Solvent-Induced Umpolung Reaction from Dioxygenation to C-S Coupling in Bis(2-phenylquinoline) Iridium(III) Thiolate Complexes.

The construction of C-S bonds is of great importance in the field of synthetic and medicinal chemistry. Herein, solvent-induced umpolung reactions from dioxygenation to interligand C-S cross-coupling in bis(cyclometalated) Ir(III) thiolate complexes are reported in good to excellent yields at room temperature. Specifically, the reaction of rac-[Ir(pq)2(aet)] (where pq is 2-phenylquinoline and aet is 2-aminoethanethiolate) can be selectively switched to dioxygenation in acetonitrile solution in the presence of O2, resulting in the formation of a sulfinato complex rac-[Ir(pq)2(aes)] (where aes is 2-aminoethanesulfinato). Alternatively, the reaction in trifluoroethanol solution leads to interligand C-S cross-coupling, affording a rac-[Ir(pq)(pqaet)](PF6) [where pqaet is 2-((2-phenylquinolin-8-yl)thio)ethan-1-amine] complex, which generates a new tetradentate ligand in situ. Mechanistically, the formation of electrophilic metal thiyl radicals is proposed as a key intermediate in the interligand C-S coupling reaction. Furthermore, the sequential oxidation of a thioether complex into a sulfoxide complex is also observed at room temperature using H2O2 as an oxidant. Additionally, a new approach for the synthesis of a hexadentate ligand is developed through sequential C-S and C-N interligand coupling of metal thiolate complexes in situ under visible light irradiation in the presence of O2.

Switching the Photoreactions of Ir(III) Diamine Complexes between C-N Coupling and Dehydrogenation under Visible Light Irradiation.

The selective photoreactions under mild conditions play an important role in synthetic chemistry. Herein, efficient and mild protocols for switching the photoreactions of Ir(III)-diamine complexes between the interligand C-N coupling and dehydrogenation are developed in the presence of O2 in EtOH solution. The photoreactions of achiral diamine complexes rac-[Ir(L)2(dm)](PF6) (L is 2-phenylquinoline or 2-(2,4-difluorophenyl)quinoline, dm is 1,2-ethylenediamine, 1,2-diaminopropane, 2-methyl-1,2-diamino-propane, or N,N'-dimethyl-1,2-ethylenediamine) are competitive in the oxidative C-N coupling and dehydrogenation at room temperature, which can be switched into the interligand C-N coupling reaction at 60 °C, affording hexadentate complexes in good to excellent yields, or the dehydrogenative reaction in the presence of a catalytic amount of TEMPO as an additive, affording imine complexes. Mechanism studies reveal that 1O2 is the major reactive oxygen species, and metal aminyl is the key intermediate in the formation of the oxidative C-N coupling and imine products in the photoreaction processes. These will provide a new and practical protocol for the synthesis of multidentate and imine ligands in situ via the postcoordinated strategy under mild conditions.

Discrepancy between Proline and Homoproline in Chiral Recognition and Diastereomeric Photoreactivity with Iridium(III) Complexes.

The chiral-recognition processes of homoproline (hpro) and [Ir(pq)2(MeCN)2](PF6) (pq is 2-phenylquinoline; MeCN is acetonitrile) are investigated, in favor of formation of the thermodynamically stable diastereomers Λ-[Ir(pq)2(d-hpro)] and Δ-[Ir(pq)2(l-hpro)]. Moreover, the diastereoselective photoreactions of Δ-[Ir(pq)2(d-hpro)] and Δ-[Ir(pq)2(l-hpro)] are reported in the presence of O2 at room temperature. Diastereomer Δ-[Ir(pq)2(l-hpro)] is dehydrogenatively oxidized into imino acid complex Δ-[Ir(pq)2(hpro-2H2)] (hpro-2H2 is 3,4,5,6-tetrahydropicalinate), while diastereomer Δ-[Ir(pq)2(d-hpro)] occurs by interligand C-N cross-coupling and dehydrogenative oxidation reactions, affording three products: Δ-[Ir(pq)(d-pqh)] [pqh is N-(2-phenylquinolin-8-yl)homoproline], Δ-[Ir(pq)2(hpro-2H2)], and Δ-[Ir(pq)2(d-hpro-2H6)] [hpro-2H6 is 2,3,4,5-tetrahydropicalinate]. The C-N cross-coupling and dehydrogenative oxidation reactions are competitive, and the dehydrogenative oxidation reactions are regioselective. By optimization of the photoreaction parameters such as the diastereomeric substrate, solvent, and temperature as well as base, each possible competitive product is selectively controlled. In addition, density functional theory calculations are performed to elucidate the distinctly chiral recognition between proline and hpro with an iridium(III) complex.

[Effect of electroacupuncture of acupoints on the healthy limb (opposing needling) on acute skeletal muscle contusion in rats].

OBJECTIVE: To observe the therapeutic effect of electroacupuncture (EA) of "Zusanli" (ST36) and "Ashi"-point on the healthy side (opposing needling) on muscular injury and expression of myogenin (myoG) and fast myosin skeletal heavy chain (Fast MyHC) proteins in the gastrocnemius muscle (GM) tissues in skeletal muscle contusion rats，so as to explore its mechanism underlying improvement of skeletal muscle injury. METHODS: A total of 54 male SD rats were divided into normal control (n ＝ 6)，model (n＝24) and opposing needling (EA, n＝24) groups. The latter two groups were further randomized into 3, 5, 7 and 14 d subgroups (n＝6 per subgroup). The skeletal muscle contusion model of the hind-limb was established by using a self-made striking device. EA (1 Hz/3 Hz，1－2 mA) was applied to ST36 and "Ashi"-point on the uninjured side of the hind-limb for 15 min every time, once a day for 3, 5, 7 and 14 days, respectively. The injured GM was harvested on the 3rd, 5th, 7th and 14th day after muscular contusion. The morphological changes of the injured GM and the mean cross-sectional areas (CSAs) of the neonatal muscle cells were observed by microscope after H．E. staining. The immunoactivity of desmin protein (myogenic marker protein of myoblast cell) of GM was detected by immunofluorescence stain on the 7th day after injury, and the expression levels of myoG (on the 3rd and 5th day after injury) and fast MyHC protein of GM tissues (on the 7thand 14th day after injury) were detected by Western blot. RESULTS: H．E. staining of GS tissue showed fewer neuronal myocytes with disordered arrangement at different sizes, and appearance of some collagenous fibers among the mesenchyme on day 7 and 14 after muscular contusion, which was relatively milder in the EA group. In the EA group, the CSA values of the neonatal muscle cells were significantly larger than those in the model group on the day 7th (P<0.05), 14th (P<0.001) after injury. On day 7 after muscular contusion, the desmin was found to express on the cellular membrane of GM in the normal control group, while in the model group, the desmin expressed mainly in the cellular plasma in the model group, and on the cellular membrane of neonatal myocytes in the EA group, respectively. The desmin positive myocytes showed disordered arrangement and different sizes after muscular contusion, whereas the situations of the EA group were close to those of the normal control group. Desmin expression was up-regulated in the EA group compared with the model group which was not significant difference (P>0.05). On the 3rd and 5th day after muscular contusion, the expression level of myoG protein was significantly up-regulated in the model group compared with the normal control group (P<0.001), and significantly up-regulated in the EA group than that in the model group (P<0.001). On the 7th and14th day after contusion, the expression level of fast MyHC protein was significantly down-regulated in the model group relevant to the normal control group (P<0.001), and markedly up-regulated in the EA group relevant to the model group (P<0.01)．. CONCLUSION: EA of ST36 and "Ashi"-point on the contralateral limb can up-regulate the expression of myoG and fast MyHC proteins of GM in acute skeletal muscle contusion rats, which may contribute to its effect in promoting the repair of skeletal muscle injury.