Mobility of Lewis acids within the secondary coordination sphere: toward a model for cooperative substrate binding

Abstract

Distance dependence of appended Lewis acids in N₂H₄ binding and deprotonation was evaluated within a series of zinc complexes. Variation of spacer-length to a tethered trialkylborane Lewis acid revealed distinct preferences for binding and stabilization of the resulting deprotonated N₂H₃^- unit.

Fig. 1

Left: Conceptual design. Right: specific substrates investigated in this study and their potential binding modes.

Fig. 2

A) Synthesis of complexes A. B) Molecular structures (50% probability ellipsoids) of A-2 and A-4 as well as their vinyl and butenyl precursors, respectively. H-atoms not attached to alkenyl moieties are omitted for clarity.

Fig.3

A) Reversible formation of C from B. B) Molecular structures (50% probability ellipsoids, only H-atoms attached to heteroatoms are displayed). B-3 is previously reported.

Fig. 4

A) Top: Dynamic solution behaviour of complexes C. Left: reversible deprotonation of C-3 to form D-3 and molecular structure of D-3 (50% probability ellipsoids, only H-atoms attached to heteroatoms displayed). B) Calculated pKa values.