Control over Selectivity in Alkene Hydrosilylation Catalyzed by Cobalt(III) Hydride Complexes.

Two new bisphosphine [PCP] pincer cobalt(III) hydrides, [(L1)Co(PMe3)(H)(Cl)] (L11, L1 = 2,6-((Ph2P)(Et)N)2C6H3) and [(L2)Co(PMe3)(H)(Cl)] (L21, L2 = 2,6-((iPr2P)(Et)N)2C6H3), as well as one new bissilylene [SiCSi] pincer cobalt(III) hydride, [(L3)Co(PMe3)(H)(Cl)] (L31, L3 = 1,3-((PhC(tBuN)2Si)(Et)N)2C6H3), were synthesized by reaction of the corresponding protic [PCP] or [SiCSi] pincer ligands L1H, L2H, and L3H with CoCl(PMe3)3. Despite the similarities in the ligand scaffolds, the three cobalt(III) hydrides show remarkably different performance as catalysts in alkene hydrosilylation. Among the PCP pincer complexes, L11 has higher catalytic activity than complex L21, and both catalysts afford anti-Markovnikov selectivity for both aliphatic and aromatic alkenes. In contrast, the catalytic activity for alkene hydrosilylation of silylene complex L31 is comparable to phosphine complex L11, but a dependence of regioselectivity on the substrates was observed: While aliphatic alkenes are converted in an anti-Markovnikov fashion, the hydrosilylation of aromatic alkenes affords Markovnikov products. The substrate scope was explored with 28 examples. Additional experiments were conducted to elucidate these mechanisms of hydrosilylation. The synthesis of cobalt(I) complex (L1)Co(PMe3)2 (L17) and its catalytic properties for alkene hydrosilylation allowed for the proposal of the mechanistic variations that occur in dependence of reaction conditions and substrates.

[Emission Inventory of Greenhouse Gas from Urban Wastewater Treatment Plants and Its Temporal and Spatial Distribution in China].

Urban wastewater treatment plants are considered important greenhouse gas resources with massive emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) during operation. Based on the emission factor approach of pollutant reduction, the 2014 emission inventory of greenhouse gases (CO2, CH4, and N2O) from urban wastewater treatment plants in China was established. In addition, the temporal and spatial distribution and influencing factors of greenhouse gas emissions were analyzed in this study. The results showed that total emissions of greenhouse gas from urban wastewater treatment plants in China was 7348.60 Gg (CO2-eq) in 2014, which included CO2, CH4, and N2O emissions of 6054.57 Gg, 27.47 Gg (769.08 Gg, CO2-eq), and 1.98 Gg (524.95 Gg, CO2-eq), respectively. The difference in greenhouse gas emissions among provinces was significant:high emissions appeared in the eastern areas of China, low emissions were observed in the northwest, and hardly any emissions were found in Xizang. From 2005 to 2014, annual greenhouse gas emissions from urban sewage treatment plants in China increased by 229.4%, and the rates of CO2, CH4, and N2O increased by 217.9%, 217.9%, and 520.3%, respectively. The regional economic development level and number of wastewater treatment plants were correlated the most with the emissions of greenhouse gasses, and the per-capita protein supply was closely related with the N2O emission.

Synthesis and catalytic activity of N-heterocyclic silylene (NHSi) cobalt hydride for Kumada coupling reactions.

The electron-rich silylene Co(i) chloride 5 was obtained through the reaction of CoCl(PMe3)3 with chlorosilylene. Complex 5 reacted with 1,3-siladiazole HSiMe(NCH2PPh2)2C6H4 to give the silylene Co(iii) hydride 6 through chelate-assisted Si-H activation. To the best of our knowledge, complex 6 is the first example of Co(iii) hydride supported by N-heterocyclic silylene. Complexes 5 and 6 were fully characterized by spectroscopic methods and X-ray diffraction analysis. Complex 6 was used as an efficient precatalyst for Kumada cross-coupling reactions. Compared with the related complex 3 supported by only trimethylphosphine, complex 6 as a catalyst supported by both chlorosilylene and trimethylphosphine exhibits a more efficient performance for the Kumada cross-coupling reactions. A novel catalytic radical mechanism was suggested and experimentally verified. As an intermediate silylene cobalt(ii) chloride 6d was isolated and structurally characterized.

Transfer hydrogenation of aldehydes catalyzed by silyl hydrido iron complexes bearing a [PSiP] pincer ligand.

The synthesis and characterization of a series of silyl hydrido iron complexes bearing a pincer-type [PSiP] ligand (2-R2PC6H4)2SiH2 (R = Ph (1) and iPr (5)) or (2-Ph2PC6H4)2SiMeH (2) were reported. Preligand 1 reacted with Fe(PMe3)4 to afford complex ((2-Ph2PC6H4)SiH)Fe(H)(PMe3)2 (3) in toluene, which was structurally characterized by X-ray diffraction. ((2-iPr2PC6H4)SiH)Fe(H)(PMe3) (6) could be obtained from the reaction of preligand 5 with Fe(PMe3)4 in toluene. Furthermore, complex ((2-iPr2PC6H4)Si(OMe))Fe(H)(PMe3) (7) was isolated by the reaction of complex 6 with 2 equiv. MeOH in THF. The molecular structure of complex 7 was also determined by single-crystal X-ray analysis. Complexes 3, 4, 6 and 7 showed good to excellent catalytic activity for transfer hydrogenation of aldehydes under mild conditions, using 2-propanol as both solvent and hydrogen donor. α,ß-Unsaturated aldehydes could be selectively reduced to corresponding α,ß-unsaturated alcohols. The catalytic activity of penta-coordinate complex 6 or 7 is stronger than that of hexa-coordinate complex 3 or 4.