We report the first discrete molecular Cr-based catalysts for the reduction of N2. This study is focused on the reactivity of the Cr-N2 complex, trans-Cr(N2)2(PPh 4NBn 4) (P 4 Cr(N 2 ) 2 ), ...bearing a 16-membered tetraphosphine macrocycle. The architecture of the 16-PPh 4NBn 4 ligand is critical to preserve the structural integrity of the catalyst. P 4 Cr(N 2 ) 2 was found to mediate the reduction of N2 at room temperature and 1 atm pressure by three complementary reaction pathways: (1) Cr-catalyzed reduction of N2 to N(SiMe3)3 by Na and Me3SiCl, affording up to 34 equiv N(SiMe3)3; (2) stoichiometric reduction of N2 by protons and electrons (for example, the reaction of cobaltocene and collidinium triflate at room temperature afforded 1.9 equiv of NH3, or at −78 °C afforded a mixture of NH3 and N2H4); and (3) the first example of NH3 formation from the reaction of a terminally bound N2 ligand with a traditional H atom source, TEMPOH (2,2,6,6-tetramethylpiperidine-1-ol). We found that trans-Cr(15N2)2(PPh 4NBn 4) reacts with excess TEMPOH to afford 1.4 equiv of 15NH3. Isotopic labeling studies using TEMPOD afforded ND3 as the product of N2 reduction, confirming that the H atoms are provided by TEMPOH.
Whenever we move, speak, or play musical instruments, our actions generate auditory sensory input. The sensory consequences of our actions are thought to be predicted via sensorimotor integration, ...which involves anatomical and functional links between auditory and motor brain regions. The physiological connections are relatively well established, but less is known about how sensorimotor integration affects auditory perception. The sensory attenuation hypothesis suggests that the perceived loudness of self-generated sounds is attenuated to help distinguish self-generated sounds from ambient sounds. Sensory attenuation would work for louder ambient sounds, but could lead to less accurate perception if the ambient sounds were quieter. We hypothesize that a key function of sensorimotor integration is the facilitated processing of self-generated sounds, leading to more accurate perception under most conditions. The sensory attenuation hypothesis predicts better performance for higher but not lower intensity comparisons, whereas sensory facilitation predicts improved perception regardless of comparison sound intensity. A series of experiments tested these hypotheses, with results supporting the enhancement hypothesis. Overall, people were more accurate at comparing the loudness of two sounds when making one of the sounds themselves. We propose that the brain selectively modulates the perception of self-generated sounds to enhance representations of action consequences.
Laundering pesticide-soiled clothing Mock, J. (North Carolina State University at Raleigh, NC); Tutterow Jennings, H
HE - North Carolina Agricultural Extension Service (USA),
19/Feb
355
Publication
PDF
