Catalytic Nitrogen Fixation Using Well-Defined Molecular Catalysts under Ambient or Mild Reaction Conditions.

Ammonia (NH3) is industrially produced from dinitrogen (N2) and dihydrogen (H2) by the Haber-Bosch process, although H2 is prepared from fossil fuels, and the reaction requires harsh conditions. On the other hand, microorganisms have fixed nitrogen under ambient reaction conditions. Recently, well-defined molecular transition metal complexes have been found to work as catalyst to convert N2 into NH3 by reactions with chemical reductants and proton sources under ambient reaction conditions. Among them, involvement of both N2-splitting pathway and proton-coupled electron transfer is found to be very effective for high catalytic activity. Furthermore, direct electrocatalytic and photocatalytic conversions of N2 into NH3 have been recently achieved. In addition to catalytic formation of NH3, selective catalytic conversion of N2 into hydrazine (NH2NH2) and catalytic silylation of N2 into silylamines have been reported. Catalytic C-N bond formation has been more recently established to afford cyanate anion (NCO-) under ambient reaction conditions. Further development of direct conversion of N2 into nitrogen-containing compounds as well as green ammonia synthesis leading to the use of ammonia as an energy carrier is expected.

Photoredox- and Nickel-Catalyzed Hydroalkylation of Alkynes with 4-Alkyl-1,4-dihydropyridines: Ligand-Controlled Regioselectivity.

Dual photoredox- and nickel-catalyzed hydroalkylation of terminal alkynes with 4-alkyl-1,4-dihydropyridines under visible light irradiation to afford Markovnikov- or anti-Markovnikov-type alkylated alkenes in good-to-high yields has been achieved, in which the regioselectivity of the products was effectively controlled by coordination ligands for nickel species. Using [NiCl2 (dtbbpy)] as a catalyst led to the formation of Markovnikov-type products, whereas using NiCl2 ⋅ 6 H2 O led to the formation of anti-Markovnikov-type products.

Comprehensive insights into synthetic nitrogen fixation assisted by molecular catalysts under ambient or mild conditions.

N2 is fixed as NH3 industrially by the Haber-Bosch process under harsh conditions, whereas biological nitrogen fixation is achieved under ambient conditions, which has prompted development of alternative methods to fix N2 catalyzed by transition metal molecular complexes. Since the early 21st century, catalytic conversion of N2 into NH3 under ambient conditions has been achieved by using molecular catalysts, and now H2O has been utilized as a proton source with turnover frequencies reaching the values found for biological nitrogen fixation. In this review, recent advances in the development of molecular catalysts for synthetic N2 fixation under ambient or mild conditions are summarized, and potential directions for future research are also discussed.

Ruthenium- and Copper-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohol Derivatives with Hydrazones.

Ruthenium- and copper-catalyzed propargylic substitution reactions of propargylic alcohol derivatives with N-monosubstituted hydrazones as ambident nucleophiles are achieved in which N-monosubstituted hydrazones exhibit impressive different reactivities depending on different catalytic systems, behaving as carbon-centered nucleophiles to give the corresponding propargylic alkylated products in ruthenium catalysis, or as nitrogen-centered nucleophiles to afford the corresponding propargylic aminated products in copper catalysis. DFT calculations were carried out to investigate the detailed reaction pathways of these two systems. Further transformation of propargylic substituted products affords the corresponding multisubstituted pyrazoles as cyclization products in good to high yields.

Ruthenium- and Copper-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohol Derivatives with Hydrazones.

Invited for the cover of this issue are Ken Sakata, Yoshiaki Nishibayashi, and co-workers at The University of Tokyo and Toho University. The image depicts the propargylic substitution reaction of a propargylic alcohol with an N-monosubstituted hydrazone, where the nucleophilicity of the hydrazone is controlled by the choice of catalytic system. Read the full text of the article at 10.1002/chem.202103287.

Cooperative Photoredox- and Nickel-Catalyzed Alkylative Cyclization Reactions of Alkynes with 4-Alkyl-1,4-dihydropyridines.

Cooperative photoredox- and nickel-catalyzed alkylative cyclization reactions of iodoalkynes with 4-alkyl-1,4-dihydropyridines as alkylation reagents under visible light irradiation have been achieved to afford the corresponding alkylated cyclopentylidenes in good to high yields. Introduction of substituents at the propargylic position of iodoalkynes has led to the stereoselective formation of E-isomers. The present reaction system provides a novel synthetic method for alkylative cyclization reactions of both terminal and internal alkynes with cooperative photoredox and nickel catalysis.

Ruthenium-Catalyzed Enantioselective Propargylic Phosphinylation of Propargylic Alcohols with Phosphine Oxides.

The development of transition metal-catalyzed enantioselective propargylic substitution reactions has gained much progress in recent years, however, no successful example with phosphorus-centered nucleophiles has yet been reported until now. Herein, we report the first successful example of ruthenium-catalyzed enantioselective propargylic substitution reactions of propargylic alcohols with diarylphosphine oxides as phosphorus-centered nucleophiles. This synthetic approach provides a new method to prepare chiral phosphorus-containing organic compounds.

Phosphine Oxidation with Water and Ferrocenium(III) Cation Induced by Visible-Light Irradiation.

Stoichiometric oxidation of phosphines with water and ferrocenium(III) cation as the oxygen atom source and the oxidizing reagent, respectively, was achieved in acetonitrile under visible-light irradiation by using 2,6-lutidine as the proton acceptor. The reaction required light irradiation, under which fluorescence was observed for the acetonitrile solution of the ferrocenium(III) cation.

Production of cloned mice using oocytes derived from ICR-outbred strain.

Recently, it has become possible to generate cloned mice using a somatic cell nucleus derived from not only F1 strains but also inbred strains. However, to date, all cloned mice have been generated using F1 mouse oocytes as the recipient cytoplasm. Here, we attempted to generate cloned mice from oocytes derived from the ICR-outbred mouse strain. Cumulus cell nuclei derived from BDF1 and ICR mouse strains were injected into enucleated oocytes of both strains to create four groups. Subsequently, the quality and developmental potential of the cloned embryos were examined. ICR oocytes were more susceptible to damage associated with nuclear injection than BDF1 oocytes, but their activation rate and several epigenetic markers of reconstructed cloned oocytes/embryos were similar to those of BDF1 oocytes. When cloned embryos were cultured for up to 4 days, those derived from ICR oocytes demonstrated a significantly decreased rate of development to the blastocyst stage, irrespective of the nuclear donor mouse strain. However, when cloned embryos derived from ICR oocytes were transferred to female recipients at the two-cell stage, healthy cloned offspring were obtained at a success rate similar to that using BDF1 oocytes. The ICR mouse strain is very popular for biological research and less expensive to establish than most other strains. Thus, the results of this study should promote the study of nuclear reprogramming not only by reducing the cost of experiments but also by allowing us to study the effect of oocyte cytoplasm by comparing it between strains.

Catalytic Dinitrogen Fixation to Form Ammonia at Ambient Reaction Conditions Using Transition Metal-Dinitrogen Complexes.

This paper presents recent progress in catalytic transformation of molecular dinitrogen into ammonia or its equivalents, such as silylamine, especially using transition metal-dinitrogen complexes under ambient reaction conditions. Several catalytic systems have been recently established using molybdenum-, iron-, and cobalt-dinitrogen complexes or their precursors as catalysts, providing new approaches to the development of novel nitrogen fixation under ambient reaction conditions.

Cleavage and formation of molecular dinitrogen in a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine.

The N≡N bond of molecular dinitrogen bridging two molybdenum atoms in the pentamethylcyclopentadienyl molybdenum complexes that bear ferrocenyldiphosphine as an auxiliary ligand is homolytically cleaved under visible light irradiation at room temperature to afford two molar molybdenum nitride complexes. Conversely, the bridging molecular dinitrogen is reformed by the oxidation of the molybdenum nitride complex at room temperature. This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli using a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine under ambient conditions.

Design and preparation of molybdenum-dinitrogen complexes with ferrocenyldiphosphine and pentamethylcyclopentadienyl moieties as auxiliary ligands.

Fix me! Molybdenum-dinitrogen complexes containing ferrocenyldiphosphine and pentamethylcyclopentadienyl moieties as auxiliary ligands have been designed, prepared, and characterized. The ferrocenyldiphosphine works as a unique ligand to inhibit dissociation of dinitrogen, as well as to make the coordinated molecular dinitrogen reactive toward electrophiles.

Interplay of diruthenium catalyst in controlling enantioselective propargylic substitution reactions with visible light-generated alkyl radicals.

Transition metal-catalyzed enantioselective free radical substitution reactions have recently attracted attention as convenient and important building tools in synthetic chemistry, although construction of stereogenic carbon centers at the propargylic position of propargylic alcohols by reactions with free radicals remains unchallenged. Here we present a strategy to control enantioselective propargylic substitution reactions with alkyl radicals under photoredox conditions by applying dual photoredox and diruthenium catalytic system, where the photoredox catalyst generates alkyl radicals from 4-alkyl-1,4-dihydropyridines, and the diruthenium core with a chiral ligand traps propargylic alcohols and alkyl radicals to guide enantioselective alkylation at the propargylic position, leading to high yields of propargylic alkylated products containing a quaternary stereogenic carbon center at the propargylic position with a high enantioselectivity. The result described in this paper provides the successful example of transition metal-catalyzed enantioselective propargylic substitution reactions with free alkyl radicals.

Emergency laparoscopic sigmoid colectomy with primary anastomosis for Hinchey stages III and IV diverticulitis.

For patients with perforated diverticulitis, many reports have focused on laparoscopic surgery without primary anastomosis. We performed laparoscopic surgery with primary anastomosis in three patients (two with Hinchey stage III, one with IV), with a median age of 53 years, all female, and no prior medical history. They all were hemodynamically stable. The median operation time was 91 minutes (range: 56-227 minutes) and the median blood loss was 50 mL (range: 0-200 mL). Their post-operative course was uneventful, and patients commenced oral intake at a median of 5 post-operative days and were discharged at a median of 12 post-operative days. This procedure may be an option for Hinchey stages III and IV diverticulitis.

Mouse Cloning Using Outbred Oocyte Donors and Nontoxic Reagents.

Somatic cell nuclear transfer (SCNT) technology has become a useful tool for animal cloning, gene manipulation, and genomic reprogramming research. However, the standard mouse SCNT protocol remains expensive, labor-intensive, and requires hard work for many hours. Therefore, we have been trying to reduce the cost and simplify the mouse SCNT protocol. This chapter describes the methods to use low-cost mouse strains and steps from the mouse cloning procedure. Although this modified SCNT protocol will not improve the success rate of mouse cloning, it is a cheaper, simpler, and less tiring method that allows us to perform more experiments and obtain more offspring with the same working time as the standard SCNT protocol.

Copper-catalyzed enantioselective propargylic amination of propargylic esters with amines: copper-allenylidene complexes as key intermediates.

The scope and limitations of the copper-catalyzed propargylic amination of various propargylic esters with amines are presented, where optically active diphosphines such as Cl-MeO-BIPHEP and BINAP work as good chiral ligands. A variety of secondary amines are available as nucleophiles for this catalytic reaction to give the corresponding propargylic amines with a high enantioselectivity. The results of some stoichiometric and catalytic reactions indicate that the catalytic amination proceeds via copper-allenylidene complexes formed in situ, where the attack of amines to the electrophilic gamma-carbon atom in the allenylidene complex is an important step for the stereoselection. Investigation of the relative rate constants for the reaction of several para-substituted propargylic acetates with N-methylanilines reveals that the formation of the copper-allenylidene complexes is involved in the rate-determining step. The result of the density functional theory calculation on a model reaction also supports the proposed reaction pathway involving copper-allenylidene complexes as key intermediates. The catalytic procedure presented here provides a versatile and direct method for the preparation of a variety of chiral propargylic amines.

Preparation and reactivity of molybdenum complexes bearing pyrrole-based PNP-type pincer ligand.

Molybdenum complexes bearing an anionic pyrrole-based PNP-type pincer ligand have been prepared and have been found to work as catalysts for the conversion of N2 into NH3 under ambient conditions.

Core expansion reactions of cyanamido/carbodiimido-bridged polynuclear iridium complexes.

Core expansion reactions of di- and tetrairidium complexes [Cp*Ir(mu(2)-NCN-N,N)](2) (1; Cp* = eta(5)-C(5)Me(5)), [Cp*Ir(mu(3)-NCN-N,N,N)](4) (2), and phosphine derivatives of 1 have been investigated, and it has been revealed that cyanamido ligands in these complexes can change their coordination modes flexibly on reactions with a second transition metal complex. Treatment of diiridium complex 1 with [Cp*IrCl(2)](2) gives the tetrairidium complex [(Cp*Ir)(2)(mu(3)-NCN-N,N,N')(2)(IrCp*Cl(2))(2)] (6) with mu(3)-kappaN,kappaN,kappaN' cyanoimido(2-) ligands. On the other hand, the reaction of 1 with [PdCl(eta(3)-C(3)H(5))](2) affords the NCN-bridged Ir(2)Pd(4) hexanuclear complex [(Cp*IrCl)(2)(mu(4)-NCN-N,N,N',N')(2){Pd(2)(mu-Cl)(eta(3)-C(3)H(5))(2)}(2)] (7) and Ir(4)Pd(4) octanuclear complex [(Cp*Ir)(4)(mu(4)-NCN-N,N,N,N')(4){PdCl(eta(3)-C(3)H(5))}(4)] (8). The NCN-bridges in 7 provide the first example of the crystallographically determined mu(4)-kappaN,kappaN,kappaN',kappaN' carbodiimido(2-) ligand. Complex 8 with mu(4)-kappaN,kappaN,kappaN,kappaN' cyanoimido(2-) ligands can also be synthesized selectively by the reaction of the parent cubane complex 2 with [PdCl(eta(3)-C(3)H(5))](2). Diphosphine derivative of 1, [{Cp*Ir(mu(2)-NCN)}(2)(mu-dppm)] (4; dppm = Ph(2)PCH(2)PPh(2)), behaves differently on reactions with [PdCl(eta(3)-C(3)H(5))](2) and [MCl(cod)](2) (cod = cycloocta-1,5-diene) to form the NCN-bridged Ir(2)M(2) (M = Pd, Rh, Ir) tetranuclear complexes [(Cp*Ir)(2)(mu(3)-NCN-N,N,N')(2){PdCl(eta(3)-C(3)H(5))}(2)(mu-dppm)] (9) and [(Cp*Ir)(2)(mu(3)-NCN-N,N,N')(2){MCl(cod)}(2)(mu-dppm)] (11a, M = Rh; 11b, M = Ir), respectively. The molecular structures for 6, 7, 8, 11a, and 11b have been determined by single-crystal X-ray analyses.

Formation of vinylidenes from internal alkynes at a cyclotriphosphato ruthenium complex.

A ruthenium cyclotriphosphato (P(3)O(9)(3-)) complex with a labile MeOH ligand can affect the vinylidene rearrangement of general internal alkynes via the 1,2-migration of alkyl, aryl, and acyl groups. This provides the first internal alkyne-to-vinylidene isomerization with high generality. Several intermediary eta(2)-alkyne complexes could be isolated and were successfully transformed into the corresponding vinylidene complexes. The reaction mechanism is also discussed on the basis of a kinetic study and migratory aptitude of alkyl, aryl, and acyl groups; the present reaction proceeds via an intramolecular process and is viewed as an uncommon electrophilic rearrangement.

Syntheses and phosphorescent properties of blue emissive iridium complexes with tridentate pyrazolyl ligands.

Novel neutral mixed-ligand Ir(N=C=N)(N=C)X complexes (N=C=N = 1,3-bis(3-methylpyrazolyl)benzene (bpzb), 1,5-dimethyl-2,4-bis(3-methylpyrazolyl)benzene (dmbpzb), and 1,5-difluoro-2,4-bis(3-methylpyrazolyl)benzene (dfbpzb); N=C = 2-phenyl pyridine (ppy); and X = Cl or CN) have been synthesized and characterized. An X-ray single-crystal structure of the complex Ir(dmbpzb)(ppy)Cl shows that the nitrogen atom in the ppy ligand occupied the trans position to the carbon atom in the tridentate N=C=N ligand of dmbpzb with the Ir-C bond length of 1.94(1) A, whereas the coordinating carbon atom occupied the trans position of chlorine. Electrochemical data show that the complexes exhibit an oxidation Ir(III/IV) process in the potential range of +0.5 approximately 0.9 V and two irreversible reductions at approximately -2.6 and -3.0 V against Fc (0)/Fc (+), respectively. All of the Ir(III) complexes do not emit phosphorescence at room temperature, although strong phosphorescence is exhibited at 77 K with the 0-0 transition centered at around 450 nm and lifetimes of 3-14 mus. DFT calculations indicate that the HOMOs are mainly localized on iridium 5dpi and chlorine ppi*, whereas the LUMOs are mainly from the ppy ligand pi* orbitals. The phosphorescence originates from a (3)LC state mixed with the (3)MLCT and (3)XLCT ones. Temperature-dependent lifetime measurements of Ir(dfbpzb)(ppy)Cl reveal the existence of a thermal deactivation process with a low activation energy (1720 cm (-1)) and very high frequency factor (2.3 x 10 (13) s (-1)). An unrestricted density functional theory indicates that the dd state, in which both the Ir-N (pyrazolyl) bond lengths increase considerably, exists almost at the same energy as that for the phosphorescent state. A thorough analysis based on the potential energy surfaces for the T 1 and S 0 states allows us to determine the reaction pathway responsible for this thermal deactivation. The calculated activation energies of 1600 approximately 1800 cm (-1) are in excellent agreement with the observed values.