Synthesis, Characterization, and Reactivity of Group 4 Metalloporphyrin Diolate Complexes

A number of group 4 metalloporphyrin diolate complexes were synthesized via various approaches. For example, treatment of imido complex (TTP)HfNAriPr with diols resulted in formation of the corresponding diolato complexes (TTP)Hf[OCR1R2CR1R2O] (R1 = R2 = Me, 1; R1 = Me, R2 = Ph, 2; R1 = R2 = Ph, 3). Treatment of (TTP)TiNiPr with diols generated (TTP)Ti[OCR1R2CR1R2O] (R1 = R2 = Me, 5; R1 = Me, R2 = Ph, 6; R1 = H, R2 = Ph, 7; R1 = H, R2= p-tolyl, 8). Alternatively hafnium and titanium pinacolates 1 and 5 were prepared through metathetical reactions of (TTP)MCl2 (M = Hf, Ti) with disodium pinacolate. The substitution chemistry of hafnium complexes correlated well with the basicity of the diolato ligands. Complexes 1−6 underwent oxidative cleavage reaction, producing carbonyl compounds and oxometalloporphyrin species. For less substituted diolates 7 and 8, an array of products including the enediolate complexes (TTP)Ti[OC(Ar)C(Ar)O] (Ar = Ph, 9; Ar = p-tolyl, 10) was observed. The possible cleavage reaction pathways are discussed

Group 4 Metalloporphyrin diolato Complexes and Catalytic Application of Metalloporphyrins and Related Transition Metal Complexes

In this work, the first examples of group 4 metalloporphyrin 1,2-diolato complexes were synthesized through a number of strategies. In general, treatment of imido metalloporphyrin complexes, (TTP)M=NR, (M = Ti, Zr, Hf), with vicinal diols led to the formation of a series of diolato complexes. Alternatively, the chelating pinacolate complexes could be prepared by metathesis of (TTP)MCl{sub 2} (M = Ti, Hf) with disodium pinacolate. These complexes were found to undergo C-C cleavage reactions to produce organic carbonyl compounds. For titanium porphyrins, treatment of a titanium(II) alkyne adduct, (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh), with aromatic aldehydes or aryl ketones resulted in reductive coupling of the carbonyl groups to produce the corresponding diolato complexes. Aliphatic aldehydes or ketones were not reactive towards (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh). However, these carbonyl compounds could be incorporated into a diolato complex on reaction with a reactive precursor, (TTP)Ti[O(Ph){sub 2}C(Ph){sub 2}O] to provide unsymmetrical diolato complexes via cross coupling reactions. In addition, an enediolato complex (TTP)Ti(OCPhCPhO) was obtained from the reaction of (TTP)Ti({eta}{sup 2}-PhC{triple_bond}CPh) with benzoin. Titanium porphyrin diolato complexes were found to be intermediates in the (TTP)Ti=O-catalyzed cleavage reactions of vicinal diols, in which atmospheric oxygen was the oxidant. Furthermore, (TTP)Ti=O was capable of catalyzing the oxidation of benzyl alcohol and {alpha}-hydroxy ketones to benzaldehyde and {alpha}-diketones, respectively. Other high valent metalloporphyrin complexes also can catalyze the oxidative diol cleavage and the benzyl alcohol oxidation reactions with dioxygen. A comparison of Ti(IV) and Sn(IV) porphyrin chemistry was undertaken. While chelated diolato complexes were invariably obtained for titanium porphyrins on treatment with 1,2-diols, the reaction of vicinal diols with tin porphyrins gave a number of products, including mono-, bis-alkoxo, and chelating diolato complexes, depending on the identity of diols and the stoichiometry employed. It was also found that tin porphyrin complexes promoted the oxidative cleavage of vicinal diols and the oxidation of {alpha}-ketols to {alpha}-diketones with dioxygen. In extending the chemistry of metalloporphyrins and analogous complexes, a series of chiral tetraaza macrocyclic ligands and metal complexes were designed and synthesized. Examination of iron(II) complexes showed that they were efficient catalysts for the cyclopropanation of styrene by diazo reagents. Good yields and high diastereoselectivity were obtained with modest enantioselectivity. A rationalization of the stereoselectivity was presented on the basis of structural factors in a carbene intermediate

Synthesis and Characterization of Chiral Tetraaza Macrocyclic Nickel(II) and Palladium(II) Complexes

Chiral tetraaza macrocyclic nickel(II) and palladium(II) complexes 2a−e, containing one or two (R,R)-(−)-1,2-cyclohexanediyl bridges, were synthesized by template condensation reactions and characterized by 1H and 13C NMR, IR, UV−vis, and mass spectrometry. The electrophilic reactivity of 2a was explored. Crystal structures of Ni complex 2b and metal-free ligand 5were determined by single-crystal X-ray diffraction

Language-Routing Mixture of Experts for Multilingual and Code-Switching Speech Recognition

Multilingual speech recognition for both monolingual and code-switching speech is a challenging task. Recently, based on the Mixture of Experts (MoE), many works have made good progress in multilingual and code-switching ASR, but present huge computational complexity with the increase of supported languages. In this work, we propose a computation-efficient network named Language-Routing Mixture of Experts (LR-MoE) for multilingual and code-switching ASR. LR-MoE extracts language-specific representations through the Mixture of Language Experts (MLE), which is guided to learn by a frame-wise language routing mechanism. The weight-shared frame-level language identification (LID) network is jointly trained as the shared pre-router of each MoE layer. Experiments show that the proposed method significantly improves multilingual and code-switching speech recognition performances over baseline with comparable computational efficiency.Comment: To appear in Proc. INTERSPEECH 2023, August 20-24, 2023, Dublin, Irelan

Abrasion Behavior of High Manganese Steel under Low Impact Energy and Corrosive Conditions

The abrasion behavior of high manganese steel is investigated under three levels of impact energy in acid-ironstone slurry. The wear test was carried out by an MLDF-10 tester with impact energy of 0.7 J, 1.2 J, and 1.7 J. The impact abrasion property of high manganese steel in corrosive condition was compared according to the wear mass loss curves. The wear mechanism was analysed by the SEM analysis of the worn surface and the optical metallographic analysis of the vertical section to the wear surface. The results show that the impact energy has a great effect on the impact corrosion and abrasion properties of it. Its abrasion mechanism in corrosive condition is mainly microplough and breakage of plastic deformed ridges and wedges under the impact energy of 0.7 J. It is mainly the spelling of plastic deformed ridges and wedges under 1.2 J and the spalling of the work-hardening layer under 1.7 J after a long time testing

Iron Porphyrin Catalyzed N−H Insertion Reactions with Ethyl Diazoacetate

A series of metalloporphyrin complexes were surveyed as catalysts for carbene insertion from ethyl diazoacetate into the N−H bonds of amines. Iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, was found to be an efficient catalyst for N−H insertion reactions with a variety of aliphatic and aromatic amines, with yields ranging from 68 to 97%. Primary amines were able to undergo a second insertion when another equiv of EDA was added by slow addition. N-Heterocyclic compounds were poor substrates, giving low yields or no N−H insertion products. Competition reactions and linear free energy relationships provided mechanistic insights for the insertion reaction. The relative rates for N−H insertion into para-substituted aniline derivatives correlated with Hammett σ+ parameters. Electron-donating groups enhanced the reaction, as indicated by the negative value of ρ (ρ = −0.66 ± 0.05, R2 = 0.93). These results are consistent with a rate-determining nucleophilic attack of the amine on an iron carbene complex. In addition, the decomposition of EDA catalyzed by FeII(TPP) or FeIII(TPP)Cl was examined with various amounts of added pyridine. The Fe(II) catalyst is strongly inhibited by the presence of pyridine. In contrast, catalysis by the Fe(III) porphyrin is accelerated by amines. These experiments suggested that an iron(III) porphyrin carbene complex is the active catalyst

NCL++: Nested Collaborative Learning for Long-Tailed Visual Recognition

Long-tailed visual recognition has received increasing attention in recent years. Due to the extremely imbalanced data distribution in long-tailed learning, the learning process shows great uncertainties. For example, the predictions of different experts on the same image vary remarkably despite the same training settings. To alleviate the uncertainty, we propose a Nested Collaborative Learning (NCL++) which tackles the long-tailed learning problem by a collaborative learning. To be specific, the collaborative learning consists of two folds, namely inter-expert collaborative learning (InterCL) and intra-expert collaborative learning (IntraCL). In-terCL learns multiple experts collaboratively and concurrently, aiming to transfer the knowledge among different experts. IntraCL is similar to InterCL, but it aims to conduct the collaborative learning on multiple augmented copies of the same image within the single expert. To achieve the collaborative learning in long-tailed learning, the balanced online distillation is proposed to force the consistent predictions among different experts and augmented copies, which reduces the learning uncertainties. Moreover, in order to improve the meticulous distinguishing ability on the confusing categories, we further propose a Hard Category Mining (HCM), which selects the negative categories with high predicted scores as the hard categories. Then, the collaborative learning is formulated in a nested way, in which the learning is conducted on not just all categories from a full perspective but some hard categories from a partial perspective. Extensive experiments manifest the superiority of our method with outperforming the state-of-the-art whether with using a single model or an ensemble. The code will be publicly released.Comment: arXiv admin note: text overlap with arXiv:2203.1535

Asymmetric Cyclopropanation of Styrene Catalyzed by Chiral Macrocyclic Iron(II) Complexes

Three chiral tetraaza macrocyclic ligands (4a−c) were synthesized by the cyclization reaction of diamines with dithioaldehydes. The iron(II) complexes of ligands 4a and 4c, as well as two chiral iron(II) porphyrin complexes, FeII(D4-TpAP) and Fe(α2β2-BNP), are efficient catalysts for the cyclopropanation of styrene with diazoacetate reagents. The cyclopropyl esters were produced with high diastereoselectivities and good yields. However, the enantioselectivities were modest at best. The rationalization of the stereoselectivity in these cyclopropanation reactions is presented. The results of a single-crystal X-ray analysis of the ligand 4a are also reported