Simple and highly Z-selective ruthenium-based olefin metathesis catalyst.

A one-step substitution of a single chloride anion of the Grubbs-Hoveyda second-generation catalyst with a 2,4,6-triphenylbenzenethiolate ligand resulted in an active olefin metathesis catalyst with remarkable Z selectivity, reaching 96% in metathesis homocoupling of terminal olefins. High turnover numbers (up to 2000 for homocoupling of 1-octene) were obtained along with sustained appreciable Z selectivity (>85%). Apart from the Z selectivity, many properties of the new catalyst, such as robustness toward oxygen and water as well as a tendency to isomerize substrates and react with internal olefin products, resemble those of the parent catalyst.

Screen-based activities and physical complaints among adolescents from the Nordic countries.

BACKGROUND: A positive association between time spent on sedentary screen-based activities and physical complaints has been reported, but the cumulative association between different types of screen-based activities and physical complaints has not been examined thoroughly. METHODS: The cross-sectional association between screen-based activity and physical complaints (backache and headache) among students was examined in a sample of 31022 adolescents from Denmark, Sweden, Norway, Finland, Iceland and Greenland, as part of the Health behaviour in school-aged children 2005/06 (HBSC) study. Daily hours spent on screen-based activities and levels of physical complaints were assessed using self-reports. RESULTS: Logistic regression analysis indicated that computer use, computer gaming and TV viewing contributed uniquely to prediction of weekly backache and headache. The magnitude of associations was consistent across types of screen based activities, and across gender. CONCLUSION: The observed associations indicate that time spent on screen-based activity is a contributing factor to physical complaints among young people, and that effects accumulate across different types of screen-based activities.