If It’s Not Broke, Break It, and then Break It Again: Understanding [Cp*Rh] Catalysts for Hydrogen Evolution by Investigation of Remarkably Inert Analogues

This undergraduate thesis was submitted in partial fulfillment of the requirements for the Degree of Bachelor of Science with Honors in ChemistryMonomeric half-sandwich rhodium hydride complexes are often proposed as intermediates in catalytic cycles, but relatively few such compounds have been isolated and studied, limiting understanding of their properties. In this thesis, the preparation of a monomeric rhodium(III) hydride complex bearing the pentamethylcyclopentadienyl (Cp*) and bis(diphenylphosphino)benzene (dppb) ligands is reported. The hydride complex is formed rapidly upon addition of weak acid to a reduced precursor complex, Cp*Rh(dppb). Single-crystal X-ray diffraction data for the [Cp*Rh] hydride, which were previously unavailable for this class of compounds, provide evidence of the direct Rh–H interaction. Complementary infrared spectra show the Rh–H stretching frequency at 1986 cm–1. In contrast to results with other [Cp*Rh] complexes bearing diimine ligands, treatment of the isolated hydride with strong acid does not result in hydrogen evolution. Electrochemical studies reveal that the hydride complex can be reduced only at very negative potentials (ca. –2.5 V vs. ferrocenium/ferrocene), resulting in Rh–H bond cleavage and hydrogen generation. Experimentally determined thermochemical parameters for reactions of the [Cp*Rh] hydride and its reduced form provide a rationale for the observed reactivity differences between the dppb and analogous diimine frameworks that can generate H2 with moderately strong acids. These results are discussed in the context of development of design rules for improved catalysts bearing the [Cp*] ligand. To gain further insight into the electronic properties of the phosphine-based ligands that favor metal hydrides and limit catalysis, a second series of [Cp*Rh] complexes supported by the redox-active bidentate diphosphine ligand bis(diphenylphosphino)ferrocene (dppf) is described, with particular attention paid to the outcomes of proton and electron transfer on this framework. Notably, Cp*Rh(dppf) exhibits a quasireversible RhII/I reduction at –0.96 V vs. Fc+/0 rather than undergoing a net 2e– RhIII/I process as is often observed on the [Cp*Rh] platform. This behavior provides access to a species in the relatively uncommon rhodium(II) oxidation state which has been characterized by electron paramagnetic resonance spectroscopy. Protonation of Cp*Rh(dppf) results in formation of an isolable [Cp*Rh] monohydride that is inert to protonolysis, providing a second example of the stabilizing effect bidentate diphosphine ligands have on Rh–H bonds. The quasireversibility of the dppf-centered FeIII/II couple of the rhodium monohydride [Cp*Rh(dppf)H]+ at +0.41 V vs. the ferrocenium/ferrocene redox couple facilitates a rigorous thermochemical analysis of the system, from which we have determined that oxidation centered at the dppf ligand results in dramatically increased acidity of the Rh–H bond by 23 pKa units

Can REDD+ reconcile local priorities and needs with global mitigation benefits? lessons from Angai Forest, Tanzania

The scope of the reducing emissions from deforestation and forest degradation (REDD) mechanism has broadened REDD+ to accommodate different country interests such as natural forests, protected areas, as well as forests under community-based management. In Tanzania the REDD+ mechanism is still under development and pilot projects are at an early stage. In this paper, we seek to understand how local priorities and needs could be met in REDD+ implementation and how these expectations match with global mitigation benefits. We examine the local priorities and needs in the use of land and forest resources in the Angai Villages Land Forest Reserve (AVLFR) in the Liwale District of Lindi Region in Tanzania. Primary data was collected in two villages, Mihumo and Lilombe, using semistructured key informant interviews and participatory rural appraisal methods. In addition, the key informant interviews were conducted with other village, district, and national level actors, as well as international donors. Findings show that in the two communities REDD+ is seen as something new and is generating new expectations among communities. However, the Angai villagers highlight three key priorities that have yet to be integrated into the design of REDD+: water scarcity, rural development, and food security. At the local level improved forest governance and sustainable management of forest resources have been identified as one way to achieve livelihood diversification. Although the national goals of REDD+ include poverty reduction, these goals are not necessarily conducive to the goals of these communities. There exist both structural and cultural limits to the ability of the Angai villages to implement these goals and to improve forestry governance. Given the vulnerability to current and future climate variability and change it will be important to consider how the AVLFR will be managed and for whose benefit

Preparation, Characterization, and Electrochemical Activation of a Model [Cp*Rh] Hydride

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.8b02160.Monomeric half-sandwich rhodium hydride complexes are often proposed as intermediates in catalytic cycles, but relatively few such compounds have been isolated and studied, limiting understanding of their properties. Here, we report preparation and isolation of a monomeric rhodium(III) hydride complex bearing the pentamethylcyclopentadienyl (Cp*) and bis(diphenylphosphino)benzene (dppb) ligands. The hydride complex is formed rapidly upon addition of weak acid to a reduced precursor complex, Cp*Rh(dppb). Single-crystal X-ray diffraction data for the [Cp*Rh] hydride, which were previously unavailable for this class of compounds, provide evidence of the direct Rh–H interaction. Complementary infrared spectra show the Rh–H stretching frequency at 1986 cm−1. In contrast to results with other [Cp*Rh] complexes bearing diimine ligands, treatment of the isolated hydride with strong acid does not result in H2 evolution. Electrochemical studies reveal that the hydride complex can be reduced only at very negative potentials (ca. −2.5 V vs. ferrocenium/ferrocene), resulting in Rh–H bond cleavage and H2 generation. These results are discussed in the context of catalytic H2 generation, and development of design rules for improved catalysts bearing the [Cp*] ligand.University of Kansas Undergraduate Research AwardS10OD016360S10RR024664NSF MRI Grant CHE-162592

Ten Simple Rules for Responsible Big Data Research

The use of big data research methods has grown tremendously over the past five years in both academia and industry. As the size and complexity of available datasets has grown, so too have the ethical questions raised by big data research. These questions become increasingly urgent as data and research agendas move well beyond those typical of the computational and natural sciences, to more directly address sensitive aspects of human behavior, interaction, and health. The tools of big data research are increasingly woven into our daily lives, including mining digital medical records for scientific and economic insights, mapping relationships via social media, capturing individuals’ speech and action via sensors, tracking movement across space, shaping police and security policy via “predictive policing,” and much more

Event attribution science in adaptation decision-making: the context of extreme rainfall in urban Senegal

Event attribution assesses the effect of climate change on individual extreme events. While scientists have suggested that results could be relevant for climate adaptation policy, this has had little empirical investigation, particularly in developing regions. Taking the case of Senegal, the national adaptation policy context regarding extreme precipitation and flooding in urban areas, and the scientific information needed to support this policy, is investigated using key informant interviews, a workshop and document analysis. Flooding in Senegal was found to be viewed primarily as an urban planning concern rather than a climate change issue, with actions to address the impacts focussing on current vulnerabilities of urban communities without considering changing climate risks. While stakeholders thought event attribution might be useful to inform about climate change impacts and future risks of extreme events, it is unclear whether there would be opportunity for this at present, due to the limited role climate information has in adaptation decision-making. While addressing vulnerability to extremes is necessary whether or not the risk is climate change-related, if long-term planning is to be resilient then knowledge about future changes in risks of extremes will need to be considered, even if individual events are not attributed to climate change

Landscape and management influences on smallholder agroforestry yields show shifts during a climate shock

Sustaining yields for smallholder perennial agriculture under a rapidly changing climate regime may require consideration of landscape features and on-farm management decisions in tandem. Optimising landscape and management may not be possible for maximising yields in any one year but maintaining heterogeneous landscapes could be an important climate adaptation strategy. In this study, we observed elevation, forest patch and shade management gradients affecting smallholder coffee (Coffea arabica) yields in a ‘normal’ year versus the 2015/16 El Niño. We generally found a benefit to yields from having leguminous shade trees and low canopy openness, while maintaining diverse shade or varying canopy openness had more complex influences during a climate shock. The two years of observed climate shock were dominated by either drought or high temperatures, with yield responses generally negative. Climate projections for East Africa predict more erratic rainfall and higher temperatures, which will disproportionately impact smallholder farmers.</p