Stoichiometric Reduction of Dinitrogen to Hydrazine Upon Protonation of Heterobimetallic Chromium–Aluminum Hydride Complexes

ABSTRACT The activation of dinitrogen (N 2 ) via heterobimetallic cooperation remains a compelling strategy for N 2 functionalization. Herein, we report the synthesis and reactivity of a well‐defined chromium–aluminum hydride dinitrogen complex, [(depe) 2 (H)Cr( μ ‐N 2 )AlH 2 ] 2 (depe = Et 2 PCH 2 CH 2 PEt 2 ). Crystallographic and spectroscopic analyses reveal substantial N 2 reduction driven by a “push–pull” interaction between the electron‐rich Cr centers and the electrophilic Al Lewis acid core. Upon stoichiometric protonation with [Ph 2 NH 2 ]OTf, the highly activated bridging N 2 units undergo selective proton‐coupled reduction to release hydrazine (N 2 H 4 ) in up to 97% yield. Crucially, structure–reactivity investigations reveal a clear correlation between the presence of the central Al─H bonds and the selective hydrazine formation. Furthermore, the central aluminum hydrides exhibit high regioselectivity toward silyl electrophiles, enabling the precise construction of fully and partially substituted derivatives; notably, in 5–8 the Cr─N 2– Al motif and terminal Cr─H units are retained. Subsequent redox investigations demonstrate that deep chemical reduction induces a core rearrangement into a unique complex, [(depe) 2 (H)Cr( μ ‐N 2 )] 2 ( μ ‐AlH 2 )( μ ‐Li), followed by multimetallic cleavage. These transformations underscore the essential role of the Lewis acidic Al(III) center in maintaining multimetallic structural integrity and sustaining N 2 activation. Overall, these findings define a heterobimetallic Cr─Al hydride framework in which the central Al─H motif governs stoichiometric hydrazine release and site‐selective hydride functionalization.