Rose Research Group

Principal Investigator: Dr. Michael J Rose

Graduate Mentor: Jeremy R Brinker

Department: Chemistry

Research Group Website: https://www.roseresearchgroup.org

Apr 2023 - May 2025

Undergraduate Researcher

Developing novel PNP, PCP pincer ligands and organometallic complexes
Synthesizing utilizing Schlenk line techniques, box techniques, column chromatography, vacuum distillation, and sublimation
Analyzing using nuclear magnetic resonance, mass spectroscopy, infrared spectroscopy, ultraviolet-visible spectroscopy, and thin-layer chromatography
Performing silicon wafer surface attachments with the following electrochemical testing
Designed and executed 50+ experiments, systematically varying 7+ critical parameters to optimize conversion and yield; managed multi-day synthesis, reaction, purification, and analysis workflows. Improved yield from 0 to 67%
Authored a poster: “Synthesis of Acridine-Based Ligands for Polarizability Control of Si(111) Interfaces”, presented at ECS Texas Section Symposium, Summer Research Scholars Poster Session
Authored a 26-page research summary paper: “Synthesis of Acridine-Based PNP Ligand for Si(111) Interface Molecular Modification and Late 3d Metal Binding”
Presented for ~1hr at 5 group meetings, for ~15min at 20+ subgroup meetings

In the silicon subgroup, my research targets the fundamental photoelectrochemistry of functionalized Si(111) wafers. By systematically varying the dipole moment and electronic polarizability of surface moieties, I probe how interfacial band alignment and charge-transfer kinetics govern the hydrogen evolution reaction (HER) overpotential. Hydrogen is an attractive energy vector because it can be stored without electrochemical batteries and reconverted to electricity or heat with high round-trip utility.¹

Prior work in the group indicates that covalent conjugation between the tethered ligand and the silicon substrate, together with increased interfacial polarizability, favors hydrogen generation.² To test and generalize this mechanism, I am preparing Si(111) surfaces bearing 3d-metal complexes to exploit d-orbital polarizability and quantify its impact on interfacial energetics and HER activity.

Acridine Project

PNP and PCP pincers are pursued for their combination of large molecular polarizability and κ³ chelation, providing thermodynamically and kinetically stable complexes with diverse 3d metals and enhancing the polarizable character of the grafted interfacial species. My work centers on the synthesis of an acridine-scaffold PNP ligand [4,5-bis(diphenylphosphino)-9-bromoacridine]; in parallel, my mentor, Jeremy Brinker, is developing the corresponding anthracene-scaffold PCP ligand. Replacing the central carbon donor (PCP) with a harder nitrogen donor (PNP) should preferentially stabilize complexes of harder transition metals, whereas PCP is expected to favor softer metals, consistent with HSAB considerations. Additionally, the nitrogen donor imparts a net molecular dipole at the interface, a feature previously correlated in our group with improved open-circuit voltage (Voc) under photoelectrochemical operation.²

Synthetic Route

The initial synthetic route was devised from primary literature and patent precedents. Because several targets lacked direct precedent, the sequence required iterative redesign and condition screening to secure reliable conversion and acceptable yields.

Ullmann Coupling

The original synthetic route, which has been altered numerous times in pursuit of better conversion.

This transformation demanded intensive optimization. Initial attempts gave no conversion. Across nearly two years and ~30 reaction runs, we systematically varied more than seven reaction parameters and applied standardized workup/purification/characterization protocols. These efforts increased the isolated yield to as high as 67%, with a modal yield of 35%.

POBr3 Mediated Ring Closing Reaction

Reactions were set up and worked up under rigorously air-free conditions (inert-atmosphere glovebox and Schlenk line). The crude material was purified by column chromatography to provide the target compound in an isolated yield of 33.45% at best.

Phosphination

Proposed arrow pushing mechanism for nucleophilic aromatic substitution reaction (SnAr)

We probed this transformation with a panel of alkali diphenylphosphides generated via diverse preparation methods and conducted reactions across several solvents. Under all conditions tested thus far, the desired product has not been obtained in isolable, analytically pure form.

We employed two model reactions to elucidate the operative pathways and optimize conditions for the target P–C bond-forming phosphination, thereby conserving limited precursors.

Research Presentations

Poster

Poster 1.pdf

Poster presented at ECS Texas Section Symposium, Summer Research Scholars Poster Session.

Research summary

Authored a 26-page research summary paper: “Synthesis of Acridine-Based PNP Ligand for Si(111) Interface Molecular Modification and Late 3d Metal Binding”

Research Talks

Presented for ~1hr at 5 group meetings, for ~15min at 20+ subgroup meetings.

Etch Pitted Si (111) & (100) Attachment of 5,5' and 3,3'-dibromo-2,2'-bipyridine

Using the same interfacial design logic as in the acridine pincer project, the bipyridine program targets bidentate κ² coordination motifs on silicon to enable stable chelation of 3d metals. We exploit substitution pattern control in 2,2′-bipyridine: the 5,5′-dibromo isomer is configured to favor dense, well-oriented grafting on Si(111), whereas the 3,3′-dibromo isomer is oriented to promote high coverage on Si(100). After covalent coupling, relative surface coverage and facet selectivity will be evaluated by etch-pit decoration on Si(111) and by XPS (e.g., N 1s, 3d quantification) across both Si(111) and Si(100).

Proposed synthetic pathway for making 3,3'-dibromo-2,2'-bipyridine.

5,5'-dibromo-2,2'-bipyridine

Two bromine atoms located at opposing ring positions provide dual, well-separated activation sites that statistically enhance coupling efficiency and favor sub-monolayer coverage on Si(111)/Si(100). As the target bipyridine is commercially available, it was procured directly, and a synthetic route was not pursued.

3,3'-dibromo-2,2'-bipyridine

The first step (Sandmeyer reaction) has been successfully executed utilizing multiple literature-based protocols.

Etch Pits

(111) Si pit etching is a known and controllable phenomenon.6, 7 The diagram illustrates the Miller indices of the resulting etch faces.

By studying the surface coverages and photoelectrochemical properties of the target moieties, the group aims at probing phenomena resulting in lower overpotentials.

Controlled pit formation on Si(111) via anisotropic wet etching is a well-characterized and tunable process.6, 7 The diagram annotates the Miller indices of the exposed facets that bound the etch pits. By quantifying ligand surface coverage and evaluating photoelectrochemical metrics (e.g., onset potential, Voc), the group aims to identify interfacial factors that systematically reduce the HER overpotential.

References

Lewis, N. and Nocera, D. “Powering the Planet: Chemical Challenges in Solar Energy Utilisation.” PNAS 103 (43), 2006, 15729-15735
Boucher, D. et al. “Tuning p-Si(111) Photovoltage via Molecule|Semiconductor Electronic Coupling.” JACS 143 (6), 2567-2580
Bansal, A.; Li, X.; Lauermann, I.; Lewis, N. S.; Yi, S. I.; Weinberg, W. H. Alkylation of Si Surfaces Using a Two-Step Halogenation/Grignard Route. JACS, 118 (30), 1996 7225–7226.
Kawai, Suzuki, et al. 12172 9 J. AM. CHEM. SOC. 2005, 127, 12172-12173
Srimani, Milstein, et al. Angew. Chem. Int. Ed. 2013, 52, 14131 –14134
Yu, X.; Ye, Y.; Zhu, P.; Wu, L.; Shen, R.; Zhu, C.-G. Wet Anisotropic Etching Characteristics of Si{111} in KOH-Based Solution. ACS Omega 2025, 10 (3), 2940–2948.
Wade, C. P.; Chidsey, C. E. D. Etch-Pit Initiation by Dissolved Oxygen on Terraces of H-Si(111). Appl. Phys. Lett. 1997, 71 (12), 1679–1681.

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