Computational and Experimental Study on Selective sp²/sp³ or Vinylic/Aryl Carbon–Hydrogen Bond Activation by Platinum(II): Geometries and Relative Stability of Isomeric Cycloplatinated Compounds

Cyclometalating ligands 6-(1-phenylethyl)-2,2′-bipyridine (<b>L4</b>), 6-(1-phenylvinyl)-2,2′-bipyridine (<b>L5</b>), and 6-(prop-1-en-2-yl)-2,2′-bipyridine (<b>L6</b>) were synthesized by the Negishi coupling of 6-bromo-2,2′-bipyridine with the corresponding organozinc reagents. The reaction of <b>L4</b> with K₂PtCl₄ produced only the cycloplatinated compound <b>4a</b> via sp² C–H bond activation. The reactions of <b>L5</b> and <b>L6</b> produced exclusively the cycloplatinated compounds <b>5b</b> and <b>6a</b>, respectively, via vinylic C–H bond activation. DFT calculations were performed on 12 possible cycloplatination products from the reaction of <i>N</i>-alkyl-<i>N</i>-phenyl-2,2′-bipyridin-6-amine (alkyl = methyl (<b>L1</b>), ethyl (<b>L2</b>), and isopropyl (<b>L3</b>)) and <b>L4</b>–<b>L6</b>. The results show that compounds <b>1b</b>–<b>3b</b> resulting from the sp³ C–H bond activation of <b>L1</b>–<b>L3</b> are thermodynamic products, and their relative stability is attributed to the planar geometry that allows for a better conjugation. Similar reasoning also applies to the stability of products from vinylic C–H bond activation of <b>L5</b> and <b>L6</b>. The relative stability of isomeric cycloplatinated compounds <b>4a</b> and <b>4b</b> may be due to the different strengths of C–Pt bonds. The steric interaction is the major cause of severe distortion from a planar coordination geometry in the cycloplatinated compounds, which leads to instability of the corresponding cyclometalated products and a higher kinetic barrier for C–H bond activation

Computational and Experimental Study on Selective sp²/sp³ or Vinylic/Aryl Carbon–Hydrogen Bond Activation by Platinum(II): Geometries and Relative Stability of Isomeric Cycloplatinated Compounds

Cyclometalating ligands 6-(1-phenylethyl)-2,2′-bipyridine (<b>L4</b>), 6-(1-phenylvinyl)-2,2′-bipyridine (<b>L5</b>), and 6-(prop-1-en-2-yl)-2,2′-bipyridine (<b>L6</b>) were synthesized by the Negishi coupling of 6-bromo-2,2′-bipyridine with the corresponding organozinc reagents. The reaction of <b>L4</b> with K₂PtCl₄ produced only the cycloplatinated compound <b>4a</b> via sp² C–H bond activation. The reactions of <b>L5</b> and <b>L6</b> produced exclusively the cycloplatinated compounds <b>5b</b> and <b>6a</b>, respectively, via vinylic C–H bond activation. DFT calculations were performed on 12 possible cycloplatination products from the reaction of <i>N</i>-alkyl-<i>N</i>-phenyl-2,2′-bipyridin-6-amine (alkyl = methyl (<b>L1</b>), ethyl (<b>L2</b>), and isopropyl (<b>L3</b>)) and <b>L4</b>–<b>L6</b>. The results show that compounds <b>1b</b>–<b>3b</b> resulting from the sp³ C–H bond activation of <b>L1</b>–<b>L3</b> are thermodynamic products, and their relative stability is attributed to the planar geometry that allows for a better conjugation. Similar reasoning also applies to the stability of products from vinylic C–H bond activation of <b>L5</b> and <b>L6</b>. The relative stability of isomeric cycloplatinated compounds <b>4a</b> and <b>4b</b> may be due to the different strengths of C–Pt bonds. The steric interaction is the major cause of severe distortion from a planar coordination geometry in the cycloplatinated compounds, which leads to instability of the corresponding cyclometalated products and a higher kinetic barrier for C–H bond activation

Modeling the Current and Future Roles of Particulate Organic Nitrates in the Southeastern United States

Organic nitrates are an important aerosol constituent in locations where biogenic hydrocarbon emissions mix with anthropogenic NO_<i>x</i> sources. While regional and global chemical transport models may include a representation of organic aerosol from monoterpene reactions with nitrate radicals (the primary source of particle-phase organic nitrates in the Southeast United States), secondary organic aerosol (SOA) models can underestimate yields. Furthermore, SOA parametrizations do not explicitly take into account organic nitrate compounds produced in the gas phase. In this work, we developed a coupled gas and aerosol system to describe the formation and subsequent aerosol-phase partitioning of organic nitrates from isoprene and monoterpenes with a focus on the Southeast United States. The concentrations of organic aerosol and gas-phase organic nitrates were improved when particulate organic nitrates were assumed to undergo rapid (τ = 3 h) pseudohydrolysis resulting in nitric acid and nonvolatile secondary organic aerosol. In addition, up to 60% of less oxidized-oxygenated organic aerosol (LO-OOA) could be accounted for via organic nitrate mediated chemistry during the Southern Oxidants and Aerosol Study (SOAS). A 25% reduction in nitrogen oxide (NO + NO₂) emissions was predicted to cause a 9% reduction in organic aerosol for June 2013 SOAS conditions at Centreville, Alabama