Nucleophilicity Scale for the Reactivity of Diazaphospholenium Hydrides: Structural Insights and Synthetic Applications

Nucleophilicity parameters (N, sN) of a group of representative diazaphospholenium hydrides were derived by kinetic investigations of their hydride transfer to a series of reference electrophiles with known electrophilicity (E) values, using the well‐established Mayr equation logk2 = sN(N + E). The achieved N scale covers over ten N units, ranging from the most reactive hydride donor (N = 25.5) to the least of the scale (N = 13.5). This immediately discloses the highest N value ever quantified in terms of Mayr's nucleophilicity scales reported previously for neutral transition metal‐free hydride donors, and hence, implies an exceptional reactivity of this reagent. Even the least reactive hydride donor of this series is still a better hydride donor than those of many other popular types of nucleophiles such as the C‐H, B‐H, Si‐H and transition metal M‐H hydride donors. Structure–reactivity analysis reveals that 2‐H‐1,3,2‐diazaphospholene's outstanding hydricity is benefited from the unsaturated skeleton.

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