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We report the development of a well-defined Fe catalyst and its application to the regio- and stereoselective 1,4-hydrosilylation of 1,3-dienes. To the best of our knowledge, this is the first example of accessing a characterized low-valent Fe catalyst by controlled reductive elimination from a readily accessible Fe precatalyst.

Ironing rubber: Iminopyridine‐based FeCl2 catalysts catalyze the polymerization of 1,3‐dienes and provide stereoselective access to elastomers such as polyisoprenes, polymyrcenes, and polyfarnesenes. The choice of ligand determines the double‐bond geometry in the polymer repeating unit, which can be varied from trans/cis >99:1 to <1:99 (see scheme).

A new intermolecular, stereo- and regioselective iron-catalyzed 1,4-addition of alpha-olefins to 1,3-dienes using as low as 1 mol % of an iminopyridine-ferrous chloride complex was developed. Importantly, both double bonds of the linear 1,4-diene addition products are obtained with absolute stereocontrol.

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Three Rh−phosphinite complexes with the general structural formula [RhCl(i-Pr2POXy)(L)]2 (Xy = 2,3-xylyl; L = PPh3, PMe3, t-BuNC) were synthesized. Characterization of these complexes using crystallographic and spectroscopic techniques revealed rare examples of preagostic C−H···M interactions. 1H NMR chemical shielding calculations on a geometry-optimized model complex were used to provide a connection between the solution and solid-state data, which additionally supported assignment of the preagostic interaction. One of these Rh−phosphinite complexes (L = PPh3) was used to catalyze the ortho alkylation of phosphinites and phenols with an unactivated alkene. Finally, DFT calculations were used to provide evidence for the involvement of the observed preagostic interaction in the cyclometalation step of the catalytic cycle.

Performance‐enhancing ligands: Two new bridged bicyclic phosphines 1 a,b based on the “phoban” skeleton (see structures of their naphth‐2‐ylmethyl bromide salts; P yellow, Br brown, C white) are central to a practical catalytic method for the direct arylation of a variety of nitrogen heterocycles using aryl bromides. Broad functional‐group tolerance was observed, and the use of microwave radiation allowed for short reaction times.

Estimating the size of stigmatized, hidden, or hard-to-reach populations is a major problem in epidemiology, demography, and public health research. Capture-recapture and multiplier methods are standard tools for inference of hidden population sizes, but they require random sampling of target population members, which is rarely possible. Respondent-driven sampling (RDS) is a survey method for hidden populations that relies on social link tracing. The RDS recruitment process is designed to spread through the social network connecting members of the target population. In this paper, we show how to use network data revealed by RDS to estimate hidden population size. The key insight is that the recruitment chain, timing of recruitments, and network degrees of recruited subjects provide information about the number of individuals belonging to the target population who are not yet in the sample. We use a computationally efficient Bayesian method to integrate over the missing edges in the subgraph of recruited individuals. We validate the method using simulated data and apply the technique to estimate the number of people who inject drugs in St. Petersburg, Russia.