A Diverse Array of Synthetic Strategies for Phosphorus Group Transfer Chemistry: From Phosphinidenes to Phosphates

Abstract

This thesis compiles the published scientific contributions of Tiansi Xin. Chapter 1 consists of a brief collection of eulogies from friends and colleagues, reflecting on his life and time at the Massachusetts Institute of Technology. The subsequent chapters describe the development of novel synthetic methods for the transfer of phosphorus-containing moieties, specifically metaphosphates and phosphinidenes. The work presented here has significant implications for both the fundamental understanding and practical advancement of synthetic inorganic and organic chemistry. Chapters 2 and 3 address the sustainable production and processing of phosphoruscontaining chemicals, focusing on mechanochemical methods to synthesize reduced phosphorus species while circumventing the need to access hazardous white phosphorus as an intermediate. In particular, Chapter 2 describes a solvent-free mechanochemical approach to producing phosphite (HPO₃²⁻) via hydride-mediated reduction of condensed phosphates. Using potassium hydride, a range of inorganic phosphate sources—including pyrophosphate, triphosphate, trimetaphosphate, fluorophosphate, and polyphosphate—were converted to phosphite in moderate to high yields. Mechanistic studies identified overreduction pathways leading to hypophosphite and other low-oxidation P-species. Chapter 3 similarly applies this mechanochemical approach to phosphorus–carbon bond formation, reporting the phosphorylation of acetylides with condensed phosphates to afford phosphonates. Biogenic polyphosphates were also shown to be viable precursors, a proof-of-concept to closing the modern phosphorus cycle using recycled inputs. These results demonstrate the possibility of accessing organophosphorus chemicals directly from condensed phosphates and may offer an opportunity toward a “greener” phosphorus industry. Chapters 4 and 5 shift focus to phosphinidene transfer chemistry and the synthesis of novel phosphorus-containing heterocycles. This expands on previously published studies from the Cummins group on the chemistry of dibenzo-7-phosphanorbornadiene “RPA” reagents. Chapter 4 reports the preparation and structural characterization of iron–phosphido complexes relevant to phosphinidene group transfer catalysis and describes the development of an improved catalytic system based on a simple diiron precursor (Fp₂), enabling efficient synthesis of phosphiranes from electron-deficient alkenes. The mechanism was thoroughly experimentally and computationally interrogated. Chapter 5 describes the novel synthesis of free, uncomplexed phosphet-2-ones via phosphinidene transfer to cyclopropenones, with experimental and theoretical studies supporting a mechanism involving ketene-derived intermediates and transformations to additional phosphorus heterocycles through subsequent reactions.