In addition, cis-1,2-disulfide-bridged complex 3 can slowly convert into trans-1,2-disulfide-bridged complex 4 and the complex [Cp*Fe(μ-η²:η²-S₂)(cis-μ-η¹:η¹-S₂)FeCp*] (5) by self-assembly reaction at ambient temperature, which is evidenced by time-dependent ¹H NMR spectroscopy.

Structural characterization and proton reduction electrocatalysis of thiolate-bridged bimetallic (CoCo and CoFe) complexes

Using an assembly method, dinuclear CoCo and CoFe complexes supported by a bdt ligand, [Cp*Co(μ–η²:η²-bdt)(μ-I)CoCp*][PF₆] (1[PF6], Cp* = η⁵-C₅Me₅, bdt = benzene-1,2-dithiolate), and [Cp*Co(μ–η²:η⁴-bdt)FeCp′][PF₆] (3[PF6], Cp′ = η⁵-C₅Me₄H) were synthesized in high yields.