Synthesis of PCP‐Supported Nickel Complexes and their Reactivity with Carbon Dioxide

The Ni amide and hydroxide complexes [(PCP)Ni(NH₂)] ( 2 ; PCP=bis‐2,6‐di‐tert‐butylphosphinomethylbenzene) and [(PCP)Ni(OH)] ( 3 ) were prepared by treatment of [(PCP)NiCl] ( 1 ) with NaNH₂ or NaOH, respectively. The conditions for the formation of 3 from 1 and NaOH were harsh (2 weeks in THF at reflux) and a more facile synthetic route involved protonation of 2 with H₂O, to generate 3 and ammonia. Similarly the basic amide in 2 was protonated with a variety of other weak acids to form the complexes [(PCP)Ni(2‐Me‐imidazole)] ( 4 ), [(PCP)Ni(dimethylmalonate)] ( 5 ), [(PCP)Ni(oxazole)] ( 6 ), and [(PCP)Ni(CCPh)] ( 7 ), respectively. The hydroxide compound 3 , could also be used as a Ni precursor and treatment of 3 with TMSCN (TMS=trimethylsilyl) or TMSN₃ generated [(PCP)Ni(CN)] ( 8 ) or [(PCP)Ni(N₃)] ( 9 ), respectively. Compounds 3–7 , and 9 were characterized by X‐ray crystallography. Although 3 , 4 , 6 , 7 , and 9 are all four‐coordinate complexes with a square‐planar geometry around Ni, 5 is a pseudo‐five‐coordinate complex, with the dimethylmalonate ligand coordinated in an X‐type fashion through one oxygen atom, and weakly as an L‐type ligand through another oxygen atom. Complexes 2–9 were all reacted with carbon dioxide. Compounds 2 – 4 underwent facile reaction at low temperature to form the κ¹‐O carboxylate products [(PCP)Ni{OC(O)NH₂}] ( 10 ), [(PCP)Ni{OC(O)OH}] ( 11 ), and [(PCP)Ni{OC(O)‐2‐Me‐imidazole}] ( 12 ), respectively. Compounds 10 and 11 were characterized by X‐ray crystallography. No reaction was observed between 5 – 9 and carbon dioxide, even at elevated temperatures. DFT calculations were performed to model the thermodynamics for the insertion of carbon dioxide into 2 – 9 to form a κ¹‐O carboxylate product and understand the pathways for carbon dioxide insertion into 2 , 3 , 6 , and 7 . The computed free energies indicate that carbon dioxide insertion into 2 and 3 is thermodynamically favorable, insertion into 8 and 9 is significantly uphill, insertion into 5 and 7 is slightly uphill, and insertion into 4 and 6 is close to thermoneutral. The pathway for insertion into 2 and 3 has a low barrier and involves nucleophilic attack of the nitrogen or oxygen lone pair on electrophilic carbon dioxide. A related stepwise pathway is calculated for 7 , but in this case the carbon of the alkyne is significantly less nucleophilic and as a result, the barrier for carbon dioxide insertion is high. In contrast, carbon dioxide insertion into 6 involves a single concerted step that has a high barrier.     

Nickel(0)‐Catalyzed Hydroalkenylation of Imines with Styrene and Its Derivatives

A nickel(0)‐catalyzed hydroalkenylation of imines with styrene and its derivatives is described. A wide range of aromatic and aliphatic imines directly coupled with styrene and its derivatives, thus providing various synthetically useful allylic amines with up to 95 % yield. The reaction offers a new atom‐ and step‐economical approach to allylic amines by using alkenes instead of alkenyl‐metallic reagents. Experiments and DFT calculations showed that TsNH₂ promotes the proton transfer from the coordinated olefin to the imine, accompanied by a new C?C bond formation.     

Redox‐Switchable 20π‐, 19π‐, and 18π‐Electron 5,10,15,20‐Tetraaryl‐5,15‐diazaporphyrinoid Nickel(II) Complexes

The first examples of air‐stable 20π‐electron 5,10,15,20‐tetraaryl‐5,15‐diaza‐5,15‐dihydroporphyrins, their 18π‐electron dications, and the 19π‐electron radical cation were prepared through metal‐templated annulation of nickel(II) bis(5‐arylamino‐3‐chloro‐8‐mesityldipyrrin) complexes followed by oxidation. The neutral 20π‐electron derivatives are antiaromatic and the cationic 18π‐electron derivatives are aromatic in terms of the magnetic criterion of aromaticity. The meso N atoms in these diazaporphyrinoids give rise to characteristic redox and optical properties for the compounds that are not typical of isoelectronic 5,10,15,20‐tetraarylporphyrins.     

Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare‐Earth Complexes: Non‐Redox Oxygen Atom Transfer

The preferential substitution of oxo ligands over alkyl ones of rare‐earth complexes is commonly considered as “impossible” due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare‐earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln‐oxo bond, but also protect the highly reactive Ln‐alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non‐redox rare‐earth‐mediated oxygen atom transfer from ketones to CS₂ and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare‐earth oxo complexes.     

Metal–Chalcogenolate Complexes with Silyl Functionalities: Synthesis and Reaction Chemistry

Metal complexes with reactive [ESiR₃]^? (E = S, Se, Te) or [S(SiMe₂)]^2? ligands provide a means for the delivery of {ME_n}^m? units in the formation of heterometallic polynuclear complexes and clusters. These complexes can be reacted with M′ salts to promote M–E–M′ interactions via the elimination of a silane side product. This research report summarizes the recent developments in the synthesis of silylchalcogenolate complexes of the d‐block metals with emphasis directed to those for which reactivity studies for the formation of ternary clusters have been carried out. The effects of varying the groups on the silyl moiety on the stability and reactivity of these precursor molecules are also discussed.     

Triangular Nickel Complexes Derived from 2‐Pyridylcyanoxime: An Approach to the Magnetic Properties of the [Ni3(μ3‐OH){pyC(R)NO}3]2+ Core

A series of nickel complexes with nuclearity ranging from Ni₃ to Ni₆ have been obtained by treatment of a variety of nickel salts with the 2‐pyridylcyanoxime ligand. The reported compounds have as a common structural feature the triangular arrangement of nickel cations bridged by a central μ₃‐oxo/alkoxo ligand. These compounds are simultaneously the first nickel derivatives of the 2‐pyridylcyanoxime ligand and the first examples of isolated, μ₃‐O triangular pyridyloximate nickel complexes. Magnetic measurements reveal antiferromagnetic interactions promoted by the μ₃‐O and oximato superexchange pathways and comparison of the experimental structural and magnetic data with DFT calculations give an in‐depth explanation of the factors that determine the magnetic interaction in this kind of system.     

Gold‐Catalyzed Fluorination–Hydration: Synthesis of α‐Fluorobenzofuranones from 2‐Alkynylphenol Derivatives

The Au^I‐catalyzed fluorination–hydration of 2‐alkynylphenol derivatives in the presence of Selectfluor [1‐chloromethyl‐4‐fluoro‐1,4‐diazoniabicyclo‐[2.2.2]octane bis(tetrafluoroborate)] has been developed. This method provides straightforward access to α‐fluorobenzofuranones with the construction of C?O, C=O, and C?F bonds in a single step on the basis of an Au^I/Au^III redox catalytic cycle. Several control experiments, including the asymmetric variant of this reaction, were also conducted to gain insight into the reaction mechanism.     

Binukleare Nickel(0)-Alkin-Koordinationsverbindungen – Zusammenhang zwischen Ligandperipherie und supramolekularer Struktur

Binuclear Nickel(0) Alkyne Coordination Compounds – Correlation between Ligand Periphery and Supramolecular Structure Reaction of Ni(cdt: 1,5,9-cyclododecatriene) with functionalized alkynes and subsequent reaction with ethylenediamines gives binuclear compounds of the type (diamine)Ni(μ-alkyne)Ni(alkyne). Compounds with alkyne-diols (N?N)Ni₂(HOR¹R²C? C?C? CR¹R²OH)₂ show supramolecular structures in which two identical intramolecular and one intermolecular hydrogen bonds are realized. 1 and 2 (chelate ligand in each case N,N,N′,N′-tetramethylethylenediamine, TMEDA, in 1 R¹ = R² = Me, in 2 R¹ = R² = Et) polymer-like chains are built up by connecting the binuclear units. Via two intermolecular hydrogen bonds per organometallic unit in 1 and via one intermoleculare hydrogen bond in 2 the chains are connected to give double chains. By substitution of one methyl group of TMEDA by hydrogen ( 3 : R¹ = R² = Me) a polymerlike network is produced by connecting the polymer-like chains. In compound 4 in which one of the methyl groups of TMEDA is substituted by CH₂CH₂NMe₂ the polymer-like chains remain unconnected. In 5 (diamine = TMEDA, alkyne = (CH₃)₃C? C?C? CMe₂OH) one intermolecular hydrogen bond per organometallic unit is observed forming again polymer-like chains that are independent of each other.     

Rhodium(III)‐Catalyzed [3+2] Annulation of 5‐Aryl‐2,3‐dihydro‐1H‐pyrroles with Internal Alkynes through C(sp2)H/Alkene Functionalization

This study describes a new rhodium(III)‐catalyzed [3+2] annulation of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles with internal alkynes using a Cu(OAc)₂ oxidant for building a spirocyclic ring system, which includes the functionalization of an aryl C(sp²)? H bond and addition/protonolysis of an alkene C?C bond. This method is applicable to a wide range of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles and internal alkynes, and results in the assembly of the spiro[indene‐1,2′‐pyrrolidine] architectures in good yields with excellent regioselectivities.     

One‐Electron Reduction of Acenaphthene‐1,2‐Diimine Nickel(II) Complexes

New nickel‐based complexes of 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene (dpp‐bian) with BF₄^? counterion or halide co‐ligands were synthesized in THF and MeCN. The nickel(I) complexes were obtained by using two approaches: 1) electrochemical reduction of the corresponding nickel(II) precursors; and 2) a chemical comproportionation reaction. The structural features and redox properties of these complexes were investigated by using single‐crystal X‐ray diffraction (XRD), cyclic voltammetry (CV), and electron paramagnetic resonance (EPR) and UV/Vis spectroscopy. The influence of temperature and solvent on the structure of the nickel(I) complexes was studied in detail, and an uncommon reversible solvent‐induced monomer/dimer transformation was observed. In the case of the fluoride complex, the unpaired electron was found to be localized on the dpp‐bian ligand, whereas all of the other nickel complexes contained neutral dpp‐bian moieties.     

Highly Enantioselective Copper(I)‐Catalyzed Conjugate Addition of Terminal Alkynes to 1,1‐Difluoro‐1‐(phenylsulfonyl)‐3‐en‐2‐ones: New Ester/Amide Surrogates in Asymmetric Catalysis

A highly enantioselective copper‐catalyzed conjugate alkynylation of monoactivated enones, namely 1,1‐difluoro‐1‐(phenylsulfonyl)‐3‐en‐2‐ones, is described. The reaction products are obtained with good yields and excellent enantioselectivities (from 92 to 99% ee). The β‐alkynylated difluoro(phenylsulfonyl) ketones can be converted into the corresponding β‐alkynylated difluoro‐ and trifluoromethyl ketones, esters and amides. This is the first example on the use of 1,1‐difluoro‐1‐(phenylsulfonyl)‐3‐en‐2‐ones as substrates in an enantioselective reaction, which have been shown to be new ester/amide surrogates.     

Rhodium(I)‐Catalyzed Reductive Cyclocarbonylation of Internal Alkynes: Atom‐Economic Process for Synthesis of 2‐Cyclopenten‐1‐ones, 5‐Alkylidenefuran‐2(5 H)‐ones and Indan‐1‐ones

Economical atoms : 2‐Cyclopenten‐1‐ones, 5‐alkylidenefuran‐2(5 H)‐ones and indan‐1‐ones have been synthesized by atom‐economic reductive cyclocarbonylation of internal alkynes with carbon monoxide catalyzed by [{RhCl(CO)₂}₂]/CO(NH₂)₂ in the presence of water (see scheme).

     

Organotin Dyes: Synthesis and Structural Characterization of Dibutyltin and Dimethyltin Complexes with 2, 2′‐Dihydroxyazobenzene

The preparation and structures of 2, 2′‐dihydroxyazobenzenato‐dibutyl‐tin [Bu₂SnL] and 2, 2′‐dihydroxyazobenzenato‐dimethyl‐tin [Me₂SnL] are described. The complexes were characterized by IR, NMR (¹H, ¹³C, ¹¹⁹Sn) and UV/VIS spectra. The crystal structures were determined by X‐ray diffraction on single crystals. [Bu₂SnL]: monoclinic, space group P2₁/c, cell constants at 208 K: a = 860.73(5), b = 973, 51(18), c = 2340.0(3) pm, β = 93.615(11)°; R₁ = 0.0546. [Me₂SnL]: orthorhombic, space group Pbcn, cell constants at 208 K: a = 1914.6(4), b = 1041.3(3), c = 1323.27(14) pm; R₁ = 0.0529.     

Fe1−yO Nanoparticles: Organometallic Synthesis and Magnetic Properties

Non‐stoichiometric wüstite particles (Fe_1?yO) are synthesized using the controlled room‐temperature hydrolysis of the organometallic precursor {Fe[N(SiMe₃)₂]₂}. Particles stabilized by hexadecylamine with a diameter of ～5 nm are obtained. For such small nanoparticles, a distorted crystallographic structure is evidenced by wide‐angle X‐ray scattering at room temperature and reported for the first time. The study of the magnetic properties indicates that these particles are composed of an antiferromagnetic core surrounded by a ferromagnetic shell. According to the Néel theory, we demonstrate that this shell consists of 1.5 % of Fe³⁺ ions ferromagnetically coupled with Fe²⁺ ions.     

3‐(Arylhydrazono)pentane‐2, 4‐diones and their Complexes with Copper(II) and Nickel(II) — Synthesis and Crystal Structures

A series of new 3‐(arylhydrazono)pentane‐2, 4‐diones ( 1 ‐ 6 ) synthesized from pentane‐2, 4‐dione and diazonium salts of respective anilines using the procedure of Japp‐Klingemann are described. Complexes with Cu^II and Ni^II salts are prepared ( 7 ‐ 10 , respectively). Spectroscopic properties of these compounds have been studied and X‐ray crystal structures of selected hydrazones ( 3 , 4 , 6 ) and of the hydrazone complexes ( 7 ‐ 10 ) are reported. The structures of the uncomplexed hydrazones feature an intramolecular N‐H···O interaction to yield a six‐membered H‐bond ring reflecting preference of the hydrazone tautomeric structure. All the complexes are mononuclear 2:1 (L:M) structures of six‐membered chelate type involving N₂O₂ binding sites that are quadratic arranged but differ in the entire coordination environment dependent on the metal and the ligand substitution including distorted octahedral and quadratic pyramidal coordination geometries in the Cu^II complexes 7 and 8 or nearly regular square planar coordination geometry in the Ni^II complexes 9 and 10 , respectively. In the crystal packings, strong and weak H‐bond interactions cause supramolecular network structures.     

FeCl3-Mediated Reaction of 1,4-Dilithio-1,3-dienes with Alkynes Affording Benzene Derivatives

Unactivated alkynes reacted with 1,4-dilithio-1,3-diene derivatives in the presence of FeCl3 affording substituted benzene derivatives via a formal[4 2] cycloaddition.