Biomimetic Catalysis with Immobilised Organometallic Ruthenium(II) Complexes: Substrate and Regioselective Transfer Hydrogenation of Ketones

Chloro-(h6-arene) complexes of Ru(II) with N-sulfonyl-1,2-ethylenediamine ligands that have one or two styrene side chains were synthesized and characterized. The chloro ligand was substituted with a diphenylphosphinato ligand and the resulting organometallic complexes are transition state analogs for the Ru-catalyzed transfer hydrogenation of benzophenone. Following the protocol of mol. imprinting, these complexes were copolymd. with ethylene glycol dimethacrylate (EGDMA) in the presence of a porogen. The polymers were ground and sieved, and the phosphinato ligand was substituted with a chloro ligand, thus generating a shape-selective cavity in close proximity to the catalytically active metal center. When tested for their ability to catalyze the redn. of benzophenone, the imprinted polymers showed a significantly higher activity (up to a factor of seven) than control polymers without cavities. Out of a mixt. of seven different arom. and aliph. ketones, benzophenone was preferentially reduced when the imprinted polymer was used. Also, the specificity of the catalyst for diaryl ketones was confirmed in a reaction with a bifunctional substrate, 4-acetyl-benzophenone; the diaryl ketone was reduced faster with the imprinted catalyst than the acetyl group. The opposite regioselectivity was obsd. with the control polymer. Both the activity and the selectivity of the imprinted catalysts are dependent on how the Ru complexes are attached to the polymer backbone. A double connection proved to give superior results

Candidate Competition and Voter Learning in the 2000-2012 US Presidential Primaries

When candidates in primary elections are ideologically differentiated (e.g., conservatives and moderates in the Republican party), then candidates with similar positions affect each others’ vote shares more strongly than candidates with different ideological positions. We measure this effect in U.S. Presidential primaries and show that it is of first order importance. We also show that voter beliefs about the candidates harden over the course of the primary, as manifested in the variability of candidate vote shares. We discuss models of sequential voting that cannot yield this pattern of results, and propose an explanation based on a model with horizontally and vertically differentiated candidates and incompletely informed voters. Consistent with the predictions of this model, we also show that, in more conservative states, low quality conservative candidates do better relative to high quality conservatives, and vice versa

Learning and coordination in the presidential primary system

In elections with three or more candidates, coordination among like-minded voters is an important problem. We analyse the trade-off between coordination and learning about candidate quality under different temporal election systems in the context of the U.S. presidential primary system. In our model, candidates with different policy positions and qualities compete for the nomination, and voters are uncertain about the candidates' valence. This setup generates two effects: vote splitting (i.e. several candidates in the same policy position compete for the same voter pool) and voter learning (as the results in earlier elections help voters to update their beliefs on candidate quality). Sequential voting minimizes vote splitting in late districts, but voters may coordinate on a low-quality candidate. Using the parameter estimates obtained from all the Democratic and Republican presidential primaries during 2000-12, we conduct policy experiments such as replacing the current system with a simultaneous system, adopting the reform proposal of the National Association of Secretaries of State, or imposing party rules that lead to candidate withdrawal when prespecified conditions are met

Heterometallic Bromo-bridged Complexes with a Re(CO)3 Fragment

Heterobimetallic complexes where half-sandwich complexes of ruthenium(II), rhodium(III) and iridium(III) are connected by three bromo-bridges to Re(CO)3 have been prepd. from metathesis reactions of [RuBr(m-Br)(h6-arene)]2 (arene = C6H6, C6H3Et3-1,3,5 or p-cymene) or [MBr(m-Br)Cp*]2 (M = Rh or Ir) with [Re(m-Br)(CO)3(C4H8O)]2. The crystal structures of [(h6-arene)Ru(m-Br)3Re(CO)3] (arene = C6H6 or C6H3Et3-1,3,5) and [Cp*M(m-Br)3Re(CO)3] (M = Rh or Ir) have been detd. by X-ray anal. In soln. all complexes were in dynamic equil. with isomeric ionic compds. of general formula [M2(m-Br)3(p-ligand)2][Re2(m-Br)3(CO)6] (M = Ru, Rh or Ir). The solid state structures of [Ru2(m-Br)3(h6-C6H3Et3-1,3,5)2][Re2(m-Br)3(CO)6] and [Ru2(m-Br)3(h6-p-MeC6H4Pri)][Re2(m-Br)3(CO)6] are described