Breaking Conventional Site Selectivity in C-H Bond Activation: Selective sp3 versus sp2 Silylation by a Pincer-Based Pocket.

A deeply ingrained assumption in the conventional understanding and practice of organometallic chemistry is that an unactivated aliphatic C(sp3)-H bond is less reactive than an aromatic C(sp2)-H bond within the same molecule given that they are at positions unbiasedly accessible for activation. Herein, we demonstrate that a pincer-ligated iridium complex catalyzes intramolecular dehydrogenative silylation of the unactivated δ-C(sp3)-H (δ to the Si atom) with exclusive site selectivity over typically more reactive ortho δ-C(sp2)-H bonds. A variety of tertiary hydrosilanes undergo δ-C(sp3)-H silylation to form 5-membered silolanes, including chiral silolanes, which can undergo further oxidation to produce enantiopure ß-aryl-substituted 1,4-diols. Combined computational and experimental studies reveal that the silylation occurs via the Si-H addition to a 14-electron Ir(I) fragment to give an Ir(III) silyl hydride complex, which then activates the C(sp3)-H bond to form a 7-coordinate, 18-electron Ir(V) dihydride silyl intermediate, followed by sequential reductive elimination of H2 and silolane. The unprecedented site selectivity is governed by the distortion energy difference between the rate-determining δ-C(sp3)-H and δ-C(sp2)-H activation, although the activation at sp2 sites is much more favorable than sp3 sites by the interaction energy.

Isolation and X-ray Crystal Structure of an Electrogenerated TEMPO-N3 Charge-Transfer Complex.

Advances in radical-based catalytic reactions have created a demand for understanding their mechanistic underpinnings. Here, we present the isolation, structural elucidation, and theoretical analysis of a catalytically relevant charge-transfer species formed between the azidyl radical and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). The unusual bond angles and pancake bonding between these two fragments highlight the weak bonding interactions present in this complex. This X-ray structure validates computational predictions as well as mechanistic proposals of TEMPO-mediated radical azidation reactions.

[Jingjin needling improves facial nerve function and psychosomatic function in Hunt facial para-lysis patients].

OBJECTIVE: To observe the clinical effectiveness of Jingjin (muscle region) needling in the treatment of Hunt facial paralysis (HFP). METHODS: A total of 80 HFP patients were randomly divided into acupuncture and medication groups (n＝40 cases/group). Jingjin needling was applied to Yangbai(GB14) to Shangxing (GV23), Touwei (ST8), Cuanzhu (BL2), Sizhukong (TE23，penetrative needling), Dicang (ST4) to Jiache (ST6, penetrative needling), Yingxiang(LI20) and Xiaguan(ST7), Hegu(LI4), Yifeng (TE17), Yuyao (EX-HN 4), and Shenmai (BL62), with the needles retained for 30 min. The treatment was conducted once daily, with 10 consecutive days being a therapeutic course, and 3 courses altogether. Patients of the medication group received oral administration of Prednisone acetate (12 days), Acyclovir (7 days), intramuscular injection of Vitamin B12 and Vitamin B1(10 days), then, oral administration of Vitamin B1, successively. The therapeutic effect was assessed by using House-Brackman (H-B) facial function grading system (grade I to VI), traditional Chinese medicine (TCM) sign and symptom score, and facial disability index (FDI) scale including FDI physical function (FDIP, food and water swallowing, speaking-pronouncing, dryness or tearing, and mouth-opening) and FDI social function (FDIS, self-rating anxiety/depression scales), separately. RESULTS: After the treatment, the TCM symptom and sign scores for depth of nasolabial groove, nose shrugging, lower lip asymmetry, food retention and post-auricular pain were significantly lower in the medication group (P<0.05)．After the treatment, the TCM symptom and sign scores for frontal muscle movement, eyelid opening and closing, depth of nasolabial groove, nose shrugging, lower lip asymmetry, cheek blowing, food retention, latissimus cervicalis contraction, taste disorder, hearing hypersensitivity, tears and discomfort and post-auricular pain were significantly lower in the acupuncture group (P<0.05)．Comparison between two groups showed that the TCM symptom and sign scores for frontal muscle movement, eyelid opening and closing, depth of nasolabial groove, nose shrugging, lower lip asymmetry, cheek blowing, food retention, latissimus cervicalis contraction, taste disorder, hearing hypersensitivity, tears and discomfort and post-auricular pain were significantly lower in the acupuncture group than in the medication group(P<0.05)．The scores of FDIP and FDIS were significantly increased in both groups (P<0.01) and notably higher in the acupuncture group than in the medication group (P<0.01) after the treatment. The total effective rate of acupuncture group was 97.5% (39/40), and that of medication group was 72.5% (29/40). The therapeutic effect of the acupuncture group was significantly superior to that of the medication group (P<0.01)．. CONCLUSION: Jingjin needling has a good therapeutic effect in improving facial nerve function, psychosomatic function and clinical signs and symptoms in HFP patients, evidently being better than medication.

A Missing Piece of the Mechanism in Metal-Catalyzed Hydrogenation: Co(-I)/Co(0)/Co(+I) Catalytic Cycle for Co(-I)-Catalyzed Hydrogenation.

Hydrogenation catalyzed by unusually low-valent Co(-I) and Fe(-I) catalysts were recently reported. In contrast to the classical M(I)/M(III) (M = Rh or Ir) or Ir(III)/Ir(V) catalytic cycles in the singlet state (adiabatic reactions) for Rh- or Ir-catalyzed hydrogenation, our systematic DFT study elucidates a new Co(-I)/Co(0)/Co(+I) catalytic cycle involving both singlet and triplet states (nonadiabatic reaction). Also, the more electron-rich cobalt center of the Co(-I) catalyst was found to contribute higher reactivity for alkene hydrogenation.

C-O/C-H Coupling of Polyfluoroarenes with Aryl Carbamates by Cooperative Ni/Cu Catalysis.

Cross-coupling of polyfluoroarenes with aryl carbamates through the cleavage of both sp(2) C-O and C-H bonds is reported. The reaction conditions are simple, and only transition-metal catalysts and ligands are essential. Mechanistic studies indicated that Ni catalyst played an important role in activating C-O bond, while the Cu one in activating C-H Bond. The developed system proved to be effective for cross-coupling of terminal alkynes with aryl carbamates.