Solid‐State Luminescence of Au?Cu?Alkynyl Complexes Induced by Metallophilicity‐Driven Aggregation

A new series of homoleptic alkynyl complexes, [{Au₂Cu₂(C₂R)₄}_n] (R=C₃H₇O ( 1 ), C₆H₁₁O ( 2 ), C₉H₁₉O ( 3 ), C₁₃H₁₁O ( 4 )), were obtained from Au(SC₄H₈)Cl, Cu(NCMe)₄PF₆, and the corresponding alkyne in the presence of a base (NEt₃). Complexes 1 – 4 aggregate upon crystallization into polymeric chains through extensive metallophilic interactions. The cluster that contains fluorenolyl functionalities, C₁₃H₉O ( 5 ), crystallizes in its molecular form as a disolvate, [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 THF. The substitution of weakly bound THF molecules with pyridine molecules leads to the complex [Au₂Cu₂(C₂C₁₃H₉O)₄] ? 2 py ( 6 ), thus giving two polymorphs in the solid state. Such structural diversity is established through metal‐chain and hydrogen‐bond formation, which depends on the stereochemical characteristics of the organic ligands. More interestingly, this solid‐state structural arrangement affords good emission properties, such as intensity and spectroscopic profile, which are otherwise very weakly emissive in solution. Metallophilic aggregation of the {Au₂Cu₂} cluster units, as observed in the crystals, results in dramatic enhancement of the room‐temperature phosphorescence, thereby reaching a maximum quantum efficiency of 95 % ( 4 ). A theoretical approach further indicates a synergistic effect of the array of the metal chain upon aggregation, which greatly enhances the spin‐orbit coupling and, hence, the phosphorescence, thereby opening up a new direction in the field of aggregate‐enhanced emission.     

Gas‐Phase Spectroscopy of Ferric Heme?NO Complexes

Weakly bound complexes between ferric heme cations and NO were synthesised in the gas phase from ion–molecule reactions, and their absorption measured based on photodissociation yields. The Soret band, which serves as an important marker band for heme‐protein spectroscopy, is maximal at 357±5 nm and significantly blue‐shifted compared to ferric heme nitrosyl proteins (maxima between 408 and 422 nm). This is in stark contrast to the Q‐band absorption where the protein microenvironment is nearly innocent in perturbing the electronic structure of the porphyrin macrocycle. Photodissociation is primarily through loss of NO. In contrast to the Q‐band region, two‐photon absorption was seen in the Soret band despite NO loss only requiring ～1 eV. A model based on intersystem crossing to a long‐lived triplet state where a barrier has to be surmounted is suggested. Finally, we summarise the measured absorption maxima of heme and its complexes with amino acids and NO.     

Synthesis of Phenanthridinones from N‐Methoxybenzamides and Aryltriethoxysilanes through RhIII‐Catalyzed C?H and N?H Bond Activation

An efficient method for the one‐pot synthesis of substituted phenanthridinone derivatives from N‐methoxybenzamides and aryltriethoxysilanes through rhodium‐catalyzed dual C? H bond activation and annulation reactions is described. A double‐cycle mechanism is proposed to account for this catalytic reaction. In addition, isotope‐labeling studies were performed to understand the intimate mechanism of the reaction.     

Hydride Reactivity of NiII?X?NiII Entities: Mixed‐Valent Hydrido Complexes and Reversible Metal Reduction

After the lithiation of PYR‐H₂ (PYR^2?=[{NC(Me)C(H)C(Me)NC₆H₃(iPr)₂}₂(C₅H₃N)]^2?), which is the precursor of an expanded β‐diketiminato ligand system with two binding pockets, its reaction with [NiBr₂(dme)] led to a dinuclear nickel(II)–bromide complex, [(PYR)Ni(μ‐Br)NiBr] ( 1 ). The bridging bromide ligand could be selectively exchanged for a thiolate ligand to yield [(PYR)Ni(μ‐SEt)NiBr] ( 3 ). In an attempt to introduce hydride ligands, both compounds were treated with KHBEt₃. This treatment afforded [(PYR)Ni(μ‐H)Ni] ( 2 ), which is a mixed valent Ni^I? μ‐H? Ni^II complex, and [(PYR‐H)Ni(μ‐SEt)Ni] ( 4 ), in which two tricoordinated Ni^I moieties are strongly antiferromagnetically coupled. Compound 4 is the product of an initial salt metathesis, followed by an intramolecular redox process that separates the original hydride ligand into two electrons, which reduce the metal centres, and a proton, which is trapped by one of the binding pockets, thereby converting it into an olefin ligand on one of the Ni^I centres. The addition of a mild acid to complex 4 leads to the elimination of H₂ and the formation of a Ni^IINi^II compound, [(PYR)Ni(μ‐SEt)NiOTf] ( 5 ), so that the original Ni^II(μ‐SEt)Ni^IIX core of compound 3 is restored. All of these compounds were fully characterized, including by X‐ray diffraction, and their molecular structures, as well as their formation processes, are discussed.     

Nano‐Cu2O‐Catalyzed Formation of C?C and C?O Bonds: One‐Pot Domino Process for Regioselective Synthesis of α‐Carbonyl Furans from Electron‐Deficient Alkynes and 2‐Yn‐1‐ols

The formation of carbon–carbon and carbon–oxygen bonds continues to be an active and challenging field of chemical research. Nanoparticle catalysis has attracted considerable attention owing to its environmentally benign and high activity toward the reactions. Herein, we described a novel and effective nano‐Cu₂O‐catalyzed one‐pot domino process for the regioselective synthesis of α‐carbonyl furans. Various electron‐deficient alkynes with 2‐yn‐1‐ols underwent this process smoothly in moderate to good yields in the presence of air at atmospheric pressure. It is especially noteworthy that a novel 2,4,5‐trisubstituted 3‐ynylfuran was formed in an extremely direct manner without tedious stepwise synthesis. Additionally, as all of the starting materials are readily available, this method may allow the synthesis of more complex α‐carbonyl furans. An experiment to elucidate the mechanism suggested that the process involved a carbene intermediate.     

M4(CH2)4 Cubane‐Type Rare‐Earth Methylidene Complexes: Unique Reactivity toward Unsaturated C?O,C?N,and C?S Bonds

The reactivity of the cubane‐type rare‐earth methylidene complex [Cp′Lu(μ₃‐CH₂)]₄ ( 1 , Cp′=C₅Me₄SiMe₃) with various unsaturated electrophiles was investigated. The reaction of 1 with CO (1 atm) at room temperature gave the bis(ketene dianion)/dimethylidene complex [Cp′₄Lu₄(μ₃‐CH₂)₂(μ₃,η²‐O‐C?CH₂)₂] ( 2 ) in 86 % yield through the insertion of two molecules of CO into two of the four lutetium–methylidene units. In the reaction with the sterically demanding N,N‐diisopropylcarbodiimide at 60 °C, only one of the four methylidene units in 1 reacted with one molecule of the carbodiimide substrate to give the mono(ethylene diamido)/trimethylidene complex [Cp′₄Lu₄(μ₃‐CH₂)₃{iPrNC(=CH₂)NiPr}] ( 3 ) in 83 % yield. Similarly, the reaction of 1 with phenyl isothiocyanate gave the ethylene amido thiolate/trimethylidene complex [Cp′₄Lu₄(μ₃‐CH₂)₃{PhNC(S)=CH₂}] ( 4 ). In the case of phenyl isocyanate, two of the four methylidene units in 1 reacted with four molecules of the substrate at ambient temperature to give the malonodiimidate/dimethylidene complex [Cp′₄Lu₄(μ₃‐CH₂)₂{PhN=C(O)CH₂(O)C?NPh}₂] ( 5 ) in 87 % yield. In this reaction, each of the two lutetium–methylidene bonds per methylidene unit inserted one molecule of phenyl isocyanate. All the products have been fully characterized by NMR spectroscopy, X‐ray diffraction, and microelemental analyses.     

Electronic Structure of Monodithiolated Iron?Oxotungsten Heterometallic Complexes: Integer‐Spin Fe?W Assembly

Fe? W heterometallic complexes, in which an FeX₂ (X=Cl, SPh) moiety is attached to monodithiolene oxotungsten through a sulfide bridge, that is, [Ph₄P]₂[Cl₂Fe(S)₂WOS₂] ( 1 ), [Ph₄P]₂[Cl₂Fe(S)₂WOS₂(DMED)] ( 2 , DMED=dimethylethylenedicarboxylate), [Ph₄P]₂[Cl₂Fe(S)₂WO(tdt)] ( 3 , tdt=toluenedithiolate), [Ph₄P]₂[(SPh)₂Fe(S)₂WO(tdt)] ( 4 ), and [Ph₄P]₂[Cl₂Fe(S)₂WO(edt)] ( 5 , edt=ethanedithiolate), are reported. Mössbauer and EPR spectroscopy, magnetism, electrochemistry, and electronic structural analysis based on DFT and TD‐DFT calculations show the transfer of electron from the iron center to the tungsten center, thus resulting in a ferromagnetically coupled Fe^IIIW^V unit, along with antiferromagnetic intermolecular interactions, from the starting Fe^II and W^VI compounds. A net spin of a S=3 ground state, which arises from ferromagnetically coupled Fe^III and W^V atoms, displays a rare X‐band EPR in normal mode at g≈7 in the solid state.     

Catalytic C?C,C?N,and C?O Ullmann‐Type Coupling Reactions

Copper‐catalyzed Ullmann condensations are key reactions for the formation of carbon–heteroatom and carbon–carbon bonds in organic synthesis. These reactions can lead to structural moieties that are prevalent in building blocks of active molecules in the life sciences and in many material precursors. An increasing number of publications have appeared concerning Ullmann‐type intermolecular reactions for the coupling of aryl and vinyl halides with N, O, and C nucleophiles, and this Minireview highlights recent and major developments in this topic since 2004.     

Cyano‐Bridged MnIII?MIII Single‐Chain Magnets with MIII=CoIII,FeIII, MnIII,and CrIII

A series of isostructural cyano‐bridged Mn^III(h.s.)–M^III(l.s.) alternating chains, [Mn^III(5‐TMAMsalen)M^III(CN)₆] ? 4H₂O (5‐TMAMsalen^2?=N,N′‐ethylenebis(5‐trimethylammoniomethylsalicylideneiminate), Mn^III(h.s.)=high‐spin Mn^III, M^III(l.s.)=low‐spin Co^III, Mn? Co ; Fe^III, Mn? Fe ; Mn^III, Mn? Mn ; Cr^III, Mn? Cr ) was synthesized by assembling [Mn^III(5‐TMAMsalen)]³⁺ and [M^III(CN)₆]^3?. The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [‐Mn^III‐NC‐M^III‐CN‐] repeating motif, for which the ‐NC‐M^III‐CN‐ motif is provided by the [M^III(CN)₆]^3? moiety adopting a trans bridging mode between [Mn^III(5‐TMAMsalen)]³⁺ cations. The Mn^III and M^III ions occupy special crystallographic positions: a C₂ axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn–Teller axis of the Mn^III(h.s.) ion is perpendicular to the N₂O₂ plane formed by the 5‐TMAMsalen tetradentate ligand. These Jahn–Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn‐N_axis‐C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter‐chain M???M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5‐TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn? Fe and Mn? Mn display intra‐chain ferromagnetic interactions, whereas Mn? Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single‐chain magnet (SCM) behavior of these three systems, whereas Mn? Co is merely paramagnetic with S_Mn=2 and D/k_B=?5.3 K (D being a zero‐field splitting parameter). At low temperatures, the Mn? M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite‐chain and finite‐chain regimes for the SCM behavior. These isostructural hetero‐spin SCMs offer a unique series of alternating [‐Mn‐NC‐M‐CN‐] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits.     

Synthesis and Structure of Amido‐ and Imido(pentafluorophenyl)borane Zirconocene and Hafnocene Complexes: N?H and B?H Activation

Treatment of Me₂S ? B(C₆F₅)_nH_3?n (n=1 or 2) with ammonia yields the corresponding adducts. H₃N ? B(C₆F₅)H₂ dimerises in the solid state through N? H???H? B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH₂B(C₆F₅)_nH_3?n]. Reaction of the n=2 reagent with [Cp₂ZrCl₂] leads to disubstitution, but [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] is in equilibrium with the product of β‐hydride elimination [Cp₂Zr(H){NH₂B(C₆F₅)₂H}], which proves to be the major isolated solid. The analogous reaction with [Cp₂HfCl₂] gives a mixture of [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] and the N? H activation product [Cp₂Hf{NHB(C₆F₅)₂H}]. [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] ? PhMe and [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? 4(thf) exhibit β‐B‐agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp₂Hf{NHB(C₆F₅)₂H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond‐length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp₂MMe(μ‐Me)B(C₆F₅)₃] (M=Zr, Hf) with Li[NH₂B(C₆F₅)_nH_3?n] (n=2) results in [Cp₂MMe{NH₂B(C₆F₅)₂H}] complexes, for which the spectroscopic data, particularly ¹J(B,H), again suggest β‐B‐agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp′′₂ZrMe(μ‐Me)B(C₆F₅)₃] precursor (Cp′′=1,3‐C₅H₃(SiMe₃)₂, n=1 or 2) to give [Cp′′₂ZrMe{NH₂B(C₆F₅)_nH_3?n}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp′′₂HfMe₂] and the formation of Li[HB(C₆F₅)₃] through hydride abstraction.     

Cp*CoIII Catalyzed Site‐Selective C?H Activation of Unsymmetrical O‐Acyl Oximes: Synthesis of Multisubstituted Isoquinolines from Terminal and Internal Alkynes

The synthesis of isoquinolines by site‐selective C H activation of O‐acyl oximes with a Cp*Co^III catalyst is described. In the presence of this catalyst, the C H activation of various unsymmetrically substituted O‐acyl oximes selectively occurred at the sterically less hindered site, and reactions with terminal as well as internal alkynes afforded the corresponding products in up to 98 % yield. Whereas the reactions catalyzed by the Cp*Co^III system proceeded with high site selectivity (15:1 to 20:1), use of the corresponding Cp*Rh^III catalysts led to low selectivities and/or yields when unsymmetrical O‐acyl oximes and terminal alkynes were used. Deuterium labeling studies indicate a clear difference in the site selectivity of the C H activation step under Cp*Co^III and Cp*Rh^III catalysis.     

Comparative Catalytic Activity of Group 9 [Cp*MIII] Complexes: Cobalt‐Catalyzed C?H Amidation of Arenes with Dioxazolones as Amidating Reagents

A procedure for the [Cp*Co^III]‐catalyzed direct C H amidation of arenes with dioxazolone has been developed. This reaction proceeds under straightforward and mild conditions with a broad range of substrates, including anilides. A comparative study on the catalytic activity of Group 9 [{Cp*MCl₂}₂] complexes revealed the unique efficiency of the cobalt catalyst.     

Protonation of 2H‐Azaphosphirene Complexes: P?N Bond Activation and Ring‐Expansion Reactions

P? N bond activation of 2H‐azaphosphirene complexes 1 and 2 by using triflic acid led to ring expansion in the presence of nitriles. In the absence of nitriles, the reaction surprisingly afforded two haptomeric N‐protonated 1‐aza‐3‐phospha‐butadiene complexes in the case of complex 1 , whereas the N‐protonated 2H‐azaphosphirene complex [H‐ 2 ]⁺ was characterized by NMR spectroscopy.